Enhanced catalytic activity of ppy-coated pencil electrode in the presence of chitosan and Au nanoparticles for hydrogen evolution reaction

Catalytically active and low-cost electrocatalysts for the production of hydrogen from water are extremely important for future renewable energy systems. Here, we report the fabrication of a facile pencil graphite electrode modified with polypyrrole-chitosan/Au nanoparticles and tested its performance for electrocatalytic hydrogen evolution reaction (HER) as a model process. The porous surface of the pencil graphite electrode (PGE) was modified potentiostically by polypyrrole (PPy) at various film thicknesses in the presence of chitosan (Chi), which is a natural biopolymer, in the electrolyte medium. After the optimum film thickness had been obtained, the Au particles electrodeposited on to the PPy/Chi composite film at the nano-scale to benefit both from its well-known high catalytic activity and to reduce the amount of precious metal Au to prepare a low-cost eletrocatalyst. The performance of this composite catalyst on the H⁺ reduction (H_ad formation) and thereby on the hydrogen evolution was investigated. Data from cyclic voltammetry (CV), Tafel polarization curves, and electrochemical impedance spectroscopy (EIS) demonstrated that the current densities related to the electron transfer rate changed with the thickness of the composite film, and the catalytic activity was enhanced more with deposition small amount of Au on to the catalyst surface.     

Glassy carbon electrode modified with poly-Neutral Red for photoelectrocatalytic oxidation of NADH

A new approach is described for the photoelectrocatalytic oxidation of Reduced ß-Nicotinamide Adenine Dinucleotide (NADH). It is based on a glassy carbon electrode (GCE) modified with a film of poly-Neutral Red (poly-NR) that is obtained by electropolymerization. Electrochemical measurements revealed that the modified electrode displays electrocatalytic and photo-electrocatalytic activity towards oxidation of NADH. If irradiated with a 250-W halogen lamp, the electrode yields a strongly increased electrocatalytic current compared to the current without irradiation. Amperometric and photo-amperometric detection of NADH was performed at +150 mV vs. Ag/AgCl/KCl_sat and the currents obtained are linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 1.0 μM to 1.0 mM for both methods. However, the slope of the current-NADH concentration curve of the photo-electrocatalytic procedure was 2-times better than that obtained without irradiation.

A new acylated neohesperidoside from Geranium purpureum

A new acylated neohesperoside derivative, 1-octyl-4'-isovaleroyl-neohesperoside (1), was isolated from Geranium purpureum Vill. (Geraniaceae) together with the known compounds quercetin-3-rutinoside and gallic acid. The identification of the isolated compounds was carried out by spectroscopic analysis including 1D- and 2D- NMR (1H, 13C, COSY, HSQC and HMBC) spectroscopy and ESI-TOF-MS.     

Reduced Graphene Oxide/Pt Nanoparticles/Zn‐MOF‐74 Nanomaterial for a Glucose Biosensor Construction

In this study, a new glucose biosensor was fabricated by immobilizing glucose oxidase (GOx) on platinum nanoparticles (Pt NPs) decorated reduced graphene oxide (rGO)/Zn‐MOF‐74 hybrid nanomaterial. Herein, the biosensor fused the advantages of rGO with those of porous Zn‐MOF and conductive Pt NPs. This has not only enlarged the surface area and porosity for the efficient GOx immobilization and faster mass transport, but also provided favorable electrochemical features such as high current density, remarkable electron mobility through metal nanoparticles, and improved electron transfer between the components. The GOx‐rGO/Pt NPs@Zn‐MOF‐74 coated electrode displayed a linear measurement range for glucose from 0.006 to 6 mM, with a detection limit of 1.8 μM (S/N: 3) and sensitivity of 64.51 μA mM^?1 cm^?2. The amperometric response of the enzyme biosensor demonstrated the typical behavior of Michaelis‐Menten kinetics. The obtained satisfying sensitivity and measurement range enabled fast and accurate glucose measurement in cherry juice using the fabricated biosensor. The water‐stable Zn‐MOF‐74 demonstrated higher enzyme loading capacity and can be potent supporting material for biosensor construction.     

Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis,kinetics and electrochemical studies

Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k_cat) numbers lying in the range 27.2–1328.4 h^?1. According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron-donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible.     

