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Thermophysical properties and ecotoxicity of new nitrile functionalised protic ionic liquids
Accepted Manuscript Thermophysical properties and ecotoxicity of new nitrile functionalised protic ionic liquids
Amir Sada Khan, Asma Nasrullah, Zahoor Ullah, A.H. Bhat, Ouahid Ben Ghanem, Nawshad Muhammad, Mamoon Ur Rashid, Zakaria Man PII: DOI: Reference:
S0167-7322(17)33343-3 doi:10.1016/j.molliq.2017.10.141 MOLLIQ 8104
To appear in:
Journal of Molecular Liquids
Received date: Revised date: Accepted date:
25 July 2017 29 October 2017 30 October 2017
Please cite this article as: Amir Sada Khan, Asma Nasrullah, Zahoor Ullah, A.H. Bhat, Ouahid Ben Ghanem, Nawshad Muhammad, Mamoon Ur Rashid, Zakaria Man , Thermophysical properties and ecotoxicity of new nitrile functionalised protic ionic liquids. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/j.molliq.2017.10.141
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Thermophysical Properties and Ecotoxicity of New Nitrile Functionalised Protic Ionic Liquids Amir Sada Khana,b*, Asma Nasrullahc, Zahoor Ullahd, A.H bhatc, Ouahid Ben Ghanema, Nawshad Muhammade*, Mamoon Ur Rashidd, Zakaria Mana a
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Centre of Research in Ionic Liquids CORIL), Department of Chemical Engineering, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia. b Department of Chemistry, University of Science and Technology, Bannu 28100, Khyber Pakhtunkhwa, Pakistan. c Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS (UTP), 31750 Tronoh, Perak, Malaysia. d Department of Chemistry, The Balochistan University of IT, Engineering and Management Sciences (BUITEMS) , Takatu Campus, Quetta-87100, Pakistan e Interdisciplinary Research Centre in Biomedical Materials, COMSAT Institute of Information Technology, Lahore Pakistan.
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*Corresponding authors; [email protected], [email protected]
Abstract
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In this present research, five nitrile functionalised imidazolium based protic ionic liquids (PILs)
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by varying alkyl chain length of anions were synthesised. The synthesised ILs were characterized with nuclear magnetic resonance spectroscopy (NMR) and elemental analyser (CHNS). Various
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thermophysical such as refractive index, density, viscosity and thermal stability were measured over wide temperature range. From the density experimental data, different volumetric properties
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were estimated using well established empirical equations. Moreover, the effect of temperature and increase of alkyl substitutions attached to anion has been evaluated for the studied properties.
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The toxicity (EC50) of the synthesized ILs have been assessed against three human pathogenic bacteria i.e, Aeromonas hydrophila A97 (AH), Escherichia coli E149 (EC), and Staphylococcus aureus S244 (SA) in light to identify the influence of increasing alkyl substitution of the anion moiety on the overall toxicity of PILs.
Keywords: Nitrile functionality; protic ionic liquids; thermophysical properties; alkyl chain length; ecotoxicity
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Introduction Currently, ionic liquids (ILs) has introduced as greener solvents and has received special interest to be used as medium for different types of reaction. This new class of molten organic salt ILs are documented as designer/tailorable solvent due possible combination of large number of cations and anions. In general, the most important and commonly interesting properties such as density, viscosity, refractive index, surface tension, thermal stability, solvation polarity of ILs can be easily
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tuned by pairing appropriate anion and cation [1-3]. Recently, ILs are getting popularity and
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largely used for different applications such as catalysis, organic synthesis, pharmaceutical and
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biological applications, gas separation, membrane separation, crude oil treatment [3-5], etc. Among the various available ILs, Bronsted acidic ILs (BAILs) or protic acidic ILs (PAILs) are easy
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to be synthesize by transfer of proton from Bronsted acid to Bronsted base by neutralization reaction. The
PILs are synthesised by simple equimolar reaction of acid and base, this is generally making the ILs simplest and cheapest to synthesise [6]. Currently, it has been investigated that the properties
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of ILs can be enhanced by incorporating functional groups either to cation or to anion or on both [7, 8]. Among various available functionalized ILs, the nitrile functional group are relatively a new
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class with distinct properties and potential application in various research areas [9-11].
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Furthermore, until now no literature available on the synthesis of ILs having nitrile functionalized imidazolium cation and carboxylate anion with various carbon chain length.
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It has been proposed that the elongation of the alkyl chain length attached to cation of ILs possess high increasing trend of toxicity compared to any other modification on the ILs structural
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features. The other structural elements such as anions, functional groups and the type of the cations were found to play a less important role in the domination of the behaviour of ILs toxicity [12].
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Recently, few studies have been performed the examine the impact of increasing the carbon chain length of the anion side on different species [13]. However, it seems to be crucial to examine the effect of increasing alkyl chain length of the anions side on the toxicity towards different organisms as the ecotoxicity data in literatures still lacked. The second aim of this present research work is to investigate the influence of increasing the carbon chain length/alkyl chain length of anion on the ILs toxicity. This study aims to synthesize and characterize new ILs containing 1-proponitrile side chain attached with cation and carboxylate anions of various carbon chain length. The effect of increasing alkyl chain length from C1-C6 on the physiochemical properties of synthesized PILs i.e. 2
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1-propanenitrileimidazolium propanenitrileimidazolium
formate, propionate,
1-propanenitrileimidazolium 1-propanenitrileimidazolium
acetate,
butanoate
and
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propanenitrileimidazolium hexanoate were investigated. Moreover, toxicity of the prepared ILs was evaluated with respect of carboxylate anions containing alkyl side chain with different length for its safer application in various fields especially in biological environment.
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Experimental
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Materials
All the chemical used in present research work were of analytical grade and used as such as received. Acrylonitrile was purchased from sigma-Aldrich. Formic acid, acetic acid, propanoic
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acid, butanoic acid and hexanoic acid were purchased from Merck. The solvents i.e. diethyl ether
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and ethyl acetate were purchased from Fisher Scientific.
Synthesis and characterization
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PILs were prepared according to the established procedure which was slightly modified [14].
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These ILs were synthesized in two step processes; in first step, imidazole (0.2 mol) solution was made in methanol under inert atmosphere in three necks round bottom flask which was followed
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by dropwise addition of 0.23 mol of acrylonitrile. The reaction mixture was continuously refluxed in inert atmosphere for 24 h at 55oC. Vacuum rotavap was run at 70 oC to remove the unreacted
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materials. In the subsequent step, 1-propanenitrileimidazolium was stirred in acetonitrile and formic acid, propanoic acid, butanoic acid and hexanoic acid was individually added dropwise to prepare the desired IL. The reaction mixture was continuously refluxed in nitrogen atmosphere for
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24 h at 55oC. The synthesized PILs were repeatedly washed with diethyl ether and ethyl acetate. The synthesized PILs were placed in vacuum oven at 60oC for 24h and then in vacuum line overnight. The physicochemical properties of acetate base IL already reported in our published research work were used in the present study [14]. For structure confirmation, A Bruker Avance 500MHz NMR was used and elucidated the 1H NMR and
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C NMR spectra of the studied ILs. CHNS-932 (LECO instruments) was used for CHNS
analysis of the samples. Karl Fisher Titration (Mettler Toledo DL39) was used for water content
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in ppm of the samples. The purity of samples was assessed from NMR (CH2 of propionitrile was considered reference and impurity was measured relatively in percentage) and CHNS values.
Physical characterization Various physiochemical properties such as refractive index, density, viscosity and thermal stability for synthesized ILs were studied in wide range of temperature. ATAGO digital refractometer (RX-
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5000α) with accuracy of ±4.5×10-5 was used for measurement of refractive index of PILs in the
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temperature ranging from 293.15 to 323.15 K with five-degree intervals. Densities and viscosity
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of prepared ILs were measured using Anton-Parr viscometer (model SVM3000) at atmospheric pressure at temperature varying from 293.15 K to 373.15 K. Before measurement of density and viscosity of ILs, the instrument was calibrated using ultrapure Millipore quality water. The
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measurement was performed in triplicate to obtain the average value. The thermal stability of synthesized PILs were measured using Perkin-Elmer TGA (pyris-1, V-3.81) in inert atmosphere
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at temperature range from 323-373 K with heating rate of 10 K/min. Differential scanning calorimetry (Perkin-Elmer, pyris-1) was used to determine the glass
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transition temperature and melting point of ILs. The ILs sample was weighted in aluminium pan and subjected to thermo-cycles. First the sample of IL was heated with 10oC/min from 0oC to
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and then reheated until 110oC.
