Article pubs.acs.org/jced
Densities and Speeds of Sound of Solutions of Glycine, L‑Alanine, and L‑Valine in Aqueous Ammonium Dihydrogen Phosphate at Different Temperatures Harsh Kumar* and Isha Behal Department of Chemistry, Dr B R Ambedkar National Institute of Technology, Jalandhar, Punjab 144011, India S Supporting Information *
ABSTRACT: Densities (ρ) and speeds of sound (c) of solutions of some α-amino acids such as glycine, L-alanine, and L-valine in aqueous ammonium dihydrogen phosphate (ADP) were measured at T = (288.15−318.15) K and experimental pressure p = 0.1 MPa. By using the experimentally measured densities, the apparent molar volume (Vϕ), the partial molar volume at infinite dilution (Voϕ), and partial molar volumes of transfer (ΔVoϕ), from water to aqueous ADP have been calculated. Further, apparent molar isentropic compression (Kϕ,s), partial molar isentropic compression at infinite dilution (koϕ,s) and partial molar isentropic compression of transfer o (ΔKϕ,s ) were calculated from the ultrasonic speeds. The group contributions of amino acid to partial molar volumes have also been discerned. From partial molar volumes of transfer and partial molar isentropic compression of transfer, the pair and triplet interaction coefficients are attained. We have also intended partial molar expansion (∂Voϕ/∂T)p and second order derivative (∂2Voϕ/∂T2)p. The achieved results are construed in terms of (solute + solvent) and (solute + solute) interactions accompanied by structure making and structure breaking behavior of amino acids in aqueous ADP solutions. biochemical studies.23−25The present work is just a continuation of our earlier laboratory work on the volumetric and ultrasonic properties of amino acids and peptides with phosphate salts of biological importance.26−29 To explore more on phosphate salts, we hereby delineate the densities and speeds of sound of glycine, L-alanine and L-valine in aqueous ammonium dihydrogen phosphate (ADP) solutions at different temperatures (288.15, 298.15, 308.15, and 318.15) K and atmospheric pressure. Ammonium dihydrogen phosphate (ADP) is also known as monoammonium phosphate (MAP) NH4H2PO4. ADP is often used in the blending of dry agricultural fertilizers. The compound is also a component of the ABC powder in some dry chemical fire extinguishers(ABC is a multipurpose dry chemical extinguishing agent used on class A, class B, and class C fires. It is a pale yellow powder that is able to put out all three classes of fire; Class A for trash, wood, and paper, Class B for liquids and gases, and Class C for energized electrical sources). This substance is also supplied in an emerald green, amethyst, or aquamarine crystal growing box kit for children. From the densities and speeds of sound, different physical parameters will be reviewed in terms of solute−solute and solute−solvent interactions which are significant to understand
1. INTRODUCTION Because of several particular interactions, it becomes onerous to perceive the interaction behavior of large biomolecules such as hormones, enzymes, and especially proteins. The stabilization or destabilization of the proteins is transmitted by the addition of specific molecules to protein solutions.1,2 Because of solvent effects or their direct binding, the protein conformation is sometimes influenced by these added cosolutes.3−7 The unmediated study of protein interactions is not feasible since the complex conformational and configurational factors strike the structure of proteins in solutions. Among the basic biomolecules, amino acids have intramolecular hydrogen bonds. Amino acids are low molar mass building blocks of more complex proteins and peptides that can be used for studying the solvation and conformational behavior of proteins.8,9 Estimable information is furnished on solute− solute and solute−solvent interactions by the physicochemical properties of amino acids in aqueous solutions that further helps in perceiving the stability of proteins and are implicated in several biochemical and physiological processes in a living cell.10 Ample research11−18 has been carried out on thermodynamic properties of amino acids in aqueous electrolyte solutions, carbohydrates, surfactants, etc. but the phosphates salts are still found in limited study.19−22 The phosphates are biologically and industrially important salts which are employed in food, cosmetics, and pharmaceutical industries and also in numerous © 2017 American Chemical Society
Received: March 14, 2017 Accepted: July 14, 2017 Published: July 27, 2017 3138
DOI: 10.1021/acs.jced.7b00257 J. Chem. Eng. Data 2017, 62, 3138−3150
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Table 1. Specification of Studied Chemicals
a
Declared by the supplier. Triple distilled and degassed water having specific conductance 0.99 mass fraction) and were used as received, without further purification. In order to avoid contamination due to moisture absorption, the chemicals used in the contemporary study were vacuum-dried over P2O5 in a desiccator for at least 48 h. The tabulated descriptions of the current bioactive chemicals are enumerated in Table 1. 2.2. Methods. We have used Anton Paar DSA 5000 M densimeter for measuring the density and speeds of sound of the samples prepared (using Sartorius CPA 225D balance having precision of ±0.00001 g) as described in the former study.30 In our earlier paper, details of the calibration and other procedures have also been specified.30 The speeds of sound measurements were done at a frequency of 3 MHz. The density and speeds of sound values are extremely sensitive to temperature, so it was controlled to ±1 × 10−3 K by a builtin Peltier device. The sensitivity of the instrument corresponds to a precision in density and speeds of sound measurements of 1 × 10−3 kg·m−3 and 1 × 10−2 m·s−1. The standard uncertainty of the density and speeds of sound are 0.05 kg·m−3 and 0.5 m· s−1, respectively.
