Quantitative Measurements of Electrocatalytic Reaction Rates with NanoSECM

Scanning electrochemical microscopy (SECM) has been extensively used for mapping electrocatalytic surface reactivity; however, most of the studies were carried out using micrometer-sized tips, and no quantitative kinetic experiments on the nanoscale have yet been reported to date. As the diffusion-limited current density at a nanometer-sized electrode is very high, an inner-sphere electron-transfer process occurring at a nanotip typically produces a kinetic current at any attainable overpotential. Here, we develop a theory for substrate generation/tip collection (SG/TC) and feedback modes of SECM with a kinetic tip current and use it to evaluate the rates of hydrogen and oxygen evolution reactions in a neutral aqueous solution from the current-distance curves. The possibility of using chemically modified nanotips for kinetic measurements is also demonstrated. The effect of the substrate size on the shape of the current-distance curves in SG/TC mode SECM experiments is discussed.

Visualizing Overall Water Splitting on Single Microcrystals of Phosphorus-Doped BiVO4 by Photo-SECM

Particulate bismuth vanadate (BiVO4) has attracted considerable interest as a promising photo(electro)catalyst for visible-light-driven water oxidation; however, overall water splitting (OWS) has been difficult to attain because its conduction band is too positive for efficient hydrogen evolution. Using photoscanning electrochemical microscopy (photo-SECM) with a chemically modified nanotip, we visualized for the first time the OWS at a single truncated bipyramidal microcrystal of phosphorus-doped BiVO4. The tip simultaneously served as a light guide to illuminate the photocatalyst and an electrochemical nanoprobe to observe and quantitatively measure local oxygen and hydrogen fluxes. The obtained current patterns for both O2 and H2 agree well with the accumulation of photogenerated electrons and holes on {010} basal and {110} lateral facets, respectively. The developed experimental approach is an important step toward nanoelectrochemical mapping of the activity of photocatalyst particles at the subfacet level.

Photo-scanning Electrochemical Microscopy Observation of Overall Water Splitting at a Single Aluminum-Doped Strontium Titanium Oxide Microcrystal

Particulate photocatalysts for the overall water splitting (OWS) reaction offer promise as devices for hydrogen fuel generation. Even though such photocatalysts have been studied for nearly 5 decades, much of the understanding of their function is derived from observations of catalyst ensembles and macroscopic photoelectrodes. This is because the sub-micrometer size of most OWS photocatalysts makes spatially resolved measurements of their local reactivity very difficult. Here, we employ photo-scanning electrochemical microscopy (photo-SECM) to quantitatively measure hydrogen and oxygen evolution at individual OWS photocatalyst particles for the first time. Micrometer-sized Al-doped SrTiO₃/Rh_2-yCr_yO₃ photocatalyst particles were immobilized on a glass substrate and interrogated with a chemically modified SECM nanotip. The tip simultaneously served as a light guide to illuminate the photocatalyst and as an electrochemical nanoprobe to observe oxygen and hydrogen fluxes from the OWS. Local O₂ and H₂ fluxes obtained from chopped light experiments and photo-SECM approach curves using a COMSOL Multiphysics finite-element model confirmed stoichiometric H₂/O₂ evolution of 9.3/4.6 μmol cm^-2 h^-1 with no observable lag during chopped illumination cycles. Additionally, photoelectrochemical experiments on a single microcrystal attached to a nanoelectrode tip revealed a strong light intensity dependence of the OWS reaction. These results provide the first confirmation of OWS at single micrometer-sized photocatalyst particles. The developed experimental approach is an important step toward assessing the activity of photocatalyst particles at the nanometer scale.

Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode

The integration of heterogeneous electrocatalysis and molecular catalysis is a promising approach to designing new catalysts for the oxygen evolution reaction (OER) and other processes. We recently showed that the electrostatic potential drop across the double layer contributes to the driving force for electron transfer between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. Here, we report high current densities and low onset potentials for water oxidation attained using a metal-free voltage-assisted molecular catalyst (TEMPO). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine faradic efficiencies for the generation of H₂O₂ and O₂. The same catalyst was employed for efficient oxidations of butanol, ethanol, glycerol, and H₂O₂. DFT calculations show that the applied voltage alters the electrostatic potential drop between TEMPO and the reactant as well as chemical bonding between them, thereby increasing the reaction rate. These results suggest a new route for designing next-generation hybrid molecular/electrocatalysts for OER and alcohol oxidations.

Electrode surface embedded manganese(iii)–pincer complexes: efficient electrocatalysts for the oxygen evolution reaction

Highly stable and robust gold electrode surface anchored Mn(iii)–pincer complex exhibits an excellent electrocatalytic activity towards the oxygen evolution reaction at a low overpotential with a medium Tafel slope under neutral pH condition.

Voltage-Driven Molecular Catalysis of Electrochemical Reactions

Heterogeneous electrocatalysis and molecular redox catalysis have developed over several decades as two distinct ways to facilitate charge-transfer processes essential for energy conversion and storage. Whereas electrocatalytic reactions are driven by the applied voltage, molecular catalytic processes are driven by the difference between standard potentials of the catalyst and the reactant. Here, we demonstrate that the rate of electron transfer between a dissolved reactant and a molecular catalyst immobilized directly on the surface of a carbon nanoelectrode is governed by combination of chemical driving force and electrostatic potential drop across the double layer. DFT calculations show that varying the applied voltage alters the potential drop between the surface-bound and dissolved redox species. These results suggest a new route for designing next-generation hybrid molecular/electrocatalysts.

Mediated Charge Transfer at Nanoelectrodes: A New Approach to Electrochemical Reactivity Mapping and Nanosensing

Scanning electrochemical microscopy (SECM) is a powerful tool for mapping surface reactivity. Electrochemical mapping of electrocatalytic processes at the nanoscale is, however, challenging because the surface of a nanoelectrode tip is easily fouled by impurities and/or deactivated by products and intermediates of innersphere surface reactions. To overcome this difficulty, we introduce new types of SECM nanotips based on bimolecular electron transfer between the dissolved electroactive species and a redox mediator attached to the surface of a carbon nanoelectrode. A tris(2,2'-bipyridine)ruthenium complex, Ru(bpy)₃, that undergoes reversible oxidation/reduction reactions at both positive and negative potentials was used to prepare the SECM nanoprobes for mapping a wide range of electrocatalytic processes through oxidation of H₂, reduction of O₂, and both oxidation and reduction of H₂O₂ at the tip. In addition to high-resolution reactivity mapping and localized kinetic measurements, chemically modified nanoelectrodes can serve as nanosensors for a number of important analytes such as reactive oxygen and nitrogen species and neurotransmitters.

Electrocatalytic oxidation of water using self-assembled copper(ii) tetraaza macrocyclic complexes on a 4-(pyridine-4′-amido)benzene grafted gold electrode

Gold surface anchored copper(ii)tetraaza macrocyclic complex showed an excellent electrocatalytic activity towards water oxidation with an overpotential of 284 mV at a current density of 1.31 mA cm⁻² and a Tafel slope of 48 mV decade⁻¹ in neutral pH.

