Investigation of aggregation behavior of ibuprofen sodium drug under the influence of gelatin protein and salt

Journal of Molecular Liquids 290 (2019) 111187

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Investigation of aggregation behavior of ibuprofen sodium drug under the influence of gelatin protein and salt Naved Azum a,b, Anwar Ahmed c,d, Malik Abdul Rub a,b,⁎, Abdullah M. Asiri a,b, Salman Freeh Alamery c a

Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia Center of Excellence in Biotechnology Research, Department of Biochemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia d Protein Research Chair, Department of Biochemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia b c

a r t i c l e

i n f o

Article history: Received 23 April 2019 Received in revised form 29 May 2019 Accepted 13 June 2019 Available online 15 June 2019 Keywords: Ibuprofen sodium salt (IBS) drug Gelatin Tensiometry Fluorescence Thermodynamic properties

a b s t r a c t The interaction of amphiphilic drug ibuprofen sodium salt (IBS) and gelatin (GT) protein have evaluated in the current system by means of conductometric, tensiometric and fluorometric techniques in aqueous as well as in aqueous electrolytes solutions at 298.15 K. IBS is utilized as an analgesic, an antipyretic and anti-inflammatory drug. Akin to surfactants and polymers interaction drug also interacts through gelatin. For that reason, in the present study, we have evaluated the drug IBS and gelatin (GT) interaction by means of conductimetry, tensiometry as fluorometry in aqueous along with in occurrence of additive (sodium chloride (NaCl)) at 298.15 K. From the graphs of specific conductivity against IBS concentration in case of conductivity and from the plots of surface tension (γ) vs. log IBS concentration, two break point was achieved in the occurrence of GT in absence and the presence of additives. The achieved primary cut-off point is entitled critical aggregation concentration (cc) that obtained lower than the characteristic critical micelle concentration (cmc) and the attained a subsequent cutoff point means the second one is entitled polymer saturation point (pp) i.e. resembling cmc. The interaction amongst IBS and GT occurs as a result of the well formation of the surface active complex by drug and GT as revealed via lessening of γ of gelatin solution through the addition of IBS in all different media. NaCl increases the interaction of IBS-GT mixtures. The achieved cc value of drug and gelatin mixtures reduce via raising the GT concentration (%w/v), while their pp value enhances viewing the clear interaction amid IBS and GT. Free energies of aggregation (ΔGagg) along with micellization (ΔGmic) were also assessed and discussed. Fluorescence spectroscopy was employed to evaluate the aggregation numbers (Nagg) of IBS and IBS-GT mixtures in the absence and occurrence of additive. © 2019 Elsevier B.V. All rights reserved.

1. Introduction The amphiphile such as surfactant is one surface active compounds that be capable of part the surface upon inward bound along with self-associate in an appropriate frame called micelle [1–3]. Micelles simply form once the concentrations of amphiphiles are larger than the critical micelle concentration (cmc) [1–5], means cmc is the concentration beyond micelles of amphiphile will appearance spontaneously. Akin to surfactant, in aqueous solution, lots of amphiphilic drugs can have ability to associate in the form of small aggregates, because of these categories of drugs hold numerous resemblances with surfactant micelles, owing to the occurrence of a minute hydrophobic portion such as an aromatic ring system [6–8].

⁎ Corresponding author at: Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia. E-mail address: [email protected] (M.A. Rub).

https://doi.org/10.1016/j.molliq.2019.111187 0167-7322/© 2019 Elsevier B.V. All rights reserved.

Gelatin (GT) is possessed chiefly of collagen, the protein that builds up the bones, connective tissues, as well as the skin of mammals (Fig. 1) [9]. Gelatin (GT) comprises a number of amino acids, the construction masses of protein. Glycine and proline is most of the amino acids which are found in gelatin [9]. It has imperative health advantages owing to their unique arrangement of amino acids, although gelatin encloses merely nine out of ten necessary amino acids, viewing that gelatin cannot be regarded as an absolute protein. In spite of the numerous pharmaceutical, along with food associated utilizes of gelatin, limited consideration has been assigned to their interaction through small molecules [10]. Gelatin, a normal protein obtained from the hydrolysis of collagen is very much biocompatible as well as eco-friendly in a physiological atmosphere [11]. Numerous methods were utilized to examine the temperament of the interaction of surfactant and protein: turbidity analysis [12], electrical conductometry along with surface tension evolution, binding determinations [12,13] for assessable concerns, however, the measurement of thermodynamics of the interaction is extremely less reported [14]. Although gelatin is commonly employed

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N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187

Fig. 1. Molecular model of gelatin (GT).

polymeric excipient by pharmaceutics, inadequate consideration has been given till date to their interaction by means of small organic compounds, as a result, here we will evaluate the interaction amongst ibuprofen sodium salt (IBS) drug and gelatin (GT) protein in two different media (H2O/NaCl). Gelatin is not behaved like folded protein due to their denatured property, therefore; their interaction with surfactant or amphiphiles is different from usual proteins [15]. It possibly will intermingle with amphiphiles in a similar way like surfactant or polymer having the subsistence of aggregation, that is to say, the forming of aggregates initiates at or after a definite concentration labeled critical aggregation concentration (cc), whichever is fine beneath the critical micelle concentration (cmc) of amphiphile [14] and the second type of aggregation is called polymer saturation point (pp) or obvious critical micelle concentration (cmc) corresponding to the congestion or overload of gelatin domain through employed amphiphilic additive and after this start of the formation of independent micelles begin [14]. Amphiphilic drug ibuprofen sodium salt (IBS), one of the most heavily prescribed nonsteroidal anti-inflammatory drug (NSAIDs) (Fig. 2) [16,17]. This drug is derived from propionic acid and their formula is sodium 2-(4-isobutylphenyl)propanoate hydrate. IBS possibly employed as a representation drug to examine the intercalation appliance through the ion exchange method amid drug and a biocompatible molecules [18]. The medical application of this category of drugs are for analgesic, antipyretic, as well as anti-inflammatory characteristics and these properties, are exceptionally well-known; on the other hand, this class of drugs was also reasons for some severe aftereffect [19]. These unwanted effects claimed as a result of the interaction of this class of drug through phospholipid layers coating the gastrointestinal membrane. These types of not needed effects possibly minimized if IBS is properly administered by the means of carries and gelatin is one of type of carriers which is used safely with a combination of the drug. As stated above that the present paper deals interaction of drug IBS which is surface active in nature and GT in water in addition to NaCl solutions. IBS is chosen as a model drug, and, in current employed situations, this attains a negative charge. Addition of electrolyte stabilized the drug micelles. Due to the presence of salt, the cmc values are likely to be decreased due to the content of inserted salt [1,20,21]. The decline of cmc values with the addition of salts to aqueous surfactant solution

Fig. 2. Molecular model of ibuprofen sodium salt (IBS).

was because of the diminution of the electrostatic repulsion between charged head groups by counter ion. It was found that the counter ions play a very important role in the micelle stabilization. In solution, the stabilization of the ionic surfactant micelles by counter ions was carried out by binding with the micelle surface along with lowering the electrostatic repulsions amongst the ionic head groups [22]. Gelatin is employed for making a capsule wall. The interaction of a lot number of drugs which is given in capsule form means in dispensed form and GT possibly will influence their discharge as well as bioavailability. The principle of the current research was to examine the binding of anionic drugs with gelatin. By keep the entire the above information in mind, herein, systematically studies the IBS-GT interaction by conductometric, tensiometric and fluorometric techniques in water and electrolytes at 298.15 K. By tensiometry method various surface parameters of drug and gelatin interaction at interfacial surfaces were evaluated and discussed.