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110oC in inert atmosphere. After this the sample temperature was decrease from 110oC to -150oC
Antimicrobial activity test
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The antimicrobial activity of the studied ILs were established by evaluating their 50% effective concentrations (EC50) using the standard micro-broth dilution test against three human pathogens
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bacteria. obtained from the Institute of Medical Research (IMR), Kuala Lumpur, Malaysia. These strains are Aeromonas hydrophila A97 (AH), Escherichia coli E149 (EC), and Staphylococcus aureus S244 (SA). Each bacterial strain was cultured in Muller-Hinton Broth (MHB) in overnight to achieve optimum growth. Prior to the preparation of 96 well-plate, standard stock solution of each strain was prepared to be equivalent to 0.5 McFarland standard solution. The 96 well-plate was then prepared as follow; 100 µl from pure MHB media was injected in the second to the last rows. Followed by injection of 100 µl of IL solution to the first two horizontal rows. Then, two fold dilution was conducted including the six middle rows, whereas the last one remains untreated to be a reference for the optimal bacterial growth. Finally, 100 µl of the standard stock solution of 4
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the strain were added to each well. The 96 well-plate was then kept in the incubator for 24 h at 37 °C. The plates were then placed in the micro plate reader [MultiskanTM FC Microplate Photometer (Type.357)] to determine the EC50 values at 620 nm. Results and Discussion In this research work, five imidazolium based nitrile functionalised ILs with carboxylate anions
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containing alkyl side chain of different length. The synthesised ILs information’s were tabulated
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in Table 1. NMR used for their structure elucidation and the data reported as below while the
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spectrum information’s are reported in supporting materials (Figure S1a,b-S5a,b)
1-propanenitrileimidazolium formate
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Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 2.88-2.19 (t), 4.32-4.34 (t), 7.26 (s), 7.35 (s), 8.28 (s), 8.63 (s)
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C NMR (500 MHz, CH3OH): 19.02, 44.37, 117.82, 120.24, 121.65, 134.97, 168.39
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CHNS elemental analysis: Calculated (%): C: 50.24, H: 5.38, N: 25.12, O: 19.14. Found (%): C: 50.29, H: 5.39, N: 25.10, O: 19.16 Elemental analysis standard uncertainty μ(E) =
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0.045%
1-propanenitrileimidazolium acetate
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Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 1.66 (s), 2.84-2.86 (t), 4.24-4.26 (t), 7.11 (s), 7.24 (s), 8.30 (s)
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C NMR (500 MHz, CH3OH): 19.26, 32.01, 43.66, 118.14, 121.09, 122.68, 135.82, 180.35
CHNS elemental analysis: Calculated (%): C: 52.98, H: 6.07, N: 23.18, O: 17.66.
0.005%
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Found (%): C: 52.96, H: 6.09, N: 23.17, O: 17.68. Elemental analysis standard uncertainty μ(E) =
1-propanenitrileimidazolium propionate Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.97-1.004 (t), 2.19-2.23 (m), 301-3.04 (t), 4.25-4.28 (t), 6.95 (s), 7.25 (s), 7.74 (s) 13
C NMR (500 MHz, CH3OH): 9.53, 19.97, 27.44, 42.18, 118.91, 119.78, 128.88, 137.815, 175.88.
CHNS elemental analysis: Calculated (%): C: 55.32, H: 6.65, N: 21.51, O: 16.39. 5
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Found (%): C: 55.30, H: 6.67, N: 21.33, O: 16.41. Elemental analysis standard uncertainty μ(E) = 0.175%
1-propanenitrileimidazolium butanoate Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.63-0.66 (t), 1.29-1.32 (t), 1.34-1.96 (m), 2.91-2.94 (t), 4.33-4.36 (t), 7.24 (s), 7.35 (s), 8.51 (s)
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C NMR (500 MHz, CH3OH): 13.14, 19.01, 19.20, 38.76, 44.02, 117.96, 121.38, 121.68, 135.480, 182.67
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CHNS elemental analysis: Calculated (%): C: 57.35, H: 7.16, N: 20.07, O: 15.29. Found (%): C: 57.37, H: 7.17, N: 20.05, S: 15.31. Elemental analysis standard uncertainty μ(E) =
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1-propanenitrileimidazolium hexanoate
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0.015%
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Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.59-0.61 (t), 1.00-1.04 (m), 1.95-1.98 (t), 2.86-2.88 (t), 4.26-4.29 (t), 7.12 (s), 7.25 (s), 8.27 (s) 13
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C NMR (500 MHz, CH3OH): 13.34, 19.34, 21.877, 25.134, 31.05, 36.29, 43.55, 118.080, 120.94, 123.32, 136.02, 181.39
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CHNS elemental analysis: Calculated (%): C: 60.68, H: 8.01, N: 17.69, O: 13.48.
Density
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0.005%
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Found (%): C: 60.67, H: 8.05, N: 17.66, O: 13.50. Elemental analysis standard uncertainty μ(E) =
The values of densities measured for synthesised are reported in Table 2 (Fitting parameters has been provided in Table S.1). These calculated values are fitted in Figure 1. The values of densities for all ILs show decreasing trend with the temperature increase as expected. So the decreasing order of the present ILs are [C2CNIM][Hex] < [C2CNIM][But] < [C2CNIM][Pro] < [C2CNIM][Ace] < [C2CNIM][For]. It is found the values of density decrease linearly with the increase in alkyl chain length of anion. The possible reason is of the anions molecular geometry. Another reason of the long alkyl chain on anion might be due to the increment of non-polar region 6
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because when non-polar region increases then it takes more space and lower the overall density. Similar observations were found in the literature [4, 15, 16]. All these ILs with temperature shows a linear dependency. For density, the values of standard deviation (SD) and correlation coefficient (R2) are listed in Table 3. Using the following equation to calculate the standard deviation values
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(𝑍𝑒𝑥𝑝 −𝑍𝑐𝑎𝑙 )2
𝑆𝐷 = √
(1)
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𝑛𝐷𝐴𝑇
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Zexp and Zcal are the experimental determined values and calculated data values and nDAT is a number of experimental points. Temperature dependence equation for density:
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𝜌 = 𝐴0 + 𝐴1 𝑇 where 𝜕𝑙𝑛𝜌
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𝛼
𝐴1 = 𝐾 = − (𝜕(𝑇−298.15))
Assessment of Volumetric Properties
(3)
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𝑝
(2)
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The present ILs molar volumes (Vm), molecular volumes (V), standard entropy (So), lattice energy (UPOT), electronic polarizability (Rm), and free volume (Vf) are calculated from the following 𝑀 𝜌
(4)
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𝑉𝑚 =
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equations and the values are tabulated in Table 3.
where, Vm is molar volume in cm3.mol-1, M is the molecular weight in g.mol-1 and ρ is the density
𝑉 =
𝑉𝑚 𝑁𝐴
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in g.cm-3.
(5)
where, NA (Avogadro’s constant) = 6.0224 × 1023 molecules per mol. 𝑆 o (303.15)/𝐽. 𝐾. 𝑚𝑜𝑙 −1 = 1246.5(𝑉𝑚 /𝑛𝑚3 ) + 29.5
(6)
𝑈𝑃𝑂𝑇 /𝑘𝐽/𝑚𝑜𝑙 −1 = 1981.2 (𝜌/𝑀)1/3 + 103.8
(7)
Where, 𝜌 and M are the density (g.cm-3) and molecular mas (g.mol-1), respectively.
𝑅𝑚 = [
2 𝑛𝐷 −1 𝑀
]
2+2 𝜌 𝑛𝐷
=[
2 𝑛𝐷 −1
] 𝑉𝑚
(8)
2+2 𝑛𝐷
where nD is the refractive index, M is the molar mass, ρ is the density, and Vm is the molar volume. 7
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𝑉𝑓 = 𝑉𝑚 − 𝑅𝑚
(9)
where Rm is the molar refraction and Vm is the molar volume. The reported values of the molar volume clearly demonstrated that the increase of anion alkyl chain increased the molar volume of the ILs. The result displayed that longer alkyl chain based ILs produce a large molar volume due to the small interaction between the counter anions. In contrast, the lower values of the molar volume is due to anion small size which leads to stronger
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interaction with counter anions [17, 18]. The molecular volumes (V) for synthesised ILs were
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calculated using the Eq. 5 and their values are listed in Table 6. It was found that the V increases
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with the increase of temperature [19].
The standard entropy (So) values for the present ILs were estimated using Eq. 6 and their resulted data are reported in Table 3. The anion of IL having longer alkyl chain length shows higher values
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of So compared to shorter chain anions. The possible reason is the large size of anion structural geometry and there is a possibility of steric hindrance which eventually cause higher values of
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standard entropy [20]. The lattice energies (Upot) values estimated by using Eq. 7 are presented in Table 6. The values of So decrease with the increase of carbon chain length of anion from C1 to C6,
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this decrease is due to decrease in packing efficiency with the increase of alkyl chain length. The So mainly depend on the electrostatic interaction which is inversely related to the anion volume
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[4]. These values comparatively lower to other imidazolium and ammonium based ILs reported in
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the literature [16, 21].
The values of electronic polarizability (Rm) can be determined from the value of refractive index
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using Lorenz-Lorentz equation 8 [22]. Rm shows the electronic polarizability of one mole of substance [23]. The values of Rm for ILs estimated by using Eq. 8 are given in Table 3. The Rm
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values were estimated at several temperatures and the anion with high molecular weight resulted larger values. Similarly as the temperature increases the Rm values also increases [18]. The free volume is one of the important parameter and this is helpful to understand the ILs transport phenomena. For the calculation using the equation no (9) and their value are reported in Table 3. As such the values of higher anion size are larger compared to lower anion size. These values were studied at several temperatures and increases with increase in temperature. The lower values might be associated with the higher van der Waals forces between the ions [24].
