基于MALDI质谱成像技术分析莲子中代谢物的组织分布

该文建立了一种可对莲子中多种代谢物进行高覆盖分析的基质辅助激光解吸附质谱成像(MALDI-MSI)方法,实现了莲子中生物碱类、黄酮类、氨基酸类、脂肪酸类、有机酸类、胆碱类、磷脂类等多种代谢物的组织原位可视化表征。结果表明,生物碱类代谢物主要分布在莲子胚芽中;黄酮类代谢物主要分布在莲子胚芽和种皮中;氨基酸类代谢物在莲子子叶中的含量显著高于莲子胚中;脂肪酸类代谢物在莲子不同组织中的分布差异很小;胆碱类代谢物在莲子胚芽和莲子子叶底部的含量更高,甘油磷酸胆碱在莲子子叶顶部的含量更高;有机酸类代谢物以及绝大多数磷脂类化合物在莲子子叶中的含量高于莲子胚。该研究为评价莲子药物质量、探究莲子中化合物的时-空代谢网络提供了新的技术支持。     

Grand canonical ensemble molecular dynamics simulation of water solubility in polyamide-6,6

Grand canonical ensemble molecular dynamics simulation is employed to calculate the solubility of water in polyamide-6,6. It is shown that performing two separate simulations, one in the polymeric phase and one in the gaseous phase, is sufficient to find the phase coexistence point. In this method, the chemical potential of water in the polymer phase is expanded as a first-order Taylor series in terms of pressure. Knowing the chemical potential of water in the polymer phase in terms of pressure, another simulation for water in the gaseous phase, in the grand canonical ensemble, is done in which the target chemical potential is set in terms of pressure in the gas phase. The phase coexistence point can easily be calculated from the results of these two independent simulations. Our calculated sorption isotherms and solubility coefficients of water in polyamide-6,6, over a wide range of temperatures and pressures, agree with experimental data.     

Determination of Occurrence Characteristics of Heavy Metals in Soil and Water Environments in Tianshan Mountains,Central Asia

China has one of the fastest-growing economies in the world, but this economic development has important implications for environmental changes in this country. Our research was to quantify the presence of heavy metals in soil and water environments in the Tianshan Mountains region of China, associated with the economic development of this region. We used anomaly analysis, correlation analysis, and principal component analysis to assess the occurrence characteristics of heavy metals in this area. Results showed that Co, Cr, As, and Ni are more prevalent in water environments than in soil environments; in contrast, Cd, Zn, Pb, Hg, and Mn are more prevalent in soil samples than in water samples. This analysis grouped 10 heavy metals in soil and water environments into three principal components. In soil environments, the prevalence order was Co, Ni, Cr, As > Mn, Zn, Pb > Hg, Cd, Cu. In water environments, the order was Cu, Co, Ni, Cr, As > Hg, Mn, Zn > Cd, Pb. It is possible to distinguish between the natural and the anthropogenic sources of heavy metals in the Tianshan Mountains. With the current rapid economic development in the Tianshan Mountains, anthropogenic sources are playing principal roles in serious heavy metal accumulations in this region. This problem warrants immediate and widespread attention to prevent further deterioration of the soil and water environments.     

Analytical strategies to determine antibiotic residues in fish

The accelerated growth of aquaculture has resulted in a series of harmful effects to human health. The widespread and unrestricted use of antibiotics in this industry, to prevent bacterial infections, leads to remaining amounts in the aquatic environment. This has resulted in the emergence of antibiotic-resistant bacteria in aquaculture environments, in the increase in antibiotic resistance in fish pathogens as well as in the transfer of these resistance determinants to human pathogens. Moreover, the use of large amounts of antibiotics may lead to the presence of residual antibiotics in fish tissue and fish products. Fluoroquinolones, tetracyclines, penicillins, sulphonamides and other antibiotics, exhibiting activity against both Gram-positive and Gram-negative bacteria, are widely used for the treatment and prevention of diseases in fish. An extended and comprehensive review on the recent analytical methodologies concerning antibiotic residues in fish reported in the literature is provided in the present article. Emphasis is given on sample preparation regarding isolation and purification, chromatographic conditions and method validation according to legislation. Results of published assays are comparatively presented and criticised.     

