β-Sonogel-Carbon electrodes: A new alternative for the electrochemical determination of catecholamines

In this work, a new alternative for the electrochemical determination of catecholamines based on β-cyclodextrin-Sonogel-Carbon electrodes is reported. The incorporation of β-CD and graphite in the preparation of the Sonogel-Carbon material leads to a modification of the electrode surface properties which causes a significant increase in the oxidation peak current of biomolecules such as dopamine, l-epinephrine, d,l-norepinephrine and catechol. This phenomenon might be attributed to the formation of an inclusion complex between β-CD and the catecholamines. The amount of β-CD necessary to form the Sonogel electrode was studied and optimization of electrochemical parameters, perm selectivity and mechanical stability of the sensor are discussed. Scanning electron microscopy and electrochemical impedance spectroscopy measurements were employed to characterize the electrical parameters and the structural properties of the new electrode surface, respectively. Cyclic voltammetry (CV) and Adsorptive differential pulse voltammetry (AdDPV) measurements were also used to explore the electrochemical behaviour of the electrode versus the quoted catecholamines. The β-CD-Sonogel-Carbon electrode offers fast and linear responses towards dopamine, norepinephrine, epinephrine and catechol, with good and low detection limits: 0.164, 0.294, 0.699 and 0.059 μmol L⁻¹, respectively.     

Photoactive materials based on semiconducting nanocarbons——A challenge opening new possibilities for photocatalysis

This perspective paper introduces the concept that nanocarbons and related materials such as carbon dots are an interesting intrinsic photocatalytic semiconducting material, and not only a modifier of the existing(semiconducting) materials to prepare hybrid materials. The semiconducting properties of the nanocarbons, and the possibility to have the band gap within the visible-light region through defect band engineering, introduction of light heteroatoms and control/manipulation of the curvature or surface functionalization are discussed. These materials are conceptually different from the classical semiconducting photocatalysts, because semiconductor domains with tuneable characteristics are embedded in a conductive carbon matrix, with the presence of various functional groups(as C=O groups) enhancing charge separation by trapping electrons. These nanocarbons open a range of new possibilities for photocatalysis both for energetic and environmental applications. The use of nanocarbons as quantum dots and photoluminescent materials was also analysed.     

Recent advances on flexible electrodes for Na-ion batteries and Li–S batteries

Flexible energy storage devices are essential for emerging flexible electronics. The existing state-of-the-art Li-ion batteries are slowly reaching their limitation in terms of cost and energy density. Hence, flexible Na-ion batteries(SIBs) with abundance Na resources and Li–S batteries with high energy density become the alternative for the Li-ion batteries in future. This review summarizes the recent advances in the development of flexible electrode materials for SIBs with metallic matrix and carbonaceous matrix such as carbon nano-tubes, carbon nano-fiber, graphene, carbon cloth, carbon fiber cloth, and cotton textiles.Then, the potential prototype flexible full SIBs are discussed. Further, the recent progress in the development of flexible electrode materials for Li–S batteries based on carbon nano-fiber, carbon nano-tubes,graphene, and cotton textiles is reviewed. Moreover, the design strategies of suitable interlayer, separator,electrolyte, and electrodes to prevent the dissolution and shuttle effect of polysulfides in flexible Li–S batteries are provided. Finally some prospective investigation trends towards future research of flexible SIBs and Li–S batteries are also proposed and discussed. The scientific and engineering knowledge gained on flexible SIBs and Li–S batteries provides conceivable development for practical application in near future.     

Nano ES GEMMA and PDMA,new tools for the analysis of nanobioparticles—Protein complexes,lipoparticles, and viruses

