Synthesis of gold nanoparticles on the surface of pyrolytic graphite using penicillin as a stabilizing reagent and the catalytic oxidation of α-naphthylamine

Electrochemical synthesis of gold nanoparticles on the surface of pyrolytic graphite using penicillin as a stabilizing reagent was proposed. The gold nanoparticles were characterized by scanning electron microscopy, cyclic voltammetry, IR spectra, UV spectra, and powder X-ray diffraction spectra. The electro-chemical catalysis of penicillin for α-naphthylamine was demonstrated.     

Radical chain mechanism of the oxidation of α-terpinene by molecular oxygen

The oxidation of -terpinene by molecular oxygen is shown to occur by a radical chain mechanism involving hydroperoxy radicals. The principal molecular reaction products are H₂O₂ and 1-methyl-4-isopropylbenzene. The rate constants for chain propagation and chain breaking measured at 35–70°C are (liter/mol·s) lgk₃ = 7.10– (6700±400)/4.57T and lgk₅ = 9.80– (2700±300)/4.57T respectively.Translated from Teoreticheskaya Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 143–146, May–June, 1994The authors thank the Ukraine National Committee for the Basic Research Fund for financing this work.     

New transformation of α-acetylenic ketones under the action of 1,2-diaminoethane

A reaction of 3-aryl-1-(3,4,5-trimethoxyphenyl)prop-2-yn-1-ones with 1,2-diaminoethane in boiling dioxane leads to 2-aryl-4,5-dihydro-1H-imidazoles and 1-(3,4,5-trimethoxy-phenyl)ethanone.     

Anode oxidation of copper in alkali media in the presence of glycine, α-alanine,and asparagine acid

The effect of glycine, α-alanine, and asparagine acid on the kinetics of anode processes occurring for copper in alkali electrolytes is studied. The experiments are performed in a background solution of 1 × 10⁻² M NaOH (pH 12). The concentrations of glycine and α-alanine are varied in the range of 1 × 10⁻⁶-1 × 10⁻¹ M, and the concentration of asparagine acid is varied in the range of 1 × 10⁻⁵-1 × 10⁻³ M. All amino acids used in this work have been found to stimulate anode oxidation of passivated copper, initiating local activation (LA) of the metal. Depending on the nature of amino acids, this effect occurs in various concentration ranges: for glycine and α-alanine, it takes place at c= 5 × 10⁻³-2 × 10⁻² M, while for asparagine acid, at c = 1 × 10⁻⁵−1 × 10⁻³ M. In addition to this general regularity, several individual peculiarities have been revealed: in the systems containing a monobasic amino acid additive, local activation occurs at E = 0.10–0.20 V, while in the presence of a dibasic amino acid, the local activation is observed at two potentials, E _LA¹ = 0.20–0.30 V and = E _LA² = 0.80–0.90 V, separated by the repassivation region.     

Equilibrium between the hydroperoxyl and 1-hydroxycyclohexylperoxyl radicals—Chain carriers in cyclohexanol oxidation with molecular oxygen

The equilibrium constant K ₂ for the dissociation of the 1-hydroxycyclohexylperoxyl radical to cyclohexanone and the hydroperoxyl radical was determined by the selective inhibition method using nitrobenzene. For cyclohexanol oxidation initiated by cumyl peroxide, (1.6 ± 0.2) × 10^?4 mol/L (373 K, ortho-dichlorobenzene).     

Chain termination in the oxidation of lipid models by α-tocopherol and its synthetic analog

The rate constants (k₁) and stoichiometric coefficients (f) of chain termination in the oxidation of lipid models (methyl esters of acids in the oleic series) by -tocopherol and its synthetic analog at 50°C were measured. The values of k₁ and f do not depend on the structure of the substituent R in the peroxide radical ROO of the lipid models undergoing oxidation, but the values of k₁ are determined by the conformation of the investigated phenols.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 5, pp. 441–444, September–October, 1993.     

New α-glucosidase inhibiting anthracenone from the barks of Harungana madagascariensis Lam

Two new 10-hydroxy-9(10H)-anthracenone, madagascenone A (1) and B (2), were isolated from the barks of Harungana madagascariensis Lam. The structures of the compounds were determined using 1D- and 2D-NMR and mass spectroscopic techniques. Both of the compounds showed an in vitro α-glucosidase inhibition with IC₅₀ = 69.9 ± 4.21 and 122.3 ± 1.13 μM, respectively, more potent than the standard acarbose (IC₅₀ = 840 ± 1.23 μM).     

