Viscosities of Glycine and l-Alanine in (0.2, 0.4, 0.6, and 0.8) mol·kg–1

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Viscosities of Glycine and L‑Alanine in (0.2, 0.4, 0.6, and 0.8) mol·kg−1 Aqueous Dipotassium Hydrogen Phosphate Solutions at Different Temperatures Harsh Kumar* and Kirtanjot Kaur Department of Chemistry, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar144 011 Punjab, India ABSTRACT: Viscosities, η, for glycine and L-alanine have been measured in (0.2, 0.4, 0.6, and 0.8) mol·kg−1 aqueous dipotassium hydrogen phosphate (DKHP) solutions at temperatures T = (288.15, 298.15, 308.15, and 318.15) K. The change in viscosity of amino acids with an increase in DKHP concentration and temperature is attributed to amino acid−DKHP interactions. The viscosity B-coefficients and viscosity interaction parameters obtained from the Jones−Dole equation and transition state theory, respectively, have been discussed to interpret interactions between ions of amino acids and dipotassium hydrogen phosphate.

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INTRODUCTION In general the electrolytes present in our body influence the properties of biological molecules like proteins1,2 which are a vital part of our body. Electrolytes like tripotassium citrate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate which are of valuable importance in industries like medicines, biosensors, optics, and cosmetics also play a significant role in various metabolic processes.3−5 The interactional behavior of large biomolecules like hormones, enzymes, and especially proteins are difficult to understand due to many specific interactions. Amino acids are the low molar mass model compounds or building blocks of proteins which can be used for studies expected to set impact on the solvation and conformation of proteins.6,7 Among the various thermophysical properties, attempts have been made to study the interaction of amino acids and peptides in aqueous salt solutions8−12 with viscometric properties. The B-coefficient values as obtained from the Jones−Dole equation are a very good parameter to describe the kosmotropic and chaotropic nature of solute in different solvents. Much work has been done on the determination of B-coefficients of amino acid and peptides in water13−18 and in aqueous electrolyte solutions,19−23 but there has been less focus on the interactions of amino acids with salts which are involved in the biochemical processes of the body24−26 like citrates and phosphates. Our main aim here is to study the interactional behavior of amino acids with these salts which will further help us in better understanding of these classes of compounds. In continuation to our research program on thermodynamics studies27,28 of amino acids with salts of citrates and phosphates, here, the viscosities, η, of glycine and −1 L-alanine in (0.2, 0.4, 0.6, and 0.8) mol·kg aqueous dipotassium hydrogen phosphate (DKHP) solutions at T = (288.15, 298.15, 308.15, and 318.15) K have been reported. As per our knowledge, measurements on the thermodynamic properties of © 2012 American Chemical Society

amino acids with dipotassium hydrogen phosphate mixtures have not been reported so far.

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EXPERIMENTAL SECTION Glycine, L-alanine, and dipotassium hydrogen phosphate with mass fraction purities > 0.99 obtained from Merck, Germany were used as supplied. However, these were vacuum-dried before use and then were kept over P2O5 in desiccator for 48 h. All of the aqueous solutions were prepared afresh in doubledistilled and degassed water having a specific conductance of < 10−6 S·cm−1. The specification of the chemicals used has also been given in Table 1. All of the weighings were made on a Table 1. Specification of Chemical Samples chemical name

source

mass fraction purity

glycine L-alanine dipotassium hydrogen phosphate

Merck, Germany Merck, Germany Merck, Germany

> 0.99 > 0.99 > 0.99

Sartorius BP 210 S balance having precision of ± 0.0001 g. The uncertainty in the solution concentration was estimated to be ± 2·10−5 mol·kg−1 in calculations. The AntonPaar Automated MicroViscometer (AMVn) was used to determine dynamic viscosities, η, of the solutions. The temperature was controlled to ± 0.01 K by a built-in Peltier thermostat. The measurement of viscosities with AMVn is based on the falling ball principle. A calibrated glass capillary with a steel ball as supplied by manufacturer with AMVn was filled with the sample to measure the ball falling time. Received: May 2, 2012 Accepted: October 30, 2012 Published: November 9, 2012 3416

