Volumetric and Viscometric Studies of Amino Acids in Vitamin B6

Article pubs.acs.org/jced

Volumetric and Viscometric Studies of Amino Acids in Vitamin B6 Aqueous Solutions at Various Temperatures Daofan Ma,† Xiaofeng Jiang,‡ Guoqiang Wei,*,† and Chunying Zhu*,‡ †

School of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, P. R. China School of Chemical Engineering and Technology, Collaborative Innovation Center of Chemical Science and Engineering, State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072, P. R. China

‡

S Supporting Information *

ABSTRACT: The densities and viscosities of glycine, L-alanine, L-valine, L-threonine, and L-arginine in (0.1 to 0.4) mol·kg−1 vitamin B6 aqueous solutions were measured and studied over the entire molality range at (293.15, 303.15, 313.15, and 323.15) K and atmospheric pressure. The apparent molar volume (Vϕ), limiting partial molar volume (V0ϕ), and limiting partial molar volume of transfer (ΔtrV0ϕ) were obtained according to the experimental density data. The viscosity data were employed to 0⇌ determine the viscosity B coefficients, the free energies of activation per mole of solvent (Δμ0⇌ 1 ) and solute (Δμ2 ). The influences of temperature, molality, and solute structure on these parameters were discussed in terms of molecular interactions. The contributions of the charged end group (NH3+, COO−) and CH2 group to the limiting partial molar volumes and viscosity B coefficients were obtained through their linear correlation as a function of the number of carbon atoms in the alkyl chains of the studied amino acids. widely studied by many researchers.12−17 However, to our best knowledge, so far no experimental work has been devoted to the thermodynamic properties of amino acids in vitamin B6 aqueous solutions. As a continuation of volumetric and viscometric studies on amino acids in vitamin aqueous solutions,18−21 we present here the densities and viscosities of glycine, L-alanine, L-valine, Lthreonine, and L-arginine in vitamin B6 aqueous solutions at T = (293.15 to 323.15) K with 10 K intervals, covering the entire composition range expressed by the molality of solute and solvent. Meanwhile, the apparent molar volume, limiting partial molar volume, and limiting partial molar volume of transfer were calculated from the density data, and the viscosity B coefficients and free energies of activation per mole of solvent (Δμ0⇌ 1 ) and solute (Δμ20⇌) were obtained by the viscosity data. The influences of the concentration and the temperature on these parameters were analyzed and discussed from the viewpoint of

1. INTRODUCTION The vitamin B complexes as essential micronutrients play a vital role in the metabolism of human and animals. Usually, they are water-soluble and are based mainly on the pyridine ring as their molecular structures.1 An improper intake of vitamin B could affect detrimentally the metabolism of sugar, fat, and protein, and even bring about neurologic disorders2 and the decay of the immune function.3,4 As is well-known, vitamin B6, a general name given to pyridoxine, pyridoxamine, pyridoxal, and their phosphorylated derivatives,5,6 is one of the most important vitamins among all vitamin B complexes because of its wide functions in various systems of the body (immune system, nervous system, lipid metabolism, gluconeogenesis, hormone modulation, niacin formation, gene expression).7 It participates in more than 100 enzymatic reactions in which the most striking function lies in its service as a cofactor for enzymes during the biosynthesis process of amino acid.8,9 Accordingly the study on the vitamin B6 system has become an interesting subject. Banipal10 and Dhondge11 have studied the volumetric and viscometric properties of vitamin B6 aqueous solutions, respectively. As an ideal model of protein, amino acid has been © XXXX American Chemical Society

Received: October 21, 2014 Accepted: March 31, 2015

A

DOI: 10.1021/je500975a J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

the efflux time. Until thermal equilibrium was reached, the efflux time of the liquids was automatically recorded in triplicate with a precision of ± 0.01 s. The average of at least three experiments reproducible values within 0.2 s was pinpointed as the final efflux time for each sample. Each capillary was calibrated by using double-distilled water (deionized and degassed) before the measurements. The viscosity values of pure water for calibration were (1.002, 0.7977, 0.6532, and 0.5470) mPa·s at temperatures of (293.15, 303.15, 313.15, and 323.15) K, respectively.23 The viscosities η of the solutions were calculated from the following equation:24,25

solute−solvent interactions. On the basis of the group analyses scheme, the limiting partial molar volumes and viscosity B coefficients were split into contributions from the zwitterionic end groups (NH3+, COO−) and CH2 group.

2. EXPERIMENTAL SECTION 2.1. Materials. The vitamin B6 (3-hydroxy-4,5-bis(hydroxymethyl)2-methylpyridine hydrochloride), was of analytical reagent grade and supplied by Aladdin, P. R. China. Glycine, L-alanine, L-valine, L-threonine, and L-arginine were purchased from Zhengzhou Jianda Chemicals, Inc., and their mass purities are all better than 99 %. The detailed specifications of these compounds are shown in Table 1. Prior to measurement,

η /ηw = ρt /ρw tw

where η, ρ, t and ηw, ρw, tw are viscosities, densities, and flow times of the solutions and pure water, respectively. The uncertainty of the experimental viscosities is ± 1 % mPa·s.

Table 1. Specification of Studied Chemicals

a

chemical name

CAS No.

molar wt/(g·mol )

source

vitamin B6

58-56-0

205.64

glycine

56-40-6

75.07

L-alanine

56-41-7

89.09

L-valine

72-18-4

117.15

L-threonine

72-19-5

119.12

L-arginine

74-79-3

174.20

Aladdin Chemical Reagent Co., Ltd. Zhengzhou Jianda Chemicals Inc. Zhengzhou Jianda Chemicals, Inc. Zhengzhou Jianda Chemicals, Inc. Zhengzhou Jianda Chemicals, Inc. Zhengzhou Jianda Chemicals, Inc.

−1

(1)

mass fraction puritya

3. RESULTS AND DISCUSSION 3.1. Density Correlation. The experimental densities of glycine, L-alanine, L-valine, L-threonine, and L-arginine in vitamin B6 aqueous solutions at T = (293.15, 303.15, 313.15 and 323.15) K are listed in Table 2. The comparison between experimental densities and viscosities of vitamin B6 aqueous solutions and the literature values is given in the Supporting Information (Figure S1). The variation tendencies of experimental densities and viscosities with molality show good agreement with literature values. It could be seen from Table 2 that the densities of all solutions increase with the molality of glycine, L-alanine, L-valine, Lthreonine, and L-arginine but decrease with increasing temperature. For the same solute, the densities increase monotonously with the molality of vitamin B6. While for the same molality of vitamin B6, the densities of all solutions increase with the molar weight of amino acids (see Figure 1). Figure 1 vividly presents the relationship of the densities of glycine, L-alanine, L-valine, L-threonine, and L-arginine versus temperature and solute molar concentration. It could be observed that from Figure 1, the densities of solutions show a very good linear relationship to the molar concentration of amino acids. Thus, the Guimarães equation26 was applied to correlate the experimental density data, ρ = A1 + A 2 T + A3C (2)

≥ 0.99 ≥ 0.99 ≥ 0.99 ≥ 0.99 ≥ 0.99 ≥ 0.99

Declared by the supplier.

the studied chemicals were subjected to vacuum at moderate temperature (T = 313.15 K) for 48 h in order to remove water. Doubly distilled water was used in the experiment. All solutions of the desired compositions were prepared by mass at room temperature, using an analytical balance (FA2204B, Shanghai Jingke, P.R. China) with uncertainty of ± 0.0001 g. The molality range of vitamin B6 is from (0.1 to 0.4) mol·kg−1 and the solutes (glycine, L-alanine, L-threonine, and L-arginine) are from 0.0 to 0.7 mol·kg−1, both with an interval of 0.1 mol·kg−1. L-Valine determinations were conducted in the molality range of (0.0 to 0.5) mol·kg−1, considering the low solubility of this material. 2.2. Density Measurement. An anton-Paar DMA 4500 M vibrating tube densimeter22 was employed to measure the densities of binary mixtures (glycine/L-alanine/L-valine/Lthreonine/L-arginine + water) and ternary mixtures (glycine/Lalanine/L-valine/L-threonine/L-arginine + vitamin B6 + water). The temperature in the measurement cell was automatically regulated to ± 0.02 K, and the accuracy in the density measurement was ± 5·10−5 g·cm−3. The apparatus was calibrated once a day with double-distilled water (deionized and degassed) and dry air for the temperature range investigated. Triplicate measurements were performed for each sample at each mentioned temperature. 2.3. Viscosity Measurement. The viscosity measurements of mixtures were operated through an iVsic capillary viscometer (LAUDA, Germany). The viscometer filled with experimental solutions was vertically immersed in a DLK thermostat (LAUDA, Germany) and the environmental temperature of the capillary was maintained constantly within ± 0.02 K. The equipment was connected to a PC-controlled Processor Viscosity System (PVS) unit for the precise measurement of

where T is the temperature, and A1, A2, and A3 are the empirical constants. C is the molar concentration of amino acids in vitamin B6 aqueous solutions at 293.15 K, converted from molality (m) by means of density. The fitting parameters, A1, A2, and A3 are shown in Table 3 alongside the values of standard deviation (SD) and the average deviation (AD). The standard deviation (SD) and the average deviation (AD) were calculated as follows: n