Electrochemical Generation of Individual Nanobubbles Comprising H2, D2, and HD

The electrochemical reduction of deuterons (2D⁺ + 2e^- → D₂) at Pt nanodisk electrodes (radius = 15-100 nm) in D₂O solutions containing deuterium chloride (DCl) results in the formation of a single gas nanobubble at the electrode surface. Analogous to that previously observed for the electrochemical generation of H₂ nanobubbles, the nucleation and growth of a stable D₂ nanobubble is characterized in voltammetric experiments by a highly reproducible and well-resolved sudden drop in the faradaic current, a consequence of restricted mass transport of D⁺ to the electrode surface following the liquid-to-gas phase transition. D₂ nanobubbles are stable under potential control due to a dynamic equilibrium existing between D₂ gas dissolution and electrochemical generation of D₂ at the circumference of the Pt nanodisk electrode. Remarkably, within the error of the experimental measurement (<6%), the electrochemical current required to nucleate a D₂ gas phase in a D₂O solution is identical to that for the H₂ gas phase in a H₂O solutions, indicating that the concentration required for nucleating a D₂ nanobubble in D₂O (0.29 M) is ∼1.25 times larger than that for a H₂ nanobubble (0.23 M), while the supersaturation is ∼300 in each case. We further demonstrate that individual nanobubbles can be electrogenerated in mixed D₂O/H₂O solutions containing both D⁺ and H⁺ at respective individual concentrations well below those required to nucleate a gas phase containing either pure D₂ or H₂. This latter finding indicates that the resulting nanobubbles comprise a mixture of D₂, H₂, and HD molecules with the chemical composition of a nanobubble determined by the concentrations and diffusivities of D⁺ and H⁺ in the mixed D₂O/H₂O solutions.

Compatibility of Flavoring Agents in Compounding Extemporaneous Omeprazole Oral Liquid

In a previous study, the results of which were provided in an article published in the International Journal of Pharmaceutical Compounding, it was determined that FLAVORx's Grape flavor in extemporaneously compounded omeprazole oral liquid was found suitable. A follow-up study was conducted in which the authors explored four additional flavors (Professional Compounding Centers of America's Cherry Concentrate and their Orange Concentrate, and FLAVORx's Bubble Gum flavor and their Watermelon flavor) to allow pharmacists and patients greater flexibility and options to flavor omeprazole oral liquid. Oral liquids were compounded using 20-mg omeprazole delayed-release capsules, 8.4% sodium bicarbonate, and each of four flavors to reach drug concentration at 2 mg/mL and flavor at 1.2% v/v (n=3). After the delayed-release pellets were disintegrated, the prescription bottles were stored in cold temperature overnight. For flavor alone in 8.4% sodium bicarbonate solution, samples were prepared the same as above except no omeprazole delayed-release capsules were added. High-performance liquid chromatographic assay was adopted from the United States Pharmacopeia's Omeprazole Monograph, but it is for the unflavored oral liquid. In order to ensure assay robustness, stability indication tests, 0.1 N HCl (acid), 0.1 N NaOH (base), 50°C (heat), and 3% hydrogen peroxide were also performed to the flavored omeprazole oral liquids, as well as to the individual flavor alone in sodium bicarbonate solution without omeprazole. Professional Compounding Centers of America's Cherry Concentrate, Orange Concentrate, and FLAVORx's Watermelon flavor showed no interference with the drug, and the assays were robust. However, FLAVORx's Bubble Gum flavor displayed five mini peaks at 280 nm with one embedded in omeprazole peak. The resolution of a Bubble Gum peak immediately next to an omeprazole peak computed by column kinetics was 0.91, while the separation factor was 1.15. A good separation is generally >1.5. This study examined only the Cherry Concentrate, Orange Concentrate, Bubble Gum flavor, and Watermelon flavor from the specified manufacturers. An insignificant interference was shown between FLAVORx's Bubble Gum flavor with omeprazole. The results are not intended to infer that all brands of the same flavor names would react the same way. Omeprazole and all four studied flavors should be protected from oxidation insult.

Electrocatalytic oxidation of water by the immobilized [CuII(l-ala)(Phen)(H2O)]+ complex on a self-assembled NCS- modified gold electrode

Copper(ii) complex [Cu^II(l-ala)(Phen)(H₂O)]⁺ (l-ala = l-phenylalanine, phen = phenanthroline) was immobilized over a self-assembled NCS⁻ modified gold electrode for the electrocatalytic oxidation of water. This surface anchored molecular complex can catalyze water oxidation reaction at a remarkably low overpotential of 327 mV with a current density of 0.5 mA cm⁻² at neutral pH.

Copper(ii) complex [Cu^II(l-ala)(Phen)(H₂O)]⁺ (l-ala = l-phenylalanine, phen = phenanthroline) was immobilized over a self-assembled NCS⁻ modified gold electrode for the electrocatalytic oxidation of water.

