The environment controlled effect of thiacalix[4]arene on the transition thermodynamics and kinetics of bovine serum albumin

Abstract

Complexation ability of water-soluble thiacalix[4]arene-tetrasulfonate towards three aromatic amino acids (Phenylalanine, Tyrosine and Tryptophane) was studied in water–ethanol mixtures by photoluminescence (PL) method as a function of the ethanol content of the bulk solutions. Job’s method followed by the application of the van’t Hoff theory was used to determine the thermodynamic parameters of the molecular association. Results show quite different thermodynamics of formation of calixarene–amino acid complexes at low and higher ethanol content of the solutions. The considerable stability of the individual calixarene–aromatic amino acids complexes supports their existence also in the case when the amino acids are in a protein. To test this idea the conversion rate, enthalpy and entropy change associated to the structural transition of BSA (bovine serum albumin) were investigated by Differential Scanning Calorimetry (DSC) in the absence and in the presence of calixarene. Results show that presence of calixarene changes significantly both the thermodynamics and the kinetics of the transition of BSA and the information collected for the individual calixarene–amino acid complexes gives insights about the possible processes at molecular level.