Amplifying Reactivity of Bio-Inspired [FeFe]-Hydrogenase Mimics by Organic Nanotubes.

A bio-inspired FeFe hydrogenase model which catalyses hydrogen evolution reaction (HER) in acidic solutions is immobilized in polyaniline (PANI)-based nanotubes. A combination of analytical techniques reveals that this construct maintains both the molecular signatures of the bio-inspired complex and the material properties of PANI. The amine and imine-rich environment of the PANI chain amplifies the inherent HER activity of the bio-inspired complex, allowing electrocatalytic HER at neutral pH, with lower overpotentials and higher current densities compared to the bio-inspired complex alone.

Introducing Phosphorus into the Overcrowded Thiele's hydrocarbon Family: Unveiling Contorted Main Group Diradicaloids with Dynamic Redox Behavior.

Thiele's Hydrocarbons (THs) featuring a 9,10-anthrylene core with switchable geometric and electronic configurations offer exciting possibilities in advanced functional materials. Despite significant advances in main group-based diradicaloids in contemporary chemistry, main group THs containing an anthrylene cores have remained elusive, primarily due to the lack of straightforward synthetic strategies and the inherent high reactivity of these species. In this study, we utilize an anthracene-based phosphine synthon to demonstrate, for the first time, a facile and high-yielding synthetic strategy for robust P-functionalized overcrowded ethylenes (OCEs) within the TH family.

Role of distal arginine residue in the mechanism of heme nitrite reductases.

Heme nitrite reductases reduce NO by 1e/2H to NO or by 6e/8H to NH which are key steps in the global nitrogen cycle. Second-sphere residues, such as arginine (with a guanidine head group), are proposed to play a key role in the reaction by assisting substrate binding and hydrogen bonding and by providing protons to the active site for the reaction. The reactivity of an iron porphyrin with a NO covalently attached to a guanidinium arm in its 2nd sphere was investigated to understand the role of arginine residues in the 2nd sphere of heme nitrite reductases.

Silver nanostructure-modified graphite electrode for in-operando SERRS investigation of iron porphyrins during high-potential electrocatalysis.

In-operando spectroscopic observation of the intermediates formed during various electrocatalytic oxidation and reduction reactions is crucial to propose the mechanism of the corresponding reaction. Surface-enhanced resonance Raman spectroscopy coupled to rotating disk electrochemistry (SERRS-RDE), developed about a decade ago, proved to be an excellent spectroscopic tool to investigate the mechanism of heterogeneous oxygen reduction reaction (ORR) catalyzed by synthetic iron porphyrin complexes under steady-state conditions in water. The information about the formation of the intermediates accumulated during the course of the reaction at the electrode interface helped to develop better ORR catalysts with second sphere residues in the porphyrin rings.

Assembly of redox active metallo-enzymes and metallo-peptides on electrodes: Abiological constructs to probe natural processes.

Redox active metallo-proteins and metallo-peptides attached to self-assembled monolayers (SAM) of thiols on Au electrodes or constituting the SAM on Au electrodes can provide unique opportunities to investigate a range of complicated biological phenomena in controlled abiological constructs. In addition to conventional biochemical tools like site-directed mutagenesis, these constructs allow control over electron transfer (ET) processes, micro solvation (SAM design), folding/misfolding and orientation of these biological entities. This article presents a review of the work done by this group in creating abiological bio-inspired SAM on Au electrodes to probe several important biological processes where redox plays or might play a major role.

Contributions to cytochrome inner- and outer-sphere reorganization energy.

Cytochromes are small water-soluble proteins that catalyze electron transfer in metabolism and energy conversion processes. cytochrome presents a curious case in displaying fluxionality of its heme axial methionine ligand; this behavior is altered by single point mutation of the Q64 residue to N64 or V64, which fixes the ligand in a single configuration. The reorganization energy () of these cytochrome variants is experimentally determined using a combination of rotating disc electrochemistry, chronoamperometry and cyclic voltammetry.

Ligand Radical Mediated Water Oxidation by a Family of Copper -Phenylene Bis-oxamidate Complexes.

Understanding the reactivity landscape for the activation of water until the formation of the O-O bond and O release in molecular chemistry is a decisive step in guiding the elaboration of cost-effective catalysts for the oxygen-evolving reaction (OER). Copper(II) complexes have recently caught the attention of chemists as catalysts for the 4e/4H water oxidation process. While a copper(IV) intermediate has been proposed as the reactive intermediate species, no spectroscopic signature has been reported so far.

Kinetic Isotope Effects on Electron Transfer Across Self-Assembled Monolayers on Gold.

Reactions requiring controlled delivery of protons and electrons are important in storage of energy in small molecules. While control over proton transfer can be achieved by installing appropriate chemical functionality in the catalyst, control of electron-transfer (ET) rates can be achieved by utilizing self-assembled monolayers (SAMs) on electrodes. Thus, a deeper understanding of the ET through SAM to an immobilized or covalently attached redox-active species is desirable.

Elucidation of Factors That Govern the 2e/2H vs 4e/4H Selectivity of Water Oxidation by a Cobalt Corrole.

Considering the importance of water splitting as the best solution for clean and renewable energy, the worldwide efforts for development of increasingly active molecular water oxidation catalysts must be accompanied by studies that focus on elucidating the mode of actions and catalytic pathways. One crucial challenge remains the elucidation of the factors that determine the selectivity of water oxidation by the desired 4e/4H pathway that leads to O rather than by 2e/2H to HO. We now show that water oxidation with the cobalt-corrole CoBr as electrocatalyst affords HO as the main product in homogeneous solutions, while heterogeneous water oxidation by the same catalyst leads exclusively to oxygen.

Hydrogen Evolution from Aqueous Solutions Mediated by a Heterogenized [NiFe]-Hydrogenase Model: Low pH Enables Catalysis through an Enzyme-Relevant Mechanism.

[NiFe]-hydrogenase enzymes are efficient catalysts for H evolution but their synthetic models have not been reported to be active under aqueous conditions so far. Here we show that a close model of the [NiFe]-hydrogenase active site can work as a very active and stable heterogeneous H evolution catalyst under mildly acidic aqueous conditions. Entry in catalysis is a Ni Fe complex, with electronic structure analogous to the Ni-L state of the enzyme, corroborating the mechanism modification recently proposed for [NiFe]-hydrogenases.

A Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reactions in Water.

Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H/4 e process, while oxygen can be fully reduced to water by a 4 e/4 H process or partially reduced by fewer electrons to reactive oxygen species such as HO and O. We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media.

A Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reactions in Water.

Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H(+)/4 e(-) process, while oxygen can be fully reduced to water by a 4 e(-)/4 H(+) process or partially reduced by fewer electrons to reactive oxygen species such as H2O2 and O2(-). We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media.

The protonation state of thiols in self-assembled monolayers on roughened Ag/Au surfaces and nanoparticles.

The protonation state of thiols in self-assembled monolayers (SAMs) on Ag and Au surfaces and nanoparticles (NPs) has been an issue of contestation. It has been recently demonstrated that deuterating the thiol proton produces ostentatious changes in the Raman spectra of thiols and can be used to detect the presence of the thiol functional group. Surface enhanced Raman spectroscopy (SERS) of H/D substituted aliphatic thiols on Ag surfaces clearly shows the presence of S-H vibration between 2150-2200 cm(-1) which shifts by 400 cm(-1) upon deuteration and a simultaneous >20 cm(-1) shift in the C-S vibration of thiol deuteration.