Single-molecule interfacial electron transfer (ET) dynamics has been studied by using single-molecule fluorescence spectroscopy and microscopic imaging. For a single-molecule zinc-tetra (4-carboxyphenyl) porphyrin (ZnTCPP)/TiO(2) nanoparticle system, the single-molecule fluorescence trajectories show strong fluctuation and blinking between bright and dark states. The intermittency and fluctuation of the single-molecule fluorescence are attributed to the variation of the reactivity of interfacial electron transfer. The nonexponential autocorrelation function and the power-law distribution of the probability density of dark times imply the dynamic and static inhomogeneities of the interfacial ET dynamics. On the basis of the power-law analysis, the variation of single-molecule interfacial ET reactivity is analyzed as a fluctuation according to the Levy statistics.

The usefulness of heterocyclic chalcone derivative as a therapeutic target in controlling hypertension and its site specific binding interaction with model transport protein to get a clear picture about its delivery mechanism. AbstractInhibition of Angiotensin Converting Enzyme (ACE) is identified as a main therapeutic target in controlling hypertension. The principal intent of this work is to investigate the ACE inhibitory property of a quinoline appended chalcone derivative (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ), and its binding mechanism with model transport protein BSA by employing steady state and time resolved fluorescence, Circular Dichroism (CD), in silico Molecular Docking, Induced Fit Docking (IFD) and Molecular Dynamics (MD) simulation. Incubation of ADMQ with kidney cortex plasma membrane shows considerable antihypertensive effect by the inhibition of ACE. ADMQ undergoes strong interaction with ACE both in absence and presence of BSA. Comparable ACE inhibitory mechanistic profile of ADMQ with standard drug captopril has been identified in terms of ligand interaction pattern, changes in secondary structural elements and protein RMSF. The steady state emission of BSA undergoes a remarkable decrement via ground state complex formation upon addition of ADMQ in aqueous buffer solution of BSA at physiological pH 7.4 contrary to the time resolved and FRET measurement where both the static andenergy transfer mechanism co-exists. Rotationally restricted ADMQ molecule shows strong binding affinity towards subdomain IIA of site I with a close proximity (2.45 nm) of the Trp 213 residue. The minor decrease of α-helical content as calculated from CD spectral measurement and 1-3 Å change in protein RMSD during MD simulation clearly indicate that the polypeptide chain is partially destabilized due to the above site specific accommodation of the host (ADMQ). A slight diminution in the ACE inhibitory profile is observed in presence of BSA; however BSA shows lesser binding towards ADMQ in presence of the target enzyme. The spectroscopic research described herein may provide enormous important information for ACE inhibition of chalcone derivative and its detail binding interaction with carrier protein for the chalcone based drug designing in medicinal chemistry research.

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The present study embodies design, in silico DNA interaction, synthesis of benzothiazole containing naphthalimide derivative, 2-(6-chlorobenzo[d]thiazol-2-yl)-1H-benzo[de] isoquinoline-1,3(2H)-dione (CBIQD) along with its systematic photophysics, solvatochromic behavior, and solvation dynamics using an experimental and theoretical spectroscopic approach. Steady-state dual emission and biexponential fluorescence decay reveals the formation of two different excited species. Ground- and excited-state optimized geometry and the potential-energy curve obtained from DFT and TD-DFT calculation ascertained the existence of nonplanar and planar conformation. When the solvent polarity is changed from nonpolar to protic polar, the feebly emissive emission band highly intensifies probably due to the reversal of n, π*-π, π* emissive state along with consequent modulation of their energy gap that is induced by H-bonding. Excluding nonpolar solvents, in all other solvents, the Stokes shift correlates linearly with orientation polarizability, whereas in water, the story remains intriguing. With photoexcitation, intermolecular H-bonding stimulates the pyramidalization tendency of imide "N" with subsequent conformational change of GS nonplanar geometry to a coplanar one through acceptor rehybridization generating a rehybridized intramolecular charge transfer (RICT) state that caused a dramatic fluorescence upsurge. This allosteric modulation is promoted by excited-state H-bonding dynamics especially in strong H-bond donor water. A close interplay between preferential solvation and the proximity effect is evident in the emission behavior in a benzene (Bn)-ethanol (EtOH) binary mixture. Molecular docking analysis delineates considerable noncovalent sandwiched π-π stacking interactions of CBIQD with the pyrimidine rings as well as with imidazole rings of dG 6 and dG 2 base pairs of B-DNA double helix, which probably suffices the design strategy adopted. Overall, a strategic design to synthesize a highly fluorescent and potential bioactive agent is executed to revolutionize the fluorophore field due its enormous progressive importance in biochemical applications.