Effect of the Central Atom of a Metal on the Structure and Frequencies of the Normal Vibrations of the Porphin Ligand

The structure and frequencies of the normal vibrations of the molecules of porphin, Mg-, Zh-, and Ni-porphin were calculated by the density-functional method in the B3LYP/6-31G(d) approximation, and correlation of their frequencies was made. The force fields have been obtained in dependent natural coordinates. It is shown that the majority of changes in the vibrational frequencies in transition from porphin to its metal complexes correlate with changes in the structure of the pyrrole and pyrrolenine rings of the porphin ligand.     

Application of surfactants in voltammetric analysis

The possibilities of applying surfactants to the voltammetry of various biologically active compounds are generalized. Attention is focused on micellar solutions and surfactant-modified electrodes in the determination of a number of organic compounds, including antioxidants. It is demonstrated that the use of surfactants makes it possible to improve analytical characteristics and, in some cases, to simultaneously determine different analytes.     

Synthesis and structural peculiarities of homeomorphic phosphorus bridgehead macrobicyclic compounds and novel dioxaphospha[3.1.1.]p,m,p-cyclophanes

The double-capping reaction of p,m,p-trinuclear diphenol 4 with PCl3 affords the three homeomorphic isomers 5-7 of a phosphite macrobicyclic compound in low yields. X-ray structures of out, out-isomer 5 and in, in-isomer 6 show very flat macrobicyclic structures with P-P distances of 4.9 A and 4.5/5.3 A (two conformers), respectively. The main product of the reaction, however, appears to be diphosphite 8, which contains two dioxaphospha[3.1.1.]p,m,p-cyclophane subunits. The structural peculiarities of 8 were studied after subsequent oxidation to the corresponding phosphate 12. At room temperature the free rotation either of the para-phenylene rings and the meta-phenylene ring in the macrocyclic moieties are hindered as could be demonstrated by means of NOESY measurements. The latter occupies an angled position in respect to the macrocyclic plane. This leads to the existence of conformational isomers due to different relative positions of the meta-phenylene ring to the P-OR substituent (cis,trans). We could isolate the cis,cis-isomer of 12 and establish its structure by X-ray diffraction.     

Surface morphology and electrocatalytic properties of nickel nanoparticles formed in track pores

Structures, each of which is composed of a conducting substrate with a protective dielectric layer containing an array of equal-sized pores formed under the action of high-energy ions and chemical etching, are created. The created pores are electrochemically filled with nickel nanoparticles. With atomic-force microscopy (AFM), it is established that Ni nanoparticles are generated exclusively within ion tracks without film formation on the surface of a silicon-dioxide layer. Histograms illustrating the nanoparticle-diameter distribution are constructed, and areas of the nickel nanoparticles are calculated. The electrochemical and electrocatalytic properties of Ni nanoparticles inherent to ethanol-oxidation reactions are investigated. The catalytic activity per unit area of the nanocatalyst is estimated using voltammograms, AFM data, and histograms characterizing the particle size distribution.     

Density Functional Study of the Structure and Infrared Spectrum of Ethyl Chlorophyllide (A)

A DFT/B3LYP calculation using the 6-31G(d) basis set was performed to obtain the structure, normal vibration frequencies, and absolute IR intensities of ethyl chlorophyllide (A). The calculated structural parameters agree well with the experimental X-ray diffraction data. The role of saturated substituents in stabilization of radical ion states of chlorophyll is discussed. The effective force field of ethyl chlorophyllide (A) was obtained in independent and dependent internal coordinates. The IR vibrational spectrum is modeled. The experimental IR spectrum of chlorophyll (A) is interpreted on the basis of the calculation.     

Electrooxidation of oxalic acid at a carbon-paste electrode with deposited palladium nanoparticles

Palladium nanoparticles deposited on the surface of a carbon-paste electrode exhibit electrocatalytic activity in the oxidation of oxalic acid. The surface topography of modified carbon-paste electrodes (CPEs) and the shapes of the metal crystallite particles were studied with atomic-force microscopy. These data were correlated with the voltammetric parameters of the electrooxidation of palladium and oxalic acid. As the dispersity of palladium nanoparticles electrodeposited on the CPE surface increased and their size diminished, the peak current of the catalytic oxidation of oxalic acid decreased, whereas the increment of this current increased as compared to the limiting current of metal oxidation. Evidently, this was due to an increase in the catalytic activity of the metal. The use of CPE modified with palladium nanoparticles instead of CPE containing palladium macrocrystals lowered the detection limit for the analyte by one order of magnitude (down to 2 × 10^?5 M).     

Aminomethylphosphonate Derivatives of Tetramethylcalix[4]resorcinolarene. Synthesis and Some Extraction Properties in Relation to the Lantane Ions

O,O-Dibutyl-N-benzylamino- and O,O-dibutyl-N-phenylaminomethylphosphonate derivatives of tetramethylcalix[4]resorcinolarenes were prepared and characterized. Their effectiveness in the extraction of lanthanum(III) ions from water to chloroform in the presence of picrate ions is demonstrated. This extraction is accompanied by the formation of a complex of the composition La(Pic)₃(L)₂.     

Formation of Co nanoparticles on a pyrolytic graphite surface in ultrahigh vacuum

Isolated cobalt nanoparticles have been obtained by annealing Co films produced by the electron-beam evaporation of a solid target onto a highly oriented pyrolytic graphite substrate in ultrahigh vacuum. Preliminary ion bombardment of the substrate reduces the average size of the particles formed during coalescence, but the shape of large particles is distorted. It is established that the Co nanoparticles retain their shape when exposed to air. Magnetic force images show that the particles of 20–40 nm in height are single-domain.     

Voltammetric Determinations of Thymol on an Electrode Modified by Coimmobilized Carboxylated Multiwalled Carbon Nanotubes and Surfactants

Thymol is oxidized at glassy carbon electrodes (GCEs) modified with coimmobilized carboxylated multiwalled carbon nanotubes (MWCNT-COOH) and surfactants of various nature in a Britton–Robinson buffer solution. The effect of the nature and concentration of surfactants in the composition of the electrode surface modifier on the amperometric response of thymol was evaluated. It was found that the best voltammetric characteristics are achieved in the case of an anionic 0.10 mM sodium dodecyl sulfate (SDS) (a decrease in oxidation potential by 50 mV and an increase in oxidation currents 2.2-fold in comparison with MWCNT-COOH/GCE). The electrooxidation of thymol at MWCNT-COOH–SDS/GCE proceeds irreversibly with the participation of one electron and one proton and is controlled by the adsorption of the analyte. The electrode response is linear in the ranges 0.500–17.0 and 17.0–150 μM of thymol with the limits of detection 0.14 μM and determination 0.48 μM. The developed method is tested on thymol-containing pharmaceutical preparations. The voltammetry data are compared with the results of an independent spectrophotometric determination.