Synaptic inhibition and γ-aminobutyric acid in the mammalian central nervous system

Signal transmission through synapses connecting two neurons is mediated by release of neurotransmitter from the presynaptic axon terminals and activation of its receptor at the postsynaptic neurons. γ-Aminobutyric acid (GABA), non-protein amino acid formed by decarboxylation of glutamic acid, is a principal neurotransmitter at inhibitory synapses of vertebrate and invertebrate nervous system. On one hand glutamic acid serves as a principal excitatory neurotransmitter. This article reviews GABA researches on; (1) synaptic inhibition by membrane hyperpolarization, (2) exclusive localization in inhibitory neurons, (3) release from inhibitory neurons, (4) excitatory action at developmental stage, (5) phenotype of GABA-deficient mouse produced by gene-targeting, (6) developmental adjustment of neural network and (7) neurological/psychiatric disorder. In the end, GABA functions in simple nervous system and plants, and non-amino acid neurotransmitters were supplemented.     

Molecular diversity of volatile compounds in rare willow (<Emphasis Type="BoldItalic">Salix</Emphasis> spp.) honeydew honey: identification of chemical biomarkers

Salix spp. honeydew honey volatiles were analyzed for the first time by headspace solid-phase microextraction (HS-SPME) and ultrasonic solvent extraction (USE) followed by gas chromatography and mass spectrometry (GC, GC-MS). The use of HS-SPME and USE had advantageous results over the use of one single technique, as it provided different complementary chromatographic profiles for a comprehensive screening of the honeydew volatile composition. The volatiles with different functionality, molecular weight, and polarity were extracted and identified. High percentages of benzoic acid, phenylacetic acid, 2-hydroxybenzoic acid, 4-hydroxyphenylacetic acid with minor percentages of 4-methoxybenzoic acid, 4-hydroxyphenylethanol, and 4-hydroxybenzoic acid from USE extracts can be emphasized as volatile biomarkers of this honeydew that probably originated from Salix spp., as well as methyl salicylate identified only by HS-SPME. The application of heat treatment at 80 °C for 2 h did not change significantly the volatile composition of this honeydew.     

基于样片厚度精确估计的THz吸收系数谱算法

利用太赫兹时域光谱技术(THz-TDS)提取物质在太赫兹波段的吸收系数谱是太赫兹应用的一个重要方面。由于样品的吸收系数与其厚度存在着复杂的非线性关系,而厚度又不便于直接准确测量,往往造成吸收系数谱的失真。根据Duvillaret等用于LiNbO3的厚度估计方法,改进了谷氨酰胺(Gln)与组氨酸(His)在0.3～2.6THz(1THz=1012 Hz)波段的吸收系数谱的测定和计算。为了说明改进后的吸收系数谱的合理性,设计了一系列实验对比了同种氨基酸在不同浓度下吸收系数的线性符合程度。结果表明,改进后计算出的氨基酸吸收系数与浓度之间存在更好的线性关系,符合Lambert-Beer定律的描述,这为进一步的定量分析奠定了基础。     

Ultrasonic versus silent methylation of vegetable oils

The profile of fatty acid methyl esters (FAME) of different vegetable oils produced under ultrasonic irradiation and conventional heating were compared. In the presence of potassium hydroxide as catalyst, the distribution of FAME was quite similar for both procedures, while in the case of sodium hydroxide ultrasonic irradiation gave better results. The FAME profile resulted from the reaction catalyzed by sulfuric acid was almost the same with the one resulted from the reaction catalyzed by KOH, while boron trifluoride can give rise to many artifacts, thus is not a reliable catalyst.     

神经节苷脂的红外、紫外光谱分析及其多聚体结构的原子力显微镜观测

神经节苷脂(gangliosides, Gls)是一类含有唾液酸的酸性鞘糖脂,是神经细胞膜的重要组成成分,在生物膜中起着非常重要的生理作用。文章用红外光谱(IR)、紫外光谱(UV)、原子力显微镜(AFM)分别对以牛脑为原料,采用Folch萃取法、硅胶吸附柱层析和DEAE-SephadexA-25离子交换柱层析得到的神经节苷脂的分子官能团和多聚体结构进行了研究。实验结果表明,从100 g湿组织中获得产品为55.2 mg,纯度达62.84%,其紫外光谱吸收在195 nm处。通过红外光谱研究证明在提纯的产品结构中含有唾液酸分子的结构片段。利用原子力显微镜对其在水中的聚集体微观形貌进行了观察研究,发现神经节苷脂在水中呈清晰的纳米级球状或椭球状结构,经测定：神经节苷脂多聚体的大小在55～380 nm之间,平均大小为(148.9±66.7) nm;高度在1.0～5.0 nm之间,平均高度为(3.25±1.01) nm。该实验结果为神经节苷脂的生物活性研究以及作为神经类药物的开发利用提供了理论和实验依据。     

