生物样品中硒的测定方法及形态分析研究进展

硒的毒性和营养功能不仅与其总量有关,而且与其存在的化学形态有关。因此,硒的测定及形态分析对于了解不同形态的硒化物在生物体和环境中的迁移转化规律具有重要意义。文章综述了生物样品中硒的测定分析方法以及形态分析研究进展。     

Trinuclear Metal Chelates of β-Aminovinylimines

The chemical and electrochemical syntheses of Cu(II), Ni(II), Co(II), Zn(II), and Cd(II) trinuclear metal chelates with a new tetradentate ligand system including bis[(2-hydroxy-, -mercapto-, and -N-tosylamino)anils] of nitro- and phenylmalonaldehyde were performed. Temperature dependences of magnetic and ESR spectral properties of the complexes were studied to show that the antiferromagnetic spin-spin exchange interactions between copper(II) ions are intra- and intermolecular in nature and depend on the composition and structure of the coordination units, steric effects, nature of the substituent in the malonaldehyde moiety of the ligand, as well as on the method of synthesis of the complex compounds.     

Redox conversions in crystalline compounds based on macrocyclic complexes of nickel(II)/(III) and aromatic carboxylates

It is shown that conversion of nickel(II) complexes, in the composition of crystalline compounds of various structures, into nickel(III) leads to the preparation of new redox-active metal-organic skeletons. The structure of the chromophore of the metal ion and the chemical properties of the compounds formed by this process (thermal stability, reactivity) depend to an important extent on the nature of the construction blocks which makes possible the creation of new materials with controlled properties.     

One and two route processes of acetone and acetonitrile bonding from the gas phase with polyoxometallates of tetraamine complexes of nickel(II) and copper(II)

It has been established that the rate of bonding of acetone or acetonitrile molecules to compounds formed from ammine complexes of copper(II) and nickel(II) with polyoxometallates, is described by one of two parallel processes. Drawing on previous data for reactions with other polar molecules, it was shown that the mechanism of interaction did not depend on the chemical nature of the adsorbate, and on this basis it was proposed that the differences in adsorption is associated with differences in the crystal structure of the adsorbents.     

Preparation and optical properties of new fluorescent iminocoumarins: Study of N-acyl-derivatives

Six new iminocoumarin dyes, bearing a cyano group at the 3-position and a diethylamino group at the 7-position, were synthesized. These compounds differ by the nature of the acyl substituent borne by the imino group. They were studied in CH₂Cl₂ and ethanol by UV/vis absorption and fluorescence spectroscopy. This work shows that the optical properties strongly depend on the nature of the substituent borne by the imino group, and indicates which type of substituent is favourable for a given application. It confirms that iminocoumarin derivatives could lead to a new generation of fluorescent probes, prone to easy modification of their chemical structure.     

Regioselective, photochemical bromination of aromatic compounds using N-bromosuccinimide

Regioselective nuclear bromination of aromatic compounds is investigated with N-bromosuccinimide as the brominating agent under UV irradiation to afford the corresponding brominated compounds. The reaction proceeds at ambient temperature (30 ± 2 °C) without any catalyst. In most of the reactions, regioselectively mono-brominated products are obtained in good to high yields. The conversion and selectivity for bromination depend on the nature of the substituent on the aromatic ring.     

The effect of electronic factors on the reactivity of heteroaromatic N-oxides

On the basis of an analysis of the reasons for the multiplicity of σ constants for substituents it has been concluded that they are variables, the absolute value and sign of which depend on the nature of the compounds being considered (in particular other substituents), the partner with which reaction occurs, and the medium (the aggregate state of participants of the interaction). The use of modifications of the Hammett equation is caused by the impossibility in principle of only varying the values and sign of ρ to describe universally linear functions of the dependence of rate (or equilibrium) constants of chemical processes from the algebraic sum of the electronic, steric, and other factors, which differ in their nature.     

Aromatic lead(IV) compounds : VIII. 13C FT-NMR spectroscopy of compounds Arn Pb(CH3)4−n (n = 0–4)

¹³C chemical shifts and ²⁰⁷Pb¹³C coupling constants are reported for some arylmethyllead compounds. The value of J(²⁰⁷Pb¹³C) is shown to depend on the number and the nature of the aryl groups.     

