Volumetric and ultrasonic studies of glycine in binary aqueous solutions of mannose, maltose and raffinose at different temperatures

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1 Indian Journal of Chemistry Vol. 49A, Octoer 21, pp Volumetric and ultrasonic studies of glycine in inary aqueous solutions of mannose, maltose and raffinose at different temperatures Amalendu Pal*, Ramniwas & Nalin Chauhan Department of Chemistry, Kurukshetra niversity, Kurukshetra , India Received 1 May 21; revised and accepted 8 Septemer 21 Apparent molar volumes and adiaatic compressiilities of glycine (.5-.3 mol kg -1 ) in aqueous mannose, maltose and raffinose solutions ranging from pure water to 6. mass % of saccharides have een determined at , and K from precise measurements of density and speed of sound. Partial molar volumes and partial molar adiaatic compressiilities of glycine at infinite dilution are evaluated. These values are used for calculating the numer of water molecules hydrated to glycine molecule. Transfer volumes and transfer adiaatic compressiilities at infinite dilution from water to aqueous saccharide solutions have also een calculated. Transfer parameters have een interpreted in terms of solute-cosolute interactions on the asis of cosphere overlap model. Pair and triplet interaction coefficients have also een calculated from transfer parameters. Keywords: Solution chemistry, Amino acids, Saccharides, Apparent molar volumes, Adiaatic compressiilities, Density, Speed of sound It is well known that saccharides are typical nonelectrolytes with several hydroxyl groups and these polyhydroxy compounds help in stailizing the native conformations of gloular proteins 1,2. Hydration ehavior of saccharides has een found to e related to the numer or configuration of hydroxyl groups 2-4. Saccharides and their derivatives are very important chemicals in life processes, while amino acids are asic components of protein molecules. In living organisms, interactions of saccharides with model molecules of proteins and the temperature dependence of these interactions play a key role in understanding the nature of action of ioactive molecules and the thermodynamic ehavior of iochemical process in the ody system. Therefore, studies on carohydrates-proteins interactions are very important in immunology, iosynthesis, pharmacology, and medicine. Literature survey 5-12 shows that experimental and theoretical works have een reported on thermodynamics of amino acids in aqueous carohydrate solutions. However, thermodynamic studies (especially on the speed of sound) of the interaction etween carohydrates and proteins in solutions are rare. Since proteins are particularly complex molecules, a direct study on proteins is very difficult and the amino acids are necessarily suitale model compounds of proteins. Studies on the thermodynamic properties for saccharides+amino acids+water system are important. Recently, attention has een focused on the thermodynamic properties of aqueous solutions of low molecular weight saccharides The main ojective of these studies is to investigate the solute-cosolute interactions in such solutions. In our previous works 17-22, thermodynamic studies of some amino acids/peptide + saccharides + water systems have een carried out y using volumetric, transport and acoustic measurements. In the present paper, we have explored the interactions etween mono-, di-, and tri-saccharides and amino acid in water. Density (ρ) and speed of sound (u) of amino acid (glycine) in aqueous mannose, maltose and raffinose solutions have een reported at , and K. From these data, the partial molar volumes ( V ϕ ) and partial molar adiaatic compressiilities ( K ϕ ) at infinite dilution have een calculated. These parameters have een used to calculate the transfer parameters ( V ϕ and K ϕ,s ) and hydration numer (n H ) of amino acid in aqueous saccharide solutions. The results are discussed in terms of cosphere,s