Dielectric spectroscopy on aqueous solutions of some zwitterionic amino acids

The complex (electric) permittivity of aqueous solutions of dipolar solutes has been measured as a function of frequency between 1 MHz and 40 GHz. Solutes are the isomers DL-2-aminobutyric acid, DL-3-aminobutyric acid, and 4-aminobutyric acid, and also 6-aminohexanoic acid. The measured dielectric spectra show two dispersion/dielectric loss regions, one due to the orientational diffusion of the solute molecules the other one due to the dielectric relaxation of the solvent water. A relaxation spectral function based on a model of the solutions has been fitted to the measured frequency dependence of the complex permittivity. The values for the electric dipole moment and reorientation time of the zwitterionic part of the solute particles derived by this analysis from the measurements fairly agree with theoretical predictions. Quite remarkably, the dipole moment in solution of 4-aminobutyric acid and 6-aminohexanoic acid up to remarkably high solute concentrations is nearly constant. A noteworthy result for the hydration water of the amino acids is, that its relaxation time is almost independent of the solute dipole moment.     

应用荧光光谱法研究植物LEA3蛋白11-氨基酸基序的保护功能

胚胎晚期富集蛋白(late embryogenesis abundant,LEA)是增强生物抵抗干旱、低温和盐渍等多种胁迫的重要功能蛋白,但其保护机理仍不清楚.本文利用紫外光谱法证实,含多拷贝11-氨基酸基序的多肽(如PM2D和PM2E)可较好的保护经冻融的乳酸脱氢酶(LDH)活性.进一步通过荧光光谱法证实,含多拷贝11-氨基酸基序的多肽可通过多位点协同结合模式,稳定LDH酶的结构.而含低拷贝11-氨基酸基序的多肽(如PM2F和PM2G)与LDH酶只有一种结合位点,二者的结合强度较弱,因而不能表现出对LDH酶活性的保护作用.此外,含多拷贝11-氨基酸的多肽与海藻糖在保护LDH酶活性上存在协同作用,且二者有着不同的保护机理.     

Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization

The cell wall of the pathogenic bacterium Streptococcus pneumoniae contains glucopyranosyl diacylglycerol (GlcDAG) and galactoglucopyranosyldiacylglycerol (GalGlcDAG). The specific GlcDAG consisting of vaccenic acid substituent at sn-2 was recently identified as another glycolipid antigen family recognized by invariant natural killer T-cells. Here, we describe a linear ion-trap multiple-stage (MS(n) ) mass spectrometric approach towards structural analysis of GalGlcDAG and GlcDAG. Structural information derived from MS(n) (n?=?2, 3) on the [M?+?Li](+) adduct ions desorbed by electrospray ionization affords identification of the fatty acid substituents, assignment of the fatty acyl groups on the glycerol backbone, as well as the location of double bond along the fatty acyl chain. The identification of the fatty acyl groups and determination of their regio-specificity were confirmed by MS(n) (n?=?2, 3) on the [M?+?NH(4) ](+) ions. We establish the structures of GalGlcDAG and GlcDAG isolated from S. pneumoniae, in which the major species consists of a 16:1- or 18:1-fatty acid substituent mainly at sn-2, and the double bond of the fatty acid is located at ω-7 (n-7). More than one isomers were found for each mass in the family. This mass spectrometric approach provides a simple method to achieve structure identification of this important lipid family that would be very difficult to define using the traditional method.     

C60富勒烯-巴比妥酸及其二聚体几何结构和电子结构的密度泛函计算研究

采用基于密度泛函理论的广义梯度近似,对C₆₀富勒烯-巴比妥酸及其二聚体的几何结构和电子结构进行了计算研究.发现：C₆₀富勒烯-巴比妥酸只有一种稳定结构,且掺杂巴比妥酸基团对C₆₀分子构型的影响是局域的.C₆₀富勒烯-巴比妥酸的二聚体有三种同素异构体,分别以［6,5］—［6,5］,［6,6］—［6,5］和［6,6］—［6,6］三种方式键合,从能隙大小顺序和总能相对大小来看,［6,6］—［6,6］结构最为稳定.电子结构方面,在C₆₀富勒烯-巴比妥酸单体中,Donor-Acceptor电荷转移体系为C₆₀富勒烯-巴比妥酸,即电荷是从C₆₀向巴比妥酸转移.由前线轨道和自旋布居数得知,C₆₀富勒烯-巴比妥酸单体很好地保留了C₆₀的电磁性质,但稳定性下降,易发生二次加成反应形成二聚体.对于C₆₀富勒烯-巴比妥酸二聚体,Mulliken电荷分析显示,在加成四元环处的碳原子分别得到0104e和0106e电荷,而与它们邻近的碳原子则失去电子,带有正电荷,且距加成位置越近的碳原子失去的电荷越多.在远离加成位置处,碳原子的净电荷变化相对较小.与单体152eV能隙相比,二聚体中的能隙为1.45eV.其前线轨道分布与单体相比,最高占据轨道几乎未变,但最低未占据轨道发生了很大变化. 关键词： 几何结构 电子结构 密度泛函     

