Binding of 5,5-diphenylhydantoin with erythrocyte membrane: local lateral order parameter and strong interaction with phospholipid head groups.

We have studied the interaction of 5,5-diphenylhydantoin (5,5-dph), an anticonvulsant drug, with erythrocyte membrane lipids and proteins using IR spectroscopic technique. The local lateral order parameter, which is directly related to the lipid packing density, has been found to be elevated due to 5,5-dph binding. This increase has been accounted for on the basis of relaxation of local discontinuity in orientational order (defects). The transition towards an ordered structure is further supported by our experimental results which exhibit a decrease in the hydrocarbon chain mobility. The reorganization of the polar head groups due to 5,5-dph-lipid interaction leads to the absence of the bands at 1150 cm-1 (C-O stretch or C-O-C antisymmetric stretch) and 1085 cm-1 (C-O-P stretch or PO2- symmetric stretch). These bands are associated with the phospholipid head groups in erythrocyte membrane. Significant intensity changes in amide I (1650 cm-1) and amide II (1520 cm-1) have been explained using the concept of transition dipole moment coupling between C-N and N-H vibrational modes of amide II.