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Investigation on molecular interactions of antibiotics in alcohols using volumetric and acoustic studies at different temperatures
J. Chem. Thermodynamics 104 (2017) 239–251
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Investigation on molecular interactions of antibiotics in alcohols using volumetric and acoustic studies at different temperatures Bushra Naseem ⇑, Madeeha Iftikhar Department of Chemistry, Lahore College for Women University, Jail Road, Lahore 54000, Pakistan
a r t i c l e
i n f o
Article history: Received 27 June 2016 Received in revised form 18 September 2016 Accepted 27 September 2016 Available online 28 September 2016 Keywords: Apparent and partial molar volume Isentropic compressibility Acoustic impedance Intermolecular free length and solute– solvent interactions
a b s t r a c t The density and sound velocity for pure alcohols (methanol, ethanol, iso-propanol and n-butanol) and molal solutions of nitroimidazoles (metronidazole (MNZ) and dimetridazole (DMZ) have been measured at different temperatures (293.15–313.15 K). Different volumetric and acoustical parameters like apparent molar volume (V/), partial molar volume (V/), apparent molar isentropic compressibility (K/), partial molar isentropic compressibility (K/), hydration number (nH), acoustic impedance (Z) and intermolecular free length (Lf) of antibiotic solutions were calculated from the experimental values of density and sound velocity. The derived values have been used to explore the solute–solute and solute–solvent interactions. The V/ values are positive and K/ values are negative in both antibiotics, indicative of strong solute–solvent interactions and closely packed structure of antibiotics in alcohols. The decreasing trend of Lf with increasing antibiotic concentration shows the presence of strong intermolecular interactions in solutions. Ó 2016 Elsevier Ltd.
1. Introduction Solubility is a basic physico-chemical property that has significant applications to different processes i.e. biological, chemical, pharmaceutical and environmental. Careful experimentation is required for reliable solubility data and these measurements are tedious, time consuming and costly [1]. Volumetric and acoustical properties like apparent molar volume and apparent molar isentropic compressibility etc. of any solution can be evaluated using density and sound velocity values [2]. Volumetric properties of the mixtures of alcohols are of technological and theoretical interest. Different types of interactions like ion–ion, solvent–solvent and ion–solvent interactions are present in the solution [3]. From the density (q), sound velocity and viscosity (g) of solutions, structural aspects and properties of the solutions can be characterized [4]. Hence volumetric properties give helpful information regarding nature of solute and solvent [5]. The partial molar and apparent molar volumes of solutes are used to distinguish solutes of different molar masses on the basis of their ion–ion and ion–solvent affinity and in assessing drug potency whereas isentropic compressibility factors reflects the compactness of the hydration layers around the core of the solutes [6]. Solubility results also serve to
⇑ Corresponding author. E-mail address: [email protected] (B. Naseem). http://dx.doi.org/10.1016/j.jct.2016.09.037 0021-9614/Ó 2016 Elsevier Ltd.
construct mathematical models that help to optimize solvent composition selection in pharmaceutical technology [1]. It has been noted that by the addition of solute, changes occur in the structure of solvent i.e. it may either make or break [4]. By ultrasonic velocity measurements, the molecular interactions in pure liquids, aqueous solutions and mixtures have been studied. It gives a useful and reliable tool to study the properties of solutions of amino acids, polymers etc. However, little work has been done for the solutions of drugs [7]. Chemical transformations can take place in a gas, liquid or solid phase but majority of reactions are carried out in liquid phase in the form of solutions [8]. Alcohol is a class of organic compounds described by one or more hydroxyl (–OH) groups attached to a carbon atom of hydrocarbon chain. These might be considered as organic imitative of water, in which a hydrogen atom has been changed by –CH2 group, which may be represented by ‘R’ in organic structures. For example, in ethanol the alkyl group is the ethyl group, –CH2CH3 [9]. Globally, infections in gastrointestinal track by different parasites and bacteria are responsible for major morbidity and deaths. 5-Nitroimidazoles, a set of medicines, is a well-established group of antiprotozoal and antibacterial agents that have ability to reduce the development of anaerobic bacteria and certain anaerobic protozoa. The significance of imidazole is established from the fact that large number of medicines contains this moiety and several 5-nitroimidazole derivatives such as metronidazole (MNZ), dimetridazole (DMZ), ipronidazole (IPZ) and ronidazole (RNZ) have
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been used since long time, for the handling of critical cases of infections caused by protozoa and anaerobic bacteria [10]. They are placed into coccidiostat substances, but it has been reported that these compounds show mutagenic, carcinogenic and toxic properties. For this reason, their use has been prohibited as additives in feed for food-producing species. Chemical nature of drugs is essential to study their behaviour in different systems. This study is an attempt to explore the interactions of these antibiotics with solvents and solvent–solvent interactions from volumetric and acoustical properties (apparent molar volume (V/), isentropic compressibility (K/), partial molar volume (V°/), partial molar compressibility (K/), acoustic impedance (Z), hydration number (nh) and intermolecular free length), which were evaluated from density and sound velocity of antibiotics (DMZ and MNZ) in different alcohols at different temperatures.
various concentrations (0.01–0.05) mol kg1 in alcohols were measured at temperatures 293.15 K, 298.15 K, 303.15 K, 308.15 K and 313.15 K and at 101 kPa pressure. The weighing of solutes (antibiotics) was done by Wiggen Hauser electronic balance with a precision of ±0.001 mg. At least three readings of each composition were reproducible to ±0.005 mg and the values obtained were averaged. The standard uncertainties in molality (m), density (d), sound velocity (us), and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±2 m s1, ±102 K and ±5 kPa respectively. The measured densities and ultrasound speeds were utilized in determining volumetric and acoustical properties of solutions as described in the next section. 3. Results and discussion 3.1. Density and sound velocity measurement of antibiotic solutions
2. Experimental 2.1. Materials Chemicals, MNZ, DMZ, methanol, ethanol, iso-propanol and nbutanol, were products of Sigma, and were used as received without any purification. All glassware was carefully washed with deionized water, cleaned and dried in oven before use. Mass fraction purity and source of chemicals used in the experiment have been given in Table 1. 2.2. Density and sound velocity measurements Density (d) and sound velocity (u) were measured by Anton Paar DSA 5000 M with high precision vibrating tube digital density meter and ultrasound speed measuring device. The instrument has a built-in thermostat to maintain the temperature. The accuracy and repeatability of DSA 5000 M for density are 5 106 g cm3 and 1 106 g cm3 and that of temperature is 0.01 °C and 0.001 °C respectively. The sample density is determined by measuring the oscillation frequency of a U-shaped sample tube completely filled with the sample liquid. The principle of sound velocity measurement is based on propagation time technique. The sample is sandwiched between two piezoelectric ultrasound transducers. One transducer emits sound waves through the sample-filled cavity (frequency around 3 MHz) and the second transducer receives those waves [11]. Thus, the sound velocity is obtained by dividing the known distance between transmitter and receiver by the measured propagation time of the sound waves up to 0.5 m s1accuracy and 0.1 ms1 repeatability. Density and sound velocity of pure alcohols and solutions of DMZ and MNZ of
Density and sound velocity of alcohols: methanol, ethanol, isopropanol and n-butanol have been measured at different temperatures (293.15 K–313.15 K). The measured density and sound velocity values for pure alcohols have been given in Table 2. Comparison of experimental with literature values showed that measured values is in accordance with literature reported values [11–17]. Density and sound velocity for the antibiotics (DMZ and MNZ) in alcohols were measured at temperatures (293.15 K–313.15 K) using antibiotic concentration range (0.01–0.05 mol kg1). Measured density values have been given in Table 3 which show that density of antibiotic solutions decreases with increasing temperature and show an increase with increasing concentration of antibiotics in alcoholic solutions. With increasing temperatures, density decreases because increasing temperature weakens the bonds between solute and solvent in a solution making the solution less dense [2]. Density increases with increasing concentration of solute (antibiotics) in alcoholic solution which can be interpreted by the enhanced structure of solvents due to added solute (antibiotics) [18]. From values shown in the tables, it is also clear that density of MNZ in all alcoholic solutions is greater than that of DMZ because the –OH group in MNZ is responsible for greater attractive forces like H-bonding etc. with solvent molecules than in DMZ and hence has a more dense structure. Sound velocity values for both antibiotics in alcoholic solutions at different temperatures (293.15–298.15) K are given in Table 6. Sound velocity decreases with increasing temperature and increases with increasing concentration of antibiotics in alcohol solutions. With increasing temperature, molecules gain kinetic energy. As the kinetic energy of molecules increases, the interactions among solute and solvent molecules become weaker. The
Table 1 Provenance and mass fraction purity of the materials studied. Chemical names
Source
Mass fraction purity
Purification method
CAS no
Methanol
Sigma Aldrich
>0.998
Used as received
67-56-1
Ethanol
Sigma Aldrich
>0.995
Used as received
64-17-5
Iso-propanol
Sigma Aldrich
>0.995
Used as received
67-63-0
n-Butanol
Sigma Aldrich
>0.994
Used as received
71-36-3
Dimetridazole
Sigma Aldrich
>0.997
Used as received
551-92-8
Metronidazole
Sigma Aldrich
>0.996
Used as received
443-48-1
Structures
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 2 Density (do/g cm3) and sound velocity (uo/m s1) of pure alcohols at different temperatures and at 101 k Pa pressure. Temperatures T/K
do/g cm3
uo/m s1
Experimental values
Literature values
Experimental values
Literature values
Methanol 293.15 298.15 303.15 308.15 313.15
0.793603 0.789271 0.784591 0.777868 0.772438
0.791300b 0.786660g 0.781901g 0.777230g 0.772500g
1106.63 1101.91 1082.73 1068.82 1059.41
1105.21b 1102.32g 1085.89g 1069.63g 1060.00g
Ethanol 293.15 298.15 303.15 308.15 313.15
0.789412 0.785413 0.782015 0.777697 0.773201
0.789501a 0.785500g 0.782001g 0.777700g 0.773700g
1159.34 1150.05 1130.28 1097.64 1090.92
1160.30a 1152.00g 1128.00g 1098.00g 1092.70a
Iso-propanol 293.15 298.15 303.15 308.15 313.15
0.785810 0.781336 0.777061 0.772019 0.769701
0.785450c 0.781260d 0.776591e 0.772201e 0.767120c
1156.65 1136.74 1125.89 1105.01 1085.11
1157.80c 1138.87d 1126.01e 1105.30e 1101.87c
n-Butanol 293.15 298.15 303.15 308.15 313.15
0.809493 0.805648 0.803676 0.800496 0.794112
0.809500a 0.8057500d 0.803700a 0.798527f 0.794101a
1258.43 1239.82 1222.97 1203.15 1191.42
1257.66a 1240.00d 1223.55a 1211.00f 1190.28a
The standard uncertainties in molality (m), density (d), sound velocity (us), and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±2 m s1, ±102 K and ±5 kPa, respectively. a Reference [11]. b Reference [12]. c Reference [13]. d Reference [14]. e Reference [15]. f Reference [16]. g Reference [17].
resulting weak interactions among molecules pose hindrance for the sound velocity to pass through solutions, therefore sound velocity decreases with increasing temperature [16]. Where sound velocity increases in antibiotics-alcohol solutions with increasing concentration of antibiotics in solutions, it could be attributed to the overall increase of cohesion brought about by the solute–solute, solute–solvent and solvent–solvent interactions in solutions. Cohesive forces are further enhanced on successive increase in solute concentration [19]. 3.2. Apparent and partial molar volume The apparent molar volume of a solute is a difference between the volume of the solution and the volume of the pure solvent per mole of solute. The apparent molar volume for antibiotics in alcohols is calculated from density using following equation [20,21]:
V / ¼ 1000ðdo dÞ=mddo þ M=d
ð1Þ 1
M is molar mass of antibiotics (DMZ = 141.128 g mol and MNZ = 171.15 g mol1), m is the molality of antibiotic solutions in alcohols; d and do are densities of solution and solvent respectively. Plots between apparent molar volume and molality of both antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures have been shown in Figs. 1–4(a and b) for DMZ (a) and MNZ (b). The V/ value is sensitive to measure solute–solvent interactions occurring in the solution. The variation of V/ is found to be linearly dependent on molality m, in the concentration range studied [19]. It has been observed that values of apparent molar volume decreases with increasing temperature and concentration of
antibiotics (MNZ and DMZ) solutions in alcohols due to the electrostriction effect [22]. Furthermore, increase in the value of apparent molar volume with increase in alkyl groups in carbon chain of alcohols i.e. from methanol to n-butanol, whereas an exception arises in the case of iso-propanol which shows the least value of apparent molar volume. For iso-propanol, the interaction of antibiotics with the alcohol is sterically hindered by the position of –OH group in carbon chain of alcohol, leading to increase in the value of apparent molar volume and the obtained order of apparent molar volume is iso-propanol > methanol > ethanol > n-butanol [23]. The values obtained for apparent molar volume are positive for both antibiotics solutions in alcohols which suggests that overall structural order is enhanced in solutions [17]. Large values of Va are obtained for MNZ as compared to DMZ at all temperatures and in all alcohols, because of the increase in molar mass that causes greater affinity for solvent and therefore enhances solute–solvent interactions [20]. The partial molar volumes (Va) were obtained by extrapolating the plots of apparent molar volume (Va) versus molality (m) of antibiotics solutions in alcohols using Masson type equation [24]:
V U ¼ V oU þ Sv m Voa
ð2Þ
The is the partial molar volume that provides information regarding solute–solvent interaction and Sv is a limiting or experimental slope which gives the pair wise interactions; Va is the apparent molar volume and m is molality of the solution [25]. The values of partial molar volume (Voa) and experimental slope (Sv) were estimated for DMZ and MNZ using the least squares fit method and the values of both parameters are listed in Tables 4 and 5 respectively.