Purification and fractionation of single-walled carbon nanotubes

This study presents the approach to the purification and subsequent metallic/semiconductive (M/S) fractionation of single-walled carbon nanotubes (SWCNTs) with diameter from 1.04 to 1.60 nm produced via laser ablation. SWCNTs were purified through 3-fold refluxing processes in nitric acid followed by the multiple washings with sodium hydroxide and hydrochloric acid. The purified-annealed SWCNTs sample was divided into seven batches. One batch was dispersed in acetone as a reference sample. Each of the remaining batches were dispersed in one of the following surface agents: sodium dodecyl sulfate, sodium cholate acid (SCA), sodium deoxycholate, cetrimonium bromide, cetylpyridinium chloride, and benzalkonium chloride (BKC). SWCNT suspensions were fractionated via free solution electrophoresis technique. The recovered fractions from electrode and control areas were analyzed via optical absorption spectroscopy in UV–Vis–NIR range to evaluate the efficiency of the separation process. Raman spectroscopy was applied to analyze the purity of the samples. The catalyst content was estimated by atomic absorption spectroscopy. The morphology of the investigated samples was observed via high-resolution transmission electron microscopy. This contribution clearly shows that among the investigated surfactants there are two promising candidates (SCA and BKC) which can efficiently enrich the bulk sample in one electronic type of carbon nanotubes when FSE is applied.     

溶液酸碱性对腺嘌呤分子吸附构型影响的SERS光谱研究

核酸碱基是构成核酸的基本单元,有关核酸碱基结构的研究是核酸研究工作的重要基础。本研究借助于表面增强拉曼散射技术,对不同pH值条件下腺嘌呤分子在金表面的吸附构型及其变化特征进行了研究。研究结果表明,随着溶液酸性的增强、腺嘌呤分子质子化程度的增大,腺嘌呤分子在金表面的吸附态倾向于由通过氨基和嘌呤环上7位的氮原子作为结合点的直立吸附转变为分子平躺的吸附形式。这一转变过程通过腺嘌呤的环呼吸全对称伸缩振动的特征谱峰其强度有规律的显著变化而得以表征。有关这一谱峰的增强作用可以通过表面增强拉曼散射的电荷传递(CT)机理来加以说明。     

Influence of HF catalyst on the microstructure properties of ultra low-k thin films prepared by sol-gel method

This paper reports that by using the hydrofluoric acid （HF） as the acid catalyst, F doped nanoporous low-k SiO2 thin films have been prepared by means of sol-gel method. The characterization of atomic force microscopy and Fourier transform infrared spectroscopy demonstrates that the HF catalyzed films are more hydrophobic. The N2 adsorption/desorption experiments show that the suited introduction of HF increases the porosity and decreases the pore size distribution （about 10 nm） in the films. The above results indicate that the hydrofluoric acid is the more suitable acid catalyst than the hydrochloric one for preparing nanoporous ultra low-k SiO2 thin films.     

SCAMP硫酸酯化多糖的制备及其光谱鉴定

用Sepharose-4B琼脂糖凝胶柱分离SCAMP得到SCAMP－F1和SCAMP－F2 2个组分，用Sepharose-4B琼脂糖凝胶层析、聚丙烯酰胺凝胶电泳、冻融离心，证明SCAMP－F2为单一组分，然后用吡啶－氯磺酸磺化试剂制备SCAMP－F2的硫酸酯化多糖，得到SO4^2-含量为19．6％的硫酸酯化多糖，比未硫酸酯化前增加6．1％，红外光谱和核磁共振碳谱分析结果表明，硫酸基取代在C－6位上。     

Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions

The heterogeneity of activated carbons (ACs) prepared from different precursors is investigated on the basis of adsorption isotherms of aniline from dilute aqueous solutions at various pH values. The APET carbon prepared from polyethyleneterephthalate (PET), as well as, commercial ACP carbon prepared from peat were used. Besides, to investigate the influence of carbon surface chemistry, the adsorption was studied on modified carbons based on ACP carbon. Its various oxygen surface groups were changed by both nitric acid and thermal treatments. The Dubinin-Astakhov (DA) equation and Langmuir-Freundlich (LF) one have been used to model the phenomenon of aniline adsorption from aqueous solutions on heterogeneous carbon surfaces. Adsorption-energy distribution (AED) functions have been calculated by using an algorithm based on a regularization method. Analysis of these functions for activated carbons studied provides important comparative information about their surface heterogeneity.     