SD = [∑ (yexp, i − ycal, i )2 /(n − m)]1/2 i=1

AD =

1 n

(3)

n

∑ |(yexp,i − ycal,i )/yexp,i | i=1

(4)

where n is the total number of experimental data points and m is the number of parameters. yexp,i and ycal,i refer to the experimental values and the calculated values, respectively. From Table 3, the maximum values of AD and SD are 0.060 % and 0.0007 g·cm−3, respectively. B



Article

Table 2. Densities (ρ), Viscosities (η), and Apparent Molar Volumes (Vϕ) of Glycine, L-Alanine, L-Valine, L-Threonine, and LArginine in Vitamin B6 Aqueous Solutions at T = (293.15, 303.15, 313.15 and 323.15) K and Pressure p = 101.3 kPaa T/K = 293.15 m mol·kg

ρ

C −1

mol·L

−1

T/K = 303.15

η −3

g·cm

mPa·s

ρ

Vϕ cm ·mol 3

−1

T/K = 313.15

η −3

g·cm

mPa·s

ρ

Vϕ cm ·mol 3

−1

T/K = 323.15

η −3

ρ

Vϕ −1

−3

η

Vϕ

mPa·s

cm ·mol−1

mPa·s

cm ·mol

0.99807 1.00118 1.00418 1.00718 1.01013 1.01303 1.01589 1.01872

0.680 0.689 0.698 0.708 0.718 0.728 0.739 0.749

44.18 44.25 44.34 44.42 44.52 44.60 44.68

0.99382 0.99689 0.99986 1.00282 1.00575 1.00863 1.01147 1.01429

0.568 0.576 0.584 0.592 0.601 0.610 0.618 0.627

44.65 44.71 44.77 44.84 44.90 44.96 45.02

1.00369 1.00675 1.00976 1.01273 1.01565 1.01853 1.02138 1.02420

0.703 0.713 0.723 0.734 0.745 0.756 0.768 0.780

44.36 44.44 44.52 44.59 44.66 44.74 44.82

0.99939 1.00240 1.00537 1.00831 1.01120 1.01405 1.01688 1.01968

0.587 0.596 0.605 0.614 0.624 0.633 0.643 0.652

44.87 44.92 44.98 45.02 45.08 45.13 45.18

1.00918 1.01219 1.01517 1.01809 1.02097 1.02380 1.02662 1.02937

0.729 0.741 0.752 0.763 0.775 0.786 0.798 0.809

44.65 44.73 44.82 44.92 45.02 45.08 45.16

1.00486 1.00782 1.01076 1.01365 1.01649 1.01931 1.02209 1.02481

0.607 0.617 0.627 0.637 0.647 0.656 0.666 0.675

45.18 45.23 45.30 45.38 45.42 45.50 45.57

1.01448 1.01747 1.02041 1.02331 1.02618 1.02902 1.03179 1.03454

0.755 0.768 0.780 0.793 0.807 0.818 0.831 0.843

44.91 44.96 45.02 45.07 45.13 45.20 45.26

1.01006 1.01300 1.01591 1.01877 1.02160 1.02443 1.02718 1.02991

0.628 0.639 0.650 0.661 0.672 0.683 0.694 0.704

45.41 45.44 45.48 45.52 45.54 45.59 45.62

0.99811 1.00088 1.00360 1.00629 1.00889 1.01144 1.01399 1.01644

0.679 0.694 0.709 0.725 0.741 0.758 0.777 0.794

61.31 61.39 61.43 61.54 61.67 61.72 61.83

0.99387 0.99662 0.99931 1.00196 1.00453 1.00707 1.00958 1.01202

0.568 0.579 0.591 0.604 0.617 0.631 0.645 0.659

61.69 61.79 61.88 61.98 62.08 62.16 62.24

1.00373 1.00646 1.00915 1.01177 1.01436 1.01689 1.01940 1.02184

0.703 0.719 0.735 0.753 0.770 0.789 0.809 0.828

61.47 61.55 61.66 61.74 61.83 61.89 61.97

0.99936 1.00207 1.00473 1.00733 1.00991 1.01242 1.01490 1.01733

0.587 0.599 0.612 0.626 0.640 0.655 0.670 0.685

61.89 61.97 62.05 62.11 62.20 62.27 62.34

g·cm

3

g·cm

3

Glycine in Vitamin B6 Aqueous Solution 0.0000 0.1009 0.1999 0.3001 0.4003 0.5002 0.6000 0.7003

0.0000 0.1009 0.1990 0.2975 0.3951 0.4915 0.5870 0.6822

1.00422 1.00744 1.01053 1.01361 1.01663 1.01959 1.02250 1.02537

1.047 1.059 1.072 1.086 1.101 1.116 1.132 1.149

43.05 43.19 43.33 43.48 43.62 43.76 43.89

1.00158 1.00474 1.00779 1.01083 1.01381 1.01675 1.01962 1.02246

0.0000 0.1002 0.2001 0.3003 0.4000 0.4999 0.6000 0.7003

0.0000 0.1008 0.2003 0.2994 0.3970 0.4940 0.5903 0.6860

1.01005 1.01321 1.01631 1.01936 1.02235 1.02528 1.02817 1.03102

1.083 1.097 1.112 1.128 1.144 1.161 1.178 1.195

43.25 43.39 43.52 43.66 43.79 43.93 44.06

1.00729 1.01040 1.01345 1.01647 1.01942 1.02232 1.02519 1.02803

0.0000 0.0999 0.2000 0.3000 0.4001 0.5000 0.6003 0.6999

0.0000 0.1010 0.2013 0.3007 0.3992 0.4966 0.5936 0.6891

1.01552 1.01864 1.02171 1.02473 1.02771 1.03062 1.03350 1.03631

1.128 1.144 1.160 1.176 1.192 1.209 1.225 1.242

43.49 43.62 43.74 43.85 43.98 44.09 44.22

1.01281 1.01588 1.01891 1.02188 1.02480 1.02768 1.03051 1.03329

43.76 43.91 44.06 44.22 44.36 44.51 44.66

1.01820 1.02124 1.02423 1.02716 1.03005 1.03290 1.03568 1.03843

0.0000 0.1002 0.2002 0.3000 0.4000 0.5006 0.6000 0.6998 L-Alanine

0.0000 0.1019 0.2026 0.3022 0.4012 0.4998 0.5964 0.6925 in Vitamin

1.02112 1.02422 1.02725 1.03021 1.03312 1.03600 1.03879 1.04153 B6 Aqueous

1.169 1.187 1.205 1.222 1.241 1.259 1.277 1.295 Solution

0.0000 0.1003 0.2002 0.3005 0.4001 0.5005 0.6005 0.6998

0.0000 0.1002 0.1986 0.2964 0.3922 0.4872 0.5817 0.6739

1.00423 1.00709 1.00987 1.01262 1.01530 1.01793 1.02054 1.02307

1.047 1.071 1.098 1.124 1.151 1.180 1.210 1.240

60.35 60.45 60.55 60.63 60.72 60.81 60.88

1.00159 1.00441 1.00715 1.00986 1.01250 1.01510 1.01767 1.02016

0.0000 0.1003 0.2002 0.3000 0.4002 0.5002 0.6004 0.7002

0.0000 0.1004 0.1998 0.2975 0.3945 0.4902 0.5848 0.6780

1.01005 1.01286 1.01562 1.01832 1.02098 1.02359 1.02616 1.02867

1.083 1.109 1.138 1.168 1.199 1.230 1.263 1.297

60.50 60.60 60.69 60.77 60.85 60.93 61.01

1.00730 1.01007 1.01279 1.01544 1.01807 1.02063 1.02317 1.02564

ma = 0.1000 0.832 0.843 0.853 0.865 0.877 0.889 0.902 0.915 ma = 0.2000 0.860 0.872 0.884 0.897 0.910 0.924 0.938 0.952 ma = 0.3000 0.895 0.908 0.921 0.934 0.948 0.961 0.975 0.989 ma = 0.4000 0.925 0.941 0.955 0.970 0.985 1.000 1.014 1.029

mol·kg−1

ma = 0.1000 0.832 0.850 0.870 0.890 0.911 0.934 0.955 0.979 ma = 0.2000 0.861 0.881 0.902 0.924 0.948 0.972 0.997 1.024

mol·kg−1

C

43.61 43.72 43.83 43.95 44.06 44.18 44.30 mol·kg−1 43.80 43.90 44.01 44.12 44.23 44.33 44.42 mol·kg−1 44.05 44.16 44.28 44.38 44.48 44.60 44.70 mol·kg−1 44.31 44.42 44.53 44.64 44.76 44.86 44.96

