Steric effects in the aerobic oxidation of pi-allylnickel(II) complexes with N-heterocyclic carbenes

Pi-allylchloro(NHC)nickel(II) complexes were synthesized and their reactions with O2 were studied. Ligand steric effects were found to determine the difference between rapid oxidation of the allyl group to produce bis-mu-hydroxonickel complexes and no observable reaction. The ability of the metal-NHC bond to rotate correlates with the ability of the complex to react with O2. In the limiting cases, conformationally restricted complexes are stable to O2 and complexes with rapid Ni-NHC bond rotation react rapidly with O2. Complexes with intermediate conformational flexibility were found to exhibit lesser reactivity with O2. On the basis of the observed inertness of complexes with saddle-shaped ligands to O2, we propose the adoption of a nonplanar geometry upon reaction with O2 to be required. The issue of conformational flexibility versus rigidity is expected to directly impact the catalytic behavior of metal-NHC complexes.     

Catalytic effect of copper on the hexacyanoferrate(III)-cyanide redox reaction-I The uncatalysed and catalysed reactions

A kinetic study of the hexacyanoferrate(III)-cyanide redox reaction has been made in connection with development of a new catalytic method for copper. The reaction kinetics change with time from first- to second-order dependence with respect to hexacyanoferrate(III). The reaction is nearly inverse first-order with respect to hexacyanoferrate(II) and first-order with respect to cyanide. The reaction shows a strong positive primary salt effect, but a very small increase in the reaction rate with temperature is found. A parallel reaction proceeds with a first-order dependence with respect to hydroxide. A tentative mechanism is proposed for the first reaction, involving the formation of cyanogen radicals. The second reaction corresponds to the well-known decomposition of hexacyanoferrate(III) in alkaline medium. The catalysed reaction exhibits similar kinetics with respect to hexacyanoferrate(II) and (III) but is zero-order with respect to cyanide and hydroxide and first-order with respect to catalyst. The proposed mechanism involves two consecutive interactions of the hexacyanoferrate(III) with copper(I) and with copper(II) cyanide complexes respectively, followed by a 2-electron oxidation of a co-ordinatively bridging cyanide group.     

Preparation of ion exchange resins from carbonaceous adsorbents

Carbonaceous adsorbents are obtained by thermolysis of sulfonated macroreticular polystyrene ion exchange resins at 300-500°C. The hard, spherical, carbonaceous particles react exothermally with elemental chlorine to form products containing up to 38% Cl. The chlorinated particles react readily with polyamines to form anion exchange resins with capacities of up to 2.2 meq/g dry resin. Less than 60% of the nitrogen atoms in the particles are utilized as ion exchange sites. The carbonaceous particles can also be chloromethylated with chloromethyl methyl ether or chlorinated with sulfuryl chloride and then aminated with polyamines to form anion exchange resins, sulfonated with sulfuric acid or chlorosulfonic acid to form strongly acidic cation exchange resins, or chlorosulfonated and then aminated with polyamines to form anion exchange resins. Model structures of the thermolyzed resins containing polycyclic aromatic hydrocarbon fragments are proposed to explain their chemical reactivities.     

Über Polyanion-Polykation-Komplexe mit Polyphosphat

Polyanion-Polycation Complexes with Polyphosphate With two Na polyphosphates of different molar weight and a series of cationic polyelectrolytes (polydimethyldiallylammonium chloride, polyethylenimine, cationically modified polyacryloamides of different charge density) polysalts (symplexes) have been prepared. The precipitates were investigated with regard to stoichiometry of cationic to anionic groups, with regard to swelling in water, and with regard to morphology. Applying special conditions of component concentration, stoichiometric 1:1 symplexes were obtained also with polyphosphate. According to our results, the cohesion in these polyphosphate symplexes is caused mainly by electrostatic forces only, in contrast to symplexes with anionic cellulose derivatives.     

Evidences of macromolecular chains confinement of ethylene–propylene copolymer in organophilic montmorillonite nanocomposites

A random ethylene–propylene copolymer (EPM) functionalized with grafted diethylsuccinate groups was melt blended with increasing amount (to 20 wt%) of organophilic montmorillonite (OMMT) to prepare nanocomposites with different morphologies as evidenced by XRD and TEM analysis. All the nanocomposites were treated with boiling toluene that did not extract a significant amount of EPM. The increase of not-extracted EPM with the increasing quantity of OMMT suggested strong interactions of the polymer chains with the inorganic substrate. The DSC measurements of nanocomposites and the corresponding insoluble residues revealed a higher T_g values with larger amount of inorganic particles. The dielectric relaxation analysis confirmed the evidence of strong interactions among montmorillonite and the polar diethylsuccinate groups for the macromolecules trapped due to the presence of the inorganic layers. The results were discussed with reference to their relevance as an evidence of nanoconfinement at polymer clay interface and correlated with the clay basal distance variation due to the intercalation process.     