Differential mobility analysis (DMA) is a technique suited for size analysis as well as preparative collection of airborne nanosized airborne particles. In the recent decade, the analysis of intact viruses, proteins, DNA fragments, polymers, and inorganic nanoparticles was possible when combining this method with a nano-electrospray charge-reduction source for producing aerosols from a sample solution/suspensions. Mass analysis of high molecular weight noncovalent complexes is also possible with this methodology due to the linear correlation of the electrophoretic mobility diameter and the molecular mass. In this work, we present the analysis (size and molecular mass) of high molecular weight multimers (noncovalent functional homocomplex) of Jack bean urease in a mass range from 275 kDa up to 2.5 MDa, with mainly present tri- and hexamers but also higher oligomers of the 91 kDa monomer subunit. In a second experiment, the size analysis of intact very-low-density (approximately 35 nm), low-density ( approximately 22 nm) and high-density lipoparticles (approximately 10 nm), which are heterocomplexes consisting of cholesterol, lipids, and proteins in different ratios, is presented. Results from mobility analysis were in excellent agreement with particle diameters found in literature. The last presented experiment demonstrates size analysis of a rod-like virus and selective sampling of a selected size fraction of electrosprayed, singly-charged tobacco mosaic virus particles. Sampling and subsequent transmission electron microscopic investigations of a specific size fraction (40 nm electrophoretic mobility diameter) revealed the folding of virus particles during the electrospray and charge reduction (electrical stress) as well as solvent evaporation (mechanical stress) process, leading to an observed geometry of 150 (length) x 35 (width) nm (average cylindrical geometry of unsprayed intact virus 300 x 18 nm).     

Preparation of palladium nanoparticles–titanium electrodes as a new anode for direct methanol fuel cells

Pd nanoparticle/Ti electrodes are prepared by electroless plating of palladium on titanium plates. The morphology and surface analysis of Pd nanoparticle/Ti electrodes are investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The results indicate that palladium nanoparticles are homogeneously deposited on the surface of titanium plates. The electro-catalytic activity of Pd nanoparticle/Ti electrodes in the methanol electro-oxidation is studied by cyclic voltammetry and chronoamperometry methods. The results show that the electro-catalytic oxidation of methanol on the Pd nanoparticle/Ti electrode improved compare to pure palladium electrode and confirmed the better electro-catalytic activity and stability of these new electrodes.     

Three-phase electrodes: simple and efficient tool for analysis of ion transfer processes across liquid-liquid interface—twenty years on

In this review, we focus on major achievements of the three-phase electrode methodology applied for studying ion transfers across an interface between two immiscible liquids. Exactly 20 years ago, the group of electrochemists led by Fritz Scholz, invented an elegant and simple set up suitable to get access to the thermodynamics of ion transfers across liquid/liquid interface. Within the last two decades, besides determination of thermodynamics of the transfer of many important ionic substances, three-phase electrodes have been applied for many other purposes. Thermodynamics of interfacial chemical reactions, kinetics of ion and electron transfer, interfacial catalysis, recognition of chiral ions, synthesis of nano-particles, and biosensor development are some of the milestones achieved by application of three-phase electrodes. While elaborating briefly major achievements, future perspectives of this simple, but powerful electrochemical tool, have been also envisaged.

     

Surface carboxyl groups enhance the capacities of carbonaceous oxygen electrodes for aprotic lithium−oxygen batteries: A direct observation on binder-free electrodes

In order to achieve the high capacities of carbonaceous oxygen diffusion electrodes for aprotic lithium–oxygen batteries (Li–O₂ batteries), most efforts currently focus on the design of rational porous architectures. Only few works study the surface chemistry effect that might be a critical factor influencing the capacities of carbonaceous electrodes. In addition, the surface chemistry effect is very difficult to be studied in composite electrodes due to the influences of binders and additives. Herein, we propose chemically activated carbon cloth (CACC) as an ideal model to investigate the effect of surface functional groups on the discharge capacities of carbonaceous oxygen electrodes for Li–O₂ batteries. The intrinsic surface chemistry effect on the performance of carbonaceous cathode is directly observed for the first time without the influences of binders and additives. Results indicate that the surface carboxyl groups introduced by the chemical treatment not only function as the appropriate nucleation sites for Li₂O₂ but also induce the formation of toroid-like Li₂O₂. Thus, the surface carboxyl modification enhances the discharge capacities from 0.48 mAh/cm² of pristine carbon cloth to 1.23 mAh/cm² of CACC. This work presents an effective way to further optimize the carbonaceous oxygen electrodes via surface functional group engineering     

855 — Electrochemical conversion of lactoperoxidase,ceruloplasmin and alkaline phosphatase on mercury electrodes

Reversible redox conversions of lactoperoxidase, ceruloplasmin and alkaline phosphatase disulfide bonds proceed in phosphate buffer solutions on the d.m.e. Irreversibly adsorbed and denaturated enzyme molecules take part in the process. Enzymes are also adsorbed irreversibly on the d.m.e. from potassium chloride solutions, but the redox conversion rates of disulfide bonds are considerably lower, due to the specific adsorption of chloride ions on the mercury electrode.     