60.83 60.92 61.01 61.11 61.19 61.28 61.37 mol·kg−1 60.99 61.08 61.19 61.25 61.35 61.43 61.51



Article

Table 2. continued T/K = 293.15

T/K = 303.15

T/K = 313.15

T/K = 323.15

m

C

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

mol·kg−1

mol·L−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

1.00919 1.01190 1.01454 1.01712 1.01966 1.02215 1.02461 1.02700

0.729 0.746 0.764 0.781 0.800 0.819 0.838 0.857

61.68 61.76 61.86 61.94 62.04 62.10 62.18

1.00484 1.00752 1.01013 1.01268 1.01520 1.01767 1.02010 1.02248

0.607 0.620 0.634 0.648 0.662 0.676 0.691 0.706

62.16 62.23 62.30 62.38 62.45 62.53 62.60

1.01454 1.01720 1.01981 1.02235 1.02485 1.02732 1.02973 1.03209

0.755 0.773 0.792 0.812 0.832 0.852 0.873 0.895

61.89 61.97 62.06 62.14 62.22 62.28 62.37

1.01010 1.01273 1.01531 1.01783 1.02030 1.02273 1.02512 1.02747

0.628 0.643 0.658 0.673 0.689 0.705 0.721 0.738

62.34 62.42 62.50 62.59 62.67 62.75 62.80

0.99815 1.00069 1.00317 1.00558 1.00792 1.01020

0.680 0.706 0.731 0.757 0.785 0.814

91.59 91.71 91.82 91.94 92.07

0.99388 0.99638 0.99882 1.00119 1.00350 1.00575

0.568 0.587 0.607 0.628 0.648 0.670

92.35 92.44 92.52 92.62 92.74

1.00372 1.00621 1.00862 1.01095 1.01324 1.01545

0.703 0.729 0.757 0.785 0.814 0.845

91.78 91.94 92.11 92.23 92.34

0.99936 1.00181 1.00418 1.00649 1.00874 1.01091

0.587 0.608 0.629 0.650 0.672 0.694

92.56 92.66 92.76 92.89 93.03

1.00918 1.01163 1.01398 1.01627 1.01849 1.02064

0.729 0.757 0.786 0.816 0.847 0.879

91.93 92.08 92.22 92.38 92.52

1.00479 1.00719 1.00951 1.01177 1.01397 1.01610

0.608 0.630 0.653 0.676 0.700 0.724

92.68 92.81 92.91 93.03 93.14

1.01452 1.01690 1.01921 1.02145 1.02362 1.02572

0.754 0.784 0.816 0.848 0.882 0.916

92.15 92.28 92.43 92.56 92.70

1.01008 1.01241 1.01468 1.01687 1.01901 1.02108

0.628 0.652 0.676 0.701 0.727 0.753

92.91 93.05 93.17 93.30 93.41

0.99807 1.00215 1.00614 1.01006 1.01389 1.01765 1.02133 1.02496

0.680 0.700 0.722 0.744 0.766 0.790 0.813 0.838

78.14 78.24 78.33 78.41 78.50 78.59 78.68

0.99378 0.99783 1.00179 1.00568 1.00948 1.01321 1.01686 1.02045

0.567 0.584 0.601 0.619 0.637 0.655 0.674 0.693

78.62 78.70 78.80 78.89 78.99 79.09 79.17

0.0000 0.1005 0.2006 0.3001 0.4000 0.5004 0.6002 0.6997

0.0000 0.1015 0.2012 0.2992 0.3966 0.4925 0.5877 0.6810

1.01563 1.01842 1.02115 1.02381 1.02644 1.02901 1.03155 1.03401

1.129 1.158 1.187 1.218 1.251 1.284 1.318 1.353

0.0000 0.0000 1.02116 1.169 0.1003 0.1018 1.02390 1.202 0.2006 0.2023 1.02660 1.234 0.3003 0.3010 1.02922 1.268 0.4001 0.3986 1.03180 1.302 0.5004 0.4955 1.03435 1.337 0.6003 0.5908 1.03683 1.375 0.7000 0.6848 1.03926 1.413 L-Valine in Vitamin B6 Aqueous Solution

60.61 60.71 60.79 60.87 60.96 61.05 61.14

1.01283 1.01558 1.01826 1.02087 1.02345 1.02597 1.02846 1.03088

60.82 60.91 61.01 61.10 61.18 61.27 61.35

1.01823 1.02093 1.02358 1.02616 1.02869 1.03118 1.03363 1.03601

ma = 0.3000 0.896 0.917 0.941 0.962 0.987 1.012 1.038 1.063 ma = 0.4000 0.926 0.949 0.973 0.999 1.024 1.052 1.080 1.108

mol·kg−1

mol·kg−1

mol·kg−1

0.0000 0.1000 0.2001 0.3001 0.4000 0.5000

0.0000 0.0995 0.1974 0.2934 0.3876 0.4802

1.00426 1.00689 1.00946 1.01195 1.01437 1.01673

1.047 1.089 1.135 1.183 1.235 1.289

90.33 90.45 90.58 90.69 90.81

1.00162 1.00421 1.00673 1.00918 1.01155 1.01386

0.0000 0.1002 0.2001 0.2999 0.4002 0.5001

0.0000 0.1003 0.1985 0.2948 0.3899 0.4829

1.01003 1.01261 1.01512 1.01756 1.01994 1.02225

1.083 1.127 1.177 1.230 1.286 1.344

90.48 90.60 90.70 90.82 90.93

1.00728 1.00982 1.01228 1.01466 1.01699 1.01921

0.0000 0.1005 0.2002 0.3000 0.4002 0.4999

0.0000 0.1011 0.1997 0.2965 0.3919 0.4852

1.01558 1.01812 1.02057 1.02294 1.02526 1.02750

1.129 1.177 1.229 1.283 1.341 1.402

90.59 90.75 90.89 91.02 91.16

1.01284 1.01534 1.01774 1.02006 1.02232 1.02449

90.80 90.94 91.08 91.22 91.35

1.01822 1.02065 1.02300 1.02528 1.02749 1.02962

ma = 0.1000 0.832 0.865 0.898 0.933 0.970 1.009 ma = 0.2000 0.860 0.894 0.931 0.969 1.009 1.051 ma = 0.3000 0.896 0.932 0.970 1.010 1.052 1.095 ma = 0.4000 0.925 0.964 1.005 1.048 1.093 1.139

76.80 76.92 77.04 77.16 77.26 77.38 77.48

1.00156 1.00569 1.00973 1.01370 1.01757 1.02136 1.02508 1.02873

ma = 0.1001 0.832 0.858 0.886 0.914 0.944 0.974 1.005 1.037

0.0000 0.0000 1.02116 1.170 0.0999 0.1011 1.02363 1.221 0.2002 0.2007 1.02604 1.277 0.3002 0.2982 1.02836 1.337 0.4003 0.3941 1.03062 1.399 0.5001 0.4879 1.03281 1.464 L-Threonine in Vitamin B6 Aqueous Solution 0.0000 0.1001 0.2000 0.3003 0.4001 0.5001 0.6000 0.7001

