An electron density based analysis to establish the electronic adiabaticity of proton coupled electron transfer reactions

Abstract

Electrons and protons are the main actors in play in proton coupled electron transfer (PCET) reactions, which are fundamental in many biological (i.e., photosynthesis and enzymatic reactions) and electrochemical processes. The mechanism, energetics and kinetics of PCET reactions are strongly controlled by the coupling between the transferred electrons and protons. Concerted PCET reactions are classified according to the electronical adiabaticity degree of the process. To discriminate among different mechanisms, we propose a new analysis based on the use of electron density based indexes. We choose, as test case, the 3‐Methylphenoxyl/phenol system in two different conformations to show how the proposed analysis is a suitable tool to discriminate between the different degree of adiabaticity of PCET processes. The very low computational cost of this procedure is extremely promising to analyze and provide evidences of PCET mechanisms ruling the reactivity of many biological and catalytic systems.

Water-Mediated Excited State Proton Transfer of Pyranine–Acetate in Aqueous Solution: Vibrational Fingerprints from Ab Initio Molecular Dynamics

“…The absorption of UV–vis radiation leads the molecule to an electronic excited state, inducing a deep rearrangement in its electronic structure. 12 − 14 The electronic excitation gives rise to a new reactivity, dramatically different from the ground state behavior, which allows the release of the proton to a nearby solvent molecule or to a base if present in solution. 15 − 19 …”

“…In excited state proton transfer (ESPT) reactions, a compound reacts to the absorption of radiation by releasing protons. , The newly formed deprotonated species usually exhibit different spectroscopic properties in terms of absorption and fluorescence spectra and vibrational signatures. , For this reason, these compounds represent a promising class of light-sensitive molecules for applications in the field of biological imaging, as optoelectronic devices, and as fluorescent probes in complex environments. − The so-called photoacid molecules belong to a large family of organic compounds known to give the excited state proton transfer reaction. − Generally, in the ground electronic state (S 0 ), the proton transfer reaction is thermodynamically and kinetically unfavorable or extremely slow, and the photoacid remains in its protonated form. The absorption of UV–vis radiation leads the molecule to an electronic excited state, inducing a deep rearrangement in its electronic structure. − The electronic excitation gives rise to a new reactivity, dramatically different from the ground state behavior, which allows the release of the proton to a nearby solvent molecule or to a base if present in solution. − …”

Modulation of proton-coupled electron transfer reactions in lysine-containing alpha-helixes: alpha-helixes promoting long-range electron transfer

“…This work provides valuable information to improve the application of a-helical peptides in biological electronic devices 2,63 and further broadens the conception of PCET reactions in proteins. [67][68][69][70][71][72][73][74][75][76][77][78]…”

Modeling Excited-State Proton Transfer to Solvent: A Dynamics Study of a Super Photoacid with a Hybrid Implicit/Explicit Solvent Model

“…Thus, the attractive choice to represent the excited-state evolution is provided by methods rooted in the time-dependent (TD) version of the density functional theory (DFT) for their convenient accuracy/cost ratio. Several studies have proven that this class of methods reliably reproduces the photochemical behavior of photoacid molecules. − Furthermore, computing on the fly TD-DFT energy and energy derivatives in ab initio molecular dynamics (AIMD) ,,, allows catching the features of the electronic, nuclear, and solute–solvent rearrangement ruling the phototriggered proton transfer (PT) in the condensed phase. Robust models of solvation are, of course, required.…”