On the equitability of multiply-connected monolayered cyclofusene

Multiply-connected monolayered cyclofusene (MMC) is a fused hexacyclic system with an exterior region and at least two interior empty regions called holes, as in figure 1. Each hexacyle has either: (a) two edges belonging to an exterior boundary and at least one hole, or (b) two edges belonging to boundaries of at least two holes. Let G be the graph of a given MMC. We show that G is equitable if and only if the set of vertices belonging to three hexacycles is equitable.     

ZnS and ZnSe Nanoparticles via Solid-State and Solution Thermolysis of Zinc Silylchalcogenolate Complexes

The thermolysis of the zinc trimethylsilylchalcogenolate complexes (N,N′-tmeda)Zn(ESiMe₃)₂ (E = S, 1; E = Se, 2) and (3,5-Me₂-C₅H₃N)₂Zn(ESiMe₃)₂ (E = S, 3; E = Se, 4) has been investigated. Solid-state thermal decomposition of complexes 1–4 above 250°C results in the formation of hexagonal ZnS and cubic ZnSe, respectively, via the liberation of TMEDA (1–2) or 3,5-lutidine (3–4) and E(SiMe₃)₂. Solid-state or solution thermolysis of these complexes up to 200°C produces nanocrystalline ZnS and ZnSe materials whose surface is protected by either coordinated TMEDA or 3,5-lutidine ligands. The progress of the step-wise solid-state decomposition of these complexes was monitored by thermogravimetric and single differential thermal analysis and volatile decomposition products in both solution and solid-state experiments were identified by GC/MS.Dedicated to Professor Brian F. G. Johnson on the occasion of his retirement.     

Assignment of the EPR spectrum of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) superoxide spin adduct

[structure: see text] Spin trapping consists of using a nitrone or a nitroso compound to "trap" an unstable free radical as a long-lived nitroxide that can be characterized by electron paramagnetic resonance (EPR) spectroscopy. The formation of DMPO-OOH, the spin adduct resulting from trapping superoxide (O(2)(*)(-)) with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), has been exploited to detect the generation of superoxide in a wide variety of biological and chemical systems. The 12-line EPR spectrum of DMPO-OOH has been either reported or mentioned in more than a thousand papers. It has been interpreted as resulting from the following couplings: A(N) approximately 1.42 mT, A(H)beta approximately 1.134 mT, and A(H)gamma(1H) approximately 0.125 mT. However, the DMPO-OOH EPR spectrum has an asymmetry that cannot be reproduced when the spectrum is calculated considering a single species. Recently, it was proposed that the 0.125 mT splitting was misassigned and actually results from the superimposition of two individual EPR spectra associated with different conformers of DMPO-OOH. We have prepared 5,5-dimethyl-[3,3-(2)H(2)]-1-pyrroline N-oxide (DMPO-d(2)), and we showed that the EPR spectrum of the corresponding superoxide spin adduct is composed of only six lines, in agreement with the assignment of the 0.125 mT splitting to a gamma-splitting from a hydrogen atom bonded to carbon 3 of DMPO. This result was supported by DFT calculations including water solvation, and the asymmetry of the DMPO-OOH EPR spectrum was nicely reproduced assuming a chemical exchange between two conformers.     

Metallic Particles from Complexing Microcapsules Dispersed in a Silica Gel

A new process to control the distribution of metal nanoparticles is proposed. It involves the use of complexing microcapsules obtained by interfacial polycondensation. The latter are hollow spheres constituted of a polymer membrane, containing an insoluble active ingredient, such as a polyacrylic acid, which can complex Co²⁺ ions. These capsules are dispersed in a silica sol followed by thermal treatments and reduction under H₂ which results in metallic Co nanoparticles confined in the capsules domains. The particles do not diffuse in the matrix.     

Reusable ethanol sensor based on a NAD-dependent dehydrogenase without coenzyme addition

An amperometric sensor for the detection of ethanol has been designed. The sensing layer consists of alcohol dehydrogenase (ADH), NADH oxidase and NAD⁺-dextran, entrapped together in a matrix of poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ). Measurements have been carried out at a low oxidizing potential (equivalent to 250 mV vs. SCE) to detect hexacyanoferrate(II), thus avoiding interferences due to presence of oxidizable compounds in real samples. The influence of the amount of polymer, enzymes and coenzyme in the sensing layer on the sensor sensitivity, linear range and operational stability has been studied. The sensitivity was close to 2 mA 1 mol⁻¹, with a linear range 3 × 10⁻⁷ −2 × 10⁻⁴M and a response time <2 min. Good operational stability was observed, allowing more than 40 reproducible assays without NAD⁺ addition. Alcoholic beverages were analysed with the use of sensor and the results showed good correlation with those obtained using a standard spectrophotometric procedure.     

Complex emulsion inversion pattern associated with the partitioning of nonionic surfactant mixtures in the presence of alcohol cosurfactant

Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three-phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composition effects.     

Flow-injection amperometric determination of pesticides on the basis of their inhibition of immobilized acetylcholinesterases of different origin

Determination of the organophosphorus pesticides paraoxon, chlorpyrifos oxon, and malaoxon has been performed by a method based on inhibition of acetylcholinesterase (AChE) and amperometric detection in a flow-injection system with enzymes obtained from the electric eel (eeAChE) and Drosophila melanogaster (dmAChE) and immobilized on the surface of platinum electrode within a layer of poly(vinyl alcohol) bearing styrylpyridinium groups. dmAChE is more sensitive than eeAChE to inhibition by chlorpyrifos oxon and paraoxon. The sensitivity difference was largest for chlorpyrifos oxon (detection limit approx. 17 times lower), and practically none for malaoxon. Determination of the analytes in spiked river water samples by use of the dmAChE biosensor resulted in recoveries from 50 to 90 % for chlorpyrifos oxon at levels of 20 to 40 nmol L(-1), 50 to 100 % for paraoxon at 0.6 to 0.8 micro mol L(-1), and 140 to 190 % for malaoxon at 0.6 to 1.2 micro mol L(-1).