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Table 3 Molality (m), density (d) and apparent molar volume (V/) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at pressure 101 kPa. m/mol kg1
d/g cm3 DMZ
d/g cm3 MNZ
0.01 0.02 0.03 0.04 0.05
0.794574 0.795553 0.796549 0.797546 0.798551
0.794604 0.795623 0.796639 0.797676 0.798708
298.15
0.01 0.02 0.03 0.04 0.05
0.790247 0.791232 0.792221 0.793214 0.794217
0.790277 0.791292 0.792311 0.793334 0.794357
303.15
0.01 0.02 0.03 0.04 0.05
0.785567 0.786551 0.787548 0.788544 0.789542
0.785597 0.786609 0.787627 0.788644 0.789672
308.15
0.01 0.02 0.03 0.04 0.05
0.778839 0.779817 0.780811 0.781815 0.782818
0.778871 0.779883 0.780899 0.781919 0.782939
313.15
0.01 0.02 0.03 0.04 0.05
0.773407 0.774382 0.775371 0.776379 0.777401
0.773439 0.774445 0.775471 0.776481 0.777519
0.01 0.02 0.03 0.04 0.05
0.790241 0.791079 0.791927 0.792782 0.793639
0.790343 0.791289 0.792231 0.793202 0.794168
298.15
0.01 0.02 0.03 0.04 0.05
0.786243 0.787082 0.787931 0.788786 0.789648
0.786348 0.787286 0.788239 0.789211 0.790178
303.15
0.01 0.02 0.03 0.04 0.05
0.782847 0.783685 0.784537 0.785397 0.786251
0.782951 0.783894 0.784841 0.785812 0.786787
308.15
0.01 0.02 0.03 0.04 0.05
0.778529 0.779371 0.780242 0.781101 0.781968
0.778631 0.779574 0.780531 0.781491 0.782468
313.15
0.01 0.02 0.03 0.04 0.05
0.774037 0.774889 0.775744 0.776604 0.777469
0.774137 0.775082 0.776037 0.776989 0.777976
0.01 0.02 0.03 0.04 0.05
0.786794 0.787781 0.788801 0.789803 0.790834
0.786911 0.788027 0.789147 0.790271 0.791419
298.15
0.01 0.02 0.03 0.04 0.05
0.782319 0.783311 0.784321 0.785331 0.786342
0.782438 0.783549 0.784671 0.785811 0.786944
303.15
0.01 0.02 0.03 0.04 0.05
0.778042 0.779031 0.780039 0.781054 0.782084
0.778164 0.779278 0.780399 0.781545 0.782671
T/K Methanol 293.15
Ethanol 293.15
Iso-propanol 293.15
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 3 (continued) T/K
m/mol kg1
d/g cm3 DMZ
d/g cm3 MNZ
308.15
0.01 0.02 0.03 0.04 0.05
0.773001 0.773987 0.774992 0.776011 0.777019
0.773122 0.774239 0.775362 0.776494 0.777624
313.15
0.01 0.02 0.03 0.04 0.05
0.770682 0.771681 0.772691 0.773695 0.774703
0.770811 0.771943 0.773077 0.774215 0.775377
0.01 0.02 0.03 0.04 0.05
0.809983 0.810491 0.811003 0.811516 0.812079
0.810078 0.810673 0.811280 0.811901 0.812531
298.15
0.01 0.02 0.03 0.04 0.05
0.806148 0.806651 0.807169 0.807699 0.808245
0.806241 0.806855 0.807478 0.808101 0.808761
303.15
0.01 0.02 0.03 0.04 0.05
0.804182 0.804701 0.80524 0.805775 0.806302
0.804277 0.804899 0.805511 0.806168 0.806799
308.15
0.01 0.02 0.03 0.04 0.05
0.801009 0.801538 0.802077 0.802629 0.803199
0.801097 0.801719 0.802369 0.803009 0.803678
313.15
0.01 0.02 0.03 0.04 0.05
0.794629 0.795169 0.795718 0.796289 0.796841
0.79431 0.795355 0.795994 0.796644 0.797299
n-Butanol 293.15
The standard uncertainties in molality (m), density (d) and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±102 K and ±5 kPa respectively.
25
57 56 55 Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
23 21 19
54 53 52 51
17
50 0
15 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 1a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in methanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
The positive values of partial molar volume (a measure of ion– solvent interactions) indicate the presence of strong interactions between antibiotics and solvents. The Sv values are negative and decrease with an increase in temperature indicating that solute– solute interactions decrease with increasing temperature for all
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 1b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in methanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
systems. The Voa values increase in the following order: isopropanol > methanol > ethanol > n-butanol. This result indicates that the steric-hindering effect becomes more significant when size of alkyl group increases, and the solvation capacity of alkyl group weakens, resulting in greater Voa values. The exceptional lower Voa values for isopropanol can be explained in terms of more
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40
47 46
38 Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
45 44 43 42 41
36 34 32
40 39 0
0.01
0.02
0.03
0.04
0.05
30
0.06
0
Molality/(mol·kg-1)
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
Fig. 2a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in ethanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 3b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in iso-propanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
68
100
67
98 Vφ /(cm3·mol-1)
66 Vφ /(cm3·mol-1)
0.01
65 64 63 62
96 94 92 90
61
88
60 0
0.01
0.02
0.03
0.04
0.05
0
0.06
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
Molality/(mol·kg-1) Fig. 2b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in ethanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 4a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in n-butanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
22
125
18
Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
20
16 14 12 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
120
115
110 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 3a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in iso-propanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 4b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in n-butanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
prominent electrostriction effect and degree of steric hindrance due to position of –OH goup [17]. 3.3. Apparent and partial molar isentropic compressibility Apparent molar isentropic compressibility is a measure of degree of compressibility of ions in solution and can be calculated using the relation [26]:
K / ¼ 1000ðbs do bos dÞ=mddo þ bs M=d
ð3Þ
The M is the molar mass of antibiotics (DMZ and MNZ), m is molality of antibiotic solutions in alcohols, do and d are densities of solvent and solution, respectively; bs and bos represent the isentropic compressibility of solution and solvent respectively, calculated using the following equation:
bs ¼ ½u2 d
1
ð4Þ
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 4 Partial molar volume (Vo/) of antibiotics (DMZ and MNZ) in alcohol solutions at different temperatures and 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
mol DMZ Methanol Ethanol Iso-propanol n-Butanol
24.40 46.35 21.27 100.37
22.53 45.78 20.28 99.20
21.80 45.10 20.27 97.92
21.84 44.73 19.04 97.22
21.60 43.04 18.07 96.50
Vo//cm3mol1 MNZ Methanol Ethanol Iso-propanol n-Butanol
57.20 68.08 40.09 123.09
55.63 67.38 39.40 121.88
55.05 66.73 38.35 120.57
54.54 66.49 37.12 121.10
54.43 65.55 35.55 118.29
Vo//cm3
1
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
Table 5 Slope of line (Sv) of plot of apparent molar volume and molality of antibiotics (DMZ and MNZ) in alcohol solutions at different temperatures and 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
Sv/kg cm3 mol1 DMZ Methanol Ethanol Iso-propanol n-Butanol
78.61 71.61 90.06 99.40
53.24 73.79 80.06 83.23
61.84 71.33 101.95 84.56
85.19 100.87 85.70 111.45
103.29 74.47 81.60 122.56
Sv/kg cm3 mol1 MNZ Methanol Ethanol Iso-propanol n-Butanol
83.38 86.89 83.33 96.18
51.19 87.01 89.19 115.21
46.80 83.67 88.44 99.89
54.43 90.86 79.82 145.71
69.74 81.94 102.12 85.74
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
Experimentally calculated data for apparent molar isentropic compressibility for both antibiotics at different temperatures has given in Table 6. The isentropic compressibility values increase with an increase in temperature at all compositions of antibiotic solutions due to an increase in thermal agitation, making the solution more compressible [16]. The KU values are negative and decrease with increase in the concentration of antibiotics in solvents. Negative KU values predict that solvent molecules around solute are less compressible than those in the bulk which is attributed to strong solute–solvent interactions in solution [27] The results show an increase in the value of apparent molar isentropic compressibility with increasing –CH2 group in the carbon chain of alcohol i.e. from methanol to n-butanol, whereas iso-propanol shows different behaviour. The decrease in the value of apparent molar isentropic compressibility in iso-propanol is due to side group which may cause steric hindrance and the obtained order of apparent molar isentropic compressibility in alcohols is iso-propanol > methanol > ethanol > n-butanol [17]. The value of apparent molar isentropic compressibility is larger for MNZ than DMZ. This is because apparent molar isentropic compressibility increases with increasing molar mass of the solute (MNZ is larger molecule than DMZ) [19]. The limiting apparent molar isentropic compressibility values given in Table 7 were evaluated by using Masson’s equation [28]:
K / ¼ K o/ þ Sk m
ð5Þ
Koa is the limiting value of isentropic compressibility and Sk is the experimental slope indicative of solute–solute interactions. Magnitude of Koa is a measure of solute–solvent interactions as solute–solute interactions are negligible at infinite dilution. Calculated values for Ko/ and Sk are given in Tables 7 and 8. The values of partial molar isentropic compressibility are negative and increase with increase in temperature of solution, this may be attributed to a decrease of electrostriction or hydration
from the second solvation layer of ionic (–OH) group of antibiotics [29]. The Sk values of the antibiotics studied are found to be positive at all temperatures thereby suggesting strong solute–solute interactions [30]. 3.4. Intermolecular free length (Lf) Intermolecular free length is another acoustical parameter describing the nature and strength of intermolecular interactions present in a solution and referred to as distance among surfaces of two molecules and can be calculated using isentropic compressibility (bs) using following equation [31]:
Lf ¼ Kðbs Þ1=2
ð6Þ 8
K ¼ ½ð93:875 þ 0:375ÞðT=K 10 It depends on intermolecular as well as intra molecular interactions existing among components of the mixture. When isentropic compressibility decreases, free length also decreases and vice versa [32,33]. The change in the free length values also shows the presence of appreciable interactions present among solute and solvent molecules due to which type of structural rearrangement is affected. Using experimental results, calculated values of Lf for both antibiotics (DMZ and MNZ) in alcoholic solutions at different temperatures are given in Table 9. Results presented show that Lf values decrease with increase in concentration of antibiotics, and temperature. This shows that specific strong intermolecular interaction among antibiotics (DMZ and MNZ) and alcohol molecules prevails in the solution. Also, the decreased value of free length indicates structure promoting behaviour of the solute molecule [34]. In all alcohol solutions, Lf for DMZ solutions are greater than for MNZ solutions. This can be attributed due to increased interactions among MNZ molecules and alcohols which could be due the presence of extra –OH group in MNZ structure than DMZ molecule.
