Proton-coupled electron transfer (PCET) plays a crucial role in a diverse array of natural and artificial energy conversion processes. Herein, we will introduce the fundamentals of electrochemical PCET with a focus on its role in water splitting. Besides, perspectives of future development of PCET are presented with regard to the investigation of reaction mechanisms and the design of advanced electrocatalysts.

Bacterial β-glycosidases are hydrolytic enzymes that depolymerize polysaccharides such as β-cellulose, β-glucans and β-xylans from different sources, which are used in a myriad of biomedical and industrial applications. It has been shown that a conformational change of the substrate, from a relaxed 4C1 conformation to a distorted 1S3/1,4B conformation of the reactive sugar, is necessary for catalysis. However, the molecular determinants that stabilize the substrate’s distortion are poorly understood. Here we use quantum mechanics/molecular mechanics (QM/MM)-based molecular dynamics methods to assess the impact of the interaction between the reactive sugar, i.e. the one at subsite -1, and the catalytic nucleophile (a glutamate) on substrate conformation. We show that the hydrogen bond involving the C2 exocyclic group and the nucleophile controls substrate conformation: its presence preserves sugar distortion, whereas its absence (e.g. in an enzyme mutant) knocks it out. We also show that 2-deoxy-2-fluoro derivatives, widely used to trap the reaction intermediates by X-ray crystallography, reproduce the conformation of the hydrolysable substrate at the experimental conditions. These results highlight the importance of the 2-OH···nucleophile interaction in substrate recognition and catalysis in endo-glycosidases and can inform mutational campaigns aimed to search for more efficient enzymes.

Iron(II) complexes containing ligands with a R2P–P–PR2 unit were synthesized by metathesis reactions. With R = tBu, a mixture of two isomers is formed; in one of them, the terminal phosphorus binds to the Fe center (ylidic structure), while in the other one, the central P atom is linked to Fe. Starting from differently functionalized parent triphosphanes and corresponding functionalized Fe complexes, the ratio of isomers does not change. The outcome of the reaction and therefore the binding modes of the triphosphane ligands in the resulting compounds can be influenced by the size of the substituents. In the case of R = iPr a chelate complex is formed (both terminal P atoms are linked to the Fe center). Applying the mixed-substituted triphosphane, the ylidic structure of the resulting complex is preferred. The new compounds were characterized by NMR spectroscopy in solution and single-crystal X-ray diffraction in solid-state. The synthetic work was supported by DFT calculations.