2. Materials and method 2.1. Materials Every chemical utilized in the existing system was of methodical ranking and used for experiment with no additional purification. The amphiphilic drug ibuprofen sodium salt (IBS, CAS number 31121-934) having purity 0.98 in mass fraction was purchased from Sigma, USA. The electrolyte NaCl (CAS number 7647-14-5) having purity 0.98 (mass fraction) was purchased from BDH, England. The employed gelatin from bovine skin (225 bloom, type B) was procured from Sigma, USA. First, accurately weight the 1.0 g of GT and put it into 100 ml conical flask in aqueous or 100 mmol.kg−1 NaCl solution for preparation of a stock solution of GT of 1.0% and then leave it for at least one night for swelling. After that, the prepared stock solution was warmed cautiously near to 315.15 K and then leaves it for cooling to normal room temperature. This process is repeated and some time stirring is also needed until a clear solution of GT is obtained and then the flask is makeup to the mark by aqueous or 100 mmol.kg−1 NaCl solution. From this stock solution of GT (1.0%) different employed of concentrations of GT (0.15%, 0.20%, 0.30%, 0.40% and 0.50%) in the present study were prepared by diluting with water/NaCl solution. These prepared solutions were further employed as a solvent for the preparation of a mixed system of IBS-GT stock solutions. The employ of buffer was escaped owing to the feasible clouding of the solution of IBS in occurrence of the electrolytes. Alternatively, the solution pH was noted at the starting as well as the conclusion of all experiment that was constantly achieved in the province of 6.86 to 6.26; viewing the well beyond the isoelectric point of employed GT (4.8) [23]. As a result, the employed GT has the tyranny of negative sites as compared to the positive spots. Double distilled water was used throughout for stock solution preparation having specific conductivity 1–6 μS cm−1.

N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187

2.2.3. Fluorescence study The fluorescence quenching technique was employed for determination the aggregation number (Nagg) in case of individual drug IBS in all different media and also in the presence of gelatin. Pyrene was used as probe and cetylpyridinium chloride (CPC) was employed as a quencher. In the current study fluorescence spectrometer (Hitachi F7500) is employed for fluorescence reading by fixing the excitation/ emission slit widths 2.5 nm and quartz corvette cell having 10-mm path length was utilized for the entire fluorescence measurements. Excitations were taken at 335 nm and emissions are recorded from 350 to 400 nm. Each and every one spectra encloses 5 well clear peaks and their intensity were reduces through the increasing the CPC concentration. For the case of pure IBS in all different media the stock solution were prepared above their cmc value for Nagg, but in case of IBS-

3.1. Conductivity measurement of IBS-GT interaction

-1

Here, in the current study, the employed compounds (IBS and gelatin (protein/polymer)) have same charges (anionic in nature) and their interaction is much more complex from a physicochemical viewpoint in comparison to interaction amid charged and nonionic amphiphiles. Electrostatic as well as hydrophobic interactions cooperate a noteworthy task amongst interaction between IBS and GT in all different media. The solubility of employed IBS was tested out above 1000 mmol.kg−1, showing that this drug is freely or highly soluble in an aqueous system. The interaction between employed drug IBS and protein gelatin (GT) having different concentration of GT (0.15%(w/v), 0.20%(w/v), 0.30%(w/v), 0.40%(w/v) and 0.50%(w/v)) in aqueous in addition to in the attendance of salt by means of a conductometric method at 298.15 K. The plots of specific conductivity against a concentration of IBS having a various employed concentration (%w/v) of gelatin were depicted in Figs. 3 and 4 in aqueous along with electrolyte solutions. In the case of pure IBS means when there is no GT in the solution, the graph of specific conductivity (κ) against concentration shows the usual behavior viewing of only one curve in the plot. The specific conductivity of IBS solution enhances as liberated ions (IBS anions (negatively charged) and Na+) enhances by means of the increase of the concentration of IBS. However, the enhancement of the κ is reduced subsequent to aggregation as micellar IBS has lesser mobility in comparison to monomeric IBS. Thus two clear linear sections can be visualized in a graph of pure IBS. The slope subsequent to start of aggregation is reduced owing to the reduction in the bound counterion in the stern layer [1]. At 298.15 K, the cmc value for singular IBS in H2O by conductivity method was achieved to 177.50 mmol.kg−1, viewing the very well conformity through the earlier reported value (Table 1) [26,27]. However, in an electrolyte solution (100 mmol.kg−1 NaCl) at 298.15 K, the value of cmc of singular IBS was decreased, viewing the 158.24 mmol.kg−1, as a result of the lessening in micelles surface charge density telling the contribution of electrolyte in the micellization. (Table 2) [28]. In the occurrence of NaCl, the existing electrostatic repulsion amidst the ionic head group of the IBS decreases owing to the shielding of electrostatic repulsion through ionic surroundings at all charged sites and leads

S.cm

2.2.2. Surface tension measurements Surface tension (γ) measurements for currently employed systems were assessed via the ring detachment process and instrument name is Attension tensiometer (Sigma 701, Germany). Attension tensiometer has auto-calibrating microbalance and this instrument is assessable over an extensive range. This phenomenon in the currently employed instrument is fulfilled by means of DDW daily before the proceeding of γ measurement. The γ was computed at 298.15 K via consecutive adding of prepared drug IBS solution in all different media in absence of gelatin for the case of pure IBS or in attendance of gelatin of different concentration in H2O/NaCl for the case of pure IBS or solvent enclosing gelatin of different concentration by means of a micropipette. The cc and cmc/pp value was determined via the intersection point amid both linear parts of γ against log [IBS] plots. The errors in cc and cmc/ pp were achieved around ±3%. The inaccuracy in temperature was below 0.2 K. The error in every obtained surface tension value is found more or less ±0.1 mNm−1.

3. Results and discussion

2

2.2.1. Conductivity measurements For accurate evaluation of concentration at which or beyond aggregation process occurs in the solution systems, a lot of experimental are needed, as a result, a conductometry technique was utilized for determination of cc and pp/critical micelle concentration (cmc) as the procedure already declared in literature [24,25]. The specific conductivity of individual drug IBS in addition to their mixtures with gelatin in different concentration (0.15% w/v, 0.20% w/v, 0.30% w/v, 0.40% w/v and 0.50% w/v) in three different media such as H2O and 100 mmol.kg−1 NaCl was noted with the help of a digital conductivity meter bridge (model 4510, Jenway, UK) outfitted through a dip cell (glassy electrode) containing cell constant (1.0 cm−1) at 298.15 K. The multimeter employed here for measurement of conductivity has the accuracy close to ±0.5%. The utilized instrument in the current system was calibrated using an appropriate concentration of KCl solution prior to performing each experiment. The conductivity of different employed solvent (H2O/NaCl) in absence of gelatine were recorded first in case of pure drug IBS or in the occurrence of gelatine and then the stock solution of IBS prepared in different media in absence/appearance of gelatine inchmeal added via a micropipette to the solution under study. After proper blending and allowing for temperature equilibration of the ensuing solution, the conductivities were recorded. Akin procedures were repeated after all addition. The attained specific conductivity (κ) of the solutions were then plotted against the corresponding IBS drug concentration with the help of Origin software and cmc was obtained from the concentration belongs to the breaking point in the plot for pure IBS only in both media. However, for the case of gelatin-IBS mixtures the graphs of κ against [IBS] demonstrated two breaks in both media. The cc was evaluated via the intersection of primary and subsequent (second) linear portions and the pp were executed from intersection spot of the second and third linear parts. The errors in cc and cmc/pp were achieved below 3%.

gelatin mixtures in both studied solvent the stock solution was prepared above their critical aggregation concentration (cc).

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2.2. Methods

3

-1

[IBS] / mmol.kg

Fig. 3. Graph of specific conductivity (κ) against [IBS] at different concentrations of gelatin (GT) in aqueous system. The scale exposed in plot represented as (■). Others plots have been moved ups by 2.5 scale units (S cm−1) all.

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N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187 Table 2 Various physicochemical parameters of IBS drug and gelatin protein mixtures in 100 mmol.kg−1 NaCl evaluated by conductivity measurement at 298.15 K and pressure p = 0.1 MPa.a cc (mmol. kg−1)

cmc/pp (mmol. kg−1)

α1

α2

0.65 0.63 0.6 0.58 0.56

0.45 0.49 0.52 0.55 0.57 0.6

ΔGagg (kJ mol−1)

S.cm

-1

% Gelatin (w/v)

10

2

0 0.15 0.20 0.30 0.40 0.50

74.5 70.02 65.5 60.01 54.4

158.24 164.9 170.01 176.6 181.4 186.3

−22.14 −22.67 −23.40 −24.04 −24.73

ΔGmic /ΔGpp (kJ mol−1) −22.53 −21.79 −21.25 −20.68 −20.30 −19.78

ΔGt (kJ mol−1)

−0.34 −1.43 −2.72 −3.74 −4.95

a Standard uncertainties (u) are u(T) = 0.20 K, u(NaCl) = 1 mmol∙kg−1, and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(cc) = ±3%, ur(cmc/pp) = ±3%, ur(α1, α2) = ±4%, ur(ΔGagg) = ±4%, ur(ΔGmic /ΔGpp) = ±4% and ur(ΔGt) = ±5%.