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Table 6 Molality (m), speed of sound (us) and apparent molar isentropic compressibility (KU) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at pressure 101 kPa. m/mol kg1
us/m s1 DMZ
KU 104/cm3 mol1 Pa1 DMZ
us/m s1MNZ
KU 104/cm3 mol1 Pa1 MNZ
0.01 0.02 0.03 0.04 0.05
1108.35 1109.82 1110.69 1111.34 1112.05
5.36 5.07 4.52 4.12 3.90
1109.05 1111.42 1113.21 1115.31 1117.12
6.70 6.65 6.17 6.11 5.94
298.15
0.01 0.02 0.03 0.04 0.05
1103.73 1105.03 1106.19 1107.03 1108.03
5.75 5.14 4.82 4.47 4.34
1104.33 1106.63 1108.71 1110.82 1112.14
6.89 6.74 6.51 6.40 5.96
303.15
0.01 0.02 0.03 0.04 0.05
1084.48 1085.72 1086.85 1087.51 1088.53
5.95 5.31 5.00 4.55 4.46
1085.06 1087.23 1089.33 1091.21 1092.61
7.12 6.90 6.77 6.55 6.18
308.15
0.01 0.02 0.03 0.04 0.05
1070.49 1071.87 1072.75 1073.47 1074.25
6.07 5.68 5.12 4.73 4.53
1071.05 1073.11 1075.11 1077.01 1078.55
7.27 7.03 6.89 6.75 6.47
313.15
0.01 0.02 0.03 0.04 0.05
1061.11 1062.51 1063.36 1064.28 1065.26
6.41 5.99 5.35 5.09 4.97
1061.59 1063.61 1065.56 1067.26 1068.91
7.43 7.20 7.06 6.80 6.63
0.01 0.02 0.03 0.04 0.05
1161.77 1164.15 1166.26 1168.03 1170.08
5.81 5.75 5.55 5.27 5.22
1162.25 1164.78 1166.69 1168.43 1170.56
6.74 6.35 5.79 5.43 5.37
298.15
0.01 0.02 0.03 0.04 0.05
1152.61 1154.76 1156.87 1158.79 1160.56
6.29 5.86 5.68 5.49 5.31
1153.01 1155.43 1157.31 1159.21 1161.19
7.10 6.51 5.94 5.67 5.54
303.15
0.01 0.02 0.03 0.04 0.05
1132.71 1134.87 1136.79 1138.57 1140.36
6.40 6.08 5.81 5.59 5.45
1133.13 1135.37 1137.71 1139.19 1141.11
7.30 6.60 6.43 5.89 5.75
308.15
0.01 0.02 0.03 0.04 0.05
1099.86 1101.86 1103.65 1105.11 1106.91
6.53 6.25 6.01 5.67 5.63
1100.22 1102.28 1104.45 1106.11 1107.61
7.37 6.72 6.60 6.22 5.92
313.15
0.01 0.02 0.03 0.04 0.05
1093.08 1095.11 1097.12 1098.23 1099.99
6.60 6.44 6.36 5.75 5.71
1093.58 1095.52 1097.68 1099.91 1101.02
7.82 6.89 6.77 6.74 6.18
0.01 0.02 0.03 0.04 0.05
1158.18 1159.47 1160.73 1161.74 1162.35
4.51 4.26 4.18 4.00 3.73
1158.77 1160.64 1162.43 1164.08 1165.31
5.74 5.49 5.34 5.19 4.94
298.15
0.01 0.02 0.03 0.04 0.05
1138.17 1139.41 1140.63 1141.83 1142.66
4.58 4.37 4.30 4.25 4.06
1138.74 1140.56 1142.28 1143.74 1144.85
5.85 5.65 5.51 5.30 5.02
303.15
0.01 0.02 0.03 0.04
1127.29 1128.66 1129.71 1130.93
4.69 4.66 4.42 4.40
1127.86 1129.62 1131.22 1132.66
6.03 5.79 5.58 5.40
T/K Methanol 293.15
Ethanol 293.15
Iso-propanol 293.15
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m/mol kg1
us/m s1 DMZ
KU 104/cm3 mol1 Pa1 DMZ
us/m s1MNZ
KU 104/cm3 mol1 Pa1 MNZ
0.05
1132.03
4.34
1133.79
5.14
308.15
0.01 0.02 0.03 0.04 0.05
1106.41 1107.65 1108.81 1109.76 1110.81
5.03 4.82 4.71 4.53 4.46
1107.01 1108.53 1110.02 1111.33 1112.65
6.53 5.94 5.72 5.50 5.37
313.15
0.01 0.02 0.03 0.04 0.05
1086.44 1087.66 1088.71 1089.73 1090.72
5.13 5.01 4.83 4.71 4.62
1087.01 1088.44 1089.83 1091.01 1092.38
6.68 6.09 5.85 5.59 5.54
0.01 0.02 0.03 0.04 0.05
1262.48 1265.76 1268.91 1271.71 1274.81
5.98 5.40 5.13 4.85 4.80
1262.82 1266.67 1269.91 1272.73 1276.01
6.43 6.01 5.56 5.18 5.08
298.15
0.01 0.02 0.03 0.04 0.05
1243.67 1246.82 1249.92 1252.47 1255.36
6.03 5.45 5.23 4.90 4.82
1244.01 1247.72 1250.84 1253.52 1256.62
6.50 6.12 5.67 5.27 5.17
303.15
0.01 0.02 0.03 0.04 0.05
1226.71 1229.79 1232.68 1235.37 1238.18
6.51 5.59 5.29 5.06 4.95
1227.06 1230.61 1233.52 1236.41 1239.31
6.67 6.21 5.69 5.44 5.27
308.15
0.01 0.02 0.03 0.04 0.05
1206.71 1209.65 1212.31 1215.11 1217.62
6.21 5.66 5.31 5.20 5.03
1207.03 1210.39 1213.54 1215.91 1218.87
6.70 6.24 5.97 5.48 5.40
313.15
0.01 0.02 0.03 0.04 0.05
1194.82 1197.78 1200.28 1203.11 1205.51
6.23 5.83 5.41 5.36 5.16
1195.11 1198.51 1201.54 1204.43 1207.56
6.72 6.43 6.10 5.88 5.82
n-Butanol 293.15
The standard uncertainties in molality (m), sound velocity (us), temperature (T) and pressure (P) are ±0.0015 mol kg1, ±2 m s1, ±102 K and ±5 kPa respectively.
Table 7 Partial molar isentropic compressibility (Ko/) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
Ko/ 104/cm3 mol1Pa1 DMZ Methanol Ethanol Iso-propanol n-Butanol
5.75 6.01 4.68 6.105
5.95 6.42 4.66 6.177
6.17 6.58 4.79 6.575
6.43 6.73 5.13 6.328
6.69 6.91 5.25 6.381
Ko/ 104/cm3 mol1 Pa1 MNZ Methanol Ethanol Iso-propanol n-Butanol
6.93 7.03 5.91 6.711
7.16 7.34 6.06 6.799
7.37 7.53 6.23 6.927
7.44 7.58 6.64 6.966
7.62 7.91 6.78 6.895
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ± 5 kPa respectively.
3.5. Acoustic impedance Acoustic impedance (Z) targeted on the molecular packing of the system in terms of different types of molecular interactions existing in solutions, dependent on both concentration and temperature of solution, can be obtained as follows [31]
Z ¼ us d
ð7Þ
The acoustic impedance of a medium can be defined as the ratio of the instantaneous pressure excess on any particle of the medium to the instantaneous velocity of that particle. Variations of pressure from one particle to another occur when a sound wave travels in medium. The inertial and elastic properties of the medium govern this factor. As internal pressure and cohesive energy increase with solute concentration, strong intermolecular hydrogen bonding
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Table 8 Slope of line (Sk) of apparent molar isentropic compressibility and molality of antibiotics (DMZ and MNZ) in different alcohol solutions at different temperatures and at 101 kPa pressure. Solvents
298.15 K
303.15 K
308.15 K
313.15 K
Sk 104/kg cm3 mol2 Pa1 DMZ Methanol 38.7 Ethanol 16.6 Iso-propanol 18.2 n-Butanol 29.1
293.15 K
34.9 23.3 11.6 29.7
37.4 23.9 9.6 36.5
40.3 23.8 14.3 28.2
37.8 24.7 13.2 26.1
Sk 104/kg cm3 mol2 Pa1 MNZ Methanol 20.6 Ethanol 36.6 Iso-propanol 19.0 n-Butanol 35.3
22.0 39.6 20.1 35.1
22.3 38.1 21.7 35.7
18.8 34.0 27.6 33.6
20.0 34.3 27.8 23.5
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
between antibiotic and alcohol molecules occurs. Hence, an increase in specific acoustic impedance is caused by an increase in instantaneous pressure excess at any molecule [35]. The calculated values of acoustic impedance are given in Table 9 where it is clear that Z increases with an increase in the concentration of antibiotics at all temperatures. This suggests that the presence of stronger molecular interactions due to closer packing structure of solute and solvent molecules (by the formation of Hbond in solutions). Greater values of Z for MNZ are observed than those for DMZ which can be explained on the basis of presence of a greater degree of hydrogen bonding between MNZ and alcohol molecules that result in greater values of Z compared to that of DMZ in alcohols. The variation of Z in different alcohols lies in following increasing order: n-butanol > ethanol > methanol > isopropanol which can be explained in terms of increase in hydrophobic–hydrophilic interactions with increasing alkyl chain length [36]. 3.6. Solvation number Solvation numbers reveal the self-motivated situation of ions as they move in solution. Two solvation numbers may be described i.e.
molecule than DMZ. The solvation number in different alcoholic solutions follows the sequence: iso-propanol > methanol > ethanol > n-butanol. Solvation numbers in methanol are higher than those in ethanol and n-butanol which can be explained in terms of steric reasons: molecules of methanol are smaller than those of ethanol and n-butanol. iso-Propanol has lowest values of solvation number due to additional steric hindrance caused by the position of –OH group in its molecule [37]. 3.7. Relative association Relative association (RA) is another parameter to analyse the extent of association in any solution. RA can be evaluated using the following formula [20]
RA ¼ ðd=do Þðuo =uÞ1=3 The addition of small quantities of additive, i.e., structure breakers generally seem to increase the cohesion between the molecules by breaking the open structure [38]. In the present case, the RA values are all positive and are equal to or near unity. They are influenced mainly by two factors: Breaking up of solvent structure upon addition of solute results in decrease in RA values Subsequent solvation of solutes by solvent molecules results in an increase in RA values
Primary solvation number Secondary solvation number Primary solvation number reflects the number of solvent molecules that have lost their own sovereignty of translational motion but move along with the ions in solution randomly. While secondary solvation number states the solvent molecules in the vicinity of the ion and hence are affected by the presence of ions. Using the isentropic compressibility data, solvation numbers can be obtained by the equation [20]
Thus increase or decrease in RA values depends upon two above mentioned factors [31]. Calculated values of RA for both antibiotics in all alcoholic solutions are given in Table 9 which show that RA values increases with increasing antibiotic concentration suggesting that the subsequent solvation of solutes by free solvent molecules is more dominant over breaking up of solvent structure.
