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.

Surface Charge Alteration in Carbon Dots Governs the Interfacial Electron Transfer and Transport

“…This is probably due to the solubilization of the organic molecule in the hydrophobic portion of the micelle bringing close contact between the substrate and borohydride. The confinement effect often results in uncommon photophysics and charge transfer phenomena. − Recently, we have found that the electrostatic interactions between the micelle and CDs influence their ET ability . We anticipate similar effects to be operating here with the highly negatively charged surface of the anionic RCDs interacting strongly with the cationic CTAB micellar surface by electrostatic attraction.…”

The role of N7 protonation of guanine in determining the structure, stability and function of RNA base pairs

“…It was shown that the presence of the sugar moiety plays an important role in controlling the protonation dynamics of adenine. 77 Hence, we have modeled the guanine with sugar at the N9 position. However, methyl substitution at the N9 position of purines is known to reduce the computational effort without significantly affecting the properties of the real systems.…”

Redox Modifications of Carbon Dots Shape Their Optoelectronics

“…The transient intermediates are generated with third harmonics output of nanosecond flash photolysis setup (applied Photo-physics) containing Nd: YAG (Lab series, model lab 150, spectra Physics) in which the sample is excited at 355 nm (FWHM = 8 ns) laser light [46][47][48] . A pulsed xenon lamp (150 W) is used to monitor the transient species in the triplet through the absorption of light.…”