Formation,growth mechanism and packing sequences of binary alloy cluster anions from laser ablation of mixtures of lead and transition metals

By using laser ablation of the mixtures of a transition metal (M: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag) plus lead, M/Pb binary cluster anions were observed except for Zn, and the number of transition metal atoms contained in the binary clusters is at most 4. This behavior is different from that reported previously for M/Ge binary clusters. The experiments indicate that it is also very difficult to form Al/Pb clusters. The distribution patterns of M/Pb binary alloy cluster anions are remarkably similar to those of pure Pb clusters, consistent with a formation mechanism in which transition metal atoms are sequentially attached to [M(x-1)Pb(y)](-) clusters and thus form [M(x)Pb(y)](-) clusters by a simple condensation process. As the number of transition metal atoms increases, the intensities of binary clusters gradually decrease. It is proposed that [MPb(4)](-) and [MPb(5)](-) cluster anions might be the unit building blocks of M/Pb binary cluster anions, and the layer packing sequences for magic clusters are predicted on this basis. The [M(x)Pb(y)](-) binary clusters containing 13 atoms (x + y = 13; x not equal 0) are proposed to have an icosahedral structure.     

A new method for inversion of hydroxyl group of carbocyclic nucleosides

The hydroxyl group of carbocyclic nucleosides was inversed when the compounds were treated with Me_3SiCl,KCN and a catalytic amount of NaI in DMF/CH_3CN.     

Improving the catalytic activity of Candida antarctica lipase B by circular permutation

Lipases (EC 3.1.1.3) play an important role in asymmetric biocatalysis. Tailoring these enzymes to novel, unnatural substrates is one of the primary challenges of protein engineering. We have used circular permutation, the intramolecular relocation of a protein's N- and C-termini, to explore the effects of altered active site accessibility and protein backbone flexibility on the catalytic performance of lipase B from Candida antarctica (CALB). Our combinatorial approach identified 63 unique functional protein permutants of CALB, and kinetic analysis of selected candidates indicated that a majority of enzyme variants either retained or surpassed wild-type CALB activity on a series of standard substrates. Beyond the potential benefits of these tailor-made lipases as new catalysts for unnatural substrates, our study validates circular permutation as a promising general method for lipase engineering.     

三乙胺与2-氯-5-甲氧基对苯醌光电子转移反应的CIDNP研究

用化学诱导动态核极化（CIDNP）方法研究了三乙胺与2-氯-5-甲氧基对苯醌在 C6D6，CH3CN溶剂中的反应机理，实验结果表明反应过程中首先形成基态电荷转移 络合物（CTC），在CD3CN中，光照电荷分离形成离子自由基对，使三乙胺亚甲基产 生发射极化信号。同时用UV-vis实验证实CTC的存在。     

Selective Determination of Trace Mercury (II) after Preconcentration with 4-(2-Pyridylazo)-Resorcinol-Modified Nanometer-Sized SiO2 Particles from Sample Solutions

A rapid, selective method that utilize 4-(2-Pyridylazo)-resorcinol (PAR)-modified nanometer SiO₂ (nanometer SiO₂–PAR) as a new solid-phase extractant for preconcentration of trace mercury (II) has been developed. The adsorption property of nanometer SiO₂–PAR for metal ions was studied by selectively extracting different metal ions from aqueous solutions. The results revealed an excellent affinity of the nanometer SiO₂–PAR for mercury (II) in presence of interfering metal ions at pH 4. The main parameters of solid-phase extraction such as shaking time, elution and sample dilution effect were studied. The extractant shows rapid kinetic sorption, and the adsorption equilibrium of mercury (II) on nanometer SiO₂–PAR was achieved in less than 2 min. The adsorbed mercury (II) was easily eluted by 4 mL of 6 mol L⁻¹ HCl. The maximum preconcentration factor was 50. The maximum static adsorption capacity was 276 μmol g⁻¹ at pH 4. The detection limit (3σ) was 0.43 μg L⁻¹ for cold vapor atomic absorption spectrometry (CVAAS), and the relative standard deviation of the eight replicate determinations was 2.4% for the determination of 2.0 μg of Hg(II) in 100 mL water sample. The method was applied to the determination of trace mercury (II) in sample solutions with satisfactory results.     

