Interaction of Poly(vinylpyrrolidone) with Amino Acids and their Related Compounds

Abstract

The interaction of poly(vinylpyrrolidone)(PVP) with amino acids and with their related compounds was studied by the measurement of the intrinsic viscosity, Pa of aqueous solution of PVP and by the determination of the amount, x, of amino acid bound to PVP per monomer unit using membrane equilibrium technique.
It was found that amino acid having both hydrophobic and hydrophilic groups, such as tryptophan (Try), combined with PVP to raise the [77] of the polymer (Fig.4). Notwithstanding the x of HCl-salt of Try. is larger than that of Na-salt, the [7i] of PVP in the latter solution is larger than that in the former, as shown in Fig.11. On the contrary, it was found that amino acid having polar groups, such as aspartic acid (Asp.) and glutamic acid (Glu), and their related compounds reduced the [V] of PVP and allowed to salt out the polymer, as shown in Figs.7 and 8. Dehydration of PVP by means of polar groups found in Asp. and Glu. became stronger as the neutralization with NaOH proceeded. The a, co dicarboxylic acids were found to have the same behavior as above which are shown in Fig.9. This effect was strengthened with the number of OH groups, e. g., in the order of succinic acid, malic acid and tartaric acid, as shown in Fig.7. Salting out effect was strongest for sodium oxalate, and this effect became weaker with increasing number of carbon atoms, n, in a hydrocarbon chain. The salts, whose n is larger than that of disodium azelaiate, raised the [77] of PVP as shown in Figs.9 and 10. The [n] of PVP became larger in the solution of monocarboxylic acid than in pure water, when chain length is larger than sodium valeriate. It was, therefore, concluded that cosolutes having a chain shorter than 3.5 units of methylene group per carboxyl group brought about shrinkage of polymer coil by dehydration and reduced the [77], but cosolutes having longer chain than the above raised the [77] because the cosolute combined with PVP and consequently the expansion of polymer coil occurred.