The heat of dissolution of uranyl nitrate in aqueous nitrate solutions

Conclusions A model has been suggested to explain the observed relationship between the measured heats of dissolution of uranyl nitrate in aqueous nitrate solutions and the concentration of the salting-out agent. The model describes the change in the structure of water in the solution with change in its concentration. On the one hand, a destruction of the water structure by ions occurs, which is weakened with increase in the distance from the ion, and leads to such irregularity in the distribution of water molecules in the solution that the mean number of molecules of water in unit volume is increased with increase in the distance from the ions. In experiments on the heat of dissolution this increase leads to increased hydration of the uranyl cation and reduction in the endothermicity of the dissolution with increase in the concentration of the solution. On the other hand, an interaction occurs between the ions of the salting-out agent and the water molecules in the solution, leading to the opposite result: There is an increase in the mean number of water molecules of the solution in unit volume in the direction of these ions. In experiments on the heat of dissolution this is revealed in the dehydration of the uranyl cation, and correspondingly in an increase in the endothermicity of the dissolution with increase in the concentration of the solution. The proposed model is in harmony with data on vapor pressure above the solutions (the relationship between the activity coefficient of the water and the concentration of the solution).Translated from Zhurnal Strukturnoi Khimii. Vol. 3, No. 2, pp. 143–150, March–April. 1962     

Polymerization of α-amino acid N-carboxy anhydride. IX. Copolymerization of α-amino acid N-carboxy anhydride in heterogeneous system

Copolymerization of NCA's was undertaken in a heterogeneous system in acetonitrile, which is not a solvent of the polypeptides. The reactivity ratio was calculated by using the Lewis-Mayo equation. Further, the conversion rate in the copolymerization and the configuration of the copolymer produced were compared with those of the copolymerization in the homogeneous system in nitrobenzene, in which the copolypeptides are swollen. The rate of copolymerization in acetonitrile was between the rates of polymerization of the individual monomers. It has been reported that the configuration of the copolymer obtained in dimethylformamide, in which the copolypeptides are swollen, is of the block type. On the other hand, many polypeptides obtained in acetonitrile, which is not a solvent of the copolypeptides, had a random configuration near to an alternating configuration.     

Simultaneous liquid chromatographic determination of 39 polycyclic aromatic hydrocarbons in indoor and outdoor air and application to a survey on indoor air pollution in Fuji, Japan

An analytical method was established for the simultaneous determination of 39 polycyclic aromatic hydrocarbons (PAHs) in air. The method was applied to a survey of gaseous and particulate PAHs in household indoor air. The survey was performed in 21 houses in the summer of 1999 and in 20 houses in the winter of 1999-2000 in Fuji, Japan. Thirty-eight PAHs were determined in indoor and outdoor air in the summer, and 39 PAHs were determined in indoor and outdoor air in the winter. The concentrations of gaseous PAHs in indoor air tended to be higher than those in outdoor air in the summer and winter. The concentrations of particulate PAHs in indoor air were the same as or lower than those in outdoor air in the summer and winter. PAH profiles, correlations between PAH concentrations, and multiple regression analysis were used to determine the factors affecting the indoor PAH concentrations. These results showed that gaseous PAHs in indoor air were primarily from indoor emission sources, especially during the summer, and that indoor particulate PAH concentrations were significantly influenced by outdoor air pollution.     

Membrane lipids are both the substrates and a mechanistically responsive environment of TMEM16 scramblase proteins

Recent discoveries about functional mechanisms of proteins in the TMEM16 family of phospholipid scramblases have illuminated the dual role of the membrane as both the substrate and a mechanistically responsive environment in the wide range of physiological processes and genetic disorders in which they are implicated. This is highlighted in the review of recent findings from our collaborative investigations of molecular mechanisms of TMEM16 scramblases that emerged from iterative functional, structural, and computational experimentation. In the context of this review, we present new MD simulations and trajectory analyses motivated by the fact that new structural information about the TMEM16 scramblases is emerging from cryo-EM determinations in lipid nanodiscs. Because the functional environment of these proteins in in vivo and in in vitro is closer to flat membranes, we studied comparatively the responses of the membrane to the TMEM16 proteins in flat membranes and nanodiscs. We find that bilayer shapes in the nanodiscs are very different from those observed in the flat membrane systems, but the function-related slanting of the membrane observed at the nhTMEM16 boundary with the protein is similar in the nanodiscs and in the flat bilayers. This changes, however, in the bilayer composed of longer-tail lipids, which is thicker near the phospholipid translocation pathway, which may reflect an enhanced tendency of the long tails to penetrate the pathway and create, as shown previously, a nonconductive environment. These findings support the correspondence between the mechanistic involvement of the lipid environment in the flat membranes, and the nanodiscs. © 2019 Wiley Periodicals, Inc.     