2 131 INDIAN J CHEM, SEC A, OCTOBER 21 overlap model. It is expected that these results and concentration effect of additives will provide information on the effect of saccharides on the staility of gloular proteins. Materials and Methods The amino acid used in this study, glycine, was of analytical reagent grade, procured from (E. Merck, Mumai) and was recrystallized twice fromethanol-water mixtures. The material was used after drying at 1 o C for 6 h and then under vacuum over silica gel at room temperature for a minimum of 24 h. The saccharides maltose monohydrate (SD Fine Chemicals, Mumai), D(+) mannose and D(+) raffinose pentahydrate (Hi Media, Mumai) were used without further purification. However, efore use the saccharides were dried over P 2 O 5 in a vacuum desiccator for 48 h. Douly distilled deionized water was freshly degassed prior to making the solutions. Solutions of saccharide were prepared y mass in the range 2-6 % and were used on the same day. Solutions of glycine in (.5-.3 mol kg -1 ) were made y mass on the molality concentration scale with a precision of ±.1 mg on an electronic alance (A&D Co. Japan, model GR-22). The uncertainties in the solution molalities were in the range±2 1-5 mol kg -1. The solution densities (ρ) and speeds of sound (u) were simultaneously and automatically measured, using an Anton Paar DSA 5 instrument. Both, speed of sound and density, are extremely sensitive to temperature, and hence were controlled to ± K with a uilt-in solid state thermostat. Before the measurements, caliration of the apparatus was carried out at each temperature with douly distilled deionized water and dry air. For pure water, the values for the density (999.1, , and kg m -3 ) and ultrasonic velocity ( , , and m s -1 ) were otained at the temperatures , and K. The apparatus was also tested with the density of aqueous sodium chloride of known molality using the data given y Pitzer et al. 23 and Millero et al. 24. The sensitivity of instruments corresponded to a precision in density and speed of sound measurements of g cm -3 and m s -1, respectively. The reproduciility of density and speed of sound estimates was found to e within g cm -3 and m s -1, respectively. Results and Discussion Apparent molar properties Densities (ρ) and speeds of sound (u) at temperatures , and K for solutions of glycine in inary aqueous solutions of mannose, maltose and raffinose (mass % of saccharides = 2 6) are given in Tale 1. All the plots of densities and speeds of sound were found to e linear. The apparent molar volumes (V ϕ ) were calculated using the Eq. (1), Vϕ = M ρ 1 ( ρ ρ) msρρ (1) where m S is the molality of solution (mol kg -1 ), M is the relative molar mass of the solute and ρ and ρ are the densities of pure solvent and solution, respectively. The values of (V ϕ ) increase with increase in temperature. The apparent molar adiaatic compressiilities K ϕ ) can e calculated using the equation, (,s Kϕ, S = M βs ρ {1 ( βs,ρ βs ρ) ms ρρ (2) where K ϕ,s, β S, and β S are the adiaatic compressiilities of solution and coefficient of adiaatic compressiilities (Pa -1 ) of pure solvent and solution, respectively. The other symols are as defined from Eq. (1). The coefficient of adiaatic compressiility (β s ) of the solute can e calculated from the speed of sound and density data using the relation, βs 1/ u 2 ρ = (3) The variation of apparent molar quantities with molality can e adequately represented y the linear relation, Yϕ Yϕ SQm where = + (4) Y ϕ ( Y ϕ denotes V ϕ or K ϕ,s ) is the infinite dilution value that is equal to the partial molar property at infinite dilution and S Q (S Q denotes S V or S K ) is the experimental or limiting slope. Equation (4) was fitted to our experimental Vϕ and K ϕ,s data in different saccharide solutions y the method of least squares to evaluate the infinite dilution partial molar volumes ( V ϕ ) and the adiaatic compressiilities ( K ϕ,s ). The values of V ϕ, K ϕ,s, S V and S K for glycine at different temperatures are given in Tale 2 together with the standard errors.

3 PAL et al.: VOLMETRIC AND LTRASONIC STDIES OF GLYCINE+SACCHARIDES BINARY MIXTRES 1311 Tale 1 Density (ρ) and speed of sound (u) of glycine in aqueous saccharides at , and K M(mol kg -1 ) K K K ρ 1-3 ρ 1-3 ρ 1-3 Glycine + 2. % Mannose Glycine % Mannose Glycine % Mannose Glycine + 2. % Maltose Glycine + 4. % Maltose Glycine + 6. % Maltose ( Contd.)

