Interactions of therapeutically active plant flavonols with biological targets : Insights from fluorescence spectroscopic studies

Biophysics Division, Saba Institute of Nuclear Physics, l/AF, Bidhannagar, Kolkata-700 064, India

E-mail: pradeepk.sengupta@saha.ac.in,_pradeepsinp@yahoo.co.in Fax : 91-33-23374637

Gandhi Centenary B. T. College, Habra. North 24-Parganas, West Bengal, India

Manuscript received 22 December 2009, accepted 29 December 2009

Plant flavonols have attracted much recent attention in view or their novel therapeutic properties (effective against various free radical mediated and other diseases) which make them promising alternatives to conventional therapeutic drugs. However, till date, not much is known, regarding their mode or Interactions and bindings affinities with relevant biological targets. This article presents perspectives highlighting the usefulness of the exquisitely sensitive 'two color' fluorescence behavior of flavonols (which arise due to highly efficient photoinduced excited state intramolecular proton transfer (ESIPT) reactions) for exploring their interactions, at the molecular level, with biomembranes and proteins, which are the principal biological targets or such drug molecules. In this context, we made exploratory studies on the Interactions of some representatives therapeutically Important flavonols with model and natural membranes (composed of phosphatidylcholine liposomes and red blood cell ghost membranes respectively) and serum albumin proteins. Since the ESIPT process is highly sensitive to external hydrogen bonding perturbation effects, the relation contribution between the two colors is strong modulated by the local environment of the fluorophore, with dramatic changes In the emission yield, energy, anisotropy (r), lifetime (τ) and related parameter of both ESIPT tautomer and normal fluorescence bands. This provides multiparametric fluorescence probing opportunities, revealing salient details about the nature and location of binding sites as well as quantitative estimates of partition coefficients/binding constants. This promising new approach may be expected to open up new avenues for the 'screening' or the most appropriate flavonoid derivatives, from among numerous structural variants found In nature, as well as the design of relevant synthetic derivatives with improved features.