Activation of Si-C bonds and synthesis of silicon-functional polycarbosilanes

The functionalization of polycarbosilanes was studied using poly(vinyltrimethylsilane) as an example. The possibility of synthesizing of silicon-functional polycarbosilanes by the catalytic activation of Si-C-bonds involving catalytic systems based on compounds of metals of III, VI, and VIII groups was shown Properties of the obtained polymers are discussed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1861–1863, July, 1996.     

固相微萃取气相色谱法(SPME-GC)测定水体中邻苯二甲酸酯

选用85μm PA纤维,考证了萃取温度、萃取时间、搅拌、离子强度及解析时间等影响因素,最后确立了65℃萃取温度、60min萃取时间、稳定的磁力搅拌、5min解析时间、用带电子捕获检测器的毛细管气相色谱（CGC—ECD）分离测定、外标标准曲线法定量分析水体中邻苯二甲酸酯（PAEs）的方法。该方法具有较好的精密度（RSD≤16％）和较低的检出限（DLDBP=0．003μg/L,DLDEDEHP=0．05μg/L）,水样加标回收率在70％～130％之间。用该法测定了长江水样、太湖水样、自来水及蒸馏水的PAEs含量,DBP在0．1～0．4μg/L,DEHP在0．2～1．2μg/L,DMP、DEP、DOP均未检测到。     

Application of inverse gas chromatography to the study of the surface properties of modified layered minerals

Inverse gas chromatography at infinite dilution has been used to study the effects of modifications of cationic (montmorillonite) and anionic (hydrotalcite) clays. By using alkanes and alkenes as probe molecules both the dispersive component of the surface energy and the surface acidic sites were characterized. The introduction of polymers into the structure of these minerals significantly changed their chemical character. Carbonization of samples whose interlayer spaces were saturated with polymers produced new carbon-modified materials. These composite materials became microporous while retaining their initial acid/base surface properties.     

Application of comprehensive two-dimensional gas chromatography to sterols analysis

The applicability of comprehensive two-dimensional gas chromatography (GCxGC) for sterol analysis was investigated by separation and identification of endogenous sterols in standards, and spiked in human urine. The modulation temperature was optimized to achieve the best separation and signal enhancement. The separation pattern of trimethylsilyl (TMS) derivatives of sterols was compared on two complementary column sets. Whilst the BPX5/BPX50 column set offers better overall separation, BPX50/BPX5 provides better peak shape and sensitivity. Comparison of the identification power of GCxGC-TOFMS against both the NIST05 MS library and a laboratory created (in-house) TOFMS library was carried out on a free sterols extract of urine, derivatised and spiked at the World Anti-Doping Agency (WADA) limit of 2 ng mL(-1). The average match quality for 19 analysed sterols on the BPX50/BPX5 column set was 950/1000 when searched against the in-house library; only four were identified against the NIST05 library, at a match threshold of 800. The match quality of GCxGC-TOFMS spectra was superior to that for analysis using 1D GC-TOFMS for sterols spiked in urine at 10 ng mL(-1). An r(2)>0.997 was obtained for the concentration range between 0.25 ng mL(-1) and 10 ng mL(-1) for three selected sterols. The lowest limit of detection (LOD) was obtained for estrone (0.1 ng mL(-1)) and the highest LOD was for 5alpha-androstan-3alpha,11beta-diol-17-one, epitestosterone and cholesteryl butyrate (1 ng mL(-1)), using a match threshold of at least 800 and signal-to-noise ratio of at least 10. TOFMS coupled to GCxGC enabled satisfactory identification of sterols in urine at their LOD. A minimum acceptable match (MAM) criterion for urinary sterols using 2D retention times and TOF mass spectra is introduced. This study shows that GCxGC-TOFMS yields high specificity for steroids derived from urine, with detection limits appropriate for use in doping control.     

Mechanistic aspects of samarium-mediated sigma-bond activations of arene C-H and arylsilane Si-C bonds.

