Electrokinetic Separation Methods

Electrophoresis is the transport of dissolved molecules or suspended particles in a homogeneous polar liquid (such as water) under the influence of an electric field. Most molecules or particles acquire a surface electric charge when dissolved or suspended in buffered water (or other polar liquids), owing to ionization or adsorption of ions present in the water. The sign of the surface charge of molecules or particles determines whether they will migrate towards the positive or the negative electrode of the applied electric field, and the velocity of migration depends on the surface potential of the molecules or particles, as well as on the potential of the electric field.     

Effect of surfactants on the stability of thin liquid film flow on a rotating disk

The effect of surfactants on surface instabilities of thin liquid film flow on a rotating disk was studied at different flow rates Q (0.5相似文献   

Reaction of 3,4-disubstituted 1,2,5-oxadiazole 2-oxides with dipolarophiles : Substituent and solvent effect on the reaction courses

A variety of symmetrically or unsymmetrically 3,4-disubstituttd furoxans such as dicyano, dialkyl, diacyl, bis(phenylsulfonyl), N.N'-dialkyldicarbamoyl, 3(or 4)-methyl-4(or -3)-phenyl(or nitro, ethoxy, phenoxy, phenylthio, pyrrolidinyl, phenylsulfonyl), 3(or 4)-ethyl-4(or -3)phcnyl, and 3(or 4)-ethoxy-4(or -3)-phenylsulfonylruroxan reacted with dipolarophiles in toluene or xylene at the refluxing temperature to give nitrone-type 1,3-dipolar cycloadducts, 5-substituted 1-aza-2,8-dioxabicyclo-[3.3.0]octanes and/or 3-substituted 2-isoxazoline 2-oxides. On the other hand, some of the furoxans gave 2-isoxazolines via nitrile oxide 1,3-dipolar cycloaddition in a toluene (or xylene)-DMF solvent at the refluxing temperature.     

Alkylation of 4,5-dichloropyridazin-6-one with α,ω-dibromoalkanes or 4,5-dichloro-1-(ω-bromoalkyl)pyridazin-6-ones

Alkylations of 4,5-dichloropyridazin-6-one (1) with dibromoalkanes 2 or 3 in the presence of potassium carbonate or tetrabutylammonium bromide/potassium hydroxide were investigated under restricted condition. Reactions of 1 with 2 or 3, except for 2b and 3b , in the presence of potassium carbonate or tetrabutylammonium bromide/potassium hydroxide gave only the N-alkylation products 3 and/or 4. Alkylation of 1 with 2b or 3b in the presence of potassium carbonate yielded the N-alkylation products 3b and/or 4b and the O-alkylation product 5 as the main product, whereas treatment of 1 with 2b or 3b in the presence of tetrabutylammonium bromide/potassium hydroxide afforded selectively the N-alkylation products 3b and/or 4b.     

Synthesis of 2'-deoxyadenosine nucleosides bearing bipyridine-type ligands and their Ru-complexes in position 8 through cross-coupling reactions

The synthesis of the title 2'-deoxyadenosine derivatives bearing bipyridine, phenanthroline or terpyridine ligands and their corresponding RuII-complexes in position 8 linked via acetylene or phenylene tethers was accomplished through cross-coupling reactions. The Suzuki-Miyaura reactions of boronic acids or the Sonogashira reactions of terminal acetylene derivatives of oligopyridine ligands were performed either on protected 8-bromoadenosines in organic solvents or, more efficiently, directly on unprotected nucleosides in aqueous acetonitrile or DMF. Direct cross-coupling reactions of unprotected nucleosides with RuII-complexes or the oligopyridine-boronic acids or -acetylenes gave the Ru-labelled nucleosides in one step in fair to good yields. This method was also proven to be applicable for direct Ru-labelling of dATP. Terpyridine-containing 2'-deoxyadenosine exerted significant antiviral and cytostatic effects.     

Structural evolution of anionic silicon clusters SiN (20 <or= N <or= 45)

Results of a combined photoelectron spectroscopy and first-principles density-functional study of SiN- clusters in the size range 20 or= 20. For 28 相似文献   

Organic-inorganic nanohybrids through the direct tailoring of semiconductor nanocrystals with conjugated polymers

Two main synthetic strategies are used to prepare conjugated oligomer- or polymer-nanocrystal nanohybrids. In the first strategy ligand exchange is invoked to either replace with a bifunctional ligand, which contains a second functional group for coupling with conjugated oligomers or polymers (COs or CPs), or exchange for the functionalized COs or CPs in a "grafting-onto" process. Alternatively, in the second strategy the nanocrystal (NC) is passivated with functional ligands from which COs or CPs are directly grown in the absence of ligand exchange. The well-defined interface between the COs or CPs and NCs facilitates an efficient charge-transfer between them.     

Application of tin and nanometer tin in allylation of carbonyl compounds in tap water

[reaction: see text] Nanometer tin-mediated allylation of aldehydes or ketones in distilled or tap water gave rise to corresponding homoallyl alcohol in high yield without any other assistance such as heat or supersonic or acidic media.     

