Phase shift calculation for low-energy electron scattering from mercury

Summary The relativistic formalism is used to study the scattering of electrons from mercury at low energy. A method of numerical integration is applied to calculate phase shifts by including a local exchange approximation and phenomenological polarization potential. The phase shifts are found to exhibit a resonant behaviour which is in conformity with the results of some earlier calculations. In contrast to the previous methods, this approach has a general validity over the entire energy range and is free from divergences. The author of this paper has agreed to not receive proofs for correction.     

Two New Dibenzofurans from the Underground Parts of Ligularia intermedia

Two new dibenzofurans,7,8-dimethoxy-4-methyldibenzofuran-1-carboxaldehyde, named ligumedial (1) and 7,8-dimethoxy-4-methyldibenzofuran-1-carboxylic acid, named ligumediaoic acid (2), have been isolated from the underground parts of Ligularia intermedia. Their structures were elucidated by spectroscopic methods.     

邻苯二甲酰化壳聚糖中酰胺酸取代度的红外测定

室温条件下从完全脱乙酰化壳聚糖出发合成了不同酰胺酸取代度的邻苯二甲酰化壳聚糖，并以此为标样，标样的取代度由X射线光电子能谱（XPS）确定，研究了以FT－IR作为工具测定此系列衍生物的总取代度的方法，以2887cm^-1的吸收峰作为参比谱带，探针谱带可用1712cm^-1或749cm^-1的吸收峰，两种探针谱带所得曲线的斜率分别为1．13和0．12，相关系数分别为0．997和0．977，此结果表明：红外法是一种既准确可靠又方便可行的测定方法。     

Linear-sweep polarographic determination of active chlorine in aqueous solutions containing phenylthiourea

The linear-sweep polarographic determination of active chlorine is based on its reaction with phenylthiourea in acidic phosphate buffer (pH 2.5) containing potassium chloride. The product, C,C-diphenyldithiodiformamidine, is strongly adsorbed and then reduced at a mercury electrode with two peaks at about ?0.35 V and ?0.87 V (vs. SCE). In the presence of 0.05 M potassium chloride, the potential of the first peak shifts positively to ?0.31 V. This peak provides high sensitivity and selectivity for the determination of traces of active chlorine. The linear range is 1×10^?7?2.5×10^?5 M and the detection limit is 5×10^?8 M (3.6 μg l^?1). The method is used for the direct determination of active chlorine in tap water. The mechanism of the reaction was studied by cyclic voltammetry, electrolysis and potentiometric titration. The first peak (?0.35 V) is ascribed to the reduction of a mercury (II) sulfide film produced by reaction of the adsorbed dithio product with mercury. In the presence of 0.05 M chloride, the formation of a mixed HgS·xHg₂Cl2 film shifts the peak to ?0.31 V.     

Simultaneous measurement of trace monoadenosine and diadenosine monophosphate in biomimicking prebiotic synthesis using high-performance liquid chromatography with ultraviolet detection and electrospray ionization mass spectrometry characterization

The method for simultaneous separation and determination of trace monoadenosine and diadenosine monophosphate (i.e. 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA) in biomimicking prebiotic synthesis was developed using high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) identification. The separation was performed on a Supelco C₁₈ column with a gradient elution (solvent A: 10 mM NH₄Ac aqueous solution; solvent B: MeOH). The flow rate was set at 1.0 ml/min. The quantitative determination was achieved by HPLC with UV detection at 260 nm. The linearity ranged from 0.5 to 100 μg/ml for each nucleotide. The limits of detection (LODs) for the four nucleotides were less than 0.30 μg/ml. The recovery ranged from 95.2 to 100.7%. The intra-day relative standard deviations (RSDs) of the retention times were between 0.7 and 1.1%. Both full-scan ESI-MS and -MS² for the four nucleotides under both positive and negative polarity were carried out and the possible cleavage pathways of them were depicted. The specific ions, [AMP + H]⁺ at m/z 348 and [ApA + H]⁺ at m/z 597, were chosen to characterize the four nucleotides in biomimicking prebiotic synthesis between N-(O,O-diisopropyl) phosphoryl amino acid (Dipp-aa) and adenosine. Using the proposed HPLC/UV/ESI-MS method, the concentration of 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA in the biomimicking prebiotic synthesis samples were determined.     

