Effect of chain length on interactions of aliphatic alcohols with suspended human serum albumin

Abstract

Enthalpy changes on the immersion of human serum albumin (HSA) into n-butanol, n-propanol, ethanol and methanol containing different amounts of water have been measured calorimetrically at 25°C. Water sorption isotherms on HSA were also determined in water-n-butanol and water-ethanol mixtures. From comparison of the calorimetric and sorption data, it was concluded that there is a significant enthalpy change on the HSA immersion into methanol and ethanol even under conditions where there is no change in the quantity of adsorbed water. No similar contribution was found in the n-butanol based suspensions. Water monolayer capacity evaluated from the Langmuir model decreases also significantly when going from ethanol to n-butanol. Considering this non water sorption contribution, values of the monolayer capacity and the shape of the experimental dependences, it was inferred that a relatively small change of the solvent molecule structure (from n-propanol to ethanol) affects strongly the interactions of the protein with the solvent.