0.0000 0.0998 0.1978 0.2947 0.3897 0.4835 0.5757 0.6667

1.00418 1.00837 1.01247 1.01649 1.02041 1.02426 1.02802 1.03173

1.047 1.082 1.118 1.157 1.195 1.236 1.278 1.321

D

61.16 61.26 61.36 61.44 61.55 61.62 61.71 mol·kg−1 61.37 61.47 61.57 61.65 61.75 61.82 61.92

90.88 91.02 91.15 91.30 91.43 mol·kg−1 91.07 91.22 91.37 91.52 91.70 mol·kg−1 91.19 91.37 91.55 91.71 91.89 mol·kg−1 91.41 91.57 91.72 91.88 92.04

77.46 77.59 77.70 77.81 77.92 78.03 78.13



Article


T/K = 303.15

T/K = 313.15

T/K = 323.15

m

C

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

mol·kg−1

mol·L−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

1.00368 1.00771 1.01167 1.01554 1.01934 1.02307 1.02673 1.03032

0.703 0.725 0.748 0.772 0.796 0.821 0.847 0.872

78.33 78.42 78.50 78.59 78.66 78.74 78.82

0.99933 1.00333 1.00725 1.01110 1.01487 1.01856 1.02220 1.02576

0.587 0.605 0.623 0.641 0.661 0.680 0.699 0.719

78.83 78.91 78.96 79.05 79.15 79.22 79.29

1.00920 1.01319 1.01710 1.02093 1.02469 1.02838 1.03199 1.03553

0.729 0.753 0.777 0.802 0.828 0.854 0.881 0.908

78.55 78.64 78.71 78.79 78.86 78.97 79.04

1.00485 1.00880 1.01268 1.01646 1.02019 1.02381 1.02741 1.03089

0.608 0.626 0.646 0.665 0.685 0.705 0.726 0.747

79.15 79.21 79.30 79.37 79.50 79.54 79.65

1.01446 1.01841 1.02228 1.02606 1.02978 1.03344 1.03702 1.04054

0.755 0.780 0.806 0.832 0.859 0.888 0.916 0.945

78.78 78.86 78.93 79.01 79.07 79.13 79.19

1.01010 1.01401 1.01784 1.02159 1.02528 1.02889 1.03244 1.03592

0.628 0.648 0.668 0.689 0.710 0.732 0.754 0.776

79.34 79.41 79.48 79.54 79.61 79.67 79.73

0.99809 1.00355 1.00859 1.01330 1.01772 1.02187 1.02575 1.02943

0.680 0.712 0.750 0.786 0.828 0.869 0.913 0.958

119.21 120.62 121.80 122.85 123.87 124.81 125.66

0.99385 0.99921 1.00420 1.00884 1.01317 1.01724 1.02113 1.02487

0.568 0.595 0.623 0.652 0.685 0.717 0.753 0.787

120.47 121.69 122.87 123.96 125.01 125.80 126.49

1.00373 1.00911 1.01424 1.01907 1.02367 1.02806 1.03216 1.03612

0.703 0.737 0.776 0.819 0.864 0.909 0.958 1.008

119.45 120.12 120.95 121.68 122.30 123.04 123.62

0.99936 1.00465 1.00970 1.01451 1.01908 1.02344 1.02758 1.03155

0.587 0.614 0.646 0.678 0.712 0.749 0.786 0.825

120.67 121.29 121.94 122.59 123.14 123.73 124.26

1.00920 1.01455 1.01966 1.02451 1.02914 1.03359 1.03782 1.04182

0.729 0.766 0.808 0.851 0.900 0.950 1.002 1.056

119.56 120.10 120.67 121.27 121.76 122.30 122.87

1.00484 1.01010 1.01512 1.01991 1.02452 1.02892 1.03315 1.03721

0.607 0.637 0.670 0.705 0.742 0.782 0.823 0.864

120.77 121.32 121.80 122.24 122.73 123.16 123.57

1.01448 1.01975

0.755 0.796

119.94

1.01008 1.01525

0.628 0.661

121.15

0.0000 0.1000 0.2000 0.3000 0.3999 0.4998 0.6001 0.7001

0.0000 0.1002 0.1989 0.2961 0.3917 0.4858 0.5789 0.6703

1.01000 1.01415 1.01821 1.02218 1.02606 1.02987 1.03360 1.03724

1.083 1.121 1.160 1.202 1.245 1.289 1.336 1.383

76.98 77.09 77.22 77.34 77.45 77.58 77.70

1.00727 1.01136 1.01536 1.01928 1.02311 1.02686 1.03053 1.03419

0.0000 0.1001 0.2002 0.2999 0.4000 0.5000 0.6001 0.7000

0.0000 0.1008 0.2002 0.2976 0.3938 0.4885 0.5819 0.6736

1.01556 1.01968 1.02371 1.02763 1.03148 1.03524 1.03893 1.04253

1.128 1.169 1.211 1.254 1.300 1.347 1.395 1.445

77.10 77.23 77.37 77.50 77.63 77.75 77.87

1.01280 1.01685 1.02082 1.02469 1.02848 1.03221 1.03584 1.03941

0.0000 0.1002 0.2001 0.2999 0.4000 0.5001 0.6001 0.7000 L-Arginine

0.0000 0.1015 0.2012 0.2992 0.3959 0.4911 0.5848 0.6769 in Vitamin

1.02110 1.169 1.02517 1.212 1.02914 1.258 1.03302 1.303 1.03682 1.352 1.04055 1.402 1.04419 1.453 1.04774 1.506 B6 Aqueous Solution

77.39 77.52 77.64 77.77 77.88 78.00 78.12

1.01818 1.02219 1.02611 1.02994 1.03371 1.03741 1.04102 1.04456

0.0000 0.1002 0.2002 0.3001 0.4000 0.5003 0.6000 0.7003

0.0000 0.0995 0.1964 0.2909 0.3831 0.4735 0.5611 0.6470

1.00426 1.00992 1.01515 1.02006 1.02457 1.02887 1.03282 1.03659

1.047 1.103 1.163 1.229 1.299 1.369 1.446 1.523

116.86 118.24 119.38 120.68 121.72 122.79 123.70

1.00162 1.00717 1.01230 1.01716 1.02161 1.02578 1.02962 1.03343

0.0000 0.0999 0.1999 0.3001 0.4004 0.5002 0.6001 0.6999

0.0000 0.0998 0.1972 0.2926 0.3857 0.4762 0.5646 0.6509

1.01006 1.01565 1.02094 1.02592 1.03063 1.03506 1.03931 1.04330

1.083 1.141 1.210 1.282 1.361 1.445 1.528 1.622

116.99 117.84 118.81 119.68 120.50 121.18 121.90

1.00731 1.01278 1.01798 1.02288 1.02755 1.03191 1.03603 1.03999

0.0000 0.1002 0.2003 0.3000 0.4000 0.5000 0.6000 0.6999

0.0000 0.1006 0.1987 0.2941 0.3875 0.4787 0.5678 0.6545

1.01562 1.02117 1.02645 1.03148 1.03628 1.04083 1.04517 1.04929

1.129 1.191 1.263 1.342 1.424 1.515 1.608 1.706

117.22 117.84 118.44 119.04 119.67 120.28 120.88

1.01284 1.01828 1.02346 1.02839 1.03309 1.03758 1.04185 1.04590

0.0000 0.1000

0.0000 0.1009

1.02112 1.02658

1.170 1.239

117.62

1.01820 1.02356

ma = 0.2000 0.861 0.889 0.918 0.949 0.981 1.013 1.047 1.081 ma = 0.3000 0.896 0.926 0.957 0.989 1.023 1.057 1.092 1.129 ma = 0.4000 0.925 0.957 0.991 1.026 1.061 1.098 1.136 1.174

mol·kg−1 77.63 77.79 77.86 78.00 78.12 78.25 78.27 mol·kg−1 77.82 77.94 78.05 78.17 78.26 78.40 78.49 mol·kg−1 78.08 78.18 78.27 78.35 78.43 78.53 78.61

ma = 0.1000 mol·kg−1 0.832 0.875 118.05 0.920 119.47 0.970 120.44 1.022 121.67 1.075 122.82 1.133 123.94 1.190 124.68 ma = 0.2000 mol·kg−1 0.861 0.905 118.29 0.955 119.06 1.010 119.94 1.069 120.69 1.128 121.48 1.195 122.28 1.257 122.93 ma = 0.3000 mol·kg−1 0.896 0.943 118.43 0.997 119.04 1.054 119.62 1.117 120.24 1.184 120.79 1.253 121.38 1.322 121.96 ma = 0.4000 mol·kg−1 0.926 0.979 118.78 E



