10大电源管理半导体供应商面临小型同业的竞争压力日增

据iSuppli公司报告,由于增长放缓、价格压力沉重和来自小型同业的竞争加剧,2007年最大的10家电源管理半导体供应商多数表现逊于总体市场.     

Increased yield of enzymatic synthesis by chromatographic selection of different N-glycoforms of yeast invertase

Invertases are glycosidases applied for synthesis of alkyl glycosides that are important and effective surfactants. Stability of invertases in the environment with increased content of organic solvent is crucial for increase of productivity of glycosidases. Their stability is significantly influenced by N-glycosylation. However, yeast N-glycosylation pathways may synthesize plethora of N-glycan structures. A total natural crude mixture of invertase glycoforms (EINV) extracted from Saccharomyces cerevisiae was subfractionated by anion-exchange chromatography on industrial monolithic supports to obtain different glycoforms (EINV1–EINV3). Separated glycoforms exhibited different stabilities in water-alcohol solutions that are in direct correlation with the amount of phosphate bound to N-glycans. Observed differences in stability of different invertase glycoforms were used to improve productivity of methyl β-d -fructofuranoside (MF) synthesis. The efficiency and yield of MF synthesis were improved more than 50% when the most stabile glycoform bearing the lowest amount of phosphorylated N-glycans is selected and utilized. These data underline the importance of analysis of glycan structures attached to glycoproteins, demonstrate different impact of N-glycans on the surface charge and enzyme stability in regard to particular reaction environment, and provide a platform for improvement of yield of industrial enzymatic synthesis by chromatographic selection of glycoforms on monolithic supports.     

Coordination modes of 3-hydroxypicolinic acid: Synthesis and structural characterization of polymeric mercury(II) complexes

Novel mercury(II) compounds of 3-hydroxypicolinic acid (HpicOH; IUPAC name: 3-hydroxy-2-pyridinecarboxylic acid) were synthesized and characterized. HgCl(picOH) (1) and HgBr₂(HpicOH) (2) were obtained as reaction products from the reaction of the corresponding mercury(II) halide with HpicOH, irrespective of the molar ratio of the reactants. From the reaction of HpicOH and mercury(II) acetate, Hg(picOH)₂ (3) was obtained, while mercury(II) nitrate monohydrate gave the 1/1 solvate with water Hg(picOH)₂ · H₂O (3a). Infrared, ¹H and ¹³C NMR spectroscopic data were analyzed for complexes 1, 2 and 3. X-ray crystal structure analysis of 1 and 2 revealed their polymeric nature and different coordination modes of HpicOH. In 1 the deprotonated picolinic acid is N,O-chelating and bridging, while in 2 HpicOH is a O-monodentate weakly bound ligand. Compound 1 consists of HgCl(picOH) moieties with two linear covalent bonds, Hg–N 2.143(4) and Hg–Cl 2.298(1) Å, and four additional Hg?O contacts (2.460(3)–2.904(3) Å) in which both oxygen atoms from the carboxylic group are bridging and involved in coordination to three neighboring mercury atoms, thus forming infinite layers. The coordination of mercury is 2 + 4. 2 consists of {HgBr₂(HpicOH)} moieties, which are linked into chains by means of mercury to bromine secondary long range interactions. The coordination sphere of mercury can be described as irregular 2 + 3 formed by two covalently bonded bromine atoms (Hg–Br 2.277(1) and 2.366(1) Å), two bridging bromine atoms (Hg?Br 3.309(1) and 3.247(1) Å) and by the HpicOH ligand attached to mercury in the zwitterionic form via the carboxylic oxygen atom (Hg?O 2.602(7) Å).     