Enantiomer ratio of MK-0767 in humans and nonclinical species

MK-0767, (+/-)-5-[(2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl)phenyl]methyl]benzamide, is a thiazolidinedione-containing dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist that has been studied as a potential treatment for patients with type 2 diabetes. MK-0767 contains a chiral center at the C-5 position of the thiazolidinedione ring and was being developed as the racemate, due to the rapid interconversion of its enantiomers in biological samples. In the present work the in vitro and in vivo concentration ratios of the (+)-(R) to (-)-(S) enantiomers of MK-0767 were determined in plasma from humans (in vitro only) and nonclinical species used in the toxicological evaluation of rac-MK-0767, namely CD-1 mice, Sprague-Dawley rats, beagle dogs, New Zealand white rabbits, and rhesus monkeys. The R/S ratio was determined by chiral liquid chromatography/tandem mass spectrometry. Species differences were observed in the in vitro and in vivo enantiomeric ratios, as well as differences between in vitro and in vivo in some species. The in vitro R/S ratio was similar in dogs and humans (approximately 1.5-1.7). In rats and monkeys, the ratio was approximately unity, both in vitro and in vivo. In mice, the ratio was higher in vitro (approximately 1) than in vivo (approximately 0.6), while in rabbits it was higher in vivo (approximately 1) than in vitro (approximately 0.5). These results suggested that differential binding of the MK-0767 enantiomers to plasma and tissue proteins and other macromolecules may be affecting the R/S ratio both in vitro and in vivo, since in protein-free systems MK-0767 exists as the racemate.     

Dendrimers with electroactive units in the core or in each branching centre

Interest in dendrimers is mostly focused on their capability of performing specific functions which, in their turn, derive from the possibility of incorporating in predetermined sites of the structure selected functional groups (‘pieces of information’). From a topological viewpoint we can distinguish dendrimers containing electroactive units (a) in the core, (b) in the branches, (c) in the surface, (d) in the core and in the branches, (e) in the core and in the surface, (f) in the branches and in the surface, and (g) in the core, branches and surface. In this article we review the behaviour of dendrimers with electroactive units buried in the core and dendrimers with electroactive units in each branching centre investigated in our laboratory. To cite this article: M. Venturi, P. Ceroni, C. R. Chimie 6 (2003).     

Particles dispersed in a dilute gas: Limits of validity of the Langevin equation

The problem of the limits of validity of the Langevin equation is considered in detail in the case of (microscopic) test-particles in very dilute gases. It is shown that, in this case, the current Langevin equation follows from the Newton’s law in an exact way only in the Maxwell test-particle–gas-particle interaction model, and in an approximate way only in the Rayleigh-gas limit and in the low-velocity limit, while in any other interaction model, or limit, only a Langevin-like equation with speed-dependent friction coefficient and speed-dependent fluctuating force can be written. Such a circumstance, although probably limited to the particular physical situation considered in this paper, suggests that, in general, some preliminary, specific check of the validity of the Langevin equation should be performed before using the said equation to interpret laboratory experiments.     

External electric field effects on absorption, fluorescence, and phosphorescence spectra of diphenylpolyynes in a polymer film

External electric field effects on absorption, fluorescence, and phosphorescence spectra of a series of unsubstituted diphenylpolyynes have been examined in a PMMA film. The analysis of the electroabsorption spectra indicates that the shorter diphenylpolyynes exhibit only the change in molecular polarizability, whereas the longer ones exhibit the change both in dipole moment and in molecular polarizability following absorption. The finding of the change in dipole moment following absorption of centrosymmetric diphenylpolyynes is interpreted in terms of the symmetry distortion upon doping a polymer film. When the external electric field is applied, the fluorescence yield is reduced and enhanced, respectively, in diphenylacetylene and diphenyloctatetrayne, indicating that the rate of the nonradiative process from the fluorescence state is accelerated in diphenylacetylene and decelerated in diphenyloctatetrayne by an external electric field. All of the diphenylpolyynes used in the present study exhibit the change in molecular polarizability following the phosphorescence process.     

