Studies 0n Ion Association of Some Α-Amino Acids with L-Ascorbic Acid In Aqueous Solution at Different Temperature

Abstract

Molar conductivity of ascorbic acid (AA) with some α–amino acids (glycine (Gly), methionine (Met), cysteine (Cys) and tryptophan (Trp)) in aqueous solution was measured at range temperatures from 298 K to 313 K. Λ_o. The limiting molar conductivity, K_A, the association constant was calculated using the Shedlovsky method, and R, the association distance calculated by Stokes–Einstein equation. The thermodynamic parameters (The heat of association ΔH^o, the change in Gibbs free energy ΔG^o, the change of entropy ΔS^o), and (ΔE_S), the activation energy were also calculated. All of the results obtained were discussed. The data showed the increasing in Λ_o, with the increasing of temperature. The positive values for (ΔS^o) and (ΔE_S) showed a decrease in solvation of ion–pair and signifying the higher mobility of the ions. The negative value of ΔH^o, refers that the association processes are exothermic. The negative values of ΔG^o, are for ion association in aqueous solution and increase with the increase in temperature.