Molecular complexing as the initial stage of some reactions of organometallic compounds

Complexing of molecular oxygen with arylmercury compounds and phenyl derivatives of Group IV and V elements has been studied by electronic spectroscopy. The type of complexing appeared to depend on the nature of the central heteroatom in the organometallic compounds.The chemical model for the reaction of R₂Hg (R = Et, n-Pr, n-Bu, Ph) with CCl₄ indicates that the complex R₂Hg · L (L = molecular oxygen, aromatic compound) is formed in the initial stage of the interaction. By studying the influence of π-donors on this process the correlation between the yield of alkylmercuric chloride and the donor properties of the ligand has been determined.     

Preparation of multicomponent oxides via non-hydrolytic sol-gel routes from novel bimetallic alkoxides

New series of double alkoxides of erbium and its oxides have been prepared by non-hydrolytic sol-gel reactions for the first time. These compounds were characterized with the help of FT-IR, NMR, Mass, DTA-TGA and SEM. The mass spectra show similar types of fragmentation pattern in all compounds. The XRD diffraction pattern shows an enhanced homogeneity at high temperature. TGA/DTA measurements show that thermal decomposition occurs in steps and entirely depends on the chemical compositions and the synthesis routes. The SEM observation reveals a high dense and smooth microstructural uniformity of polycrystalline nature. The physico-chemical properties show that crystallization behaviors can be controlled with the help of fine-tuning the chemical properties of chelating agents in order to increase the solubility of metal alkoxides.     

Dinuclear Diphosphine Complexes of Gold(I) Alkynyls,the Effects of Alkynyl Substituents onto Photophysical Behavior

A series of dinuclear diphosphine complexes of gold(I) alkynyls containing bis(diphenylphosphanyl)ethane/propane and alkynyl ligands with aromatic substituents (biphenyl, pyrene, and azobenzene) was synthesized and characterized using X‐ray crystallography and NMR spectroscopy. Photophysical parameters of the compounds obtained strongly depend on the nature of aromatic substituents in the alkynyl ligands. Azobenzene containing derivatives are non‐luminescent, whereas biphenyl and pyrene containing complexes display moderate emission both in solution and in solid state. The complexes with biphenyl substituents display strong heavy atom effect and show typical phosphorescent emission. In contrast, the complexes containing pyrene chromophore are fluorescent that points to the absence of spin orbit coupling in these systems, which additionally display static excimer emission in solid phase due to ground state π‐stacking of the pyrene moieties.     

Synthesis, Chemistry, and Applications of Heterocyclic Cage Compounds (V)

The synthesis and chemistry of polycyclic of cage compounds have attracted considerable attention in recent years. The vast majority of the work reported in this area has dealt with carbocylic cage compounds. On the other hand, the synthesis and chemistry of heterocyclic cage compounds have received less attention. Recently, we envisioned that studies on the synthesis and chemistry of heterocyclic cage compounds can greatly expand the scopes and utilities of cage compounds.1 As part of a program that involves the synthesis, chemistry, and application of heterocyclic cage compounds, we report here the synthesis of new thia-oxa-cage compounds and the chemical nature of these thia-cages.     

Mg-Al layered double hydroxides: Synthesis,structure, and catalytic potential in condensation of cyclohexanone with acetonitrile

Basic properties of synthetic Mg-Al layered double hydroxides were studied. It was shown that these properties strongly depend on the chemical composition and calcination temperature and are of key importance for determining the activity of catalysts based on these compounds. A relationship was found between the basic properties of these materials and the selectivity of conversion of the starting reagents to N-cyclohexylideneacetonitrile in condensation of cyclohexanone with acetonitrile.     

Comparison of the Topological and Dynamic Characteristics of Molecules for Calculating Retention Indices of Organic Compounds

This paper reports on a comparative analysis of the linear correlation equations relating the gas-chromatographic retention indices (RI) of several groups of isomeric organic compounds to the topological (Wiener and Hosoya indices) and dynamic (intramolecular energies estimated by molecular dynamic methods and the vibrational components of this energy estimated with simple models) parameters of molecules. It is shown that the choice of one of these parameters does not ensure the best approximation to RI, since the results depend on the chemical nature of substances. Correlations between all of the above quantities have been established. The correlations serve as a basis for physicochemical interpretation of the topological parameters of molecules as quantities proportional to the intramolecular vibrational and rotation energies.     