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Thermal expansion coefficient Thermal expansion coefficient (α) for synthesised ILs were calculated from their respective density values using the below Eq. 10.
p
A1 1 . T p A0 A1T
(10)
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The values of thermal expansion coefficient based on eq. 10 are listed in Table 4. It is found that
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thermal expansion coefficients values gradually increasing with the increase in temperature
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because the intermolecular forces decrease as well as with anion alkyl chain. It was earlier reported by Sharma et al [4] that the thermal expansion coefficient increases with the elongation of anion
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alkyl chain substitutions. In the case of carboxylate anions it increases from acetate to propanoate anion with 4% while the butanoate, propanoate and hexanoate is very close to acetate the possible
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difference is less than 1%. Hence, the thermal expansion coefficient values of the studied set agreed well with the data reported in the literature [16]. Moreover, the thermal expansion
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coefficients of the ILs are smaller than those for the traditional organic solvents.
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Viscosity
The dynamic viscosity experimental values were measured at different temperature is presented in
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Table 5 (Fitting parameters has been provided in Table S.2). The trend in Figure 2 shows that as the temperature increases the viscosity values decreases as reported by others also [2, 25]. The
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viscosity of ILs depends on various factors among which the cohesive forces and size of molecule play an important role. In this study, [C2CNIM][Ace] is more viscose then [C2CNIM][For] which
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is attributed to more cohesive forces as well as bigger size of acetate anion. However, if increase the size of anion from acetate to propionate the viscosity dropped which related to decrease in basicity (cohesive forces) of propionate anion. Beyond to propionate anion, the viscosity again increases which might be attributed to the size of anions. The general expectation is that, when the chain length increases the overall strong interaction contribution decreases and the weaker dispersion forces contribution increases. With the increase of alkyl chain length, the van dar Waals interaction increase between the ions as well as increases the bulkiness which contributes in resistance to flow and therefor increasing the viscosity.
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Refractive index Refractive index (n) is an important physical property used for the sample purity determination, electronic polarizability and solute concentration in solution [18]. The values of refractive index measured for synthesized PILs are investigated at temperature range of 293.15 to 333.15 K. The values of refractive index are listed in Table 6. The trend shows that as the temperature increases the refractive index values are decreases as expected (Figure 3). The tabulated data show that IL
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[C2CNIM][Ace] has the highest value 1.4666 at 333.15 K while the IL [C2CNIM][Hex] has the
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lowest value at 333.15 K. The synthesized ILs refractive index decreasing order is [C2CNIM][Ace]
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> [C2CNIM][For] > [C2CNIM][Pro] > [C2CNIM][But] > [C2CNIM][Hex]. Therefore, the decreasing order shows that the refractive index slightly depends upon the anionic volume. These
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refractive index values are in good agreement with the other nitrile factionalized imidazolium ILs [23, 26] and similarly also in the near range to our other group members reported ILs in the
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literature [20, 27]. The present ILs refractive index standard deviations (SDs) and fitting
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parameters values are tabulated in Table S.1.
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Thermogravimetric Analysis
The thermogravimetric analysis (TGA) curves for ILs are graphically shown in Figure 3. The thermal degradation temperatures obtained from TGA and are presented in Table 7. These ILs
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onset data shows medium stability towards heating but the complete decomposition temperature shows high thermal stability compared to similar anions with pyrrolidinium based ILs [15] and is
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also in the near range to other ILs reported in the literature [16]. All the ILs decomposition temperature seems very close to each other except the IL [C2CNIM][Hex] which shows lowest
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decomposition temperature. However, previous studies reported that IL with acetate anion is less stable than other anion based PILs which might be related to its easy degradation [18]. The PILs stability also depends on the proton transfer effectiveness. Hence the lower decomposition temperature could be attributed to N–H weak bonding due to less efficient proton transfer [15]. Many researchers reported the unstability of PILs compared to APILs due to the N–H bonding in their cations structure [28]. These ILs measured thermal stability is in reasonable range and it is assumed that the ILs decomposition temperature mostly depends upon the cation and anion structure.
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Effective concentration (EC50) of the synthesized ILs The antimicrobial activities of the PILs set were investigated using ELISA plate reader against three bacterial species to examine their indirect ecotoxicity impact. The EC50 values of the studied PILs are summarized in Table 8 and Figure 5. The reported EC50 values for the PILs showed comparable antimicrobial activities to imidazolium based IL which carried alkyl chain length ranged from 2-6 carbon atoms within the cation structure[29]. Based on the studied anion, the
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antimicrobial activities were increased in the following order [Ace] < [Pro] < [But] < [For] <
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[Hex]. Apart from formate anion, the reported EC50 values clearly demonstrated an increasing
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activity trend with increasing the anion alkyl chain length. [Hex] IL possesses the highest antimicrobial inhibition effect due to the presence of 6 carbon atom within its anion structure.
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Acetate based IL where the least active one among the PILs. It was expected that formate based IL will possess the lowest antimicrobial activity against the bacterial species due to the presence
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of a single carbon atom within its anion structure. Surprisingly, the antimicrobial activity established with formate anion was comparable to the one for the most active anion [Hex]. The same finding was early reported by Peric et al., [13]. Formate based IL was found to be more toxic
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than other IL paired same cation but longer alkyl chain such as [But] anion against Vibrio fischeri.
Conclusions
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Five nitriles functionalized PILs were synthesized and characterized and their structure have been successfully confirmed. A change in temperature has been identified to affect the physiochemical
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properties of the ILs. Moreover, alkyl chain length of anion considerably affects the thermophysical properties. The density, refractive index, and viscosity decrease with the increase
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of attached alkyl substitutions, exception to acetate based ILs for values of viscosity and refractive index. The various volumetric properties were determined and the intermolecular interactions between the molecules of have been discussed with the help of these properties. All the ILs decomposition temperature seems very close to each other except the IL [C2CNIM][Hex] which shows lower decomposition temperature. Based on the studied anions, the antimicrobial activities were increased in the following order [Ace] < [Pro] < [But] < [For] < [Hex]. Formate based IL was found to be more toxic than other IL paired same cation but longer alkyl chain within the anion structures against the studied microorganisms.
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Acknowledgment The authors are thankful to Ministry of Higher Education (MOHE) for funding the research work under the YUTP project (0153AA-E76) and Centre of Research in Ionic Liquids (CORIL). References T. L. Greaves, K. Ha, B. W. Muir, S. C. Howard, A. Weerawardena, N. Kirby, et al., "Protic ionic liquids (PILs) nanostructure and physicochemical properties: development of highthroughput methodology for PIL creation and property screens," Physical Chemistry Chemical Physics, vol. 17, pp. 2357-2365, 2015.
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F. Mazille, Z. Fei, D. Kuang, D. Zhao, S. M. Zakeeruddin, M. Grätzel, et al., "Influence of ionic liquids bearing functional groups in dye-sensitized solar cells," Inorganic chemistry, vol. 45, pp. 1585-1590, 2006.
[10]
J. Y. Kim, T. H. Kim, D. Y. Kim, N.-G. Park, and K.-D. Ahn, "Novel thixotropic gel electrolytes based on dicationic bis-imidazolium salts for quasi-solid-state dye-sensitized solar cells," Journal of Power sources, vol. 175, pp. 692-697, 2008.
[11]
A. E. Visser, R. P. Swatloski, W. M. Reichert, R. Mayton, S. Sheff, A. Wierzbicki, et al., "Task-specific ionic liquids incorporating novel cations for the coordination and extraction
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of Hg2+ and Cd2+: synthesis, characterization, and extraction studies," Environmental science & technology, vol. 36, pp. 2523-2529, 2002. M. I. A. Mutalib and O. B. Ghanem, "Ecotoxicity of Ionic Liquids Towards Vibrio fischeri: Experimental and QSAR Studies," in Progress and Developments in Ionic Liquids, ed: InTech, 2017.
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B. Peric, J. Sierra, E. Marti, R. Cruanas, M. A. Garau, J. Arning, et al., "(Eco)toxicity and biodegradability of selected protic and aprotic ionic liquids," J Hazard Mater, vol. 261, pp. 99-105, Oct 15 2013.
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A. S. Khan, Z. Man, M. A. Bustam, G. Gonfa, F. K. Chong, Z. Ullah, et al., "Effect of Structural Variations on the Thermophysical Properties of Protic Ionic Liquids: Insights from Experimental and Computational Studies," Journal of Chemical & Engineering Data, 2017.
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S. Panda and R. L. Gardas, "Measurement and correlation for the thermophysical properties of novel pyrrolidonium ionic liquids: Effect of temperature and alkyl chain length on anion," Fluid Phase Equilibria, vol. 386, pp. 65-74, 2015.
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B. K. Chennuri and R. L. Gardas, "Measurement and correlation for the thermophysical properties of hydroxyethyl ammonium based protic ionic liquids: Effect of temperature and alkyl chain length on anion," Fluid Phase Equilibria, vol. 427, pp. 282-290, 11/15/ 2016.
[17]
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A. S. Khan, Z. Man, A. Arvina, M. A. Bustam, A. Nasrullah, Z. Ullah, et al., "Dicationic imidazolium based ionic liquids: Synthesis and properties," Journal of Molecular Liquids, vol. 227, pp. 98-105, 2017.
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B. a. González, E. Gómez, A. n. Domínguez, M. Vilas, and E. Tojo, "Physicochemical characterization of new sulfate ionic liquids," Journal of Chemical & Engineering Data, vol. 56, pp. 14-20, 2010.