Article


T/K = 303.15

T/K = 313.15

T/K = 323.15

m

C

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

ρ

η

Vϕ

mol·kg−1

mol·L−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

g·cm−3

mPa·s

cm3·mol−1

1.02481 1.02966 1.03431 1.03878 1.04307 1.04719

0.844 0.895 0.953 1.016 1.079 1.151

120.33 120.78 121.23 121.58 121.98 122.37

1.02024 1.02504 1.02965 1.03410 1.03838 1.04253

0.698 0.739 0.787 0.836 0.887 0.943

121.44 121.77 122.17 122.46 122.79 123.07

0.2000 0.3001 0.4003 0.5000 0.6000 0.7000

0.1994 0.2957 0.3898 0.4812 0.5707 0.6581

1.03181 1.03683 1.04162 1.04620 1.05056 1.05476

1.319 1.408 1.502 1.606 1.722 1.839

118.11 118.57 119.09 119.56 120.09 120.54

1.02870 1.03363 1.03835 1.04289 1.04722 1.05136

ma = 0.4000 mol·kg−1 1.038 119.19 1.104 119.66 1.179 120.15 1.254 120.53 1.338 120.98 1.430 121.44

a m stands for the molality of glycine/L-alanine/L-threonine/L-valine/L-arginine in (vitamin B6 + water) mixture solvents. ma stands for the molality of vitamin B6 aqueous solutions. Standard uncertainty: in molality u(m) = ± 1·10−4 mol·kg−1; in density u(ρ) = ± 5·10−5 g·cm−3, u(T) = ± 0.02 K; in viscosities u(η) = ± 1%, u(T) = ± 0.02 K.

Table 3. Fitting Coefficients A1, A2, A3 of eq 2 for Amino Acids + Vitamin B6 + Water Ternary Solutions ma mol·kg

Figure 1. Density (ρ) of amino acids in 0.1 mol·kg−1 vitamin B6 aqueous solutions: ■, L-arginine; ▲, L-threonine; ▼, glycine; ★, L-alanine; ○, Lvaline.

3.2. Volumetric Properties. The apparent molar volumes, Vϕ of glycine, L-alanine, L-valine, L-threonine and L-arginine in vitamin B6 solutions were computed by the following relation:27−29 Vϕ = M /ρ − 1000(ρ − ρ0 )/mρρ0

(5)

where M is the molar weight of the solute, m is the molality of the solute in mixture solvent, and ρ and ρ0 are the densities of the mixture and the solvent, respectively. The calculated apparent molar volumes, Vϕ, are also included in Table 2. Figure 2 shows the plot of apparent molar volumes of glycine in (0.1 to 0.4) mol·kg−1 vitamin B6 aqueous solutions at 293.15 K. It could be easily found that the apparent molar volumes vary linearly with the molar concentration of the solute. Consequently, the limiting partial molar volumes, V0ϕ (i.e., apparent molar volumes at infinite dilution) could be obtained through the following equation:30 Vϕ = V ϕ0 + SvC

104A2

A1 −1

g·cm

−3

0.1000 0.2000 0.3000 0.4000

1.1106 1.1202 1.1251 1.1335

0.1000 0.2000 0.3000 0.4000

1.1096 1.1189 1.1253 1.1336

0.1000 0.2000 0.3000 0.4000

1.1094 1.1080 1.1249 1.1333

0.1001 0.2000 0.3000 0.4000

1.1111 1.1194 1.1135 1.1339

0.1000 0.2000 0.3000 0.4000

1.1156 1.1224 1.1299 1.1376

−3

g·cm ·K

A3 −1

SD −1

g·mol

Glycine −3.6040 0.0305 −3.7285 0.0300 −3.7285 0.0295 −3.8104 0.0291 L-Alanine −3.5734 0.0274 −3.6899 0.0270 −3.7195 0.0264 −3.8139 0.0258 L-Valine −3.5643 0.0253 −3.3598 0.0259 −3.7087 0.0239 −3.8052 0.0232 L-Threonine −3.6215 0.0406 −3.7079 0.0400 −3.3602 0.0406 −3.8264 0.0387 L-Arginine −3.7448 0.0487 −3.7909 0.0501 −3.8583 0.0503 −3.9366 0.0501

100AD

g·cm−3

0.039 0.038 0.039 0.037

0.0004 0.0004 0.0004 0.0004

0.039 0.038 0.036 0.035

0.0004 0.0004 0.0004 0.0004

0.040 0.057 0.040 0.036

0.0004 0.0007 0.0004 0.0004

0.039 0.038 0.060 0.034

0.0004 0.0004 0.0007 0.0004

0.048 0.038 0.036 0.034

0.0006 0.0005 0.0005 0.0005

Apparently, from Table 4, the V0ϕ of amino acids are all positive and increase with temperature, which gives an insight that there exists the solute−solvent interaction and higher temperature could facilitate this kind of interaction. When the molality of vitamin B6 aqueous solutions climbs, the corresponding values of V0ϕ will also go up under the specified temperature. Additionally, it could also be found that the V0ϕ of amino acids are in the order glycine < L-alanine < L-valine < L-threonine < L-arginine. Under the condition of infinite dilution, the interactions between solute and solute is negligible, therefore, the solute− solvent interactions would become dominated in the solutions. The limiting partial molar volume of transfer means the difference between the water solvent and the mixed solvent and could provide much valuable information about solute− solvent interactions.

(6)

where Sv is the experimental slope and C is the molar concentration of amino acids in vitamin B6 aqueous solutions at 293.15 K. In this case, the values of V0ϕ were obtained by the least-squares regression analysis and listed in Table 4. F



Article

water to vitamin B6 aqueous solutions could be calculated as follows: Δtr V ϕ0 = V ϕ0[VB6 + water] − V ϕ0[water]

(7)

It should be noted that the limiting partial molar volumes of amino acids in pure water were taken from our previous research.18 The results of limiting partial molar volumes of transfer, ΔtrV0ϕ are summarized in Table 4. The ΔtrV0ϕ of amino acids from water to vitamin B6 aqueous solutions are positive except for L-arginine, and increase monotonically with both the molality of solvent and the temperature of the solution. The values of ΔtrV0ϕ of amino acids from water to vitamin B6 aqueous solutions could be observed to shift in the following order: ΔtrV0ϕ [L-arginine] < 0 < ΔtrV0ϕ [L-valine] < ΔtrV0ϕ [L-alanine] < ΔtrV0ϕ [glycine] < ΔtrV0ϕ [Lthreonine]. This could be reasonably explained by the cosphere overlap model.24,31,32 According to specific structure and properties of amino acids and vitamin B6, there mainly exists five types of interactions between amino acids and vitamin B6 molecules: (a) ion−ion interactions between zwitterionic end groups (NH3+,COO−) of amino acids and the ions (H+,Cl−) ionized or hydrolyzed from vitamin B6 molecules

Figure 2. Apparent molar volumes of glycine as a function of its molar concentration in vitamin B6 aqueous solutions at T = 293.15 K: ■, 0.1 mol·kg−1; ●, 0.2 mol·kg−1; ▲, 0.3 mol·kg−1; ▼, 0.4 mol·kg−1.

