Synthesis and pharmacological activity of a silicon—zinc—boron-containing glycerohydrogel

Russian Chemical Bulletin - A new pharmacologically active nanostructured silicon—zinc—boron-containing glycerohydrogel was synthesized by the sol—gel method using silicon, zinc,...     

Electrocatalytic activity of platinum—polyaniline and palladium—polyaniline systems obtained by cycling the electrode potential

Steady-state current densities of electrooxidation of CH₃OH, HCOOH, and CO at the Pt-PAN-GC electrodes (where PAN and GC stand for polyaniline and glassy carbon, respectively) and those of electrooxidation of HCOOH at the Pd-PAN-GC electrodes are measured (per cm₂ of the true metal-catalyst surface area). The found higher activity of Pt and Pd particles incorporated in PAN, as compared with Pt/Pt and Pd/Pt, is attributed to interaction between metal-catalyst particles and the polymeric matrix. The activation effect is the most pronounced for the HCOOH electrooxidation at Pd-PAN-GC. The data concerning hydrogen evolution testify in favor of a decrease in exchange currents of this reaction upon going from Pt to Pt-PAN-GC electrodes     

Synthesis of complex Si–O–N–H derivatives by molecular bombardment of silicon and silicon dioxide

Bombardment of a silicon target in a high vacuum with a molecular beam (mixture of high energy H₂+N₂, obtained by charge exchange) and a thermal beam of O₂ produces on the target a variety of compounds. The target is then bombarded by the same molecular beams which produce, extracted by an electrostatic field at an energy of about 10 keV, molecular ions due to the compounds thus formed. These ions are analysed (electromagnet) to give a primary spectrum of ions according to their mass, which are individually selected and dissociated in a collision cell (same H₂+N₂ mixture). Mass analysis of the dissociation fragments leads to the identification of silicon clusters (Si)_n and of Si–O–N–H derivatives, the fragmentations of which permit a definitive determination of their molecular complexity. Dissociation spectra have thus been obtained for some of the most intense peaks of the primary spectrum, on the one hand, and on the other hand for some peaks of lower intensity but of special interest to us (see below). The composition of the fragments is confirmed by the study of the satellite ions derived from the natural 28, 29 and 30 isotopes of silicon, and by the use of deuterium instead of hydrogen. None of the Si–O–N–H derivatives obtained was apparently known earlier. It is shown that some of these molecules (those ‘of special interest to us’) may be identical with sila-analogues of standard amino acids and of nucleic bases: the fact that their fragmentations are identical with those of the corresponding carbon analogues speaks in favour of a structural identity. However, one cannot yet distinguish between the various possible isomeric arrangements, as none of them has been independently prepared, which excludes a direct comparison with reference samples, and as these isomers might give identical fragments; we hope to be able to resolve this ambiguity later. Anyhow, the substances formed are the most complex molecular silicon derivatives so far produced: e.g. Si₂O₂NH₅, Si₃O₂NH₇, Si₄O₃NH₉, Si₄O₂N₂H₄, Si₄ON₃H₅, Si₅O₃N₂H₁₀, Si₅O₂NH₁₁, corresponding to sila-glycine, sila-alanine, sila-threonine, sila-uracile, sila-cytosine, sila-valine, sila-glutamine, – or isomers. Similar results have been obtained using a silicon dioxide target and high energy molecular beams of hydrogen and of nitrogen, without thermal oxygen, or with a carborundum target. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASmolecular impact / silicon derivatives / amino-acid silicon analogues     

Comparison of the results of thermal denaturation of β-lactoglobulin obtained by DSC and UV-spectroscopy

The thermal denaturation of β-lactoglobulin in the presence of urea and alkylurea solutions were measured. In the presence of a high concentration of urea this protein shows not only heat but also cold denaturation. For studying the effect of temperature two methods were used, differential scanning calorimetry (DSC) and UV-spectroscopy. DSC provides direct model-independent determination of the transition enthalpy in comparison with UV-spectroscopy, which gives only apparent or van't Hoff enthalpy of transition. The UV-melting curves were analyzed on the basis of a two-state approximation. The apparent standard enthalpies of thermal denaturation, ΔH _app. ^o , were compared with calorimetric ones.     

Formation and Characterization of Europium Bisphthalocyanine Organic Nanowires by Electrochemical Deposition

Europium bisphthalocyanine (EuPc2) nanowires were prepared by electrochemicaldeposition method. Scanning electron microscopy (SEM) images show the evolution of themorphologies of nanowires obtained under different deposition time (Td). The optical properties ofeuropium bisphthalocyanine films were studied by UV-Vis absorption spectra. The morphology of EuPc2 nanowires could be controlled by changing deposition conditions, which provides a usefulmethod to make organic nanowires.     

