Effect of nanocavity confinement on the rotational relaxation dynamics: 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micelles

Abstract

In continuation of our recent study on the steady state photophysics of a biologically active beta-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in the present article we have investigated the effect of nanocavity confinement on the excited state dynamics and rotational relaxation of the probe using picosecond time resolved fluorescence and fluorescence anisotropy techniques. The polarity dependent intramolecular charge transfer process is responsible for the remarkable sensitivity of this biological fluorophore in micellar environments. The fluorescence anisotropy decay of AODIQ incorporated inside the micelle is biexponential. The rotational motion of the probe was interpreted on the basis of a two step model consisting of a fast restricted rotation of the probe and a slow lateral diffusion of the probe in the micelle; both coupled to the overall rotation of the micelle. Experimental results reveal that micellar environment causes significant retardation of both the wobbling as well as the translational motion of the probe.

Photophysics of a β-carboline based non-ionic probe in anionic and zwitterionic liposome membranes

“…This reflects that the probe resides in a slower relaxation zone within the lipids compared to the aqueous buffer medium. The slower anisotropy in the liposomal environments compared to that in buffer medium is consistent with a similar observation in different micellar media (Das et al, 2006).…”

“…The lifetime values of the fluorophore in different environments are collected in Table 2. The bi-exponential decay behavior of AODIQ in aqueous buffer solution has already been rationalized (Mallick et al, 2005a;Das et al, 2006Das et al, , 2007a.…”

“…An increase in the rigidity of the neighboring environment of a fluorophore results in an increase in its fluorescence anisotropy. The time-dependent decay of the fluorescence anisotropy provides additional information about the rotational motion and/or rotational relaxation of the fluorophore in organized assemblies (Maiti et al, 1997;Lakowicz, 1999;Dutta et al, 2003;Dutt, 2003;Das et al, 2006). In order to see how the rigidity of the lipid membranes affect the dynamics of the probe, the time-resolved fluorescence anisotropy of AODIQ in buffer and in membranes have been studied.…”

Photophysics and rotational relaxation dynamics of a β-carboline based fluorophore in cationic alkyltrimethylammonium bromide micelles

“…Dynamic behavior includes the rotational and/or tumbling motion of the bound fluorophore within the microheterogeneous environments on the picosecond/nanosecond time scale [3,19]. Development of pico-and femtosecond lasers has enabled the researchers to directly probe into the ultrafast relaxation processes in micellar environments by time-resolved fluorescence depolarization techniques [8,14,[19][20][21]. Dutt characterized various components of rotational motion of two structurally similar dyes in Triton X-100 (TX-100) micelle, where the growth of the micelle was induced by the addition of sodium chloride [3].…”

“…Depolarization of the fluorescence of probes is one of the most powerful techniques elucidating the information on the dynamic behavior of the fluorophore in the complex microheterogeneous environments like micelles, reverse micelles, lipids, cyclodextrin, etc [14][15][16][17][18]. Dynamic behavior includes the rotational and/or tumbling motion of the bound fluorophore within the microheterogeneous environments on the picosecond/nanosecond time scale [3,19].…”