Application of electron-attachment reactions to enhance selectivity of electron-capture detector for nitroaromatic explosives

The differences in the extent of electron-attachment reactions between thermal electrons and selected classes of organic molecules with high electron affinities were investigated. The investigations showed that interactions of thermal electrons with nitroaromatic compounds lead to the formation of neutral products with very low electron affinities. By contrast, a number of other analytes with high electron affinities such as polyhalogenated organic compounds, lead to products with high electron affinities. This difference was exploited to differentiate between nitroaromatic and polychlorinated organic compounds with a tandem arrangement consisting of two electron-capture detectors connected in series with an electron-attachment reactor.     

Asymmetric addition of alkylzinc reagents to cyclic alpha,beta-unsaturated ketones and a tandem enantioselective addition/diastereoselective epoxidation with dioxygen

Although over 100 catalysts have been reported to catalyze the asymmetric addition of alkyl groups to aldehydes, these catalysts fail to promote additions to ketones with >90% enantioselectivity. This paper describes the asymmetric 1,2-addition of alkyl groups to conjugated cyclic enones to give allylic alcohols with chiral quaternary centers. The resultant allylic alcohols are converted into epoxy alcohols with excellent diastereoselectivities. Treatment of the epoxy alcohols with BF3.OEt2 induces a semipinacol rearrangement to provide alpha,alpha-dialkyl-beta-hydroxy ketones with all-carbon chiral quaternary centers. We also report a one-pot procedure for the asymmetric addition/diastereoselective epoxidation reaction. Simply exposing the reaction mixture to dioxygen after the asymmetric addition reaction is complete results in epoxidation of the allylic alcohol with high diastereoselectivity.     

Gas separation membrane cascades I. One-compressor cascades with minimal exergy losses due to mixing

In this first part of this two part paper, attention is paid to the one-compressor cascades with minimal exergy loss due to mixing of streams with different compositions. The desire to avoid mixing losses leads to the development of several new binary gas separation process schemes with no exergy losses due to mixing of streams with different compositions. These schemes are simulated and compared with the “series type two unit separation cell” for higher purity/recovery separations, and with other conventional schemes for enrichment or rejection of the more permeable component. These comparisons show that schemes with no mixing losses are much more efficient than conventional schemes in most cases, although they are only marginally more efficient for low pressure side feed schemes with high permeate purity requirements.     

Amination of Bis(trimethylsilyl)-1,2-bisketene with secondary amines: formation of aminodihydrofuranones

The bisketene (Me(3)SiC=C=O)(2) (3) reacts rapidly with 1 equiv of secondary amines to form aminodihydrofuranones 11 as the only observable products. This is in contrast to previous studies (J. Org. Chem. 1999, 64, 4690) of the reactions of 3 with primary amines in which 3 with 1 equiv of amine gives ketenyl amides 4, which slowly cyclize to succinimides 7. The kinetics of the reaction of 3 with morpholine obeyed a rate law with the term [morpholine](2), consistent with rate-limiting formation of the enol amide 14 with catalysis by a second amine molecule. The subsequent formation of 11 is attributed to hindrance of ketonization of intermediate enol amides 14. The furanones 11 react with Me(3)SiOTf to form silyloxyfurans 16, and these react with diethyl diazodicarboxylate, forming maleamide derivatives 17.     

Energy fluctuations and rate of molecule evaporation from small particles

The problem of the rate of molecule evaporation from particles with fluctuating energy, which is of importance for the nucleation theory is considered. The evaporation rate of a particle with a preset energy is estimated in terms of the detailed balance principle combined with the relation describing the energy balance during molecule evaporation from a particle. The average rates of particle evaporation calculated with regard to the energy fluctuation are shown to coincide with the rates calculated from the condition of the particle-vapor thermodynamic equilibrium. At the moment of evaporation, particles with fluctuating energy have excess energy, which is, on average, equal to the heat of molecule evaporation; however, the evaporation rate of these particles is close to the value corresponding to their thermodynamic equilibrium with vapor.     

Effect of Phase Composition and Acidity on the Catalytic Properties of Molecular Sieves Containing Zirconium in Oxidative Reactions and in the Reduction of Nitrogen Monoxide

Comparative investigations of the catalytic activity of molecular sieves of different types containing zirconium showed that Zr-pentasil, doped with cobalt oxide, had considerable oxidation activity with respect to nitrogen monoxide, but SCR activity of these samples is connected to the acidity of the surface, which is necessary to activate methane to reduce nitrogen monoxide. Mesoporous molecular sieves, doped with cobalt oxide, chromium and cerium oxides, did not appear to have catalytic activity with respect to selective reduction of nitrogen monoxide with methane or propane–butane mixtures. This is connected with the effect of structural factors and the absence of acidic B-centers.     