-1

[IBS] / mmol.kg

Fig. 4. Graph of specific conductivity (κ) against [IBS] at different concentrations of gelatin (GT) in 100 mmol.kg−1 NaCl. The scale exposed in plot represented as (■). Others plots have been moved ups by 2.5 scale units (S cm−1) all.

to reduce the cmc of the pure drug IBS [29]. The repulsion involving head groups of compounds is one of the chief issues to oppose the aggregation [30]. In the current paper, GT is employed which is anionic in nature to view the interaction with anionic drug and, we have achieved several remarkable outcomes of their interaction via IBS. The extent of interaction of drug and GT depends on charges site along with hydrophobicity. The employed concentration is not too high that it crosses the critical overlap concentrations; the maximum concentration of gelatin was kept 0.5% (w/v). In the occurrence of gelatin in a solution of IBS drug as the graph shown in Figs. 3 and 4, we can easily see two clear breaks as compared to only one break achieved for pure IBS in aqueous in addition to the presence of NaCl [31]. In attendance of GT in the solution of IBS, two breaks were achieved in all studied systems, viewing the happening of two types of association process. The primary or initial break spot entitled critical aggregation concentration (cc) viewing the start of binding or interaction between IBS and GT and the subsequent break means the second one symbolize polymer saturation point (pp). PP is indicative that all GT binding sites are saturated by means of IBS (drug) molecules along with aggregation of gelatin-free micelles formation of the drug also occur [32]. Anionic nature amphiphiles interact through proteins somewhat additional strongly as compared to the cationic nature of amphiphiles [33,34]. Above stated phenomena is clarified as occurring from hydrophobic bonding amongst the hydrocarbon portion of the amphiphile and hydrophobic amino acid side chain of comparatively bulky size of such portion with a positively charged

Table 1 Various physicochemical parameters of IBS drug and gelatin protein mixtures in aqueous solution evaluated by conductivity measurement at 298.15 K and pressure p = 0.1 MPa.a % gelatin (w/v) 0 0.15 0.20 0.30 0.40 0.50

cc (mmol. kg−1) 177.50 80.55 77.1 74.05 71.05 65.25

cmc/pp (mmol. kg−1)

181.2 185.8 191.2 195.1 203.1

α1

α2

0.68 0.66 0.63 0.61 0.59

0.46 0.51 0.54 0.57 0.60 0.63

ΔGagg (kJ mol−1)

−21.38 −21.85 −22.47 −22.94 −23.57

ΔGmic /ΔGpp (kJ mol−1) −21.94 −21.16 −20.64 −20.11 −19.62 −19.07

ΔGt (kJ mol−1)

−0.22 −1.21 −2.36 −3.32 −4.50

a Standard uncertainties (u) are u(T) = 0.20 K and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(cc) = ±3%, ur(cmc/pp) = ±3%, ur(α1, α2) = ±4%, ur(ΔGagg) = ±4%, ur(ΔGmic /ΔGpp) = ±4% and ur(ΔGt) = ±5%.

amino acid. For that reason, it is considered as a sign of amphiphile provoked protein unfolding. A number of believable situations have been projected by interaction amongst negatively charged studied constituents (GT and IBS) in aqueous along with electrolyte solution and their interaction can be separated into 3 major parts: (i) attachment of particular anionic drug molecules to the amino acid chain i.e. GT, (ii) attachment of formed drug micelles or similar associate to amino acid chain of GT, as well as (iii) a merger of both above situations (i) and (ii), through which drug molecules start to bind with GT, create “nuclei” for more binding of micelles. After cc formation start and before pp formation, the drug monomers are mainly occurs as following form: (1) at the interfacial surface of solution mixed system, (2) free drug micelles in solution, (3) individual monomers of the drug in solution and (4) some on the GT binding sites. cc is independent of GT amount present in the solution, however reliant on the hydrophobicity of constituents'. The information regarding the cc possibly of significance as the interaction of IBS through GT initiates at this concentration. pp is reliant on GT and IBS concentration but it is independent of molecular weight over an assured molecular weight [33,34]. The values of pp vary linearly by means of GT concentration. Tables 1 and 2 show the effect of diverse concentrations of GT on the cc as well as pp of the employed drug IBS in both studied media. The primary breakpoint i.e. cc, analogous to the beginning of accommodating binding between IBS and GT fragments, the obtained first cut-off point is always below the cut-off point achieved in case of micellization of the individual drug, i.e., below the cmc of pure IBS. Apparent current investigation viewed that the practical reduce in cc as compared to cmc by means of the presence of gelatin proposes support to the involvement that curtails chiefly from electrostatic interaction amid GT and IBS in aqueous/electrolyte solution since this would make possible energetically preferential lessening of hydrocarbon-H2O interface [1]. As we increase the concentration of GT in solution mixtures of GT and IBS, the cc values are moved towards inferior concentrations of the IBS, viewing that the binding between drug and GT start at lower concentration with increases in concentration (% (w/v)) of GT (Tables 1 and 2). As stated above gelatin bears the polar sites surface along with also contains a number of hydrophobic sites, therefore, their binding with a drug is directed via both electrostatic plus hydrophobic interactions. Quite the opposite, the second break spot in the current study, i.e., pp is more than the cc in addition to also beyond the cmc of pure drug IBS in aqueous/electrolyte solution (Tables 1 and 2). As a result, in contrast to reduce in cc, pp enhances due to the presence of GT and their value further enhances by increasing the concentration of GT in the solution mixtures. At upper GT concentration, there is enhance of number of binding sites of GT for IBS molecules or IBS associates structures (micellized form), as a result, higher quantity of the IBS is needed to fasten with gelatin amino acid chain. When the whole binding sites of GT are occupied,

N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187

Knowing the micellar counterions binding is a precondition for investigation of association as well as all further type of associations in water along with other solvents [39]. The conductometric method is one of the finest techniques to examine the micellization phenomena of amphiphiles. Figs. 3 and 4 demonstrate the change of κ against the [IBS] drug at 298.15 having different concentration of GT. From the plot it is clear that the graphs of κ against [IBS] are divided into three portions having two cut-off points as a result, two degree of dissociation were computed. The primary breakpoint stands for the initiate of interaction between IBS and GT mean the start of adsorption of IBS on the binding site of amino acids of gelatin. The slopes before the cc and amid the cc and pp are the S1 (slope 1), and S2 (slope) correspondingly as obtained from the conductivity graph, the first degree of dissociation (α1), is estimated from the ratio of S2 and S1 (S2/ S1) and their value are given in Tables 1–2. The subsequent breakpoint means the second one signifies the pp. Beyond the pp, third slope S3 was achieved and from their slope, the second degree of dissociation (α2) was evaluated using S3/S2 and evaluated α2 values are recorded in Tables 1–2. The breakpoint is attributable to the lessening in the effectual charge on the associate's structure in favor of the binding of a number of counter-ions to the micelles beyond the micelles formation. The degree of dissociation (α) is reliant on the size or volume of micelles. The smaller micelles show a lesser propensity to entice counter-ions as compared to the larger ones, providing a higher degree of dissociation (α) value [40]. From Tables 1 and 2, it is clear that the α2 value in case of pure IBS micelles means in absence of GT is found to be lesser than those of IBS-GT solution mixtures. The higher α2 value for micellization of IBS-GT mixtures is sign of enhanced extent of dissociation, viewing the interaction amid GT and employed drug but micellization of drug is delayed due to GT. The lesser value of α1, showing the good interaction or aggregation of drug-GT complex takes place means the interaction between studied constituents happens at an inferior concentration of IBS. Herein, the α1 values reduce by means of enhance in GT concentration (% (w/v)) in solution mixtures, i.e., cc reduces via enhance of GT concentration (Tables 1 and 2). Quite the opposite, the α2 values raise as the %(w/v) of GT enhances which signifying the pp values enhances by means of rise of GT concentration in the solution (Tables 1 and 2). In attendance of electrolyte in the mixtures of IBS –