A synthetic chemist's guide to electroanalytical tools for studying reaction mechanisms

Monitoring reactive intermediates can provide vital information in the study of synthetic reaction mechanisms, enabling the design of new catalysts and methods. Many synthetic transformations are centred on the alteration of oxidation states, but these redox processes frequently pass through intermediates with short life-times, making their study challenging. A variety of electroanalytical tools can be utilised to investigate these redox-active intermediates: from voltammetry to in situ spectroelectrochemistry and scanning electrochemical microscopy. This perspective provides an overview of these tools, with examples of both electrochemically-initiated processes and monitoring redox-active intermediates formed chemically in solution. The article is designed to introduce synthetic organic and organometallic chemists to electroanalytical techniques and their use in probing key mechanistic questions.

Synthesis of ultrasmall and monodisperse sulfur nanoparticle intercalated CoAl layered double hydroxide and its electro-catalytic water oxidation reaction at neutral pH

Ultrasmall and monodisperse sulfur nanoparticle (S-NP) intercalated CoAl-layered double hydroxide (CoAl-LDH) electrocatalyst exhibits an excellent electrocatalytic activity towards water oxidation with a low overpotential of 250 mV at a high current density of 7.9 mA cm-2 and a Tafel slope of 61 mV dec-1 at the neutral pH condition. The fabrication strategy to achieve a high-performance, robust and durable electrocatalyst is a scale-up in next generation renewable energy fields.

Electrochemically Driven, Ni-Catalyzed Aryl Amination: Scope, Mechanism, and Applications

C-N cross-coupling is one of the most valuable and widespread transformations in organic synthesis. Largely dominated by Pd- and Cu-based catalytic systems, it has proven to be a staple transformation for those in both academia and industry. The current study presents the development and mechanistic understanding of an electrochemically driven, Ni-catalyzed method for achieving this reaction of high strategic importance. Through a series of electrochemical, computational, kinetic, and empirical experiments, the key mechanistic features of this reaction have been unraveled, leading to a second generation set of conditions that is applicable to a broad range of aryl halides and amine nucleophiles including complex examples on oligopeptides, medicinally relevant heterocycles, natural products, and sugars. Full disclosure of the current limitations and procedures for both batch and flow scale-ups (100 g) are also described.

Electrocatalytic oxidation of water at a polyoxometalate nanoparticle modified gold electrode

Polyoxometalate nanoparticles, [H₃PMo₁₂O₄₀]NPs, modified gold electrode showed excellent electrocatalytic activity towards water oxidation reaction at an overpotential of 350 mV with a current density of 1.7 mA cm⁻² in neutral pH medium.

Cerium(III) Complex Modified Gold Electrode: An Efficient Electrocatalyst for the Oxygen Evolution Reaction

Exploring efficient and inexpensive electrocatalysts for the oxidation of water is of great importance for various electrochemical energy storage and conversion technologies. In the present study, a new water-soluble [Ce(III)(DMF) (HSO4)3] complex was synthesized and characterized by UV-vis, photoluminescence, and high-resolution X-ray photoelectron spectroscopy techniques. Owing to classic 5d → 4f transitions, an intense photoluminescence in the UV region was observed from the water-soluble [Ce(III)(DMF) (HSO4)3] complex. A stacking electrode was designed where self-assembled l-cysteine monolayer modified gold was immobilized with the synthesized cerium complex and was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The resulting electrode, i.e., [Ce(III)(DMF) (HSO4)3]-l-cysteine-Au stacks shows high electrocatalytic water oxidation behavior at an overpotential of η ≈ 0.34 V under neutral pH conditions. We also demonstrated a way where the overpotential is possible to decrease upon irradiation of UV light.

Hybrid Mn3O4–NiO nanocomposites as efficient photoelectrocatalysts towards water splitting under neutral pH conditions

Dual oxide Mn₃O₄–NiO nanocomposites synthesised by seed-mediated epitaxial growth have been exploited as electrocatalysts towards water splitting at an applied overpotential of 280 mV under neutral pH conditions.