1/2 ⎡ ∑4 (x − xi ,ref[22])2 ⎤ i = 1 i ,exp ⎢ ⎥ RMSD = ⎢⎣ ⎥⎦ 4
(1)
4
BIAS =
∑i = 1 (xi ,exp − xi ,ref[22]) (2)
4
where summations are performed over all four concentrations of ADP and x stands for density values (xi,ref[22] value from ref 22). The values come out to be 0.00029 kg·m−3, 0.00024 kg· m−3, 0.0003 kg·m−3, and 0.00037 kg·m−3 at 288.15, 298.15, 308.15, and 318.15 K, respectively. The values of RMSD and BIAS are identical. Besides this, exclusively positive values of BIAS indicate that measured data are systematically (in an average) higher than those taken from the literature.22 3.1.2. Apparent Molar Volume. The apparent molar volumes (Vϕ) are calculated from the experimental values of density (ρ) by using the following equation: Vϕ = (M /ρ) − {(ρ − ρο )/mA ρρο }
(3)
where M is the molar mass of the solute (kg·mol−1), mA is the molality (mol·kg−1) of the amino acids, that is, amount of solute (amino acids) per one kilogram of solvent (mixture of water + ADP), and ρo and ρ are the densities (kg·m−3) of the solvent and solution, respectively. The values of apparent molar volume along with densities are outlined in Table 2. The estimate of uncertainty values for Vϕ are ± (0.05−0.007) × 106 m3·mol−1. The positive Vϕ values demonstrate intense solute− solvent interactions between amino acids (NH+3 ,COO−) and ions of the phosphate salt which undergo primary, secondary, and tertiary dissociations in aqueous medium (i.e., NH4+, H2PO4−, HPO42−, PO43−). It might also be possible that the extreme interactions (attractive) could cause negative apparent
3. RESULTS AND DISCUSSION 3.1. Volumetric Properties. 3.1.1. Density. The experimental value of solution densities, ρ of glycine, L-alanine, and Lvaline in (0.5, 1.0, 1.5, 2.0) mol·kg−1 aqueous solutions of ADP were measured at temperatures T = (288.15, 298.15, 308.15, 318.15) K and are reported in Table 2.The experimental value of densities for aqueous solutions of ADP at different temperatures has been compared with literature values22 as reported in Table 2. Further, the quantitative comparison of 3139
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Table 2. Values of Densities, ρ, and Apparent Molar Volumes, Vϕ of Amino Acids in Aqueous Solutions of ADP at Different Temperatures and Experimental Pressure, p = 0.1 MPa ρ × 10−3/(kg·m−3)
mAa −1
(mol·kg )
T/K = 288.15
T/K = 298.15
T/K = 308.15
Vϕ × 106/(m3·mol−1) T/K = 318.15
T/K = 288.15
T/K = 298.15
T/K = 308.15
T/K = 318.15
44.89 44.95 45.02 45.10 45.18 45.25 45.34 45.44
45.17 45.22 45.30 45.38 45.45 45.53 45.62 45.72
45.42 45.46 45.53 45.61 45.69 45.77 45.86 45.97
46.09 46.13 46.19 46.27 46.35 46.43 46.51 46.60
46.35 46.41 46.49 46.58 46.67 46.75 46.86 46.98
46.66 46.72 46.81 46.90 46.98 47.06 47.15 47.26
47.25 47.29 47.36 47.44 47.53 47.61 47.69 47.77
47.47 47.51 47.59 47.67 47.75 47.84 47.93 48.01
47.77 47.82 47.91 47.99 48.08 48.15 48.24 48.33
48.46 48.52 48.59 48.68 48.75 48.82 48.91 49.02
48.65 48.71 48.79 48.88 48.97 49.05 49.15 49.25
48.93 48.98 49.06 49.14 49.22 49.32 49.43 49.55
61.49 61.52 61.58 61.66 61.74 61.80 61.89 61.99
61.73 61.75 61.80 61.86 61.92 61.98 62.07 62.16
61.93 61.96 62.03 62.11 62.18 62.26 62.34 62.45
62.65 62.68
62.91 62.93
63.12 63.15
−1
0.00000
1.029895 1.02960522 1.030187 1.030487 1.031082 1.031695 1.032275 1.032871 1.033568 1.034305
1.026926 1.02668422 1.027216 1.027512 1.028101 1.028708 1.029283 1.029873 1.030563 1.031291
1.057212 1.05692222 1.057484 1.057822 1.058347 1.058893 1.059458 1.059992 1.060640 1.061348
1.054111 1.05386922 1.054381 1.054716 1.055237 1.055779 1.056338 1.056867 1.057510 1.058214
1.082488 1.08219822 1.082782 1.083031 1.083540 1.084042 1.084562 1.085029 1.085674 1.086282
1.079387 1.07914522 1.079679 1.079927 1.080432 1.080930 1.081446 1.081909 1.082550 1.083159
0.01099 0.02028 0.04048 0.06058 0.08012 0.10077 0.12502 0.15043
1.105650 1.10536022 1.105913 1.106134 1.106612 1.107082 1.107535 1.108007 1.108553 1.109120
1.102498 1.10225622 1.102760 1.102980 1.103455 1.103922 1.104373 1.104845 1.105393 1.105956
0.00000 0.01031 0.02068 0.04119 0.05989 0.08031 0.10003 0.12507 0.14983
1.029895 1.030171 1.030448 1.030992 1.031484 1.032018 1.032528 1.033172 1.033802
1.026926 1.027201 1.027476 1.028017 1.028505 1.029034 1.029542 1.030180 1.030802
0.00000 0.01031 0.02164
1.057212 1.057463 1.057739
1.054111 1.054361 1.054635
0.00974 0.01977 0.03977 0.06053 0.08034 0.10082 0.12497 0.15071 0.00000 0.00967 0.02172 0.04059 0.06035 0.08092 0.10058 0.12459 0.15113 0.00000 0.01125 0.02084 0.04052 0.06008 0.08059 0.09917 0.12503 0.14982 0.00000
Glycine + 0.5 mol·kg ADP 1.019889 1.01951822 1.020174 44.58 1.020467 44.63 1.021048 44.70 1.021647 44.78 1.022213 44.85 1.022794 44.93 1.023474 45.02 1.024190 45.11 Glycine + 1.0 mol·kg−1 ADP 1.050638 1.046759 1.05030222 1.04638822 1.050906 1.047024 45.81 1.051238 1.047353 45.86 1.051754 1.047864 45.93 1.052290 1.048395 46.01 1.052843 1.048943 46.07 1.053367 1.049463 46.15 1.053999 1.050092 46.24 1.054690 1.050778 46.34 Glycine + 1.5 mol·kg−1 ADP 1.075632 1.071692 1.07529622 1.07132122 1.075922 1.071980 47.05 1.076169 1.072223 47.08 1.076671 1.072720 47.14 1.077165 1.073209 47.21 1.077678 1.073717 47.29 1.078138 1.074173 47.37 1.078774 1.074803 47.46 1.079378 1.075400 47.57 Glycine + 2.0 mol·kg−1 ADP 1.098679 1.094705 1.09834322 1.09433422 1.098940 1.094964 48.28 1.099159 1.095181 48.33 1.099631 1.095650 48.41 1.100096 1.096111 48.49 1.100543 1.096555 48.57 1.101011 1.097017 48.66 1.101553 1.097554 48.77 1.102115 1.098107 48.87 −1 L-Alanine + 0.5 mol·kg ADP 1.023680 1.019889 1.023953 1.020161 61.24 1.024227 1.020435 61.27 1.024766 1.020971 61.33 1.025254 1.021456 61.40 1.025783 1.021981 61.46 1.026290 1.022484 61.53 1.026926 1.023118 61.61 1.027548 1.023734 61.69 −1 L-Alanine +1.0 mol·kg ADP 1.050638 1.046759 1.050887 1.047007 62.44 1.051160 1.047279 62.47 1.023680 1.02334422 1.023967 1.024262 1.024846 1.025448 1.026019 1.026603 1.027288 1.028010
