| Abstract |
Density data for very diluted aqueous solutions of proline-leucine are reported for eight different temperatures from (283.15 to 318.15) K. Measurements were made using a vibrating tube densimeter. Apparent molar volumes of the dipeptide were calculated, at each temperature, and least squares fitted to linear equations. A weighted method with weighting factors inversely proportional to the square of the individual uncertainties has been used. Limiting partial molar volumes, V-m,2(infinity), and S-v values were obtained from the intercepts and slopes of those equations. Negative slopes were obtained for the lower temperatures against positive values for the higher. Trends of the values obtained are an evidence of the overwhelming contribution of the hydrophobic interactions at lower temperatures. Limiting partial molar isobaric expansions, E-P,m,2(infinity), have been also calculated using the temperature derivatives of the corresponding volumes, showing negative values. The decrease of their absolute values, with increasing temperature, points out to predominant structure maker behaviour of the solute. (C) 2004 Elsevier Ltd. All rights reserved. |
