Chemistry of Azobenzazole Systems. 3. Reactions of 2-Hydrazinobenzoxazole with Carbonyl Compounds

The reaction of 2-hydrazinobenzoxazole with various carbonyl compounds was studied. Only the corresponding azides were obtained with acylating agents such as acid anhydrides and acid chlorides and products with a fused triazole ring were not obtained. Only the corresponding hydrazones were obtained from furfural and 2-carboxy-3,4-dimethoxybenzaldehyde.     

INAA of enamel and dentine samples of a group of children and adults: A comparative study

Instrumental neutron activation analysis (INAA) was applied to determine Ca, Cl, Mg, Mn, Na, Sr and Zn in dentine and enamel tissues from human permanent and deciduous teeth. Comparisons were made between the results obtained in these different dental tissues as well as those obtained in permanent and deciduous teeth. The findings obtained were also compared with the published data. The accuracy and the precision of the results were evaluated by analyzing certified reference material.     

Development and characterisation of a molecularly imprinted polymer prepared by precipitation polymerisation for the determination of phenylurea herbicides

New materials based on molecularly imprinted polymers (MIPs) have been developed for use as sorbents in solid phase extraction to preconcentrate some urea herbicides. In the preconcentration step, different molecularly imprinted polymers were tested using methacrylic acid (MAA) and 2-(trifluoromethyl)acrylic acid (TFMAA) as functional monomers, and linuron and isoproturon as templates. The best results were obtained when the polymer was synthesised using MAA with isoproturon as template. Another parameter evaluated was the way in which the polymer was obtained. We observed that the imprinted polymers obtained by precipitation displayed a greater capacity to retain the phenylureas. Studies conducted using scanning electron microscopy (SEM) revealed that the bulk polymerisation method is far from ideal owing to the random shape and size distribution of the particles obtained, whereas when polymerisation was carried out in precipitation microspheres were obtained. In order to confirm the interaction between the functional monomer and the template, 1H NMR (CD2Cl2) analyses were conducted. The results obtained suggest that the hydrogen and/or nitrogen of the amino group of the template would be involved in the formation of hydrogen bonds with the functional monomer. The imprinted polymer obtained by precipitation polymerisation with MAA as functional monomer and isoproturon as template can be applied to preconcentrate phenylureas when the sample is dissolved in toluene. The proposed methodology was employed to evaluate polymer selectivity towards humic acids and towards other herbicides.     

三苯甲基取代烯烃的环氧化研究

合成了6种三苯甲基取代烯烃. 以二甲基二氧杂环丙烷作为主要氧化剂, 在催化剂(R,R)-Salen Mn(III)的催化下, 进行不对称环氧化, 其不对称环氧化产物ee值较高(81%). 初步研究表明, 二甲基二氧杂环丙烷(DMD)和(R,R)-Salen Mn(III)的环氧化体系对于含亚甲基的三苯甲基取代的烯烃的氧化产率高但对映选择性差, 对于不含亚甲基的三苯甲基取代的烯烃的氧化产率低但对映选择性好.     

A study of microporous aluminophosphates obtained in the presence of symmetrical di-n-alkylamines

Microporous aluminophosphates and silicoaluminophosphates were obtained by hydrothermal synthesis with a number of symmetrical di-n-alkylamines as templates. The influence of the reagents and chemical composition of the starting reaction gel on the phase composition of the products obtained was studied. Pure ATO-type crystals were formed when the organic component was abundant in the reaction mixture and aluminum isopropoxide served as an aluminum source. Various physicochemical investigations revealed that the properties of the products obtained depend on the amine nature.     

丁烯自由基和O2反应机理的理论研究

应用量子化学密度泛函理论(DFT)对丁烯自由基C₄H₇和O₂的反应机理进行了研究. 在B3LYP/6-31G(d,p)水平上优化了反应通道上的反应物、中间体、过渡态和产物的几何构型, 并计算出它们的振动频率和零点能(ZPVE), 并对能量进行了零点能校正. 计算结果表明, C₄H₇和O₂形成三种氧环中间体, 再分别分解, 这是主要的反应形式. 生成物主要为羰基化合物, 其次还有一定比例的CO.     

A method for bulk hydrogen analysis based on transmission and back scattering of fast neutrons

A method was proposed for bulk hydrogen analysis. It is based on simultaneous detection of transmitted fast neutrons and back scattered thermal neutrons from the investigated samples by ³He detectors. The fast neutron beams were obtained from ²⁵²Cf and Pu–Be neutron sources. The experimental set-up as well as samples preparation were described. Incident thermal neutrons beams obtained from either ²⁵²Cf or Pu–Be sources, were used to investigate the samples by neutron backscattering. The results obtained from transmission and backscattering of fast neutrons were compared and discussed. The advantage and capabilities of the proposed method were presented. The results obtained using fast neutron beams are more sensitive than those obtained using thermal neutron beams. Validation procedures were proposed to credit the results.     