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Table 2. continued ρ × 10−3/(kg·m−3)
mAa (mol·kg−1)
T/K = 288.15
T/K = 298.15
Vϕ × 106/(m3·mol−1)
T/K = 308.15
T/K = 318.15
T/K = 288.15
+1.0 mol·kg−1 ADP 1.047714 62.53 1.048196 62.60 1.048667 62.67 1.049117 62.75 1.049682 62.83 1.050254 62.92 −1 L-Alanine + 1.5 mol·kg ADP 1.071692 1.071908 63.52 1.072120 63.56 1.072564 63.63 1.072982 63.71 1.073402 63.78 1.073814 63.86 1.074324 63.95 1.074836 64.05 −1 L-Alanine + 2.0 mol·kg ADP 1.094705 1.094904 64.75 1.095084 64.77 1.095468 64.82 1.095839 64.87 1.096210 64.93 1.096578 64.99 1.097029 65.07 1.097473 65.15 −1 L-Valine + 0.5 mol·kg ADP 1.019889 1.020126 91.15 1.020361 91.17 1.020820 91.21 1.021271 91.26 1.021731 91.31 1.022175 91.37 1.022737 91.45 1.023276 91.53 −1 L-Valine + 1.0 mol·kg ADP 1.046759 1.046970 92.64 1.047154 92.66 1.047547 92.71 1.047927 92.76 1.048310 92.82 1.048687 92.88 1.049149 92.96 1.049621 93.05 −1 L-Valine + 1.5 mol·kg ADP 1.071692 1.071864 94.22 1.072022 94.23 1.072330 94.26 1.072634 94.30 1.072941 94.34 1.073241 94.38 1.073619 94.44 1.073975 94.53
T/K = 298.15
T/K = 308.15
T/K = 318.15
62.75 62.81 62.88 62.95 63.03 63.12
62.98 63.05 63.13 63.20 63.28 63.36
63.22 63.28 63.35 63.43 63.52 63.60
63.79 63.82 63.88 63.94 64.01 64.08 64.16 64.24
63.99 64.02 64.09 64.16 64.23 64.31 64.39 64.47
64.17 64.21 64.28 64.36 64.44 64.52 64.61 64.70
64.95 64.97 65.03 65.09 65.16 65.23 65.32 65.42
65.16 65.20 65.27 65.35 65.42 65.49 65.57 65.66
65.33 65.36 65.43 65.50 65.58 65.65 65.74 65.82
91.53 91.55 91.60 91.65 91.71 91.77 91.85 91.93
91.94 91.97 92.04 92.09 92.17 92.25 92.33 92.42
92.40 92.42 92.48 92.54 92.59 92.65 92.73 92.81
92.98 93.01 93.07 93.13 93.18 93.25 93.33 93.42
93.42 93.44 93.49 93.55 93.60 93.67 93.74 93.81
93.80 93.84 93.91 93.99 94.07 94.15 94.25 94.34
94.55 94.57 94.63 94.69 94.75 94.82 94.89 94.97
94.99 95.01 95.06 95.12 95.18 95.23 95.30 95.38
95.45 95.46 95.50 95.56 95.61 95.67 95.74 95.81
L-Alanine
0.03991 0.06031 0.08046 0.09991 0.12455 0.14974
1.058179 1.058667 1.059144 1.059600 1.060172 1.060750
1.055074 1.055560 1.056035 1.056490 1.057061 1.057636
1.051597 1.052080 1.052552 1.053004 1.053572 1.054147
0.00000 0.00994 0.01973 0.04038 0.06007 0.08011 0.09997 0.12479 0.15003
1.082488 1.082707 1.082921 1.083369 1.083791 1.084217 1.084634 1.085149 1.085664
1.079387 1.079604 1.079817 1.080262 1.080683 1.081107 1.081522 1.082036 1.082553
1.075632 1.075849 1.076061 1.076505 1.076924 1.077346 1.077759 1.078271 1.078786
0.00000 0.01037 0.01978 0.04001 0.05980 0.07992 0.10006 0.12508 0.14997
1.105650 1.105851 1.106032 1.106418 1.106794 1.107170 1.107543 1.108000 1.108449
1.102498 1.102698 1.102878 1.103263 1.103636 1.104010 1.104379 1.104832 1.105273
1.098679 1.098878 1.099058 1.099441 1.099810 1.100182 1.100550 1.101002 1.101443
0.00000 0.01017 0.02025 0.04015 0.05985 0.08012 0.09989 0.12519 0.14976
1.029895 1.030139 1.030379 1.030851 1.031314 1.031787 1.032244 1.032821 1.033375
1.026926 1.027168 1.027406 1.027874 1.028333 1.028802 1.029254 1.029826 1.030375
1.023680 1.023920 1.024156 1.024619 1.025074 1.025536 1.025981 1.026546 1.027087
0.00000 0.01063 0.01999 0.04009 0.05982 0.07996 0.10001 0.12501 0.15082
1.057212 1.057428 1.057617 1.058020 1.058412 1.058807 1.059196 1.059675 1.060162
1.054111 1.054325 1.054513 1.054912 1.055301 1.055694 1.056079 1.056554 1.057036
1.050638 1.050850 1.051036 1.051432 1.051816 1.052206 1.052587 1.053059 1.053540
0.00000 0.01083 0.02077 0.04040 0.06001 0.08002 0.09986 0.12525 0.14949
1.082488 1.082665 1.082828 1.083146 1.083461 1.083779 1.084091 1.084485 1.084850
1.079387 1.079563 1.079724 1.080039 1.080349 1.080661 1.080966 1.081352 1.081713
1.075632 1.075806 1.075965 1.076277 1.076584 1.076893 1.077197 1.077579 1.077937
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Table 2. continued ρ × 10−3/(kg·m−3)
mAa (mol·kg−1)
T/K = 288.15
T/K = 298.15
Vϕ × 106/(m3·mol−1)
T/K = 308.15
T/K = 318.15
T/K = 288.15
+ 2.0 mol·kg−1 ADP 1.094705 1.094832 95.93 1.094943 95.96 1.095180 96.03 1.095406 96.10 1.095633 96.16 1.095850 96.22 1.096123 96.29 1.096382 96.37
T/K = 298.15
T/K = 308.15
T/K = 318.15
96.24 96.27 96.34 96.4 96.46 96.53 96.62 96.71
96.65 96.67 96.73 96.80 96.87 96.95 97.04 97.13
97.09 97.11 97.16 97.22 97.28 97.36 97.43 97.52
L-Valine
0.00000 0.01068 0.02014 0.04038 0.06010 0.08022 0.10006 0.12509 0.14974
1.105650 1.105781 1.105896 1.106138 1.106369 1.106602 1.106828 1.107108 1.107377
1.102498 1.102628 1.102742 1.102983 1.103213 1.103445 1.103668 1.103944 1.104208
1.098679 1.098807 1.098921 1.099159 1.099387 1.099616 1.099835 1.100107 1.100368
a mA is the molality of amino acid in aqueous ADP solutions; Standard uncertainties u are u(m) = 2 × 10−5 mol·kg−1, u(T) = 0.001 K, u(ρ) = 0.05 kg· m−3, and u(p) = 0.01 MPa.