Synthesis of a New Thermal and Photostable Reference Probe for Qf Measurement in Aqua: Water Soluble N,N′-bis-(2-Hydroxy-4-benzoic Acid)-3,4,9,10-perylenebis(dicarboximide)

N,N′-bis(2-hydroxy-4-benzoic acid)-3,4,9,10-perylenebis(dicarboximide) is synthesized from perylene 3,4,9,10-tetracarboxylic dianhydride and 4-amino-3-hydroxy benzoic acid in 90% yield. Together with the photostability the dye is also very stable thermally. The fluorescence quantum yield is measured as one, Q_f=1.The diimide dissolves in water at PH = 8 completely. The diimide is an ideal reference probe for fluorescence quantum yield measurements in 500–650 nm region and an attractive photosensitizer for the photoreactions occur in water.     

二氮杂萘酮衍生物的核磁共振结构鉴定

用¹H, ¹³C NMR及多种二维核磁共振谱确定了一系列新合成的二氮杂萘酮衍生物的结构,完成了¹H和¹³C NMR 谱的归属,给出了该系列衍生物的氢、碳原子的准
确化学位移.     

1H spin–lattice relaxation in water solution of 209Bi counterparts of Gd3+contrast agents

ABSTRACT

¹H spin–lattice relaxation studies of water solutions of Bismuth-ethylenediamine-tetraacetic acid (Bi-EDTA), Bismuth-ethylenediamine-tetrakis(methylenephosphonic) acid (Bi-EDTP), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Bi-DOTA), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid) (Bi-DOTP) and Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (Bi-DO3A) have been performed in order to compare Quadrupole Relaxation Enhancement (QRE) effects with Paramagnetic Relaxation Enhancement (PRE) from the perspective of exploiting the first one as a novel contrast mechanism for Magnetic Resonance Imaging (MRI). The selected compounds can be considered as ²⁰⁹Bi counterparts of Gd³⁺ complexes. The relaxation experiments have been performed in a broad frequency range of 5?kHz–30?MHz. The relaxation contribution associated with QRE has been extracted from the data and compared with PRE. Similarities and differences between the two effects have been discussed.     

From collisions to clusters: first steps of sulphuric acid nanocluster formation dynamics

The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)₁(base)₁(water)_n cluster. Here, we present results from direct first-principles molecular dynamics collision simulations of (sulphuric acid)₁(water)_{0, 1} + (dimethylamine) → (sulphuric acid)₁(dimethylamine)₁(water)_{0, 1} cluster formation processes. The simulations indicate that the sticking factor in the collisions is unity: the interaction between the molecules is strong enough to overcome the possible initial non-optimal collision orientations. No post-collisional cluster break up is observed. The reasons for the efficient clustering are (i) the proton transfer reaction which takes place in each of the collision simulations and (ii) the subsequent competition over the proton control. As a consequence, the clusters show very dynamic ion pair structure, which differs from both the static structure optimisation calculations and the equilibrium first-principles molecular dynamics simulations. In some of the simulation runs, water mediates the proton transfer by acting as a proton bridge. In general, water is able to notably stabilise the formed clusters by allocating a fraction of the released clustering energy.     

Conformational Transition of Poly （Acrylic Acid） Detected by Microcantilever Sensing

Poly （acrylic acid） （PAA） chains are grafted on one side of a microcantilever by the self-assembled method and the deflections of the microcantilever are detected as a function of medium pH from 3 to 11. It is found that when the pH varies, the microcantilever deflects because of the changing surface stress. By analysing the electrostatic repulsive effect, the surface stress change is related to the conformation transition of PAA from a collapse state to a swelling state. This method offers the interaction information among the polymer chains during the conformational transition and affords an alternative way to study conformational change of polymers.     

Metabolic and Isotopic Correlations between D-Glucose,L-Ascorbic Acid and L-Tartaric Acid

Abstract

L-Ascorbic acid in fruit juices is enriched in ¹³C by 4.8 δ-units relative to its precursor glucose, and this enrichment is mainly located in position C-1. On the other hand, biotechnologically produced L-ascorbic acid preserves the pattern as expected from glucose. In grapes L-tartaric acid is synthesized from glucose via L-ascorbic acid and it is one of its main products. It preserves C-atoms 1 to 4 from glucose and the measured δ¹³C-value is identical to that calculated from this precursor.

The findings are interpreted as overlapping influences of isotope discriminations after metabolic branching and relative turnover rates leading to isotopic balances. The results can also be used to distinguish between identical products by different synthetic processes.