Self-assembled mono- and bilayers on gold electrodes to assess antioxidants—a comparative study

Oxidative stress is considered as an imbalance of reactive species over antioxidants, leading to diseases and cell death. Various methods have been developed to determine the antioxidant potential of natural or synthetic compounds based on the ability to scavenge free radicals. However, most of them lack biological relevance. Here, a gold-based self-assembled monolayer (SAM) was compared with a gold-supported lipid bilayer as models for the mammalian cell membrane to evaluate the free radical scavenging activity of different antioxidants. The oxidative damage induced by reactive species was verified by cyclic and differential pulse voltammetry and measured by the increase of electrochemical peak current of a redox probe. Trolox, caffeic acid (CA), epigallocatechin gallate (EGCG), ascorbic acid (AA), and ferulic acid (FA) were used as model antioxidants. The change in the decrease of the electrochemical signal reflecting oxidative membrane damage confirms the expected protective role. Both model systems showed similar efficacies of each antioxidant, the achieved order of radical scavenging potential is as follows: Trolox > CA > EGCG > AA > FA. The results showed that the electrochemical assay with SAM-modified electrodes is a stable and powerful tool to estimate qualitatively the antioxidative activity of a compound with respect to cell membrane protection against biologically relevant reactive species.

     

Quantum chemical investigation on solvation of Ginkgolides

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Thick-film electrodes for measurement of superoxide and hydrogen peroxide based on direct protein–electrode contacts

Cytochrome c was immobilized on screen-printed thick-film gold electrodes by a self-assembly approach using mixed monolayers of mercaptoundecanoic acid and mercaptoundecanol. Cyclic voltammetry revealed quasi-reversible electrochemical behavior of the covalently fixed protein with a formal potential of +10 mV vs. Ag/AgCl. Polarized at +150 mV vs. Ag/AgCl the electrode was found to be sensitive to superoxide radicals in the range 300–1200 nmol L^–1. Compared with metal needle electrodes sensitivity and reproducibility could be improved and combined with the easiness of preparation. This allows the fabrication of disposable sensors for nanomolar superoxide concentrations. By changing the electrode potential the sensor can be switched from response to superoxide radicals to hydrogen peroxide—another reactive oxygen species. H₂O₂ sensitivity can be provided in the range 10–1000 mol L^–1 which makes the electrode suitable for oxidative stress studies.     

Cytochrome c′ from Chromatium vinosum on gold electrodes

Cytochrome c′ from Chromatium vinosum (CVCP) was immobilized at a surface-modified gold electrode. Characterization of the CVCP electrode showed a quasi-reversible, diffusionless electrochemical redox behavior of the surface adsorbed protein with a formal potential of −128±5 mV vs. Ag/AgCl. The heterogeneous electron transfer rate constant of adsorbed CVCP was determined to be about 50 s⁻¹. Different immobilization strategies were compared. The interaction of the immobilized CVCP with nitric oxide (NO) was investigated and applied for a primary amperometric detection of NO in solution.     

Bacterial protein secretion — a target for new antibiotics?

The heavy use of antibiotics over recent decades has resulted in widespread resistance of bacteria to many drugs. Overcoming resistance requires new approaches to antibiotic development, including the exploitation of new targets in the bacterial cell. Protein secretion is essential for bacterial cell growth and virulence, so it could be a suitable target for new therapeutic agents.     

A new synthetic approach based on (−)-menthone for chiral liquid crystals

Starting from (?)-menthone, a new chiral building block useful for liquid crystal preparation was synthesized. This chiral moiety was attached to selected phenols under mild conditions by esterification. Rigid cores of tolanebenzoates and phenylbenzoates were prepared using the palladium cross-coupling reaction or by traditional liquid crystal synthesis methods. This convergent approach ended with a second esterification or palladium cross-coupling reaction to furnish new liquid crystal materials with smectic A, smectic C* and N* phases, as well as blue phases (BP). Thermal behavior, and the effect of chiral moiety branches and molecular packing in the smectic phases, have been investigated using differential scanning calorimetry, optical microscopy and X-ray diffraction.     