To investigate the potential role of Sm-Ph species as intermediates in the samarium-catalyzed redistribution of PhSiH3 to Ph2SiH2 and SiH4, the samarium phenyl complex [Cp*2SmPh]2 (1) was prepared by oxidation of Cp2*Sm (2) with HgPh2. Compound 1 thermally decomposes to yield benzene and the phenylene-bridged disamarium complex Cp*2Sm(mu-1,4-C6H4)SmCp*2 (3). This decomposition reaction appears to proceed through dissociation of 1 into monomeric Cp*2SmPh species which then react via unimolecular and bimolecular pathways, involving rate-limiting Cp* metalation and direct C-H activation, respectively. The observed rate law for this process is of the form: rate = k1[1] + k2[1]2. Complex 1 efficiently transfers its phenyl group to PhSiH3, with formation of Ph2SiH2 and [Cp*2Sm(mu-H)]2 (4). Quantitative Si-C bond cleavage of C6F5SiH3 is effected by the samarium hydride complex 4, yielding silane and [Cp*2Sm(mu-C6F5)]2 (5). In contrast, Si-H activation takes place upon reaction of 4 with o-MeOC6H4SiH3, affording the samarium silyl species [structure: see text] Cp*2SmSiH2(o-MeOC6H4) (7). Complex 7 rapidly decomposes to [Cp*2Sm(mu-o-MeOC6H4)]2 (6) and other samarium-containing products. Compounds 5 and 6 were prepared independently by oxidation of 2 with Hg(C6F5)2 and Hg(o-MeOC6H4)2, respectively. The mechanism of samarium-mediated redistribution at silicon, and chemoselectivity in sigma-bond metathesis reactions, are discussed.     

Application of fused-silica capillary gas chromatography to the analysis of underivatized drugs

The feasibility of using fused-silica capillary chromatography for the routine analysis of several common drugs is illustrated. Considerations for optimizing on-column and splitless injection are discussed as part of a study of system discrimi nation and reproducibility. The peak shape of polar solutes is improved through the use of a binary solvent and non-extractable stationary phase columns. Cold on-column injection with cross-linked polysiloxane deactivated columns produced linear quantitation from 1 to 100 ng with precisions of 0.1–2% for selected anticonvulsant drugs.     

Application of capillary gas chromatography to studies on solvation thermodynamics

The potentiality of capillary gas chromatography (GC) as a means for research on solubility phenomena is focused. Basic thermodynamic information can be obtained in a simple and direct way from this technique relying on few parameters with their associated errors tightly controlled. An unexplored field of solvation phenomenology inaccessible to other techniques is revealed by the accuracy of capillary GC, provided that relevant chromatographic variables are utilized and an adequate treatment of the experimental information performed. The present article reviews different approaches for the attainment of basic thermodynamic information through capillary GC. Some traditional concepts on the treatment of chromatographic data for physicochemical measurement are questioned. Applications of the technique to research on solubility phenomena are depicted.     

Activation of carbon-oxygen bonds by palladium: toward a mild, catalytic approach to alpha-amino acid derivatives

A Lewis acid mediated method to induce the carbon-oxygen bond of amide-substituted ethers to undergo addition to palladium is described. The product of this reaction has been crystallographically characterized. This reaction suggests the potential use of such ethers as an alternative to organic halides in palladium catalyzed carbon-carbon bond formation. As an illustration of this potential, this reaction has been used to design a mild, catalytic route to alpha-amino acid derivatives from alpha-phenoxyamides and carbon monoxide.     

Glass capillary gas chromatography of amino acid enantiomers

Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable.     

Determination of toluenesulfonic acid isomers by gas chromatography

Summary A gas chromatographic method for the determination of isomeric distribution in toluenesulfonic acid samples is described. The acids are transformed into the corresponding ethyl esters by reaction with triethyl orthoformate in toluene. The reaction mixture can be injected, without further purification, into the gas chromatograph. The separation is best performed on columns containing OV-210 or polyphenyl ether (6 rings) as the stationary phase.     

