Enzymatic Catalysis of Proton Transfer and Decarboxylation Reactions

Non-trivial ground and excited state photophysics of a substituted phenol

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) shows solvent dependent single or dual emission. The photophysics of 5-tBHI has been studied in a variety of solvents and the results were compared with that of the methyl derivative of the probe as well as the 5-tBHI anion. It has been found that the intramolecular H-bonded conformer of 5-tBHI predominantly exists in non-polar solvents, and undergoes facile excited state intramolecular proton transfer (ESIPT). On the other hand, a dynamic equilibrium can be found in polar, protic solvents, even in the ground state, except in water. NMR analyses confirm the loss of aromaticity of the probe in the ground state via anion formation, in equilibrium with the solvent mediated intermolecularly H-bonded state, in neat polar protic solvents like methanol. The proton transfer process, either intramolecularly or intermolecularly, was found to be of the order of 1 ps, and even faster than the instrumental resolution in the case of water. The current finding provides important insights on the photophysics of this small, substituted phenol.

Enzymatic reactions in the production of biomethane from organic waste

Enzymatic reactions refer to organic reactions catalyzed by enzymes. This review aims to enrich the documentation relative to enzymatic reactions occurring during the anaerobic degradation of residual organic substances with emphasis on the structures of organic compounds and reaction mechanisms. This allows to understand the displacement of electrons between electron-rich and electron-poor entities to form new bonds in products. The detailed mechanisms of enzymatic reactions relative to the production of biomethane have not yet been reviewed in the scientific literature. Hence, this review is novel and timely since it discusses the chemical behavior or reactivity of different functional groups, thereby allowing to better understand the enzymatic catalysis in the transformations of residual proteins, carbohydrates, and lipids into biomethane and fertilizers. Such understanding allows to improve the overall biomethanation efficiency in industrial applications.

Catalysis in Enzymatic Decarboxylations: Comparison of Selected Cofactor-dependent and Cofactor-independent Examples

This review is focused on three types of enzymes decarboxylating very different substrates: (1) Thiamin diphosphate (ThDP)-dependent enzymes reacting with 2-oxo acids; (2) Pyridoxal phosphate (PLP)-dependent enzymes reacting with α-amino acids; and (3) An enzyme with no known co-factors, orotidine 5'-monophosphate decarboxylase (OMPDC). While the first two classes have been much studied for many years, during the past decade studies of both classes have revealed novel mechanistic insight challenging accepted understanding. The enzyme OMPDC has posed a challenge to the enzymologist attempting to explain a 10¹⁷-fold rate acceleration in the absence of cofactors or even metal ions. A comparison of the available evidence on the three types of decarboxylases underlines some common features and more differences. The field of decarboxylases remains an interesting and challenging one for the mechanistic enzymologist notwithstanding the large amount of information already available.