Kinetic study in water-ethylene glycol cationic, zwitterionic, nonionic, and anionic micellar solutions

The spontaneous hydrolysis of phenyl chloroformate was studied in water-ethylene glycol, EG, cationic, zwitterionic, nonionic, and anionic micellar solutions, the surfactants being tetradecyltrimethylammonium bromide, tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, tricosaoxyethylene glycol ether, and sodium dodecyl sulfate. The dependence of the observed rate constant on surfactant concentration as well as on the percentage by weight of EG, varying from 0 to 50 wt %, was investigated. Information about changes in the critical micelle concentrations, in the micellar ionization degrees (for ionic surfactants), in the aggregation numbers, and in the polarity of the interfacial region of the micelles upon changing the weight percent of EG was obtained through conductivity, surface tension, spectroscopic, and fluorescence measurements. A simple pseudophase model was adequate to rationalize the kinetic data. Micellar medium effects were explained by considering charge-charge interactions and polarity, ionic strength, and water content in the micellar interfacial region. The acceleration of the reaction produced by an increase in the amount of EG present in the mixture was explained on the basis of the substantial decrease in the equilibrium binding constant of phenyl chloroformate molecules to the micelles, resulting in the contribution of the reaction taking place in the bulk water-EG phase being more important. The weight percent of EG did not substantially influence the rate constant in the micellar pseudophase.     

Interactions between carbonic anhydrase and its inhibitors revealed by gel electrophoresis and circular dichroism

Structural properties, and especially the differential stability, of complexes between carbonic anhydrase (CA) and three sulfonamide inhibitors, acetazolamide, dorzolamide and methazolamide, were investigated by spectroscopic and electrophoretic techniques. These included denaturant gradient gel electrophoresis either across a urea or a steady-state transverse sodium dodecyl sulfate (SDS) gradient. Acetazolamide, the smallest and most hydrophilic of the sulfonamides, forms the most stable complex in the presence of urea, whereas dorzolamide, with a bulky and hydrophobic structure, is most stable against the effects of SDS. At pH 7.4, complexes with dorzolamide show minimal changes in mobility across the SDS gradient, as if unaffected by the detergent, both in the presence and in the absence of excess ligand in the gel. When bound to both acetazolamide and methazolamide, on the other hand, CA displays an increase in mobility above 0.05% SDS, lower in the presence than in the absence of excess ligand. The finding of a distinct pattern for the unliganded enzyme, however, suggests the complexes can still retain the ligand, although binding of the surfactant changes their charge density. Under saturating conditions and in the presence of SDS, the surface charge of all complexes is much lower than for unliganded, denatured CA. Circular dichroism (CD) spectra clearly indicate that the increase in secondary structure and the decrease in tertiary structure brought about in CA by the presence of low concentrations of SDS are largely prevented by complexing with the inhibitors. These observations point out peculiar properties of each CA inhibitor, of potential value in the definition of their biological activities and also in the potential development of novel antagonist molecules.     

中性溶质在反相毛细管电色谱中的保留行为

分别在以甲醇、乙腈、异丙醇和四氢呋喃为有机改性剂的４种二元流动相体系中对中性溶质在反相毛细管电色谱中的保留行为进行了研究。不仅考察了有机改性剂的种类和浓度对电渗淌度的影响,而且建立了溶质容量因子与有机改性剂在流动相中体积分数间的定量关系,此外还对样品在反相毛细管电色谱和反相毛细管高效液相色谱中的保留行为进行了比较,发现中性溶质在这两种分离模式中的容量因子基本相同。     

有机合成的“百宝箱”

20世纪所涌现的新试剂和新方法深刻地影响了有机合成的发展,其中很多开创性的成果获得了诺贝尔化学奖。这些试剂的结构不仅限于碳、氢、氧和氮这些有机合成中的基本元素,还扩充至元素周期表中其他元素。为了解这些碳、氢、氧和氮以外的元素在有机合成中的应用,本文以获得诺贝尔化学奖的有机化学相关成果为主要内容,对元素周期表中以硼、磷为代表的非金属,以锂、镁、铝为代表的主族金属,以及以钯为代表的过渡金属在有机合成中的应用作了简单梳理。     