Physically adsorbed chiral stationary phase of avidin on monolithic silica column for capillary electrochromatography and capillary liquid chromatography

The physical adsorption method proposed previously has been successfully applied to a monolithic silica column. By virtue of the physical adsorption, a chiral stationary phase of avidin was prepared onto the silica monolith. The phase ratio of resulting stationary phase was evaluated with frontal analysis. The method proved to be comparable in phase ratio to the chemical bonding methods used in high-performance liquid chromatography (HPLC). Enantiomer separations were carried out in capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) modes. Due to its larger phase ratio, the resulting column showed more powerful separation capability as compared to open-tubular CEC (OTCEC). Twelve chiral compounds were baseline-resolved. The resulting column showed high separation efficiency, with average theoretical plate numbers of 66 000/m for CLC and 122 000/m for CEC. Good reproducibility was observed, with RSD value less than 1.3% for retention time, retention factor and separation factor, and less than 6.6% for plate counts and resolution (n = 40). Fast separations were achieved with a short column. The test enantiomers were baseline-resolved within 4 min under CLC and CEC modes. In addition, field-enhanced sample injection (FESI) was coupled to CLC as well as CEC to improve the detection sensitivity.     

氮杂冠醚研究Ⅶ、双仲胺型氮杂冠醚对过渡金属离子的选择性萃取作用

合成了五种新型双仲胺型氦杂冠醚，研究了它们对过渡金属离子进行液—液萃取，并用原子吸收法测定其浓度。实验结果表明：这类冠醚对Ａｇ￣＋、Ｐｄ￣（２＋）、和Ｐｔ￣（４＋）等贵金属离子有较强的选择配位性能，对选择性分离这些金属离子有重要的意义。     

壳聚糖修饰玻碳电极卷积伏安法测定环境水中的EDTA

制备了壳聚糖修饰玻碳电极 ,研究了Fe(EDTA) -在修饰电极上的吸附还原行为 ,用卷积伏安法通过Fe(EDTA) -的检测测定了环境水中的EDTA。在优化的实验条件下 ,峰电流值与 8.0× 1 0 -7～ 5 .0× 1 0 -6mol L的EDTA呈线性关系 ,回归方程为epp′ =0 .75 2 5c - 0 .661 3,r =0 .991 ,最低检出限为 5 .0× 1 0 -7mol L ,5次测定的相对标准偏差小于 5 .8%。对实际样品测定的回收率为98 1 %～ 1 0 5 % ,对比HPLC的结果 ,相对偏差小于 5 %。     

Fe-Co-Ni合金纳米线有序阵列的模板合成与磁性

以二次阳极氧化的氧化铝膜为模板，用电化学沉积的方法成功地合成了Fe-Co-Ni三组份有序纳米线阵列.扫描电子显微镜（SEM）和透射电子显微镜(TEM)观察表明纳米线表面光滑、有序、高长径比；磁性测量表明,其矫顽力较同组份的膜材料有较大的提高.将样品在惰性气体氛围中不同温度下退火，随着退火温度增加，其纵向矫顽力有一个极值，而对应的横向矫顽力没有类似的变化，关于这一现象的机理,本文进行了初步的讨论. 图5参15     

Electrodeposition of nanocrystalline zinc from acidic sulfate solutions containing thiourea and benzalacetone as additives

Nanocrystalline zinc coatings were produced by pulse electrodeposition in acid sulfate bath containing thiourea and benzalacetone additives and characterized by X-ray diffraction and scanning electron microscopy techniques. The influence of benzalacetone concentration and pulse peak current density on the grain size and crystallographic orientation of zinc deposits was investigated. Zinc electrodeposited from additive-free solutions or with one of the two additives is not composed of nanosized crystals. The mixture additives of thiourea and benzalacetone give rise to the formation of particle-like nanocrystalline zinc with a (10ī1) random orientation. A change in peak current density from 2 to 1 A/cm² only increases the grain size from 60 to 62 nm.