Ultraviolet photolysis of adenine: Dissociation via the π1σ* state

Abstract

High resolution total kinetic energy release (TKER) spectra of the H atom fragments resulting from photodissociation of jet-cooled adenine molecules at 17 wavelengths in the range 280>lambda(phot)>214 nm are reported. TKER spectra obtained at lambda(phot)>233 nm display broad, isotropic profiles that peak at low TKER ( approximately 1800 cm(-1)) and are largely insensitive to the choice of excitation wavelength. The bulk of these products is attributed to unintended multiphoton dissociation processes. TKER spectra recorded at lambda(phot)<or=233 nm display additional fast structure, which is attributed to N(9)-H bond fission on the 1pisigma* potential energy surface (PES). Analysis of the kinetic energies and recoil anisotropies of the H atoms responsible for the fast structure suggests excitation to two 1pisigma* excited states (the (1)L(a) and (1)B(b) states) at lambda(phot) approximately 230 nm, both of which dissociate to yield H atoms together with ground state adeninyl fragments by radiationless transfer through conical intersections with the 1pisigma* PES. Parallels with the photochemistry exhibited by other, smaller heteroaromatics (pyrrole, imidazole, phenol, etc.) are highlighted, as are inconsistencies between the present conclusions and those reached in two other recent studies of excited state adenine molecules.

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

“…In addition to these findings, a photoproduct signal is observed in TEAS between 340 and 360 nm together with eaq, the latter forming through conclude that 1 πσ* mediated N-H bond fission is not an active process in aqueous Ade after excitation at ≥220 nm. Furthermore, if an onset for this channel does exist in aqueous solution, it must be significantly blue-shifted relative to the measured threshold for N9-H bond fission via isolated 9H-Ade's 1 πσ* state in the gas phase (233 nm), 43 in broad agreement with previous theoretical findings. 18,31 through the ERC Advanced Grant 290966 CAPRI and EPSRC via Programme Grant EP/G00224X.…”

“…18,21 However, high-resolution photofragment translational spectroscopy measurements by Nix et al. more definitively identified the onset for N9-H bond fission via the 1 πσ* state as ≥5.3 eV (≤233 nm), 43 in-line with findings from more recent time-resolved measurements in the gas phase by both Stavros and co-workers 44 and Ullrich and Evans. 39 Stavros and co-workers also confirmed that by 200 nm, N-H bond fission in the N10H2 amino group is activated and N-H bond scission along both coordinates takes ~100 fs, 44 in general agreement with theory.…”

“…[36][37][38][39] With specific regard to the participation of the 1 πσ* state in 9H-Ade's photochemistry, a number of studies have been performed to investigate the activity of this channel. [38][39][40][41][42][43][44] Early work in both the time and frequency domains led a number of research groups to infer that ultrafast relaxation via this state may in fact be active following excitation at 267 nm; 38, 41, 42 a much longer wavelength than initially predicted by Domcke and co-workers 14 and later theoretical work. 18,21 However, high-resolution photofragment translational spectroscopy measurements by Nix et al.…”

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

“…4 Much of the experimental effort has been devoted to the fate of adenine (Ade) following excitation to its 1 ππ* states. Gas-phase spectroscopy [5][6][7][8][9][10][11] synergised with theoretical calculations [12][13][14][15][16][17] in particular has provided deep insight. However, there remains disagreement about the basic radiationless decay mechanism and, in particular, how the dynamics of Ade relate to those of its more biologically relevant nucleotide and oligonucleotides in aqueous solution.…”

Absorption spectroscopy of adenine, 9-methyladenine, and 2-aminopurine in helium nanodroplets

“…5,[27][28][29][30][31] Other channels that have attracted considerable attention involve conical intersections with repulsive 1 ps* states along the N 9 -H and N 10 -H coordinates. [32][33][34][70][71][72] These channels, however, only open up at wavelengths shorter than 233 nm 71 and would thus a priori not be expected to be involved in the decay of the 1 np* and 1 L b (pp*) levels studied here. This is confirmed by our measurements on 9-methyladenine, a molecule in which the N 9 -H dissociation channel is closed.…”