Zinc(II), cadmium(II), mercury(II), and ethylmercury(II) complexes of phosphinothiol ligands

Neutral zinc, cadmium, mercury(II), and ethylmercury(II) complexes of a series of phosphinothiol ligands, PhnP(C6H3(SH-2)(R-3))3-n (n = 1, 2; R = H, SiMe3) have been synthesized and characterized by IR and NMR ((1)H, (13)C, and (31)P) spectroscopy, FAB mass spectrometry, and X-ray structural analysis. The compounds [Zn{PhP(C6H4S-2)2}] (1) and [Cd{Ph2PC6H4S-2}2] (2) have been synthesized by electrochemical oxidation of anodic metal (zinc or cadmium) in an acetonitrile solution of the appropriate ligand. The presence of pyridine in the electrolytic cell affords the mixed complexes [Zn{PhP(C6H4S-2)2}(py)] (3) and [Cd{PhP(C6H4S-2)2}(py)] (4). [Hg{Ph2PC6H4S-2}2] (5) and [Hg{Ph2PC6H3(S-2)(SiMe3-3)}2] (6) were obtained by the addition of the appropriate ligand to a solution of mercury(II) acetate in methanol in the presence of triethylamine. [EtHg{Ph2PC6H4S-2}] (7), [EtHg{Ph2P(O)C6H3(S-2)(SiMe3-3)}] (8), [{EtHg}2{PhP(C6H4S-2)2}] (9), and [{EtHg}2{PhP(C6H3(S-2)(SiMe3-3))2}] (10) were obtained by reaction of ethylmercury(II) chloride with the corresponding ligand in methanol. In addition, in the reactions of EtHgCl with Ph2PC6H4SH-2 and with the potentially tridentate ligand PhP(C6H3(SH-2)(SiMe3-3)) 2, cleavage of the Hg-C bond was observed with the formation of [Hg{Ph2PC6H4S-2}2] (5) and [Hg(EtHg) 2{PhP(O)(C6H3(S-2)(SiMe3-3))2}2] (11), respectively, and the corresponding hydrocarbon. The crystal structures of [Zn3{PhP(C6H4S-2)2}2{PhP(O)(C6H4S-2)2}] (1*), [Cd2{Ph2PC6H4S-2}3{Ph2P(O)C6H4S-2}] (2*), 3, 5, 6, [EtHg{Ph2P(O)C6H4S-2}] (7*), 8, 9, [{EtHg}2{PhP(O)(C6H3(S-2)(SiMe3-3))2}] (10*), and 11 are discussed. The molecular structures of 1, 2, 4, 7, and 10 have also been studied by means of density functional theory (DFT) calculations.     

Interface microstructure and diffusion kinetics in diffusion bonded Mg/Al joint

The interface microstructure, formation of diffusion bonded joint and regulation of atom diffusion were studied by means of scanning electron microscope (SEM), energy dispersion spectroscopy (EDS) and electron probe microanalyser (EPMA). The experimental results indicated that an obvious interfacial transition zone was formed between Mg and Al, and there are three intermetallic layers Mg₁₇Al₁₂, MgAl and Mg₂Al₃ in this zone. Diffusion activation energy of Mg and Al in the above layers was lower than that in the Mg and Al base metals. The thickness (x) of each layer can be expressed as x ² = 4.14exp(−28780/RT)(t−t ₀), x ² = 31.4exp(−25550/RT)(t−t ₀) and x ² = 0.6exp(−22600/RT)(t−t ₀) corresponding to Mg₁₇Al₁₂, MgAl and Mg₂Al₃ with heating temperature (T) and holding time (t).     

Abiesanol A, a novel biflavanol with unique six connective hexacyclic rings isolated from Abies georgei

A novel biflavanol with unique six connective hexacyclic rings, abiesanol A (1), was isolated from the aerial parts of Abies georgei together with four known flavanols. The structure of new compound was elucidated mainly by the analysis of 1D and 2D NMR spectroscopic data. In addition, single-crystal X-ray diffraction analysis was adopted to confirm the structure of abiesanol A (1). In biological assay for inhibitory activities against LPS-induced nitric oxide (NO) production in RAW264.7 macrophages, abiesanol A (1) showed potent effects at 50 μg/mL with the inhibition rate of 43.0%. Under the same concentration, abiesanol A (1) did not show any cytotoxicity against RAW264.7 macrophages.     

Synthesis,crystal structures and electrochemical properties of group 6 metal carbonyl anion complexes

A series of [M(CO)₅I]⁻ and [M₂(CO)₁₀I]⁻ anion complexes have been synthesized by the photochemical reaction of PhCH₂N(CH₃)₃I or FcCH₂N(CH₃)₃I (Fc=ferrocenyl) with M(CO)₆ (M = Cr, Mo or W), and characterized by elemental analyses, i.r., ¹H-n.m.r. and ¹³C-n.m.r. spectra in the case of the molybdenum and tungsten complexes. These complexes exhibit considerably different electrochemical behavior, when investigated by cyclic voltammetry. The crystal structures of [PhCH₂N(CH₃)₃][Cr(CO)₅I] and [FcCH₂N(CH₃)₃][W₂(CO)₁₀I] have been determined by X-ray diffraction, indicating that only weak contacts maybe exist between anions and cations by the I...H bond in the former, and there are no direct interactions between anions and cations in the latter.     