Solvent Effect on the Volume of the Diels-Alder Reaction between Tetracyanoethylene and trans,trans-1,4-Diphenyl-1,3-butadiene

From the partial molar volumes of tetracyanoethylene, trans,trans-1,4-diphenyl-1,3-butadiene, and their Diels-Alder adduct, the volumes of the reaction in a series of solvents at 25°C (cm³ mol^{- 1}) were calculated: in dioxane, -26.4; in chloroform, -34.9; in ethyl acetate, -34.5; in acetonitrile, -4.4; in cyclohexanone, -34.0; in 1,2-dichloroethane, -31.8; in benzene, -26.9; in toluene, -24.5; in o-xylene, -21.1; and in mesitylene, -16.9. The solvent effects on the activation and reaction volumes and on the partial molar volumes of the reactants, activated complex, and adduct were discussed.     

Spectroscopic studies of molybdenum and tungsten enzymes

Molybdenum and tungsten are the only second and third-row transition elements with a known function in living systems. Molybdenum fulfills functional roles in enzyme systems in almost all living creatures, from bacteria through plants to invertebrates and mammals, while tungsten takes the place of molybdenum in some prokaryotes, especially the hyperthermophilic archaea. The enzymes contain the metal bound by an unusual sulfur-containing cofactor. Despite possessing common structural elements, the enzymes are remarkable in the range of different chemical reactions that are catalyzed, although almost all are two-electron oxidation–reduction reactions in which an oxygen atom is transferred to or from the molybdenum. The functional roles filled by molybdenum enzymes are equally diverse; for example, they play essential roles in microbial respiration, in the uptake of nitrogen in green plants, in controlling insect eye color, and in human health. Spectroscopic studies, in particular electron paramagnetic resonance and X-ray absorption spectroscopy, have played an essential role in our understanding of the active site structures and catalytic mechanisms of the molybdenum and tungsten enzymes. This review summarizes the role spectroscopy has played in the state of our knowledge of the molybdenum and tungsten enzymes, with particular regard to structural information on the molybdenum sites.     

Formation of benzenediols upon electron-beam distillation of lignin mixtures with alkanes

In the process of the electron-beam distillation of lignin, its conversion into benzenediols increases in the presence of alkanes in the irradiated sample. An increase in the yield of benzenediols is accompanied by a decrease in the fractions of guaiacol, creosol, ethylguaiacol, and vinylguaiacol in the tar distilled off. It has been noted that alkanes serve as an additional source of atomic hydrogen and alkyl radicals, which, in turn, play a key role in the formation of benzenediols. In the presence of alkanes in the irradiated sample, guaiacol can be the main precursor of catechols; the proportion of guaiacol in the tar is almost three times below that in the case of distillation of individual lignin. It has been hypothesized that the chain decomposition of lignin can occur with the participation of ?H and ?CH₃ radicals.     

Synthesis of Ga-incorporated SAPO-34s (GaAPSO-34) and their catalytic performance on methanol conversion

This study has been focused on the synthesis of GaAPSO-34s substituted gallium for aluminum in order to improve the acidic property in SAPO-34 crystal. As the result, GaAPSO-34s with various Al/Ga ratios (Al/Ga=∞, 40, 20, 10, 5, and 0) were successfully synthesized. These were characterized by XRD, SEM, ICP, TG-DTA, MAS-NMR, and BET surface areas. The crystallinity identified from the intensity of XRD peak (for angles of 22.5° and 9.7°) and the particle size observed from SEM photographs decreased with an increase in the Ga content incorporated into the SAPO-34 framework. On the other hand, decrease in the acid sites in crystal as a target in this study was confirmed in the Ga-incorporated samples. In particular, a surprising result was that the selectivity to ethylene on methanol conversion increased in catalyst with Al/Ga=20 compared with pure SAPO-34 catalyst. However, in spite of the decreases in acid sites and particle size in catalyst with much more Ga content, the selectivity to ethylene was not enhanced, rather the methane which related to catalytic deactivation increased in GaAPSO-34 catalysts. This is ascribed to collapses of framework of SAPO-34 with an increase in Ga content.