Experimental investigation of the effects of beta-cyclodextrin on the unfolding and aggregation of human serum albumin

Effects of â-cyclodextrin (â-CD) on the unfolding and aggregation of human serumalbumin (HSA) was investigated employing isothermal titration calorimetry (ITC) at 300 K in 50mMphosphate buffer solution. â-CD inhibited aggregation and its inhibition was generally in the order of a-CD< a- CD< â-CD. Hydrophilic â-CD reduced the thermally induced unfolding and it was suggested that â-CD destabilises native HSA or stabilises the unfolded state of HSA. The obtained heats for HSA + â-CD interactions were reported and analysed in terms of the extended solvation model, this model was used to reproduce the enthalpies of HSA interaction with â-CD in a broad range of complex concentration. The parametersi¤ i±A andi¤ i±B reflected to the net effect of â-CD on the HSA stability in the low and high cyclodextrin concentrations, respectively. The positive values fori¤ i±A indicated that â-CD stabilises the HSAstructure in low concentrations. Variations of the UV-Vis and fluorescence spectra of HSAshowed that â-CD in low concentrations has a strong ability to quench the fluorescence launching from HSA by reacting and forming a certain kind of new compound.