Non-enzymatic electrochemical sensing of glucose and hydrogen peroxide using a bis(acetylacetonato)oxovanadium(iv) complex modified gold electrode

A bis(acetylacetonato)oxovanadium(iv) complex modified gold electrode shows excellent sensing ability towards glucose and hydrogen peroxide in a neutral pH medium.

Simultaneous electrochemical detection of dopamine and epinephrine in the presence of ascorbic acid and uric acid using a AgNPs–penicillamine–Au electrode

A silver nanoparticle immobilized penicillamine self-assembled electrode, AgNPs–PCA–Au, can simultaneously sense dopamine, epinephrine, ascorbic acid and uric acid at neutral pH.

Mosquito-borne diseases in Assam, north-east India: current status and key challenges

Mosquito-borne diseases, including malaria, Japanese encephalitis (JE), lymphatic filariasis and dengue, are major public health concerns in the north-eastern state of Assam, deterring equitable socioeconomic and industrial development. Among these, malaria and JE are the predominant infections and are spread across the state. The incidence of malaria is, however, gradually receding, with a consistent decline in cases over the past few years, although entry and spread of artemisinin-resistant Plasmodium falciparum remains a real threat in the country. JE, formerly endemic in upper Assam, is currently spreading fast across the state, with confirmed cases and a high case-fatality rate affecting all ages. Lymphatic filariasisis is prevalent but its distribution is confined to a few districts and disease transmission is steadily declining. Dengue has recently invaded the state, with a large concentration of cases in Guwahati city that are spreading to suburban areas. Control of these diseases requires robust disease surveillance and integrated vector management on a sustained basis, ensuring universal coverage of evidence-based key interventions based on sound epidemiological data. This paper aims to present a comprehensive review of the status of vector-borne diseases in Assam and to address the key challenges.

Electrocatalytic oxidation of water by a self-assembled oxovanadium(iv) complex modified gold electrode

An oxovanadium(iv) complex modified gold electrode showed efficient electrocatalytic activity towards water oxidation at neutral pH.

Fluid interface-mediated nanoparticle membrane as an electrochemical sensor

A poly(ethyleneglycol)-stabilised magnetic Fe₃O₄ nanoparticle decorated ultra-thin membrane has been devised at the water/CCl₄ interface by ligand cross-linking with terephthaloyl chloride and the membrane was exploited as an electrochemical sensor for the detection of l-Dopa up to nanomolar concentration.

Electrochemical detection of adenine and guanine using a self-assembled copper(ii)–thiophenyl-azo-imidazole complex monolayer modified gold electrode

A self-assembled copper(ii)–thiophenyl-azo-imidazole complex monolayer modified gold electrode exhibits an excellent electrochemical sensing ability towards adenine and guanine at physiological pH.

Bifunctional gold–manganese oxide nanocomposites: benign electrocatalysts toward water oxidation and oxygen reduction

Gold–manganese oxide nanocomposites exhibit efficient electrocatalytic activity toward water oxidation and oxygen reduction at a low overpotential and under neutral pH conditions.

Quality and shelf life evaluation of pork nuggets incorporated with fermented bamboo shoot (Bambusa polymorpha) mince

Pork nuggets were processed by incorporating fermented bamboo shoot mince and their physico-chemical, microbiological and sensory characteristics were evaluated during 35 day storage at refrigeration temperature (4±1 °C). Addition of fermented bamboo shoot significantly affects the pH, moisture, protein, fat, fiber, instrumental color values and texture profiles of nuggets, especially at 6% and 8% addition levels. Nuggets with 6% and 8% FBSM had significantly lower TBARS values at the end of the storage period (i.e. 0.39 and 0.33 mg malonaldehyde/kg respectively) compared to the control (0.84 mg malonaldehyde/kg). Bamboo shoot addition significantly improved the microbial and sensory qualities of the pork nuggets. Incorporation of fermented bamboo shoot at 8% level increased the shelf life of pork nuggets by at least two weeks i.e. from 21 days to 35 days at 4±1 °C compared to the control.

