Studies on the binding of benzodiazepines to human serum albumin by circular dichroism measurements

Abstract

The binding of twenty-one different benzodiazepine derivatives to human serum albumin (HSA) has been studied by circular dichroism (CD) measurements in 0.1 M KCl and 0.005 M phosphate buffer at pH 7.4 and 25°. The binding has been related to the qualitative changes of the CD spectra of HSA between 250 and 350 nm and, in some representative benzodiazepine derivatives, to the electron distribution as calculated by the CNDO/2-method. The binding has also been quantitatively studied with a continuous CD titration technique. The data were numerically analyzed with computer programs based on one-site, two-sites and three-sites models. It is concluded that most derivatives will bind primarily to one site on HSA. It is moreover concluded that variations of the C 2-amino side chains will not influence the binding properties. Oxygens at C 2 or C 3 will increase the binding, while oxygens in both positions will decrease the binding. A derivative with a C 7-amino group will show only weak affinity for HSA, which might be explained by the positive character of the hydrogens in the amino group according to the CNDO/2-calculation. A C 7-nitro group will also impair the binding, as well as large substituents at N 1.