Secondary metabolites, cytotoxic response by neutral red retention and protective effect against H2O2 induced cytotoxicity of Sedum caespitosum

The EtOAc, n-BuOH and H20 subextracts of the crude MeOH extract of the aerial parts of Sedum caespitosum (cav.) Dc. were screened for cytotoxicity using the neutral red assay in Chinese hamster ovary cells as well as their protective effect against H2O2 induced cytotoxicity in human red blood cells. While the extracts did not show cytotoxicity, they displayed a protective effect compared to a blank and ascorbic acid. Gallic acid (1), kaempferol 3-O-alpha-rhamnopyranoside (2), quercetin 3-O-beta-glucopyranoside (3), quercetin 3-O-alpha-rhamnopyranoside (4) and myricetin 3-O-alpha-rhamnopyranoside (5) were isolated from the EtOAc extract and identified by 1D- and 2D-NMR. The protective effects of the isolated compounds against H2O2 induced cytotoxicity in human red blood cells were evaluated and 5 was the most active.     

Modeling company failure: a longitudinal study of Turkish banks

Determining the factors related to the financial failure of a company is important. In this paper, we extend literature on bank failure prediction by modelling bank failures in Turkey from 1998 to 2000 using three statistical models combined with a principal component analysis on financial ratios. The three statistical models employed are a logistic regression, a logistic regression that takes serial correlation into account via generalized estimating equations and a marginalized transition model (MTM). Time and financial ratios that are related with capital adequacy and profitability, risk, non-interest income and Fx assets to Fx liabilities are found to be significant in classifying failed banks. Each of our methods achieves a correct classification rate of 93.3%. Among the three models, MTM, which is the soundest model in terms of statistical assumptions, shows slightly better model fit properties.     

An Error‐in‐Variables Method for Determining Reactivity Ratios by On‐Line Monitoring of Copolymerization Reactions

Summary: A new error‐in‐variables method was developed to estimate the reactivity ratios in copolymerization systems. It brings the power of automatic, continuous, on‐line monitoring of polymerization (ACOMP) to copolymerization calculations. In ACOMP systems, monomer and polymer concentrations are measured by the monitoring of two independent properties of the system. The reactivity ratios are found by taking into account errors in the monomer concentrations determined from measurements and from calibration of the instruments. All the error sources are taken into account according to the error‐in‐variables method, and their effects are reflected in determining the confidence intervals of the reactivity ratios by the usual error propagation technique.

Distribution of concentrations [a] and [b] for the simulated experiment I. Random errors are 1% of the initial value in both observed variables.     

Using UV-absorbance of intrinsic dithiothreitol (DTT) during RP-HPLC as a measure of experimental redox potential in vitro

Many in-vitro experiments performed to study the response of thiol-containing proteins to changes in environmental redox potentials use dithiothreitol (DTT) to maintain a preset redox environment throughout the experiments. However, the gradual oxidation of DTT during the course of the experiments, and the interaction between DTT and other components in the system, can significantly alter the initial redox potential and complicate data interpretation. Having an internal reporter of the actual redox potential of the assayed sample facilitates direct correlation of biochemical findings with experimental redox status. Reversed-phase high-performance liquid chromatography (RP-HPLC) is a widely used, well-established tool for analysis and purification of biomolecules, including proteins and peptides. Here, we describe a simple, robust, and quantitative RP-HPLC method we developed and tested for determination of the experimental redox potential of an in-vitro sample at the time of the experiment. It exploits the specific UV-absorbance of the oxidized intrinsic DTT in the samples and retains the high resolving power and high sensitivity of RP-HPLC with UV detection.     

Modeling time allocation for prevention in primary care

This paper discusses the problem of allocating time for prevention at the primary care level, focusing on a general practitioner (GP) practice. The basic trade-off is between improved state of the health of the population, which translates into less demand for the GP services, and a decreased capacity for curative services, which translates into increased congestion. The problem of how much time to devote to prevention is modeled as a non-linear optimization problem. As an extension of the problem, selection of preventive activities to perform among recommended alternatives is modeled using a knapsack formulation, and its application is illustrated with a numerical example. The author is supported in part by Türkiye Bilimsel ve Teknik Araştirma Kurumu (TüBİTAK) Career Grant No. 106K260.