Fluorimetric determinations of nucleic acids using iron, osmium and samarium complexes of 4,7-diphenyl-1,10-phenanthroline

New sensitive, reliable and reproducible fluorimetric methods for determining microgram amounts of nucleic acids based on their reactions with Fe(II), Os(III) or Sm(III) complexes of 4,7-diphenyl-1,10-phenanthroline are proposed. Two complementary single stranded synthetic DNA sequences based on calf thymus as well as their hybridized double stranded were used. Nucleic acids were found to react instantaneously at room temperature in Tris-Cl buffer pH 7, with the investigated complexes resulting in decreasing their fluorescence emission. Two fluorescence peaks around 388 and 567 nm were obtained for the three complexes using excitation lambda(max) of 280 nm and were used for this investigation. Linear calibration graphs in the range 1-6 microg/ml were obtained. Detection limits of 0.35-0.98 microg/ml were obtained. Using the calibration graphs for the synthetic dsDNA, relative standard deviations of 2.0-5.0% were obtained for analyzing DNA in the extraction products from calf thymus and human blood. Corresponding Recovery% of 80-114 were obtained. Student's t-values at 95% confidence level showed insignificant difference between the real and measured values. Results obtained by these methods were compared with the ethidium bromide method using the F-test and satisfactory results were obtained. The association constants and number of binding sites of synthetic ssDNA and dsDNA with the three complexes were estimated using Rosenthanl graphic method. The interaction mechanism was discussed and an intercalation mechanism was suggested for the binding reaction between nucleic acids and the three complexes.     

Investigation of novel sol-gel hydrophobic surfaces for desorption electrospray ionization-mass spectrometry analysis

Sol-gel-based materials were synthesized, characterized and finally tested as solid supports for desorption electrospray ionization-mass spectrometry (DESI-MS) analysis of a mixture of compounds of different polarity. Films with thickness in the 2-4 μm range were obtained by a dip-coating process using tetraethoxysilane (TEOS) and octyltriethoxysilane (OTES) as sol-gel precursors. Three types of surface with different hydrophobic character were obtained by varying the TEOS/OTES ratio in the sol-gel mixture. Each coating was characterized by atomic force microscopy investigations, gaining insight into homogeneity, smoothness and thickness of the obtained films. To study hydrophobicity of each surface, surface free energy measurements were performed. Different DESI-MS responses were observed when different solvent mixture deposition procedures and solvent spray compositions were investigated. Results were finally compared to those obtained by using commercial polytetrafluoroethylene-coated slides. It was found that surface free energy plays an important role in the desorption/ionization process as a function of the polarity of analytes.     

DIAR黄成色剂的合成

DIAR黄成色剂的合成;DIAR成色剂;异丙氨基苯硫酚;固体光气     

A study of molecular weight of methyl methacrylate–styrene copolymer

An alternating copolymer of methyl methacrylate and styrene was obtained by the reaction of these two monomers in the aqueous phase and in presence of zinc chloride acting as complexing agent. It was found that the optimum conditions were obtained when the monomer concentrations are equal. The molecular weight and the molecular weight distribution were obtained by gel permeation chromatography (GPC). The polymers obtained have a very narrow molecular weight distribution. A model which takes into account the various parameters is proposed.     

The reaction of vinyl ethers with acridine

The reaction of vinyl ethers with acridine gives new acridine derivatives in the presence of an organic ammonium salt and alcohol. An organic ammonium salt such as acridinium chloride affect this reaction. All of the addition products were obtained as dihydroacridinyl derivatives. Moreover, in the reaction of ketene silyl acetal with acridine, the addition products were also obtained as the dihydroacridine derivatives.     

Enantioselective addition of organolithium reagents to quinoline catalyzed by 1,2-diamines

Some enantiomerically enriched 2-substituted-1,2-dihydroquinolines were obtained by the enantioselective addition of organolithium reagents to quinoline. 1,2-Diamines were used as external chiral ligands and enantiomeric excesses up to 64% were obtained.     