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Table 2. Dynamic Viscosities, η, of Glycine and L-Alanine in Aqueous Solutions of DKHP at Different Temperatures η/(mPa·s)

ma mol·kg

−1

0.00000 0.03590 0.05907 0.09179 0.14485 0.26875 0.00000 0.03943 0.05925 0.10296 0.15917 0.20702 0.26359 0.35021 0.00000 0.04302 0.08234 0.14601 0.17662 0.22791 0.26448 0.32849 0.00000 0.04184 0.09827 0.16446 0.20374 0.25129 0.00000 0.05075 a

T = 288.15 K

T = 298.15 K

T = 308.15 K

Glycine + 0.2 mol·kg−1 DKHP 1.2013 0.9528 0.7809 1.2297 0.9717 0.7868 1.2341 0.9841 0.7905 1.2353 0.9863 0.8012 1.2439 0.9991 0.8084 1.2458 1.0028 0.8183 Glycine + 0.4 mol·kg−1 DKHP 1.3288 1.0567 0.8672 1.3300 1.0592 0.8682 1.3355 1.0601 0.8697 1.3431 1.0648 0.8872 1.3564 1.0735 0.8997 1.3666 1.0817 0.9082 1.3791 1.0923 0.9127 1.3861 1.1094 0.9141 Glycine + 0.6 mol·kg−1 DKHP 1.4093 1.1182 0.9164 1.4211 1.1227 0.9231 1.4374 1.1399 0.9338 1.4490 1.1509 0.9411 1.4569 1.1564 0.9466 1.4819 1.1762 0.9600 1.4882 1.1815 0.9680 1.4947 1.1853 0.9692 Glycine + 0.8 mol·kg−1 DKHP 1.5343 1.2165 0.9966 1.5501 1.2308 1.0067 1.5606 1.2398 1.0131 1.5942 1.2623 1.0336 1.6047 1.2794 1.0458 1.6165 1.2847 1.0466 −1 L-Alanine + 0.2 mol·kg DKHP 1.2013 0.9528 0.7809 1.2297 0.9725 0.7983

η/(mPa·s)

ma T = 318.15 K

mol·kg

−1

T = 288.15 K

T = 298.15 K

0.6593 0.6775 0.6789 0.6806 0.6894 0.6901

0.11076 0.15256 0.20019 0.25144 0.32211 0.36239

0.7303 0.7452 0.7517 0.7618 0.7711 0.7742 0.7761 0.7781

0.00000 0.04944 0.16042 0.22190 0.26730 0.31720 0.35409 0.00000 0.06819 0.11883 0.16947 0.25609 0.30064 0.35684

0.7703 0.7784 0.7848 0.7902 0.7953 0.8012 0.8033 0.8123

0.00000 0.07497 0.17715 0.22784 0.27826 0.32913 0.37594

0.8332 0.8451 0.8522 0.8679 0.8689 0.8729

T = 308.15 K

+ 0.2 mol·kg−1 1.2479 0.9894 1.2737 1.0021 1.2981 1.0239 1.3069 1.0291 1.3186 1.0362 1.3327 1.0422 −1 L-Alanine + 0.4 mol·kg 1.3288 1.0567 1.3314 1.0580 1.3733 1.0870 1.3892 1.1000 1.4133 1.1133 1.4260 1.1241 1.4494 1.1405 −1 L-Alanine + 0.6 mol·kg 1.4093 1.1182 1.5295 1.2306 1.5346 1.2312 1.5486 1.2327 1.5638 1.2348 1.5799 1.2472 1.6056 1.2651 −1 L-Alanine + 0.8 mol·kg 1.5343 1.2165 1.6341 1.2922 1.6466 1.3011 1.6732 1.3243 1.6967 1.3385 1.7181 1.3718 1.7377 1.3805 L-Alanine

