Photophysics and photostability of adenine in aqueous solution: A theoretical study

Abstract

a b s t r a c tThe sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pp * and np * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pp* and np* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the np* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi-to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Mapping the Ultrafast Dynamics of Adenine onto Its Nucleotide and Oligonucleotides by Time-Resolved Photoelectron Imaging

“…These trends are in agreement with high-level ab initio calculations. 18,19,31,33 Our calculations together with the available literature show that the energy of the 1 πσ* state associated with the N9 position increases in energy in dAMP -relative to Ade and Ade-9Me, suggesting that this state is not involved in the decay of dAMP -. However, it is the relative ordering between the 1 ππ* to 1 nπ* states that is most revealing about the probable decay mechanism.…”

“…This conclusion is in agreement with some theoretical studies that have stressed a similar independence on environment and a pathway dominated by the 1 ππ* → S 0 internal conversion mechanism. 18,31 On the other hand, in solution, strong mixing of state character often prevents a strict diabatic label from being applied. 33 This makes definitive assignment of mechanism difficult.…”

“…This is in agreement with some theoretical 4 predictions and suggestions that the excited state dynamics proceed primarily on a single excited state. 14,[18][19][20] But how do the base dynamics extend to larger oligomeric systems? In aqueous solution, new mechanisms become accessible, which occur alongside apparently monomeric dynamics.…”

On the Participation of Photoinduced N–H Bond Fission in Aqueous Adenine at 266 and 220 nm: A Combined Ultrafast Transient Electronic and Vibrational Absorption Spectroscopy Study

“…The biologically relevant 9H tautomer of Ade (Scheme 1, blue) has received considerable theoretical attention. 9,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] A number of conical intersections can potentially facilitate repopulation of S0 from the initially excited 1 ππ* state(s), depending on the initial excitation energy. There has been some debate regarding the dominant pathway for re-accessing S0 after UV excitation in 9H-Ade, although the general consensus is that out-ofplane ring distortion at either the C2 or C6 sites (see Scheme 1) leads to conical intersections which facilitate ultrafast (and near barrierless) internal conversion (IC) back to S0; we note for completeness that recent work suggests direct 1 ππ* → S0 IC is likely to be the dominant process, 9,21,26,31 rather than a sequential 1 ππ* → 1 nπ* → S0 process.…”

Communication: Electronic UV-Vis transient spectra of the ·OH reaction products of uracil, thymine, cytosine, and 5,6-dihydrouracil by using the complete active space self-consistent field second-order perturbation (CASPT2//CASSCF) theory

“…[39][40][41][42][43][44][45][46] In the present work, we have used the CASPT2 method to compute the vertical electronic spectra of the uracil, thymine, and cytosine · OH adducts and the 5,6-dihydrouracil H-abstraction products. The aim is to provide a unified description of the spectroscopic features of adducts formed in the reaction between the · OH radical and the natural pyrimidine nucleobases and determine the origin of the Vis band measured in transient spectroscopy experiments.…”