Antimicrobial Studies Of Ammonium Based Ionic Liquids Biology Essay

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Ammonium based Ionic Liquids (AILs) were synthesized from alkanolamine by simply acid base neutralization reaction. The synthesized eight compounds were tested to evaluate their antibacterial properties for the first time. Five microbial strains were used in this study: Staphylococcus aureus, Listeria monocytogenes and gram-negative Salmonella typhi, Vibrio cholerae and Klebsiella pneumonia. The antimicrobial efficiency was measured by bacterial growth inhibition expressed as minimal inhibitory concentration (MIC) values. Ionic Liquids (ILs) are shown to display antimicrobial activity with the activities being greatly affected by increasing alkyl chain length. Increase of the substituents in ammonium based ionic liquids show high anti-microbial activities.

Keywords: Ionic Liquids, Toxicity, Antimicrobial screenings, Inhibition potential.

INTRODUCTION

Ionic Liquids (ILs) are organic salts with low melting point and boiling point that are being considered as green alternative for industrial volatile organic compounds (Welton, 1999). The reputation of these solvents as "environmental friendly" chemicals is based primarily on their negligible vapor pressure (Brennecke and Maginn, 2001). Nonetheless, the solubility of ILs in water and a number of literatures describing the toxicity of ILs to aquatic organism highlight a real cause for concern. The knowledge of ILs behavior in the terrestrial environment, which includes microbial degradation, sorption and desorption, is equally important since both soil and aquatic surroundings are possible recipients of IL contamination. Some (eco)toxicological studies of ILs have been done so far with bacteria, phytoplankton, freshwater invertebrates and fishes and they showed that ILs are toxic to aquatic organisms ranging from bacteria to fish (Bernot et al., 2005a, 2005b, Pretti et al., 2006, 2009). Nonetheless, a detail study of those organisms is just as important if we are fully understood the prospective fate and effects of ILs in the aquatic environment.

The history of modern antiseptics and disinfectants was from several decades back. The previous list includes benzalkonium chloride (BAC) and cetylpyridinium chloride (CPC), both of which are quaternary ammonium compounds and are still now broadly used. Quaternary ammonium compounds (QAC) are considered as bioactive substances and are mainly used for environmental disinfection, disinfection of medical equipment, and in hospitals. In 1926, Browning et al., described the antibacterial and antifungal activity of heterocyclic QACs derivatives. In 1968, Reginald et al., introduced the first QACs based on the disinfectant known as Zephird. In 1983, Preston et al., detailed the effect of a number of structural features on the efficiency of dialkyl QACs; total carbon atom contents of 22-24 were expected to be the most effective.

T.L. Greaves, A. Weerawardena, C. Fong, I. Krodkiewska, C.J. Drummond, J. Phys. Chem. B 110 (2007) 22479-22487.

C. Zhao, G. Burrell, A.A.J. Torriero, F. Separovic, N.F. Dunlop, D.R. MacFarlane, A.M. Bond, J. Phys. Chem. B 111 (2008) 6923-6936.

I. Cota, R. Gonzalez-Olmos, M. Iglesias, F. Medina, J. Phys. Chem. B 111 (2007) 12468-12477.

Bacteria play a vital role as an ideal starting point for ILs toxicity estimations as they have short generation times (Pham et al., 2010). Preliminary toxicological investigations have shown quaternary ammonium and pyridinium compounds have potential inhibitory effects on a variety of bacteria and fungi. It was also observed a trend of increasing toxicity with an increase in the alkyl chain length substituent in the pyridinium, imidazolium and quaternary ammonium salts to various bacteria including rods, cocci and fungi (Roslonkiewicz et al., 2005, Pernak et al., 2003). The aim of present work is to synthesize some ammonium based ionic liquids and carry out the microbial studies to predict the toxicity concerning the chemical structure and physiochemical properties of those compounds. The compounds were assayed for antibacterial activity against five registered bacterial isolates, which were obtained from the Institute of Medical Research (IMR), Kuala Lumpur, Malaysia and the tests were being done in the Department of Cell and Molecular Biology, University Putra Malaysia (UPM). The antibacterial activity of all the titled compounds was evaluated against the growth of gram-positive Staphylococcus aureus, Listeria monocytogenes and gram-negative Salmonella typhi, Vibrio cholerae and Klebsiella pneumonia at concentration 1%, 10% and 20% (v/v) in deionised water.