DKHP 0.8067 0.8171 0.8384 0.8393 0.8422 0.8501 DKHP 0.8672 0.8754 0.8874 0.9023 0.9078 0.9164 0.9281 DKHP 0.9164 0.9599 0.9756 0.9848 1.0076 1.0153 1.0303 DKHP 0.9966 1.0506 1.0606 1.0730 1.0897 1.1240 1.1290

T = 318.15 K 0.6778 0.6951 0.6985 0.6991 0.7080 0.7144 0.7303 0.7376 0.7442 0.7542 0.7605 0.7671 0.7757 0.7703 0.8112 0.8180 0.8223 0.8432 0.8367 0.8534 0.8332 0.8664 0.8870 0.9007 0.9096 0.9214 0.9341

0.6593 0.6731

m is the molality of amino acid in aqueous DKHP solution. Standard uncertainty: in molality u(m) = ± 2·10−5 mol·kg−1, in temperature u(T) = ± 0.01 K, in viscosity u(η) = ± 1.5·10−2 mPa·s. The combined expanded uncertainty (k = 2) for viscosity Uc (η) = ± 3.0·10−2 mPa·s.

different temperatures. The viscosity values show an increase with the increase in amino acid concentration. This may be due to an increase in the number of cations and anions like NH3+, COO−, K+, and HPO4‑ amino acids and DKHP in solutions which may in turn lead to increase in the interactions between them and therefore increase in frictional resistance in the solutions for their flow. The elevated temperatures of the solutions decrease the viscosities of the solutions. The viscosity A- and B-coefficients which describes ion−ion and ion−solvent interactions were determined using the Jones−Dole equation.29 The special behavior at low concentrations made Jones and Dole conclude that there must be some effect which is of relatively greater importance and which is responsible for the curvature found in dilute end of η versus C plots. Furthermore, this effect always tends to increase whether the overall effect of the addition of the salt is to increase or decrease the viscosity. The increase in viscosity was attributed to the interionic forces. Inspired by the results of Debye and Hückel, who had earlier shown that the effect of interionic forces in opposing the motion of ions is proportional

The ball falling time and densities were used to estimate kinematic as well as dynamic viscosities. The calibration of capillary was performed by the manufacturer using viscosity standard fluids. The experimental uncertainty in viscosity measurement was estimated to be less than ± 1.5·10−2 mPa·s, and the combined expanded uncertainties (k = 2) for viscosity are ± 3·10−2 mPa·s. The densities used in the calculations have been taken from our earlier reported results.28

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RESULTS AND DISCUSSION The values of dynamic viscosities, η, for glycine and L-alanine in (0.2, 0.4, 0.6, and 0.8) mol·kg−1 dipotassium hydrogen phosphate solutions at temperatures T = (288.15, 298.15, 308.15, and 318.15) K are given in Table 2. The plots of viscosities against molalities of amino acids are given in Figures 1 and 2. Figure 1 shows the experimental viscosities for amino acids in different DKHP solutions at T = 288.15 K whereas Figure 2 shows the experimental viscosities for glycine in 0.6 mol·kg−1 solution of DKHP and L-alanine in 0.8 mol·kg−1 solution of DKHP at 3417

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Table 3. Values of A- and B-Parameters of the Jones−Dole Equation for Glycine and L-Alanine in Aqueous DKHP Solutions at Different Temperatures ma mol·kg 0.2

0.4

0.6

0.8

Figure 1. Experimental viscosities, η, for glycine in aqueous DKHP solutions: ○, 0.2 mol·kg−1; △, 0.4 mol·kg−1; □, 0.6 mol·kg−1; ◊, 0.8 mol·kg−1, and L-alanine in aqueous DKHP solutions: ●, 0.2 mol·kg−1; ▲, 0.4 mol·kg−1; ■, 0.6 mol·kg−1; ◆, 0.8 mol·kg−1, at T = 288.15 K. Solid lines and dotted lines have been drawn for glycine and L-alanine, respectively.