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[22]
A. K. Ziyada and C. D. Wilfred, "Physical properties of ionic liquids consisting of 1-butyl3-propanenitrile-and 1-decyl-3-propanenitrile imidazolium-based cations: Temperature dependence and influence of the anion," Journal of Chemical & Engineering Data, vol. 59, pp. 1232-1239, 2014.
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Table 1. Name, abbreviation and chemical structure of the synthesized ILs. Abbreviation
Purity (%)
O
[C2CNIM][For]
H H N
C O
[C2CNIM][Ace]
H3C
400
O
C
N
99.5
99.1 O
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1-propanenitrileimidazolium acetate
Water content (ppm)
Anion
T
1-propanenitrileimidazolium formate
Cation
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Name
450
C 2H5
[C2CNIM][But]
AN
C N
[C2CNIM][Hex]
C3H7
PT CE AC
15
C
420
98.7
480
98.3
390
97.6
O
O C
O
O
C5H11
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1-propanenitrileimidazolium hexanoate
[C2CNIM][Pro]
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1-propanenitrileimidazolium butanoate
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O
1-propanenitrileimidazolium propionate
C
O
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Table 2. Experimental values of density () of the PILs from (293.15-363.15 K) at atmospheric pressure. /(g.cm-3) T/K [C2CNIM] [C2CNIM] [C2CNIM] [Pro]
293.15
1.2156
1.1277
1.1028
1.0766
1.0409
303.15
1.2071
1.1205
1.0938
1.0686
1.0331
313.15
1.1987
1.1130
1.0856
1.0607
1.0253
323.15
1.1903
1.1052
1.0777
1.0528
1.0176
333.15
1.1820
1.0977
1.0704
1.0447
1.0097
343.15
1.1737
1.0898
1.0624
1.0362
1.0019
353.15
1.1636
1.0820
1.0544
1.0290
0.9941
363.15
1.1547
1.0732
1.0462
1.0219
0.9863
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Standard uncertainty values are u(ρ) = 0.001 g·cm−3 u(T) = 0.01 K, and u(p) = 0.01 bar.
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a
T
[Ace][14]
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[C2CNIM][But] [C2CNIM][Hex]
[For]
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176.82 178.27 179.62 180.94 182.17 183.54 184.93 186.38
0.29 0.29 0.29 0.30 0.30 0.30 0.30 0.30
293.15 303.15 313.15 323.15 333.15 343.15 353.15
194.12 195.58 197.03 198.51 200.05 201.69 203.10
0.32 0.32 0.32 0.32 0.33 0.33 0.33
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CE
107.91 107.88 107.85 107.83 107.80 107.77 107.74 107.71
45.66 45.69 45.70 45.74 45.74
114.91 115.92 116.99 118.11 119.23
107.53 107.50 107.47 107.44 107.42 107.39 107.37 107.34
49.72 49.82 49.86 49.90 49.90
127.10 128.45 129.75 131.04 132.26
107.20 107.17 107.15 107.12 107.10 107.07 107.05
54.31 54.35 54.40 54.44 54.48
139.81 141.22 142.63 144.07 145.57
17
T
293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
98.36 99.30 100.24 101.22 102.19
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0.26 0.26 0.27 0.27 0.27 0.27 0.27 0.28
39.01 39.04 39.07 39.07 39.09
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160.58 161.61 162.70 163.85 164.97 166.16 167.36 168.73
108.60 108.57 108.54 108.50 108.47 108.44 108.40 108.36
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293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
313.86 315.86 317.87 319.91 321.94 324.01 326.57 328.86 [C2CNIM][Ace] 362.00 364.14 366.39 368.77 371.09 373.56 376.04 378.88 [C2CNIM][Pro] 395.62 398.64 401.42 404.15 406.71 409.55 412.43 415.43 [C2CNIM][But] 431.46 434.47 437.48 440.55 443.73 447.13 450.05
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0.22 0.22 0.23 0.23 0.23 0.23 0.23 0.24
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137.38 138.34 139.31 140.30 141.28 142.28 143.52 144.62
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293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
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Table 3. Values of molar volumes (Vm), molecular volume (V), standard entropy (So), crystal energy (UPOT), molar refraction (RM) and free volume (Vf) calculated for PILs at selected temperatures. T/K Vm V So UPOT RM Vf 3 -1 3 -1 (cm .mol ) (nm ) (cm3.mol-1) (cm3.mol-1) (J.K .mol-1) (kJ.mol-1) [C2CNIM][For]
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293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
227.97 229.69 231.43 233.19 235.02 236.83 238.70 240.59
0.37 0.38 0.38 0.38 0.39 0.39 0.39 0.39
452.94 107.029 [C2CNIM][Hex] 501.54 106.69 505.11 106.67 508.70 106.65 512.35 106.63 516.13 106.60 519.88 106.58 523.76 106.56 527.67 106.54
63.58 63.64 63.69 63.75 63.78
T
0.339
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204.50
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363.15
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164.39 166.05 167.73 169.44 171.23
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Table 4. Thermal expansion coefficient for PILs as a function of temperature.
104/(K-1) [C2CNIM] [Ace]
[C2CNIM] [Pro]
[C2CNIM] [But]
[C2CNIM] [Hex]
293.15
7.12
6.88
7.24
7.32
7.49
303.15
7.17
6.93
7.29
7.37
7.55
313.15
7.22
6.98
7.34
7.43
7.61
323.15
7.27
7.03
7.40
7.49
7.67
333.15
7.33
7.08
7.45
7.54
7.72
343.15
7.38
7.13
7.51
7.60
7.79
353.15
7.44
7.18
7.57
7.66
7.85
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T
[C2CNIM] [For]
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T/K
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363.15 7.49 7.23 7.62 7.72 7.91 -1 Standard uncertainties are u() = 0.001 kK , µ(p) = 0.01 bar and u(T) = ±0.01.
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Table 5. Experimental dynamic viscosities for PILs at temperature in the range of 293.15 363.15 K and at atmospheric pressure a.
/(m.Pa)
T/K [C2CNIM][Ace] 108.22
[C2CNIM][Pro] 84.899
[C2CNIM][But] 115.293
[C2CNIM][Hex] 125.936
303.15
52.83
55.284
48.693
65.022
74.426
313.15
33.657
31.575
30.319
42.142
48.041
323.15
22.651
19.789
18.974
333.15
14.991
13.323
13.099
343.15
10.466
9.483
9.061
353.15
7.478
7.118
6.754
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31.091
18.562
21.632
12.78
14.743
9.512
10.698
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27.557
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5.425 5.294 5.091 7.404 7.595 Standard uncertainties are ur() = 0.0032, u(T) = 0.01 K and u(p) = 0.01 bar.
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363.15
T
293.15
[C2CNIM][For] 90.321
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Table 6. Experimental values of refractive index (nD) of the PILs from (293.15-333.15 K) at atmospheric pressure nD T/K [C2CNIM][For]
[C2CNIM][Ace] [C2CNIM][Pro]
[C2CNIM][But]
[C2CNIM][Hex]
1.4798
1.4853
1.4743
1.4715
1.4698
298.15
1.4780
1.4836
1.4726
1.4697
1.4680
303.15
1.4763
1.4819
1.4709
1.4679
308.15
1.4747
1.4802
1.4691
1.4661
1.4644
313.15
1.4729
1.4785
1.4673
318.15
1.4711
1.4768
1.4655
323.15
1.4691
1.4750
328.15
1.4674
1.47358
333.15
1.4655
1.47188
1.4662
1.4643
1.4626
1.4625
1.4608
1.4637
1.4607
1.459
1.4619
1.4589
1.4571
1.4570
1.4552
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T
293.15
1.4601
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Standard uncertainty values are u(nD) = 3 ×10-3 and u(T) = 0.05 K, u(p)=0.01 bar).
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Table 7. Thermal decomposition properties of PILs. Tmax / K
[C2CNIM][For]
214
512.95
[C2CNIM][Ace]
202
516.91
[C2CNIM][Pro]
207
510.53
[C2CNIM][But]
205.46
[C2CNIM][Hex]
198.75
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T
Tonse/ K
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ILs
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Standard uncertainty is u(T) = 2 °C
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508.89 485.70
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Table 8. Antimicrobial activity of PILs expressed as 50% effective concentration in mmol. L-1 Escherichia coli
Staphylococcus aureus
[C2CNIM][For]
22.9
14.5
12.14
[C2CNIM][Ace]
81.26
72.39
56.24
[C2CNIM][Pro]
43.07
60
29.97
[C2CNIM][But]
34.94
28.27
[C2CNIM][Hex]
13.86
14.02
T
Aeromonas hydrophila
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23.08
AC
CE
PT
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AN
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IL
23
11.33
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1.25 [C2CNIM][For] [C2CNIM][Ace] [C2CNIM][Pro]
1.20
[C2CNIM][But] [C2CNIM][Hex]
T IP
1.10
1.05
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(g/cm3)
1.15
0.95 290
310
320
330
AN
300
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1.00
340
350
360
T (K)
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Figure 1. Effect of temperature and anions on density of the PILs.
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[C2CNIM][For] [C2CNIM][Ace]
120
[C2CNIM][Pro] [C2CNIM][But] [C2CNIM][Hex]
T
80 60
IP
(mPa.s)
100
CR
40
0 290
300
310
320
330
340
AN
T (K)
US
20
350
360
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Figure 2. Effect of temperature and anions on the viscosity of PILs.