3.3. Surface tension measurements of IBS-GT solution mixtures Surface tension measurements of macromolecules and amphiphiles mixtures interaction investigation are frequently employed technique [41], because surface tension measurements are functional for all nature of compounds in the dilute reasons, whereas conductivity is suitable merely for the charged molecules. In the current study, the surface tension measurements of individual drug IBS along with their mixed systems with GT of 5 dissimilar concentrations at 298.15 K were performed in water as well as in a salt solution. Gelatin is an excellent stabilizer for a variety of systems in addition to this GT is acknowledged that it demonstrate surface activity, that is to say, it has the propensity to adsorb at the interfacial surface, as a result, lessening surface tension. In the attendance of ionic amphiphiles such as drug employed in the current study, as a result of their interactions, conformation of macromolecules (gelatin) alters which have an effect on the constitution of adsorption films and be able to even bring on desorption of GT from the interface. Modifies at the interfacial surface attributable to interaction might be sensed through the tensiometric method. Figs. 5 and 6 list the graphs of surface tension (γ) against the IBS drug concentration in the occurrence of different concentration of GT at 298.15 K in water as well as in the occurrence of electrolyte. For the case of pure IBS in aqueous in addition to in presence of salt, each reading was taken at the gap of 5 min after each addition of drug solution, whereas the for the case of drug and GT mixtures, readings were noted at the gap of 10 min after every addition of stock solutions to attain the equilibration. For that reason, the γ values were not varying further with time. In the case of individual IBS, γ of IBS solution in aqueous as well as NaCl systems reduces by means of rising drug concentration until their value reaches near about 31.72 mN.m−1. Afterward, γ value becomes constant and also becomes independent of IBS concentration. Reduce in γ value is caused by adsorption of drug monomers at the interface. As soon as the interface turns out to be saturated by means of amphiphile monomers, micelles commence to form in a studied solvent, and that essential concentration described as the cmc [1]. The acquired cmc value in case of pure IBS in water and in 100 mmol.kg−1 NaCl was 179.45 mmol.kg−1 and 159.50 mmol.kg−1 respectively from tensiometry technique, which

Aqueous system

-1

3.2. Degree of micelle dissociation

macromolecule (gelatin), the both degree of dissociation (α) values (α1 and α2) were decreases as compared to their absence (Table 2). The lesser α values in occurrence of electrolyte entail the fine-packed aggregation are formed. As a result the counter-ions binding at the micellar surface of increases.

mN.m

then further IBS molecules are open to forming self-governing associate structures i.e., micelles formation, therefore pp values increase with increase in GT concentration [35,36]. It is noteworthy that the interaction of GT and IBS in aqueous/electrolyte solution, the achieved pp value is only the overload of GT amino acids chains through the IBS monomers, for that reason, pp does not keep much significance as compared to the cc value that viewing the starting point of interaction amid constituents. The reduce in cc possibly owing to the electrostatic interaction amongst drug and GT and compounds both are anionic in nature, sustained via the nonpolar interactions amongst the hydrophobic parts of studied constituents. The values of cc and pp of drug-GT mixed systems were decreases by means of the adding of 100 mmol.kg−1 NaCl in the system (Table 2). NaCl salt stabilized the gelatin sustained drug micelles. The decline of cc and pp values with the addition of NaCl to drug-GT mixed systems was owing to the diminution of the electrostatic repulsion between charged head groups by counter ion. In solution, the stabilization of the ionic drug micelles by counter ions was carried out by binding with the micelle surface and lowering the electrostatic repulsions amongst involving the ionic head groups. Consequently, the hydrophobic group in the monomer of the drug is salted-out and lowers the cmc values. Accordingly, in the attendance of electrolyte, the opening of interaction amid drug and GT occurs at a lower concentration of IBS, ensuring the decrease in cc as well as pp/cmc value of studied systems [37,38].

5

-1

log [IBS] / mmol.kg

Fig. 5. Variation of ST with the log [IBS] in presence of gelatin in aqueous system at 298.15 K.

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N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187

Gibbs' surface excess (Γmax), stating the effectiveness of employed drug along with their mixed system with gelatin having different concentration to be adsorbed at interfacial surface in comparison to the bulk solution, was analyzed from the slope of γ vs. log[IBS] plot close to the cc break point of the surface tension graph in water along with electrolyte solution by means of Eq. (1) [44,45].

-1

100 mmol.kg NaCl

mN.m

-1

  1 ∂γ Γ max ¼ – 2:303nRT ∂ logðIBSÞ

mol m−2




ð1Þ

∂γ is the slope and R, T have their usual meaning. n ∂ logðIBSÞ is the numeral of species for every ionic amphiphiles molecule in aqueous and electrolyte solution (n is taken 2 in the present case for pure IBS and 3 for IBS-GT mixtures). Accepting full monolayer formation just before micelles formation, the area of leaving out for each amphiphile monomer was estimated using Eq. (2) In Eq. (1),

-1

log [IBS] / mmol.kg

Fig. 6. Variation of ST with the log [IBS] in presence of gelatin in 100 mmol.kg−1 NaCl at 298.15 K.

viewing the fine conformity through cmc value determined by conductivity method. By the addition the gelatin in pure H2O, the γ value decreased to inferior values means gelatin demonstrates fewer surface activity (γ of water = 71.0 mNm−1 and γ of 0.15% (w/v) gelatin solution = 64.526 mNm−1). The γ values reduced more on raising the gelatin concentration but in our case, there is no specific trend were obtained. Figs. 5 and 6 show that GT and IBS mixed systems demonstrate lessening of ST. There are two breakpoints in the γ versus log (IBS) concentration isotherms in case of drug-GT mixtures were achieved in aqueous/electrolyte solutions owing to the interaction between the IBS and GT by forming of complexes of drug-GT mixtures [42]. At the primary breakpoint, IBS starts to adsorb at the negatively charged free spaces occurs in GT means drug and GT mixtures formed complexes and γ of the mixed systems became lesser as compared to that of pure GT solution. The primary breakpoint is called the critical aggregate concentration (cc) and cc is allied with the characteristics of the gelatin and the employed drug. The cc is always found to be inferior to cmc, signifying that the adsorption of IBS on GT surface occurs by hydrophobic interaction and it is easier as compared to their micellization [43]. At the second break point called pp (polymer saturation point), the surface is saturated with GT and IBS monomers, furthermore more addition of IBS monomers does not cause varies in adsorption at the surface, moreover the free IBS micelles start to form by means of additional enhance in the IBS concentration. The pp values were always found to be higher than cmc of a drug, owing to the adsorption of IBS on gelatin available surface sites. At this point, surface tension becomes constant and also becomes independent from IBS concentration. At lower concentration of GT in a solution of IBS in absence and presence of NaCl the cc, is not achieved very sharp although turns out to be clearer as the GT concentration enhances in the solution (Figs. 5 and 6). This possibly attributed to the reason that at low concentration of GT weaker interaction occurs between GT and drug which happens to additional prominent as gelatin concentration enhances. The achieved value of both cc and pp by means of both methods, i.e., conductometry and tensiometry, were in fine validation through each other (cc and pp data evaluated by surface tension measurement are not given in tabular form). The cc and pp values of IBS-GT mixtures were reduced by means of the adding of NaCl in the solution because (Table 2). The decrease in cc and pp values is mainly owed to lessen in the electrostatic repulsions amongst the charged hydrophilic parts within the micelles that stabilize formed aggregates. The amphiphile concentrations are at all times more at the airsolution interfacial surface as compared to the bulk solution. The