The limiting partial molar volumes of transfer, ΔtrV0ϕ of glycine, L-alanine, L-valine, L-threonine, and L-arginine from pure

Table 4. Limiting Partial Molar Volumes (V0ϕ) and Limiting Partial Molar Volumes of Transfer (ΔtrV0ϕ) of Amino Acids in Vitamin B6 Aqueous Solutions at T = (293.15 to 323.15) K T/K = 293.15 maa mol·kg

−1

−1

cm ·mol 3

T/K = 303.15

ΔtrV0ϕ

V0ϕ

cm ·mol 3

−1

cm ·mol 3

T/K = 313.15

ΔtrV0ϕ

V0ϕ −1

−1

cm ·mol 3

T/K = 323.15

ΔtrV0ϕ

V0ϕ −1

ΔtrV0ϕ

V0ϕ −1

−1

cm3·mol−1

cm ·mol

cm ·mol

cm ·mol

43.76 44.08 44.29 44.56 44.84

0.32 0.53 0.80 1.08

44.25 44.58 44.81 45.10 45.37

0.33 0.56 0.85 1.12

61.03 61.20 61.39 61.59 61.81

0.17 0.36 0.56 0.78

61.39 61.60 61.81 62.07 62.26

0.21 0.42 0.68 0.87

91.32 91.47 91.65 91.77 92.00

0.15 0.33 0.45 0.68

92.07 92.24 92.42 92.57 92.39

0.17 0.35 0.50 0.72

77.84 78.0 78.25 78.46 78.71

0.21 0.41 0.62 0.87

78.27 78.51 78.74 79.04 79.28

0.24 0.47 0.77 1.01

125.68 118.26 118.67 118.93 119.48

−7.42 −7.01 −6.75 −6.20

126.67 119.53 120.02 120.30 120.77

−7.14 −6.65 −6.37 −5.90

3

3

3

Glycine

a

0.0000 0.1000 0.2000 0.3000 0.4000

42.61 42.90 43.12 42.36 43.60

0.29 0.51 0.75 0.99

43.17 43.48 43.69 43.94 43.20

0.0000 0.1000 0.2000 0.3000 0.4000

60.14 60.27 60..42 60.52 60.73

0.13 0.28 0.38 0.59

60.59 60.74 60.90 61.07 61.28

0.0000 0.1000 0.2000 0.3000 0.4000

90.11 90.20 90.36 90.45 90.65

0.09 0.25 0.34 0.54

90.61 90.73 90.90 91.01 91.25

0.0000 0.1001 0.2000 0.3000 0.4000

76.51 76.68 76.84 76.97 76.26

0.17 0.33 0.46 0.75

77.16 77.35 77.53 77.71 77.99

0.0000 0.1000 0.2000 0.3000 0.4000

123.97 115.74 116.13 116.52 117.05

−8.23 −7.84 −7.45 −6.92

124.88 116.95 117.42 117.77 118.27

0.31 0.52 0.77 1.03 L-Alanine 0.15 0.31 0.48 0.69 L-Valine 0.12 0.29 0.40 0.64 L-Threonine 0.19 0.37 0.55 0.83 L-Arginine −7.93 −7.46 −7.11 −6.61

ma stands for the molality of vitamin B6 in water. G



Article

(b) ion−hydrophilic group interactions between zwitterionic end groups (NH3+,COO−) of amino acids and the OH groups in vitamin B6 molecules (c) hydrophilic−hydrophilic group interactions between the hydrophilic groups of amino acid (such as OH, and NH2) and the OH groups in vitamin B6 molecules (d) ion−hydrophobic group interactions between the zwitterionic end groups (NH3+,COO−) of amino acids and the alkyl chain of vitamin B6 molecules (e) hydrophobic−hydrophobic group interactions between the alkyl chain of amino acids and the alkyl chain of vitamin B6 molecules The interaction of types (a), (b), and (c) contributes positively to the limiting partial molar volumes of transfer, while types (d) and (e) make a negative contribution to the limiting partial molar volumes of transfer. From Table 3, the positive values of ΔtrV0ϕ of glycine, L-alanine, L-valine, and L-threonine adequately imply that the ion−ion interactions, and ion−hydrophilic and hydrophilic− hydrophilic group interactions surpass the ion−hydrophobic and hydrophobic−hydrophobic group interactions. When the temperature or the molality of mixture solvents increases, the dominant effect would be much more notable. Naturally, different amino acids would show various interactions. Considering the structure of amino acids, that is, CH2−(glycine), CH3−CH−(L-alanine), (CH3)2−CH−CH-(L-valine), CH3− CH(OH)-(L-threonine), CNHNHNH2−(L-arginine), there only exists type (a), (b), (d), and (e) for glycine, L-alanine, and L-valine, while all these five kinds of interactions are available for L-threonine and L-arginine. Commonly, the contribution of the alkyl chain of amino acids to ΔtrV0ϕ exerts great dependence on the size of alkyl chain, thereby it is not difficult to conclude the results: ΔtrV0ϕ [L-valine] < ΔtrV0ϕ [L-alanine] < ΔtrV0ϕ [glycine]. Nevertheless, the ΔtrV0ϕ of L-threonine are larger than that of Lvaline owing to its additional type (c) interactions. As to the dramatically large negative values of ΔtrV0ϕ for L-arginine, maybe this is not purely caused by its additional type (c) interactions. It could be interpreted by the fact that L-arginine is an alkaline amino acid, while vitamin B6 is acidic, just like L-ascorbic acid. In the vitamin B6 aqueous solutions, L-arginine could neutralize and exchange an electric charge with a vitamin B6 molecule, which leads to the electrostriction of the water to be enhanced rapidly, and finally results in a relatively large and negative value of the limiting partial molar volumes of transfer. It is worth noting that the ΔtrV0ϕ for L-arginine from water to vitamin B6 aqueous solutions seems to be less negative than from water to L-ascorbic acid aqueous solutions, this is probably because of the occurrence of strong and positive ion−ion interactions, as opposed to the interactions in amino acids + L-ascorbic acid + water solutions. 3.3. Viscometric Properties. The experimental viscosities of glycine, L-alanine, L-valine, L-threonine, and L-arginine in vitamin B6 aqueous solutions at T = (293.15, 303.15, 313.15 and 323.15) K are displayed in Table 2 and partly depicted in Figure 3. It could be clearly found from Figure 3 that the viscosities of amino acids are in nonlinear relationship to the molar concentration of solute. In this work, the extended Jones-Dole equation33 were utilized to correlate the viscosities of solutions. η = 1 + BC + DC 2 ηr = η0 (8)

Figure 3. Viscosities, η of amino acids in 0.1 mol·kg−1 vitamin B6 aqueous solutions at T = 293.15 K: ■, glycine; ●, L-alanine; ▲, L-valine; ▼, L-threonine; ◆, L-arginine.

Coefficients B and D are the physicochemical properties at a given temperature. Generally, the B coefficient gives a significant insight into solute−solvent interactions34 and the D coefficient seems to stand for solute−solute interactions.31 The fitting parameters B and D of viscosity are obtained by the least-squares deviations and shown in Table 5. From Figure 3, it could be found the viscosities of amino acids are largely associated with their molar weights. The larger is the molar weight of the amino acid, the slower is the motion of the molecule, and naturally the larger is the viscosity. Viscosity B coefficient is a valuable parameter regarding the solute−solvent interactions.35,36 It could be clearly observed from Table 5 that the viscosity B coefficients are positive for these amino acids and retain an increasing trend with the molality of vitamin B6, implying the existence of strong solute−solvent interactions in the presence of vitamin B6. Additionally, the relationship between the viscosity B coefficient and temperature, expressed as the derivative form of dB/dT, could provide more information about the solute−solvent interactions in terms of the structuremaking and structure-breaking nature. Normally, dB/dT is negative for structure-makers and positive for structure-breakers. It is observed that the dB/dT of glycine is positive while that of other amino acids are negative. Consequently, we could determine that glycine may tend to act as structure-breakers, whereas the other amino acids are more likely to be structuremakers. Similar results could be found in the literature.37,38 On the basis of the Feakin’s transition state theory,39 the viscosity could be applied to analyze the free energy of activation per mole of solvent (Δμ0⇌ 1 ) and the free energy of activation per mole of solute (Δμ0⇌ 2 ). The B coefficients could be expressed as the following equation:40 B = (V1̅ 0 − V2̅ 0)/1000 + V1̅ 0(Δμ20 ⇌ − Δμ10 ⇌)/(1000RT ) (9)

where V1̅ 0 (=∑xiMi/ρ0)

is the mean molar volume of the mixture solvents (vitamin B6 + water), ρ0 is the density of the mixture solvents. The xi and Mi specify the mole fraction and molar weight of water and vitamin B6 in solvent mixtures, respectively. V2̅ 0 is the standard partial molar volume of the solute at infinite dilution, equivalent to the limiting partial molar volume, V0φ, which has been obtained in the front section 3.2.

where ηr is the relative viscosity; η and η0 are the viscosities of solutions and the mixed solvents, respectively. The molar concentration, C, is converted from the molality, m, at 293.15 K. H



Article

Table 5. B and D Coefficients of Jones−Dole Equation, and the Free Energies of Activation per Mole of Solvent (Δμ0⇌ 1 ) and Solute (Δμ0⇌ 2 ) at T = (293.15, 303.15, 313.15 and 323.15) K T K