0.2

0.4

0.6

0.8

a

K 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15 288.15 298.15 308.15 318.15

A·103/2 −1/2

m ·mol 3/2

Glycine 0.1470 (± 0.0074) 0.1463 (± 0.0183) 0.0385 (± 0.0199) 0.1608 (± 0.0149) −0.0118 (± 0.0113) −0.0391 (± 0.0043) 0.0168 (± 0.0330) 0.1503 (± 0.0182) 0.0141 (± 0.0167) 0.0051 (± 0.0205) 0.0110 (± 0.0172) 0.0288 (± 0.0063) −0.0021 (± 0.0208) 0.0016 (± 0.0268) −0.0015 (± 0.0317) 0.0577 (± 0.0244) L-Alanine 0.0810 (± 0.0271) 0.0857 (± 0.0252) 0.0830 (± 0.0309) 0.0756 (± 0.0246) −0.0732 (± 0.0173) −0.0659 (± 0.0128) −0.0271 (± 0.0190) −0.0272 (± 0.0219) 0.3446 (± 0.0409) 0.4450 (± 0.0560) 0.1593 (± 0.0102) 0.2004 (± 0.0309) 0.1858 (± 0.0443) 0.1478 (± 0.0539) 0.0873 (± 0.0612) 0.0002 (± 0.0085)

B·103 m3·mol−1 −0.1461 −0.0777 0.1173 −0.1328 0.1613 0.2140 0.1597 −0.0523 0.1891 0.2078 0.1858 0.1237 0.2738 0.2788 0.2425 0.1132

(± (± (± (± (± (± (± (± (± (± (± (± (± (± (± (±

0.0018) 0.0442) 0.0482) 0.0361) 0.0243) 0.0092) 0.0699) 0.0382) 0.0365) 0.0446) 0.0374) 0.0137) 0.0554) 0.0682) 0.0771) 0.0618)

0.1826 0.1356 0.1190 0.1077 0.3919 0.3443 0.2458 0.2208 −0.2055 −0.4174 0.0949 −0.0371 0.0598 0.1351 0.2335 0.2936

(± (± (± (± (± (± (± (± (± (± (± (± (± (± (± (±

0.0542) 0.0502) 0.0616) 0.0489) 0.0341) 0.0252) 0.0375) 0.0429) 0.0842) 0.1149) 0.0209) 0.0633) 0.0880) 0.1069) 0.1212) 0.0167)

m is the molality of aqueous DKHP solution.

where ηr (= η/η0) is the relative viscosity, η is the viscosity of (amino acid + DKHP + water) solution, and η0 is the viscosity of solvent (DKHP + water). A and B are the constants which are characteristics of ion−ion and ion−solvent interactions, respectively. C (mol·m−3) is the concentration in moles per unit volume (molarity). The conversion of molality m to molarity C was done by using density values. The experimental viscosity data was fitted to Jones−Dole using the least-squares method to obtain A- and B-coefficients. The A-coefficient is characteristic of amino acid−amino acid interactions whereas the B-coefficient is characteristic of amino acid−DKHP−water interactions. The values of A- and B-coefficients as obtained are reported in Table 3. Also, the values of B-coefficients are graphically represented in Figure 3. Table 3 shows that the values of A-coefficients are positive for glycine in all concentrations of DKHP at all temperatures except at lower temperatures in 0.4 mol·kg−1 and 0.8 mol·kg−1 DKHP and positive for L-alanine in all concentrations except in 0.4 mol·kg−1. The small negative or positive values of A-coefficients in aqueous DKHP solutions indicate the weak amino acid−amino acid interactions. The values of B-coefficient are positive for glycine and L-alanine in aqueous DKHP solutions

