title: 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.
abstract: 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.
authors.affiliation: Chemical Sciences Division, Saha Institute of Nuclear Physics, Bidhannagar, Kolkata, India.
authors.forename: Manas Kumar
authors.initials: MK
authors.lastname: Sarangi
authors.forename: Dhananjay
authors.initials: D
authors.lastname: Bhattacharyya
authors.forename: Samita
authors.initials: S
authors.lastname: Basu
mesh_terms: D000166:Acridines / Q000737:chemistry*; D000225:Adenine / Q000737:chemistry*; D003839:Deoxyadenosines / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D008823:Micelles; D011522:Protons; D011789:Quantum Theory; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D000166:Acridines; D003839:Deoxyadenosines; D008823:Micelles; D011522:Protons; D012967:Sodium Dodecyl Sulfate; D000225:Adenine