Optical Rotatory Dispersion of Complexes of Native DNA and Helical Poly-,αL-glutamic Acid with Proflavine

Abstract

RECENTLY, Blake and Peacocke¹ reported the appearance of an induced Cotton effect in the complex of deoxyribonucleic acid (DNA) with proflavine. The magnitude of the trough at 452 mµ was almost twice as large as that of the peak at 480 mµ. They considered the absorption band of the complex to be associated with a single electronic transition and made it appear that the anomalous optical rotatory dispersion (ORD) induced by the bound dye was a single rather than a multiple Cotton effect. Their interpretation of the observed Cotton effect challenges theories of optical activity which predict a single Cotton effect associated with a single circular dichroic (CD) band nearly symmetric with respect to either the centre of the CD band or the inflexion point of the ORD (refs. 2–4). We propose an alternative interpretation, which is in harmony with existing theories, of the ORD results of Blake and Peacocke.