No abstract

A detailed photophysical characterization of biologically imperative drugs, 3‐hydroxyflavone (3HF) and quercetin (QCT) upon binding with taurula yeast RNA (ribonucleic acid) has been studied. The steady‐state absorption, emission and anisotropy profiles of these anti‐cancer drugs evidence for the binding interaction through interconversion between prototropic conformations. Although diminution of fluorescence (at ∼ 515 nm for 3HF and ∼ 545 nm for QCT) was attributable to the protonated form indicating suppression of ESIPT phenomenon, the excitation spectra aids in identification of the actual conformation of the drugs after prototropic conversion. The dynamical aspects were displayed by time‐resolved fluorescence decay and rotational relaxation behavior (‘dip‐and‐rise’ decay pattern) of the drugs within RNA helix. The quenching study hints for the probable binding location and the mode of binding but the circular dichroism study confirms it to be groove binding. This study endows with not only the biological insight of RNA‐binding of naturally abundant flavonols but also photophysical depiction of spectroscopically challenging phenomenon in an aspect of its structural interconversion.

No abstract

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, w 0 ) 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. The differential degrees of steric interactions offered by the drug molecules (presence of methyl substitutions on the planar phenazinium ring in SO) are also found to affect the extent of intercalation of the drugs to DNA. In this context, it is imperative to state that the water pool of the reverse micellar core is often argued to approach bulk-like properties of water with increasing micellar size (typically w 0 ≥ 10), so that deviation from the bulk water properties is likely to be minimized in large reverse micelles ( w 0 ≥ 10). On the contrary, our results (particularly quantitative elucidation of micropolarity and dynamical aspects of the interaction) explicitly demonstrate that the bulk-like behavior of the nanoconfined water is not truly achieved even in large reverse micelles.

No abstract