Amin ¼

1020 NA Γ max



2

Å



ð2Þ

The Γmax and minimum area per molecule (Amin) values for the pure in addition to mixed systems are disclosed in Tables 3 and 4. Increase in Γmax value signifies increased effectiveness of the amphiphiles molecules to occupy the interfacial surface. Employed drug IBS has higher Γmax as compared to their mixed systems with GT in both aqueous and electrolyte solution viewing that pure IBS is more surface active means IBS adsorb on surface easily as compared to IBS-GT mixtures. In being of NaCl in solution, the Γmax value of pure IBS increases signifying that the efficiency of the IBS monomers to occupy the air-solution interface is enhanced owing to the occurrence of electrolyte means the compactness of IBS molecules at surfaces increases by the presence of salt. As it is shown from Tables 3 and 4 the values of Γmax decreases for IBS-GT mixed systems or value of Amin increases as compared to pure drug IBS but not showing any particular trend with enhancing of concentration of GT in the solution of IBS drug viewing the looseness of IBS-GT mixtures at the interfacial surface [1]. The efficiency of γ reduction (πpp/mc) illustrates the maximum lessening of the γ and is acknowledged through Eq. (3) [46]: πpp=cmc ¼ γo –γpp=cmc

ð3Þ

The γ0 and γcmc is the γ of water and γ of the employed drug IBS at the pp/cmc. The values of πpp/cmc for IBS and IBS-GT mixed system in aqueous and electrolyte solution are represented in Tables 3 and 4. The higher is the πpp/cmc value, larger the efficacy of the system is in dropping the surface tension. The πpp/cmc value shows that for the case of pure IBS in presence of NaCl was achieved to be highest followed by pure IBS in aqueous solution, however, for IBS-GT mixtures were found too much lower both in occurrence and absence of NaCl but in presence NaCl their values were little bit low. Table 3 Surface and thermodynamic parameters of IBS and IBS-gelatin mixed systems in aqueous solution at temperature T = 298.15 K and pressure p = 0.1 MPa (data were taken from tensiometric measurement).a % Gelatin (w/v) 0 0.15 0.20 0.30 0.40 0.50

107 Γmax (mol m−2) 22.57 6.33 9.62 7.41 6.13 5.28

Amin (Ǻ2) 73.55 262.42 172.66 224.13 270.67 314.73

Gmin (kJ∙mol−1)

ΔGoads (kJ∙mol−1)

πpp/cmc

13.98 47.70 31.35 40.44 46.89 54.88

−39.41 −76.07 −56.46 −67.20 −77.21 −84.44

39.43 34.75 34.45 34.88 35.32 34.49

a Standard uncertainties (u) are u(T) = 0.20 K, and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(Γmax) = ±5%, ur(Amin) = ±5%, ur(πcmc) = ±2%, ur(ΔGoads) = ±4%, and ur(Gmin) = ±4%.

N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187 Table 4 Surface and thermodynamic parameters of IBS and IBS-gelatin mixed systems in 100 mmol.kg−1 NaCl at temperature T = 298.15 K and pressure p = 0.1 MPa (data were taken from tensiometric measurement).a % Gelatin (w/v) 0 0.15 0.20 0.30 0.40 0.50

107 Γmax (mol m−2) 22.83 4.78 5.81 6.27 6.65 5.26

Amin (Ǻ2) 72.73 347.01 285.63 264.62 249.74 315.78

Gmin (kJ∙mol−1)

ΔGoads (kJ∙mol−1)

πpp/cmc

13.01 62.30 50.84 47.16 44.48 55.96

−40.62 −93.07 −78.22 −74.09 −71.19 −82.72

41.30 34.11 33.12 33.51 33.83 33.09

a Standard uncertainties (u) are u(T) = 0.20 K, u(NaCl) = 1 mmol∙kg−1 and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(Γmax) = ±5%, ur(Amin) = ±5%, ur(πcmc) = ±2%, ur(ΔGoads) = ±4%, and ur(Gmin) = ±4%.

3.4. Thermodynamics of IBS–gelatin interactions The free energy of aggregation (ΔGagg) and free energy of micellization (ΔGmic), along with free energy of polymer saturation (ΔGpp) process for IBS and IBS-GT mixed systems in water/NaCl solution was computed via the following equation [47,48]. ΔGagg ¼ RT ð2−α1 Þ ln X cc

ð4Þ

ΔGmic ¼ RT ð2−α2 Þ ln X cmc

ð5Þ

ΔGpp ¼ RT ð2−α2 Þ lnX pp

ð6Þ

The standard free energy (ΔGagg) allied through the interactions amongst IBS drug and GT, the free energy of transfer (ΔGt), depicted via the difference in the ΔGagg of IBS monomer from aqueous system to the micellar system in GT free as well as in the attendance of GT both in aqueous and electrolytes media, is estimated via the employing of following equation [49]: ΔGt ¼ ΔGagg −ΔGpp

ð7Þ

The evaluated values of ΔGagg, ΔGmic, ΔGpp and ΔGt of current studied systems were given in Tables 1–2 and their values were found to negative. The value of free energy of micellization (ΔGmic) in case of singular IBS was achieved negative in both studied medium viewing that association of pure drug is spontaneous in nature and showing more spontaneity in presence of NaCl. The negative value of ΔGagg increases with the increase of amount of GT in solution viewing the interaction between IBS and GT increases through enhances in a concentration of GT and their values were found to more with NaCl solution again confirming that due to NaCl medium for IBS and GT the interaction between them increases more as compared to salt free solution and these outcomes are also found in parallel with the cc values. The negative value of ΔGmic for IBS is found to a little bit more than those obtained in IBS-GT solution mixtures mean ΔGpp (free energy of polymer saturation) value. This proposes that the presence of GT in solution mixtures slowly down the micellization phenomena of IBS in both studied media. In attendance of GT in the solution of IBS drug, the ΔGagg values was obtained more negative in comparison to ΔGpp values of analogues concentration of GT (Tables 1–2). The above stated trends were achieved as a result of the interaction amongst the drug and GT and viewing the aggregation phenomena are more favorable as compared to polymer saturation phenomena and in the presence of NaCl the interaction amongst ingredients more feasible. As a result, by reason of these observations, it is verified that interaction amongst GT and IBS occurs in both studied media and their interaction is because of the dominating anionic sites of the employed constituents in current situations. In addition, the decrease in the magnitude of ΔGpp values on growing the GT concentration in the solution possibly attributed to the delayed free micellization of the drug once the more GT occurs in the solution.

7

Furthermore the ΔGt values pursue a similar as shown by ΔGagg that is chiefly coupled through the shift of drug from the aggregation form to the GT-IBS complex. The negative values of ΔGt enhance through enhance in GT concentration (%w/v) signifying that the move of the IBS molecules turns into additional favorable from the solvent to the GT bound micelles by means of enhance of concentration of gelatin (Tables 1 and 2). In attendance of NaCl, the negative values of ΔGagg, ΔGpp along with ΔGt were obtained more negative in value signifying that, interactions amongst GT and IBS are thermodynamically approving; along with the extent of interaction was noticeably increased in attendance of electrolyte. The increase in negative value of ΔGt in attendance of salt viewing the enhance ability of transport of IBS from micellar to the GT-drug bound means salt induce early aggregation as well as also enhance the ability of transport of IBS from associates structure to the GT bound with drug complex (Tables 1–2). The values of Standard Gibb's energy of adsorption (ΔGoads) for current studied systems were computed by employing Eqs. (8) and (9) [1,50]. πcmc ΔGoads ¼ ΔGmic − Γ max

ð8Þ

π cmc ΔGoads ¼ ΔGpp − Γ max

ð9Þ

The all evaluated ΔGoads values were found to be negative in both media, furthermore also their negative values are larger as compared to ΔGmic and ΔGpp value at their corresponding concentration of GT in the solution of IBS, verifying that the micellization phenomenon takes place at latter stage and initially interfacial adsorption of monomers takes place, as a result some work has been required for transporting of compounds from the surface monomeric form towards the micellar structure (Tables 3 and 4). The ΔGoads value in case of singular IBS was achieved less negative in comparison to their mixed systems with drug i.e. IBS-GT in aqueous and electrolyte solution, demonstrating that the IBS-GT mixtures are found to more surface active as compared to pure IBS. The minimum molar free energy (Gmin) at the maximum adsorption achieved at polymer saturation point (pp) is accessed by means of employing the Eq. (10) [51]: Gmin ¼ Amin γcmc=pp NA

