Dibakar Sahoo

Quest for Mode of Binding of 2-(4-(Dimethylamino)styryl)-1-methylpyridinium Iodide with Calf Thymus DNA

The mode of binding of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) with calf thymus DNA as revealed from different steady state and time-resolved emission spectroscopic measurements has been reported in this paper. Fluorescence enhancement of DASPMI and its quenching by potassium iodide (KI) points to groove binding of dye with ct-DNA, rather than intercalation in the ct-DNA helix. An increase in steady state anisotropy and fluorescence lifetime hints at binding with ct-DNA. The value of binding constant from emission and association constant from circular dichroic spectrum also indicates weak binding. The strong dependence on ionic strength or salt in controlling the binding of DASPMI with ct-DNA by electrostatic interaction confirms groove binding. The high semicone angle of DASPMI in ct-DNA certainly rules out the possibility of intercalated bonding. A theoretical modeling shows that the probe is bound to ct-DNA as a crescent with a curvature of 11.35 A, which is the previously known curvature of probe in the minor groove.

Reverse Micelle Induced Flipping of Binding Site and Efficiency of Albumin Protein with an Ionic Styryl Dye

The effect of reverse micelle environment on the binding mechanism of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) with Bovine Serum Albumin (BSA) compared with that in buffer solution has been investigated in this paper with the help of steady state and time-resolved emission spectroscopy along with molecular docking to have a correct picture about binding. The binding of DASPMI with attachment efficiency of 30% and 70% at site I (subdomain IIA) and site II (subdomain IIIA) of BSA, respectively, in buffer solution gets reversed inside a reverse micelle. The bigger cavity size of site II in buffer solution ushers the dye with increased attachment efficiency and in reverse micelle change in pi-stacking and hydrophobic interaction control the attachment efficiency. The calculated Forster distance gets curtailed as the environment changes from buffer to reverse micelle. The binding becomes stronger with a smaller gap between the probe and Trp-214 inside the reverse micelle than that in buffer solution.

On the Spectral Behavior of an Ionic Styryl Dye: Effect of Micelle−Polyethylene-block-polyethylene Glycol Diblock Copolymer Assembly

The interaction of anionic micelle sodium dodecyl sulfate (SDS) and amphiphilic block copolymers polyethylene-b-polyethylene glycol (PE-b-PEG) and the sharp change of excited-state charge-transfer complex photophysics of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) inside of the supramolecular assembly have been addressed in the paper. The dramatic enhancement of emission intensity of DASPMI incorporated inside of the nanostructure formed by micellar and polymeric chains indicates a completely different environment compared to that in the water and micellar system. A huge increase in the rotational relaxation time obtained from time-resolved anisotropy decay and the value of the order parameter is indicative of a very restrictive regime in the self-assembly system. The wobbling and translational motion of the probe is also restricted inside of the micelle-polymer aggregate due to the presence of polymer chains. The translational diffusion coefficient is drastically reduced due to the aggregation.

Spectral Signature of 2-[4-(Dimethylamino)styryl]-1-methylquinolinium Iodide: A Case of Negative Solvatochromism in Water

Photophysics of the 2-[4-(dimethylamino) styryl]-1-methylquinolinium iodide (DASQMI) molecule has been studied in different solvents by steady-state and time-resolved emission spectroscopy and also with quantum chemical calculations. The probe molecule exhibits a strong solvent-polarity-dependent characteristic. The low-energy fluorescence band of DASQMI shows an anomalous 40 nm blue shift in water from that in dimethyl sulfoxide (DMSO); though in deuterium oxide the normal trend of red shift was observed. A marked increase in intensity of this band at 77 K and an increase in lifetime in viscous solvent point clearly to the intramolecular charge-transfer (ICT) character of the low-energy band. From the temperature-dependent emission and emission spectra in mixed solvents, the negative solvatochromism of DASQMI has been established, which means that the ICT state moves toward ground state with polarity and hydrogen-bond ability and beyond a critical dielectric constant coupled with protic nature of the solvent ground state gets further stabilized to show anomalous blue shift. In ethanol, below a critical temperature, 253 K, a blue shift starts due to greater solvent molecular polarization. A third long-lifetime component with dominant 75% amplitude was observed only in aqueous solution and may be due to the cis-isomer of hydrophobic DASQMI, a stable form in the excited state predicted from polarizable continuum model (PCM) calculations in water with 6-31G+(d,p) as basis set.