Figure 2. Experimental viscosities, η for (a) glycine in 0.6 mol·kg−1 DKHP solutions and (b) L-alanine in 0.8 mol·kg−1 DKHP solutions at different temperatures: ◇, 288.15 K; □, 298.15 K; △, 308.15 K; ○, 318.15 K.

to the square root of concentration in very dilute solutions, Jones and Dole gave the equation (ηr − 1)/C1/2 = A + BC1/2

T −1

(1) 3418

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except at lower and higher temperatures for glycine in 0.2 mol·kg−1 DKHP, L-alanine in 0.6 mol·kg−1 DKHP, and at higher temperatures for glycine in 0.4 mol·kg−1 DKHP. The positive and large values of B-coefficient as compared to A-coefficient indicates that the amino acid−DKHP−water interactions are dominant over amino acid−amino acid interactions30 and also the structuremaking tendency of glycine and L-alanine with DKHP. It is also observed from Table 3 that values of B-coefficients are higher for L-alanine than glycine which means L-alanine has a greater kosmotropic effect than glycine in DKHP solutions. The sign of derivative of B-coefficient, that is, dB/dT predicts the solute ability to act as a structure maker or breaker in a particular solvent.31,32 It is also observed from Table 3 that the magnitude of B-coefficient for both amino acids decreases as temperature increases. The positive dB/dT values indicate structure-breaker characteristics, while negative dB/dT values indicate structure-maker characteristics. The dB/dT values for glycine and L-alanine changes sign from positive to negative, but overall negative values of dB/dT predicts glycine and L-alanine as structure makers in DKHP−water mixtures. The analysis of viscosity data of glycine and L-alanine was done with the help of transition state treatment by Feakins et al.33 for relative viscosities. According to transition state theory,34,35 every solvent molecule in one mole of solution must pass through the transition state and interact more or less strongly with solute molecules. Hence, the Gibbs free energy of transfer of a solute

Figure 3. Viscosity B-coefficients for glycine in aqueous DKHP solutions: ○, 0.2 mol·kg−1; △, 0.4 mol·kg−1; □, 0.6 mol·kg−1; ◊, 0.8 mol·kg−1, and −1 −1 L-alanine in aqueous DKHP solutions: ●, 0.2 mol·kg ; ▲, 0.4 mol·kg ; ■, 0.6 mol·kg−1; ⧫, 0.8 mol·kg−1, at different temperatures. Solid lines and dotted lines have been drawn for glycine and L-alanine, respectively.

Table 4. Values of V̅ 01, V̅ 02, Δμ01*, and Δμ02* for Glycine and L-Alanine in Aqueous DKHP Solutions at Different Temperatures ma/(mol·kg−1)

T = 288.15 K

T = 298.15 K

T = 308.15 K

T = 318.15 K

18.68 47.62 26.54 19.86 19.26 48.24 26.87 60.05 19.72 48.88 27.07 59.32 20.32 49.49 27.35 69.05

18.74 48.06 26.93 47.62 19.33 48.89 27.28 53.89 19.80 49.21 27.48 57.64 20.40 49.79 27.77 65.68

18.82 48.45 27.37 12.41 19.41 49.25 27.72 24.47 19.88 49.73 27.92 50.04 20.48 50.26 28.21 48.71

18.73 60.78 26.47 50.81 19.33 61.36 26.73 79.39 19.56 62.03 26.85 24.36 20.28 62.39 27.09 51.40

18.79 61.8 26.86 49.73 19.40 62.34 27.13 67.73 19.63 62.86 27.26 20.17 20.35 63.24 27.49 66.38

18.87 62.67 27.29 49.29 19.48 63.29 27.57 65.84 19.72 63.85 27.69 28.93 20.44 64.22 27.92 76.66

Glycine 0.2

0.4

0.6

0.8

V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1)