ð10Þ

Gmin is the minimum free energy of the particular air-solution interface by way of entirely absorbed molecules monomers. Inferior the value of Gmin, more thermodynamically stable interface is produced. The lesser values of Gmin reveals thermodynamically higher stability of air-solution interface. In the presence of different concentration GT in solution of IBS in both studied media, the value of Gmin were found to higher as compared to pure Gmin of pure IBS, demonstrating that stability of formed surface by IBS-GT complex are less but by the change in concentration of GT, the Gmin value does not illustrate any expected trend in aqueous as well as in electrolyte solution (Tables 3 and 4). 3.5. Fluorescence measurements of IBS-GT mixtures 3.5.1. Aggregation number (Nagg) The fluorescence technique is a well-situated way for evaluating the micelle aggregation numbers (Nagg) for a solo in addition to mixed amphiphiles systems in the aqueous and non-aqueous solvent [52]. The adding of pyrene to the micellar solution of a drug as well as IBS-GT complex in aqueous/electrolyte solution are partition amongst micelles. The pyrene quenching via the CPC is employed to detect aggregation number (Nagg) for pure drug IBS plus their mixtures with GT of different concentration in both studied media (aqueous/NaCl/) by means of the

8

N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187

6500

subsequent equations [53,54]:

5000

3.5.2. Micropolarity (I1/I3) The achieved outcomes were additionally clarified on the basis of other evaluated parameters such as micropolarity and dielectric constant. Figs. 7 and 8 signifies a diagram of intensity versus wavelength to give up I1/I3 (I1 and I3 is the intensity of first and third vibronic peaks respectively). The ratio of I1 and I3 shows the micropolarity [55]. The obtained I1/I3 values for the micellar solution of pure IBS along with their mixtures with GT in different concentration in both studied solvent are shown in Tables 5 and 6. For any studied system if I1/I3 4500 4000

-1

CPC/mmol.kg 0 -2 0.50 x 10 -2 0.99 x 10 -2 1.48 x 10 -2 1.96 x 10 -2 2.44 x 10 -2 2.91 x 10

3500 3000

Intensity

5500

ð11Þ

2500 2000 1500

4500 4000

Intensity

In Eq. (11), I1 and I0 is fluorescence intensity in the attendance of CPC and absence of CPC correspondingly. [Q] symbolized the utilized concentration of CPC and ST is the total concentration of the prepared drug. A linear graph view amid ln(Io/I) and [Q] having a slope and it is equal to Nagg/([S]T-cmc). By the obtained slope values Nagg were computed. Figs. 7 and 8 show the variation of intensity as a function of concentration of CPC for IBS + 0.30% GT mixed systems in aqueous system and 100 mmol.kg−1 NaCl respectively and each spectrum is showing five clear separate emission bands start from smaller to higher wavelengths. The evaluated Nagg values for pure IBS and IBS-GT complex systems are presented in Tables 5 and 6. For the calculation of Nagg for the case of pure IBS, cmc is in use instead of cc in both studied media. The value Nagg for the pure IBS in aqueous solution was attained in good consistency through stated value [26,27]. In the presence of salts in all studied solution the value of Nagg were found to more in all cases due to micelles formation of larger size. NaCl is acknowledged to lessen the electrostatic repulsion amid the negatively charged portion of IBS sourcing the higher Nagg value. For the mixture of IBS and GT, the value of Nagg increases via raising the concentration GT in solution in both studied media and found to be always higher than Nagg of pure IBS but the increment is more in salt solution as compared to aqueous solution viewing the encouraging ingredients interaction of the solution (Tables 5 and 6). The enhance in Nagg possibly as a result of the electrostatic interaction amongst both anionic charged head group of IBS and gelatin as well as also sustained by the nonpolar interactions amid the hydrophobic part of both studied constituents in aqueous/electrolyte solutions.

3500 3000 2500 2000 1500 1000 500 0

350 360 370 380 390 400 410 420 430 440 450

wavelength / nm Fig. 8. Representative illustration of variation of intensity as a function of concentration of quencher (CPC) for IBS + 0.30% gelatin mixtures in 100 mmol.kg−1 NaCl.

was found to less than unity showing that nonpolar environment of pyrene whereas if I1/I3 is obtained more than unity then viewing that polar environment of pyrene [56]. In our case I1/I3 values were found to in the range of 1.17–1.56 showing that the obtained values are closer to the I1/I3 value of CH3-OH [57]. By seeing these observed values it is supposed that the pyrene is solubilized in the polar region of the associates' structures (palisade layer). In attendance of NaCl in case of individual IBS solution, the I1/I3 value is found to more in comparison to aqueous system viewing that the polarity decreases owing to the attendance of NaCl. The effectiveness of hydrophobic atmosphere can be predictable through assessing the first-order quenching rate constant and evaluated parameter is known as Stern-Volmer binding constant (Ksv), and it is determined by employing the following equation [58,59]. I0 ¼ 1 þ K SV ½Q  I1

500

380 390 400

410 420 430

440 450

wavelength / nm Fig. 7. Representative illustration of variation of intensity as a function of concentration of quencher (CPC) for IBS + 0.30% gelatin mixtures in aqueous system.

ð12Þ

The Ksv values were estimated from I0/I versus [Q] plot for IBS along with IBS-GT mixtures in different ratio of GT. The obtained values of KSV of current systems have been revealed in Tables 5 and 6. In any case, if larger the solubility of the probe along with quencher occurs, then, in that case, the evaluated Ksv value will obtain high. In case of an aqueous solution of IBS-GT mixed systems the Ksv values were achieved higher than Ksv value of singular IBS micelles viewing the additional hydrophobic environment in case of the mixed system but in the case of GT-IBS mixtures in NaCl solution Ksv value were found to higher than pure

Table 5 Different parameters evaluated from fluorometric measurements for IBS-gelatin mixed systems in aqueous solutions at temperature T = 298.15 K and pressure p = 0.1 MPa.a % Gelatin (w/v)

1000

0 360 370

-1

CPC/mmol.kg 0 -2 0.50 x 10 -2 0.99 x 10 -2 1.48 x 10 -2 1.96 x 10 -2 2.44 x 10 -2 2.91 x 10

6000

  Nagg ½Q  I0 ¼ ln ST −cc I1

0.0 0.15 0.20 0.30 0.40 0.50

Nagg

I1/I3

Ksv·10−4

Dexp

44 51 58 69 77 91

1.26 1.36 1.56 1.37 1.19 1.17

0.94 3.61 3.77 2.93 9.11 4.71

20.50 28.25 44.31 29.48 14.52 5.51

a Standard uncertainties (u) are u(T) = 0.2 K and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(Nagg) = ±4%, ur(Ksv) = ±3% and ur(Dexp) = ±4%.