4 1312 INDIAN J CHEM, SEC A, OCTOBER 21 Tale 1 Density (ρ) and speed of sound (u) of glycine in aqueous saccharides at , and K. ( Contd.) M(mol kg -1 ) K K K ρ 1-3 ρ 1-3 ρ 1-3 Glycine % Raffinose Glycine % Raffinose Glycine % Raffinose Tale 2 Limiting partial molar properties ( V ϕ and K ϕ,s ) a and experimental slopes (S V and S K ) of glycine in aqueous saccharide solutions at , and K Mass % V ϕ 1 6 (m 3 mol -1 ) at temp. (K) = S V 1 6 (m 3 L 1/2 mol -3/2 ) at temp. (K) = K ϕ,s 1 6 (m 3 mol -1 GPa -1 ) at temp. (K) = S K 1 6 (kg m 3 mol -2 GPa -1 ) at temp. (K) = (±.1) (±.1) (±.2) 1.46 (±.6) 1.3 (±.6) 1.13 (±.9) (±.62) (±.46) (±.37) 1.45 (±3.31) 2.64 (±2.46) 7.12 (±1.97) (±.1) 43.3 (±.1) (±.1) 1.2 (±.3) 1.44 (±.7) 1.8 (±.9) (±.4) (±.9) (±.7) 5.29 (±.24) 2.64 (±.5) 3.65 (±.42) (±.2) 43.4 (±.1) 43.9 (±.1) 2.26 (±.13) 1.95 (±.6) 1.79 (±.7) (±.19) (±.7) (±.24) 4.53 (±1.6).65 (±3.89) 1.15 (±1.31) (±.1) (±.) (±.) (±.9) (±.3) (±.1) (±1.8) (±1.53) (±.1) (±14.35) (±12.22) (±158.55) (±.3) (±.1) 43. (±.1) 13. (±.24) (±.9) (±.8) (±2.49) (±2.65) (±2.7) (±18.22) 1.14 (±19.45) 9.9 (±18.54) (±.2) (±.1) (±.) (±.19) 11.2 (±.1).92 (±.1) (±4.4) (±3.33) (±3.44) (±29.24) (±24.16) (±29.24) (±.2) (±.1) (±.1) 1.92 (±.13) 1.58 (±.5) 1.61 (±.5) (±.7) (±.47) (±.33) (±5.) (±3.37) 1.99 (±2.35) (±.3) (±.1) (±.1) 3.72 (±.2) 3.2 (±.5) 3.68 (±.11) (±.37) (±.45) (±.14).39 (±2.77) -.33 (±3.33) 6.12 (±1.2) (±.3) 43.3 (±.3) (±.1) 3.5 (±.18) 3.56 (±.17) 3.26 (±.8) (±.38) (±.22) (±.13) 4.91 (±2.69) 6.93 (±1.55) 6.1 (±.93) a V ϕ for glycine in water: m 3 mol -1 at K, m 3 mol -1 at K, and x 1-6 m 3 mol -1 at K and K ϕ,s for glycine in water: (±.4) 1-6 m 3 mol -1 GPa -1, at K, (±.1) 1-6 m 3 mol -1 GPa -1, at K and (±.5) 1-6 m 3 mol -1 GPa -1, at K are taken from refs 17 & 25.

5 PAL et al.: VOLMETRIC AND LTRASONIC STDIES OF GLYCINE+SACCHARIDES BINARY MIXTRES 1313 The experimental values of V ϕ and K ϕ,s for glycine are given in in water reported in literatures 17,25 the footnote in Tale 2. The types of interactions occurring etween glycine and mannose, maltose and raffinose can e classified as follows 26 : (1) Hydrophilic-ionic interactions etween the -OH group of the saccharides and the zwitterionic centers of the amino acid; (2) Hydrophoic-hydrophoic interactions etween the non-polar side groups of the saccharides and the non-polar group of the amino acid; (3) Hydrophilic-hydrophilic interactions etween the -OH group of the saccharides and the NH 2 group of the amino acid meditated through the hydrogen onding; (4) Hydrophilic-hydrophoic interactions etween the -OH group of the saccharide molecules and the non-polar group of the amino acid. Perusal of Tale 2 shows that the amino acid studied here has positive V ϕ and negative K ϕ,s in aqueous saccharides solutions at different temperatures therey showing the presence of strong solute-solvent interactions 27. Further, the V ϕ values increase at all temperature from 2 to 6 mass % of D (+) mannose, whereas V ϕ values increase at lower and higher mass percentage, and at higher temperatures of D (+) raffinose. It indicates that the cosolute mannose-solvent interaction increases on increasing mass % of mannose. So, it may e said that the interactions etween the mannose and charged end group (NH + 3 COO - ) of glycine are much stronger than those etween mannose and non-polar group. Similar oservations were oserved in the case of glycine with monosaccharide, i.e. glucose 17,28,29, maltose, sucrose 3 and also in the case of diglycine with monosaccharides The V ϕ values decrease from 2 to 4 mass % of maltose and raffinose and then increases at all temperatures with increasing mass % of saccharides in oth the cases. Similar oservations have een oserved in our previous