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.
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.
Change of a-helical structure of heme protein (Hb) to a b-sheet and random coil conformation because of the interaction of glycine capped gold nanoparticles (20-60 nm) as observed from attenuation total reflectance, absorption, Fourier transform infra red, and Circular Dichroism spectroscopy has been reported in this article. Upon interaction, protein takes a cylindrical shape of length 12 lm and diameter 0.35 lm as revealed from scanning electron microscopy and transmission electron microscopy. The Selected-Area Electron beam Diffraction pattern shows change of crystalline structure in GNP to amorphous nature with the interaction of Hb.
The structure and dynamics of a charge transfer drug molecule 4,4-diaminodiphenyl sulfone (dapsone) inside the cyclodextrins (R-, β-, γ-CDs) in aqueous solution have been studied using steady state and time-resolved emission spectroscopies. The quantum yields were significantly larger in the presence of βand γ-CDs than in water, wherein the β-CD confinement shows the largest effect. The results reveal that dapsone forms 1:1 complexes with both β-CD and γ-CD. At higher concentrations of β-CD a combination of 1:1 and 1:2 inclusion complexes could be observed. The average lifetime of the probe inside the CD cavity is larger than that observed in water due to hydrophobic and polarity effects of the nanocage. Anisotropy decay has been used to study the rotational dynamics of the molecule inside the cyclodextrin cavity. 1 H NMR data also confirm shallow inclusion of dapsone in β-CD. PM3 semiempirical calculations indicate that for unimolar complex a partial (3.8 Å) encapsulation of the dapsone molecule in β-CD at an angle of 72°with the CD axis. The DFT calculations with solvent effect show that the formation of inclusion is spontaneous and enthalpy driven.
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