N. Azum et al. / Journal of Molecular Liquids 290 (2019) 111187 Table 6 Different parameters evaluated from fluorometric measurements for IBS-gelatin mixed systems in 100 mmol.kg−1 NaCl at temperature T = 298.15 K and pressure p = 0.1 MPa.a −4

% Gelatin (w/v)

Nagg

I1/I3

Ksv·10

0.0 0.15 0.20 0.30 0.40 0.50

53 63 74 85 97 110

1.24 1.53 1.46 1.34 1.31 1.28

4.17 2.79 3.48 4.50 5.01 5.59

Dexp 18.63 41.78 36.21 26.98 24.66 21.74

a Standard uncertainties (u) are u(T) = 0.2 K, u(NaCl) = 1 mmol∙kg−1 and u(p) = 5 kPa (level of confidence = 0.68). Relative standard uncertainties (ur) are ur(Nagg) = ±4%, ur (Ksv) = ±3% and ur(Dexp) = ±4%.

micellar IBS in NaCl only at higher concentration of GT. Ksv values also disclose that their numeral value was not much significant to a great level because their value was acquired little. The investigational or experimental dielectric constant (Dexp) of the medium is evaluated via the subsequent equation [60]. I1 ¼ 1:00461 þ 0:01253Dexp I3

ð13Þ

Here, we have calculated the Dexp values for the micellar solution IBS in two studied medium along in the presence of GT in various concentration from their corresponding I1/I3 data. The evaluated Dexp values were exposed in Tables 5 and 6. The obtained Dexp values for current studied systems do not demonstrate any specific trend with an increase in GT concentration in the solution mixtures but their value was found to below 45, yet again showing that the environment of pyrene is polar in nature. 4. Conclusions Herein, the interaction amongst amphiphilic drug IBS and gelatin (GT) protein have evaluated via conductometric, tensiometric and fluorometric techniques in aqueous/electrolytes solutions at 298.15 K. The values of cc were found to decrease, whereas their pp values were achieved an increase in magnitude on raising the GT concentration in solution of IBS-GT mixtures in both studied media. The value of cc and pp of IBS-GT systems decreased in presence of salt, in comparison to aqueous solution owing to the electrostatic repulsion amid the studied constituents, gets decreased. The complex formed IBS and GT mixtures are well surface active in both studied media as disclosed by tensiometric measurements. The increases in a negative value of ΔGagg along with ΔGt were found while a decrease in a negative value of ΔGpp occurs on raising the GT concentration in solution mixtures in both studied media. The negative ΔGmic/ΔGpp and ΔGoads values demonstrate that micellization, as well as adsorption of IBS in absence and the occurrence of GT, are energetically constructive in both media, along with by seeing the negative value, it is concluded that first adsorption followed by micellization takes place. The value of Nagg for IBS-GT mixtures increases by way of the increase of GT concentration and their value further increases in the presence of NaCl. The micropolarity (I1/I3) of pure IBS is achieved more in NaCl solution in comparison to aqueous system visioning that NaCl decreases the polarity of the drug solution. The Ksv values of IBS-GT aqueous mixed systems were attained higher than Ksv value of pure drug showing the more hydrophobic environment for a mixed system. Acknowledgment The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through the research group project No. RG-1439-74.

9

References [1] M.J. Rosen, Surfactants and Interfacial Phenomena, third ed. John Wiley & Sons, New York, 2004. [2] D. Kumar, M.A. Rub, Studies of interaction between ninhydrin and Gly-Leu dipeptide: influence of cationic surfactants (m-s-m type gemini), J. Mol. Liquids 269 (2018) 1–7. [3] D. Kumar, M.A. Rub, Interaction of ninhydrin with chromium-glycylglycine complex in the presence of dimeric gemini surfactants, J. Mol. Liquids 250 (2018) 329–334. [4] D. Kumar, M.A. Rub, Synthesis and characterization of dicationic gemini surfactant micelles and their effect on the rate of ninhydrin–copper-peptide complex reaction, Tenside Surf. Detergents 55 (2018) 78–84. [5] D. Kumar, M.A. Rub, M. Akram, Kabir-ud-Din, Role of gemini surfactants (m-s-m type; m= 16, s=4–6) on the reaction of [Zn(II)-Gly-Phe]+ with ninhydrin, J. Phys. Org. Chem. 27 (2014) 729–734. [6] D. Attwood, A.T. Florence, Surfactant Systems, Their Chemistry, Pharmacy and Biology, Chapman and Hall, New York, 1983. [7] F. Khan, M.A. Rub, N. Azum, A.M. Asiri, Mixtures of antidepressant amphiphilic drug imipramine hydrochloride and anionic surfactant: micellar and thermodynamic investigation, J. Phys. Org. Chem. 31 (2018) e3812. [8] M.A. Rub, M.S. Sheikh, F. Khan, S.B. Khan, A.M. Asiri, Bile salts aggregation behavior at various temperatures under the influence of amphiphilic drug imipramine hydrochloride in aqueous medium, Z. Phys. Chem. 228 (2014) 747–767. [9] H.J. Yoon, S.R. Shin, J.M. Cha, S.-H. Lee, J.-H. Kim, J.T. Do, H. Song, H. Bae, Cold water fish gelatin methacryloyl hydrogel for tissue engineering application, PLoS One 11 (2016) e0163902. [10] C.M. Ofner, H. Schott, Swelling studies of gelatin ii: effect of additives, J. Pharm. Sci. 76 (1987) 715–723. [11] S.H. Nezhadi, P.F. Choong, F. Lotfipour, C.R. Dass, Gelatin-based delivery systems for cancer gene therapy, J. Drug Target. 17 (2009) 731–738. [12] C. Buron, C. Filiatre, F. Membrey, A. Foissy, J.-F. Argillier, Interactions between gelatin and sodium dodecyl sulphate: binding isotherm and solution properties, Colloid Polym. Sci. 282 (2004) 446–453. [13] S. Magdassi, Y. Vinetsky, Microencapsulation of O/W emulsions by formation of a protein–surfactant insoluble complex, J. Microencapsul. 12 (1995) 537–545. [14] A. Chatterjee, S.P. Moulik, P.R. Majhi, S.K. Sanyal, Studies on surfactant–biopolymer interaction. I. Microcalorimetric investigation on the interaction of cetylmethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) with gelatin (Gn), lisozyme (Lz) and deoxyribonucleic acid (DNA), Biophys. Chem. 98 (2002) 313–327. [15] P.C. Griffiths, I.A. Fallis, P. Teerapornchaisit, T. Grillo, Hydrophobically modified gelatin and its interaction in aqueous solution with sodium dodecyl sulfate, Langmuir 17 (2001) 2594–2601. [16] M.A. Rub, Aggregation and interfacial phenomenon of amphiphilic drug under the influence of pharmaceutical excipients (green/ biocompatible gemini surfactant), PLoS One 14 (2019) e0211077. [17] L.M. Lichtenberger, Y. Zhou, E.J. Dial, R.M. Raphael, NSAID injury to the gastrointestinal tract: evidence that NSAIDs interact with phospholipids to weaken the hydrophobic surface barrier and induce the formation of unstable pores in membranes, J. Pharm. Pharmacol. 58 (2006) 1421–1428. [18] V. Ambrogi, G. Fardella, G. Grandolini, L. Perioli, Intercalation compounds of hydrotalcite-like anionic clays with antiinflammatory agents - I. Intercalation and in vitro release of ibuprofen, Int. J. Pharm. 220 (2001) 23–32. [19] J.L. Goldstein, B. Cryer, Gastrointestinal injury associated with NSAID use: a case study and review of risk factors and preventative strategies, Drug Health Patient Saf. 7 (2015) 31–41. [20] D. Kumar, S. Hidayathulla, M.A. Rub, Association behavior of a mixed system of the antidepressant drug imipramine hydrochloride and dioctyl sulfosuccinate sodium salt: effect of temperature and salt, J. Mol. Liquids 271 (2018) 254–264. [21] D. Kumar, M.A. Rub, Aggregation behavior of amphiphilic drug promazine hydrochloride and sodium dodecylbenzenesulfonate mixtures under the influence of NaCl/urea at various concentration and temperatures, J. Phys. Org. Chem. 29 (2016) 394–405. [22] N. Edrinc, S. Gokturk, M. Tuncay, Interaction of epirubicin HCl with surfactants: effect of NaCl and glucose, J. Pharm. Sci. 93 (2004) 1566–1576. [23] R. Zakia, L. Stroebel, The Focal Encyclopedia of Photography, 3rd ed. Butterworth– Heinemann, Woburn MA, 1993. [24] N. Azum, M.A. Rub, A.M. Asiri, Interaction of triblock-copolymer with cationic gemini and conventional surfactants: a physicochemical study, J. Disp. Sci. Technology 38 (2017) 1785–1791. [25] M.A. Rub, A.M. Asiri, J.M. Khan, F. Khan, R.H. Khan, Kabir-ud-Din, A study of interaction between antidepressant drug nortriptyline hydrochloride with gelatin, J. Taiwan Institute Chem. Engineers 45 (2014) 2068–2074. [26] A. Ridell, H. Evertsson, S. Nilsson, L.O. Sundelöf, Amphiphilic association of ibuprofen and two nonionic cellulose derivatives in aqueous solution, J. Pharm. Sci. 88 (1999) 1175–1181. [27] M.A. Rub, N. Azum, A.M. Asiri, Binary mixtures of sodium salt of ibuprofen and selected bile salts: interface, micellar, thermodynamic, and spectroscopic study, J. Chem. Eng. Data 62 (2017) 3216–3228. [28] N. Azum, M.A. Rub, A.M. Asiri, Analysis of surface and bulk properties of amphiphilic drug ibuprofen and surfactant mixture in the absence and presence of electrolyte, Colloids Surf. B 121 (2014) 158–164. [29] G. Para, E. Jarek, P. Warszynski, The Hofmeister series effect in adsorption of cationic surfactants-theoretical description and experimental results, Adv. Colloid Interf. Sci. 122 (2006) 39–55.