18.05 47.04 26.12 10.58 18.11 47.85 26.37 51.65 18.17 48.34 26.52 55.44 18.25 48.72 26.74 66.67

V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1) V̅ 01·106 (m3·mol−1) V̅ 02·106 (m3·mol−1) Δμ01* (kJ·mol−1) Δμ02* (kJ·mol−1)

18.10 60.03 26.13 55.84 18.17 60.59 26.38 83.63 18.02 61.41 26.50 4.95 18.21 61.93 26.73 40.33

L-Alanine

0.2

0.4

0.6

0.8

a

m is the molality of aqueous DKHP solution. 3419

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from the ground state to the transition state solvents is the first contribution and Gibbs free energy of solute through its own viscous transition state is the second contribution to Δμ02* which is equal to Δμ01*. The B-coefficient as per transition state treatment is given by following relationship

(4) Van Ness, J. H. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Wiley-Interscience: New York, 1984; Vol. 13, pp 80−103. (5) Kertes, A. S.; King, C. J. Extraction chemistry of fermentation product carboxylic acids. Biotechnol. Bioeng. 1986, 28, 269−281. (6) Von Hippel, P. H.; Schleich, T. In Structure and Stability of Biological Macromolecules; Timasheff, S. N., Fasman, G. D., Eds; Marcel Dekker: New York, 1969; pp 417−574. (7) Hedwig, G. R.; Hoiland, H. Thermodynamic properties of peptide solutions 8. Isentropic pressure coefficients (∂V2/∂p)s of the apparent molar volume V2 for each of the aqueous solutes: diglycine, triglycine, and tetraglycine. J. Chem. Thermodyn. 1991, 23, 1029−1035. (8) Soto, A.; Arce, A.; Khoshkbarchi, M. K. Effect of cation and anion of an electrolyte on apparent molar volume, isentropic compressibility and refractive index of glycine in aqueous solutions. Biophys. Chem. 1999, 76, 73−82. (9) Wadi, R. K.; Goyal, R. K. Temperature dependence of apparent molar volumes and viscosity B-coefficients of amino acids in aqueous potassium thiocyanate solutions from 15 to 35 °C. J. Solution Chem. 1992, 21, 163−170. (10) Yuan, Q.; Li, Z.; Wang, B. Partial molar volume of L-alanine, DL-serine, DL-threonine, L-histidine, glycine, and glycylglycine in water, NaCl and DMSO aqueous solutions at T = 298.15 K. J. Chem. Thermodyn. 2006, 38, 20−33. (11) Ogawa, T.; Mizutani, K.; Yasuda, M. The volume, adiabatic compressibility and viscosity of amino acids in aqueous alkali chloride solutions. Bull. Chem. Soc. Jpn. 1984, 57, 2064−2068. (12) Badarayani, R.; Kumar, A. The mixing effect of glycylglycine with KCl, KBr, and Na2SO4 from volumetric and viscometric investigation at 298.15 K. J. Solution Chem. 2004, 33, 407−426. (13) Wadi, R. K.; Ramaswami, P. Partial molal volumes and adiabatic compressibilities of transfer of glycine and DL-alanine from water to aqueous sodium sulfate at 288.15, 298.15 and 308.15 K. J. Chem. Soc., Faraday Trans. 1997, 93, 243−247. (14) Belibagli, K. B.; Ayranci, E. Viscosities and apparent molar volumes of some amino acids in water and in 6 M guanidine hydrochloride at 25 °C. J. Solution Chem. 1990, 19, 867−882. (15) Banipal, T. S.; Singh, G. Thermodynamic study of solvation of some amino acids, diglycine and lysozyme in aqueous and mixed aqueous solutions. Thermochim. Acta 2004, 412, 63−83. (16) Yan, Z.; Wang, J.; Lu, J. Viscosity behavior of some α-amino acids and their groups in water- sodium acetate mixtures. Biophys. Chem. 2002, 99, 199−207. (17) Tsangaris, J. M.; Martin, R. B. Viscosities of aqueous solutions of dipolar ions. Arch. Biochem. Biophys. 1965, 112, 267−272. (18) Banipal, T. S.; Bhatia, A.; Banipal, P. K.; Singh, G.; Kaur, D. Partial molar volumes and viscosities of some amino acids in aqueous electrolyte and non-electrolyte solutions. J. Indian Chem. Soc. 2004, 81, 126−131. (19) Wang, J.; Yan, Z.; Lu, J. Effect of sodium caproate on the volumetric and viscometric properties of glycine, DL-α-alanine, and DL- α -amino n-butyric acid in aqueous solutions. J. Chem. Thermodyn. 2004, 36, 281−288. (20) Natarajan, M.; Wadi, R. K.; Gaur, H. C. Apparent Molar Volumes and Viscosities of Some α- and α, ω-Amino Acids in Aqueous Ammonium Chloride Solutions at 298.15 K. J. Chem. Eng. Data 1990, 35, 87−93. (21) Badarayani, R.; Kumar, A. Viscometric study of glycine, Lalanine, glycylglycine in aqueous tetra-n-alkylammonium bromide solutions at 298.15 K. J. Chem. Thermodyn. 2004, 36, 983−991. (22) Yan, Z.; Wang, J.; Liu, D.; Lu, J. Viscosity B-coefficients of some α-amino acids in aqueous guanidine hydrochloride solution from 278.15 to 308.15 K. Z. Phys. Chem. 1999, 211, 121−131. (23) Sinha, B.; Dakua, V. K.; Roy, M. N. Apparent molar volumes and viscosity B-coefficients of some amino acids in aqueous tetramethylammonium iodide solutions at 298.15 K. J. Chem. Eng. Data 2007, 52, 1768−1772.