molar volume, that is, decrease of volume on adding one mole of solute to the solution. In other words strong attractive interactions may over compensate volume increase caused by “hard core volume” of solute. The graphical representation of calculated apparent molar volumes is presented in Figures 1 and 2. Figure 1 represent the apparent molar volumes for amino acids in 0.5 mol·kg−1 aqueous solutions of ADP at different temperatures while Figure 2 represent the apparent molar volumes for amino acids in aqueous solutions of ADP at 298.15 K. The data reported in Table 2 and represented in Figures 1 and 2 implies that apparent molar volumes for glycine, L-alanine, and L-valine increase with increase in ADP concentration and temperature. It is also noticed that apparent molar volume increases with increase in molality of amino acid for a particular concentration of ADP. The increased value of Vϕ with temperature causes greater affinity for solvent and therefore intensifies pronounced interactions between the zwitterions of amino acids and ions of ADP. Furthermore, with an increase in the number of alkyl groups present in amino acids, the Vϕ values increase, that is, Vϕ value increases from glycine to L-valine at all temperatures and concentrations of ADP, which additionally intimate that amino acid−ADP interactions increase from glycine to L-alanine to L-valine at all temperatures as shown in Scheme 1. 3.1.3. Partial Molar Volume at Infinite Dilution. By using eq E1of the Supporting Information, the partial molar volume at infinite dilution Voϕ is calculated by means of least-squares fit of the Vϕ values. The values of Voϕ and SV* together with standard errors are outlined in Table S1 of the Supporting Information. Table S1 also reports the literature values31 of Voϕ for aqueous amino acids. It is expected that, because of enhanced amino acid−salt interactions, the positive Voϕ values increase with an increase in the ADP concentration and temperature for all amino acids as shown in Figure 3. Besides this, at each temperature, the Voϕ values increase with size of alkyl group, that is, increase in chain length of alkyl part from glycine to L-alanine to L-valine, which can probably be due to the larger hydrophobic/nonpolar character of the side chain of amino acids from glycine to L-alanine to L-valine causing greater electrostriction at the terminal charged groups and hence increase in Voϕ values. According to the cosphere overlap model,32,33 there is an increase in volume when the cospheres of two ionic species overlap, whereas volume decreases by an overlap of hydrophobic−hydrophobic groups and ion-hydrophobic groups. Therefore, the observed positive Voϕ values indicate ion−hydrophilic interactions that are stonger than
Figure 1. Apparent molar volume Vϕ for (a) glycine, (b) L-alanine, and (c) L-valine in 0.5 mol·kg−1 aqueous solutions of ADP at different temperatures: ◆, 288.15 K; ■, 298.15; ▲, 308.15 K; ●, 318.15 K.
ion−hydrophobic interactions and hydrophobic−hydrophobic interactions. Vital information on solute−solvent interactions occurring between amino acids and phosphate salt solute− solvent interactions is provided by the temperature dependence 3142
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Figure 3. Plot of variation of partial molar volumes for amino acids against temperature and molality of aqueous ADP: ●, glycine; ■, Lalanine, ▲, L-valine.
solvent, leading to the expansion of solution at higher temperature. An information about structural volume of solute in solvent and volume change of solvent in the process of shell formation around the ion34,35 is provided by partial molar volumes, which are known to be sensitive to solute solvation. In our current study, L-valine having the higher molar mass among the three has the highest values of Voϕ ; that is, Voϕ increases by increasing the molar mass and size of amino acid owing to the hydrophobic36−38 alkyl chain of the amino acids. It is perceived from Table S1 that the magnitude of SV* is positive for all concentrations of ADP at all temperatures. The solute−solute interactions in solution of amino acids in ADP are implied by the positive S*V values. The solute−solvent interactions dominate the solute−solute interactions as recommended by very small values of S*V as compared to Voϕ values. There are innumerable supplementary features which may influence the solute−solute interactions since the trend observed in SV* values is not very regular.39
Figure 2. Apparent molar volume Vϕ for glycine (blue), L-alanine (red), and L-valine (green) in aqueous solutions of ADP at T = 298.15 K: ⧫, 0.5 mol·kg−1; ●, 1.0 mol·kg−1; ▲, 1.5 mol·kg−1; ■, 2.0 mol·kg−1.
