Electrochemical Analysis and Inhibition Assay of Immune-Modulating Enzyme, Indoleamine 2,3-Dioxygenase

Background: An accurate and rapid analysis of human indoleamine 2,3-dioxygenase (hIDO) is crucial for the development of anticancer pharmaceuticals because of the role of hIDO in promoting tumoral immune escape. However, the conventional assay of hIDO is limited by interference from reductants, which are used to reduce the heme iron to begin the hIDO catalytic reaction. Methods: A direct electrochemical method was applied to drive the hIDO reaction. Results: The nanostructured gold electrode enabled the electrochemical reduction of the heme iron of hIDO1. In the presence of substrates (tryptophan and oxygen), a bioelectrocatalytic current was observed, confirming an electrochemically driven hIDO reaction. A well-known inhibitor of hIDO, epacadostat, hindered this catalytic signal according to its concentration, demonstrating the rapid evaluation of its inhibition activity for the hIDO reaction. Through an in silico study using the proposed electrochemical assay system, we discovered a strong inhibitor candidate with a half-maximal inhibitory concentration of 10 nM. Conclusions: An accurate and rapid assay system in drug discovery for hIDO and kynureine pathway-targeted immunotherapy has been developed.

Facile synthesis of nanoporous Mg crystalline structure by organic solvent-based reduction for solid-state hydrogen storage

Nanoporous metals have unique potentials for energy applications with a high surface area despite the percolating structure. Yet, a highly corrosive environment is required for the synthesis of porous metals with conventional dealloying methods, limiting the large-scale fabrication of porous structures for reactive metals. In this study, we synthesize a highly reactive Mg nanoporous system through a facile organic solution-based approach without any harsh etching. The synthesized nanoporous Mg also demonstrates enhanced hydrogen sorption kinetics and reveals unique kinetic features compared to Mg nanoparticles. The well-crystallized Mg nanoporous structure exhibits crystalline facet-dependent hydrogen sorption characteristics, featuring gradually improved hydrogen storage capacity up to 6 wt.% upon cycling. Also, continuum kinetics models coupled to atomistic simulations reveal that the compressive stress developed during the hydrogenation of nanoporous Mg enhances the sorption kinetics, as opposed to the sluggish kinetics under tensile stress in core-shell nanoparticles. It is expected that the synthetic strategy conceived in this study can be further implemented to prepare different kinds of reactive porous metals in a facile and scalable way for the development of large-scale and distributed hydrogen storage systems for the emerging low-carbon hydrogen economy.

Catalytic and Electrocatalytic Mechanisms of Cytochromes P450 in the Development of Biosensors and Bioreactors

Cytochromes P450 are a unique family of enzymes found in all Kingdoms of living organisms (animals, bacteria, plants, fungi, and archaea), whose main function is biotransformation of exogenous and endogenous compounds. The review discusses approaches to enhancing the efficiency of electrocatalysis by cytochromes P450 for their use in biotechnology and design of biosensors and describes main methods in the development of reconstituted and electrochemical catalytic systems based on the biochemical mechanism of cytochromes P450, as well as and modern trends for their practical application.

Electrochemical Molecular Conversion of α-Keto Acid to Amino Acid at a Low Overpotential Using a Nanoporous Gold Catalyst

A nanoporous gold (NPG) electrode prepared through a facile anodization technique was employed in the electrochemical reductive amination of biomass-derivable α-keto acids in the presence of a nitrogen source to produce the corresponding amino acids. NPG showed a clear reductive current in the presence of α-keto acid and NH₂OH, and the electrolysis experiments confirmed the production of L-amino acid. A reductive voltammetric signal at the NPG electrode appeared at a more positive potential by 0.18-0.79 V, compared with those at the planar-gold electrode without anodization and other previously reported electrode systems, indicating the high activity of the prepared nanostructure for the electrochemical reaction. Maximum Faradaic efficiencies (FEs) of 74-93% in the reductive molecular conversion to amino acids of Ala, Asp, Glu, Gly, and Leu were obtained under the optimized conditions. The FE values were strongly dependent on the applied potential in the electrolysis, suggesting that the hydrogen evolution reaction at the electrode surface was more significant as the applied potential became more negative. The effect of potential at the NPG was lower than that at the planar-gold electrode. These results indicate that nanostructurization decreases the overpotential for the electrochemical reductive amination, resulting in high FE.

Redox State Control of Human Cytoglobin by Direct Electrochemical Method to Investigate Its Function in Molecular Basis

The direct electron transfer between human cytoglobin (Cygb) and the electrode surface, which would allow manipulating the oxidation states of the heme iron in Cygb, was first observed by immobilizing Cygb on a nanoporous gold (NPG) electrode via a carboxy-terminated alkanethiol. The voltammetric performances of the wild type and mutated Cygb-immobilized NPG electrodes were evaluated in the absence or presence of potential substrates. The obtained results demonstrated that the usefulness of the proposed method in understanding the function of Cygb in molecular basis.

Nanostructured Porous Electrodes by the Anodization of Gold for an Application as Scaffolds in Direct-electron-transfer-type Bioelectrocatalysis

In this study, nanostructured porous gold electrodes were prepared by the anodization of gold in the presence of oxalic acid or glucose as a reductant, and applied as scaffolds for direct electron transfer (DET)-type bioelectrocatalysis. Gold cations generated in the anodization seem to be reduced by the reductant to construct a porous gold structure. The DET-type performance of the electrode was examined using two DET-type model enzymes, bilirubin oxidase (BOD) and peroxidase (POD), for the four-electron reduction of dioxygen and the two-electron reduction of peroxide, respectively. BOD and POD on the anodized porous gold electrodes exhibited well-defined sigmoidal steady-state waves corresponding to DET-type bioelectrocatalysis. Scanning electron microscopy images revealed sponge-like pores on the electrodes. The anodized porous gold electrodes demonstrate promise as scaffolds for DET-type bioelectrocatalysis.

Preparation, Modification, Characterization, and Biosensing Application of Nanoporous Gold Using Electrochemical Techniques

Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning pore and ligament sizes. The np-Au electrodes that are prepared using electrochemical techniques are robust and are easier to handle for their use in electrochemical biosensing. Here, we review different electrochemical strategies for the preparation, post-modification, and characterization of np-Au along with the synergistic use of both electrochemistry and np-Au for applications in biosensing.