Dye-surfactant interaction: modulation of photophysics of an ionic styryl dye.

The interesting modulation of multibond rotation–induced intramolecular charge transfer photophysics of 2‐(4‐(dimethylamino) styryl)‐1‐methylpyridinium iodide in different micelles due to different contributions of twisted intramolecular charge transfer (TICT) and hydrogen bonding deactivation channels have been reported in this paper. 2‐(4‐(dimethylamino) styryl)‐1‐methylpyridinium iodide enters into all the micelles in different positions from the water solution due to active hydrophobic force and electrostatic field, as revealed from the shift and intensity of intramolecular charge transfer (ICT) band. The presence of mechanically trapped water with the addition of salt and inherent thermodynamic water controls the ICT emission. Analysis of spectral data before and after the addition of salt confirms the orientation of 2‐(4‐(dimethylamino) styryl)‐1‐methylpyridinium iodide in cationic and anionic micelles.

Theoretical study of excited state proton transfer in pyrrole-2-carboxylic acid

Pyrrole 2-carboxylic acid (PCA) shows dual emission (310 nm and 430 nm) in water on photo-excitation, which indicates that more than one species is in the excited state. This paper reports on the quantum chemical analysis of pyrrole 2-carboxylic acid (PCA) in the light of a possible excited state proton transfer. Dipole moment, excited state energy and findings in molecular orbital calculations (HOMO, LUMO) establish that PCA is a likely candidate for transfer of a proton from the pyrrole moiety to the C=O of carboxylic moiety (possible zwitterionic form) in the excited state. Overall, the computed predicted results of intramolecular and intermolecular excited state proton transfer corroborates the experimental results.

Sensing of Different Human Telomeric G-Quadruplex DNA Topologies by Natural Alkaloid Allocryptopine Using Spectroscopic Techniques

This article describes how a natural alkaloid allocryptopine (ALL) is able to differentiate two forms of biologically relevant human telomeric (htel22) G-quadruplex DNAs (GQ-DNA) depending on the presence of K+ and Na+ ions by steady-state and time-resolved spectroscopic techniques. For both interactions, predominant involvements of static-type quenching mechanism with the negligible influence of dynamic collision are established by UV-vis absorption and fluorescence emission study, which is further supported by fluorescence lifetime measurements. ALL exhibits appreciable affinity toward both GQ-DNAs. Both the mixed-hybrid (3 + 1) quadruplex structures in K+ ions and the basket-type antiparallel quadruplex structure under Na+ condition are converted to parallel types in the presence of ALL. Fluorescence intercalator displacement assay experiment revealed modest selectivity of ALL to both quadruplexes over duplex DNA along with higher selectivity for antiparallel types among the two quadruplexes via groove and/or loop binding, which is distinct from the conventional π-stacking of the ligands on external G-quartets. ALL stabilized both GQ-DNA topologies moderately. The differences in the dynamics of ALL within both DNA environments have been demonstrated vividly by time-resolved anisotropy measurements using the wobbling-in-cone model. These results suggest groove binding with antiparallel G-quartet with high affinity and moderate loop binding with mixed-hybrid G-quartet accompanied by the partial end stacking additionally in both of the cases. Our conclusions are further supported by steady-state anisotropy measurements and molecular docking. The present investigation can be used in the development of a biocompatible antitumour/anticancer agent targeting particular GQ-DNA conformation.