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1.490 [C2CNIM][For] [C2CNIM][Ace]
1.485
[C2CNIM][Pro] [C2CNIM][But] [C2CNIM][Hex]
1.480
T
1.470
IP
n
1.475
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1.465 1.460
1.450 290
295
300
305
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1.455
310
315
320
325
330
335
AN
T (K)
AC
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Figure 3. Effect of temperature and anions on refractive index of the PILs.
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100 [C2CNIM][For] [C2CNIM][Ac] [C2CNIM][Pro]
80
[C2CNIM][But]
60
T
40
IP
% weight loss
[C2CNIM][Hex]
0 330
360
390
420
450
CR
20
480
510
540
570
600
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T (K)
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Figure 4. Thermal decomposition profile of the PILs.
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Figure 5. Influence of the anion alkyl chain length on the toxicity of studied PILs towards A. hydrophila, E.coli and S.aureus.
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Highlights
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New nitrile functionalized ionic liquids were synthesized and characterized. Effect of anion and temperature on physiochemical properties was evaluated. Ecotoxicity was evaluated for the prepared ionic liquids
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Amir Sada Khan, Asma Nasrullah, Zahoor Ullah, A.H. Bhat, Ouahid Ben Ghanem, Nawshad Muhammad, Mamoon Ur Rashid, Zakaria Man PII: DOI: Reference:
S0167-7322(17)33343-3 doi:10.1016/j.molliq.2017.10.141 MOLLIQ 8104
To appear in:
Journal of Molecular Liquids
Received date: Revised date: Accepted date:
25 July 2017 29 October 2017 30 October 2017
Please cite this article as: Amir Sada Khan, Asma Nasrullah, Zahoor Ullah, A.H. Bhat, Ouahid Ben Ghanem, Nawshad Muhammad, Mamoon Ur Rashid, Zakaria Man , Thermophysical properties and ecotoxicity of new nitrile functionalised protic ionic liquids. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/j.molliq.2017.10.141
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Thermophysical Properties and Ecotoxicity of New Nitrile Functionalised Protic Ionic Liquids Amir Sada Khana,b*, Asma Nasrullahc, Zahoor Ullahd, A.H bhatc, Ouahid Ben Ghanema, Nawshad Muhammade*, Mamoon Ur Rashidd, Zakaria Mana a
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Centre of Research in Ionic Liquids CORIL), Department of Chemical Engineering, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia. b Department of Chemistry, University of Science and Technology, Bannu 28100, Khyber Pakhtunkhwa, Pakistan. c Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS (UTP), 31750 Tronoh, Perak, Malaysia. d Department of Chemistry, The Balochistan University of IT, Engineering and Management Sciences (BUITEMS) , Takatu Campus, Quetta-87100, Pakistan e Interdisciplinary Research Centre in Biomedical Materials, COMSAT Institute of Information Technology, Lahore Pakistan.
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*Corresponding authors; [email protected], [email protected]
Abstract
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In this present research, five nitrile functionalised imidazolium based protic ionic liquids (PILs)
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by varying alkyl chain length of anions were synthesised. The synthesised ILs were characterized with nuclear magnetic resonance spectroscopy (NMR) and elemental analyser (CHNS). Various
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thermophysical such as refractive index, density, viscosity and thermal stability were measured over wide temperature range. From the density experimental data, different volumetric properties
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were estimated using well established empirical equations. Moreover, the effect of temperature and increase of alkyl substitutions attached to anion has been evaluated for the studied properties.
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The toxicity (EC50) of the synthesized ILs have been assessed against three human pathogenic bacteria i.e, Aeromonas hydrophila A97 (AH), Escherichia coli E149 (EC), and Staphylococcus aureus S244 (SA) in light to identify the influence of increasing alkyl substitution of the anion moiety on the overall toxicity of PILs.
Keywords: Nitrile functionality; protic ionic liquids; thermophysical properties; alkyl chain length; ecotoxicity
1
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Introduction Currently, ionic liquids (ILs) has introduced as greener solvents and has received special interest to be used as medium for different types of reaction. This new class of molten organic salt ILs are documented as designer/tailorable solvent due possible combination of large number of cations and anions. In general, the most important and commonly interesting properties such as density, viscosity, refractive index, surface tension, thermal stability, solvation polarity of ILs can be easily
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tuned by pairing appropriate anion and cation [1-3]. Recently, ILs are getting popularity and
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largely used for different applications such as catalysis, organic synthesis, pharmaceutical and
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biological applications, gas separation, membrane separation, crude oil treatment [3-5], etc. Among the various available ILs, Bronsted acidic ILs (BAILs) or protic acidic ILs (PAILs) are easy
US
to be synthesize by transfer of proton from Bronsted acid to Bronsted base by neutralization reaction. The
PILs are synthesised by simple equimolar reaction of acid and base, this is generally making the ILs simplest and cheapest to synthesise [6]. Currently, it has been investigated that the properties
AN
of ILs can be enhanced by incorporating functional groups either to cation or to anion or on both [7, 8]. Among various available functionalized ILs, the nitrile functional group are relatively a new
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class with distinct properties and potential application in various research areas [9-11].
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Furthermore, until now no literature available on the synthesis of ILs having nitrile functionalized imidazolium cation and carboxylate anion with various carbon chain length.
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It has been proposed that the elongation of the alkyl chain length attached to cation of ILs possess high increasing trend of toxicity compared to any other modification on the ILs structural
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features. The other structural elements such as anions, functional groups and the type of the cations were found to play a less important role in the domination of the behaviour of ILs toxicity [12].
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Recently, few studies have been performed the examine the impact of increasing the carbon chain length of the anion side on different species [13]. However, it seems to be crucial to examine the effect of increasing alkyl chain length of the anions side on the toxicity towards different organisms as the ecotoxicity data in literatures still lacked. The second aim of this present research work is to investigate the influence of increasing the carbon chain length/alkyl chain length of anion on the ILs toxicity. This study aims to synthesize and characterize new ILs containing 1-proponitrile side chain attached with cation and carboxylate anions of various carbon chain length. The effect of increasing alkyl chain length from C1-C6 on the physiochemical properties of synthesized PILs i.e. 2
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1-propanenitrileimidazolium propanenitrileimidazolium
formate, propionate,
1-propanenitrileimidazolium 1-propanenitrileimidazolium
acetate,
butanoate
and
11-
propanenitrileimidazolium hexanoate were investigated. Moreover, toxicity of the prepared ILs was evaluated with respect of carboxylate anions containing alkyl side chain with different length for its safer application in various fields especially in biological environment.
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Experimental
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Materials
All the chemical used in present research work were of analytical grade and used as such as received. Acrylonitrile was purchased from sigma-Aldrich. Formic acid, acetic acid, propanoic
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acid, butanoic acid and hexanoic acid were purchased from Merck. The solvents i.e. diethyl ether
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and ethyl acetate were purchased from Fisher Scientific.
Synthesis and characterization
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PILs were prepared according to the established procedure which was slightly modified [14].
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These ILs were synthesized in two step processes; in first step, imidazole (0.2 mol) solution was made in methanol under inert atmosphere in three necks round bottom flask which was followed
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by dropwise addition of 0.23 mol of acrylonitrile. The reaction mixture was continuously refluxed in inert atmosphere for 24 h at 55oC. Vacuum rotavap was run at 70 oC to remove the unreacted
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materials. In the subsequent step, 1-propanenitrileimidazolium was stirred in acetonitrile and formic acid, propanoic acid, butanoic acid and hexanoic acid was individually added dropwise to prepare the desired IL. The reaction mixture was continuously refluxed in nitrogen atmosphere for
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24 h at 55oC. The synthesized PILs were repeatedly washed with diethyl ether and ethyl acetate. The synthesized PILs were placed in vacuum oven at 60oC for 24h and then in vacuum line overnight. The physicochemical properties of acetate base IL already reported in our published research work were used in the present study [14]. For structure confirmation, A Bruker Avance 500MHz NMR was used and elucidated the 1H NMR and
13
C NMR spectra of the studied ILs. CHNS-932 (LECO instruments) was used for CHNS
analysis of the samples. Karl Fisher Titration (Mettler Toledo DL39) was used for water content
3
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in ppm of the samples. The purity of samples was assessed from NMR (CH2 of propionitrile was considered reference and impurity was measured relatively in percentage) and CHNS values.
Physical characterization Various physiochemical properties such as refractive index, density, viscosity and thermal stability for synthesized ILs were studied in wide range of temperature. ATAGO digital refractometer (RX-
T
5000α) with accuracy of ±4.5×10-5 was used for measurement of refractive index of PILs in the
IP
temperature ranging from 293.15 to 323.15 K with five-degree intervals. Densities and viscosity
CR
of prepared ILs were measured using Anton-Parr viscometer (model SVM3000) at atmospheric pressure at temperature varying from 293.15 K to 373.15 K. Before measurement of density and viscosity of ILs, the instrument was calibrated using ultrapure Millipore quality water. The
US
measurement was performed in triplicate to obtain the average value. The thermal stability of synthesized PILs were measured using Perkin-Elmer TGA (pyris-1, V-3.81) in inert atmosphere
AN
at temperature range from 323-373 K with heating rate of 10 K/min. Differential scanning calorimetry (Perkin-Elmer, pyris-1) was used to determine the glass
M
transition temperature and melting point of ILs. The ILs sample was weighted in aluminium pan and subjected to thermo-cycles. First the sample of IL was heated with 10oC/min from 0oC to
PT
and then reheated until 110oC.
