Ab Initio QM/MM Molecular Dynamics Study on the Excited-State Hydrogen Transfer of 7-Azaindole in Water Solution

Abstract

Ab initio molecular dynamics (AIMD) simulations for the excited-state hydrogen transfer (ESHT) reaction of 7-azaindole (7AI−(H2O)n; n = 1, 2) clusters in the gas phase and in water are presented. The effective fragment potential (EFP) is employed to model the surrounding water molecules. The AIMD simulations for 7AI−H2O and 7AI−(H2O)2 clusters show an asynchronous hydrogen transfer at t ∼ 50 fs after the photoexcitation. While the ESHT mechanism for 7AI−H2O in water does not change appreciably compared with that in the gas phase, the AIMD simulations on 7AI−(H2O)2 in water solution exhibit two different mechanisms. Since the tautomer form is lower in energy compared to the normal form in the S1 state, 7AI and (H2O)n fragments separate from each other after the ESHT. With the use of the results of the AIMD trajectories, the minimum energy conical intersection point in the tautomer region has also been located. Disciplines Chemistry CommentsReprinted (adapted) ReceiVed: May 17, 2008; ReVised Manuscript ReceiVed: July 16, 2008 Ab initio molecular dynamics (AIMD) simulations for the excited-state hydrogen transfer (ESHT) reaction of 7-azaindole (7AI-(H 2 O) n ; n ) 1, 2) clusters in the gas phase and in water are presented. The effective fragment potential (EFP) is employed to model the surrounding water molecules. The AIMD simulations for 7AI-H 2 O and 7AI-(H 2 O) 2 clusters show an asynchronous hydrogen transfer at t ∼ 50 fs after the photoexcitation. While the ESHT mechanism for 7AI-H 2 O in water does not change appreciably compared with that in the gas phase, the AIMD simulations on 7AI-(H 2 O) 2 in water solution exhibit two different mechanisms. Since the tautomer form is lower in energy compared to the normal form in the S 1 state, 7AI and (H 2 O) n fragments separate from each other after the ESHT. With the use of the results of the AIMD trajectories, the minimum energy conical intersection point in the tautomer region has also been located.

Solvent-Induced Shifts in Electronic Spectra of Uracil

“…As noted above, the fully self-consistent solution to eqs 8 and 13 has previously been implemented for the CASSCF method. 33 Following the derivation of the interface between the EFP and CIS methods, 32 the SA-CASSCF/EFP interface has been implemented according to method 1. In this case the ground-state polarization energy is computed according to eq 13, and the total energy for each excited state is computed as…”

Multiconfiguration Molecular Mechanics Studies for the Potential Energy Surfaces of the Excited State Double Proton Transfer in the 1:1 7-Azaindole:H2OComplex

“…As a result, an OH-like moiety is formed at about 50 fs of the ab initio MD trajectory as presented in ref. 15, which is inconsistent with the fact that 7AI becomes acidic in the S 1 state upon π-π* electronic excitation, 37 and other high level electronic structure calculations. 2 This study shows that the ESDPT in the 1:1 7-azaindole:water complex occurs asynchronously to make an H3O + -like moiety at the TS.…”

“…The two protons in flight move very asynchronously. Kina et al 15 carried out ab initio MD simulations for the ESDPT in the 1:1 7-azaindole: water complex and reported that the two protons were transferred asynchronously and concertedly. Their results are consistent with this study, except that the order of transferring protons is opposite.…”

“…In the trajectory of the AIMD simulations, the O-H proton moves first to the 6-membered ring followed by movement of the N-H proton from the 5-membered ring to water. However, the TS structures obtained by Chaban et al 2 and Kina et al 15 suggest that the N-H proton from the 5-membered ring moves first, and the water proton follows. The AIMD trajectory was far from the intrinsic reaction coordinate that might be one of the high-energy reaction paths, thus further investigation is required.…”

“…Very recently, Kina et al 15 performed ab initio molecular dynamics (AIMD) simulations for the 7AI-H2O complex; they showed that the ESDPT occurs at t = ~50 fs after the photoexcitation in the gas phase via a concerted and asynchronous process. They also presented the AIMD simulation including the surrounding water molecules by effective fragment potential and suggested that the ESDPT takes places asynchronously in both the gas phase and in solution.…”