Photoinduced Proton‐Coupled Electron Transfers in Biorelevant Phenolic Systems

Abstract

Proton-coupled electron transfer (PCET) reactions have received much attention over the past 10 years, from an experimental as well as from a theoretical point of view. At the heart of many chemical and biological processes, such reactions are of particular interest in energy conversion and enzymatic processes. Among the numerous examples of PCET reactions, photosynthesis and particularly reactions inside the Photosystem II (PSII) subunit, involving a global four electrons and four protons process to perform water oxidation and respiration, is the most emblematic one. This review focuses on the photochemical approaches of PCET reactions involving phenolic molecules. Indeed, a significant part of photochemical PCET studies were conducted on tyrosine or phenol relevant to PSII and charge transport in enzymes. The mechanisms of these reactions, sequential or concerted, with particular emphasis on the influence of pH, temperature, solvent nature and H-bonding pattern are presented based on photochemical techniques and related theoretical analysis.

Using Raman Spectroscopy as a Fast Tool to Classify and Analyze Bulgarian Wines—A Feasibility Study

“…The RPD values (> 2.5) indicated that the calibration models were adequate to measure phenolic compounds as low, medium, and high, qualitatively. Results from this study agree with those reported in Cabernet Sauvignon by other authors using Raman spectroscopy [23,24]. SECV: standard error of cross-validation, SD: standard deviation, RPD: residual predictive deviation (SD/SECV) value, R 2 : coefficient of determination in cross-validation.…”

“…It has been reported that the strong fluorescence background associated with the absorption of hydroxycinnamic acids (phenolics) and related phenolic compounds determine a Raman shift depending on the excitation [18][19][20][21][22], where, the observed emission in the wines is attributed to the excited state proton transfer [23,24].…”

“…Overall, the performance of the calibration models developed clearly showed that phenolic compounds could be measured/predicted in wines using the combination of Raman spectroscopy and chemometrics. However, some other authors reported that Raman spectroscopy might be considered as a less sensitive technique comparing with other vibrational spectroscopic methods, although it might offers the advantage of being less sensitive to the presence of water in samples such as wine [18][19][20][21][22][23][24]. Overall, Raman spectroscopy might be considered as a good alternative to avoid the interference of these major components in the wine matrix to measure or predict different minor compounds in wine (e.g., phenolic compounds) that are of importance in determining provenance and the quality.…”

The role of hydrogen bonding in excited state intramolecular charge transfer

“…54,55 However, such hydrogen bonds rather increase the electron donating capacity of the amino group, thus favoring the formation of the ICT state. Datta et al showed that the ICT emission of 3-aminoquinoline (20) was favored in aprotic solvents such as dimethyl sulfoxide by a similar type of hydrogen bonding (21). 56 On the other hand hydrogen bonding inhibits the ICT emission of 20 in protic solvents, where the charge donor acts as a hydrogen bond acceptor 22, but the protonation of the acceptor enhances the ICT process (23).…”

Flux-correlation approach to characterizing reaction pathways in quantum systems: a study of condensed-phase proton-coupled electron transfer

“…We employ the new approach to investigate the reaction dynamics of condensed-phase protoncoupled electron transfer (PCET), an important prototype for quantum systems that exhibit multiple reaction pathways [12][13][14][15][16][17][18] . Numerical results demonstrate the practicality and utility of the new method for the mechanistic analysis of coupled quantum dynamical processes.…”