K. Rajagopal and S.S. Jayabalakrishnan*

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Volumetric and Viscometric Studies of 4-Aminobutyric Acid in Aqueous Solutions of Salbutamol Sulphate at 308.15, 313.15 and 318.15 K

K. Rajagopal1and S.S. Jayabalakrishnan2,*

1Department of Physics, Government College of Engg, Tirunelveli-627007 Tamil Nadu, India2Department of Physics, P.S.R. Engg. College, Sivakasi, Tamil Nadu, India

density, standard partial molar volume, hydration number, relative viscosity,-coefficient, activation parameters

1 INTRODUCTION

Amino acids are considered as model compound instead of proteins in the presence of aqueous salt solutions to obtain thermodynamic information as the structure of proteins are highly complicated [1-4]. Some amino acids in the presence of aqueous minerals, such as sodium sulphate [2], CaCl2[5], NaCl [6], potassium thiocynate [7], are available in literature. However, the study of amino acids in the presence of aqueous salbutamol sulphate has not been reported so far. We have recently investigated some homologousa-amino acids such as glycine, L-alanine, L-valine and L-leucine in the presence of aqueous salbutamol sulphate through volumetric and viscometric studies. In this paper, we report 4-aminobutyric acid in aqueous salbutamol sulphate solutions.

2 EXPERIMENTAL

3 RESULTS AND DISCUSSION

The reported values of apparent molar volume data for the amino acids were found to be adequately represented by the linear equation [13].

Table 1 Values of density (ρ) and apparent molar volume () of the 4-amino butyric acid in aqueous salbutamol sulphate

Table 1 (Continued)

T/KmS/mol·kg－1mA/mol·kg－1Density(r)×103/kg·m－3m3·mol－1T/KmS/mol·kg－1mA/mol·kg－1Density(r)×103/kg·m－3m3·mol－1 318.150 (in water)00.99021318.150.012500.99383 0.020.9907974.7750.020.9943776.686 0.040.9913674.8080.040.9949076.707 0.060.9919374.8410.060.9954376.729 0.080.9924974.8750.080.9959676.751 0.100.9930674.8980.100.9964976.773 0.004100.992970.020700.99547 0.020.9935276.1380.020.9959977.809 0.040.9940776.1650.040.9965077.819 0.060.9946176.2070.060.9970177.833 0.080.9951476.2410.080.9975277.845 0.100.9956876.2730.100.9980377.857

Note:S, molality of salbutamol sulphate;A, molality of amino acids.

Table 2 Values of standard partial molar volume () of 4-amino butyric acid in aqueous salbutamol sulphate

① Ref. [14, 15],② Ref. [16],③ Ref. [17].

Note:S, molality of salbutamol sulphate. Parentheses indicate standard errors.

The results are given in Table 3.

Table 3 Values of standard partial molar volumes of transfer () of 4-amino butyric acid in aqueous salbutamol sulphate solutions

Note:S, molality of salbutamol sulphate.

Table 4 Values of hydration number of 4-amino butyric acid in aqueous salbutamol sulphate solutions

The transfer volumes of the 4-aminobutyric acid may also be expressed by the McMillan Mayer theory [30] of solutions, which permits the formal separation of the effects due to interactions between the pairs of the solute molecules and those due to interactions between three or more solute molecules by the following equation.

where A stands for the amino acids and S stands for salbutamol sulphate.ASandASSare the pair and triplet volumetric interaction parameters. Using the above equation volumetric interaction parameters were estimated and given in Table 5.

TheASandASSvalues are positive and negative respectively. The large positiveASvalues suggest the domination of pair interactions for the 4-aminobutyric acid over triplet volumetric interaction parameters. Similar reports are available in the literature by Banipal[31].

Table 5 Values of pair and triplet interaction coefficients VAS and VASS of 4-amino butyric acid in aqueous salbutamol sulphate solutions

The coefficients,andhave been determined and Eq. (5) has the following forms for the amino acids reported in this work.

The relative viscositiesrof studied amino acid in water and in cosolute solutions were calculated using the following equation and are summarized in Table 6.

whereand0are the viscosities of the solution and solvent.

Thecoefficients were evaluated by fitting thervalues to the Jones-Dole equation by a least squares method [35] as follows

whereis the molarity (calculated from molality data). The values ofcoefficients are summarized in Table 7.

Table 6 Values of relative viscosity of the 4-amino butyric acid in aqueous salbutamol sulphate

Table 6 (Continued)

T/KmS/mol·kg－1Molarity (C)/mol·dm－3Relativeviscosity (ηr)T/KmS/mol·kg－1Molarity (C)/mol·dm－3Relativeviscosity (ηr) 313.150.01250.0200321.005545318.150.00410.0198791.004727 0.0399831.0117590.0396881.010262 0.0598931.0182440.0594571.016459 0.0797221.0242650.0791561.022586 0.0995121.0308240.0987861.029156 0.02070.0201411.0057100.01250.0199951.005171 0.0402201.0122110.0399091.010778 0.0602461.0188450.0597821.017257 0.0802091.0248280.0795741.023160 0.1001111.0312740.0993261.030009 318.150 (in water)0.0197751.0037470.02070.0201071.005359 0.0394921.0095580.0401511.011220 0.0591501.0138970.0601421.017726 0.0787501.0215570.0800721.023737 0.0982931.0278940.0999381.030464

Note:S, molality of salbutamol sulphate.

Table 7 Values of viscosity B coefficients of 4-amino butyric acid in water and in aqueous salbutamol sulphate

①Ref. [7],② Ref. [36].

Note:S, molality of salbutamol sulphate. Parentheses indicates standard errors.

The literature-values for the 4-aminobutyric acid in water are also given in Table 7 for comparison. There is a close agreement onvalues reported in this work with literature values for AA validates our viscosity data.

Table 8 Values of activation free energy of solvent?, solute??and average molar volume of solvent?, solute??of aqueous salbutamol sulphate solutions

Table 9 Values of thermodynamic activation parameter transfer??of 4-amino butyric acid from ground state to transition state in aqueous salbutamol sulphate solutions

Table 10 Values of activation entropy T??(kJ·mol－1) and activation enthalpy??(kJ·mol－1) of 4-amino butyric acid in aqueous salbutamol sulphate solutions

4 CONCLUSIONS

NOMENCLATURE

viscosity-coefficient, dm3·mol－1

molarity of amino acid, mol·dm－3

Planck constant

molar mass of amino acid

molality of amino acid

AAvagadro’s number

Hhydration number

universal gas constant (8.314 J·mol－1·K－1)

vcoefficient in Eq. (2)

temperature, K

flow time of solution in viscometer

rrelative viscosity

density, kg·m－3

Superscripts

0 binary solvent (in aqueous salbutamol sulphate)

Subscripts

1 binary solvent property

2 solute property

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* To whom correspondence should be addressed. E-mail: krishnanpsr@yahoo.com