INTERACTION BETWEEN DRUGS AND WATER-SOLUBLE POLYMERS .3. BINDING POSITION OF IBUPROFEN WITH BOVINE SERUM-ALBUMIN DETERMINED BY MEASURING NUCLEAR-MAGNETIC-RESONANCE RELAXATION-TIME

The binding of ibuprofen (IB) to bovine serum albumin (BSA) was predominantly attributed to a hydrophobic interaction based on the thermodynamic parameters obtained by equilibrium dialysis. Little variation in the proton chemical shift of IB was observed when concentrations of the IB were changed (1-10 mM), or with the addition of BSA (7.25 x 10(-5) M). The spin-lattice relaxation time (T1) of IB was almost concentration-independent, but decreased in the presence of BSA to 36-45% for the phenyl group and its neighborhood, and to 70-97% for the other positions. The spin-spin relaxation rate (1/T2) of IB was also almost concentration-independent, but significantly increased ca. 37 times for the phenyl group and 12-24 times for the alkyl group in the presence of BSA. The ratio of the spin-spin relaxation rate of the free IB to the bound IB ((1/T2)b/(1/T2)f) of the phenyl group was 2-3 times larger than that of the alkyl group as shown by a contour plot (Chart 1). The binding of IB to BSA was considered to involve mainly the phenyl group of IB.