Drug-receptor recognition: molecular orientation and dielectric effects.

1 The orientation of ethidium and its carboxyphenyl derivative was computed at various positions around one turn of the B-DNA helical receptor. 2 Dielectric effects of solvent were included using values for the bulk constant and a dielectric vector to simulate dielectric inhomogeneities. 3 From the electrostatic energy values for the orientations, the corresponding Boltzmann distributions were obtained to assess the orientation restriction to the drug imposed by the receptor. 4 A correlation was observed between the direction of the drug molecular dipole and the local line of force generated by the receptor vector field. 5 These findings are discussed with respect to the phenomenon of drug-receptor recognition.