Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of glycine (G), diglycine (DG), and triglycine (TG), from water to aqueous mixtures of glycerol (GL) and urea (UH) have been determined from solubility measurements at different temperatures. This was also extended to an ionic cosolvent system like aqueous sodium nitrate solutions for G and DG. The observed [Formula: see text] and [Formula: see text]–composition profiles, as well as those obtained after correcting for the "cavity effect" as estimated by scaled particle theory (SPT), were examined in the light of various interactions. The corrected [Formula: see text]and [Formula: see text] values show a regular function of the peptide chain length of the amino acids and impart useful information regarding the involved relative structural effects of these ionic and non-ionic cosolvents.

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HIMANSU TALUKDAR, SIBAPRASAD RUDRA, and KIRON K. KUNDU. Can. J. Chem. 67, 315 (1989). Deprotonation constants, K,(RH~+) and Ka(RHk), of glycine (RH') have been determined at five equidistant temperatures ranging from 15 to 35°C by measuring the emf of galvanic cells comprising Pt/H2 and Ag-AgC1 electrodes in aqueous mixtures of protophilic protic urea (UH) and protophobic protic glycerol (GL). Medium effects on deprotonation of the acid: 6(~%;:) = -, A P (X = G or S) have been dissected into transfer free energies (AGy(i)) and entropies (A$(i)) of the species involved as obtained by measuring the transfer energetics A* of RH' from solubility measurements at different temperatures and of H + based on tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption determined earlier. The AGlqch(i) values obtained after due correction from the cavity effect based on scaled particle theory (SPT) and electrostatic effects including Born and ion-dipole effects for the charged species involved in the two deprotonation equilibria enable better understanding of the solvent effect on the deprotonation constants. Moreover, the ~A~~h ( i ) -~~m~~~i t i~n profiles are found to exhibit similar characteristic maxima and minima as for simple cations and anions in these solvent systems, thus providing useful information on the structural characteristic of these cosolvents.

HIMANSU TALUKDAR, SIBAPRASAD RUDRA, and KIRON K. KUNDU. Can. J. Chem. 67, 321 (1989). Single-ion transfer free energies [AGY(i)] and entropies [AsP(i)] of some ions from water to aqueous mixtures of urea and glycerol have been determined using the widely used tetraphenylarsonium tetraphenylborate reference electrolyte assumption from solubility and emf measurements of some appropriate electrolytes at five different temperatures (15 to 35OC). Analysis of AGY(i) and TAsP(~) values of the ions as well as their respective "chemical" effect, AGtCh(i) and T A S &~(~) , as obtained after correcting for their cavity and Born-type electrostatic effects, estimated by the scaled particle theory (SPT) and simple Born equation, respectively, show a complex dependence upon solvent composition. Attempts have been made to explain the observed mirror-image entropic behaviour of simple cations and anions in the light of Kundu et 01,'s four-step transfer process and to compare the results with those obtained in other aquo-ionic and nonionic systems.Key words: single ion, transfer energetics, TATB assumption, aqueous glycerol, aqueous urea. Introduction It is now well recognised that transfer enthalpies (AH:) and entropies (AS:) of electrolytes and non-electrolytes often provide useful information regarding the relative structuredness of solvents. However, the interpretation of the experimental results on AS: lately proved somewhat difficult and conflicting with the general recognition that the entropic behaviour of the oppositely charged species like H+ and X-(X = C1, Br, or I) as based on the widely used tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte (RE) assumption (1) show nearly mirror-image behaviour in some aquo-organic (2-6) and aquo-ionic (7) systems imparting more refined information on the solvent structural features.Evidently, it should be of particular interest to extend this type of study to some other aquo-organic solvents and especially

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