ED
110oC in inert atmosphere. After this the sample temperature was decrease from 110oC to -150oC
Antimicrobial activity test
CE
The antimicrobial activity of the studied ILs were established by evaluating their 50% effective concentrations (EC50) using the standard micro-broth dilution test against three human pathogens
AC
bacteria. obtained from the Institute of Medical Research (IMR), Kuala Lumpur, Malaysia. These strains are Aeromonas hydrophila A97 (AH), Escherichia coli E149 (EC), and Staphylococcus aureus S244 (SA). Each bacterial strain was cultured in Muller-Hinton Broth (MHB) in overnight to achieve optimum growth. Prior to the preparation of 96 well-plate, standard stock solution of each strain was prepared to be equivalent to 0.5 McFarland standard solution. The 96 well-plate was then prepared as follow; 100 µl from pure MHB media was injected in the second to the last rows. Followed by injection of 100 µl of IL solution to the first two horizontal rows. Then, two fold dilution was conducted including the six middle rows, whereas the last one remains untreated to be a reference for the optimal bacterial growth. Finally, 100 µl of the standard stock solution of 4
ACCEPTED MANUSCRIPT 5
the strain were added to each well. The 96 well-plate was then kept in the incubator for 24 h at 37 °C. The plates were then placed in the micro plate reader [MultiskanTM FC Microplate Photometer (Type.357)] to determine the EC50 values at 620 nm. Results and Discussion In this research work, five imidazolium based nitrile functionalised ILs with carboxylate anions
T
containing alkyl side chain of different length. The synthesised ILs information’s were tabulated
IP
in Table 1. NMR used for their structure elucidation and the data reported as below while the
CR
spectrum information’s are reported in supporting materials (Figure S1a,b-S5a,b)
1-propanenitrileimidazolium formate
US
Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 2.88-2.19 (t), 4.32-4.34 (t), 7.26 (s), 7.35 (s), 8.28 (s), 8.63 (s)
AN
13
C NMR (500 MHz, CH3OH): 19.02, 44.37, 117.82, 120.24, 121.65, 134.97, 168.39
M
CHNS elemental analysis: Calculated (%): C: 50.24, H: 5.38, N: 25.12, O: 19.14. Found (%): C: 50.29, H: 5.39, N: 25.10, O: 19.16 Elemental analysis standard uncertainty μ(E) =
ED
0.045%
1-propanenitrileimidazolium acetate
13
PT
Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 1.66 (s), 2.84-2.86 (t), 4.24-4.26 (t), 7.11 (s), 7.24 (s), 8.30 (s)
CE
C NMR (500 MHz, CH3OH): 19.26, 32.01, 43.66, 118.14, 121.09, 122.68, 135.82, 180.35
CHNS elemental analysis: Calculated (%): C: 52.98, H: 6.07, N: 23.18, O: 17.66.
0.005%
AC
Found (%): C: 52.96, H: 6.09, N: 23.17, O: 17.68. Elemental analysis standard uncertainty μ(E) =
1-propanenitrileimidazolium propionate Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.97-1.004 (t), 2.19-2.23 (m), 301-3.04 (t), 4.25-4.28 (t), 6.95 (s), 7.25 (s), 7.74 (s) 13
C NMR (500 MHz, CH3OH): 9.53, 19.97, 27.44, 42.18, 118.91, 119.78, 128.88, 137.815, 175.88.
CHNS elemental analysis: Calculated (%): C: 55.32, H: 6.65, N: 21.51, O: 16.39. 5
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Found (%): C: 55.30, H: 6.67, N: 21.33, O: 16.41. Elemental analysis standard uncertainty μ(E) = 0.175%
1-propanenitrileimidazolium butanoate Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.63-0.66 (t), 1.29-1.32 (t), 1.34-1.96 (m), 2.91-2.94 (t), 4.33-4.36 (t), 7.24 (s), 7.35 (s), 8.51 (s)
T
13
IP
C NMR (500 MHz, CH3OH): 13.14, 19.01, 19.20, 38.76, 44.02, 117.96, 121.38, 121.68, 135.480, 182.67
CR
CHNS elemental analysis: Calculated (%): C: 57.35, H: 7.16, N: 20.07, O: 15.29. Found (%): C: 57.37, H: 7.17, N: 20.05, S: 15.31. Elemental analysis standard uncertainty μ(E) =
AN
1-propanenitrileimidazolium hexanoate
US
0.015%
M
Spectroscopic data: 1H NMR (500 MHz, CH3OH): δ = 0.59-0.61 (t), 1.00-1.04 (m), 1.95-1.98 (t), 2.86-2.88 (t), 4.26-4.29 (t), 7.12 (s), 7.25 (s), 8.27 (s) 13
ED
C NMR (500 MHz, CH3OH): 13.34, 19.34, 21.877, 25.134, 31.05, 36.29, 43.55, 118.080, 120.94, 123.32, 136.02, 181.39
PT
CHNS elemental analysis: Calculated (%): C: 60.68, H: 8.01, N: 17.69, O: 13.48.
Density
AC
0.005%
CE
Found (%): C: 60.67, H: 8.05, N: 17.66, O: 13.50. Elemental analysis standard uncertainty μ(E) =
The values of densities measured for synthesised are reported in Table 2 (Fitting parameters has been provided in Table S.1). These calculated values are fitted in Figure 1. The values of densities for all ILs show decreasing trend with the temperature increase as expected. So the decreasing order of the present ILs are [C2CNIM][Hex] < [C2CNIM][But] < [C2CNIM][Pro] < [C2CNIM][Ace] < [C2CNIM][For]. It is found the values of density decrease linearly with the increase in alkyl chain length of anion. The possible reason is of the anions molecular geometry. Another reason of the long alkyl chain on anion might be due to the increment of non-polar region 6
ACCEPTED MANUSCRIPT 7
because when non-polar region increases then it takes more space and lower the overall density. Similar observations were found in the literature [4, 15, 16]. All these ILs with temperature shows a linear dependency. For density, the values of standard deviation (SD) and correlation coefficient (R2) are listed in Table 3. Using the following equation to calculate the standard deviation values
T
(𝑍𝑒𝑥𝑝 −𝑍𝑐𝑎𝑙 )2
𝑆𝐷 = √
(1)
IP
𝑛𝐷𝐴𝑇
CR
Zexp and Zcal are the experimental determined values and calculated data values and nDAT is a number of experimental points. Temperature dependence equation for density:
US
𝜌 = 𝐴0 + 𝐴1 𝑇 where 𝜕𝑙𝑛𝜌
AN
𝛼
𝐴1 = 𝐾 = − (𝜕(𝑇−298.15))
Assessment of Volumetric Properties
(3)
M
𝑝
(2)
ED
The present ILs molar volumes (Vm), molecular volumes (V), standard entropy (So), lattice energy (UPOT), electronic polarizability (Rm), and free volume (Vf) are calculated from the following 𝑀 𝜌
(4)
CE
𝑉𝑚 =
PT
equations and the values are tabulated in Table 3.
where, Vm is molar volume in cm3.mol-1, M is the molecular weight in g.mol-1 and ρ is the density
𝑉 =
𝑉𝑚 𝑁𝐴
AC
in g.cm-3.
(5)
where, NA (Avogadro’s constant) = 6.0224 × 1023 molecules per mol. 𝑆 o (303.15)/𝐽. 𝐾. 𝑚𝑜𝑙 −1 = 1246.5(𝑉𝑚 /𝑛𝑚3 ) + 29.5
(6)
𝑈𝑃𝑂𝑇 /𝑘𝐽/𝑚𝑜𝑙 −1 = 1981.2 (𝜌/𝑀)1/3 + 103.8
(7)
Where, 𝜌 and M are the density (g.cm-3) and molecular mas (g.mol-1), respectively.
𝑅𝑚 = [
2 𝑛𝐷 −1 𝑀
]
2+2 𝜌 𝑛𝐷
=[
2 𝑛𝐷 −1
] 𝑉𝑚
(8)
2+2 𝑛𝐷
where nD is the refractive index, M is the molar mass, ρ is the density, and Vm is the molar volume. 7
ACCEPTED MANUSCRIPT 8
𝑉𝑓 = 𝑉𝑚 − 𝑅𝑚
(9)
where Rm is the molar refraction and Vm is the molar volume. The reported values of the molar volume clearly demonstrated that the increase of anion alkyl chain increased the molar volume of the ILs. The result displayed that longer alkyl chain based ILs produce a large molar volume due to the small interaction between the counter anions. In contrast, the lower values of the molar volume is due to anion small size which leads to stronger
T
interaction with counter anions [17, 18]. The molecular volumes (V) for synthesised ILs were
IP
calculated using the Eq. 5 and their values are listed in Table 6. It was found that the V increases
CR
with the increase of temperature [19].
