Theoretical Study of Shallow Distance Dependence of Proton-Coupled Electron Transfer in Oligoproline Peptides

Hybrid bilayer membranes as platforms for biomimicry and catalysis

Hybrid bilayer membrane (HBM) platforms represent an emerging nanoscale bio-inspired interface that has broad implications in energy catalysis and smart molecular devices. An HBM contains multiple modular components that include an underlying inorganic surface with a biological layer appended on top. The inorganic interface serves as a support with robust mechanical properties that can also be decorated with functional moieties, sensing units and catalytic active sites. The biological layer contains lipids and membrane-bound entities that facilitate or alter the activity and selectivity of the embedded functional motifs. With their structural complexity and functional flexibility, HBMs have been demonstrated to enhance catalytic turnover frequency and regulate product selectivity of the O₂ and CO₂ reduction reactions, which have applications in fuel cells and electrolysers. HBMs can also steer the mechanistic pathways of proton-coupled electron transfer (PCET) reactions of quinones and metal complexes by tuning electron and proton delivery rates. Beyond energy catalysis, HBMs have been equipped with enzyme mimics and membrane-bound redox agents to recapitulate natural energy transport chains. With channels and carriers incorporated, HBM sensors can quantify transmembrane events. This Review serves to summarize the major accomplishments achieved using HBMs in the past decade.

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

The proton-coupled electron transfer (PCET) reaction plays an important role in promoting many biological and chemical reactions. Usually, the rate of the PCET reaction increases with an increase in the electron transfer distance because long-range electron transfer requires more free energy barriers. Our density functional theory calculations here reveal that the mechanism of PCET occurring in lysine-containing alpha(α)-helixes changes with an increasing number of residues in the α-helical structure and the different conformations because of the modulation of the excess electron distribution by the α-helical structures. The rate constants of the corresponding PCET reactions are independent of or substantially shallower dependent on the electron transfer distances along α-helixes. This counter-intuitive behavior can be attributed to the fact that the formation of larger macro-cylindrical dipole moments in longer helixes can promote electron transfer along the α-helix with a low energy barrier. These findings may be useful to gain insights into long-range electron transfer in proteins and design α-helix-based electronics via the regulation of short-range proton transfer.

Thermodynamics regulated organic hydride/acid pairs as novel organic hydrogen reductants

Organic hydride/acid pairs could realize transformation of N-substituted organic hydrides from hydride reductants to thermodynamics regulated hydrogen reductants on conveniently choosing suitable organic hydrides and acids with various acidities.

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

Finding the relation between thermodynamics and kinetics for a reaction is of fundamental importance. Here, the thermodynamics and kinetics correlation of excited-state intramolecular proton transfer (ESIPT) was investigated by the TD-DFT calculation under the CAM-B3LYP/6-311+G** level. We choose the family 2-(2'-aminophyenyl)benzothiazole and its amino derivatives as paradigms, which all possess the NH-type intramolecular hydrogen bond (H-bond), and investigate the corresponding ESIPT reaction. The H-bond strength can be systematically tuned, so both activation energy ΔG^‡ and free energy difference between proton transfer tautomer (T*, product) and normal species (N*, reactant) ΔG_T*-N* can be varied. To minimize the environmental interference such as solvent external H-bond and polarity perturbation, a nonpolar solvent such as cyclohexane is chosen as a bath with a polarizable continuum solvation model for the calculation. As a result, the comprehensive computational approach reveals a linear relationship between ΔG_T*-N* and ΔG^‡, which can be expressed as ΔG^‡ = ΔG₀ + αΔG_T*-N*. The fundamental insight is reminiscent of the Bell-Evans-Polanyi (BEP) principle where α represents the character of the position of the transition state along the proton motion coordinate. In other words, the more exergonic the ESIPT reaction is, the faster the proton transfer rate can be observed. To verify that such a correlation is not a sporadic event, another ESIPT family with an -OH proton, 1-hydroxy-11H-benzo[b]fluoren-11-one and its derivatives, was also investigated and proved to follow the BEP principle as well. Unlike the quantum mechanics description of proton transfer where either proton tunneling is dominant or solute/solvent is coupled in ESIPT, this work demonstrates that reaction kinetics and thermodynamics are strongly correlated within the same class of ESIPT molecules with an intrinsic barrier free from solvent perturbation, being faster with the more exergonic reaction.