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[30] M. Shamsipur, N. Alizadeh, H. Gharibi, Physicochemical studies of the hexadecylpyridinium bromide micellar system in the presence of various concentrations of sodium bromide using a surfactant-selective electrode, Indian J. Chem. 36A (1997) 1031–1037. [31] E.D. Goddard, Polymer-surfactant interaction Part I. uncharged water-soluble polymers and charged surfactants, Colloids Surf 19 (1986) 255–300. [32] V. Sovilj, Conductometric and potentiometric investigations of ionic surfactant- gelatin interaction, Colloid Polym. Sci. 276 (1998) 328–334. [33] Y. Moroi, Micelles: Theoretical and Applied Aspects, Plenum Press, New York, 1992. [34] S. Magdassi, Y. Vinetsky, P. Relkin, Formation and structural heat-stability of βlactoglobulin/surfactant complexes, Colloids Surf. B 6 (1996) 353–362. [35] I.A. Khan, K. Anjum, M.S. Ali, Kabir-ud Din, A comparative study of interaction of ibuprofen with biocompatible polymers, Colloids and Surfaces B 88 (2011) 72–77. [36] M.S. Ali, M. Suhail, G. Ghosh, M. Kamil, Kabir-ud-Din, Interactions between cationic gemini/conventional surfactants with polyvinylpyrrolidone: specific conductivity and dynamic light scattering studies, Colloids Surf. A Physicochem. Eng. Asp. 350 (2009) 51–56. [37] N. Azum, M.A. Rub, A.M. Asiri, H.A. Kashmery, Synergistic effect of an antipsychotic drug chlorpromazine hydrochloride with pluronic triblock copolymer: a physicochemical study, J. Mol. Liquids 260 (2018) 159–165. [38] M.A. Hoque, M.M. Alam, M.R. Molla, S. Rana, M.A. Rub, M.A. Halim, M.A. Khan, A. Ahmed, Effect of salts and temperature on the interaction of levofloxacin hemihydrate drug with cetyltrimethylammonium bromide: conductometric and molecular dynamics investigations, J. Mol. Liquids 244 (2017) 512–520. [39] S. Mahbub, M.A. Rub, M.A. Hoque, M.A. Khan, Mixed micellization study of dodecyltrimethylammonium chloride and cetyltrimethylammonium bromide mixture in aqueous/urea medium at different temperatures, theoretical and experimental view, J. Phys. Org. Chem. 31 (2018) e3872. [40] M. Ao, P. Huang, G. Xu, X. Yang, Y. Wang, Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length, Colloid Polym. Sci. 287 (2009) 395–402. [41] K. Holmberg, B. Jonsson, B. Kronberg, B. Lindman, Surfactants and Polymers in Aqueous Solution, John Wiley & Sons, England, 2002. [42] S. Liu, X. Yang, S. Wang, X. Dai, T. Li, Y. Wang, Interaction between EPTAC-modified gelatin and surfactants: surface tension and conductivity methods, J. Disp. Sci. Technology 36 (2015) 731–739. [43] V. Sovilj, J. Milanovic, L. Petrovic, Influence of gelatin–sodium stearoyl lactylate interaction on the rheological properties of gelatin gels, Colloids and Surfaces A 417 (2013) 211–216. [44] F. Khan, U.S. Siddiqui, M.A. Rub, I.A. Khan, Kabir-ud-Din, Micellization and interfacial properties of cationic gemini surfactant (12–4–12) in the presence of additives in aqueous electrolyte solution: a tensiometric study, J. Mol. Liquids 191 (2014) 29–36. [45] N. Azum, M.A. Rub, A.M. Asiri, Micellization and interfacial behavior of the sodium salt of ibuprofen–BRIJ-58 in aqueous/brine solutions, J. Solut. Chem. 45 (2016) 791–803.

[46] K.S. Rao, T. Singh, T.J. Trivedi, A. Kumar, Aggregation behavior of amino acid ionic liquid surfactants in aqueous media, J. Phys. Chem. B 115 (2011) 13847–13853. [47] J.R. Lu, A. Marrocco, T.J. Su, Adsorption of dodecyl sulfate surfactants with monovalent metal counterions at the air-water interface studied by neutron reflection and surface tension, J. Colloid Interface Sci. 158 (1993) 303–316. [48] M.A. Rub, N. Azum, S.B. Khan, F. Khan, A.M. Asiri, Physicochemical properties of amphiphilic drug and anionic surfactant mixtures: experimental and theoretical approach, J. Dispersion Sci. Tech. 36 (2015) 521–531. [49] N. Kamenka, I. Burgaud, C. Trenier, R. Zana, Interaction of copper(II) dodecyl sulfate with poly(ethylene oxide) and poly(vinylpyrrolidone): self-diffusion, fluorescence probing, and conductivity study, Langmuir 10 (1994) 3455–3460. [50] M.A. Rub, N. Azum, F. Khan, A.M. Asiri, Aggregation of sodium salt of ibuprofen and sodium taurocholate mixture in different media: a tensiometry and fluorometry study, J. Chem. Thermodynamics 121 (2018) 199–210. [51] G. Sugihara, A.M. Miyazono, S. Nagadome, T. Oida, Y. Hayashi, J.S. Ko, Adsorption and micelle formation of mixed surfactant systems in water II: a combination of cationic gemini-type surfactant with MEGA-10, J. Oleo Sci. 52 (2003) 449–461. [52] N. Azum, M.A. Rub, A.M. Asiri, K.A. Alamry, H.M. Marwani, Self-aggregation of cationic dimeric and anionic monomeric surfactants with nonionic surfactant in aqueous medium, J. Disp. Sci. Technology 35 (2014) 358–363. [53] N.J. Turro, A. Yekta, Luminescent probes for detergent solutions. A simple procedure for determination of the mean aggregation number of micelles, J. Am. Chem. Soc. 100 (1978) 5951–5952. [54] M.K. Al-Muhanna, M.A. Rub, N. Azum, S.B. Khan, A.M. Asiri, Effect of gelatin on micellization and microstructural behavior of amphiphilic amitriptyline hydrochloride drug solution: a detailed study, J. Chem. Thermodynamics 89 (2015) 112–122. [55] F.M. Winnik, Photophysics of preassociated pyrenes in aqueous polymer solutions and in other organized media, Chem. Rev. 93 (1993) 587–614. [56] K.K. Rohatgi-Mukherjee, Fundamentals of Photochemistry, Wiley Eastern, New Delhi, 1992. [57] K. Kalyanasundaran, J.K. Thomas, Environmental effects on vibronic band intensities in pyrene monomer fluorescence and their application in studies of micellar systems, J. Am. Chem. Soc. 99 (1977) 2039–2044. [58] M.R. Eftink, C.A. Ghiron, Fluorescence quenching of indole and model micelle systems, J. Phys. Chem. 80 (1976) 486–493. [59] M.A. Rub, F. Khan, M.S. Sheikh, N. Azum, A.M. Asiri, Tensiometric, fluorescence and 1 H NMR study of mixed micellization of non-steroidal anti-inflammatory drug sodium salt of ibuprofen in the presence of non-ionic surfactant in aqueous/urea solutions, J. Chem. Thermodynamics 96 (2016) 196–207. [60] N.J. Turro, P.L. Kuo, P. Somasundaran, K. Wong, Surface and bulk interactions of ionic and nonionic surfactants, J. Phys. Chem. 90 (1986) 288–291.