MATERIALS AND METHODS

Chemicals and reagents

All these hydroxyl ammonium ionic liquids were prepared by neutralization of ethanolamines with different acids. Ethanolamines include monoethanolamine (AR grade, 99%, Aldrich), diethanolamine (AR grade, 98%, Aldrich), and methyl diethanolamine (AR grade, 98%, Aldrich) and acids include formic acid (AR grade 98%), acetic acid (AR grade 98%) and lactic acid (AR grade, 88%). Solvents include acetonitrile, ethanol, acetone, methanol, chloroform was obtained from Sigma-Aldrich Company (Spruce St., St. Louis, MO, USA) and Merck-KGaA (Darmstadt, Germany). All of the starting materials were purified under reduced pressure before use. Disposable glassware were obtained from Cell culture media, Muller Hinton broth and agar, were purchased from Merck KGaA, Darmstadt, Germany. Antibiotics, gentamycin, were obtained from Roche Diagnostics (Mannheim, Germany).

Antibacterial Screening

The synthesized compounds were screened in vitro for their antimicrobial activities against bacteria S. aureus, L. monocytogenes, S. typhi, V. cholerae and K. pneumonia using Well diffusion method (Magaldi and Camero, 1997, Magaldi et al., 1998, 1999). The preparation of test plates was as follows: 20 ml Muller Hinton Agar was melted and cooled to 55°C to inoculate 1 ml of the bacterial suspension. The inoculated agar was poured onto an assay plate (9 cm diameter), and allowed to cool to room temperature. Once the medium was solidified, 100 µl from the overnight culture of the strain bacteria were swabbed on the agar by using cotton bud/hockey stick. The wells, each diameter 6 mm, were cut out of the agar. 20 µl of ionic liquid solution in different percentage (1%, 10% and 20%) was placed into the wells. Deionised water was used, as a solvent to prepare desired solutions of the compounds initially. A total of the petri dishes were then placed in an incubator, at 37°C for 24 hours. After incubation, the diameters of the inhibition-cleared zones were calculated. The results were compared with the standard antibiotic Gentamycin.

EXPERIMENTAL

IR and 1H-NMR spectrophotometer were used to characterize the products. The IR spectra were obtained on a Shimadzo Fourier Transform Infrared Spectrophotometer whereas the 1H-NMR spectra were obtained on a Bruker 400 MHz instrument. The thermal analyses were conducted using Pyris 1 Thermalgravimetric Analyzer with temperature precision ±2°C. The density of hydroxyl ammonium ionic liquids was measured with Anton Paar DMA-5000 digital vibrating-tube densitometer. Viscosity of each salt was measured using a Brookfield Cap Viscometer Model Cap 2000+. Glass transition temperatures were measured using differential scanning microcalorimetry (DSC) at a 10°C min-1 scanning rate. All of the starting materials were purified under reduced pressure before use. The synthesized ionic liquids were kept in glass vials and closed with screw caps fitted with a silicone septum, to ensure a secure seal and preventing their contact with moisture in air. The ionic liquids were taken from the vials with a syringe and immediately transferred into the apparatus for each experimental measurement to minimize the humid effects of atmosphere.

