Absorption and fluorescence spectra of the probe Hoechst 33258
ABSTRACT The steric and electronic structure and absorption spectra of the fluorophore Hoechst 33258 (I) and a number of model compounds in various protonated forms were calculated by the semi-empirical quantum chemical methods PM3 and CNDO/S. The low-frequency transition was shown to provide an increase in electron affinity of the imidazole rings. The fluorescence quenching of I in neutral aqueous solutions was suggested to result from the keto form (or bipolar structure), derived via proton transfer in the excited state of the dimer associate of I. The polar (approximately 10 D) fluorescence state of I due to intramolecular charge transfer is markedly sensitive to the polarity of the environment.
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ABSTRACT: Exploration of environmental dynamics using intrinsic biological probe tryptophan is very important; however, it suffers from various difficulties. An alternative probe, kynurenine (KN), has been found to be an efficient probe for the ultrafast dynamics in the biological environment (Goswami et al.,  J. Phys. Chem. B., 114, 15236-15243). In the present study, we have investigated the efficacy of KN for the exploration of relatively slower dynamics of biologically relevant environments. A detailed investigation involving UV-Vis, steady-state/time-resolved fluorescence spectroscopy and Förster resonance energy transfer (FRET) studies on KN compared to a well-known solvation probe, H33258, a DNA-minor groove binder in a model nonionic reverse micelle reveals that ultrafast internal conversion associated with the hydrogen-bonding dynamics masks KN to become a dynamical reporter of the immediate environments of the probe.Photochemistry and Photobiology 09/2011; 88(1):38-45. DOI:10.1111/j.1751-1097.2011.01007.x · 2.68 Impact Factor
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ABSTRACT: Picosecond resolved photophysical studies on a DNA minor groove binder, H33258 in bulk buffer and various restricted media including DNA reveal excited state charge transfer as an important mode of excited state relaxation. The charge transfer is found to be essentially associated with intramolecular twisting of the probe, being absent in SDS micellar environment and in DNA where twisting is hindered. Solvation and rotational dynamics of the probe in various restricted media including DNA are explored. A significantly longer component (8.5ns) in DNA-solvation dynamics, which is well known to be associated with δ-relaxation of the DNA, is identified.Chemical Physics Letters 12/2006; 432(1):257-262. DOI:10.1016/j.cplett.2006.10.018 · 1.99 Impact Factor
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ABSTRACT: The groove binding dye Hoechst 33258 was investigated both in aqueous solution and in the adsorbed form on silver colloids and island films. Fourier transform Raman, resonance Raman and surface enhanced resonance Raman spectra were used together with the results of a normal coordinate analysis for a comprehensive assignment of the rich vibrational spectrum. Relative band intensities in the SERRS spectra indicate that the molecule is adsorbed with its long axis oriented along the silver surface and with the planes of the benzimidazole rings approximately parallel to the surface. The molecule is bound to the surface as a cation protonated at a piperazine nitrogen atom and is desorbed on complete deprotonation.Journal of Raman Spectroscopy 04/2005; 26(6):435 - 441. DOI:10.1002/jrs.1250260607 · 2.68 Impact Factor