Living Radical Polymerization in Homogeneous System by Using Iniferter: Design of Block Copolymers

Benzyl N-ethyldithiocarbamate(BEDC) and xylylene bis(N-ethyl-dithiocarbamate)(XEDC) were prepared, and used as mono- and bi-functional photoiniferters, respectively, of the polymerization of styrene and methyl methacrylate. These photopolymerizations were performed via a living radical polymerization mechanism in homogeneous system. The polymers obtained by BEDC and XEDC still contained one and two reactive N-ethyldithiocarbamate end groups, respectively, bonded at their chain ends. When these polymers were reacted with nucleophiles and copper(n) ion, the chain extension reactions were observed to occur depending on their functionality. By using the polymers obtained by BEDC and XEDC as mono- and bi-functional polymeric photoiniferters, the AB and ABA block copolymers were also obtained, respectively. Similar results were obtained by using benzyl N,N-diethyldithiocarbamate(BDC) and xylylene bis(N,N-diethyldithiocarbamate)(XEDC) as mono- and bifunctional photoiniferters, respectively. These results were also compared and discussed.     

Metal hydroxides as catalysts for the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide

This paper reports the results obtained in the Baeyer-Villiger oxidation of cyclohexanone with a hydrogen peroxide/benzonitrile mixture as oxidant in the presence of synthetic metal hydroxides or their calcined products as catalysts. The metal hydroxides were obtained by coprecipitation. The best ε-caprolactone conversion results were provided by magnesium hydroxide.     

Preparation and chiral recognition ability of crosslinked beads of polysaccharide derivatives

The spherical beads consisting of cellulose 3,5-dimethylphenylcarbamate with partial hydroxyl groups were prepared to be used as chiral packing materials (CPMs) for HPLC. The beads were obtained without using macroporous silica gel, which is usually used as the support of the CPMs based on the polysaccharide derivatives. After the crosslinking in the bead with diisocyanates, such as 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-dibenzyl diisocyanate (DBDI), tolylene-2,4-diisocyanate (TDI), and m-xylylene diisocyanate (XDI), the obtained beads were packed into an HPLC column. As the content of the hydroxyl groups of the cellulose derivatives decreased, the obtained CPM exhibited a higher chiral recognition ability. The beads possessed a higher loading capacity than the CPM prepared by coating the cellulose derivative on silica gel. The crosslinked beads could be used with the eluent containing chloroform. The amylose derivative beads were also prepared as a CPM for chiral HPLC.     

Selectivity in nickel-catalyzed rearrangements of cyclopropylen-ynes

The Ni/NHC-catalyzed rearrangement of cyclopropylen-ynes is described. Two different heterocycles, cyclopentane- or cycloheptene-based, were obtained. However, by employing ItBu as the NHC ligand, cyclopentane products were obtained selectively under mild conditions.     

Effect of accelerated thermal ageing on the thermal behaviour of the recently made parchments

To reveal the fire injuring of parchment, the changes in the thermal behaviour of some goat parchments, obtained from skins originating from different animals, as a result of thermal aging were determined by thermal analysis methods (DSC; simultaneous TG/DTG, DSC; micro hot table (MHT)). Thermal aging of parchments was revealed to bring about the decrease in shrinkage temperature, absolute value of enthalpy of denaturation in water and some changes in non-isothermal parameters characteristic for dehydration process in static air atmosphere. The results obtained by DSC analysis performed in N₂ and O₂ flows as well as those obtained by simultaneous TG/DTG, DSC analyses have shown that both softening (melting) process parameters and parameters of thermo-oxidative processes have not been changed by thermal ageing. The results obtained by thermal analysis methods were correlated with those obtained by microscopic investigation of parchment samples immersed in water and scanning electron microscopy (SEM). The application of these microscopic techniques has revealed the morphology changes in the investigated parchments as a result of thermal degradation.     

Flourination of halogeno alcohols with 1,1,2,3,3,3-hexafluoropropyl diethylamine

Fluorination of halogeno alcohols with 1,1,2,3,3,3-hexafluoropropyl diethylamine (PPDA) was investigated. 2-Bromo-l-fluorobutane was obtained from the reaction of PPDA and 2-bromo-l-butanol (yield 50 %). Similar results were obtained from other aliphatic and aromatic halogeno alcohols. However, the corresponding 2,3,3,3-tetra-fluoropropionate esters were obtained from the reactions of PPDA and α-halogeno cycloalkanols, such as 2-chlorocyclohexanol.     

Synthesis of imidazo-1,4-oxazinone derivatives and investigation of reaction mechanism

In this study, nine different C-2 aroyl imidazole derivatives were synthesized in a one pot reaction with two steps, and the reduction reactions of these derivatives with NaBH₄ were carried out under mild conditions. Substitution reaction of obtained imidazo methanol derivatives with chloroacetylchloride reagent and ring reaction of substitution products were investigated. It was determined that 1,4-imidazoxazinone derivative was obtained as a result of the cyclization reaction. The intermediate products obtained during the cyclization reaction were isolated, and the path of the reaction under different conditions was discussed.