A simple method for the oxidation of α-amino acid esters to α-oximino esters

Magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) was found to be an effective reagent for the oxidation of various α-amino acid esters to the corresponding α-oximino acid esters. This transformation could be completed under mild conditions within 2.5 h using 1.1 equiv of MMPP in THF. Clean oximino esters were obtained after quenching and extracting the reaction from sodium thiosulfate solution. The O-phosphorylated derivative of 2-oximinoglutarate exhibited slow binding inhibitory potency for the metallopeptidase prostate-specific membrane antigen (PSMA) with an IC₅₀ value of 58 nM.     

Kinetics of peroxidase-catalyzed oxidation of quercetin in the presence of β-cyclodextrin

It is established that the rate of peroxidase-catalyzed oxidation of flavonoid quercetin is increased by 20% in the presence of macrocyclic complexing agent β-cyclodextrin. The comparison of the kinetic parameters of the indicated reaction in the presence and in the absence of β-cyclodextrin shows that its introduction does not significantly influence the specificity of the enzyme with respect to the reducing substrate (characterized as k _cat/K _M ratio), while the increase in the reaction rate does not depend on the duration of the incubation of quercetin with β-cyclodextrin. It is assumed that the increase of the reaction rate is associated with nonspecific interaction between β-cyclodextrin and quercetin oxidation product.     

The role of low levels of water in the electrochemical oxidation of α-tocopherol (vitamin E) and other phenols in acetonitrile

The phenol, α-tocopherol, can be electrochemically oxidised in a -2e(-)/-H(+) process to form a diamagnetic cation that is long-lived in dry organic solvents such as acetonitrile and dichloromethane, but in the presence of water quickly reacts to form a hemiketal. Variable scan rate cyclic voltammetry experiments in acetonitrile with carefully controlled amounts of water between 0.010 M-0.6 M were performed in order to determine the rate of reaction of the diamagnetic cation with water. The water content of the solvent was accurately determined by Karl Fischer coulometric titrations and the voltammetric data were modelled using digital simulation techniques. The oxidation peak potential of α-tocopherol measured during cyclic voltammetry experiments was found to shift to less positive potentials as increasing amounts of water (0.01-0.6 M) were added to the acetonitrile, which was interpreted based on hydrogen-bonding interactions between the phenolic hydrogen atom and water. Several other phenols were examined and they displayed similar voltammetric features to α-tocopherol, suggesting that interactions of phenols with trace amounts of water were a common occurrence in acetonitrile. The H-bonding interactions of α-tocopherol with water were also examined via NMR and UV-vis spectroscopies, with the voltammetric and spectroscopic studies extended to include other coordinating solvents (dimethyl sulfoxide and pyridine).     

The role of cobalt phosphate in enhancing the photocatalytic activity of α-Fe2O3 toward water oxidation

Transient absorption spectroscopy was used to probe the dynamics of photogenerated charge carriers in α-Fe(2)O(3)/CoO(x) nanocomposite photoelectrodes for water splitting. The addition of cobalt-based electrocatalysts was observed to increase the lifetime of photogenerated holes in the photoelectrode by more than 3 orders of magnitude without the application of electrical bias. We therefore propose that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.     

Synthesis of the unusual α-amino acid component of some novel histone deacetylase inhibiting cyclic peptides

A flexible protocol for the synthesis of three lipophilic α-amino acid components of some novel cyclic peptides having important histone deacetylase inhibiting properties has been developed from a common source, which featured a cross-metathesis reaction between two unhindered terminal olefins as the key step.     

Octahedral Complexes in the Polymerization of α-Olefins

Summary : A series of dimethyl titanium benzamidinate complexes has been prepared containing various functional groups at the aromatic ring. These functional groups were selected to study their electronic or steric effects at the cationic metal center in the polymerization of propylene. Quantitative structure activity relationship (QSAR) studies showed that a linear relationship is observed only for the Taft Parameter (Es). Mono- and bis-benzamidinate complexes were found to produce similar polymers indicating that alike active species are obtained regardless of the starting complex. Deuterium labeled 2-D-propene showed that a new epimerization mechanism for this type of complexes is operative.     