Sn ¼ M 1 =M2 ð1 bs =bos Þð100 X=XÞ
4. Conclusions
ð8Þ
The M1 and M2 represent the molar mass of solute and solvent respectively; bs and bos are the isentropic compressibility of solution and pure solvent and X is the mole fraction of solute. The degree of interaction can also be measured in terms of solvation number (Sn). Negative Sn values indicate the structure breaking tendency of solute molecules in solution. The resultant values depend upon solute–solute and solute–solvent interactions [36]. The values of Sn given in Table 9 showed that Sn values are positive which suggests the structure forming tendency of antibiotics in all alcohols. The variation in Sn with rise in temperature indicates increased solute–solvent interactions in these systems. The solvation number for MNZ solutions is greater than DMZ solutions as highly hydrated molecules possess greater nH values and according to the present experimental results MNZ is a more hydrated
From the present study, it is concluded that the values of apparent molar volume at all concentrations of antibiotic solution at different temperatures are found positive which indicates the presence of strong solute–solvent interactions in antibiotic and alcohols. Decrease in value of Vo/ with increasing chain length of alcohols has been observed. This can be attributed to decreasing solubility of antibiotics in pure alcohols with increasing chain length. The values of the slope of the line of apparent molar volume are negative showing the presence of weak interactions among antibiotic molecules in the presence of alcohols. Highly negative values of apparent molar isentropic compressibility (K/) indicate a closely-packed structure in both antibiotic solutions owing to antibiotic–alcohol interactions. The higher negative values of par-
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Table 9 Molality (m), acoustic impedance (Z), solvation number (Sn), intermolecular free length (Lf) and relative association (RA) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at 101 kPa pressure. m/mol kg1
Z 103/kg m2 s1 DMZ
Sn DMZ
Lf 1011/m DMZ
RA DMZ
Z 103/kg m2 s1 MNZ
Sn MNZ
Lf 1011/m MNZ
RA MNZ
Methanol 293.15 K 0.01 0.02 0.03 0.04 0.05
880.67 882.92 884.72 886.34 888.03
1.88 3.56 4.78 5.82 6.91
16.23 16.17 16.12 16.08 16.04
1.0007 1.0015 1.0024 1.0035 1.0045
881.26 884.27 886.83 889.66 892.25
2.97 5.87 8.22 10.85 13.20
16.21 16.12 16.05 15.97 15.89
1.0005 1.0011 1.0018 1.0025 1.0032
298.15 K 0.01 0.02 0.03 0.04 0.05
872.22 874.34 876.35 878.11 880.02
1.97 3.53 4.97 6.17 7.48
16.45 16.39 16.34 16.29 16.24
1.0007 1.0015 1.0024 1.0034 1.0044
872.73 875.67 878.44 881.25 883.44
2.98 5.84 8.47 11.11 13.01
16.43 16.34 16.26 16.18 16.12
1.0005 1.0011 1.0018 1.0024 1.0033
303.15 K 0.01 0.02 0.03 0.04 0.05
851.93 853.97 855.95 857.55 859.44
1.94 3.47 4.92 5.99 7.34
17.14 17.08 17.03 16.98 16.93
1.0007 1.0016 1.0025 1.0035 1.0045
852.42 855.22 857.99 860.58 862.80
2.94 5.71 8.40 10.86 12.86
17.12 17.04 16.95 16.87 16.81
1.0006 1.0012 1.0018 1.0026 1.0034
308.15 K 0.01 0.02 0.03 0.04 0.05
833.74 835.86 837.62 839.25 840.94
1.90 3.56 4.82 5.95 7.12
17.75 17.68 17.63 17.58 17.53
1.0007 1.0016 1.0026 1.0036 1.0046
834.21 836.9 839.55 842.13 844.44
2.00 3.87 5.70 7.44 8.94
17.73 17.64 17.55 17.46 17.39
1.0006 1.0012 1.0019 1.0026 1.0034
313.15 K 0.01 0.02 0.03 0.04 0.05
820.67 822.79 824.50 826.28 828.13
1.94 3.62 4.87 6.17 7.52
18.19 18.12 18.07 18.01 17.95
1.0071 1.0015 1.0026 1.0036 1.0045
821.08 823.71 826.31 828.71 831.1
5.07 9.83 14.46 18.61 22.68
18.176 18.083 17.993 17.913 17.834
1.0006 1.0012 1.0020 1.0027 1.0036
Ethanol 293.15 K 0.01 0.02 0.03 0.04 0.05
918.08 920.93 923.59 925.99 928.62
1.58 3.13 4.54 5.76 7.12
0.01485 0.01478 0.01471 0.01465 0.01458
1.0004 1.0007 1.0012 1.0018 1.0022
918.58 921.68 924.29 926.8 929.62
2.27 4.29 5.91 7.43 9.17
14.84 14.76 14.69 14.63 14.56
1.0003 1.0008 1.0015 1.0022 1.0028
298.15 K 0.01 0.02 0.03 0.04 0.05
906.23 908.89 911.53 914.04 916.43
1.66 3.10 4.52 5.83 7.06
15.16 15.09 15.02 14.95 14.89
1.0003 1.0008 1.0012 1.0018 1.0023
906.67 909.65 912.24 914.86 917.55
2.32 4.28 5.90 7.53 9.19
15.15 15.07 15.01 14.94 14.87
1.0003 1.0008 1.0015 1.0022 1.0029
303.15 K 0.01 0.02 0.03 0.04 0.05
886.74 889.38 891.85 894.23 896.61
1.62 3.08 4.42 5.68 6.94
15.77 15.69 15.62 15.56 15.49
1.0003 1.0008 1.0012 1.0017 1.0023
887.19 890.01 892.92 895.19 897.81
2.28 4.16 6.09 7.48 9.13
15.76 15.67 15.59 15.53 15.46
1.0004 1.0009 1.0014 1.0022 1.0030
308.15 K 0.01 0.02 0.03 0.04 0.05
856.27 858.76 861.11 863.2 865.57
1.54 2.96 4.27 5.39 6.68
16.82 16.74 16.67 16.60 16.53
1.0004 1.0008 1.0014 1.0021 1.0027
856.67 859.31 862.06 864.42 866.67
2.16 3.96 5.84 7.36 8.79
16.81 16.72 16.64 16.57 16.50
1.0004 1.0010 1.0016 1.0023 1.0031
313.15 K 0.01 0.02 0.03 0.04 0.05
846.08 848.59 851.08 852.89 855.21
1.52 2.97 4.40 5.33 6.61
17.13 17.04 16.96 16.91 16.84
1.0004 1.0009 1.0014 1.0022 1.0027
846.58 849.12 851.84 854.62 856.57
2.22 3.96 5.84 7.75 8.93
17.11 17.03 16.94 16.85 16.80
1.0004 1.0010 1.0016 1.0021 1.0031
Iso-propanol 293.15 K 0.01 0.02 0.03
911.25 913.41 915.58
0.90 1.70 2.50
15.01 14.96 14.91
1.0008 1.0016 1.0026
911.85 914.62 917.33
1.42 2.72 3.97
14.99 14.92 14.86
1.0004 1.0009 1.0014 (continued on next page)
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Table 9 (continued) m/mol kg1
Z 103/kg m2 s1 DMZ
Sn DMZ
Lf 1011/m DMZ
RA DMZ
Z 103/kg m2 s1 MNZ
Sn MNZ
Lf 1011/m MNZ
RA MNZ
0.04 0.05
917.55 919.23
3.19 3.73
14.86 14.83
1.0036 1.0047
919.94 922.25
5.15 6.14
14.79 14.74
1.0018 1.0023
298.15 K 0.01 0.02 0.03 0.04 0.05
890.41 892.51 894.62 896.71 898.52
0.87 1.67 2.46 3.24 3.86
15.63 15.58 15.53 15.47 15.43
1.0008 1.0017 1.0027 1.0036 1.0047
890.99 893.68 896.31 898.76 900.93
1.38 2.67 3.91 5.02 5.96
15.61 15.54 15.47 15.41 15.36
1.0008 1.0017 1.0026 1.0036 1.0047
303.15 K 0.01 0.02 0.03 0.04 0.05
877.08 879.26 881.22 883.32 885.34
0.86 1.72 2.45 3.24 3.99
16.02 15.96 15.91 15.85 15.81
1.0008 1.0017 1.0027 1.0036 1.0047
877.66 880.29 882.80 885.22 887.38
1.38 2.65 3.84 4.95 5.90
16.01 15.93 15.86 15.80 15.74
1.0008 1.0018 1.0028 1.0037 1.0048
308.15 K 0.01 0.02 0.03 0.04 0.05
855.26 857.31 859.32 861.19 863.12
0.88 1.69 2.47 3.17 3.90
16.74 16.68 16.62 16.57 16.52
1.0009 1.0018 1.0027 1.0037 1.0047
855.85 858.27 860.67 862.94 865.22
1.41 2.59 3.74 4.80 5.86
16.72 16.65 16.58 16.52 16.45
1.0008 1.0018 1.0028 1.0038 1.0049
313.15 K 0.01 0.02 0.03 0.04 0.05
837.3 839.33 841.24 843.12 844.98
0.86 1.68 2.42 3.15 3.87
17.41 17.35 17.29 17.24 17.19
1.0009 1.0018 1.0028 1.0038 1.0048
837.88 840.21 842.52 844.68 847.01
1.39 2.53 3.65 4.66 5.77
17.39 17.32 17.25 17.19 17.12
1.0009 1.0019 1.0029 1.0040 1.0051
n-Butanol 293.15 K 0.01 0.02 0.03 0.04 0.05
1022.59 1025.89 1029.09 1032.01 1035.25
1.32 2.40 3.44 4.37 5.39
12.27 12.2 12.13 12.07 12.01
0.9995 0.9992 0.9991 0.9989 0.9988
1022.98 1026.85 1030.25 1033.33 1036.79
1.75 3.29 4.60 5.77 7.08
12.26 12.18 12.11 12.04 11.97
0.9995 0.9992 0.9991 0.9992 0.9991
298.15 K 0.01 0.02 0.03 0.04 0.05
1002.58 1005.75 1008.89 1011.62 1014.64
1.28 2.34 3.38 4.25 5.22
12.70 12.63 12.56 12.50 12.43
0.9995 0.9993 0.9991 0.9991 0.9990
1002.97 1006.73 1010.03 1012.97 1016.31
1.70 3.22 4.51 5.64 6.92
12.69 12.61 12.54 12.47 12.41
0.9996 0.9993 0.9993 0.9993 0.9993
303.15 K 0.01 0.02 0.03 0.04 0.05
986.48 989.61 992.58 995.43 998.35
1.26 2.32 3.31 4.24 5.20
13.09 13.01 12.94 12.88 12.81
0.9996 0.9994 0.9992 0.9992 0.9991
986.89 990.52 993.61 996.75 999.87
1.69 3.17 4.40 5.63 6.85
13.08 12.99 12.92 12.85 12.78
0.9996 0.9994 0.9994 0.9994 0.9994
308.15 K 0.01 0.02 0.03 0.04 0.05
966.59 969.58 972.37 975.28 977.99
1.23 2.26 3.20 4.18 5.07
13.58 13.51 13.44 13.37 13.30
0.9996 0.9995 0.9994 0.9993 0.9993
966.95 970.39 973.71 976.39 979.58
1.63 3.07 4.42 5.47 6.74
13.57 13.48 13.41 13.34 13.27
0.9996 0.9995 0.9994 0.9996 0.9996
313.15 K 0.01 0.02 0.03 0.04 0.05
949.44 952.44 955.08 958.02 960.60
1.19 2.24 3.14 4.15 5.01
13.96 13.88 13.82 13.74 13.68
0.9997 0.9995 0.9995 0.9994 0.9995
949.79 953.24 956.42 959.5 962.79
1.58 3.04 4.36 5.62 6.95
13.95 13.86 13.78 13.71 13.62
0.9997 0.9995 0.9995 0.9995 0.9995
The standard uncertainties in molality (m), temperature (T) and pressure (P) are ±0.0015 mol kg1, ±102 K and ±5 kPa respectively.
tial molar isentropic compressibility (Ko/) indicate weak interactions among antibiotic molecules. Acoustical parameters like intermolecular free length, acoustic impedance, relative association and solvation number were calculated to strengthen the results of volumetric parameters. Decreasing values of intermolecular free length indicate the presence of strong intermolecular interactions, positive values of solvation number showed the structure making behaviour of antibiotics in alcoholic solutions.
Acknowledgments We gratefully acknowledge Lahore College for Women University for providing us the required chemicals. References [1] P. Bustamante, S. Muela, B. Escalera, Á. Pena, Chem. Pharm. Bull. 58 (2010) 644–649.