of the partial molar property since solute−solute interactions such as ion−ion or zwitterion−zwitterion interactions are negligible at infinite dilution. The various reasons that may be involved in the change of partial molar volume with temperature are thermal expansion, weakening of H-bond network, release of molecules from the solvation layers, etc. Here, the increase in Voϕ values with an increase in temperature for all amino acids may be justified as a release of some solvent molecules from the loose solvation layers of the solutes in solution. Further it can be elucidated by taking into account of the size of solvation layers (primary as well as secondary) around the zwitterions. The larger values of Voϕ at high temperature may be due to the release of the solvent from the secondary solvation layers of amino acid zwitterions to the bulk Scheme 1. Amino Acid and ADP Interactions
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3.1.4. Partial Molar Volume of Transfer. The utilization of eq E2 leads to the computation of transfer volume of amino acids from water to aqueous ADP solutions at infinite dilution. The transfer volumes are detailed in Table S2 of Supporting Information. From our already published work, we have taken the values of Voϕ for amino acids in water.31 The calculated values of ΔVoϕ as obtained in Table S2 are all positive and increase with an increase in ADP concentration. With an increase in temperature, the ΔVoϕ values decrease as shown in Figure 4.The noted positive values of ΔVoϕ conclude strong
interactions that may occur between amino acids and ADP molecules are distinguished as ion−hydrophilic interactions, hydrophilic−hydrophilic interactions, ion−hydrophobic interactions, and hydrophobic−hydrophobic interactions between various constituents of ADP and amino acids. As per the cosphere overlap model, a negative contribution is carried by ion−hydrophobic interactions and hydrophobic−hydrophobic interactions, whereas ion−hydrophilic and hydrophilic−hydrophilic interactions carry positive contribution toward ΔVϕo values. Hence, the dominance of ion−hydrophilic and hydrophilic−hydrophilic interactions over other interactions is reflected in our current study of amino acid + water + ADP mixtures. 3.1.5. Temperature-Dependent Partial Molar Volume at Infinite Dilution. The use of general polynomial eq E3 given in the Supporting Information leads to the study of variation of Voϕ with the temperature. The values of empirical constants for amino acids in aqueous ADP solutions are reported in Table S3 of the Supporting Information. The coefficient C, which is barely statistically significant, has positive values for all amino acids except in the case of glycine + 0.5 mol·kg−1 ADP and Lalanine in aqueous solutions of (0.5, 1.5, and 2.0) mol·kg−1 ADP. The positive values of C are simply a manifestation of scatter in the Voϕ values but very small values seem to give best fit of the data, which is evident from R2 values. Presumably, if the Voϕ data for amino acids were determined over a wider temperature range, then a negative value of C would ensue. Since the primary objective of the current Voϕ(T) study is to obtain limiting apparent molar expansivities, the current Voϕ results are deemed sufficient. The Voϕ values were also calculated by using empirical constants A, B, and C reported in Table S3 of the Supporting Information. In Table S3, we have also reported the standard deviations (σ) obtained from experimental Voϕ and Voϕ values obtained from empirical parameters using eq E4 of the Supporting Information. By using the relation E5 of the Supporting Information, the temperature dependence of apparent partial molar volume (Voϕ) can be expressed in terms of the absolute temperature (T).40 The Eoϕ values are reported in Table S4 of Supporting Information. At all temperatures and concentrations of ADP, the positive Eoϕ values have been found. As already indicated by apparent molar volume data, the positive Eoϕ values also signify the presence of interactions between amino acid zwitterions and solvated ions of phosphate salt in these mixtures. Although in some cases of aqueous amino acid solutions the negative values of Eoϕ have been obtained. The caging or packing effect41,42 points toward the positive Eoϕ values indicating the interactions between amino acid and ADP molecules. The Eoϕ values do not show a regular trend with an increase in the concentration of ADP solutions. 3.1.6. Group Contributions in Amino Acids. The study of the separate contributions of polar (NH+3 ,COO−) and nonpolar (CH2) groups toward Voϕ of the amino acids in aqueous solutions of ADP is very beneficial. The homologous series of amino acids having corresponding alkyl chains are −CH2− (glycine), −CHCH3− (L-alanine), and −CH(CH(CH3)2)− (Lvaline). The certain assumptions for the separate contribution of polar (NH+3 ,COO−) and nonpolar (CH2) groups toward Voϕ of the amino acids in aqueous solutions of ADP as proposed by Hakin et al.43,44 are provided in the eqs E6, E7, and E8 of the Supporting Information. The values are reported in Table S5 of the Supporting Information. The Voϕ(NH+3 ,COO−) values are
Figure 4. Variation of partial molar volume of transfer (ΔVoϕ) of (a) glycine, (b) L-alanine, (c) L-valine against temperature in aqueous solutions of ADP: ◆, 0.5 mol·kg−1; ■, 1.0 mol·kg−1; ▲, 1.5 mol·kg−1; ●, 2.0 mol·kg−1.
ion−ion interactions of ADP with all amino acids under study. The interactions between ADP and amino acids are enhanced as the structural moiety of ADP and amino acids contains polar groups which further promotes the structure maker ability of solute in the solution. Also, the observed positive values of transfer volume indicate structure promoter/maker nature of these solutes which is due to their solvophobic solvation as well as the structural interaction for two cospheres according to cosphere overlap model.32,33 The most probable different 3144
DOI: 10.1021/acs.jced.7b00257 J. Chem. Eng. Data 2017, 62, 3138−3150
