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Influence of 2′‐Deoxy Sugar Moiety on Excited‐State Protonation Equilibrium of Adenine and Adenosine with Acridine inside SDS Micelles: A Time‐Resolved Study with Quantum Chemical Calculations
Author(s) -
Sarangi Manas Kumar,
Bhattacharyya Dhananjay,
Basu Samita
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100763
Subject(s) - chemistry , protonation , photochemistry , deoxyadenosine , deprotonation , micelle , quenching (fluorescence) , acridine , fluorescence , adenosine , organic chemistry , aqueous solution , ion , biochemistry , physics , quantum mechanics
The protonation dynamics of the DNA base adenine (Ade) and its nucleoside 2′‐deoxyadenosine (d‐Ade) are investigated by monitoring the deprotonation kinetics of an N‐heterocyclic DNA intercalator, acridine (Acr), in the confined environment of sodium dodecyl sulfate (SDS) micelles. Protonation of acridine (AcrH + ) occurs at the hydrophilic interface and this species remains in dynamic equilibrium with its deprotonated counterpart (Acr) inside the hydrophobic core of SDS micelles. Quenching of the fluorescence of AcrH + * at 478 nm is observed after addition of Ade and d‐Ade with Stern–Volmer constant ( K SV ) 298 and 75 M −1 , respectively, with a concomitant increment in Acr* at 425 nm. Time‐resolved fluorescence studies reveal quenching in the lifetime of AcrH + *. The relative amplitude of AcrH + * decreases from 0.97 to 0.51 and 0.97 to 0.89 with equimolar addition of Ade and d‐Ade, respectively. These observations are explained by excited‐state proton transfer (ESPT) from AcrH + * to the bases. The reduced K SV value and negligible change in the relative amplitudes of AcrH + * with d‐Ade infer that ESPT is hindered substantially by the presence of a 2′‐deoxy sugar unit. Transient time‐resolved absorption spectra of Acr reflect that Ade reduces the absorbance of 3 AcrH + *; however, d‐Ade keeps it unaltered for more than a time delay of 2 μs. The optimized geometries calculated by quantum chemical methods reflect deprotonation of AcrH + * with protonation at the N1 position of Ade, while it remains protonated with d‐Ade. The hindered ESPT between AcrH + * and d‐Ade singles out the significance of the 2′‐deoxy sugar moiety in controlling the deprotonation kinetics.