How Does Nanoconfinement within a Reverse Micelle Influence the Interaction ofPhenazinium-Based Photosensitizers with DNA?

摘要

The major focus of the present work lies in exploring the influence of nanoconfinement within aerosol-OT (AOT) reverse micelles on the binding interaction of two phenazinium-based photosensitizers, namely, phenosafranin (PSF) and safranin-O (SO), with the DNA duplex. Circular dichroism and dynamic light-scattering studies reveal the condensation of DNA within the reverse micellar interior (transformation of the B-form of native DNA to ψ-form). Our results unveil a remarkable effect of the degree of hydration of the reverse micellar core on the stability of the stacking interaction (intercalation) of the drugs (PSF and SO) into DNA; increasing size of the water nanopool (that is, w0) accompanies decreasing curvature of the DNA duplex structure with the consequent effect of increasing stabilization of the drug:DNA intercalation. The marked differences in the dynamical aspects of the interaction scenario following encapsulation within the reverse micellar core and the subsequent dependence on the size of the water nanopool are also meticulously explored. Thedifferential degrees of steric interactions offered by the drug molecules(presence of methyl substitutions on the planar phenazinium ring inSO) are also found to affect the extent of intercalation of the drugsto DNA. In this context, it is imperative to state that the waterpool of the reverse micellar core is often argued to approach bulk-likeproperties of water with increasing micellar size (typically w0 ≥ 10), so that deviation from the bulkwater properties is likely to be minimized in large reverse micelles(w0 ≥ 10). On the contrary, ourresults (particularly quantitative elucidation of micropolarity anddynamical aspects of the interaction) explicitly demonstrate thatthe bulk-like behavior of the nanoconfined water is not truly achievedeven in large reverse micelles.