Multi-residue pesticide analysis in fruits and vegetables by liquid chromatography-time-of-flight mass spectrometry

In this work, a new multi-residue methodology using liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) for the quantitative (routine) analysis of 15 pesticide residues has been developed. The analytical performance of the method was evaluated for different types of fruit and vegetables: pepper, broccoli, tomato, orange, lemon, apple and melon. The accurate mass measurements were compared in different matrices at significantly different concentration levels (from 0.01 to 0.5 mg/kg) obtaining accuracy errors lower than 2 ppm, which is well within the accepted limits for elemental confirmation. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression or enhancement of the response were frequently observed, most notably in broccoli and citrus. Instrumental limits of detection (LOD) were between 0.0005 and 0.03 mg/kg depending on the commodity and pesticide studied, all being within European Union regulations for food monitoring program. Finally, the methodology was applied to the analysis of two samples from an inter-laboratory exercise. The high degree of confirmation for target pesticides by accurate mass measurements demonstrated the applicability of the method in routine analysis. This study is a valuable indicator of the potential of LC-TOF-MS for quantitative multi-residue analysis of pesticides in vegetables and fruits.     

On the nature of the transition state in catechol O-methyltransferase. A complementary study based on molecular dynamics and potential energy surface explorations

The way in which enzymes influence the rate of chemical processes is still a question of debate. The protein promotes the catalysis of biochemical processes by lowering the free energy barrier in comparison with the reference uncatalyzed reaction in solution. In this article we are reporting static and dynamic aspects of the enzyme catalysis in a bimolecular reaction, namely a methyl transfer from S-adenosylmethionine to the hydroxylate oxygen of a substituted catechol catalyzed by catechol O-methyltransferase. From QM/MM optimizations, we will first analyze the participation of the environment on the transition vector. The study of molecular dynamics trajectories will allow us to estimate the transmission coefficient from a previously localized transition state as the maximum in the potential of mean force profile. The analysis of the reactive and nonreactive trajectories in the enzyme environment and in solution will also allow studying the geometrical and electronic changes, with special attention to the chemical system movements and the coupling with the environment. The main result, coming from both analyses, is the approximation of the magnesium cation to the nucleophilic and the hydroxyl group of the catecholate as a result of a general movement of the protein, stabilizing in this way the transition state. Consequently, the free energy barrier of the enzyme reaction is dramatically decreased with respect to the reaction in solution.     

Stereoselective syntheses of polyhydroxylated azepane derivatives from sugar-based epoxyamides. Part 1: synthesis from d-mannose

An approach to the synthesis of polyhydroxyazepane derivatives from sugar-based epoxyamides or epoxyalcohols, in which the total regioselective epoxide opening by nitrogen nucleophiles is the key step, is described. Thus, novel polyhydroxyazepane carboxamides and aminomethyl polyhydroxyazepanes, with potential pharmacological interest, are synthesized from diacetone d-mannose. Configurational assignments of the obtained products were determined.     

Straightforward synthesis of [(2S,4R)-1-cyclohexyl-4-methylpiperidin-2-yl]methanol and [(2S,4R)-1-cyclohexyl-4-methylpiperidin-2-yl](diphenyl)methanol: novel chiral ligands for the catalytic addition of diethylzinc to benzaldehyde to give rise to an extensive turn in the sense of asymmetric induction

Enantiopure [(2S,4R)-1-cyclohexyl-4-methylpiperidin-2-yl]methanol 5a and [(2S,4R)-1-cyclohexyl-4-methylpiperidin-2-yl]-(diphenyl)methanol 5b, new β-amino alcohols based on l-pipecolinic acid (homoproline), have been prepared straightforwardly from rac-alaninol and rac-2-amino-1,1-diphenylpropan-1-ol, respectively. The described route constitutes as a model procedure for the preparation of other related C(4) or/and C(3)-substituted 2-piperidinylmethanols.The new chiral ligands have shown a singular behaviour on the stereocontrol of the benchmark reaction of benzaldehyde and diethylzinc compared with other C(4)-unsubstituted analogues prepared by ourselves from l-pipecolinic acid (compounds 5c, 5d, 5e and 5f). The catalytic activity, the sense of asymmetric induction and the degree of the enantioselectivity depend on the appropriate combination of the substituents on the structural scaffold, but also on the metal-alkoxide involved in the catalysis (zinc or lithium alkoxides). The enantioselective addition of diethylzinc to benzaldehyde mediated by ligands 5a and 5c has been studied with DFT methods. The theoretical evaluation was performed in connection with a working hypothesis based on the different loadings of cis- and trans-catalysts in the reaction medium.     

无轴承旋翼柔性梁载荷特性研究

应用Hamilton原理建立了双路传力的无轴承旋翼运动方程。采用均匀入流模型,基于直升机飞行平衡条件,建立了无轴承旋翼柔性梁载荷的计算模型,并通过算例验证了模型的精度。利用该模型,研究了全机重心位置、机身气动阻力以及平尾安装角对柔性梁载荷特性的影响,给出了各因素对柔性梁载荷的影响趋势,得出了降低柔性梁载荷的方法。数值结果表明:2cm左右重心位置的变化能够引起9%~11%的柔性梁载荷变化量,15%气动阻力的增加会导致约9%的柔性梁载荷的增大;2°平尾安装角的变化引起约10%柔性梁载荷的变化量,3°平尾安装角的变化引起约26%柔性梁载荷的变化。