A Comparison of Four Different Electrode Matrices on the Performance of Amperometric Hydrogen Peroxide (Bio)Sensors

A comparison of the analytical performances of four different (bio)sensor designs in H₂O₂ determination is discussed. The (bio)sensor designs developed were based on the use of (i) multiwalled carbon nanotubes (MWCNT), zinc oxide nanoparticles (ZnONP), prussian blue (PB); (ii) MWCNT, ZnONP, PB and ionic liquid (IL); (iii) MWCNT, ZnONP and horseradish peroxidase (HRP) and (iv) MWCNT, ZnONP, HRP and IL modified glassy carbon electrode (GCE). A performance comparison of (bio)sensors showed that the one based on HRP/IL-MWCNT-ZnONP/GCE showed the best analytical characteristics with a linear dynamic range of 9.99×10⁻⁸–7.55×10⁻⁴ M, detection limit of 1.37×10⁻⁸ M and sensitivity of 17.00 μA mM⁻¹.     

Mechanism of antioxidant capacity assays and the CUPRAC (cupric ion reducing antioxidant capacity) assay

We report on the application of a simple and versatile antioxidant capacity assay for dietary polyphenols, vitamin C and vitamin E utilizing the copper(II)-neocuproine (Cu(II)-Nc) reagent as the chromogenic oxidant, which we term the CUPRAC (cupric reducing antioxidant capacity) method. It involves mixing the antioxidant solution (directly or after acid hydrolysis) with solutions of CuCl₂, neocuproine, and ammonium acetate at pH 7, and measuring the absorbance at 450 nm after 30 min. Slowly reacting antioxidants required an incubation at 50 °C for 20 min for color development. The flavonoid glycosides were hydrolyzed to their corresponding aglycones by refluxing in 1.2 M HCl-containing 50% MeOH for fully exhibiting their antioxidant potencies. Certain compounds also needed incubation after acid hydrolysis for color development. The CUPRAC absorbances of mixture constituents were additive, indicating lack of chemical deviations from Beer’s law. The CUPRAC antioxidant capacities of a wide range of polyphenolics are reported in this work and compared to those found by ABTS/persulfate and Folin assays. The trolox-equivalent capacities of the antioxidants were linearly correlated (r = 0.8) to those found by ABTS but not to those of Folin. The highest antioxidant capacities in the CUPRAC method were observed for epicatechin gallate, epigallocatechin gallate, quercetin, fisetin, epigallocatechin, catechin, caffeic acid, epicatechin, gallic acid, rutin, and chlorogenic acid in this order, in accordance with theoretical expectations. The experiences of other CUPRAC users also are summarized. Correspondence: Reşat Apak, Department of Chemistry, Faculty of Engineering, Istanbul University, Avcilar, TR-34320 Istanbul, Turkey     

Critical Behavior of the Blume-Emery-Griffiths Model for a Simple Cubic Lattice on the Cellular Automaton

The spin-1 Ising model with the nearest-neighbour bilinear and biquadratic interactions and single-ion anisotropy is simulated on a cellular automaton which improved from the Creutz cellular automaton (CCA) for a simple cubic lattice. The simulations have been made for several k=K/J and d=D/J in the 0≤d<3 and −2≤k≤0 parameter regions. We confirm the existence of the re-entrant and the successive re-entrant phase transitions near the phase boundary. The phase diagrams characterizing phase transitions are presented for comparison with those obtained from other calculations. The static critical exponents are estimated within the framework of the finite-size scaling theory at d=0, 1 and 2 in the interval −2≤k≤0. The results are compatible with the universal Ising critical behavior.     

Finite-size scaling and power law relations for dipole-quadrupole interaction on Blume-Emery-Griffiths model

The Blume-Emery-Griffiths model with the dipole-quadrupole interaction ($ \ell = \frac{I} {J} $ \ell = \frac{I} {J} ) has been simulated using a cellular automaton algorithm improved from the Creutz cellular automaton (CCA) on the face centered cubic (fcc) lattice. The finite-size scaling relations and the power laws of the order parameter (M) and the susceptibility (χ) are proposed for the dipole-quadrupole interaction (ℓ). The dipole-quadrupole critical exponent δ_χ has been estimated from the data of the order parameter (M) and the susceptibility (χ). The simulations have been done in the interval $ 0 \leqslant \ell = \frac{I} {J}0 \leqslant 0.01 $ 0 \leqslant \ell = \frac{I} {J}0 \leqslant 0.01 for $ d = \frac{D} {J} = 0,k = \frac{K} {J} = 0 $ d = \frac{D} {J} = 0,k = \frac{K} {J} = 0 and $ h = \frac{H} {J} = 0 $ h = \frac{H} {J} = 0 parameter values on a face centered cubic (fcc) lattice with periodic boundary conditions. The results indicate that the effect of the ℓ parameter is similar to the external magnetic field (h). The critical exponent δ_ℓ are in good agreement with the universal value (δ _h = 5) of the external magnetic field.     

Computation of critical exponents for two-dimensional ising model on a cellular automaton

Static critical exponents for the two-dimensional Ising model are computed on a cellular automaton. The analysis of the data within the framework of the finite-size scaling theory reproduces their well-established values.     