The standard entropy (So) values for the present ILs were estimated using Eq. 6 and their resulted data are reported in Table 3. The anion of IL having longer alkyl chain length shows higher values
US
of So compared to shorter chain anions. The possible reason is the large size of anion structural geometry and there is a possibility of steric hindrance which eventually cause higher values of
AN
standard entropy [20]. The lattice energies (Upot) values estimated by using Eq. 7 are presented in Table 6. The values of So decrease with the increase of carbon chain length of anion from C1 to C6,
M
this decrease is due to decrease in packing efficiency with the increase of alkyl chain length. The So mainly depend on the electrostatic interaction which is inversely related to the anion volume
ED
[4]. These values comparatively lower to other imidazolium and ammonium based ILs reported in
PT
the literature [16, 21].
The values of electronic polarizability (Rm) can be determined from the value of refractive index
CE
using Lorenz-Lorentz equation 8 [22]. Rm shows the electronic polarizability of one mole of substance [23]. The values of Rm for ILs estimated by using Eq. 8 are given in Table 3. The Rm
AC
values were estimated at several temperatures and the anion with high molecular weight resulted larger values. Similarly as the temperature increases the Rm values also increases [18]. The free volume is one of the important parameter and this is helpful to understand the ILs transport phenomena. For the calculation using the equation no (9) and their value are reported in Table 3. As such the values of higher anion size are larger compared to lower anion size. These values were studied at several temperatures and increases with increase in temperature. The lower values might be associated with the higher van der Waals forces between the ions [24].
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Thermal expansion coefficient Thermal expansion coefficient (α) for synthesised ILs were calculated from their respective density values using the below Eq. 10.
p
A1 1 . T p A0 A1T
(10)
T
The values of thermal expansion coefficient based on eq. 10 are listed in Table 4. It is found that
IP
thermal expansion coefficients values gradually increasing with the increase in temperature
CR
because the intermolecular forces decrease as well as with anion alkyl chain. It was earlier reported by Sharma et al [4] that the thermal expansion coefficient increases with the elongation of anion
US
alkyl chain substitutions. In the case of carboxylate anions it increases from acetate to propanoate anion with 4% while the butanoate, propanoate and hexanoate is very close to acetate the possible
AN
difference is less than 1%. Hence, the thermal expansion coefficient values of the studied set agreed well with the data reported in the literature [16]. Moreover, the thermal expansion
M
coefficients of the ILs are smaller than those for the traditional organic solvents.
ED
Viscosity
The dynamic viscosity experimental values were measured at different temperature is presented in
PT
Table 5 (Fitting parameters has been provided in Table S.2). The trend in Figure 2 shows that as the temperature increases the viscosity values decreases as reported by others also [2, 25]. The
CE
viscosity of ILs depends on various factors among which the cohesive forces and size of molecule play an important role. In this study, [C2CNIM][Ace] is more viscose then [C2CNIM][For] which
AC
is attributed to more cohesive forces as well as bigger size of acetate anion. However, if increase the size of anion from acetate to propionate the viscosity dropped which related to decrease in basicity (cohesive forces) of propionate anion. Beyond to propionate anion, the viscosity again increases which might be attributed to the size of anions. The general expectation is that, when the chain length increases the overall strong interaction contribution decreases and the weaker dispersion forces contribution increases. With the increase of alkyl chain length, the van dar Waals interaction increase between the ions as well as increases the bulkiness which contributes in resistance to flow and therefor increasing the viscosity.
9
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Refractive index Refractive index (n) is an important physical property used for the sample purity determination, electronic polarizability and solute concentration in solution [18]. The values of refractive index measured for synthesized PILs are investigated at temperature range of 293.15 to 333.15 K. The values of refractive index are listed in Table 6. The trend shows that as the temperature increases the refractive index values are decreases as expected (Figure 3). The tabulated data show that IL
T
[C2CNIM][Ace] has the highest value 1.4666 at 333.15 K while the IL [C2CNIM][Hex] has the
IP
lowest value at 333.15 K. The synthesized ILs refractive index decreasing order is [C2CNIM][Ace]
CR
> [C2CNIM][For] > [C2CNIM][Pro] > [C2CNIM][But] > [C2CNIM][Hex]. Therefore, the decreasing order shows that the refractive index slightly depends upon the anionic volume. These
US
refractive index values are in good agreement with the other nitrile factionalized imidazolium ILs [23, 26] and similarly also in the near range to our other group members reported ILs in the
AN
literature [20, 27]. The present ILs refractive index standard deviations (SDs) and fitting
M
parameters values are tabulated in Table S.1.
ED
Thermogravimetric Analysis
The thermogravimetric analysis (TGA) curves for ILs are graphically shown in Figure 3. The thermal degradation temperatures obtained from TGA and are presented in Table 7. These ILs
PT
onset data shows medium stability towards heating but the complete decomposition temperature shows high thermal stability compared to similar anions with pyrrolidinium based ILs [15] and is
CE
also in the near range to other ILs reported in the literature [16]. All the ILs decomposition temperature seems very close to each other except the IL [C2CNIM][Hex] which shows lowest
AC
decomposition temperature. However, previous studies reported that IL with acetate anion is less stable than other anion based PILs which might be related to its easy degradation [18]. The PILs stability also depends on the proton transfer effectiveness. Hence the lower decomposition temperature could be attributed to N–H weak bonding due to less efficient proton transfer [15]. Many researchers reported the unstability of PILs compared to APILs due to the N–H bonding in their cations structure [28]. These ILs measured thermal stability is in reasonable range and it is assumed that the ILs decomposition temperature mostly depends upon the cation and anion structure.
10
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Effective concentration (EC50) of the synthesized ILs The antimicrobial activities of the PILs set were investigated using ELISA plate reader against three bacterial species to examine their indirect ecotoxicity impact. The EC50 values of the studied PILs are summarized in Table 8 and Figure 5. The reported EC50 values for the PILs showed comparable antimicrobial activities to imidazolium based IL which carried alkyl chain length ranged from 2-6 carbon atoms within the cation structure[29]. Based on the studied anion, the
T
antimicrobial activities were increased in the following order [Ace] < [Pro] < [But] < [For] <
IP
[Hex]. Apart from formate anion, the reported EC50 values clearly demonstrated an increasing
CR
activity trend with increasing the anion alkyl chain length. [Hex] IL possesses the highest antimicrobial inhibition effect due to the presence of 6 carbon atom within its anion structure.
US
Acetate based IL where the least active one among the PILs. It was expected that formate based IL will possess the lowest antimicrobial activity against the bacterial species due to the presence
AN
of a single carbon atom within its anion structure. Surprisingly, the antimicrobial activity established with formate anion was comparable to the one for the most active anion [Hex]. The same finding was early reported by Peric et al., [13]. Formate based IL was found to be more toxic
ED
M
than other IL paired same cation but longer alkyl chain such as [But] anion against Vibrio fischeri.
Conclusions
PT
Five nitriles functionalized PILs were synthesized and characterized and their structure have been successfully confirmed. A change in temperature has been identified to affect the physiochemical
CE
properties of the ILs. Moreover, alkyl chain length of anion considerably affects the thermophysical properties. The density, refractive index, and viscosity decrease with the increase
AC
of attached alkyl substitutions, exception to acetate based ILs for values of viscosity and refractive index. The various volumetric properties were determined and the intermolecular interactions between the molecules of have been discussed with the help of these properties. All the ILs decomposition temperature seems very close to each other except the IL [C2CNIM][Hex] which shows lower decomposition temperature. Based on the studied anions, the antimicrobial activities were increased in the following order [Ace] < [Pro] < [But] < [For] < [Hex]. Formate based IL was found to be more toxic than other IL paired same cation but longer alkyl chain within the anion structures against the studied microorganisms.
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Acknowledgment The authors are thankful to Ministry of Higher Education (MOHE) for funding the research work under the YUTP project (0153AA-E76) and Centre of Research in Ionic Liquids (CORIL). References T. L. Greaves, K. Ha, B. W. Muir, S. C. Howard, A. Weerawardena, N. Kirby, et al., "Protic ionic liquids (PILs) nanostructure and physicochemical properties: development of highthroughput methodology for PIL creation and property screens," Physical Chemistry Chemical Physics, vol. 17, pp. 2357-2365, 2015.
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[24]
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Table 1. Name, abbreviation and chemical structure of the synthesized ILs. Abbreviation
Purity (%)
O
[C2CNIM][For]
H H N
C O
[C2CNIM][Ace]
H3C
400
O
C
N
99.5
99.1 O
CR
1-propanenitrileimidazolium acetate
Water content (ppm)
Anion
T
1-propanenitrileimidazolium formate
Cation
IP
Name
450
C 2H5
[C2CNIM][But]
AN
C N
[C2CNIM][Hex]
C3H7
PT CE AC
15
C
420
98.7
480
98.3
390
97.6
O
O C
O
O
C5H11
ED
1-propanenitrileimidazolium hexanoate
[C2CNIM][Pro]
M
1-propanenitrileimidazolium butanoate
US
O
1-propanenitrileimidazolium propionate
C
O
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Table 2. Experimental values of density () of the PILs from (293.15-363.15 K) at atmospheric pressure. /(g.cm-3) T/K [C2CNIM] [C2CNIM] [C2CNIM] [Pro]
293.15
1.2156
1.1277
1.1028
1.0766
1.0409
303.15
1.2071
1.1205
1.0938
1.0686
1.0331
313.15
1.1987
1.1130
1.0856
1.0607
1.0253
323.15
1.1903
1.1052
1.0777
1.0528
1.0176
333.15
1.1820
1.0977
1.0704
1.0447
1.0097
343.15
1.1737
1.0898
1.0624
1.0362
1.0019
353.15
1.1636
1.0820
1.0544
1.0290
0.9941
363.15
1.1547
1.0732
1.0462
1.0219
0.9863
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Standard uncertainty values are u(ρ) = 0.001 g·cm−3 u(T) = 0.01 K, and u(p) = 0.01 bar.