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JCT 16-517
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Investigation on molecular interactions of antibiotics in alcohols using volumetric and acoustic studies at different temperatures Bushra Naseem ⇑, Madeeha Iftikhar Department of Chemistry, Lahore College for Women University, Jail Road, Lahore 54000, Pakistan
a r t i c l e
i n f o
Article history: Received 27 June 2016 Received in revised form 18 September 2016 Accepted 27 September 2016 Available online 28 September 2016 Keywords: Apparent and partial molar volume Isentropic compressibility Acoustic impedance Intermolecular free length and solute– solvent interactions
a b s t r a c t The density and sound velocity for pure alcohols (methanol, ethanol, iso-propanol and n-butanol) and molal solutions of nitroimidazoles (metronidazole (MNZ) and dimetridazole (DMZ) have been measured at different temperatures (293.15–313.15 K). Different volumetric and acoustical parameters like apparent molar volume (V/), partial molar volume (V/), apparent molar isentropic compressibility (K/), partial molar isentropic compressibility (K/), hydration number (nH), acoustic impedance (Z) and intermolecular free length (Lf) of antibiotic solutions were calculated from the experimental values of density and sound velocity. The derived values have been used to explore the solute–solute and solute–solvent interactions. The V/ values are positive and K/ values are negative in both antibiotics, indicative of strong solute–solvent interactions and closely packed structure of antibiotics in alcohols. The decreasing trend of Lf with increasing antibiotic concentration shows the presence of strong intermolecular interactions in solutions. Ó 2016 Elsevier Ltd.
1. Introduction Solubility is a basic physico-chemical property that has significant applications to different processes i.e. biological, chemical, pharmaceutical and environmental. Careful experimentation is required for reliable solubility data and these measurements are tedious, time consuming and costly [1]. Volumetric and acoustical properties like apparent molar volume and apparent molar isentropic compressibility etc. of any solution can be evaluated using density and sound velocity values [2]. Volumetric properties of the mixtures of alcohols are of technological and theoretical interest. Different types of interactions like ion–ion, solvent–solvent and ion–solvent interactions are present in the solution [3]. From the density (q), sound velocity and viscosity (g) of solutions, structural aspects and properties of the solutions can be characterized [4]. Hence volumetric properties give helpful information regarding nature of solute and solvent [5]. The partial molar and apparent molar volumes of solutes are used to distinguish solutes of different molar masses on the basis of their ion–ion and ion–solvent affinity and in assessing drug potency whereas isentropic compressibility factors reflects the compactness of the hydration layers around the core of the solutes [6]. Solubility results also serve to
⇑ Corresponding author. E-mail address: [email protected] (B. Naseem). http://dx.doi.org/10.1016/j.jct.2016.09.037 0021-9614/Ó 2016 Elsevier Ltd.
construct mathematical models that help to optimize solvent composition selection in pharmaceutical technology [1]. It has been noted that by the addition of solute, changes occur in the structure of solvent i.e. it may either make or break [4]. By ultrasonic velocity measurements, the molecular interactions in pure liquids, aqueous solutions and mixtures have been studied. It gives a useful and reliable tool to study the properties of solutions of amino acids, polymers etc. However, little work has been done for the solutions of drugs [7]. Chemical transformations can take place in a gas, liquid or solid phase but majority of reactions are carried out in liquid phase in the form of solutions [8]. Alcohol is a class of organic compounds described by one or more hydroxyl (–OH) groups attached to a carbon atom of hydrocarbon chain. These might be considered as organic imitative of water, in which a hydrogen atom has been changed by –CH2 group, which may be represented by ‘R’ in organic structures. For example, in ethanol the alkyl group is the ethyl group, –CH2CH3 [9]. Globally, infections in gastrointestinal track by different parasites and bacteria are responsible for major morbidity and deaths. 5-Nitroimidazoles, a set of medicines, is a well-established group of antiprotozoal and antibacterial agents that have ability to reduce the development of anaerobic bacteria and certain anaerobic protozoa. The significance of imidazole is established from the fact that large number of medicines contains this moiety and several 5-nitroimidazole derivatives such as metronidazole (MNZ), dimetridazole (DMZ), ipronidazole (IPZ) and ronidazole (RNZ) have
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been used since long time, for the handling of critical cases of infections caused by protozoa and anaerobic bacteria [10]. They are placed into coccidiostat substances, but it has been reported that these compounds show mutagenic, carcinogenic and toxic properties. For this reason, their use has been prohibited as additives in feed for food-producing species. Chemical nature of drugs is essential to study their behaviour in different systems. This study is an attempt to explore the interactions of these antibiotics with solvents and solvent–solvent interactions from volumetric and acoustical properties (apparent molar volume (V/), isentropic compressibility (K/), partial molar volume (V°/), partial molar compressibility (K/), acoustic impedance (Z), hydration number (nh) and intermolecular free length), which were evaluated from density and sound velocity of antibiotics (DMZ and MNZ) in different alcohols at different temperatures.
various concentrations (0.01–0.05) mol kg1 in alcohols were measured at temperatures 293.15 K, 298.15 K, 303.15 K, 308.15 K and 313.15 K and at 101 kPa pressure. The weighing of solutes (antibiotics) was done by Wiggen Hauser electronic balance with a precision of ±0.001 mg. At least three readings of each composition were reproducible to ±0.005 mg and the values obtained were averaged. The standard uncertainties in molality (m), density (d), sound velocity (us), and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±2 m s1, ±102 K and ±5 kPa respectively. The measured densities and ultrasound speeds were utilized in determining volumetric and acoustical properties of solutions as described in the next section. 3. Results and discussion 3.1. Density and sound velocity measurement of antibiotic solutions
2. Experimental 2.1. Materials Chemicals, MNZ, DMZ, methanol, ethanol, iso-propanol and nbutanol, were products of Sigma, and were used as received without any purification. All glassware was carefully washed with deionized water, cleaned and dried in oven before use. Mass fraction purity and source of chemicals used in the experiment have been given in Table 1. 2.2. Density and sound velocity measurements Density (d) and sound velocity (u) were measured by Anton Paar DSA 5000 M with high precision vibrating tube digital density meter and ultrasound speed measuring device. The instrument has a built-in thermostat to maintain the temperature. The accuracy and repeatability of DSA 5000 M for density are 5 106 g cm3 and 1 106 g cm3 and that of temperature is 0.01 °C and 0.001 °C respectively. The sample density is determined by measuring the oscillation frequency of a U-shaped sample tube completely filled with the sample liquid. The principle of sound velocity measurement is based on propagation time technique. The sample is sandwiched between two piezoelectric ultrasound transducers. One transducer emits sound waves through the sample-filled cavity (frequency around 3 MHz) and the second transducer receives those waves [11]. Thus, the sound velocity is obtained by dividing the known distance between transmitter and receiver by the measured propagation time of the sound waves up to 0.5 m s1accuracy and 0.1 ms1 repeatability. Density and sound velocity of pure alcohols and solutions of DMZ and MNZ of
Density and sound velocity of alcohols: methanol, ethanol, isopropanol and n-butanol have been measured at different temperatures (293.15 K–313.15 K). The measured density and sound velocity values for pure alcohols have been given in Table 2. Comparison of experimental with literature values showed that measured values is in accordance with literature reported values [11–17]. Density and sound velocity for the antibiotics (DMZ and MNZ) in alcohols were measured at temperatures (293.15 K–313.15 K) using antibiotic concentration range (0.01–0.05 mol kg1). Measured density values have been given in Table 3 which show that density of antibiotic solutions decreases with increasing temperature and show an increase with increasing concentration of antibiotics in alcoholic solutions. With increasing temperatures, density decreases because increasing temperature weakens the bonds between solute and solvent in a solution making the solution less dense [2]. Density increases with increasing concentration of solute (antibiotics) in alcoholic solution which can be interpreted by the enhanced structure of solvents due to added solute (antibiotics) [18]. From values shown in the tables, it is also clear that density of MNZ in all alcoholic solutions is greater than that of DMZ because the –OH group in MNZ is responsible for greater attractive forces like H-bonding etc. with solvent molecules than in DMZ and hence has a more dense structure. Sound velocity values for both antibiotics in alcoholic solutions at different temperatures (293.15–298.15) K are given in Table 6. Sound velocity decreases with increasing temperature and increases with increasing concentration of antibiotics in alcohol solutions. With increasing temperature, molecules gain kinetic energy. As the kinetic energy of molecules increases, the interactions among solute and solvent molecules become weaker. The
Table 1 Provenance and mass fraction purity of the materials studied. Chemical names
Source
Mass fraction purity
Purification method
CAS no
Methanol
Sigma Aldrich
>0.998
Used as received
67-56-1
Ethanol
Sigma Aldrich
>0.995
Used as received
64-17-5
Iso-propanol
Sigma Aldrich
>0.995
Used as received
67-63-0
n-Butanol
Sigma Aldrich
>0.994
Used as received
71-36-3
Dimetridazole
Sigma Aldrich
>0.997
Used as received
551-92-8
Metronidazole
Sigma Aldrich
>0.996
Used as received
443-48-1
Structures
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 2 Density (do/g cm3) and sound velocity (uo/m s1) of pure alcohols at different temperatures and at 101 k Pa pressure. Temperatures T/K
do/g cm3
uo/m s1
Experimental values
Literature values
Experimental values
Literature values
Methanol 293.15 298.15 303.15 308.15 313.15
0.793603 0.789271 0.784591 0.777868 0.772438
0.791300b 0.786660g 0.781901g 0.777230g 0.772500g
1106.63 1101.91 1082.73 1068.82 1059.41
1105.21b 1102.32g 1085.89g 1069.63g 1060.00g
Ethanol 293.15 298.15 303.15 308.15 313.15
0.789412 0.785413 0.782015 0.777697 0.773201
0.789501a 0.785500g 0.782001g 0.777700g 0.773700g
1159.34 1150.05 1130.28 1097.64 1090.92
1160.30a 1152.00g 1128.00g 1098.00g 1092.70a
Iso-propanol 293.15 298.15 303.15 308.15 313.15
0.785810 0.781336 0.777061 0.772019 0.769701
0.785450c 0.781260d 0.776591e 0.772201e 0.767120c
1156.65 1136.74 1125.89 1105.01 1085.11
1157.80c 1138.87d 1126.01e 1105.30e 1101.87c
n-Butanol 293.15 298.15 303.15 308.15 313.15
0.809493 0.805648 0.803676 0.800496 0.794112
0.809500a 0.8057500d 0.803700a 0.798527f 0.794101a
1258.43 1239.82 1222.97 1203.15 1191.42
1257.66a 1240.00d 1223.55a 1211.00f 1190.28a
The standard uncertainties in molality (m), density (d), sound velocity (us), and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±2 m s1, ±102 K and ±5 kPa, respectively. a Reference [11]. b Reference [12]. c Reference [13]. d Reference [14]. e Reference [15]. f Reference [16]. g Reference [17].
resulting weak interactions among molecules pose hindrance for the sound velocity to pass through solutions, therefore sound velocity decreases with increasing temperature [16]. Where sound velocity increases in antibiotics-alcohol solutions with increasing concentration of antibiotics in solutions, it could be attributed to the overall increase of cohesion brought about by the solute–solute, solute–solvent and solvent–solvent interactions in solutions. Cohesive forces are further enhanced on successive increase in solute concentration [19]. 3.2. Apparent and partial molar volume The apparent molar volume of a solute is a difference between the volume of the solution and the volume of the pure solvent per mole of solute. The apparent molar volume for antibiotics in alcohols is calculated from density using following equation [20,21]:
V / ¼ 1000ðdo dÞ=mddo þ M=d
ð1Þ 1
M is molar mass of antibiotics (DMZ = 141.128 g mol and MNZ = 171.15 g mol1), m is the molality of antibiotic solutions in alcohols; d and do are densities of solution and solvent respectively. Plots between apparent molar volume and molality of both antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures have been shown in Figs. 1–4(a and b) for DMZ (a) and MNZ (b). The V/ value is sensitive to measure solute–solvent interactions occurring in the solution. The variation of V/ is found to be linearly dependent on molality m, in the concentration range studied [19]. It has been observed that values of apparent molar volume decreases with increasing temperature and concentration of
antibiotics (MNZ and DMZ) solutions in alcohols due to the electrostriction effect [22]. Furthermore, increase in the value of apparent molar volume with increase in alkyl groups in carbon chain of alcohols i.e. from methanol to n-butanol, whereas an exception arises in the case of iso-propanol which shows the least value of apparent molar volume. For iso-propanol, the interaction of antibiotics with the alcohol is sterically hindered by the position of –OH group in carbon chain of alcohol, leading to increase in the value of apparent molar volume and the obtained order of apparent molar volume is iso-propanol > methanol > ethanol > n-butanol [23]. The values obtained for apparent molar volume are positive for both antibiotics solutions in alcohols which suggests that overall structural order is enhanced in solutions [17]. Large values of Va are obtained for MNZ as compared to DMZ at all temperatures and in all alcohols, because of the increase in molar mass that causes greater affinity for solvent and therefore enhances solute–solvent interactions [20]. The partial molar volumes (Va) were obtained by extrapolating the plots of apparent molar volume (Va) versus molality (m) of antibiotics solutions in alcohols using Masson type equation [24]:
V U ¼ V oU þ Sv m Voa
ð2Þ
The is the partial molar volume that provides information regarding solute–solvent interaction and Sv is a limiting or experimental slope which gives the pair wise interactions; Va is the apparent molar volume and m is molality of the solution [25]. The values of partial molar volume (Voa) and experimental slope (Sv) were estimated for DMZ and MNZ using the least squares fit method and the values of both parameters are listed in Tables 4 and 5 respectively.