Synthesis and characterization of quaternary ammonium based ionic liquids (AILs):

All these hydroxyl ammonium ionic liquids were prepared by neutralization of ethanolamines with different acids. To equal molar amounts of ethanolamine, acids were added drop-wise to a three-necked, round bottom flask equipped with reflux condenser, a magnetic stirrer, and an inlet and outlet for N2 gas. It is due to reduce the production of heat in the reaction system. After mixing, the mixture was kept with stirring in room temperature for 2 hours. Then the temperature was stepwise risen upto 333.15 K for the completion of reaction. The reaction was followed by a thin layer chromatography using aluminium sheets silica gel and methanol as eluent. The resulting viscous liquid was kept in vacuum over overnight to remove any unreacted materials. The product yield was estimated for different ionic liquids and they were about 80%. The ionic liquids were stored under a N2 atmosphere. The water contents of hydroxyl ammonium ionic liquids were investigated using a coulometric Karl Fischer titrator DL 39 (Mettler Toledo). The water content was found to be less than 425Ã-10-6 for all the eight ionic liquids studied in the present work. The samples of ionic liquids were characterized by their IR and 1H-NMR spectrum. The structure of ionic liquids used in this work are shown in figure 1.

2-Hydroxyethylammonium acetate (HEA)

Yield: 86%, IR spectra: 3350 cm-1 (broad peak for OH), 2970 cm-1 (CH3), 2930 cm-1 (CH2), 1594 cm-1 (ionic bonding), 1390 cm-1 (COO),. 1H-NMR (400 MHz, methanol-D3): 1.88 (s, 3H, -CH3 acetate), 3.00 (t, 2H, -N-CH2-), 3.30 (s, 3H, -NH3), 3.74 (t, 2H, -O-CH2-), 5.37 (s, 1H, OH)

2-Hydroxyethylammonium formate (HEF)

Yield: 82%, IR spectra: 3290, 3058, 2939, 2879, 1650, 1531, 1382, 1174, 1062 cm-1, 1H-NMR (400 MHz, methanol-D3): 3.10 (t, 2H, -N-CH2-), 3.50 (s, 3H, -NH3), 3.74 (t, 2H, -O-CH2-), 5.60 (s, 1H, OH)

2-Hydroxyethylammonium lactate (HEL)

Yield: 78%, IR spectra: 2970, 2931, 2877, 1566, 1411, 1355, 1309, 1120, 1070, 1022 cm-1, 1H-NMR (400 MHz, methanol-D3): 1.29 (s, 3H, -CH3), 2.97 (t, 2H, -N-CH2), 3.27 (q, 1H, -CH), 3.71 (t, 2H, -O-CH2), 5.02 (m, 3H, -OH)

Bis(2-hydroxyethyl)ammonium acetate (BHEAA)

Yield: 90%, IR spectra: 3400, 2050, 1670, 1590, 1080 cm-1, 1H-NMR (400 MHz, methanol-D3): 1.91 (s, 3H, -CH3 acetate), 3.14 (t, 4H, -N-CH2-), 3.60 (s, 2H, -NH2), 3.80 (t, 4H, -O-CH2-), 5.37 (s, 2H, -OH)

Bis(2-hydroxyethyl)ammonium lactate (BHEAL)

Yield: 80%, IR spectra: 3188, 2923, 2852, 1554, 1395, 1334, 1066, 1043, 1016, 956, 1H-NMR (400 MHz, methanol-D3): 1.30 (s, 3H, -CH3), 3.08 (t, 4H, -N-CH2), 3.80 (t, 4H, -O-CH2), 3.98 (q, 1H, -CH),5.02 (m, 4H, -OH)

2-Hydroxy-N-(2-hydroxyethyl)-N-methyl ethanaminium acetate (HEMAA)

Yield: 81%, IR spectra: 3208, 2893, 2852, 1564, 1395, 1344, 1026, 1011 cm-1, 1H-NMR (400 MHz, methanol-D3): 1.91 (s, 3H, -CH3), 2.88 (s, 3H, -CH3), 3.26 (t, 4H, -N-CH2), 3.87 (t, 4H, -O-CH2), 5.27 (m, 4H, -OH)

2-Hydroxy-N-(2-hydroxyethyl)-N-methyl ethanaminium acetate (HHEMAF)

Yield: 70%, IR spectra: 3217, 2788, 2696, 1587, 1463, 1375, 1340, 1137, 1074, 1008, 759 cm-1.