兴奋剂马钱子碱的电化学氧化及其伏安法测定

以玻碳电极为工作电极，硫酸钾为支持电解质，在合适的ｐＨ条件下，通过循环伏安法，首次观测到了马钱子碱的不可逆氧化峰。在浓度为２０×１０－４～４０×１０－３ｍｏｌ／Ｌ范围内其峰电流与浓度呈线性关系，检测限为１０×１０－５ｍｏｌ／Ｌ。在正常人体的尿样中，采用标准加入法进行回收实验，其平均回收率为１００８％。该法简便、快速，用５０×１０－４ｍｏｌ／Ｌ的马钱子碱溶液重复测定１０次，相对标准偏差为１８％。对其反应机理作了初步探讨。     

邻苯二甲酰化壳聚糖的合成与溶致液晶表征

从全脱乙酰化壳聚糖出发,在室温下合成了一系列不同取代度的邻苯二甲酰化壳聚糖(PhCS),由于反应条件温和,产物未发生进一步的酰亚胺化.X射线电子能谱(XPS)被用来测定PhCS的取代度.测定结果表明在N上和O上均发生取代,N上反应的取代度随酸酐用量的增加基本保持不变(0.26±0.03),而O上的取代度却不断变大(0.01～1.54),合成产物的总取代度为0.26～1.81.邻苯二甲酰化壳聚糖可溶解于普通的有机溶剂,如DMSO、二氯乙酸和甲酸,并形成溶致液晶.测定了PhCS在这些溶剂中的临界浓度(c),结果表明c基本上不受取代度变化的影响.     

阿西美辛的合成新方法

报道了一条合成阿西美辛的新路线。以吲哚美辛为起始原料，先与溴乙酸苄酯反应制得阿西美辛苄酯，然后在AlCl₃催化下选择性脱除苄基得阿西美辛粗品，最后用丙酮和水重结晶制得阿西美辛一水合物(Acn·H₂O, CCDC: 1856291); Acn·H₂O于80 ℃真空干燥24 h得阿西美辛,其结构经¹H NMR和¹³C NMR确证。采用XRD表征了Acn·H₂O的晶体结构。结果表明：Acn·H₂O属三斜晶系，P-1空间群，晶胞参数a=7.773(3) , b=10.222(4) , c=13.517(5) , α=97.306(6)°, β=96.162(6)°, γ=106.944(6)°。     

Two New Sesquiterpenes from Ligularia lankongensis

In continuation of a systematic investigation into the chemotaxonomic and bioactive components of pyrrolizidine alkaloids and sesquiterpenoids of Ligularia plants, two new, highly oxygenated, rare bisabolene sesquiterpenes, compounds 1 and 2 , were isolated from the roots of Ligularia lankongensis. Their structures and relative configurations were elucidated by means of 1D‐ and 2D‐NMR as well as MS analyses.     

Spectrophotometric determination of trace nitrite based on catalytic oxidation of thionine by potassium bromate

A kinetic method for the determination of trace nitrite (7 × 10^?9–1.2 × 10^?6 M) based on its catalytic effect on the reaction between potassium bromate and thionine in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decreasing colour of thionine at 602 nm by the fixed-time method. At a given time of 5 min at 30°C, the detection limit is 2 × 10^?9 M (0.001 absorbance ratio, b = 1 cm) and the relative standard deviation for 1 × 10^?6 M nitrite is 2.6% (n = 6). The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural water and sausage samples without preconcentration and separation.