B = (V1̅ 0 − V2̅ 0)/1000 + V1̅ 0(Δμ20 * − Δμ10 *)/1000RT (2)

V̅ 01

V̅ 02

where and are the mean volume of the solvent and partial molar volumes of the solute at infinite dilution. Δμ01* and Δμ02* are the free energy of activation per mole of the solvent and per mole of the solute, respectively. The free energy of activation per mole of the solvent and solute can further be calculated as follows.36 Δμ10 * = RT ln(η0V1̅ 0/hN )

(3)

Δμ10 * = Δμ10 * + RT[1000B − (V1̅ 0 − V2̅ 0)]/V1̅ 0

(4)

where η0 is the viscosity of the solvent, R is gas constant, h is Planck’s constant, and N is Avogadro’s number. The calculated values of V̅ 01, V̅ 02, Δμ01*, and Δμ02* at both temperatures are given in Table 4. From Table 4 we observe that glycine and L-alanine show large positive values of Δμ02* as compared to Δμ01* except for glycine in 0.2 mol kg−1 DKHP at (288.15, 298.15, and 318.15) K, glycine in 0.4 mol·kg−1 DKHP at higher temperatures, and −1 L-alanine in 0.6 mol·kg at low temperatures. The high values of Δμ02* as compared to Δμ01* indicate solute−solvent interactions which further suggests the smaller tendency toward the formation of transition state due to simultaneous breaking of intermolecular bonding in solvent molecules due to presence of amino acids. Feakins et al.33 in this transition state treatment also suggested that solute molecules having high values of Δμ02* will have high tendencies to act as a structure maker. From Table 4 it is clear that the values of Δμ02* for glycine and L-alanine are higher at higher concentrations of DKHP, and these also have negative dB/dT which supports that fact that glycine and L-alanine shows strong structure-making abilities in aqueous DKHP solutions.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Funding

One of the authors (K.K.) is thankful to The Director and Head, Department of Chemistry, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar for providing a MHRD fellowship. Notes

The authors declare no competing financial interest.

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REFERENCES

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