Lewis acid-promoted deoxygenative di[beta,beta-bis(ethylthio)]vinylation of aldehydes with trimethylsilylketene bis(ethylthio)acetal

Silylketene dithioacetal 1 reacted with aldehydes 2a-o, 14, or cinnamaldehyde (11) in the presence of Lewis acid to give deoxygenative divinylation products, 3-substituted 1,4-pentadienes 3a-o, 15, or 5-phenyl-1,3,6-heptatriene 13b, in good to moderate yields. Similar reaction with 2-aminobenzaldehyde (16) or salicylaldehyde (17) produced quinoline 19 or chroman 20 in 40-58% yield. Treatment of 1 with alpha-diketones 22a-c or alpha-ketoester 24 led to tetrasubstituted furans 23a-c or allylic alcohol 25, respectively, in rather low yields. The formation mechanisms of these products are discussed.     

Stacking design of inverse perovskites: the systems (Sr3-xBaxN)E, E = Bi, Sb

The first representatives of 4H (BaMnO3-type structure, P63/mmc, Z = 4) and 9R (BaMnO3-type structure, Rm, Z = 9) inverse Perovskite phases are presented. The phases are obtained within the solid solutions (Sr3-xBaxN)E with E = Bi, Sb. The crystal structures and homogeneity ranges were studied by combined X-ray and neutron diffraction as well as chemical analyses. The cubic Perovskite phase with Bi (Sb) is stable in the range of 0.00 < or = x < or = 0.90(5) (0.00 < or = x < or = 1.30(5)), the 4H variant is stable for 1.55(5) < or = x < or = 2.10(5) (1.85(5) < or = x < or = 2.45(5)), the 9R structure is stable for 2.50(2) < or = x < or = 2.55(2) (2.56(2) < or = x < or = 2.60(2)), and the 2H phase is stable for 2.75(5) < or = x < or = 3.00 (2.80(5) < or = x < or = 3.00). Ba occupies preferable sites in the hexagonal stacking of close packed layers of alkaline earth metal ions and E3-; Sr is mainly located in cubic stacked layers. The phase order upon going from cubic (Sr3N)E to 2H-type (Ba3N)E concomitant to the pronounced Sr/Ba partial order can, in general, be rationalized considering the Coulomb repulsion of nitride ions, as well as the size and charge density of the alkaline earth metal ions.     

Preliminary Investigation on the Action Modes of an Oligosaccharide-Producing Multifunctional Amylase

The action modes of an oligosaccharide-producing multifunctional amylase (OPMA) were investigated using glucose and some oligosaccharides as its substrates. OPMA did not cause the hydrolysis of maltose or isomaltose, but it catalyzed the α-1,6-transglycosylation of maltose to produce isomaltose or did the self-condensation of isomaltose to form isomaltotetraose and 4-O-α-isomaltosyl isomaltose. OPMA exhibited strong α-1,6-transglycosylation activity in addition to its α-1,4-hydrolytic activity on higher oligosaccharides substrates rather than bisaccharides. OPMA displayed high acceptor specificity in its transglycosylation or condensation reaction. OPMA seemed to only take glucose or isomaltose as the acceptor molecule in its transglycosylation or condensation reaction, which made glucose or isomaltose form higher products, and as a result, glucose or isomaltose were absent in the final products. In view of the simultaneously formation of several transglycosylation or condensation products, it was predicted that there might be separate donor and acceptor sites in OPMA’s active center and the fact that the catalytically active form of this enzyme included its homodimer or homotrimer supported this prediction. Accordingly, a special pathway, isomaltose pathway, for OPMA catalysis was proposed to emphasize the central or important signification of isomaltose in OPMA catalysis.     

三甲基硅化合物复合体系引发1,3-戊二烯阳离子聚合研究

研究了三甲基硅化合物 ,主要是三甲基硅酯和三甲基硅氯化物 (TMSCI)与路易斯酸所形成的复合引发体系引发聚合 ,1,3 戊二烯 (PD)的聚合反应行为 ,考察了引发体系引发PD聚合所得聚合物的产率 ,分子量及分子量分布 ,聚合反应速率和聚合反应机理等 ;研究了多种给电体———醚、酮对聚合反应的影响     

Lebensmittelinhaltsstoffe und ‐kontaminanten: Aus toxikologischer Sicht

Food contains a variety of compounds of natural origin that may be harmful when consumed too frequently or at a very high dose level or under inappropriate conditions. Examples for such constituents include the glucosinolates in cabbage or tyrpsin inhibitors in raw beans. Other constituents such as vicin in broad beans or glycyrrhizic acid in liquorice may be harmful for a subpopulation only, e.g., in patients suffering from high blood pressure or in individuals bearing certain genetic defects of metabolism. Furthermore, food may contain compounds which have been added by purpose (legal food additives) such as emulsifiers, preservatives, synthetic colors etc. These compounds are under strict regulation and their safety has been tested rigorously. Contaminants in food such as dioxins, pesticides, drug residues etc. may originate from illegal or inappropriate production or treatment. At lower levels they may reflect background contamination, e.g., in the environment. Finally, nutritional supplements and ingredients of ‘functional food’ require special toxicological testing and evaluation since not all compounds considered as ‘healthy’ in certain concentrations are also beneficial or safe when consumed at higher doses.     