work 19 for L-alanine in the case of maltose. The V ϕ results, and those of the V ϕ results of L-alanine with maltose at , and K 19 show that for each amino acid, at each particular temperature, V ϕ increases in the sequence: L-alanine > glycine. The experimental S V values are a measure of solute-solute interactions. It is evident from Tale 2 that the values of S V are negative at lower mass % of maltose at the measured temperatures. In the case of raffinose and mannose, S V values are positive and smaller than the corresponding V ϕ values at all mass % and at all temperatures. The lower values of S V suggest that the solute-solute interactions are weaker than the solute-solvent interactions. It may e said that the solvation of ion decreases with the increase in mass % of saccharide. Transfer molar properties The partial molar volumes of transfer ( V ϕ ) and partial molar adiaatic compressiilities of transfer ( K ϕ,s ) from water to aqueous saccharide solutions have een calculated y Eq. (5), Y ϕ = Y ϕ (in aqueoussaccharidesolution) Yϕ (in water) (5) where Y ϕ denotes V ϕ or K ϕ,s. The calculated results are given in Tale 3. As can e seen in Tale 3, the values of V ϕ for glycine are positive with mannose and maltose except at lower mass % of mannose (at higher temperature) and at 4 mass % of maltose while for raffinose oth positive and negative V ϕ values have een oserved at all temperatures. The more positive V ϕ values of glycine in the case of mannose and maltose at higher concentrations of saccharides indicate the overlap of the hydration cosphere of the ion (COO - and NH + 3 )/(-NH 2 ) of the glycine and OH group of the saccharides. This leads to the release of the water to the ulk therey increasing volume. This is more compressile than the water in electrostriction region. This suggests that glycine is a structure reaker in higher mass % of mannose and maltose solutions. The negative values of V ϕ at lower mass % of mannose (at higher temperature) and also in the case of raffinose indicate the effect of hydrophoic

6 1314 INDIAN J CHEM, SEC A, OCTOBER 21 part. This indicates the weak structure-reaking effect of glycine in lower mass % region of mannose or raffinose due to the interactions etween -OH group of mannose or raffinose with the zwitterionic centre of glycine. Tale 3 shows that values of K ϕ,s for glycine are negative at lower mass % of raffinose and ecome positive at higher mass % of trisaccharide (raffinose). This is again due to the overlap of the hydration cosphere of the ions (COO - and NH + 3 )/(NH 2 ) of the glycine and OH group of the trisaccharide. A large dip in K ϕ,s values in the case of maltose at higher mass % suggests that increase in the interaction etween the OH group of the saccharide and non-polar group of the glycine leads to the disruption of the hydration sphere of the charged centre of amino acid and thus the positive contriution to K ϕ,s gets reduced. We have also explained the V ϕ values on the asis of the co-sphere overlap model 31,32 in terms of solute-cosolute interactions. According to this model, hydrophilic-ionic group interactions contriute positively, whereas hydrophilic-hydrophoic group interactions contriute negatively to the V ϕ values. For glycine in aqueous saccharide solutions, the former type of interactions predominates over the latter. With the increase of the saccharide concentrations, the interactions etween the -OH group of the saccharide and the zwitterionic center of the glycine also increase gradually which are not compensated y the interactions etween the -OH group of the saccharide and non-polar group of the glycine. It may e noted that V ϕ values of maltose are higher than those of glycine in mannose and