B

Δμ0⇌ 1

D −1

dm ·mol 3

dm ·mol 6

−2

−1

kJ·mol

Δμ0⇌ 2

T

−1

kJ·mol

K

Glycine 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 L-Alanine 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 L-Valine 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15

0.1 mol·kg−1 0.111 (±0.001) 0.121 (±0.001) 0.131 (±0.001) 0.140 (±0.000) 0.2 mol·kg−1 0.128 (±0.001) 0.133 (±0.001) 0.144 (±0.001) 0.150 (±0.000) 0.3 mol·kg−1 0.136 (±0.000) 0.142 (±0.000) 0.151 (±0.001) 0.163 (±0.000) 0.4 mol·kg−1 0.148 (±0.001) 0.159 (±0.001) 0.165 (±0.001) 0.171 (±0.001)

Vitamin B6 Aqueous 0.046 (±0.001) 0.037 (±0.001) 0.027 (±0.001) 0.020 (±0.001) Vitamin B6 Aqueous 0.034 (±0.001) 0.032 (±0.001) 0.023 (±0.001) 0.019 (±0.001) Vitamin B6 Aqueous 0.016 (±0.001) 0.015 (±0.001) 0.011 (±0.001) 0.000 (±0.001) Vitamin B6 Aqueous 0.011 (±0.001) 0.003 (±0.001) 0.005 (±0.001) 0.006 (±0.001)

Solution 9.42 9.17 8.96 8.77 Solution 9.53 9.28 9.07 8.89 Solution 9.65 9.40 9.19 9.00 Solution 9.76 9.51 9.31 9.12

0.1 mol·kg−1 0.227 (±0.001) 0.216 (±0.002) 0.206 (±0.002) 0.199 (±0.001) 0.2 mol·kg−1 0.240 (±0.001) 0.222 (±0.001) 0.213 (±0.001) 0.202 (±0.001) 0.3 mol·kg−1 0.245 (±0.001) 0.231 (±0.002) 0.223 (±0.001) 0.212 (±0.001) 0.4 mol·kg−1 0.259 (±0.002) 0.242 (±0.001) 0.233 (±0.001) 0.226 (±0.001)



0.1 mol·kg−1 Vitamin B6 Aqueous Solution 0.386 (±0.001) 0.200 (±0.002) 9.42 0.368 (±0.002) 0.154 (±0.006) 9.17 0.354 (±0.003) 0.113 (±0.006) 8.96 0.335 (±0.002) 0.082 (±0.004) 8.77 0.2 mol·kg−1 Vitamin B6 Aqueous Solution 0.398 (±0.003) 0.211 (±0.007) 9.53 0.378 (±0.001) 0.169 (±0.003) 9.28 0.364 (±0.002) 0.110 (±0.006) 9.07 0.343 (±0.001) 0.067 (±0.003) 8.89

293.15 303.15 313.15 323.15

27.59 29.36 31.24 33.04 29.78 30.92 32.96 34.37

293.15 303.15 313.15 323.15 L-Threonine

30.77 32.06 33.85 36.12

293.15 303.15 313.15 323.15

32.25 34.25 35.67 37.13

293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15

45.44 44.86 44.33 44.14

293.15 303.15 313.15 323.15 L-Arginine

46.92 45.44 45.09 44.35 47.34 46.44 46.26 45.57

293.15 303.15 313.15 323.15

48.92 47.68 47.41 47.33

293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15

70.73 69.99 69.67 68.48

293.15 303.15 313.15 323.15

71.84 70.87 70.59 69.17

Δμ0⇌ 1

D −1

dm ·mol

−2

dm ·mol 6

−1

kJ·mol

0.3 mol·kg−1 Vitamin B6 Aqueous Solution 0.404 (±0.002) 0.195 (±0.004) 9.65 0.383 (±0.001) 0.156 (±0.003) 9.41 0.370 (±0.002) 0.111 (±0.004) 9.19 0.355 (±0.001) 0.077 (±0.003) 9.01 0.4 mol·kg−1 Vitamin B6 Aqueous Solution 0.415 (±0.002) 0.209 (±0.006) 9.76 0.398 (±0.001) 0.155 (±0.003) 9.51 0.382 (±0.001) 0.118 (±0.002) 9.30 0.364 (±0.001) 0.086 (±0.002) 9.12 0.1 mol·kg−1 0.324 (±0.001) 0.310 (±0.001) 0.298 (±0.001) 0.287 (±0.001) 0.2 mol·kg−1 0.336 (±0.001) 0.317 (±0.001) 0.306 (±0.001) 0.293 (±0.001) 0.3 mol·kg−1 0.341 (±0.001) 0.324 (±0.001) 0.313 (±0.001) 0.302 (±0.001) 0.4 mol·kg−1 0.353 (±0.001) 0.335 (±0.001) 0.323 (±0.001) 0.311 (±0.001)



0.1 mol·kg−1 Vitamin B6 Aqueous 0.508 (±0.003) 0.301 (±0.006) 0.489 (±0.003) 0.271 (±0.005) 0.468 (±0.004) 0.255 (±0.008) 0.449 (±0.004) 0.229 (±0.008) 0.2 mol·kg−1 Vitamin B6 Aqueous 0.519 (±0.005) 0.376 (±0.009) 0.497 (±0.007) 0.328 (±0.012) 0. 476 (±0.003) 0.296 (±0.005) 0.455 (±0.002) 0.261 (±0.003) 0.3 mol·kg−1 Vitamin B6 Aqueous 0.525 (±0.003) 0.393 (±0.005) 0.502 (±0.005) 0.347 (±0.008) 0.483 (±0.004) 0.310 (±0.007) 0.466 (±0.004) 0.278 (±0.007) 0.4 mol·kg−1 Vitamin B6 Aqueous 0.534 (±0.004) 0.509 (±0.007) 0.513 (±0.005) 0.474 (±0.009) 0.494 (±0.005) 0.459 (±0.009) 0.473 (±0.004) 0.438 (±0.008)


Δμ0⇌ 2 kJ·mol−1 72.14 71.08 70.95 70.42 73.11 72.62 72.14 71.23

60.64 60.15 59.80 59.46 61.83 60.71 60.55 59.96 62.10 61.28 61.15 60.89 63.30 62.39 62.16 61.80

90.48 90.34 89.67 89.11 91.30 90.79 90.16 89.35 91.46 90.82 90.49 90.28 92.02 91.68 91.40 90.66

Where η0 is the viscosity of the solvent; R, NA and h are gas constant, Avogadro’s number and Planck’s constant, respectively. When eq 9 undergoes a rearrangement, we could get the relation of free energy of activation per mole of solute (Δμ0⇌ 2 ):

The free energy of activation per mole of solvent (Δμ0⇌ 1 ) could be calculated by the following equation: Δμ10 ⇌ = RT lnη0V1̅ 0/hNA

B 3

(10) I



Article

Table 6. Contributions of All Groups to the Limiting Partial Molar Volumes (V0ϕ) and the Viscosity B-Coefficients for Amino Acids in Vitamin B6 Aqueous Solutions at T = (293.15, 303.15, 313.15 and 323.15) K V0ϕ/(cm3·mol−1) groups

T/K = 293.15

T/K = 303.15

B/(dm3·mol−1)

T/K = 313.15

NH3+, COO− CH CH2 CH3 OH CNHNHNH2

27.94 7.83 15.65 23.48 9.62 33.02

28.48 7.82 15.64 23.47 9.76 33.89

28.95 7.85 15.70 23.55 9.85 34.36


28.15 7.82 15.64 23.46 9.60 33.25

28.69 7.82 15.63 23.45 9.77 34.13

29.16 7.85 15.69 23.54 9.86 34.59


28.40 7.79 15.59 23.38 9.59 33.55

28.97 7.79 15.59 23.38 9.77 34.25

29.47 7.82 15.64 23.46 9.88 34.71


28.64 7.79 15.58 23.37 9.67 33.88

29.21 7.79 15.58 23.38 9.82 34.56

29.74 7.82 15.63 23.45 9.89 35.03

Δμ20 ⇌ = Δμ10 ⇌ + RT[1000B − (V1̅ 0 − V2̅ 0)]/V1̅ 0

T/K = 323.15

ma = 0.1000 mol·kg−1 29.26 7.90 15.81 23.71 9.74 34.95 ma = 0.2000 mol·kg−1 29.51 7.89 15.79 23.68 9.76 35.25 ma = 0.3000 mol·kg−1 29.85 7.87 15.74 23.61 9.84 35.29 ma = 0.4000 mol·kg−1 30.11 7.86 15.73 23.59 9.85 35.62