Development of a rapid resolution HPLC method for the separation and determination of 17 phenolic compounds in crude plant extracts

Rapid Resolution HPLC/DAD method, on a 1.8 μm, 4.6×50 mm column, was developed to enable a rapid separation of a mixture of 17 compounds, which consisted of hydroxybenzoic acids, hydroxycinnamic acids, flavones, flavonols, flavanone, flavonol-glycoside and antraquinone, in a single run, within 22 minutes. The developed method is precise, accurate and sensitive enough for simultaneous quantitative evaluation of major compounds in crude and hydrolyzed extracts of parsley, buckthorn, mint, caraway and birch. In order to overcome the inability to quantify all the phenolic compounds present in the samples caused by lack of external standards, HPLC approaches for the total phenolic content estimation based on sum of all integrated peak areas were made. These results were compared with the total phenolic content determined by Folin-Cioacalteu method. Although the correlation between the series of data was not significant (p<0.05), the difference between the results of total phenolic content obtained spectrophotometrically and by HPLC was not high in the case of parsley, buckthorn and mint extract. Regarding the obtained results, the HPLC approach could serve as an excellent tool for total phenolic content estimation, without the need for complete identification of the individual compounds.      

Preparation,structural and thermal characterization of cobalt(II) and copper(II) complexes with 3-hydroxypicolinamide

Cobalt(II) and copper(II) complexes of 3-hydroxypicolinamide (3-OHpia), namely [Co(3-OHpia)₂(H₂O)₂](NO₃)₂ (1), [Co(3-Opia)₂(H₂O)₂] (2) and [Cu(3-OHpia)₂(NO₃)₂] (3), were prepared and characterized by IR spectroscopy and TG/DTA methods. The molecular and crystal structures of 1 and 3 were determined by X-ray crystal structure analysis. Complexes 1 and 3 were obtained by reaction of 3-hydroxypicolinamide with cobalt(II) nitrate or copper(II) nitrate, respectively, in a mixture of ethanol and water. Complex 2 was prepared by reaction of cobalt(II) acetate and 3-OHpia in aqueous solution. X-ray structural analysis revealed octahedral coordination polyhedra in both 1 and 3 and the same N,O-chelated coordination mode of 3-OHpia. The coordination sphere of the cobalt(II) center in 1 is completed by two coordinated water ligands and that of the copper(II) center in 3 by two coordinated nitrate anions. There are also two uncoordinated nitrate ions in 1 which compensate the positive charge of cobalt(II). The crystal structures of 1 and 3 are dominated by intermolecular O–H···O and N–H···O hydrogen bonds. The thermogravimetric study indicated the loss of two coordinated water molecules in 1 and 2 and of one 3-OHpia ligand together with N₂ molecule in 3 at lower temperatures (up to 300 °C).     

Thiocyanate complexes of the group 12 metals with pyridine-2-carboxamide: Synthesis and structural characterization

Three complexes of picolinamide (pyridine-2-carboxamide, pia) and metal thiocyanates, M(SCN)₂, (M = Zn, Cd, Hg), namely two polymorphs of bis(picolinamide-N,O)-bis-(thiocyanato-N)zinc(II) (1a and 1b), catena-[bis(μ-thiocyanato-S,N)-picolinamide-N,O-cadmium(II)] (2) and bis[(μ₂-thiocyanato-S-thiocyanato-S-picolinamide-N,O)mercury(II)] (3) have been prepared and characterized by spectroscopic, thermal and X-ray crystallographic methods. The IR and thermal data correlate with the structures of the complexes in the solid state. The vibration bands of diagnostic value are compared to the values of the free ligands.     

Production of porous silica microparticles by membrane emulsification

A method for the production of near-monodispersed spherical silica particles with controllable porosity based on the formation of uniform emulsion droplets using membrane emulsification is described. A hydrophobic metal membrane with a 15 μm pore size and 200 μm pore spacing was used to produce near-monodispersed droplets, with a mean size that could be controlled between 65 and 240 μm containing acidified sodium silicate solution (with 4 and 6 wt % SiO(2)) in kerosene. After drying and shrinking, the final silica particles had a mean size in the range between 30 and 70 μm. The coefficient of variation for both the droplets and the particles did not exceed 35%. The most uniform particles had a mean diameter of 40 μm and coefficient of variation of 17%. By altering the pH of the sodium silicate solution and aging the gel particles in water or acetone, the internal structure of the silica particles was successfully modified, and both micro- and mesoporous near-monodispersed spherical particles were produced with an average internal pore size between 1 and 6 nm and an average surface area between 360 and 750 m(2) g(-1). A material balance and particle size analysis provided identical values for the internal voidage of the particles, when compared to the voidage as determined by BET analysis.     

