Manas Kumar Sarangi

Influence of Heterogeneity of Confined Water on Photophysical Behavior of Acridine with Amines: A Time-Resolved Fluorescence and Laser Flash Photolysis Study

The photophysical behavior of acridine (Acr) shows facilitated water-assisted protonation equilibrium between its deprotonted (Acr* ∼ 10 ns) and protonated forms (AcrH(+*) ∼ 28 ns) within confined region of ordered water molecules inside AOT/H(2)O/n-heptane reverse micelles (RMs). The time-resolved-area-normalized-emission spectra confirm both Acr* and AcrH(+*), while time-resolved-emission spectra depict time evolution between them. Quenching of AcrH(+*) with N,N-dimethylaniline (DMA) is a purely diffusion-controlled bimolecular quenching with linear Stern-Volmer (S-V) plot, while nonlinearity arises with triethylamine (TEA) that forms ground state complex with AcrH(+) (AcrH(+)··H(2)O··TEA) indicating both static and dynamic quenching. Transient intermediates, DMA(•+) and AcrH(•) infer photoinduced electron transfer from DMA to Acr, while those from AcrH(+)··H(2)O··TEA complex suggest water mediated excited-state proton transfer (ESPT) between AcrH(+) and TEA. The ESPT becomes faster in larger RMs due to enhanced mobility of hydronium ions in AcrH(+)··H(2)O··TEA, which reduces in smaller RMs as water becomes much more constrained owing to stronger complexation by excess confinement.

Prototropic Interactions of Pyrimidine Nucleic Acid Bases with Acridine: A Spectroscopic Investigation

In this article, we have investigated the interactions of three pyrimidine nucleic acid bases, cytosine (C), thymine (T), and uracil (U) with acridine (Acr), an N-heterocyclic DNA intercalator, through the changes in photophysics of Acr inside SDS micelles. Fluorescence of AcrH(+)* at 478 nm and its lifetime are quenched on addition of C, T, and U, while a concomitant increment of Acr* is observed only with C. However, the relative amplitude of Acr* increases with a simultaneous decrease in AcrH(+)* only with C. The fluorescence quenching of AcrH(+)* is explained by photoinduced electron transfer (PET), while changes in the relative contributions of Acr* and AcrH(+)* with C are due to associated excited-state proton transfer (ESPT). The rate of electron transfer (kET) is maximum for T, followed by U and C. The associated ESPT from AcrH(+)* is the reason behind the reduced efficiency of PET with C. The lack of proton transfer with T and U as well as the higher kET for T compared to U are explained by keto-enol tautomerization and subtle changes in the structure and geometry of the pyrimidine bases.

Distance dependence of magnetic field effect inside confined environment of reverse micelles

In this article, we emphasize on the distance dependence of the magnetic field effect (MFE) on the donoracceptor (D-A) pair inside the confined environment of AOT/H2O/n-heptane reverse micellar (RMs) system. For this study N, N-dimethyl aniline (DMA) is used as an electron donor while the protonated form of Acr is treated as an electron acceptor. We report of the occurrence of an associated excited state proton transfer with the photoinduced electron transfer between Acr and DMA forming corresponding radical pair (RP) and radical ion pairs (RIP). The fate of these reaction products has been tested in the presence of an external magnetic field (∼0.08T) by varying the size of the RMs. The MFE between Acr and DMA has been compared to the results with the earlier reported interactions between Acr and TEA (Chemical Physics Letters, 2011, 506, 205-210). We accentuate the importance of the localization of the D and A inside the RMs, and the intervening distance between the pair to be the critical component for o...