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Table 3 Molality (m), density (d) and apparent molar volume (V/) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at pressure 101 kPa. m/mol kg1
d/g cm3 DMZ
d/g cm3 MNZ
0.01 0.02 0.03 0.04 0.05
0.794574 0.795553 0.796549 0.797546 0.798551
0.794604 0.795623 0.796639 0.797676 0.798708
298.15
0.01 0.02 0.03 0.04 0.05
0.790247 0.791232 0.792221 0.793214 0.794217
0.790277 0.791292 0.792311 0.793334 0.794357
303.15
0.01 0.02 0.03 0.04 0.05
0.785567 0.786551 0.787548 0.788544 0.789542
0.785597 0.786609 0.787627 0.788644 0.789672
308.15
0.01 0.02 0.03 0.04 0.05
0.778839 0.779817 0.780811 0.781815 0.782818
0.778871 0.779883 0.780899 0.781919 0.782939
313.15
0.01 0.02 0.03 0.04 0.05
0.773407 0.774382 0.775371 0.776379 0.777401
0.773439 0.774445 0.775471 0.776481 0.777519
0.01 0.02 0.03 0.04 0.05
0.790241 0.791079 0.791927 0.792782 0.793639
0.790343 0.791289 0.792231 0.793202 0.794168
298.15
0.01 0.02 0.03 0.04 0.05
0.786243 0.787082 0.787931 0.788786 0.789648
0.786348 0.787286 0.788239 0.789211 0.790178
303.15
0.01 0.02 0.03 0.04 0.05
0.782847 0.783685 0.784537 0.785397 0.786251
0.782951 0.783894 0.784841 0.785812 0.786787
308.15
0.01 0.02 0.03 0.04 0.05
0.778529 0.779371 0.780242 0.781101 0.781968
0.778631 0.779574 0.780531 0.781491 0.782468
313.15
0.01 0.02 0.03 0.04 0.05
0.774037 0.774889 0.775744 0.776604 0.777469
0.774137 0.775082 0.776037 0.776989 0.777976
0.01 0.02 0.03 0.04 0.05
0.786794 0.787781 0.788801 0.789803 0.790834
0.786911 0.788027 0.789147 0.790271 0.791419
298.15
0.01 0.02 0.03 0.04 0.05
0.782319 0.783311 0.784321 0.785331 0.786342
0.782438 0.783549 0.784671 0.785811 0.786944
303.15
0.01 0.02 0.03 0.04 0.05
0.778042 0.779031 0.780039 0.781054 0.782084
0.778164 0.779278 0.780399 0.781545 0.782671
T/K Methanol 293.15
Ethanol 293.15
Iso-propanol 293.15
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 3 (continued) T/K
m/mol kg1
d/g cm3 DMZ
d/g cm3 MNZ
308.15
0.01 0.02 0.03 0.04 0.05
0.773001 0.773987 0.774992 0.776011 0.777019
0.773122 0.774239 0.775362 0.776494 0.777624
313.15
0.01 0.02 0.03 0.04 0.05
0.770682 0.771681 0.772691 0.773695 0.774703
0.770811 0.771943 0.773077 0.774215 0.775377
0.01 0.02 0.03 0.04 0.05
0.809983 0.810491 0.811003 0.811516 0.812079
0.810078 0.810673 0.811280 0.811901 0.812531
298.15
0.01 0.02 0.03 0.04 0.05
0.806148 0.806651 0.807169 0.807699 0.808245
0.806241 0.806855 0.807478 0.808101 0.808761
303.15
0.01 0.02 0.03 0.04 0.05
0.804182 0.804701 0.80524 0.805775 0.806302
0.804277 0.804899 0.805511 0.806168 0.806799
308.15
0.01 0.02 0.03 0.04 0.05
0.801009 0.801538 0.802077 0.802629 0.803199
0.801097 0.801719 0.802369 0.803009 0.803678
313.15
0.01 0.02 0.03 0.04 0.05
0.794629 0.795169 0.795718 0.796289 0.796841
0.79431 0.795355 0.795994 0.796644 0.797299
n-Butanol 293.15
The standard uncertainties in molality (m), density (d) and temperature (T) and pressure (P) are ±0.0015 mol kg1, ±1 103 g cm3, ±102 K and ±5 kPa respectively.
25
57 56 55 Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
23 21 19
54 53 52 51
17
50 0
15 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 1a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in methanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
The positive values of partial molar volume (a measure of ion– solvent interactions) indicate the presence of strong interactions between antibiotics and solvents. The Sv values are negative and decrease with an increase in temperature indicating that solute– solute interactions decrease with increasing temperature for all
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 1b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in methanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
systems. The Voa values increase in the following order: isopropanol > methanol > ethanol > n-butanol. This result indicates that the steric-hindering effect becomes more significant when size of alkyl group increases, and the solvation capacity of alkyl group weakens, resulting in greater Voa values. The exceptional lower Voa values for isopropanol can be explained in terms of more
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40
47 46
38 Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
45 44 43 42 41
36 34 32
40 39 0
0.01
0.02
0.03
0.04
0.05
30
0.06
0
Molality/(mol·kg-1)
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
Fig. 2a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in ethanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 3b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in iso-propanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
68
100
67
98 Vφ /(cm3·mol-1)
66 Vφ /(cm3·mol-1)
0.01
65 64 63 62
96 94 92 90
61
88
60 0
0.01
0.02
0.03
0.04
0.05
0
0.06
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
Molality/(mol·kg-1) Fig. 2b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in ethanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 4a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in n-butanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
22
125
18
Vφ /(cm3·mol-1)
Vφ /(cm3·mol-1)
20
16 14 12 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1)
120
115
110 0
0.01
0.02
0.03
0.04
0.05
0.06
Molality/(mol·kg-1) Fig. 3a. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (DMZ) solutions in iso-propanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
Fig. 4b. Plot between molality (m) and apparent molar volume (Vu) of antibiotic (MNZ) solutions in n-butanol at temperatures 293.15 K (r), 298.15 K (h), 303.15 K (▲), 308.15 K (⁄) and 313.15 K (d).
prominent electrostriction effect and degree of steric hindrance due to position of –OH goup [17]. 3.3. Apparent and partial molar isentropic compressibility Apparent molar isentropic compressibility is a measure of degree of compressibility of ions in solution and can be calculated using the relation [26]:
K / ¼ 1000ðbs do bos dÞ=mddo þ bs M=d
ð3Þ
The M is the molar mass of antibiotics (DMZ and MNZ), m is molality of antibiotic solutions in alcohols, do and d are densities of solvent and solution, respectively; bs and bos represent the isentropic compressibility of solution and solvent respectively, calculated using the following equation:
bs ¼ ½u2 d
1
ð4Þ
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 4 Partial molar volume (Vo/) of antibiotics (DMZ and MNZ) in alcohol solutions at different temperatures and 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
mol DMZ Methanol Ethanol Iso-propanol n-Butanol
24.40 46.35 21.27 100.37
22.53 45.78 20.28 99.20
21.80 45.10 20.27 97.92
21.84 44.73 19.04 97.22
21.60 43.04 18.07 96.50
Vo//cm3mol1 MNZ Methanol Ethanol Iso-propanol n-Butanol
57.20 68.08 40.09 123.09
55.63 67.38 39.40 121.88
55.05 66.73 38.35 120.57
54.54 66.49 37.12 121.10
54.43 65.55 35.55 118.29
Vo//cm3
1
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
Table 5 Slope of line (Sv) of plot of apparent molar volume and molality of antibiotics (DMZ and MNZ) in alcohol solutions at different temperatures and 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
Sv/kg cm3 mol1 DMZ Methanol Ethanol Iso-propanol n-Butanol
78.61 71.61 90.06 99.40
53.24 73.79 80.06 83.23
61.84 71.33 101.95 84.56
85.19 100.87 85.70 111.45
103.29 74.47 81.60 122.56
Sv/kg cm3 mol1 MNZ Methanol Ethanol Iso-propanol n-Butanol
83.38 86.89 83.33 96.18
51.19 87.01 89.19 115.21
46.80 83.67 88.44 99.89
54.43 90.86 79.82 145.71
69.74 81.94 102.12 85.74
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
Experimentally calculated data for apparent molar isentropic compressibility for both antibiotics at different temperatures has given in Table 6. The isentropic compressibility values increase with an increase in temperature at all compositions of antibiotic solutions due to an increase in thermal agitation, making the solution more compressible [16]. The KU values are negative and decrease with increase in the concentration of antibiotics in solvents. Negative KU values predict that solvent molecules around solute are less compressible than those in the bulk which is attributed to strong solute–solvent interactions in solution [27] The results show an increase in the value of apparent molar isentropic compressibility with increasing –CH2 group in the carbon chain of alcohol i.e. from methanol to n-butanol, whereas iso-propanol shows different behaviour. The decrease in the value of apparent molar isentropic compressibility in iso-propanol is due to side group which may cause steric hindrance and the obtained order of apparent molar isentropic compressibility in alcohols is iso-propanol > methanol > ethanol > n-butanol [17]. The value of apparent molar isentropic compressibility is larger for MNZ than DMZ. This is because apparent molar isentropic compressibility increases with increasing molar mass of the solute (MNZ is larger molecule than DMZ) [19]. The limiting apparent molar isentropic compressibility values given in Table 7 were evaluated by using Masson’s equation [28]:
K / ¼ K o/ þ Sk m
ð5Þ
Koa is the limiting value of isentropic compressibility and Sk is the experimental slope indicative of solute–solute interactions. Magnitude of Koa is a measure of solute–solvent interactions as solute–solute interactions are negligible at infinite dilution. Calculated values for Ko/ and Sk are given in Tables 7 and 8. The values of partial molar isentropic compressibility are negative and increase with increase in temperature of solution, this may be attributed to a decrease of electrostriction or hydration
from the second solvation layer of ionic (–OH) group of antibiotics [29]. The Sk values of the antibiotics studied are found to be positive at all temperatures thereby suggesting strong solute–solute interactions [30]. 3.4. Intermolecular free length (Lf) Intermolecular free length is another acoustical parameter describing the nature and strength of intermolecular interactions present in a solution and referred to as distance among surfaces of two molecules and can be calculated using isentropic compressibility (bs) using following equation [31]:
Lf ¼ Kðbs Þ1=2
ð6Þ 8
K ¼ ½ð93:875 þ 0:375ÞðT=K 10 It depends on intermolecular as well as intra molecular interactions existing among components of the mixture. When isentropic compressibility decreases, free length also decreases and vice versa [32,33]. The change in the free length values also shows the presence of appreciable interactions present among solute and solvent molecules due to which type of structural rearrangement is affected. Using experimental results, calculated values of Lf for both antibiotics (DMZ and MNZ) in alcoholic solutions at different temperatures are given in Table 9. Results presented show that Lf values decrease with increase in concentration of antibiotics, and temperature. This shows that specific strong intermolecular interaction among antibiotics (DMZ and MNZ) and alcohol molecules prevails in the solution. Also, the decreased value of free length indicates structure promoting behaviour of the solute molecule [34]. In all alcohol solutions, Lf for DMZ solutions are greater than for MNZ solutions. This can be attributed due to increased interactions among MNZ molecules and alcohols which could be due the presence of extra –OH group in MNZ structure than DMZ molecule.