T/K = 293.15

T/K = 303.15

T/K = 313.15

T/K = 323.15

0.032 0.045 0.090 0.135 0.068 0.162

0.046 0.041 0.081 0.122 0.061 0.159

0.057 0.037 0.074 0.112 0.055 0.151

0.072 0.033 0.065 0.098 0.051 0.148

0.049 0.044 0.088 0.133 0.066 0.161

0.056 0.041 0.080 0.122 0.059 0.158

0.068 0.037 0.074 0.111 0.052 0.150

0.080 0.033 0.065 0.098 0.050 0.147

0.056 0.044 0.088 0.132 0.065 0.161

0.066 0.040 0.080 0.120 0.059 0.157

0.077 0.037 0.073 0.110 0.053 0.149

0.092 0.033 0.065 0.098 0.048 0.147

0.070 0.044 0.087 0.131 0.065 0.159

0.081 0.040 0.079 0.119 0.056 0.154

0.091 0.036 0.073 0.109 0.051 0.149

0.102 0.033 0.065 0.097 0.047 0.144

Since the V0ϕ values of the studied amino acids in binary and ternary solutions vary linearly with the number of carbon atoms (nc) in their alkyl chains, a linear regression analysis32,42 could be performed through the following relation:

(11)

0⇌ The calculated values of Δμ0⇌ 1 and Δμ2 at different temperatures are listed in Table 5. The Δμ0⇌ 2 values in Table 5 are positive at the whole temperature range under investigation, suggesting the presence of solute−solvent interactions between the solute (amino acids) and solvent (vitamin B6 + water) 0⇌ molecules. The much higher Δμ0⇌ 2 values, as opposed to Δμ1 , reveal that the solute−solvent interactions in the ground state are relatively stronger than that in the transition state and hinder the formation of transition state in the presence of vitamin B6.41 It could be found that for the same temperature and molality of values are positive vitamin B6 aqueous solution, the Δμ0⇌ 2 dependence on the molar weight of solute, that is to say they follow in the order: L-arginine > L-valine > L-threonine > Lalanine > glycine. This trend is just in accordance with the viscosity B coefficients. It should be noted that the molar weights of L-threonine and L-valine are nearly the same, 119.12 g·mol−1 for L-threonine and 117.15 g·mol−1 for L-valine), respectively, but the Δμ0⇌ 2 of L-threonine is obviously smaller than that of L-valine. The reason may be the strong solute−solvent interactions between L-threonine and vitamin B6 aqueous solutions due to its strong hydrophilicity of OH groups. 3.4. Group Additivity Analyses. Group additivity schemes, a crucial method of modeling the thermodynamic properties of solutions, have been widely investigated by many researchers.19,27,33,35−37 Here we attempt to analyze two typical volumetric and viscometric properties: V0ϕ and B coefficients by this method.

V ϕ0 = V ϕ0(NH3+, COO−) + nc(CH 2)

(12)

The V ϕ0 (NH 3 + ,COO − ) and V ϕ0 (CH 2 ) represent the corresponding contributions of the zwitterionic end group and the methylene group to Vϕ0 , respectively. Similar linear correlations have been reported in the literature.19,34,38,43 The alkyl chains of the homologous series of amino acids investigated in this work are CH2−(glycine), CH3−CH−(L-alanine), CH3− CH3−CH−CH−(L-valine). As proposed by Hakin,44 V ϕ0(CH3) = 1.5V ϕ0(CH 2)

(13)

V ϕ0(CH) = 0.5V ϕ0(CH 2)

(14)

It should be pointed out that V0ϕ(CH2) refers to the mean value of V0ϕ(CH) and V0ϕ(CH3). With the help of eqs 13 and 14, the contribution values from the zwitterionic end group (NH3+,COO−) and methylene group (CH2) were correlated by eq 12 through a linear regression analysis. The oxhydryl group (OH) contribution of L-threonine and the amino-group (CNHNHNH2) of L-arginine to V0ϕ are obtained by eqs 15 and 16. J



Article

valine < L-alanine < glycine < L-threonine. The dB/dT for glycine is positive while that of other amino acids is negative, indicating that glycine maybe tends to act as structure-breaker, whereas the other amino acids are more inclined to be structure-maker. The group additivity analysis shows that the CNHNHNH2 group contributes greatly to both the V0ϕ and the viscosity B coefficients, only the zwitterionic end group (NH3+,COO−) group tends to be structure-breaker.

V ϕ0(OH) = V ϕ0(L‐threonine) − V ϕ0(NH3+, COO−) − 2V ϕ0(CH) − V ϕ0(CH3)

(15)

Vϕ 0(CNHNHNH 2) = Vϕ 0(L‐arginine) − Vϕ 0(NH3+, COO−) − 3Vϕ 0(CH 2) − Vϕ 0(CH)

(16)

■

The results are given in Table 6. The V0ϕ (NH3+,COO−) and V0ϕ (CH2) are in good agreement with the values in the literature.44,45 With the contribution values of different groups, we could easily predict and conclude the trend of V0ϕ in the former section 3.2: glycine < L-alanine < L-threonine < L-valine < L-arginine. Similarly, viscosity B coefficients of amino acids also vary linearly with nc B = B(NH3+, COO−) + ncB(CH 2)

ASSOCIATED CONTENT

* Supporting Information S

Comparison between experimental densities and viscosities of vitamin B6 and the literature values. This material is available free of charge via the Internet at http://pubs.acs.org.

■

(17)

AUTHOR INFORMATION

Corresponding Authors

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

B(OH) and B(CNHNHNH2) could be calculated through the similar method of eqs 15 and 16, respectively. Table 6 also gives the contributions of zwitterionic end group (NH3+,COO−), the methylene group (CH2), the oxhydryl group (OH), and the amino-group (CNHNHNH2) to viscosity B coefficients. From Table 6 we could also find that no matter what the limiting partial molar volumes or the viscosity B coefficients, the contributions of all groups are positive under the whole molality and temperature range. V0ϕ (NH3+,COO−), V0ϕ (CH2), V0ϕ (OH), and V0ϕ (CNHNHNH2) all show a monotonically increasing relationship to temperature, but only V0ϕ (NH3+,COO−) and V0ϕ (CNHNHNH2) increase with the increase of the molality of vitamin B6 aqueous solutions. For the viscosity B coefficients, B(NH3+,COO−) increases monotonically with the temperature as well as the molality of vitamin B6 aqueous solutions. However, B(CH2), B(OH), and B(CNHNHNH2) show the reverse trend with the above two factors. Surprisingly, V0ϕ (CNHNHNH2) and B(CNHNHNH2) values are found to be the largest among these groups owing to its long alkyl chain and large steric hindrance, maybe that is why L-arginine has such higher values of V0ϕ and viscosity B coefficients. Moreover, the effects of the temperature and the molality of vitamin B6 aqueous solutions on V0ϕ(OH) and B(OH) values demonstrate that the interaction between the OH group and vitamin B6 is more intensive due to the strong hydrophilic ability of the OH group. Finally, positive dB/dT for (NH3+,COO−) indicates that the zwitterionic end group tends to be structure-breaker, while negative dB/dT for CH 2 , CNHNHNH2, and OH group signifies that the methylene group, amino-group, and oxhydryl group are more likely to be structure-maker.

Notes

The authors declare no competing financial interest.

■

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4. CONCLUSIONS We measured the densities and viscosities of glycine/L-alanine/Lvaline/L-threonine/L-arginine in vitamin B6 aqueous solutions at T = (293.15, 303.15, 313.15 and 323.15) K and presented a series of volumetric and viscometric properties. The Guimarães equation and extended Jones−Dole equation were applied to correlate the experimental densities and viscosities, respectively, and the results indicate the great feasibility of these empirical equations. The positive values of V0ϕ, viscosity B coefficients, and free energies of activation per mole of solute (Δμ0⇌ 2 ) suggest the presence of strong solute−solvent interactions in amino acids + vitamin B6 + water ternary system. The ΔtrV0ϕ are positive for glycine, L-valine, L-alanine, and L-threonine, while negative for Larginine, and the values of ΔtrV0ϕ follow the order L-arginine < LK



Article

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L


Volumetric and Viscometric Studies of Amino Acids in Vitamin B6

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