Preparation of novel meta- and para-substituted N-benzyl protected quinuclidine esters and their resolution with butyrylcholinesterase

Since the optically active quinuclidin-3-ol is an important intermediate in the preparation of physiologically or pharmacologically active compounds, a new biocatalytic method for the production of chiral quinuclidin-3-ols was examined. Butyrylcholinesterase (BChE; EC 3.1.1.8) was chosen as a biocatalyst in a preparative kinetic resolution of enantiomers. A series of racemic, (R)- and (S)-esters of quinuclidin-3-ol and acetic, benzoic, phthalic and isonicotinic acids were synthesized, as well as their racemic quaternary N-benzyl, meta- and para-N-bromo and N-methylbenzyl derivatives. After the resolution, all N-benzyl protected groups were successfully removed by catalytic transfer hydrogenation with ammonium formate (10% Pd-C). Hydrolyses studies with BChE confirmed that (R)-enantiomers of the prepared esters are much better substrates for the enzyme than (S)-enantiomers. Introduction of bromine atom or methyl group in the meta or para position of the benzyl moiety resulted in a considerable improvement of the stereoselectivity compared to the non-substituted compounds. Optically pure quinuclidin-3-ols were prepared in high yields and enantiopurity by the usage of various N-benzyl protected groups and BChE as a biocatalyst.     

[NH4][(CH3)2NH2]2[Ta(C2O4)4]·2H2O: the first (oxalato)tantalate(V) complex structurally characterized

Abstract  The compound [NH₄][(CH₃)₂NH₂]₂[Ta(C₂O₄)₄]·2H₂O has been synthesized and characterized by elemental and TG/DTA analyses, IR spectroscopy and by the single-crystal X-ray diffraction study. The structure comprises the [Ta(C₂O₄)₄]³⁻ anion, NH₄ ⁺ and [(CH₃)₂NH₂]⁺ cations and crystallization water molecules. The Ta atom is octacoordinated by oxygen atoms from four bidentate oxalate groups forming a coordination polyhedron close to the triangular dodecahedron. The charge-assisted hydrogen bonds from both cations connect the [Ta(C₂O₄)₄]³⁻ anions into a three-dimensional framework. Graphical Abstract  The synthesis and properties of [NH₄][(CH₃)₂NH₂]₂[Ta(C₂O₄)₄]·2H₂O, the first structurally characterized compound with the tetra(oxalato)tantalate(V) anion, is reported.      

Crystal Structure and Characterization of [Ni(RPOEt)<Subscript>2</Subscript>(C<Subscript>2</Subscript>H<Subscript>5</Subscript>OH)<Subscript>2</Subscript>](ClO<Subscript>4</Subscript>)<Subscript>2</Subscript> [RPOEt = bis{(diphenylphosphinyl)methyl}ethyl phosphinate]

Abstract  

The compound [Ni(RPOEt)₂(C₂H₅OH)₂](ClO₄)₂ (1) [RPOEt = bis{(diphenylphosphinyl)methyl}ethyl phosphinate] has been prepared in the form of single crystals and characterized by elemental and thermal analyses, IR spectroscopy and by a single crystal X-ray diffraction study. The complex crystallizes in the triclinic P[`1] P\bar{1} space group with a = 9.8773(5), b = 13.741(1), c = 14.287(1) ?, α = 64.313(9), β = 70.280(5), γ = 89.973(7)o, V = 1620.5(2) ?³, and Z = 1. The nickel(II) atom in 1, situated at the centre of symmetry, is coordinated by four oxygen atoms from two RPOEt ligands and two oxygen atoms from two ethanol molecules in a slightly distorted octahedral environment. The third phosphoryl-oxygen atom from the phosphinate ligand is hydrogen bonded to the oxygen atom of the ethanol molecule coordinated to nickel(II). The complex [Ni(RPOEt)₂(C₂H₅OH)₂]²⁺ cations are linked by the C–H···O hydrogen bonds into one-dimensional chains and by the composite π···π and C–H···π phenyl interactions into a final three-dimensional structure.