UV-induced hydrogen transfer in DNA base pairs promoted by dark nπ* states

Abstract

Formation of an excited-state complex enables ultrafast photorelaxation of dark nπ* states in GC and HC base pairs.

Fragment Diabatization Linear Vibronic Coupling Model for Quantum Dynamics of Multichromophoric Systems: Population of the Charge-Transfer State in the Photoexcited Guanine–Cytosine Pair

“…As a first test application of the FrD-LVC method, we choose to study a minimal, yet extremely relevant, system: the dimer formed by Guanine and Cytosine connected by three hydrogen bonds in a Watson and Crick (WC) arrangement, hereafter simply GC (see Fig-ure 1). GC constitutes ∼40% of the human genome and its photoactivated behavior has been thoroughly investigated in the gas phase, [32][33][34][35][36][37][38][39][40][41] in chloroform solution, [42][43][44][45][46] and in DNA duplexes, 39,40,47,48 due to its possible involvement in the Proton Coupled Electron Transfer (PCET) processes in DNA. [49][50][51] Timeresolved (TR) experiments in the gas phase show that when GC is in a WC arrangement, after a UV pulse, the absorption of the infrared probe is broad and featureless, suggesting an ultrashort excited state lifetime.…”

Caveat when using ADC(2) for studying the photochemistry of carbonyl-containing molecules

“…Plasser et al 18 investigated the application of different single-reference methods in excited-state molecular dynamics of adenine, placing ADC(2) as a serious competitor to the commonly-accepted TDDFT for nonadiabatic dynamics. Following these reports, an explosion of studies employing ADC(2) in excited-state dynamics appeared in the literature, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] also mapping the reaction paths between the Franck-Condon (FC) geometry and the electronic states crossings, [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] and calculating absorption properties of functional molecules. 46,47 The community has gained a large confidence with ADC(2), to the point where many studies employing it do not contain systematic comparisons with high-level multireference methods.…”

Deciphering the Chemical Basis of Fluorescence of a Selenium‐Labeled Uracil Probe when Bound at the Bacterial Ribosomal A‐Site

“…This molecular orbital has a strong contribution of the n electrons of the Se atom as shown in Figure 5 A. Its contribution is relevant when ξ =±90°, what turns S 1 into dark state due to a nπ* electronic transition, which usually does not emit in nucleobases [26, 27] . The system will be trapped for a longer time on this dark S 1 and it will need more time to relax, and possibly, via nonradiative mechanisms.…”

“…[25] This molecular orbital has as trong contribution of the ne lectrons of the Se atom as shown in Figure 5A.I ts contribution is relevant when x = AE 908,w hat turns S 1 into dark state due to an p* electronic transition, which usually does not emit in nucleobases. [26,27] The system will be trapped for al ongert ime on this dark S 1 and it will need more time to relax, andp ossibly,v ia nonradiative mechanisms. This fact could open new possibilities of exploring the use of Se Ua sp hotoreactivep robes because i) Se Ui sa ble to absorb enoughe nergy in the range of % 4eV( brightest state S 5 in our calculations) and ii)rotation aroundt he C2''ÀC5 bond can be restrained, fore xample, by chemicalm odification of the adjacent positions to the former bond with bulky groups.…”