AC
a
T
[Ace][14]
IP
[C2CNIM][But] [C2CNIM][Hex]
[For]
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176.82 178.27 179.62 180.94 182.17 183.54 184.93 186.38
0.29 0.29 0.29 0.30 0.30 0.30 0.30 0.30
293.15 303.15 313.15 323.15 333.15 343.15 353.15
194.12 195.58 197.03 198.51 200.05 201.69 203.10
0.32 0.32 0.32 0.32 0.33 0.33 0.33
PT
CE
107.91 107.88 107.85 107.83 107.80 107.77 107.74 107.71
45.66 45.69 45.70 45.74 45.74
114.91 115.92 116.99 118.11 119.23
107.53 107.50 107.47 107.44 107.42 107.39 107.37 107.34
49.72 49.82 49.86 49.90 49.90
127.10 128.45 129.75 131.04 132.26
107.20 107.17 107.15 107.12 107.10 107.07 107.05
54.31 54.35 54.40 54.44 54.48
139.81 141.22 142.63 144.07 145.57
17
T
293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
98.36 99.30 100.24 101.22 102.19
IP
0.26 0.26 0.27 0.27 0.27 0.27 0.27 0.28
39.01 39.04 39.07 39.07 39.09
CR
160.58 161.61 162.70 163.85 164.97 166.16 167.36 168.73
108.60 108.57 108.54 108.50 108.47 108.44 108.40 108.36
US
293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
313.86 315.86 317.87 319.91 321.94 324.01 326.57 328.86 [C2CNIM][Ace] 362.00 364.14 366.39 368.77 371.09 373.56 376.04 378.88 [C2CNIM][Pro] 395.62 398.64 401.42 404.15 406.71 409.55 412.43 415.43 [C2CNIM][But] 431.46 434.47 437.48 440.55 443.73 447.13 450.05
AN
0.22 0.22 0.23 0.23 0.23 0.23 0.23 0.24
M
137.38 138.34 139.31 140.30 141.28 142.28 143.52 144.62
ED
293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
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Table 3. Values of molar volumes (Vm), molecular volume (V), standard entropy (So), crystal energy (UPOT), molar refraction (RM) and free volume (Vf) calculated for PILs at selected temperatures. T/K Vm V So UPOT RM Vf 3 -1 3 -1 (cm .mol ) (nm ) (cm3.mol-1) (cm3.mol-1) (J.K .mol-1) (kJ.mol-1) [C2CNIM][For]
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293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15
227.97 229.69 231.43 233.19 235.02 236.83 238.70 240.59
0.37 0.38 0.38 0.38 0.39 0.39 0.39 0.39
452.94 107.029 [C2CNIM][Hex] 501.54 106.69 505.11 106.67 508.70 106.65 512.35 106.63 516.13 106.60 519.88 106.58 523.76 106.56 527.67 106.54
63.58 63.64 63.69 63.75 63.78
T
0.339
IP
204.50
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CR
363.15
18
164.39 166.05 167.73 169.44 171.23
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Table 4. Thermal expansion coefficient for PILs as a function of temperature.
104/(K-1) [C2CNIM] [Ace]
[C2CNIM] [Pro]
[C2CNIM] [But]
[C2CNIM] [Hex]
293.15
7.12
6.88
7.24
7.32
7.49
303.15
7.17
6.93
7.29
7.37
7.55
313.15
7.22
6.98
7.34
7.43
7.61
323.15
7.27
7.03
7.40
7.49
7.67
333.15
7.33
7.08
7.45
7.54
7.72
343.15
7.38
7.13
7.51
7.60
7.79
353.15
7.44
7.18
7.57
7.66
7.85
US
CR
T
[C2CNIM] [For]
IP
T/K
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PT
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363.15 7.49 7.23 7.62 7.72 7.91 -1 Standard uncertainties are u() = 0.001 kK , µ(p) = 0.01 bar and u(T) = ±0.01.
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Table 5. Experimental dynamic viscosities for PILs at temperature in the range of 293.15 363.15 K and at atmospheric pressure a.
/(m.Pa)
T/K [C2CNIM][Ace] 108.22
[C2CNIM][Pro] 84.899
[C2CNIM][But] 115.293
[C2CNIM][Hex] 125.936
303.15
52.83
55.284
48.693
65.022
74.426
313.15
33.657
31.575
30.319
42.142
48.041
323.15
22.651
19.789
18.974
333.15
14.991
13.323
13.099
343.15
10.466
9.483
9.061
353.15
7.478
7.118
6.754
IP
31.091
18.562
21.632
12.78
14.743
9.512
10.698
US
CR
27.557
CE
PT
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AN
5.425 5.294 5.091 7.404 7.595 Standard uncertainties are ur() = 0.0032, u(T) = 0.01 K and u(p) = 0.01 bar.
AC
363.15
T
293.15
[C2CNIM][For] 90.321
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Table 6. Experimental values of refractive index (nD) of the PILs from (293.15-333.15 K) at atmospheric pressure nD T/K [C2CNIM][For]
[C2CNIM][Ace] [C2CNIM][Pro]
[C2CNIM][But]
[C2CNIM][Hex]
1.4798
1.4853
1.4743
1.4715
1.4698
298.15
1.4780
1.4836
1.4726
1.4697
1.4680
303.15
1.4763
1.4819
1.4709
1.4679
308.15
1.4747
1.4802
1.4691
1.4661
1.4644
313.15
1.4729
1.4785
1.4673
318.15
1.4711
1.4768
1.4655
323.15
1.4691
1.4750
328.15
1.4674
1.47358
333.15
1.4655
1.47188
1.4662
1.4643
1.4626
1.4625
1.4608
1.4637
1.4607
1.459
1.4619
1.4589
1.4571
1.4570
1.4552
AN
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IP
T
293.15
1.4601
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Standard uncertainty values are u(nD) = 3 ×10-3 and u(T) = 0.05 K, u(p)=0.01 bar).
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Table 7. Thermal decomposition properties of PILs. Tmax / K
[C2CNIM][For]
214
512.95
[C2CNIM][Ace]
202
516.91
[C2CNIM][Pro]
207
510.53
[C2CNIM][But]
205.46
[C2CNIM][Hex]
198.75
IP
T
Tonse/ K
CR
ILs
AC
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Standard uncertainty is u(T) = 2 °C
22
508.89 485.70
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Table 8. Antimicrobial activity of PILs expressed as 50% effective concentration in mmol. L-1 Escherichia coli
Staphylococcus aureus
[C2CNIM][For]
22.9
14.5
12.14
[C2CNIM][Ace]
81.26
72.39
56.24
[C2CNIM][Pro]
43.07
60
29.97
[C2CNIM][But]
34.94
28.27
[C2CNIM][Hex]
13.86
14.02
T
Aeromonas hydrophila
IP
23.08
AC
CE
PT
ED
M
AN
US
CR
IL
23
11.33
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1.25 [C2CNIM][For] [C2CNIM][Ace] [C2CNIM][Pro]
1.20
[C2CNIM][But] [C2CNIM][Hex]
T IP
1.10
1.05
CR
(g/cm3)
1.15
0.95 290
310
320
330
AN
300
US
1.00
340
350
360
T (K)
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Figure 1. Effect of temperature and anions on density of the PILs.
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[C2CNIM][For] [C2CNIM][Ace]
120
[C2CNIM][Pro] [C2CNIM][But] [C2CNIM][Hex]
T
80 60
IP
(mPa.s)
100
CR
40
0 290
300
310
320
330
340
AN
T (K)
US
20
350
360
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Figure 2. Effect of temperature and anions on the viscosity of PILs.
25
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1.490 [C2CNIM][For] [C2CNIM][Ace]
1.485
[C2CNIM][Pro] [C2CNIM][But] [C2CNIM][Hex]
1.480
T
1.470
IP
n
1.475
CR
1.465 1.460
1.450 290
295
300
305
US
1.455
310
315
320
325
330
335
AN
T (K)
AC
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Figure 3. Effect of temperature and anions on refractive index of the PILs.
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100 [C2CNIM][For] [C2CNIM][Ac] [C2CNIM][Pro]
80
[C2CNIM][But]
60
T
40
IP
% weight loss
[C2CNIM][Hex]
0 330
360
390
420
450
CR
20
480
510
540
570
600
US
T (K)
AC
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PT
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Figure 4. Thermal decomposition profile of the PILs.
27
ACCEPTED MANUSCRIPT
AN
US
CR
IP
T
28
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Figure 5. Influence of the anion alkyl chain length on the toxicity of studied PILs towards A. hydrophila, E.coli and S.aureus.
28
ACCEPTED MANUSCRIPT 29
Highlights
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New nitrile functionalized ionic liquids were synthesized and characterized. Effect of anion and temperature on physiochemical properties was evaluated. Ecotoxicity was evaluated for the prepared ionic liquids
29