Interactions of glycine with aqueous solutions of sodium phosphate buffer at T = (288.15, 293.15, 298.15, 303.15, 308.15, 310.15, 313.15, 318.15, 323.15 and 328.15) K: Volumetric and UV absorption studies

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Interactions of glycine with sodium phosphate buffer have been investigated by volumetric and UV absorption studies. Densities have been measured for glycine in water of pH=(1.00, 7.40 and 13.40) and in 0.1M, 0.5M and 1M aqueous sodium phosphate buffer (NaPB) solutions as a function of concentration at T=(288.15 to 328.15) K and at pH=(1.00, 7.40 and 13.40) by using digital density meter. Apparent molar volumes (V∅) and partial molar volumes (V2o) obtained from these density data have been used to calculate partial molar volumes of transfer (∆trV2o) from water to aqueous sodium phosphate buffer solutions, which are positive for zwitterionic and deprotonated form of glycine. Interaction coefficients have been obtained from McMillan-Mayer's approach. Effect of temperature on these thermodynamic properties have been studied by determining the partial molar expansibilities (∂V2o/∂T)P at infinite dilution and their second order derivative (∂2V2o/∂T2)P at different temperatures and at pH=(1.00, 7.40 and 13.40). Hydration number (nH) of glycine at pH7.40 have been determined from the V2o data. The results have been rationalized in terms of various interactions taking place in these systems. Further, absorption spectra have also been recorded for the present system with the help of UV–visible spectrophotometer at 298.15K which is helpful in interpreting the possible molecular interactions between glycine and NaPB.