Nomenclature

α = coefficient of thermal expansion (T-1)

ρ = density (g. cm-3)

η = dynamic viscocity (MPa s)

nD = refractive indicies (K)

T = temperature (°C)

T = mass loss of function of temperature

dTA = first derivative of TA

Td = thermal decomposition

W = mass

PROPERTIES OF AMMONIUM BASED IONIC LIQUIDS:

Water Content

Density

The density of ionic liquids was measured withan anton paar oscillating U-tube density meter, (DMA - 5000) at T = (293.15 to 363.15) K with an uncertainty of ±0.01 K. The apparatus was calibrated by measuring the density of Millipore quality water at regular intervals according to the supplier instructions. The calibrated apparatus was also verified using pure imidazolium ionic liquids with known densities (X.L. Yuan, S.J. Zhang, X.M. Lu, J. Chem. Eng. Data, 52, 2007, 596-599) The densimeter has the viscocity correction applied. The overall accuracy in experimental density measurements for all samples was found to be better than ±2.10-5 gcm-3.

Viscosity

The viscosity of each ionic liquid was measured using a cone and plate, CAP 2000, L-series, Brookfield viscometer at T = (278.2 to 348.2) K with a temperature control accuracy of ±0.2 K. The viscometer was calibrated frequency according to the instructions using standard calibration fluids provided by the supplier. The viscometer was placed in a dry place and the viscosity measurement proceeded as soon as the sample was placed on viscometer plate. The sample is considered to be no longer in contact with the external environment, as soon as the cone is highly pressed on plate. The viscosity measurements were preformed in triplicate and the results are reported as an average agreeing to within 10 MPa.s.

Refractive Indices

The refractive indices of all ionic liquids, were determined using ATAGO programmable digital refractometer, (RX-5000 alpha), with a measuring accuracy of 4.10-5. All the measurements were performed at T = (302.95 to 332.95) K with a temperature control accuracy of 0.05 K. The apparatus was calibrated by measuring the refractive indices of Millipore quality water before each series of measurements according to the instructions and checked for pre imidazolium ionic liquids with known refractive indices (.L. Yuan, S.J. Zhang, X.M. Lu, J. Chem. Eng. Data, 52, 2007, 596-599).

Thermal decomposition

Thermal stability of hydroxyl ammonium ionic liquids was investigated using a thermogravimetric analyzer, TGA, Perkin-Elmer, Pyris V-3.81, at temperatures T = (25 to 500) K. The effect of temperature on the decomposition of hydroxyl ammonium was studied using a platinum pan under N2 atmosphere, at a heating rate of 10°C. min-1, with temperatue accuracy better than ±3k.

Antimcrobial Screening

Ammonium based ionic liquids were assayed for antibacterial activity against five registered bacterial isolates, which were obtained from the Institute of Medical Research (IMR), Kuala Lumpur, Malaysia. The antibacterial activity of all the titled compounds was evaluated against the growth of gram-positive Staphylococcus aureus, Listeria monocytogenes and gram-negative Salmonella typhii, Vibrio cholerae and K. pneumonia at concentration 1%, 10% and 20% (v/v) in deionised water. Muller Hinton Agar was melted and cooled to 55°C to inoculate the bacterial suspension. The inoculated agar was transferred onto petri-plate and allowed to cool to normal temperature. Once the medium was solidified, 6 mm diameter holes were made in the central part of the agar plate and 20 µl of ionic liquid solution in different percentage (1%, 10% and 20%) was poured into the wells. Plates were incubated at room temperature for 24 h or for more days until adequate growth were present. The bacteria were rejuvenated on Muller Hinton broth and subcultured as needed. The solutions were added in the well of the petri plate and deionised water was used as control. After incubation, the diameters of the inhibition-cleared zones were determined. The plates were incubated at 37°C and examined the zone of inhibition around each well after 24 hours. The results were compared with the standard antibiotic Gentamycin (1, 10 and 20 percent).

