Mode-specific vibrational relaxation of photoexcited guanosine 5′-monophosphate and its acid form: a femtosecond broadband mid-IR transient absorption and theoretical study

Abstract

UV-pump/broadband-mid-IR-probe transient absorption (TA) experiments and ab initio quantum mechanical (QM) calculations were used to investigate the photophysics in heavy water of the neutral and acid forms of guanosine 5'-monophosphate (GMP and GMPD(+), respectively). Excited GMP undergoes ultrafast internal conversion (IC) and returns to the electronic ground state in less than one picosecond with a large amount of excess vibrational energy. The spectroscopic signals are dominated by vibrational cooling - a process in which the solute dissipates vibrational energy to the solvent. For neutral GMP, cooling proceeds with a time constant of 3 ps. Following IC, at least some medium-frequency modes such as the carbonyl stretch and an in-plane ring vibration are excited, suggesting that the vibrational energy distribution is non-statistical. This is consistent with predicted structural changes upon passage through the S1/S0 conical intersection. GMPD(+) differs from GMP by a single deuteron at the N7 position, but has a dramatically longer lifetime of 200 ps. Vibrational cooling of the S1 state of GMPD(+) was monitored via several medium-frequency modes that were assigned using QM calculations. These medium-frequency modes are also vibrationally excited in a non-statistical fashion. Excitation of these modes is in line with the change in geometry at the S1 minimum of GMPD(+) predicted by QM calculations. Furthermore, these modes relax at different rates, fully consistent with QM calculations, which predict that excited vibrational states of the carbonyl stretch couple strongly to the D2O solvent and thus deactivate via intermolecular energy transfer (IET). In contrast, the ring stretch couples strongly to other ring modes of the guanine chromophore and appears to decay via intramolecular vibrational energy redistribution (IVR).

Photochemistry of Nucleic Acid Bases and Their Thio- and Aza-Analogues in Solution

“…The mode-specific vibrational energy transfer model proposed by Nielsen and co-workers [155,181] is further supported by the recent studies of Kohler and co-workers [152,154]. These authors investigated the vibrational relaxation dynamics of guanosine 5 0 -monophosphate by femtosecond broadband transient absorption spectroscopy in the 1,400-1,750 cm À1 probe region in deuterated aqueous buffer solution (pD ¼ 7.2) [154].…”

“…These authors investigated the vibrational relaxation dynamics of guanosine 5 0 -monophosphate by femtosecond broadband transient absorption spectroscopy in the 1,400-1,750 cm À1 probe region in deuterated aqueous buffer solution (pD ¼ 7.2) [154]. In agreement with earlier studies [153,181,190], the authors found that the bleach recovery signals of the ν N3C4 + ν amino (1,517 cm À1 ) and the ν CO (1,662 cm À1 ) vibrational modes are dominated by dynamics that occur on the ground state potential energy surface.…”

Hierarchical chirality expression of gemini surfactant aggregates via equilibrium between chiral nucleotide and nonchiral mono‐anions

“…The band at 1663 cm −1 is assigned to the carbonyl stretching vibration, and the bands in the 1600–1520 cm −1 region can be described as collective in‐plane purine ring vibrations. The band at 1579 cm −1 comes from the imidazole ring and has a strong contribution of the C–N stretching of the pyrimidine ring whereas the shoulder at 1566 cm −1 is mainly due to the pyrimidine ring with a significant contribution from the C–NH 2 group 29 . The IR spectrum of 12‐2‐12Br 2 + GMP‐Na 2 mixture in D 2 O (10 mM) shows marked modifications from that of the unassociated GMP.…”

“…The band at 1579 cm −1 comes from the imidazole ring and has a strong contribution of the C-N stretching of the pyrimidine ring whereas the shoulder at 1566 cm −1 is mainly due to the pyrimidine ring with a significant contribution from the C-NH 2 group. 29 The IR spectrum of 12-2-12Br 2 + GMP-Na 2 mixture in D 2 O (10 mM) shows marked modifications from that of the unassociated GMP. The carbonyl band shifts to higher wavenumbers (ca.…”

Efficient UV-induced charge separation and recombination in an 8-oxoguanine-containing dinucleotide

“…TRIR spectra recorded with excitation at 295 nm, a wavelength that is expected to excite O and not A ( (17). Absolute integrated absorption coefficients from the calculations were scaled by a constant factor that gave the best agreement with the experimental cross-sections for the O and A fundamentals.…”