Therapeutic efficacies of antimalarial drugs in the treatment of uncomplicated,Plasmodium falciparummalaria in Assam, north-eastern India

In the Indian state of Assam, the current therapeutic efficacies of the drugs commonly used in the area for the treatment of uncomplicated, Plasmodium falciparum malaria were investigated. As is routine in this area, subjects found positive for P. falciparum malaria were initially treated with chloroquine (CQ). They were given sulfadoxine-pyrimethamine (SP) if this treatment failed, and subsequently quinine if the SP failed. The protocol of the World Health Organization's extended in-vivo test was used to follow parasite clearance and clinical cure. Therapeutic response was assessed by comparing the baseline (day-0) level of parasitaemia with that observed on day 3. Many (75.7%) of the 144 evaluable subjects were treatment successes after CQ, but six early (4.2%) and 29 (20.1%) late CQ-treatment failures were observed. Of the 34 CQ-treatment failures followed, 31 (91.2%) responded adequately to SP but the other three were early (one) or late (two) SP-treatment failures. Two (66.7%) of the SP-treatment failures responded adequately to parenteral quinine but the other (a late quinine-treatment failure) had to be given an artemisinin derivative to achieve a clinical cure. The foci in which multidrug-resistant cases of malaria are developing in India need to be identified quickly, so that such cases can be cured before the mutant strains of P. falciparum that are resistant to several drugs have a chance to become more widespread.

Temporal lobe involvement in Japanese encephalitis: problems in differential diagnosis

BACKGROUND AND PURPOSE

On MR imaging and CT, Japanese encephalitis (JE) shows lesions in the thalami, substantia nigra, basal ganglia, cerebral cortex, cerebellum, brain stem, and white matter, whereas temporal lobe involvement is characteristically seen in Herpes simplex encephalitis (HSE). Temporal lobe involvement in JE may cause problems in differentiating it from HSE. We undertook this study to show the temporal lobe involvement pattern in JE and highlight differentiating features from temporal lobe involvement in HSE.

METHODS

Sixty-two patients with JE underwent CT or MR imaging or both. MR imaging was done in 53 and CT in 53. The diagnosis of JE was confirmed by cerebrospinal fluid (CSF) IgM enzyme-linked immunosorbent assay.

RESULTS

Eleven (17.7%) patients showed temporal lobe involvement with abnormal MR imaging in all. All the patients showed hippocampal involvement. Two patients showed extension of lesions into the amygdala and uncus with insular involvement in 1. The rest of the temporal lobe was spared. All patients had thalamic and substantia nigra involvement with basal ganglia involvement in 7. Six of 9 CT scans were abnormal and the temporal lesions were seen in 2.

CONCLUSIONS

The temporal lobe involvement pattern is fairly characteristic and mostly involves the hippocampus, usually sparing the rest of the temporal lobe. This and the concurrent involvement of the thalami, substantia nigra (SN), and basal ganglia allow differentiation from HSE. However, if the temporal lobe involvement is more severe, laboratory tests may be the only way to differentiate it from HSE, and it may be prudent to start antiviral therapy in the interim period.

An outbreak of Plasmodium falciparum malaria due to Anopheles minimus in central Assam, India

Epidemiological investigations were conducted in Nellie subcentre, PHC Jhargaon, under Morigaon district (Assam). The results of fever cases revealed 68 per cent slide positivity rate (SPR) and 40 per cent slide falciparum rate (SfR). The Pf proportion was > 87 per cent and remaining cases were P. vivax infections. An. minimus was incriminated as a malaria vector during the study period. The sporozoite rate was 3.08 per cent. The indoor man mosquito contact was 35 per bait/night as against 23 in outdoors. Results of susceptibility test revealed that the vector was still susceptible to both DDT and malathion at discriminating dosages. The study revealed that inadequate surveillance and vector control measures were contributing factors for malaria outbreak. In view of this, insecticide treated nets may be introduced to provide cost-effective control of malaria.