raffinose at higher mass percentages. As a result greater electrostriction of solvent water is produced as in the case of glycine in mannose and raffinose, leading to lower values of V ϕ. Partial molar expansiilities The variation of limiting partial molar volume, with temperature can e expressed y Eq. (6), V ϕ, 2 V a T ct ϕ = + + (6) where T is the temperature in Kelvin and a, and c are constants. The partial molar expansiilities at infinite dilution E ( ϕ ) were otained y differentiating Eq. (6) with respect to temperature, ϕ E = ( Vϕ / T ) T = + 2cT (7) The ϕe values of glycine at , , and K in aqueous saccharide solutions were determined and are reported in Tale 3. It may e noted that ϕ E values are positive (except at 4 mass % of maltose at higher temperature) favoring the solute-solute interactions. The ϕ E values of glycine decrease with rise in temperature in the case of mannose (except at lower temperature) and raffinose, Tale 3 Transfer volumes ( V ϕ ), limiting partial molar expansiilities ( ϕ E ) and transfer adiaatic compressiilities ( K ϕ,s ) of glycine in aqueous saccharide solutions at (288.15, and 38.15) K Mass % V ϕ 1 6 (m 3 mol -1 ) ϕ E 1 6 (m 3 mol -1 K -1 ) K ϕ,s 1 6 (m 3 mol -1 GPa -1 ) K K 38.15K K K 38.15K K K 38.15K Mannose Maltose Raffinose

7 PAL et al.: VOLMETRIC AND LTRASONIC STDIES OF GLYCINE+SACCHARIDES BINARY MIXTRES 1315 whereas in the case of maltose where it increases, indicating that glycine acts as weak structure-reaker in lower mass % of saccharides. At all mass % of saccharides (except at higher mass % in the case of maltose) the ϕ E values for glycine decrease with increase in temperature. This indicates maximum structure-reaking of saccharides on addition of glycine in the higher concentration region of saccharides. The effect is that electrostricted water may e released from the loose solvation layers of glycine y elevation of temperature. This is reflected y the higher V ϕ values. Further, the removal of water molecules favors glycinesaccharides or glycine-glycine interactions, indicating the structure-reaking effect of glycine in higher concentration region of saccharides and at higher temperatures. The K ϕ,s values are negative for glycine which ecomes increasingly positive at higher concentration range of mannose and raffinose. This oservation again supports the conclusion that the dehydration of solute and co-solute occurs more in glycine and increases with the increase in concentrations of mannose and raffinose. Pair and triplet interaction coefficients Kozak et al. 33 proposed a theory ased on the McMillan-Mayer 34 theory of solutions. This has further een discussed y Friedman and Krishnan 35 and Frank et al. 36 in order to include the solutecosolute interactions in the solvation spheres. According to this treatment, a thermodynamic transfer function at infinite dilution can e expressed as Eq. (8), Y ϕ (water to aqueous cosolute solution) = = 2Y AB m B + 3Y 2 ABB m B (8) where Y ϕ denotes V ϕ or K ϕ,s, A denotes amino acids and B denotes cosolute, and m B is the molality of cosolute. Constants Y AB and Y ABB are pair and triplet interaction coefficients. The Y ϕ data have een fitted to Eq. (8) to otain Y AB and Y ABB. The corresponding parameters, V AB and V ABB for volumes, and K AB and K ABB for adiaatic compressiilities, estimated from V ϕ and K ϕ,s respectively, are summarized in Tale 4. The pair and triplet interaction parameters, V AB Y ABB, K AB and K ABB contriute positively as well as Tale 4 Pair (Y AB ) and triplet (Y ABB ) interaction coefficients of glycine in aqueous saccharide solutions at , and K a T (K) From volume From compressiility V AB 1 6 (m 3 mol -2 kg) V ABB 1 6 (m 3 mol -3 kg 2 ) K AB 1 6 (m 3 mol -2 Kg GPa -1 ) K ABB 1 6 (m 3 mol -3 kg 2 GPa -1 ) (±.23) (±.35) (±.925) (±6.36) (±.374) (±12.25) (±4.983) (±3.49) (±4.188) u ncertainties given in parantheses Glycine in aqueous mannose (±.489) (±1.78) (±.75) (±3.572) (±1.968) (±4.37) Glycine in aqueous maltose (±25.72) (±56.717) (±27.163) (±51.24) (±36.64) (±19.7) Glycine in aqueous raffinose (±35.321) (±25.992) (±24.741) (±31.178) (±29.687) (±8.43) (±2.293) (±7.596) (±9.294) (± ) (± ) (±8.992) (± ) (±22.999) (±59.563)