In vivo antioxidant activity of Pinus koraiensis nut oil obtained by optimised supercritical carbon dioxide extraction

In this study, an orthogonal array design OA? (3?) was employed to optimise the conditions of supercritical carbon dioxide (SC-CO?) extraction of Pinus koraiensis nut oil. The effects of pressure, temperature and extraction time on the oil yield were investigated. Next, the fatty acid composition of the oil was examined by gas chromatography-mass spectrometry (GC-MS). The in vivo antioxidant activity of the oil was determined by estimating the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC) and the content of malondialdehyde (MDA) in rats fed with a high-fat diet. The results showed that extraction pressure and time were the main variables that influenced the oil yields. The optimal conditions with which to obtain highest yield of oil were determined to be 5760.83?psi, 50°C and 3.0?h (extraction yield was 458.5?g?kg?1); nine compounds, constituting about 99.98% of the total oil, were identified. The most abundant polyunsaturated fatty acids identified in the oil, linoleic acid and α-linolenic acid, constituted 41.79% and 15.62% of the oil, respectively. Moreover, the results on their antioxidant activities showed that the oil could improve the activities of SOD, GSH-Px and T-AOC, and reduce the content of MDA significantly, in the serum. These results indicate that P. koraiensis nut oil obtained by SC-CO? extraction had excellent antioxidant activities.     

Synthesis and biological activity of isoalantolactone—tryptamine conjugates

Previously unknown adducts of substituted tryptamines with sesquiterpene lactones, viz., isoalantolactone and its epoxy derivative, were synthesized by the Michael reaction. The compounds obtained were tested for various types of biological activity.     

Formation of the pyrroline N-oxide ring by interaction of α-isonitrosoketones — derivatives of tetrahydrobenzofurazan and -furoxan with aldehydes and morpholine and some of the reactions of these compounds

-Isonitroso ketones, derivatives of tetrahydrobenzofurazan and furoxan, react with aldehydes (acetaldehyde and propionaldehyde) and morpholine to form derivatives of tetrahydropyrrolo[2,3-e]-2,1,3-benzoxadiazole 6-oxide. Treatment of the latter with hydrazine hydrate gave derivatives of 4,5-dihydro-1,2,5-oxadiazolo[3,4-f]cinnoline which are readily dehydrogenated with tetrachloro-benzoquinone to derivatives of 1,2,5-oxadiazolo[3,4-f]cinnoline. Reduction of tetrahydropyrrolo[2,3-e]-2,1,3-benzoxadiazole 6-oxides with sodium borohydride gave derivatives of N-hydroxyhexahydro-pyrrolo[2,3-e]-2,1,3-benzoxazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1558–1563. October, 2004.     

Nanostructures of surfaces of silica films obtained by sol—gel method in the presence of organic additives

The dependence of the antireflection properties of film coatings deposited on the silicate glass obtained by sol—gel method in the presence of organic additives on the dimensions of nanostructures of the silica films was studied.     

Admittance studies of hydrogen-induced states at the silicon—silicon dioxide interface

The admittance of Pd-thin SiO₂Si MOSCAP devices was studied as a function of the following variables: temperature, measurement frequency, oxide preparation conditions, applied gate voltage and ambient atmospheres of 100 ppm hydrogen in nitrogen and pure oxygen. Transient current, capacitance and annealing studies were also conducted for many of these variables. It is shown that hydrogen atoms produced by the catalytic action of the Pd on hydrogen molecules can be injected into the oxide—semiconductor interface where, depending on the choice of oxidation conditions for growing the oxide, they modify the density and capture cross-sections of the hydrogen-induced interfacial states. It is also demonstrated that below 125 °C, the injected hydrogen can be reversibly removed by changing the ambient gas from the H₂/N₂ mixture to pure oxygen.     

Formation of Oligosaccharide from Monosaccharide by Pentacoordinate Oxyphosphorane

PhosphorusphalymanybioChemicalreactions['j,suchasthereactionsofADPandAtw].H....ersofarlndeisknownaboathowthePhoSPhruspeesPartintheformationofoligosaccharides.Duhatheinvesigallonofthereaedonofglucose(l)wAnOxyPhosPhorane(2),weisolatedtheproduCtwhosemolecularweighwasverifiedbytheFAB-MS.ItwasAnownthatwhenglycosidesweremixedwAnAnmetalinns,OulytheadductionsofmoleculewAnalkalimetalionsaPPearedinthehighmassregionlcyAforeddinganaPPrOPateaznountofNa+ormp+tothefinalProdCtS,StrOngadduCtinn…     

Selective Formation of 4,4′-Biphenols by Anodic Dehydrogenative Cross- and Homo-Coupling Reaction

A simple and selective electrochemical synthesis by dehydrogenative coupling of unprotected 2,6- or 2,5-substituted phenols to the desired 4,4′-biphenols is reported. Using electricity as the oxidizing reagent avoids pre-functionalization of the starting materials, since a selective activation of the substrates takes place. Without the necessity for metal-catalysts or the use of stoichiometric reagents it is an economic and environmentally friendly transformation. The elaborated electrochemical protocol leads to a broad variety of the desired 4,4′-biphenols in a very simplified manner compared to classical approaches. This is particular the case for the cross-coupled products.     