Photophysics and photochemical studies of 1,4-dihydropyridine derivatives

The absorption and fluorescence properties of nifedipine (NPDHP), felodipine (CPDHP) and a series of structurally related 1,4-dihydropyridines were studied in aqueous solution and organic solvents of different properties. The absorption and fluorescence spectra were found to depend on the chemical nature of the substituents at the position 4 of the 1,4-dihydropyridine ring (DHP) and on solvent properties. In aqueous solution, the fluorescence spectra of 4-phenyl substituted compounds are blue-shifted with respect to the alkyl substituted compounds. The more fluorescent compound is CPDHP. Nifedipine is not fluorescent. All compounds, with the exception of CPDHP, present monoexponential fluorescence decay with very short lifetime (0.2-0.4 ns). CPDHP showed a biexponential emission decay with a long-lived component of 1.7 ns; this behavior is explained in terms of different conformers because of the hindered rotation of the phenyl group by the ortho-substitution. Analysis of the solvent effect on the maximum of the absorption spectrum by using the linear solvent-energy relation solvato-chromic equation indicates the redshifts are influenced by the polarizability, hydrogen bonding ability and the hydrogen bond acceptance of the solvent. Whereas, the fluorescence characteristics (spectra, quantum yields and lifetimes) are sensitive to the polarizabilty and hydrogen bond ability of the solvents. Photo-decomposition of nifedipine is dependent on the solvent properties. Faster decomposition rates were obtained in nonprotic solvents. The 4-carboxylic derivative goes to decarboxylation. Under similar conditions, the other DHP compounds did not show appreciable photodecomposition.     

Chemistry of phosphorus ylides: Part 45 synthesis of phosphoranylidene,thietane, azetidine and thiazinane derivatives as potent chemo preventative agents

Reactions of nucleophilic active phosphacumulenes with iso(thio)cyanate compounds were performed. The reaction products depend on the nature of the reagent, substrate and the condition of the reaction used. New heterocyclic 4-membered or 6-membered sulfur and nitrogen compounds such as phosphoranylidene thietane, azetidine and thiazinane were obtained. On the other hand, the stable phosphonium ylides with the iso(thio)cyanate afforded phosphoranylidene thiocarbamoyl derivatives. Possible reaction mechanisms are considered and the structural assignments are based on compatible analytical and spectroscopic data.     

Influence of combustion conditions on hydrophilic properties and microstructure of flame soot

Previous studies suggest that structure and reactivity of soot depend on combustion conditions like the fuel/oxygen ratio and nature of fuels. However, the essence of how combustion conditions affect physical and chemical properties of soot is still an open question. In this study, soot samples were prepared by combusting toluene, n-hexane, and decane under controlled conditions, and their hydrophilic properties, morphology, microstructure, content of volatile organic compounds, and functional groups were characterized. The hydrophilicity of n-hexane and decane flame soot increased with decreasing fuel/oxygen ratio, while it almost did not change for toluene flame soot. Fuel/oxygen ratio had little effect on the morphology of aggregates and the graphite crystallite size. The primary particle size and the content of volatile organic compounds on soot decreased with decreasing fuel/oxygen ratio. Less hydrophobic groups (C-H) and more hydrophilic groups (C═O) were observed on lean n-hexane and decane flame soot than that on the corresponding rich flame soot. Volatile organic compounds had little effect on the hydrophilicity of soot while the hydrophilicity correlated linearly with the ratio of C═O content to C-H content. The hydrophilic functional groups were found to be mainly located at graphene layer edges and on surface graphene layers in soot.     

几种碳卤化物多通道激光化学的研究

本文用CW和TEA CO2激光器研究了F12(CF2Cl2)、F114(CF2ClCF2Cl)和F22(CF2HCl)等碳卤化合物的激光诱导解离反应, 实验发现, 在激光作用下, 这些化合物的解离方式不仅与化合物的性质有关, 还与激光的能量密度密切相关; F22的激光解离为一级反应,并存在“瓶颈效应".     

Dimethylthiophosphinic esters for the gas chromatographic determination of monohydroxy-steroids with the alkali flame detector : VI. Steroid phosphorus compounds

Dimethylthiophosphinic chloride has been found to react readily at 70–90° with monohydroxy-steroids to yield dimethylthiophosphinic esters. These derivatives have good gas chromatographic properties and can be detected at the lower picogram level (10–15 pg) with the alkali flame detector. The reaction kinetics were examined, and depend on steric influences and the chemical nature of the hydroxyl group. The esters are stable to heat and hydrolysis, and since their formation is highly reproducibile and they offer a very low detection limit, they are suitable for gas-liquid chromatographic determination of various compounds of biological interest.