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Table 6 Molality (m), speed of sound (us) and apparent molar isentropic compressibility (KU) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at pressure 101 kPa. m/mol kg1
us/m s1 DMZ
KU 104/cm3 mol1 Pa1 DMZ
us/m s1MNZ
KU 104/cm3 mol1 Pa1 MNZ
0.01 0.02 0.03 0.04 0.05
1108.35 1109.82 1110.69 1111.34 1112.05
5.36 5.07 4.52 4.12 3.90
1109.05 1111.42 1113.21 1115.31 1117.12
6.70 6.65 6.17 6.11 5.94
298.15
0.01 0.02 0.03 0.04 0.05
1103.73 1105.03 1106.19 1107.03 1108.03
5.75 5.14 4.82 4.47 4.34
1104.33 1106.63 1108.71 1110.82 1112.14
6.89 6.74 6.51 6.40 5.96
303.15
0.01 0.02 0.03 0.04 0.05
1084.48 1085.72 1086.85 1087.51 1088.53
5.95 5.31 5.00 4.55 4.46
1085.06 1087.23 1089.33 1091.21 1092.61
7.12 6.90 6.77 6.55 6.18
308.15
0.01 0.02 0.03 0.04 0.05
1070.49 1071.87 1072.75 1073.47 1074.25
6.07 5.68 5.12 4.73 4.53
1071.05 1073.11 1075.11 1077.01 1078.55
7.27 7.03 6.89 6.75 6.47
313.15
0.01 0.02 0.03 0.04 0.05
1061.11 1062.51 1063.36 1064.28 1065.26
6.41 5.99 5.35 5.09 4.97
1061.59 1063.61 1065.56 1067.26 1068.91
7.43 7.20 7.06 6.80 6.63
0.01 0.02 0.03 0.04 0.05
1161.77 1164.15 1166.26 1168.03 1170.08
5.81 5.75 5.55 5.27 5.22
1162.25 1164.78 1166.69 1168.43 1170.56
6.74 6.35 5.79 5.43 5.37
298.15
0.01 0.02 0.03 0.04 0.05
1152.61 1154.76 1156.87 1158.79 1160.56
6.29 5.86 5.68 5.49 5.31
1153.01 1155.43 1157.31 1159.21 1161.19
7.10 6.51 5.94 5.67 5.54
303.15
0.01 0.02 0.03 0.04 0.05
1132.71 1134.87 1136.79 1138.57 1140.36
6.40 6.08 5.81 5.59 5.45
1133.13 1135.37 1137.71 1139.19 1141.11
7.30 6.60 6.43 5.89 5.75
308.15
0.01 0.02 0.03 0.04 0.05
1099.86 1101.86 1103.65 1105.11 1106.91
6.53 6.25 6.01 5.67 5.63
1100.22 1102.28 1104.45 1106.11 1107.61
7.37 6.72 6.60 6.22 5.92
313.15
0.01 0.02 0.03 0.04 0.05
1093.08 1095.11 1097.12 1098.23 1099.99
6.60 6.44 6.36 5.75 5.71
1093.58 1095.52 1097.68 1099.91 1101.02
7.82 6.89 6.77 6.74 6.18
0.01 0.02 0.03 0.04 0.05
1158.18 1159.47 1160.73 1161.74 1162.35
4.51 4.26 4.18 4.00 3.73
1158.77 1160.64 1162.43 1164.08 1165.31
5.74 5.49 5.34 5.19 4.94
298.15
0.01 0.02 0.03 0.04 0.05
1138.17 1139.41 1140.63 1141.83 1142.66
4.58 4.37 4.30 4.25 4.06
1138.74 1140.56 1142.28 1143.74 1144.85
5.85 5.65 5.51 5.30 5.02
303.15
0.01 0.02 0.03 0.04
1127.29 1128.66 1129.71 1130.93
4.69 4.66 4.42 4.40
1127.86 1129.62 1131.22 1132.66
6.03 5.79 5.58 5.40
T/K Methanol 293.15
Ethanol 293.15
Iso-propanol 293.15
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B. Naseem, M. Iftikhar / J. Chem. Thermodynamics 104 (2017) 239–251 Table 6 (continued) T/K
m/mol kg1
us/m s1 DMZ
KU 104/cm3 mol1 Pa1 DMZ
us/m s1MNZ
KU 104/cm3 mol1 Pa1 MNZ
0.05
1132.03
4.34
1133.79
5.14
308.15
0.01 0.02 0.03 0.04 0.05
1106.41 1107.65 1108.81 1109.76 1110.81
5.03 4.82 4.71 4.53 4.46
1107.01 1108.53 1110.02 1111.33 1112.65
6.53 5.94 5.72 5.50 5.37
313.15
0.01 0.02 0.03 0.04 0.05
1086.44 1087.66 1088.71 1089.73 1090.72
5.13 5.01 4.83 4.71 4.62
1087.01 1088.44 1089.83 1091.01 1092.38
6.68 6.09 5.85 5.59 5.54
0.01 0.02 0.03 0.04 0.05
1262.48 1265.76 1268.91 1271.71 1274.81
5.98 5.40 5.13 4.85 4.80
1262.82 1266.67 1269.91 1272.73 1276.01
6.43 6.01 5.56 5.18 5.08
298.15
0.01 0.02 0.03 0.04 0.05
1243.67 1246.82 1249.92 1252.47 1255.36
6.03 5.45 5.23 4.90 4.82
1244.01 1247.72 1250.84 1253.52 1256.62
6.50 6.12 5.67 5.27 5.17
303.15
0.01 0.02 0.03 0.04 0.05
1226.71 1229.79 1232.68 1235.37 1238.18
6.51 5.59 5.29 5.06 4.95
1227.06 1230.61 1233.52 1236.41 1239.31
6.67 6.21 5.69 5.44 5.27
308.15
0.01 0.02 0.03 0.04 0.05
1206.71 1209.65 1212.31 1215.11 1217.62
6.21 5.66 5.31 5.20 5.03
1207.03 1210.39 1213.54 1215.91 1218.87
6.70 6.24 5.97 5.48 5.40
313.15
0.01 0.02 0.03 0.04 0.05
1194.82 1197.78 1200.28 1203.11 1205.51
6.23 5.83 5.41 5.36 5.16
1195.11 1198.51 1201.54 1204.43 1207.56
6.72 6.43 6.10 5.88 5.82
n-Butanol 293.15
The standard uncertainties in molality (m), sound velocity (us), temperature (T) and pressure (P) are ±0.0015 mol kg1, ±2 m s1, ±102 K and ±5 kPa respectively.
Table 7 Partial molar isentropic compressibility (Ko/) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at 101 kPa pressure. Solvents
293.15 K
298.15 K
303.15 K
308.15 K
313.15 K
Ko/ 104/cm3 mol1Pa1 DMZ Methanol Ethanol Iso-propanol n-Butanol
5.75 6.01 4.68 6.105
5.95 6.42 4.66 6.177
6.17 6.58 4.79 6.575
6.43 6.73 5.13 6.328
6.69 6.91 5.25 6.381
Ko/ 104/cm3 mol1 Pa1 MNZ Methanol Ethanol Iso-propanol n-Butanol
6.93 7.03 5.91 6.711
7.16 7.34 6.06 6.799
7.37 7.53 6.23 6.927
7.44 7.58 6.64 6.966
7.62 7.91 6.78 6.895
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ± 5 kPa respectively.
3.5. Acoustic impedance Acoustic impedance (Z) targeted on the molecular packing of the system in terms of different types of molecular interactions existing in solutions, dependent on both concentration and temperature of solution, can be obtained as follows [31]
Z ¼ us d
ð7Þ
The acoustic impedance of a medium can be defined as the ratio of the instantaneous pressure excess on any particle of the medium to the instantaneous velocity of that particle. Variations of pressure from one particle to another occur when a sound wave travels in medium. The inertial and elastic properties of the medium govern this factor. As internal pressure and cohesive energy increase with solute concentration, strong intermolecular hydrogen bonding
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Table 8 Slope of line (Sk) of apparent molar isentropic compressibility and molality of antibiotics (DMZ and MNZ) in different alcohol solutions at different temperatures and at 101 kPa pressure. Solvents
298.15 K
303.15 K
308.15 K
313.15 K
Sk 104/kg cm3 mol2 Pa1 DMZ Methanol 38.7 Ethanol 16.6 Iso-propanol 18.2 n-Butanol 29.1
293.15 K
34.9 23.3 11.6 29.7
37.4 23.9 9.6 36.5
40.3 23.8 14.3 28.2
37.8 24.7 13.2 26.1
Sk 104/kg cm3 mol2 Pa1 MNZ Methanol 20.6 Ethanol 36.6 Iso-propanol 19.0 n-Butanol 35.3
22.0 39.6 20.1 35.1
22.3 38.1 21.7 35.7
18.8 34.0 27.6 33.6
20.0 34.3 27.8 23.5
The standard uncertainties in temperature (T) and pressure (P) are ±102 K and ±5 kPa respectively.
between antibiotic and alcohol molecules occurs. Hence, an increase in specific acoustic impedance is caused by an increase in instantaneous pressure excess at any molecule [35]. The calculated values of acoustic impedance are given in Table 9 where it is clear that Z increases with an increase in the concentration of antibiotics at all temperatures. This suggests that the presence of stronger molecular interactions due to closer packing structure of solute and solvent molecules (by the formation of Hbond in solutions). Greater values of Z for MNZ are observed than those for DMZ which can be explained on the basis of presence of a greater degree of hydrogen bonding between MNZ and alcohol molecules that result in greater values of Z compared to that of DMZ in alcohols. The variation of Z in different alcohols lies in following increasing order: n-butanol > ethanol > methanol > isopropanol which can be explained in terms of increase in hydrophobic–hydrophilic interactions with increasing alkyl chain length [36]. 3.6. Solvation number Solvation numbers reveal the self-motivated situation of ions as they move in solution. Two solvation numbers may be described i.e.
molecule than DMZ. The solvation number in different alcoholic solutions follows the sequence: iso-propanol > methanol > ethanol > n-butanol. Solvation numbers in methanol are higher than those in ethanol and n-butanol which can be explained in terms of steric reasons: molecules of methanol are smaller than those of ethanol and n-butanol. iso-Propanol has lowest values of solvation number due to additional steric hindrance caused by the position of –OH group in its molecule [37]. 3.7. Relative association Relative association (RA) is another parameter to analyse the extent of association in any solution. RA can be evaluated using the following formula [20]
RA ¼ ðd=do Þðuo =uÞ1=3 The addition of small quantities of additive, i.e., structure breakers generally seem to increase the cohesion between the molecules by breaking the open structure [38]. In the present case, the RA values are all positive and are equal to or near unity. They are influenced mainly by two factors: Breaking up of solvent structure upon addition of solute results in decrease in RA values Subsequent solvation of solutes by solvent molecules results in an increase in RA values
Primary solvation number Secondary solvation number Primary solvation number reflects the number of solvent molecules that have lost their own sovereignty of translational motion but move along with the ions in solution randomly. While secondary solvation number states the solvent molecules in the vicinity of the ion and hence are affected by the presence of ions. Using the isentropic compressibility data, solvation numbers can be obtained by the equation [20]
Thus increase or decrease in RA values depends upon two above mentioned factors [31]. Calculated values of RA for both antibiotics in all alcoholic solutions are given in Table 9 which show that RA values increases with increasing antibiotic concentration suggesting that the subsequent solvation of solutes by free solvent molecules is more dominant over breaking up of solvent structure.