Table 1: Zone of Inhibition (in mm) found (including diameter of well) for different concentration of ionic liquids:

Bacteria &treatment

Conc.

K. pneumonia

S. aureus

S. typhii

V. cholerae

Lis. monocytogenes

Gentamicin

20%

10

21

20

10

20

Deionised

Water

-

-

-

-

-

HEA

1%

-

-

-

-

-

10%

-

7

-

-

-

20%

-

11

-

-

-

HEF

1%

-

-

-

-

-

10%

9

12

11

9

-

20%

10

14

14

10

-

HEL

1%

-

-

-

-

-

10%

-

7

-

-

-

20%

-

9

-

-

-

BHEAA

1%

-

-

-

-

-

10%

-

12

10

-

-

20%

-

14

14

-

-

BHEAF

1%

-

-

-

-

-

10%

-

7

-

-

-

20%

-

11

-

-

-

BHEAL

1%

-

-

-

-

-

10%

-

-

-

-

-

20%

-

7

-

-

-

HEMAA

1%

-

-

-

-

-

10%

-

13

13

8

16

20%

-

17

16

9

18

HHEMAF

1%

-

-

-

-

-

10%

7

9

-

-

-

20%

9

10

-

-

-

RESULTS AND DISCUSSION

In this work, eight hydroxyl ammonium ionic liquids; 2-hydroxyethylammonium acetate [HEA], 2-Hydroxyethylammonium formate (HEF), 2-hydroxyethylammonium lactate [HEL], bis-(2-hydroxyethyl)ammonium acetate [BHEAA], Bis(2-hydroxyethyl)ammonium formate (BHEAF), bis-(2-Hydroxyethyl) ammonium lactate [BHEAL], 2-Hydroxy-N-(2-hydroxyethyl)-N-methyl ethanaminium acetate (HEMAA), 2-Hydroxy-N-(2-hydroxyethyl)-N-methyl ethanaminium acetate (HHEMAF) were synthesized and characterized. The reaction is a simple acid-base reaction forming salt of ethanolamine with the anion from the corresponding acid. Since the reaction of ethanolamine with acid is highly exothermic, an efficient cooling is essential throughout the reaction. The addition of acid to ethanolamine under continuous stirring gives a viscous clear liquid. IR spectra of these compounds showed the formation of the salts giving the peak at ~1595 cm-1 for ionic bonding. The other peaks, broad 3350 cm-1 for strong hydrogen bonding in OH, 1390 cm-1 for carboxyl group as asymmetric vibration, methyl and methelene group peak at about 2970 and 2930 cm-1 indicates the existence of desired compounds. The broad band in the 3500-2400 cm-1 range exhibits characteristic ammonium structure for all the neutralization products.

Figure 1: Some Hydroxyl Ammonium ILs synthesized for antimicrobial screening.

The 1H NMR and FT-IR spectra indicate a simple salt structure of the hydroxyl ammonium ionic liquids. Thus, in IR spectrum the broad band (3500 to 2500) cm-1 ranges imply typical ammonium structure. The carbonyl stretching and N-H plane bonding vibrations are observed as a combined bond centred around 1600 cm-1. The samples of ionic liquids were also characterized by its 1H NMR (400 MHz, methanol-D3). The spectra data of 2-hydroxyethanaminium acetate [HEA] are: 1.88.10-6 (s, 3H, -CH3 Acetate), 3.00.10-6 (t, 2H, -N-CH2-), 3.74.10-6 (t, 2H, -O-CH2-).