Mass fragmentographic determination of 4-hydroxy-3-methoxyphenylglycol (HMPG) in urine, cerebrospinal fluid, plasma and tissues using a deuterium-labelled internal standard.

4-Hydroxy-3-methoxyphenylglycol (HMPG) with the three hydrogen atoms in the side-chain replaced with deuterium (HMPG-D3) was used as the internal standard in the mass fragmentographic determination of free and conjugated HMPG in human urine, cerebrospinal fluid and plasma and in rat urine, liver and brain. HMPG-D3 was added to body fluids or homogenates followed by enzymatic hydrolysis of conjugates. HMPG was extracted with ethyl acetate, converted into the trifluoroacetyl derivative and analyzed by mass fragmentography. HMPG levels were 7.4 nmoles/ml plus or minus 2.8% in human urine, 73 pmoles/ml plus or minus 8.2% in human cerebrospinal fluid, 56 pmoles/ml plus or minus 5.4% in human plasma, 24 nmoles/ml plus or minus 3.6% in rat urine, 0.26 nmoles/g plus or minus 6.2% in rat brain and 99 pmoles/g plus or minus 13% in rat liver. The method is highly specific and sensitive, permitting analysis in small samples or in plasma and in tissues for which previously no methods for HMPG analysis were available.     

Synthesis of polydentate chalcogen-containing ligands using the system hydrazine hydrate–base

The reaction of dichlorodiethyl ether or dichlorodiethylamine hydrochloride with potassium or ethanolammonium dichalcogenides prepared in situ from elemental sulfur or selenium in the system hydrazine hydrate–alkali results in oligomeric dichalcogenides, whose further splitting at the chalcogen–chalcogen bond in the same system and subsequent alkylation affords bis(organylsulfanyl)- or bis(organylselanyl)-substituted derivatives of diethyl ether or diethylamine. Ligands with aryl substituents at the chalcogens have been prepared in 48-59% yield by splitting of diaryldichalcogenides in the system hydrazine hydrate–alkali and subsequent reaction with dichlorodiethyl ether or dichlorodiethylamine. A ditopic tetradentate ligand has been synthesized by the use of dichlorodiethylformal.     

Cobalt-catalyzed direct electrochemical cross-coupling between aryl or heteroaryl halides and allylic acetates or carbonates

The electroreduction of a mixture of functionalized aromatic or heteroaromatic bromides or chlorides and allylic compounds such as acetates or carbonates in an electrochemical cell fitted with a sacrificial iron anode affords, in the presence of cobalt halide associated with pyridine as ligand in acetonitrile or DMF, the corresponding coupling product in good yields.     

Regulation of lymphocyte transformation responses to phytohaemagglutinin,concanavalin A or lipopolysaccharide by normal serum

Lymphocyte blastogenesis of guinea-pig spleen cells induced by various loses of phytohaemagglutinin (PHA), concanavalin A (conA) or lipopolyaccharide (LPS) was assayed in the absence or in the presence of normal guinea-pig serum, foetal calf serum or heterologous albumin or gamma-globulins. Opposute effects of diluted and of concentrated sera were observed in blastogenesis induced either by PHA or by ConA: high concentrations inhibited blastogenesis whereas low concentrations enhanced mitogenesis. Homologous serum inhibited LPS-induced blastogenesis whatever the concentration used. These results could be explained by the interaction of serum with the membrane of lymphocytes stimulated by ConA, PHA or LPS. Furthermore sera could interfere with ConA. The implications of these experiments are discussed.     

Expedient synthesis of pseudo-Pro-containing peptides: towards constrained peptidomimetics and foldamers

The reaction of sulfonyl peptides containing L- or D-configured Ser or Thr with bis(succinimidyl) carbonate in the presence of a catalytic amount of a base affords, in solution or in the solid phase, the corresponding peptides with one or two, consecutive or alternate oxazolidin-2-ones (Oxd). The Oxd ring can be regarded to as a pseudo-Pro with an exclusively trans conformation of the preceding peptide bond; homochiral Oxd-containing peptides adopt extended conformations, while the presence of a D-configured Oxd favours folded conformations.     

Cascade cyclization intermolecular dipolar cycloaddition by multi-component couplings—synthesis of indolizidines and pyrrolizidines

A three-component coupling reaction of a primary amine (an amino-acid or amino-ester or hydroxylamine), an alkene or alkyne dipolarophile and an aldehyde bearing a halide as a leaving group has been developed. Condensation of the amine with the aldehyde and cyclization (intramolecular N-alkylation) provides, after decarboxylation or deprotonation, a cyclic azomethine ylide (or nitrone) that undergoes intermolecular dipolar cycloaddition with the dipolarophile. This sets up, in a single step, the bicyclic indolizidine or pyrrolizidine ring system, depending on the length of the tether between the aldehyde and the halide. The reaction is successful with stabilized and non-stabilized azomethine ylides that result from using primary amino-esters or amino-acids, respectively.