Comment on “a new rism integral equation for solvent polymers”

This comment draws attention to the connections and distinctions between the RISM integral equation calculations of Hirata and Levy, and prior work by Chandler et al. (1984).     

ESR studies on the solvation of perfluoro-n-alkyl t-butyl nitroxides — A new scale for electronegativity of perfluoro-n-alkyl groups

Pentafluoroethyl t-butyl nitroxides (3) have been generated by the use of electron-transfer reactions of O-benzoyl-N-t-butylhydroxylamine (1) and pentafluoropropanoyl peroxide (2) in F113 (CFCl₂CF₂Cl) solution. ESR measurement of a_N and a_F ^β values for 3 in 11 solvents have been carried out at 17 ± 2 °C. The a_N values for 3 in 10 aprotic solvents (but not in i-PrOH) show a linear correlation with the cybotactic solvent parameter E_T, i.e. a_N = 3.02 × 10⁻² E_T ± 10.46. Together with the similar correlation analysis for trifluoromethyl t-butyl nitroxide (4) and heptafluoropropyl t-butyl nitroxide (5) reported previously, the physical significance for the slope, slope × E_T, the extrapolated intercept on the a_N axis, is linked to the sensitivity of the nitroxide toward solvation, the magnitude of the overall solution effect on the a_N values, and the intrinsic a_N values of 3, 4, 5 in the ideal gaseous state, respectively. The intercepts on the a_N axis, 11.34 G, 11.56 G and 11.37 G may serve a new measure of electronegativity for CF₃, C₂F₅ and n-C₃F₇, respectively. The plots of a_N versus noncybotactic solvent constants, such as dipolar moment (μ) and dielectric constant (ɛ), all show random cases.     

An electrochemical signal switch–based (on–off) aptasensor for sensitive detection of insulin on gold-deposited screen-printed electrodes

Journal of Solid State Electrochemistry - Insulin hormone is of great importance for many diseases, especially for diabetes management. Therefore, different detection strategies have been used for...     

401 — The development of bienzyme glucose electrodes

Amperometric glucose electrodes are constructed on the basis of glucose oxidase and peroxidase. The first two types of electrodes employ a Pt or glassy carbon electrode and a bienzyme membrane. In the third type of electrode peroxidase was adsorbed on the organic metal electrode and the electrode obtained was covered with a glucose oxidase membrane. In the first two types of devices the electron exchange between the peroxidase-active center and the electrode is carried out by potassium ferrocyanide.The electrodes possess a linear dependence of the stationary current on the glucose concentration in the range of 0.01–1 mM. The stationary current is attained in 2–4 min. The sensitivity of the first and second types of electrodes shows little dependence in the potential ranging from 0.1 to 0.3 V (vs. saturated Ag⋎AgCl) and from 0.3 to −0.1 V respectively. The lowest sensitivity of the electrode based on organic metal is displayed at 0.1 V; the potential increase (up to 0.2 V) orthe decrease (to −0.1 V) leads to negligible sensitivity rise.The electrodes (types I and II) retain their activity for more than 100 days, whereas the third type for 4–6 days only. These electrodes possess a high selectivity, showing no response to the ascorbic acid and other electrode-active compounds present in blood plasma.     

Quantum Chemical Study on the Thermolysis of Dicyanofuroxan

Recently,thegeometricandelectronicstrUctUreofdicyanofuroxan(3,4-dicyano-l,2,5-oxadiazole-2-oxide)wasstUdiedbyT.Pasinszkiandco-workers,usingabinitiocalcula-honattheHF/6-3lGlevelandx-raycyrstallograPhy.'Beforetheabovework,exPerdrientalstUdyhadsuggestedthatdicyanofuroxancanundergothermolyticcycloreversiontotWomolesofthenovelpenta-atondcmolecule,NCCNO,'whichisofpotentialastrophysicalinterest.Here,theresultSoftheorehcalstUdiesbyAMl'andPM3'methods,usingtheunrestrictedHartree-Fock(UHF)calc…