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Table 3. Values of Speeds of Sound, c, and Apparent Molar Isentropic Compression, Kϕ,s of Amino Acids in Aqueous Solutions of ADP at Different Temperatures and Experimental Pressure, p = 0.1 MPa c/(m·s−1)
mAa −1
(mol·kg )
T/K = 288.15
T/K = 298.15
Kϕ,s × 106/(m3·mol−1·GPa−1)
T/K = 308.15
T/K = 318.15
T/K = 288.15
T/K = 298.15
T/K = 308.15
T/K = 318.15
−38.34 −40.45 −41.50 −41.87 −42.06 −42.19 −42.29 −42.38
−37.29 −39.35 −40.38 −40.74 −40.93 −41.05 −41.15 −41.23
−36.55 −38.59 −39.60 −39.96 −40.14 −40.26 −40.36 −40.44
−36.83 −38.94 −39.74 −40.06 −40.24 −40.34 −40.44 −40.52
−35.93 −38.00 −38.79 −39.09 −39.27 −39.37 −39.47 −39.54
−35.29 −37.34 −38.12 −38.43 −38.60 −38.70 −38.79 −38.87
−36.00 −37.37 −38.17 −38.46 −38.62 −38.71 −38.80 −38.87
−35.21 −36.57 −37.35 −37.64 −37.79 −37.89 −37.98 −38.04
−34.67 −36.01 −36.79 −37.07 −37.23 −37.32 −37.41 −37.48
−34.66 −35.95 −36.72 −36.99 −37.13 −37.23 −37.30 −37.36
−33.99 −35.27 −36.03 −36.30 −36.43 −36.53 −36.60 −36.66
−33.53 −34.80 −35.56 −35.82 −35.96 −36.05 −36.13 −36.19
−38.57 −40.54 −41.53 −41.86 −42.05 −42.17 −42.28 −42.36
−37.51 −39.44 −40.41 −40.73 −40.92 −41.03 −41.14 −41.22
−36.77 −38.67 −39.63 −39.94 −40.13 −40.25 −40.35 −40.43
−37.07 −38.93 −39.72 −40.05 −40.22 −40.33
−36.16 −37.99 −38.76 −39.09 −39.25 −39.36
−35.52 −37.33 −38.10 −38.42 −38.59 −38.69
−1
0.00000 0.00974 0.01977 0.03977 0.06053 0.08034 0.10082 0.12497 0.15071
1507.20 1508.20 1508.82 1510.20 1511.21 1511.88 1512.55 1514.05 1515.58
1534.68 1535.59 1536.17 1537.46 1538.36 1539.02 1539.72 1541.18 1542.49
1555.74 1556.58 1557.13 1558.35 1559.08 1559.81 1560.64 1561.79 1563.13
0.00000 0.00967 0.02172 0.04059 0.06035 0.08092 0.10058 0.12459 0.15113
1544.35 1544.88 1545.17 1546.33 1547.42 1548.34 1549.32 1550.89 1552.32
1569.47 1569.96 1570.23 1571.27 1572.26 1573.19 1574.12 1575.52 1576.87
1588.63 1589.07 1589.33 1590.32 1591.17 1592.14 1593.20 1594.28 1595.58
0.00000 0.01125 0.02084 0.04052 0.06008 0.08059 0.09917 0.12503 0.14982
1579.46 1579.96 1581.07 1581.93 1582.83 1583.77 1584.57 1586.69 1588.68
1602.24 1602.71 1603.78 1604.64 1605.45 1606.27 1607.04 1609.11 1611.01
1619.54 1619.98 1621.01 1621.79 1622.57 1623.37 1624.08 1625.99 1627.89
0.00000 0.01099 0.02028 0.04048 0.06058 0.08012 0.10077 0.12502 0.15043
1613.60 1614.52 1614.97 1616.16 1617.18 1618.29 1619.46 1620.47 1621.66
1634.12 1634.98 1635.41 1636.51 1637.51 1638.61 1639.62 1640.59 1641.68
1649.64 1650.45 1650.85 1651.84 1652.84 1653.93 1654.84 1655.87 1656.79
0.00000 0.01031 0.02068 0.04119 0.05989 0.08031 0.10003 0.12507 0.14983
1507.2 1508.36 1509.23 1510.50 1511.95 1513.26 1514.50 1516.75 1519.01
1534.68 1535.82 1536.37 1537.75 1539.08 1540.31 1541.43 1543.65 1545.78
1555.74 1556.81 1557.49 1558.59 1559.72 1561.00 1562.01 1564.12 1566.18
0.00000 0.01031 0.02164 0.03991 0.06031 0.08046 0.09991
1544.35 1545.74 1545.99 1547.55 1548.60 1549.92 1551.28
1569.47 1570.77 1571.01 1572.28 1573.55 1574.56 1575.86
1588.63 1589.82 1590.04 1591.14 1592.26 1593.55 1594.59
Glycine + 0.5 mol·kg ADP 1570.81 1571.61 −39.78 1572.14 −41.95 1573.31 −43.03 1574.49 −43.42 1575.75 −43.61 1577.15 −43.74 1577.56 −43.85 1577.92 −43.94 Glycine + 1.0 mol·kg−1 ADP 1602.26 1602.59 −38.06 1603.09 −40.23 1603.81 −41.05 1604.65 −41.38 1605.53 −41.56 1606.33 −41.67 1607.58 −41.77 1608.82 −41.85 Glycine + 1.5 mol·kg−1 ADP 1631.66 1632.54 −37.06 1633.03 −38.47 1633.67 −39.28 1634.54 −39.58 1635.27 −39.74 1635.99 −39.84 1637.89 −39.93 1639.70 −40.00 Glycine + 2.0 mol·kg−1 ADP 1660.38 1661.12 −35.56 1661.52 −36.88 1662.50 −37.67 1663.42 −37.94 1664.33 −38.08 1665.27 −38.18 1666.32 −38.26 1667.18 −38.32 −1 L-Alanine + 0.5 mol·kg ADP 1570.81 1571.84 −40.02 1572.49 −42.05 1573.49 −43.07 1574.71 −43.40 1576.05 −43.60 1576.73 −43.72 1578.67 −43.84 1580.75 −43.92 −1 L-Alanine + 1.0 mol·kg ADP 1602.26 1603.28 −38.31 1603.52 −40.22 1604.55 −41.03 1605.60 −41.37 1606.65 −41.54 1607.80 −41.65 3145
DOI: 10.1021/acs.jced.7b00257 J. Chem. Eng. Data 2017, 62, 3138−3150
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Table 3. continued c/(m·s−1)
mAa (mol·kg−1)
T/K = 288.15
T/K = 298.15
Kϕ,s × 106/(m3·mol−1·GPa−1)
T/K = 308.15
T/K = 318.15
T/K = 288.15
+ 1.0 mol·kg−1 ADP 1609.11 −41.75 1610.38 −41.82 −1 L-Alanine + 1.5 mol·kg ADP 1631.66 1632.70 −36.66 1633.30 −38.37 1634.39 −39.28 1635.28 −39.57 1636.64 −39.73 1637.84 −39.83 1638.97 −39.91 1640.07 −39.98 −1 L-Alanine + 2.0 mol·kg ADP 1660.38 1661.21 −35.43 1661.77 −36.88 1662.83 −37.69 1663.76 −37.97 1664.68 −38.11 1665.62 −38.20 1667.02 −38.28 1668.31 −38.34 −1 L-Valine + 0.5 mol·kg ADP 1570.81 1571.72 −39.96 1572.83 −42.00 1574.45 −43.04 1576.11 −43.40 1577.21 −43.59 1578.26 −43.71 1580.35 −43.82 1582.61 −43.90 −1 L-Valine + 1.0 mol·kg ADP 1602.26 1603.20 −38.42 1603.77 −40.07 1605.31 −41.03 1606.81 −41.36 1608.32 −41.53 1610.01 −41.64 1611.89 −41.73 1613.97 −41.80 −1 L-Valine +1.5 mol·kg ADP 1631.66 1633.02 −36.94 1633.94 −38.46 1635.29 −39.27 1636.63 −39.56 1637.97 −39.71 1639.24 −39.81 1641.22 −39.89 1643.24 −39.95 −1 L-Valine +2.0 mol·kg ADP 1660.38 1662.10 −35.48 1662.54 −36.86 1663.80 −37.65 1665.10 −37.91
T/K = 298.15
T/K = 308.15
T/K = 318.15
−40.42 −40.49
−39.45 −39.52
−38.78 −38.85
−35.60 −37.28 −38.16 −38.45 −38.60 −38.70 −38.79 −38.85
−34.82 −36.48 −37.34 −37.63 −37.78 −37.88 −37.96 −38.02
−34.28 −35.92 −36.79 −37.07 −37.22 −37.31 −37.40 −37.46
−34.49 −35.91 −36.71 −36.98 −37.12 −37.21 −37.28 −37.34
−33.82 −35.22 −36.01 −36.28 −36.42 −36.51 −36.58 −36.64
−33.36 −34.76 −35.54 −35.81 −35.95 −36.04 −36.11 −36.17
−38.52 −40.50 −41.50 −41.85 −42.04 −42.16 −42.26 −42.34
−37.46 −39.40 −40.38 −40.72 −40.91 −41.02 −41.12 −41.20
−36.71 −38.63 −39.60 −39.94 −40.12 −40.23 −40.34 −40.41
−37.17 −38.79 −39.72 −40.04 −40.21 −40.31 −40.40 −40.47
−36.26 −37.85 −38.76 −39.07 −39.24 −39.34 −39.43 −39.50
−35.62 −37.19 −38.10 −38.41 −38.57 −38.67 −38.76 −38.83
−35.88 −37.36 −38.16 −38.44 −38.59 −38.68 −38.76 −38.82
−35.10 −36.56 −37.34 −37.61 −37.76 −37.86 −37.94 −37.99
