Novel Enzymatic Method for Imine Synthesis via the Oxidation of Primary Amines Using D-Amino Acid Oxidase from Porcine Kidney

Carbon Quantum Dots: Synthesis, Structure, Properties, and Catalytic Applications for Organic Synthesis

Carbon quantum dots (CQDs), also known as carbon dots (CDs), are novel zero-dimensional fluorescent carbon-based nanomaterials. CQDs have attracted enormous attention around the world because of their excellent optical properties as well as water solubility, biocompatibility, low toxicity, eco-friendliness, and simple synthesis routes. CQDs have numerous applications in bioimaging, biosensing, chemical sensing, nanomedicine, solar cells, drug delivery, and light-emitting diodes. In this review paper, the structure of CQDs, their physical and chemical properties, their synthesis approach, and their application as a catalyst in the synthesis of multisubstituted 4H pyran, in azide-alkyne cycloadditions, in the degradation of levofloxacin, in the selective oxidation of alcohols to aldehydes, in the removal of Rhodamine B, as H-bond catalysis in Aldol condensations, in cyclohexane oxidation, in intrinsic peroxidase-mimetic enzyme activity, in the selective oxidation of amines and alcohols, and in the ring opening of epoxides are discussed. Finally, we also discuss the future challenges in this research field. We hope this review paper will open a new channel for the application of CQDs as a catalyst in organic synthesis.

DadY (PA5303) is required for fitness of Pseudomonas aeruginosa when growth is dependent on alanine catabolism

Pseudomonas aeruginosa inhabits diverse environmental niches that can have varying nutrient composition. The ubiquity of this organism is facilitated by a metabolic strategy that preferentially utilizes low-energy, non-fermentable organic acids, such as amino acids, rather than the high-energy sugars preferred by many other microbes. The amino acid alanine is among the preferred substrates of P. aeruginosa. The dad locus encodes the constituents of the alanine catabolic pathway of P. aeruginosa. Physiological roles for DadR (AsnC-type transcriptional activator), DadX (alanine racemase), and DadA (D-amino acid dehydrogenase) have been defined in this pathway. An additional protein, PA5303, is encoded in the dad locus in P. aeruginosa. PA5303 is a member of the ubiquitous Rid protein superfamily and is designated DadY based on the data presented herein. Despite its conservation in numerous Pseudomonas species and membership in the Rid superfamily, no physiological function has been assigned to DadY. In the present study, we demonstrate that DadA releases imino-alanine that can be deaminated by DadY in vitro. While DadY was not required for alanine catabolism in monoculture, dadY mutants had a dramatic fitness defect in competition with wild-type P. aeruginosa when alanine served as the sole carbon or nitrogen source. The data presented herein support a model in which DadY facilitates flux through the alanine catabolic pathway by removing the imine intermediate generated by DadA. Functional characterization of DadY contributes to our understanding of the role of the broadly conserved Rid family members.

The Stability of Dimeric D-amino Acid Oxidase from Porcine Kidney Strongly Depends on the Buffer Nature and Concentration

The first step of the inactivation of the enzyme D-amino acid oxidase (DAAO) from porcine kidney at pH 5 and 7 is the enzyme subunit dissociation, while FAD dissociation has not a relevant role. At pH 9, both dissociation phenomena affect the enzyme stability. A strong effect of the buffer nature and concentration on enzyme stability was found, mainly at pH 7 and 9 (it was possible at the same temperature to have the enzyme fully inactivated in 5 mM of Hepes while maintaining 100% in 5 mM of glycine). The effect of the concentration of buffer on enzyme stability depended on the buffer: at pH 5, the acetate buffer had no clear effect, while Tris, Hepes and glycine (at pH 7) and carbonate (at pH 9) decreased enzyme stability when increasing their concentrations; phosphate concentration had the opposite effect. The presence of 250 mM of NaCl usually increased enzyme stability, but this did not occur in all cases. The effects were usually more significant when using low concentrations of DAAO and were not reverted upon adding exogenous FAD. However, when using an immobilized DAAO biocatalyst which presented enzyme subunits attached to the support, where dissociation was not possible, this effect of the buffer nature on enzyme stability almost disappeared. This suggested that the buffers were somehow altering the association/dissociation equilibrium of the enzyme.