Interaction mode of dicumarol and its derivatives with human serum albumin, alpha 1-acid glycoprotein and asialo alpha 1-acid glycoprotein.

The interaction of dicumarol and its seven other derivatives with human serum albumin (HSA), alpha 1-acid glycoprotein (AGP) and desialylatedAGP (asialoAGP) has been investigated by circular dichroism (CD) and fluorescence. The binding parameters of dicumarol and its derivatives obtained from fluorescence almost agreed with those obtained from CD. The binding data indicated that the total binding affinities (nK) to HSA were higher than the binding affinities to AGP and asialoAGP. Hydrophobic interaction was the driving force for the binding to all the three proteins and nK values in the binding process were found to be increased with the increase of hydrophobicity of the compound. This was evidenced by the attempts taken to correlate binding affinities with partition coefficients. Both electrostatic and van der Waals interactions were not found to play any significant role in the binding of these compounds to any of these three proteins. However, in case of the AGP and asialoAGP binding, apart from the hydrophobic interaction, some other forces may be involved as evidenced from the experimental data. Binding was exothermic, entropy driven and spontaneous. The change of enthalpy (delta H degree) was compensated for by the change in entropy (delta S degree). Relative contribution of hydrophobic interactions in the binding of these compounds to HSA was higher than to AGP or asialoAGP. Sialic acid was not found to impart any significant role in the binding of these compounds to AGP.