−34.55 −36.00 −36.78 −37.05 −37.20 −37.29 −37.37 −37.43
−34.58 −35.93 −36.71 −36.96
−33.91 −35.25 −36.01 −36.27
−33.45 −34.78 −35.54 −35.80
L-Alanine
0.12455 0.14974
1552.71 1554.43
1576.84 1578.80
1595.88 1597.31
0.00000 0.00994 0.01973 0.04038 0.06007 0.08011 0.09997 0.12479 0.15003
1579.46 1580.71 1581.46 1582.62 1583.88 1585.37 1586.97 1588.35 1589.72
1602.24 1603.42 1604.10 1605.28 1606.35 1607.72 1609.22 1610.57 1611.80
1619.54 1620.65 1621.31 1622.36 1623.39 1624.72 1626.10 1627.29 1628.47
0.00000 0.01037 0.01978 0.04001 0.05980 0.07992 0.10006 0.12508 0.14997
1613.60 1614.61 1615.27 1616.53 1617.71 1618.84 1620.00 1621.70 1623.24
1634.12 1635.31 1635.70 1636.89 1637.96 1639.09 1640.09 1641.63 1643.11
1649.64 1650.54 1651.13 1652.26 1653.25 1654.27 1655.23 1656.63 1658.08
0.00000 0.01017 0.02025 0.04015 0.05985 0.08012 0.09989 0.12519 0.14976
1507.20 1508.44 1509.27 1511.61 1514.02 1515.56 1517.02 1519.94 1522.77
1534.68 1535.79 1537.18 1538.48 1540.89 1542.29 1543.75 1546.22 1548.81
1555.74 1556.74 1558.07 1559.16 1561.44 1562.66 1563.79 1566.22 1568.62
0.00000 0.01063 0.01999 0.04009 0.05982 0.07996 0.10001 0.12501 0.15082
1544.35 1545.70 1546.51 1548.57 1550.49 1552.60 1554.64 1557.59 1560.41
1569.47 1570.68 1571.72 1573.29 1575.00 1577.16 1579.15 1581.60 1584.07
1588.63 1589.73 1590.38 1592.17 1593.79 1595.49 1597.18 1599.42 1601.51
0.00000 0.01083 0.02077 0.04040 0.06001 0.08002 0.09986 0.12525 0.14949
1579.46 1581.16 1582.36 1584.19 1585.96 1588.15 1590.18 1592.43 1594.56
1602.24 1603.8 1604.91 1606.86 1608.17 1610.21 1612.02 1614.01 1616.07
1619.54 1621.01 1622.01 1623.49 1624.98 1626.69 1628.48 1630.33 1632.18
0.00000 0.01068 0.02014 0.04038 0.06010
1613.6 1615.83 1616.37 1618.11 1619.70
1634.12 1636.35 1636.67 1638.26 1639.75
1649.64 1651.51 1651.98 1653.39 1654.82
3146
DOI: 10.1021/acs.jced.7b00257 J. Chem. Eng. Data 2017, 62, 3138−3150
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Table 3. continued c/(m·s−1)
mAa (mol·kg−1)
T/K = 288.15
T/K = 298.15
Kϕ,s × 106/(m3·mol−1·GPa−1)
T/K = 308.15
T/K = 318.15
L-Valine
0.08022 0.10006 0.12509 0.14974
1621.77 1623.80 1625.85 1627.87
1641.71 1643.47 1645.39 1647.20
1656.57 1658.23 1659.94 1661.60
T/K = 288.15
+2.0 mol·kg−1 ADP 1666.48 −38.05 1667.72 −38.14 1669.54 −38.21 1671.31 −38.26
T/K = 298.15
T/K = 308.15
T/K = 318.15
−37.10 −37.18 −37.26 −37.30
−36.40 −36.49 −36.56 −36.60
−35.93 −36.01 −36.08 −36.13
a mA is the molality of amino acids in aqueous ADP solutions; standard uncertainties u are u(m) = 2 × 10−5 mol·kg−1, u(T) = 0.001 K, u(c) = 0.5 m· s−1 and u (p) = 0.01 MPa
greater than Voϕ(CH2) values as reported by data represented in Table S5 and these values increase with increase in temperature for all amino acids in aqueous solutions of ADP. From these results, the interaction of amino acids with the ions of ADP is indicated, which causes reduction in the electrostriction of the solvent water and thereby contributes positive values of partial molar volumes. As surveyed from the table, the Voϕ(CH2) values do not change much with temperature in comparison to Vϕo (NH3+,COO−) which further leads to speculation that thermal expansibility of the hydrophobic CH2− group is low and that of the hydrophilic group (NH+3 ,COO−) is high.45 3.2. Ultrasonic Properties. 3.2.1. Speeds of Sound. The experimentally measured speeds of sound, c of glycine, Lalanine, and L-valine in (0.5, 1.0, 1.5, 2.0) mol·kg−1 aqueous solutions of ADP at temperatures T = (288.15, 298.15, 308.15, 318.15) K are listed in Table 3. From the table it is observed that speeds of sound of amino acids in aqueous solutions of ADP increase with increase in temperature and concentration of ADP. Also, for a particular concentration of ADP, speeds of sound increase with increase in molality of amino acid. 3.2.2. Apparent Molar Isentropic Compression. By using eq 4, the apparent molar isentropic compression for amino acids in aqueous and mixed aqueous solutions of ADP at different temperatures were determined Kϕ ,s = (Mκs/ρ) − {(ks,oρ − ksρo )/mA ρρo }
concentration of amino acids can be represented by using eq E9 of the Supporting Information. In Table S6 of the Supporting Information, the Koϕ,s and S*K values are reported along with standard errors determined using by least-squares fit. Table S6 also reports the literature values46 Koϕ,s for aqueous amino acids. The small SK* values predict that solute−solute interactions are negligible in comparison to solute−solvent interactions47 prevailing in the mixtures. With an increase in temperature and concentration of ADP, the negative values of Koϕ,s decrease. The more negative values of Koϕ,s at low temperature39 are attributed to strong attractive interactions between amino acid and water. Due to a decrease in electrostriction, the release of some water molecules is suggested by smaller Koϕ,s values at higher temperatures. The dehydration of amino acid is induced by the attractive interactions between ADP and water molecules, and therefore at high ADP concentrations the water molecules around the amino acids are more compressible than those at lower ADP concentrations. Using eq E10 of the Supporting Information, we have calculated the partial molar isentropic compressions of transfer (ΔKoϕ,s) of amino acid from water to aqueous ADP solutions at infinite dilution. From our earlier work, we have taken the values of Koϕ,s for amino acids in water.46 The values of ΔKoϕ,s at all concentrations of ADP, as reported in Table S7 of the Supporting Information, are all positive for each amino acid. It is inferred from the table that ΔKoϕ,s values increase with an increase in the concentration of ADP as also shown in Figure 5. o Further, the ΔKϕ,s values decrease with an increase in temperature, for all amino acids, at all concentrations of ADP. The interactions between the zwitterionic center of amino acid and ADP dominate as anticipated by positive values of ΔKoϕ,s indicating the structure making tendency of the ions. With the increase in concentration of ADP, electrostriction