Many of these ammonium salts, exists the possibility to undergo a condensation reaction and form an amide compound. Therefore, an adequate control of temperature is essential during the chemical reaction of salt formation; otherwise heat evolution may produce the dehydration of the salt to give the corresponding amide as in the case of nylon salts (salts of diamines with dicarboxy acids) (Iglesias et al., 2010).

Table 1: Water content of the ionic liquids studied in the present work:

Ionic Liquids

Water Content

HEA

HEF

HEL

BHEAA

BHEAF

BHEAL

HEMAA

HHEMAF

Table 2,3: Data used for calibration of equipment for measurement of physical properties of hydroxyl ammonium ionic liquids at T = 298.15 K. Experimental values of densities (ρ), and refractive indices (nD) at T = 298.15 K, present work and literature.

Ionic Liquids

ρ/(g.cm-3)

η/(MPa.s)

nD

HMIM PF6

1.29341 [18], 1.2935 [19]

607 [18], 586 [20]

1.41694a[18], 1.4163b[21]

HEA

1.14866c, 1.12 [14]

1.43682, 1.469 [15]

HEL

1.20452c, 1.228 [15]

1.43758, 1.4489 [15]

BHEMA

1.20634c, 1.22 [16]

a at T = 302.95 K, b at T = 303.15 K, c at T = 293.15 K

14. X.L. Yuan, S.J. Zhang, X.M. Lu, J. Chem. Eng. Data 52 (2007) 596-599.

15. T.L. Greaves, A. Weerawardena, C. Fong, I. Krodkiewska, C.J. Drummond, J. Phys. Chem. B 110 (2007) 22479-22487.

16. C. Zhao, G. Burrell, A.A.J. Torriero, F. Separovic, N.F. Dunlop, D.R. MacFarlane, A.M. Bond, J. Phys. Chem. B 111 (2008) 6923-6936.

17. I. Cota, R. Gonzalez-Olmos, M. Iglesias, F. Medina, J. Phys. Chem. B 111 (2007), 12468-12477.

18. A. Muhammad, M.I. Abdul Mutalib, C.D. Wilfred, T. Murugesan, A. Shafeeq, J. Chem. Thermodyn. 40 (2008) 1433-1438.

19. T.M. Letcher, P. Reddy, J. Chem. Thermodyn. 37 (2005) 415-421.

20. J.G. Huddleston, A.E. Visser, W.M. Reickert, H.D. Willauer, G.A. Broker, R.D. Rogers, Green Chem. 3 (2001) 156-169.

21. A.B. Pereiro, E. Tojo, A. Rodriguez, J. Canosa, J. Tojo, J. Chem. Thermodyn. 38 (2006) 651-661.

All instruments used for measurement of physical properties were calibrated using pure Millipore quality water with known density, refractive index and dynamic viscosity, and further tested with [C6mim][PF6]. It was found that the results were in good agreement with the current published data from our research group as can be seen in table 1 [18]. The physical properties of hydroxyl ammonium ionic liquids investigated in the present work is compared with the recent literature value and listed in table 2. The present experimental values of density, dynamic viscosity, and refractive indices for hydroxyl ammonium ionic liquids are presented in tables 3 to 5. The discrepancies in the physical properties values of hydroxyl ammonium ionic liquids when compared with the literature may be due to water content and method used to determine it. The varying degree of water contents associated with ionic liquids when compared with the literature data could be due to the difficulty involved in drying at very low moisture contents as well as the drying method involved.

The density of hydroxyl ammonium ionic liquids decreased linearly with increasing temperature. The most notable attribute seen in table 1 is that ionic liquids with lactate anion show similar but high density, regardless of the cation. It appears that density of hydroxyl ammonium ionic liquids investigated in this work showed high dependence on the molar mass of anion. The values of refractive indices also decreased with increase in temperature and the values are found to be in same order as that of density. However for the dynamic viscosity, the values also decreased with increasing temperature, but in a non- linear fashion.