氯代苯甲酸异构体的毛细管气相色谱分析

氯代苯甲酸是一种重要的精细化工产品,用途广泛,如用于合成临床治疗精神抑郁症的吗氯贝胺[1]及有机颜料中间体N (3 氨基 4 氯代苯甲酰基) 2 甲基 3 氯代苯胺[2]。但是氯代苯甲酸各异构体的性质差异极大,用途也不尽相同[3,4]。工业产品或多或少都会含有位置异构体,因此测定[5 7]氯代苯甲酸中各异构体含量就显得相当重要。已有报道的分析方法,或对仪器性能要求高,或操作繁琐,或分离效果不甚理想,因而在实际应用中受到一定的限制。考虑到氯代苯甲酸具有强极性、低挥发性等特点,本文采用甲酯化衍生物法对氯代苯甲酸异构体进行了气相色谱分…     

First-principles molecular dynamics study on aqueous sulfuric acid solutions

The properties of aqueous sulfuric acid have been studied employing density functional theory-based molecular dynamics simulations in conjunction with norm-conserving pseudopotentials. The simulations were carried out for two different concentrations whose molar concentrations were fixed at 0.84 and 10.2 mol/l. The structural features of aqueous sulfuric acid solutions show a strong dependency on the concentration. The Gr?tthuss-type proton transfer mechanism is not effectively operative at the higher concentration because of the broken hydrogen bond network of water induced by ions generated by the dissociation of sulfuric acid. In addition, to evaluate electrical properties, we carried out a simulation that takes an electric field into account. Results are compared with those of the simulation undertaken with no external electric field.     

Quantum mechanical study of sulfuric acid hydration: atmospheric implications

The role of the binary nucleation of sulfuric acid in aerosol formation and its implications for global warming is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the thermodynamics of sulfuric acid hydration using ab initio quantum mechanical methods. For H(2)SO(4)(H(2)O)(n) where n = 1-6, we used a scheme combining molecular dynamics configurational sampling with high-level ab initio calculations to locate the global and many low lying local minima for each cluster size. For each isomer, we extrapolated the M?ller-Plesset perturbation theory (MP2) energies to their complete basis set (CBS) limit and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled harmonic vibrational frequencies. We found that ionic pair (HSO(4)(-)·H(3)O(+))(H(2)O)(n-1) clusters are competitive with the neutral (H(2)SO(4))(H(2)O)(n) clusters for n ≥ 3 and are more stable than neutral clusters for n ≥ 4 depending on the temperature. The Boltzmann averaged Gibbs free energies for the formation of H(2)SO(4)(H(2)O)(n) clusters are favorable in colder regions of the troposphere (T = 216.65-273.15 K) for n = 1-6, but the formation of clusters with n ≥ 5 is not favorable at higher (T > 273.15 K) temperatures. Our results suggest the critical cluster of a binary H(2)SO(4)-H(2)O system must contain more than one H(2)SO(4) and are in concert with recent findings (1) that the role of binary nucleation is small at ambient conditions, but significant at colder regions of the troposphere. Overall, the results support the idea that binary nucleation of sulfuric acid and water cannot account for nucleation of sulfuric acid in the lower troposphere.     

Application of comprehensive two-dimensional gas chromatography to the quantification of overlapping faecal sterols

Standard solutions containing a mixture of seven sterols and 5alpha-cholestane as internal standard, and sample mixtures that comprised varying ratios of sterol and stanols from green lip mussel tissue and dried cow faeces were analysed by using comprehensive two-dimensional gas chromatography (GC x GC). Quantitative results were compared with single-column GC analysis. The latter samples included sterols of interest, but which cannot be readily obtained elsewhere. It may also mimic potential environmental samples where dairy production and aquaculture (oyster, mussel cultivation) share the same catchment; environmental sterol signatures may exhibit characteristics of both sample types comprising this mixture. Whereas single-column GC-flame ionisation detection was unable to reliably quantitate target sterols, the GC x GC experiment permitted small amounts of sterols and stanols to be detected and separated. Likewise GC-MS analysis was unable to detect some of the minor sterols which coeluted on a single column. The GC x GC mode allows complete separation of several important sterols and stanols, such as 24-ethylcoprostanol, campesterol and 24-methylenecholesterol, demonstrating the enhanced resolving power of the GC x GC system. Separation of 24-ethyl-epi-coprostanol from several algal-derived interfering components was achieved, leading to higher degree of confidence in the quantitative analysis of faecal sterols. The effects of a number of operating variables--column length, carrier flow-rate and elution temperature--on component resolution and presentation of data in the two-column analysis are described.