Revisiting Alternating Current Electrolysis for Organic Synthesis.

This review summarizes the recent advancements in alternating current (AC)-driven electroorganic synthesis since 2021 and discusses the reactivities AC electrolysis provides to achieve new and unique organic transformations.

Electrochemical hydrogen isotope exchange of amines controlled by alternating current frequency.

Here, we report an electrochemical protocol for hydrogen isotope exchange (HIE) at α-C(sp3)-H amine sites. Tetrahydroisoquinoline and pyrrolidine are selected as two model substrates because of their different proton transfer (PT) and hydrogen atom transfer (HAT) kinetics at the α-C(sp3)-H amine sites, which are utilized to control the HIE reaction outcome at different applied alternating current (AC) frequencies. We found the highest deuterium incorporation for tetrahydroisoquinolines at 0 Hz (i.e., under direct current (DC) electrolysis conditions) and pyrrolidines at 0.5 Hz. Analysis of the product distribution and D isotope incorporation at different frequencies reveals that the HIE of tetrahydroisoquinolines is limited by its slow HAT, whereas the HIE of pyrrolidines is limited by the overoxidation of its α-amino radical intermediates. The AC-frequency-dependent HIE of amines can be potentially used to achieve selective labeling of α-amine sites in one drug molecule, which will significantly impact the pharmaceutical industry.

Oxidative stress generated at nickel oxide nanoparticle interface results in bacterial membrane damage leading to cell death.

Metal oxide nanoparticles (NPs) have shown enhanced antibacterial effects against many bacteria. Thus, understanding the potential antibacterial effects of nickel oxide nanoparticles (NiO NPs) against Gram-positive and Gram-negative pathogenic bacteria is an urgent need to enable the exploration of NiO NP use in biomedical sciences. To this end, NiO NPs were synthesized by microwave assisted hydrothermal synthesis method. The synthesized NPs were characterized by X-ray diffraction (XRD) and Fourier Transfer Infrared (FT-IR) and UV-visible spectroscopy. The morphological features of the synthesized NiO NPs were analysed using Transmission Electron Microscopy (TEM) and FE-SEM analysis. The antibacterial activity of NiO NP was explored using different antimicrobial and biophysical studies. The obtained data reveals that the NiO NP has stronger antibacterial activity against Gram-positive bacteria compared to Gram-negative bacteria. The mechanism behind the antibacterial activity of the NiO NP was explored by evaluating the amount of ROS generation at the NiO NP interface. The effect of ROS generation on the bacterial membrane was evaluated by BacLight assay and morphological analysis of the bacterial membrane using FE-SEM. The data altogether suggested that the oxidative stress generated at the NiO NP interface resulted in membrane damage leading to bacterial cell death.

Functional molecule guided evolution of MnO x nanostructure patterns on N-graphene and their oxygen reduction activity.

In this work, we systematically followed the growth of MnO x nanostructures on trimesic acid (TMA)/benzoic acid (BA) functionalised nitrogen doped graphene (NG) and studied their electrocatalytic activity towards oxygen reduction reaction (ORR). In these hybrid materials the MnO x phase, their morphology and Mn surface valency were guided by the functional molecules, their concentration and the duration of reaction, which in turn significantly affected the ORR activity. During the growth in the presence of TMA, agglomerated nanostructures were formed at 2 h reaction, which transformed to well dispersed 4-7 nm particles at 6 h over a large area of NG. However, in the presence of BA, MnOOH nano-flecks were formed at 2 h and transformed to MnOOH nanowires and oval shaped Mn3O4 particles at 8 h of reaction. The valency of surface Mn on the different MnO x nanostructures was ascertained by X-ray photoelectron spectroscopy (XPS). The ORR activity of samples were studied by cyclic voltammetry (CV) and rotating disc electrode (RDE) in alkaline medium. Among all the studied samples, the highest ORR activity with most efficient 4e- transfer process is observed for TMA modified NG-MnO X obtained at 6 h of reaction, which is due to its well dispersed nanostructure morphology.

Stimulation of electrocatalytic oxygen reduction activity on nitrogen doped graphene through noncovalent molecular functionalisation.

Molecular doping on graphene, through noncovalent functionalization offers a great opportunity to tune charge density on graphene for catalytic applications. Although enhanced oxygen reduction activity has been reported in heteroatom doped graphene, the synergistic advantage of molecular and heteroatom co-doping has not yet been studied. Here, we report the remarkably enhanced catalytic activity of benzoate or 1-pyrenebutyrate functionalized N-doped graphene (BA-NrGO/PB-NrGO) towards the oxygen reduction reaction (ORR) in alkaline medium. An efficient 4e(-) reduction process with a more positive onset potential (Eonset = 0.85 V vs. RHE) and high ORR activity (Jk = 3.16 mA cm(-2) at 0.65 V) has been observed in BA-NrGO. DFT studies show that the stimulated ORR activity is due to functionalisation induced increased charge density on active sites.

Self-assembly of peptide-amphiphile forming helical nanofibers and in situ template synthesis of uniform mesoporous single wall silica nanotubes.

A lysine based peptide amphiphile (PA) is designed and synthesized for efficient water immobilization. The PA with a minimum gelation concentration (MGC) of 1% w/v in water shows prolonged stability and can also efficiently immobilize aqueous mixtures of some other organic solvents. The presence of a free amine induced pH dependency of the gelation as the PA could form hydrogel at a pH range of 1-8 but failed to do so above that pH. Various spectroscopic and microscopic experiments such as steady state fluorescence, NMR, IR, CD, and FESEM reveal the presence of hydrophobic interaction, hydrogen bond, and π-π stacking interaction in the self-assembly process. The self-aggregation has been correlated with the design of the molecule to show the involvement of supramolecular forces and the hierarchical pathway. While the L analogue formed left-handed helical nanofibers, the other enantiomer showed opposite helicity. Interestingly the equimolar mixture of the isomers failed to form any fibrous aggregate. Although fibers formed at a subgel concentration, no helical nature was observed at this stage. The length and thickness of the fibers increased with increase in the gelator concentration. The nanofibers formed by the gelator are used as a template to prepare mesoporous single wall silica nanotubes (SWSNTs) in situ in plain water without the requirement of any organic solvent as well as any external hydrolyzing agent. The SWSNTs formed are open at both ends, are few micrometers in length, and have an average diameter of ~10 nm. The BET isotherm showed a type IV hysteresis loop suggesting mesoporous nature of the nanotubes.