Regulation of β-amylase activity by alkylresorcinols

The effects of two alkylresorcinols, namely, methylresorcinol (MR) and hexylresorcinol (HR), which are chemical analogues of the natural anabiosis factors of some bacteria, on the catalytic activity of β-amylase has been investigated. When water-soluble potato starch is used as a substrate, MR in a concentration ranging from 0.8 to 12.9 mmol/L raises the activity of β-amylase to 170%. HR at a concentration ranging from 0.05 to 0.35 mmol/L stimulates a weak increase in the activity of β-amylase to 115%. A further increase in the concentration (0.75 mmol/L) leads to inhibition by 50%. The interaction of MR with β-amylase allows one to increase the general yield of the hydrolysis products of potato and malt starch by 1.5 to 1.6 times, to enhance the rate of hydrolysis by 4 to 5 times, and to extend the temperature and pH ranges of catalysis. Non-competitive activation in the presence of MR and non-competitive inhibition in the presence of HR are observed upon determining the kinetic parameters of the starch hydrolysis by β-amylase modified with alkylresorcinols.     

Selective Formation of Methyl α-Methylsulfanyl Dimethylphosphonothioacetate and Thiopropanoate by Phase Transfer Catalysis

The sulfanylation of methyl dimethylphosphonothioacetate was investigated by a phase transfer catalysis procedure which was shown to be superior to the noncatalytic method. The possibility of electrophilic substitution of the α-sulfanylated phosphonothioacetate to give a quaternary α-carbon atom is shown by the reaction with methyl iodide.

     

Formation of radical cations and dose response of α-terthiophene-cellulose triacetate films irradiated by electrons and gamma rays

The radiation-induced UV-vis spectrum of α-terthiophene radical cation in solid is reported. The radical cation initiates an oligomerization in the CTA matrix producing permanently coloured conjugated polarons. The specific net absorbance at 465 nm is linearly related with dose up to 2×10⁶ Gy, for electrons and gamma irradiation. The decrease of the UV typical absorption (355 nm) and of four IR bands of α-terthiophene is linear with dose, as well. Although sensitivity is influenced by dose rate, it turned out that a linear relationship holds between sensitivity and log dose rate, in the range from 2 to 10⁵ Gy/min. These findings suggest a potential application of the system for dosimetric purposes over a wide range of dose and dose rate.     

Formation of Stilbene Azo-Dimer by Direct Irradiation of p-Azidostilbene†

Triplet arylnitrenes may provide direct access to aryl azo-dimers, which have broad commercial applicability. Herein, the photolysis of p-azidostilbene ( 1 ) in argon-saturated methanol yielded stilbene azo-dimer ( 2 ) through the dimerization of triplet p-nitrenostilbene (³ 1N ). The formation of ³ 1N was verified by electron paramagnetic resonance spectroscopy and absorption spectroscopy (λ_max ~ 375 nm) in cryogenic 2-methyltetrahydrofuran matrices. At ambient temperature, laser flash photolysis of 1 in methanol formed ³ 1N (λ_max ~ 370 nm, 2.85 × 10⁷ s⁻¹). On shorter timescales, a transient absorption (λ_max ~ 390 nm) that decayed with a similar rate constant (3.11 × 10⁷ s⁻¹) was assigned to a triplet excited state (T) of 1 . Density functional theory calculations yielded three configurations for T of 1 , with the unpaired electrons on the azido (T_A) or stilbene moiety (T_Tw, twisted and T_Fl, flat). The transient was assigned to T_Tw based on its calculated spectrum. CASPT2 calculations gave a singlet–triplet energy gap of 16.6 kcal mol⁻¹ for 1 N ; thus, intersystem crossing of ¹ 1N to ³ 1N is unlikely at ambient temperature, supporting the formation of ³ 1N from T of 1 . Thus, sustainable synthetic methods for aryl azo-dimers can be developed using the visible-light irradiation of aryl azides to form triplet arylnitrenes.     

Toward the optimization of continuous-flow aldol and α-amination reactions by means of proline-functionalized silicon packed-bed microreactors

The activity and stability under flow conditions of covalently and non-covalently silica supported proline and proline-like organocatalysts is herein described. The slow aldol reaction of cyclohexanone with p-nitro benzaldehyde and the fast α-amination of isovaleraldehyde with dibenzyl azodicarboxylate have been selected as model reactions for this study. Prospects and limitations of the disclosed continuous-flow organocatalytic approach are widely discussed.     

Synthesis and characterization of hydroxyapatite obtained from different organic precursors by sol–gel method

The synthesis of four types of hydroxyapatite synthesized from calcium chloride and four different organic phosphites is presented. The method of synthesis chosen is the sol–gel route, which has a number of advantages compared to other methods, like the intimate contact between reactants and the milder synthesis conditions. The samples were thermally treated, the TG/DTG/DTA curves being obtained at four heating rates, namely: 7, 10, 12 and 15 °C min⁻¹. The samples were characterized before and after the thermal treatment using FT-IR analysis. The FT-IR spectra certified that the formed compounds represent hydroxyapatite. Based on the information from the TG curves and IR spectra interpretation, a reaction mechanism was proposed.