Thermodynamic Analysis of Homologous α-Amino Acids in Aqueous Potassium Fluoride Solutions at Different Temperatures

Abstract

Partial molal volumes (\(V_{\phi} ^{0}\)) and partial molal compressibilities (\(K_{\phi} ^{0}\)) for glycine, L-alanine, L-valine and L-leucine in aqueous potassium fluoride solutions (0.1 to 0.5 mol⋅kg−1) have been measured at T=(303.15,308.15,313.15 and 318.15) K from precise density and ultrasonic speed measurements. Using these data, Hepler coefficients (\(\partial^{2}V_{\phi} ^{0}/\partial T^{2}\)), transfer volumes (\(\Delta V_{\phi} ^{0}\)), transfer compressibilities (\(\Delta K_{\phi} ^{0}\)) and hydration number (nH) have been calculated. Pair and triplet interaction coefficients have been obtained from the transfer parameters. The values of \(V_{\phi} ^{0}\) and \(K_{\phi} ^{0}\) vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. The contributions of charged end groups (\(\mathrm{NH}_{3}^{+}\), COO−), CH2 group and other alkyl chains of the amino acids have also been estimated. The results are discussed in terms of the solute–cosolute interactions and the dehydration effect of potassium fluoride on the amino acids.