Transition metal-free oxidation of ynamides for synthesis of α-keto-imides

Transition metal-free double oxidation of triple bonds in ynamides for synthesis of α-keto-imides is described. The successful key was combination of NIS and DMSO under atmospheric air in CPME solvent, and the reaction quickly proceeds at 0 °C within 1 h. Although the yields and substrate generality are moderate, yet the prototype protocol avoids the use of expensive, moisture-sensitive, toxic, and explosive additives, which make it potentially and significantly greener than current alternatives.     

Direct C-nitration of cyclic α,β-unsaturated oximes under the action of sodium nitrite and acetic acid in methanol

Using a number of cyclic ,-unsaturated oximes of the terpene series and some simplest model compounds as examples, unsaturated oximes bearing a hydrogen atom at the -carbon atom were demonstrated to be converted into -hydroxyiminonitroalkenes under the action of sodium nitrite and acetic acid in methanol. In the case of the introduction of an alkyl substituent at the terminal carbon atom of the diene C=C—C=NOH fragment, the reaction performed under the same conditions gave rise exclusively to conjugated ketone (a deoximation product).     

Experimental validation of the α-effect in the gas phase

The α-effect-enhanced nucleophilicity of an anion with a lone pair of electrons adjacent to the attacking atom-has been well documented in solution; however, there is continuing disagreement about whether this effect is a purely solvent-induced phenomenon or an intrinsic property of the α-nucleophiles. To resolve these discrepancies, we explore the α-effect in the bimolecular nucleophilic substitution reaction in the gas phase. Our results show enhanced nucleophilicity for HOO(-) relative to "normal" alkoxides in three separate reaction series (methyl fluoride, anisole, and 4-fluoroanisole), validating an intrinsic origin of the α-effect. Caution must be employed when making comparisons of the α-effect between the condensed and gas phases due to significant shifts in anion basicity between these media. Variations in electron affinities and homolytic bond strengths between the normal and α-anions indicate that HOO(-) has distinctive thermochemical properties.     

Origins of stereoselectivity in the α-alkylation of chiral hydrazones

Density functional theory calculations and experiment reveal the origin of stereoselectivity in the deprotonation-alkylation of chiral N-amino cyclic carbamate (ACC) hydrazones. When the ACC is a rigid, camphor-derived carbamate, the two conformations of the azaenolate intermediate differ in energy due to conformational effects within the oxazolidinone ring and steric interactions between the ACC and the azaenolate. An electrophile adds selectively to the less-hindered π-face of the azaenolate. Although it was earlier reported that use of ACC auxiliaries led to α-alkylated ketones with er values of 82:18 to 98:2, B3LYP calculations predict higher stereoselectivity. Direct measurement of the dr of an alkylated hydrazone prior to removal of the auxiliary confirms this prediction; the removal of the auxiliary under the reported conditions can compromise the overall stereoselectivity of the process.     

Multistep derivatization method for the determination of multifunctional oxidation products from the reaction of α-pinene with ozone

A novel three-step analytical method was developed which enables the simultaneous detection and identification of multifunctional oxygenated products resulting from the reaction of α-pinene with ozone. The method consists of the following steps: conversion of carbonyl groups to methyloximes using methyloxyamine, conversion of carboxylic acids to methyl esters using trimethylsilyldiazomethane (TMSD), and conversion of alcohols to trimethylsilyl ethers using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA). The derivatization procedure at each stage was optimized yielding the appropriate amount of derivatization reagent, reaction temperature and time. The newly developed analytical procedure manages without processes of extraction and evaporation to dryness at any stage. Total time for sample analysis is short ca. 3h. The characteristic ions of derivatives and common pattern for ion fragmentation in capillary gas chromatography electron impact mass spectrometry (GC-EI-MS) analysis were elucidated and discussed.     

Voltammetric determination of α-tocopherol in the presence of surfactants

As established, α-tocopherol is electrochemically active on glassy carbon electrode in the available range of anodic potentials in acetonitrile and its aqueous mixtures. However, an increase in the water percentage up to 50% and beyond leads to a substantial decrease and then the total disappearance of the analytical signal. A scheme of electrode reaction responsible for the signal formation is proposed. The effect of surfactants on the oxidation of α-tocopherol in aqueous acetonitrile is estimated. As found, surfactants (N-dodecylpyridinium bromide, Triton X-100 and N-cetylpyridinium bromide) enhance the current of α-tocopherol oxidation. The surfactants reduce the detection limit and extend the analytical range. Analytical methods for the voltammetric quantification of α-tocopherol in drugs in the presence of surfactants are elaborated and may be recommended for the control of pharmaceuticals.