8 1316 INDIAN J CHEM, SEC A, OCTOBER 21 negatively with all saccharides at any particular temperature. The maximum positive values of pair interaction coefficients V AB in the case of glycine with mannose at lower temperatures suggest that interactions occur due to the overlap of hydration spheres of solute-cosolute molecules. Hydration numer The partial molar volume of the amino acids can e examined y a simple model 37 using Eq. (9), V ϕ (amino acid) = where V ϕ (int) + V ϕ (elect)... (9) V ϕ (elect) is the electrostriction partial molar volume due to the hydration of the amino acid and can e estimated from experimentally measured values of V ϕ (amino acid) and Vϕ (int) is the intrinsic partial molar volume of the amino acid and has een calculated from the following expressions 37, Vϕ (int) = (.7 /.6) Vϕ ( cryst) (1) and Vϕ (int) = (.7 /.674) Vϕ ( cryst) (11) where V ϕ ( cryst) (= mol. wt./d cryst ) is the crystal molar volume,.7 is the packing density for molecules in organic crystals and.634 is the packing density for random packing spheres. The values of Vϕ (int) for the amino acids have een estimated from Eqs (1) and (11) using d cryst values for glycine (1.598 g cm 3 ) taken from the work of Berlin and Pallansch 38. The change in volume due to electrostriction can e related to the numer of water molecules (n H ) hydrated to the amino acid as follows 39,4, nh Vϕ ( elect) / ( Vϕ, e V ϕ, ) where = (12) V ϕ,e is the molar volume of electrostricted water and V ϕ, is the molar volume of ulk water ( m 3 mol -1 at K). The reported value 37 of ( Vϕ, e V ϕ, ) is m 3 mol -1 at K. sing the value of ( Vϕ values of, e V ϕ, ) and the V ϕ ( elect), calculated from oth the methods, the n H values were estimated from Eqs (1) and (11) (Tale 5). Further, the numer of water molecules, n H, hydrated to the amino acids were calculated y using the method given y Millero et al. 37,41, n H K ϕ, s (elect) / V ϕ, K s, where =... (13) K s, is the isothermal compressiility of ulk V, K s, water. The value of ϕ was m 3 mol -1 GPa -1. The electrostriction partial molar compressiility K ϕ, s (elect) can e calculated from the experimentally measured values of from Eq. (14), Kϕ, s (elect) Kϕ, s (amino acids) Kϕ, s (int) K ϕ,s (amino acid) =... (14) where K ϕ, s (int) 37,42 = K ϕ, s (isomer) for glycine ( m 3 mol -1 GPa -1 ). Since one would expect K ϕ, s (int) to e small (it is less than m 3 mol -1 GPa -1 for ionic crystals and many organic solutes in water 37 ), it may e assumed that K ϕ, s (int). Therefore, for K ϕ, s (int), Eq. (14) ecomes, Kϕ, s (elect) Kϕ, s (amino acids) =... (15) The values of n H calculated from Eqs (14 and 15) using the Kϕ, ( elect) values determined y these two s Tale 5 Hydration numer (n H ) of glycine in aqueous saccharide solutions at K Mass % From volume using n H From compressiility using Eq.1 Eq.11 Eq.14 Eq.15 Mannose Maltose Raffinose

