Nanocavity effect on photophysical properties of colchicine: a proof by circular dichroism study and picosecond time-resolved analysis in various reverse micellar assemblies.

In August 2009, colchicine won Food and Drug Administration (FDA) approval in the United States as a stand-alone drug for the treatment of acute flares of gout and familial Mediterranean fever. Recently, it is now the center of attraction in medicinal research. In this present paper, we have employed two other analogues of colchicine for exploring the photophysical properties inside nanocavity environment in details. Here we have a series of interesting results that have interesting similarity with the colchinoid-tubulin interaction. To monitor fluorescence properties of colchinoids, we have used absorption, emission, and time-resolved spectroscopy and to monitor structural properties we have measured circular dichroism. Steady-state anisotropy and dynamic light scattering results give an idea about the microenvironment sensed by the colchinoids molecules. A sharp increment for colchicine, very small increment for isocolchicine and no increment for colcemid in fluorescence and different circular dichroism (CD) spectra of all of these colchinoids upon embedment inside nanocavity of reverse micelle made a supposition that all these changes of fluorescence properties and CD results of colchinoids is not solely due to viscosity effect but also the constraint, that is, very narrow space to spread over, given by the nanocavity of reverse micelle. Moreover, we have noticed that the B ring of the colchinoids also have a pronounced effect on the interaction nature as well as on conformational change of these compounds after entrapment.