Sn ¼ M 1 =M2 ð1 bs =bos Þð100 X=XÞ
4. Conclusions
ð8Þ
The M1 and M2 represent the molar mass of solute and solvent respectively; bs and bos are the isentropic compressibility of solution and pure solvent and X is the mole fraction of solute. The degree of interaction can also be measured in terms of solvation number (Sn). Negative Sn values indicate the structure breaking tendency of solute molecules in solution. The resultant values depend upon solute–solute and solute–solvent interactions [36]. The values of Sn given in Table 9 showed that Sn values are positive which suggests the structure forming tendency of antibiotics in all alcohols. The variation in Sn with rise in temperature indicates increased solute–solvent interactions in these systems. The solvation number for MNZ solutions is greater than DMZ solutions as highly hydrated molecules possess greater nH values and according to the present experimental results MNZ is a more hydrated
From the present study, it is concluded that the values of apparent molar volume at all concentrations of antibiotic solution at different temperatures are found positive which indicates the presence of strong solute–solvent interactions in antibiotic and alcohols. Decrease in value of Vo/ with increasing chain length of alcohols has been observed. This can be attributed to decreasing solubility of antibiotics in pure alcohols with increasing chain length. The values of the slope of the line of apparent molar volume are negative showing the presence of weak interactions among antibiotic molecules in the presence of alcohols. Highly negative values of apparent molar isentropic compressibility (K/) indicate a closely-packed structure in both antibiotic solutions owing to antibiotic–alcohol interactions. The higher negative values of par-
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Table 9 Molality (m), acoustic impedance (Z), solvation number (Sn), intermolecular free length (Lf) and relative association (RA) of antibiotics (DMZ and MNZ) solutions in different alcohols at different temperatures and at 101 kPa pressure. m/mol kg1
Z 103/kg m2 s1 DMZ
Sn DMZ
Lf 1011/m DMZ
RA DMZ
Z 103/kg m2 s1 MNZ
Sn MNZ
Lf 1011/m MNZ
RA MNZ
Methanol 293.15 K 0.01 0.02 0.03 0.04 0.05
880.67 882.92 884.72 886.34 888.03
1.88 3.56 4.78 5.82 6.91
16.23 16.17 16.12 16.08 16.04
1.0007 1.0015 1.0024 1.0035 1.0045
881.26 884.27 886.83 889.66 892.25
2.97 5.87 8.22 10.85 13.20
16.21 16.12 16.05 15.97 15.89
1.0005 1.0011 1.0018 1.0025 1.0032
298.15 K 0.01 0.02 0.03 0.04 0.05
872.22 874.34 876.35 878.11 880.02
1.97 3.53 4.97 6.17 7.48
16.45 16.39 16.34 16.29 16.24
1.0007 1.0015 1.0024 1.0034 1.0044
872.73 875.67 878.44 881.25 883.44
2.98 5.84 8.47 11.11 13.01
16.43 16.34 16.26 16.18 16.12
1.0005 1.0011 1.0018 1.0024 1.0033
303.15 K 0.01 0.02 0.03 0.04 0.05
851.93 853.97 855.95 857.55 859.44
1.94 3.47 4.92 5.99 7.34
17.14 17.08 17.03 16.98 16.93
1.0007 1.0016 1.0025 1.0035 1.0045
852.42 855.22 857.99 860.58 862.80
2.94 5.71 8.40 10.86 12.86
17.12 17.04 16.95 16.87 16.81
1.0006 1.0012 1.0018 1.0026 1.0034
308.15 K 0.01 0.02 0.03 0.04 0.05
833.74 835.86 837.62 839.25 840.94
1.90 3.56 4.82 5.95 7.12
17.75 17.68 17.63 17.58 17.53
1.0007 1.0016 1.0026 1.0036 1.0046
834.21 836.9 839.55 842.13 844.44
2.00 3.87 5.70 7.44 8.94
17.73 17.64 17.55 17.46 17.39
1.0006 1.0012 1.0019 1.0026 1.0034
313.15 K 0.01 0.02 0.03 0.04 0.05
820.67 822.79 824.50 826.28 828.13
1.94 3.62 4.87 6.17 7.52
18.19 18.12 18.07 18.01 17.95
1.0071 1.0015 1.0026 1.0036 1.0045
821.08 823.71 826.31 828.71 831.1
5.07 9.83 14.46 18.61 22.68
18.176 18.083 17.993 17.913 17.834
1.0006 1.0012 1.0020 1.0027 1.0036
Ethanol 293.15 K 0.01 0.02 0.03 0.04 0.05
918.08 920.93 923.59 925.99 928.62
1.58 3.13 4.54 5.76 7.12
0.01485 0.01478 0.01471 0.01465 0.01458
1.0004 1.0007 1.0012 1.0018 1.0022
918.58 921.68 924.29 926.8 929.62
2.27 4.29 5.91 7.43 9.17
14.84 14.76 14.69 14.63 14.56
1.0003 1.0008 1.0015 1.0022 1.0028
298.15 K 0.01 0.02 0.03 0.04 0.05
906.23 908.89 911.53 914.04 916.43
1.66 3.10 4.52 5.83 7.06
15.16 15.09 15.02 14.95 14.89
1.0003 1.0008 1.0012 1.0018 1.0023
906.67 909.65 912.24 914.86 917.55
2.32 4.28 5.90 7.53 9.19
15.15 15.07 15.01 14.94 14.87
1.0003 1.0008 1.0015 1.0022 1.0029
303.15 K 0.01 0.02 0.03 0.04 0.05
886.74 889.38 891.85 894.23 896.61
1.62 3.08 4.42 5.68 6.94
15.77 15.69 15.62 15.56 15.49
1.0003 1.0008 1.0012 1.0017 1.0023
887.19 890.01 892.92 895.19 897.81
2.28 4.16 6.09 7.48 9.13
15.76 15.67 15.59 15.53 15.46
1.0004 1.0009 1.0014 1.0022 1.0030
308.15 K 0.01 0.02 0.03 0.04 0.05
856.27 858.76 861.11 863.2 865.57
1.54 2.96 4.27 5.39 6.68
16.82 16.74 16.67 16.60 16.53
1.0004 1.0008 1.0014 1.0021 1.0027
856.67 859.31 862.06 864.42 866.67
2.16 3.96 5.84 7.36 8.79
16.81 16.72 16.64 16.57 16.50
1.0004 1.0010 1.0016 1.0023 1.0031
313.15 K 0.01 0.02 0.03 0.04 0.05
846.08 848.59 851.08 852.89 855.21
1.52 2.97 4.40 5.33 6.61
17.13 17.04 16.96 16.91 16.84
1.0004 1.0009 1.0014 1.0022 1.0027
846.58 849.12 851.84 854.62 856.57
2.22 3.96 5.84 7.75 8.93
17.11 17.03 16.94 16.85 16.80
1.0004 1.0010 1.0016 1.0021 1.0031
Iso-propanol 293.15 K 0.01 0.02 0.03
911.25 913.41 915.58
0.90 1.70 2.50
15.01 14.96 14.91
1.0008 1.0016 1.0026
911.85 914.62 917.33
1.42 2.72 3.97
14.99 14.92 14.86
1.0004 1.0009 1.0014 (continued on next page)
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Table 9 (continued) m/mol kg1
Z 103/kg m2 s1 DMZ
Sn DMZ
Lf 1011/m DMZ
RA DMZ
Z 103/kg m2 s1 MNZ
Sn MNZ
Lf 1011/m MNZ
RA MNZ
0.04 0.05
917.55 919.23
3.19 3.73
14.86 14.83
1.0036 1.0047
919.94 922.25
5.15 6.14
14.79 14.74
1.0018 1.0023
298.15 K 0.01 0.02 0.03 0.04 0.05
890.41 892.51 894.62 896.71 898.52
0.87 1.67 2.46 3.24 3.86
15.63 15.58 15.53 15.47 15.43
1.0008 1.0017 1.0027 1.0036 1.0047
890.99 893.68 896.31 898.76 900.93
1.38 2.67 3.91 5.02 5.96
15.61 15.54 15.47 15.41 15.36
1.0008 1.0017 1.0026 1.0036 1.0047
303.15 K 0.01 0.02 0.03 0.04 0.05
877.08 879.26 881.22 883.32 885.34
0.86 1.72 2.45 3.24 3.99
16.02 15.96 15.91 15.85 15.81
1.0008 1.0017 1.0027 1.0036 1.0047
877.66 880.29 882.80 885.22 887.38
1.38 2.65 3.84 4.95 5.90
16.01 15.93 15.86 15.80 15.74
1.0008 1.0018 1.0028 1.0037 1.0048
308.15 K 0.01 0.02 0.03 0.04 0.05
855.26 857.31 859.32 861.19 863.12
0.88 1.69 2.47 3.17 3.90
16.74 16.68 16.62 16.57 16.52
1.0009 1.0018 1.0027 1.0037 1.0047
855.85 858.27 860.67 862.94 865.22
1.41 2.59 3.74 4.80 5.86
16.72 16.65 16.58 16.52 16.45
1.0008 1.0018 1.0028 1.0038 1.0049
313.15 K 0.01 0.02 0.03 0.04 0.05
837.3 839.33 841.24 843.12 844.98
0.86 1.68 2.42 3.15 3.87
17.41 17.35 17.29 17.24 17.19
1.0009 1.0018 1.0028 1.0038 1.0048
837.88 840.21 842.52 844.68 847.01
1.39 2.53 3.65 4.66 5.77
17.39 17.32 17.25 17.19 17.12
1.0009 1.0019 1.0029 1.0040 1.0051
n-Butanol 293.15 K 0.01 0.02 0.03 0.04 0.05
1022.59 1025.89 1029.09 1032.01 1035.25
1.32 2.40 3.44 4.37 5.39
12.27 12.2 12.13 12.07 12.01
0.9995 0.9992 0.9991 0.9989 0.9988
1022.98 1026.85 1030.25 1033.33 1036.79
1.75 3.29 4.60 5.77 7.08
12.26 12.18 12.11 12.04 11.97
0.9995 0.9992 0.9991 0.9992 0.9991
298.15 K 0.01 0.02 0.03 0.04 0.05
1002.58 1005.75 1008.89 1011.62 1014.64
1.28 2.34 3.38 4.25 5.22
12.70 12.63 12.56 12.50 12.43
0.9995 0.9993 0.9991 0.9991 0.9990
1002.97 1006.73 1010.03 1012.97 1016.31
1.70 3.22 4.51 5.64 6.92
12.69 12.61 12.54 12.47 12.41
0.9996 0.9993 0.9993 0.9993 0.9993
303.15 K 0.01 0.02 0.03 0.04 0.05
986.48 989.61 992.58 995.43 998.35
1.26 2.32 3.31 4.24 5.20
13.09 13.01 12.94 12.88 12.81
0.9996 0.9994 0.9992 0.9992 0.9991
986.89 990.52 993.61 996.75 999.87
1.69 3.17 4.40 5.63 6.85
13.08 12.99 12.92 12.85 12.78
0.9996 0.9994 0.9994 0.9994 0.9994
308.15 K 0.01 0.02 0.03 0.04 0.05
966.59 969.58 972.37 975.28 977.99
1.23 2.26 3.20 4.18 5.07
13.58 13.51 13.44 13.37 13.30
0.9996 0.9995 0.9994 0.9993 0.9993
966.95 970.39 973.71 976.39 979.58
1.63 3.07 4.42 5.47 6.74
13.57 13.48 13.41 13.34 13.27
0.9996 0.9995 0.9994 0.9996 0.9996
313.15 K 0.01 0.02 0.03 0.04 0.05
949.44 952.44 955.08 958.02 960.60
1.19 2.24 3.14 4.15 5.01
13.96 13.88 13.82 13.74 13.68
0.9997 0.9995 0.9995 0.9994 0.9995
949.79 953.24 956.42 959.5 962.79
1.58 3.04 4.36 5.62 6.95
13.95 13.86 13.78 13.71 13.62
0.9997 0.9995 0.9995 0.9995 0.9995
The standard uncertainties in molality (m), temperature (T) and pressure (P) are ±0.0015 mol kg1, ±102 K and ±5 kPa respectively.
tial molar isentropic compressibility (Ko/) indicate weak interactions among antibiotic molecules. Acoustical parameters like intermolecular free length, acoustic impedance, relative association and solvation number were calculated to strengthen the results of volumetric parameters. Decreasing values of intermolecular free length indicate the presence of strong intermolecular interactions, positive values of solvation number showed the structure making behaviour of antibiotics in alcoholic solutions.
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JCT 16-517