9 PAL et al.: VOLMETRIC AND LTRASONIC STDIES OF GLYCINE+SACCHARIDES BINARY MIXTRES 1317 methods are listed in Tale 5. The values of n H (in water) calculated y these methods, from volume and compressiility data are given in Tale 5. These values decrease with the increase in the concentration of mannose or raffinose except with maltose, which again indicates the increase in solute-cosolute interaction with the increase in mannose or raffinose concentration. Furthermore, the values of n H for glycine at lower concentration of raffinose are higher than in water and reverse is the case with mannose and maltose. That indicates the hydrophilic-hydrophoic group interactions are higher and as a result, greater electrostriction of solvent water is produced, leading to higher values of n H at lower concentration and smaller values of V ϕ as compared to those of glycine with maltose. Conclusions In this paper, new measurements of density (ρ) and speed of sound (u) at , and K for glycine in aqueous mannose, maltose and raffinose solutions are reported. Various parameters ( V ϕ, K ϕ,s, V ϕ, K ϕ,s and n H ) have een calculated using the experimental data. These parameters reflects that the solute-solvent interactions are predominant over the solute-solute interactions for the glycine in aqueous saccharide solutions and glycine ehaves as a structure-reaker in the higher mass % of the saccharides. Acknowledgement Financial support for this project (no. 1 (2187)/7/EMR II) y the Government of India through the Council of Scientific and Industrial Research (CSIR), New Delhi is gratefully acknowledged. References 1 Back J F, Oakenfull D & Smith M B, Biochemistry, 18 (1979) edaira H & edaira H, Bull Chem Soc Japan, 53 (198) Galema S A, Howard E, Engerts J B F N & Grigera J R, Carohydr Res, 265 (1994) Banipal P K, Banipal T S, Lark B S & Ahluwalia J C, J Chem Soc Faraday Trans 1, 93 (1997) Chen Y, Liu H, Lin R & Zhang H, J Sol Chem, 36 (27) Liu H, Lin R & Zhang H, J Sol Chem, 32 (23) Liu H, Lin R & Zhang H, J Sol Chem, 35 (26) Quiocho F A & Vyas N K, Nature (London), 31 (1984) Quiocho F A, Pure Appl Chem, 61 (1989) Johnson M A, Rotondo A & Pinto B M, Biochemistry, 41 (22) Jasra R V & Ahluwalia J C, J Chem Thermodyn, 16 (1984) Lin R S, Ma L, Wang X & Xu L, Chem J Chinese niv, 27 (26) Zhuo K, Liu Q, Wang Y, Ren Q & Wang J, J Chem Eng Data, 51 (26) Liu H, Chen Y, Zhang H & Lin R, J Chem Eng Data, 52 (27) Li S, Hu X, Lin R & Zong H, Thermochim Acta, 342 (1999) Barone G, Castronuovo G, Doucas D, Elia V & Mattia C A, J Phys Chem, 87 (1983) Pal A & Kumar S, J Indian Chem Soc, 79 (22) Pal A & Kumar S, J Chem Thermodyn, 37 (25) Pal A & Chauhan N, Indian J Chem, 48A (29) Pal A & Chauhan N, J Mol Liq, 149 (29) Pal A & Singh N, J Indian Chem Soc. 86 (29) Pal A & Chauhan N, J Sol Chem, (21) (accepted). 23 Pitzer K S, Peiper J C & Busey R H, J Phy Chem, Ref Data 13 (1984) Surdo A L, Alzola E M & Millero F J, J Chem Thermodyn, 14 (1982) Ogawa T, Yasuda M & Mizutani K, Bull Chem Soc Japan, 57 (1984) Bhat R, Kishore N & Ahluwalia J C, J Chem Soc Faraday Trans 1, 88 (1988) Beliagli K B & Ayranci E, J Sol Chem, 19 (199) Ali A, Hyder S, Sair S, Chand D & Nain A K, J Chem Thermodyn, 38 (26) Li S, Sang W & Lin R, J Chem Thermodyn, 34 (22) Parfenyuk E V, Davydova O I & Leedeva N S, J Sol Chem, 33 (24) Frank H S & Evans M W, J Chem Phys, 13 (1945) Gurney R W, Ionic Process in Solution, Vol. III, (McGraw Hill, New York) 1953, Chap. XII. 33 Kozak J J, Knight W S & Kauzmann W, J Chem Phys, 48 (1968) McMillan W G Jr & Mayer J E, J Chem Soc, 13 (1945) Friedman H L & Krishnan C V, J Sol Chem, 2 (1973) Franks F, Pedley M & Reid D S, J Chem Soc Faraday Trans 1, 72 (1976) Millero F J, Surdo A L & Shin C, J Phys Chem, 82 (1978) Berlin E & Pallansch M J, J Phys Chem, 72 (1968) Padova J, J Chem Phys, 39 (1963) 1552, J Chem Phys, 4 (1964) Harned H S & Owen B B, The Physical Chemistry of Electrolytic Solutions, 3 rd Edn, ACS Monograph Series No. 137, (Reinhold, New York) Millero F J, Ward G K, Lepple F K & Hoff E V, J Phys Chem, 78 (1974) Gucker F T Jr & Haaq R M, J Acoust Soc Amer, 25 (1953) 47.