Synthesis,characterization, crystal structure,and antimicrobial studies of 2-morpholinoethyl-substituted benzimidazolium salts and their silver(I)-N-heterocyclic carbene complexes

Research on Chemical Intermediates - This article describes synthesis of N-morpholinoethylbenzimidazole (1), 2-morpholinoethyl-substituted benzimidazolium salts (NHC precursors, 2a–c), and...     

Reconstruction and crosstalk of protein-protein interaction networks of Wnt and Hedgehog signaling in Drosophila melanogaster

In the last few years, researchers have an intense interest in the evolutionarily conserved signaling pathways which have crucial roles during embryonic development. The most intriguing factor of this interest is that malfunctioning of these signaling pathways (Hedgehog, Notch, Wnt etc.) leads to several human diseases, especially to cancer. This study deals with the β-catenin dependent branch of Wnt signaling and the Hedgehog signaling pathways which offer potential targeting points for cancer drug development. The identification of all proteins functioning in these signaling networks is crucial for the efforts of preventing tumor formation. Here, through integration of protein-protein interaction data and Gene Ontology annotations, Wnt/β-catenin and Hedgehog signaling networks consisting of proteins that have statistically high probability of being biologically related to these signaling pathways were reconstructed in Drosophila melanogaster. Next, by the structural network analyses, the crucial components functioning in these pathways were identified. The proteins Arm, Frizzled receptors (Fz and Fz2), Arr, Apc, Axn, Ci and Ptc were detected as the key proteins in these networks. Futhermore, the hub protein Mer having tumor suppressor function may be proposed as a putative drug target for cancer and deserves further investigation via experimental methods. Finally, the crosstalk analysis between the reconstructed networks reveals that these two signaling networks crosstalk to each other.     

Transient thermal response of phase change material embedded with graphene nanoplatelets in an energy storage unit

This research was focused on the preparation of mixed metal oxide pigments doped with terbium ions with the general formula of Sn_0.752Co_0.08P_0.16Tb_0.008O₂. These pigments were synthesised by solid-state reactions at high calcination temperatures. The temperature range was chosen from 1350 to 1500 °C. The goal was to develop conditions for the synthesis of this type of pigments and to determine the influence of terbium ions on the colour properties of these compounds. All prepared pigments were applied into the organic matrix and into the ceramic glaze. Thermal behaviours of the reaction mixtures were investigated using differential thermal and thermogravimetric analysis. Synthesised Sn_0.752Co_0.08P_0.16Tb_0.008O₂ pigments were compared with concurrently prepared pigment Sn_0.760Co_0.08P_0.16O₂ depending on the calcination temperature with respect to the colour properties in CIE L*a*b* colour space, furthermore from the point of particle size distribution and phase composition. All compounds provided blue–violet hues that are stable in ceramic glazes.     

Comparative evaluation of various total antioxidant capacity assays applied to phenolic compounds with the CUPRAC assay

It would be desirable to establish and standardize methods that can measure the total antioxidant capacity level directly from vegetable extracts containing phenolics. Antioxidant capacity assays may be broadly classified as electron transfer (ET)- and hydrogen atom transfer (HAT)-based assays. The majority of HAT assays are kinetics-based, and involve a competitive reaction scheme in which antioxidant and substrate compete for peroxyl radicals thermally generated through the decomposition of azo compounds. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes colour when reduced. ET assays include the ABTS/TEAC, CUPRAC, DPPH, Folin-Ciocalteu and FRAP methods, each using different chromogenic redox reagents with different standard potentials. This review intends to offer a critical evaluation of existing antioxidant assays applied to phenolics, and reports the development by our research group of a simple and low-cost antioxidant capacity assay for dietary polyphenols, vitamins C and E, and human serum antioxidants, utilizing the copper(II)-neocuproine reagent as the chromogenic oxidizing agent, which we haved named the CUPRAC (cupric ion reducing antioxidant capacity) method. This method offers distinct advantages over other ET-based assays, namely the selection of working pH at physiological pH (as opposed to the Folin and FRAP methods, which work at alkaline and acidic pHs, respectively), applicability to both hydrophilic and lipophilic antioxidants (unlike Folin and DPPH), completion of the redox reactions for most common flavonoids (unlike FRAP), selective oxidation of antioxidant compounds without affecting sugars and citric acid commonly contained in foodstuffs and the capability to assay -SH bearing antioxidants (unlike FRAP). Other similar ET-based antioxidant assays that we have developed or modified for phenolics are the Fe(III)- and Ce(IV)-reducing capacity methods.     

Synthesis and Crystal Structure of Rubidium Lanthanum Tetraacetate,RbLa(CH3COO)4

The anhydrous rubidium tetraacetato lanthanate, RbLa(CH₃COO)₄, is obtained together with Rb₂La(CH₃COO)₅(H₂O) as colourless single crystals from a 1 : 2 mixture of Rb₂CO₃ and La(CH₃COO) · 1.5 H₂O in acetic acid by slow evaporation. The crystal structure [orthorhombic, Pnnm, Z = 2, a = 1242.0(3), b = 1650.1(4), c = 698.0(4) pm, R = 0.028, R_w = 0.071] contains La³⁺ nine coordinate by oxygen atoms of six acetate ligands. The polyhedra are connected to dimers and further to double chains running parallel to [001]. These [La(CH₃COO)₄]^– double chains are surrounded by four like double chains and connected by Rb⁺ ions that are seven coordinate by oxygen atoms.