decreases and the structure making tendency of ions increase leading to the interaction between the zwitterionic center of amino acids and ADP. As a consequence, the electrostricted water is much less compressible than bulk water thereby leading to a large decrease in the compressibility with an increase in ADP concentration.48−50 Therefore, negative Koϕ,s values and positive ΔKoϕ,s values have been found for all amino acids with different concentrations of ADP. This is because more water molecules were associated with the ions at lower temperature as well as at lower concentrations of ADP. 3.3. Pair and Triplet Interaction Coefficients. On the basis of the McMillan−Mayer theory51 of solutions, the pair and triplet interaction coefficients have been calculated which permits the separation of effects due to interaction between the pairs of solute molecules and those due to its interaction between more than two solute molecules. Further discussed by Friedmann and Krishnan,52 the solute−cosolute interactions
(4)
where M, mA, ρo, and ρ have the same meaning as given in eq 1. κs,o and κs are the isentropic compressibility of pure solvent and solution, respectively. By using the following relation, the isentropic compression is calculated as
κs = 1/c 2ρ
(5)
where c is the speeds of sound and ρ is the density of the solution. The calculated values of Kϕ,s as well as speeds of sound values for molal concentrations (mA) of amino acids in (0.5, 1.0, 1.5, 2.0) mol·kg−1 ADP at different temperatures have been outlined in Table 3. The Kϕ,s values are negative at all temperatures and concentrations of ADP as spotted from the data revealed in Table 3. The Kϕ,s values become less negative with an increase in temperature. The water molecules in the bulk solution are more compressible than water molecules surrounding the ionic charged groups of amino acids as predicted by negative Kϕ,s values. This additionally indicates the strong solute−solvent interactions between ions of amino acid and salt molecules being due to the ordering of water molecules around the solute (or the negative Kϕ,s values indicate greater loss of structural compressibility of water implying a greater ordering effect by the solute on the solvent). 3.2.3. Partial Molar Isentropic Compression. The variation of apparent molar isentropic compression Kϕ,s with the molal 3147
DOI: 10.1021/acs.jced.7b00257 J. Chem. Eng. Data 2017, 62, 3138−3150
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4. CONCLUSIONS Thermodynamic studies such as density and speed of sound measurements provide information regarding the interactions that may occur in the mixtures. The presence of strong solute− solvent interactions {between amino acids (NH+3 ,COO−) and ions of the salt which undergo primary, secondary, and tertiary dissociations in aqueous medium (i.e NH4+, H2PO4−, HPO42−, PO43−)} are anticipated by apparent molar properties and partial molar properties in the studied ternary mixtures. The level of interaction increases with an increase in the concentration of ADP solution and increase in the molar mass of amino acids; that is, the solute−solvent interactions increase from glycine to L-alanine to L-valine. It has been found that with increase in concentration of ADP, the contributions of zwitterionic (NH+3 ,COO−) groups to the value of the partial molar volumes Voϕ increase. The structure-making property of amino acids in ADP solution is shown by the second derivative of temperature (∂2Voϕ/∂T2)p. On further interpreting the results, the ion−hydrophilic and hydrophilic−hydrophilic interactions are found to dominate the hydrophobic−hydrophobic and ion−hydrophobic interactions in the ternary system with the explication of solute−solvent interactions in the system.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00257. Equations and tables for partial molar volume at infinite dilution, partial molar volume of transfer, temperature dependence of partial molar volume at infinite dilution, group contributions in amino acids, partial molar isentropic compression, partial molar isentropic compression of transfer, pair and triplet interaction coefficients (PDF)
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AUTHOR INFORMATION
Corresponding Author
Figure 5. Variation of partial molar isentropic compression of transfer (ΔKoϕ,s) of (a) glycine, (b) L-alanine, (c) L-valine against temperature in aqueous solutions of ADP: [◆, 0.5 mol·kg−1; ■, 1.0 mol·kg−1; ▲, 1.5 mol·kg−1; ●, 2.0 mol·kg−1].
*E-mail:
[email protected];
[email protected]. ORCID
Harsh Kumar: 0000-0003-3874-4614 Funding
can be included in the solvation spheres. By employing eqs E11 and E12 of the Supporting Information partial molar volume of transfer and partial molar isentropic compression of transfer can be expressed. The pair and triplet interaction coefficients are described by the corresponding parameters VAB, VABB for volume and KAB, KABB for isentropic compression. By fitting ΔVoϕ and ΔKoϕ,s values to the above equations, the values of these parameters obtained are reported in Table S8 of the Supporting Information. The positive values have been observed for the pair interaction coefficients VAB and KAB, whereas triplet interaction coefficients VABB and KABB are negative at all temperatures (except for positive VABB values of L-valine). The higher positive values of pair interaction coefficients VAB as compared to negative values of VABB for amino acids conclude the overlap of hydration spheres53 of solute−cosolute molecules which may lead to the interactions. The positive values of pair interaction coefficient for volumetric and compressibility measurements illustrate the dominance of pairwise interactions in the ternary mixtures.
Isha Behal thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, for providing Senior Research Fellowship (SRF)vide sanction order no. (09/1127(0001)/ 2014-EMR-I). Notes
The authors declare no competing financial interest.
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