The density ρ, the dynamic viscosity η, and the refractive indices nD, values were fitted by the method of least squares using the following equations [1,2],

And

Where ρ is density of hydroxyl ammonium ionic liquids, η is dynamic viscosity of ionic liquids, nD is refractive index of the hydroxyl ammonium ionic liquids, T is the temperature, and A0 and A1 are correlation coefficients. The values of Ao and A1 are estimated using the method of least square fitting equations (1)-(3) and presented in table 4 along with the standard deviation (SD) values calculated using the following expression:

Where nDAT is the number of experimental points, Zexp and Zcal are experimental and calculated data values, respectively.

The comparison between the experimental and calculated values of the density, dynamic viscosity, and refractive indices of the studied hydroxyl ammonium ionic liquids are shown in figures 1 to 3.

Table 4: Experimental values of density (ρ), of hydroxyl ammonium ionic liquids at several temperatures (T).

T/K

HEA

BHEAA

BHEMA

HEL

BHEAL

BHEML

293.15

1.14866

1.17385

1.14142

1.20452

1.20634

1.18323

303.15

1.14339

1.16639

1.13276

1.19784

1.19877

1.17619

313.15

1.13802

1.16012

1.12585

1.19186

1.19247

1.16954

323.15

1.13252

1.15396

1.11875

1.18578

1.18614

1.16277

333.15

1.12694

1.14764

1.11146

1.17964

1.17973

1.1559

343.15

1.12126

1.14122

1.10398

1.17345

1.17325

1.14893

353.15

1.11547

1.13466

1.09628

1.16719

1.16669

1.14186

363.15

1.10955

1.12797

1.08836

1.16086

1.16003

1.13468

Dynamic viscosity

T/K

HEA

BHEAA

BHEMA

HEL

BHEAL

BHEML

298.2

313.15

566.89

198.91

254.25

288.56

225.15

303.2

224.68

376.59

144.69

181.45

204.15

162.02

308.2

162.91

260.02

108.33

133.32

148.54

120.26

313.2

120.26

183.97

83.56

100.02

110.25

91.15

318.2

92.56

136.06

64.12

76.88

84.34

73.15

323.2

70.68

101.06

50.96

60.18

65.45

55.26

328.2

56.56

78.35

40.45

48.12

51.78

43.15

333.2

43.91

60.25

32.15

38.12

42.15

35.15

338.2

34.98

48.79

25.98

31.02

33.45

29.15

343.2

29.04

38.65

22.32

24.98

27.15

26.15

348.2

24.05

31.51

18.45

21.26

22.45

18.36

Density results for hydroxyl ammonium ionic liquids were used to derive other thermodynamic properties such as the coefficient of thermal expansion. The coefficient of thermal expansion of ionic liquids is defined by the following equation:

Where α is the coefficient of thermal expansion, ρ is the density of hydroxyl ammonium ionic liquids, T is the temperature and A0 and A1 are correlation coefficients taken from equation (1) by fitting density data.

It is observed that most of the compounds exhibited antibacterial activity when compared with that of standard. 2-Hydroxy-N-(2-hydroxyethyl)-N-methyl ethanaminium acetate (HEMAA) possesses highest inhibition for S. aureus, S. typhi, V. cholera and L. monocytogenes, and to some extent it is higher than the standard Gentamycin (Figure 2). Similarly, it is gratifying to observe that all these compounds are extremely more effective against bacteria S. aureus. The observation proves the effectiveness of antimicrobial activity with the increase of substitution in nitrogen central atom in ammonium ionic liquids.

Figure 2: Inhibition potential for HEMAA with the concentration of 10% and 20% ionic liquid solution.

CONCLUSION

It is revealed that hydroxyl functionalized Ammonium based Ionic Liquids are having antimicrobial activities to some extent with human pathogenic bacteria. It can help to understand the effect for other substituted ammonium ionic liquids and to predict their inhibition potential. Further studies will be needed to check the broad applicability of these types of ionic liquids with other common bacterial strains.

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