Tributylstibine-mediated olefination of carbonyl compounds with bromomalonic ester and with dibromomalonic ester—A possible pathway through a stibonium ylide via halophilic initiation by tertiary stibines

Tributylstibine can mediate the olefination of carbonyl compounds with bromomalonic ester and with dibromomalonic ester. An initial halophilic attack of tributylstibine on the bromine of bromomalonic or dibromomalonic ester forming an ion pair of bromotributylstibonium cation and malonic (A) or bromomalonic ester carbanion (B) , respectively, is proposed. These ion pairs react with carbonyl compounds to achieve subsequent olefination. Alternatively, 2 equiv of A collapse, with elimination of malonic ester, to form stiborane D , and the ion pair B reacts with another equivalent of tributylstibine to form stiborane D. This last undergoes a Wittig-type reaction with carbonyl compound to achieve olefination.     

Studies on alkaloids binding to GC-rich human survivin promoter DNA using positive and negative ion electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the binding of 13 alkaloids to two GC-rich DNA duplexes which are critical sequences in human survivin promoter. Negative ion ESI-MS was first applied to screen the binding of the alkaloids to the duplexes. Six alkaloids (including berberine, jatrorrhizine, palmatine, reserpine, berbamine, and tetrandrine) show complexation with the target DNA sequences. Relative binding affinities were estimated from the negative ion ESI data, and the alkaloids show a binding preference to the duplex with higher GC content. Positive ion ESI mass spectra of the complexes were also recorded and compared with those obtained in negative ion mode. Only the 1 : 1 complex with berbamine was observed with lower abundance in the positive ion mass spectrum while complexes with the other alkaloids were absolutely absent. Collision-induced dissociation (CID) experiments indicate that the complexes with the protoberberine alkaloids (berberine, jatrorrhizine, and palmatine) dissociate via base loss and covalent cleavage. In contrast, product ion spectra of the complexes with the alkaloids reserpine, berbamine, and tetrandrine show the predominant loss of a neutral alkaloid molecule, accompanied by base loss and covalent cleavage to a lesser extent. A comparison of the gas-phase behaviors of complexes with the alkaloids to those with the traditional DNA binders has suggested an intercalative binding mode of these alkaloids to the target DNA duplexes.     

Novel Synthesis of Dihydroquinoxalinylpyridazine Derivatives

Methylquinoxaline derivative 1 undergoes bromination to give bromomethyl quinoxaline 2 , which could be transferred to cyanomethyl quinoxaline 3 . The latter compound 3 readily coupled with arene diazonium salts to give hydrazone derivatives 5a‐c . Compounds 5a,b reacted with active methylene reagents to give the target ring system, quinoxalinylpyridazine derivatives 8a‐c . Compound 1 reacted with DMFDMA to give the enamine derivative 9 , which coupled with arene diazonium salts to give the aldehydic hydrazone derivatives 10a‐c . Compound 10 reacted with active methylene compounds to give quinoxalinylpyridazine derivatives. UV characterization of some of the prepared compounds was reported.     

偶联剂对丙烯酸酯改性聚氨酯聚合物接枝率和乳液性能的影响

合成了含双羟基的甲基丙烯酸甘油酯(GM)并将其作为偶联剂用于聚丙烯酸酯(PAC)对水基聚氨酯(PU)的改性.采用核磁共振、红外光谱和气相色谱等对GM进行了表征.分别以该双羟基GM和单羟基的丙烯酸羟乙酯(HEA)与异氰酸酯基(NCO)封端的PU预聚体进行反应以在PU分子链上引入双键,然后再与丙烯酸酯类单体通过自由基聚合制...     

Role of thiol-disulfide exchange in insulin binding to its receptor.

The effects of reduction by DTT, oxidation by DTNB and treatment with NEM on the thiol contents and insulin binding to its receptor in mice liver membranes were studied. Reduction with DTT leads to a parallel increase in the thiol content and the specific binding of insulin to the membrane. Scatchard analysis of the results shows little change in the number of binding sites but a twofold increase of the binding constant. Washing the membrane with bound insulin by a DTT containing buffer results in a more marked increase in the release of bound insulin than washing with buffer alone, suggesting that part of the insulin is bound to its receptor by covalent disulfide linkages through a thiol-disulfide exchange reaction and reduction with DTT leads to a marked increase in this "disulfide-linked" insulin. Treatment with DTNB or NEM of the DTT-reduced membrane seems to reverse the effect of DTT reduction, although the reaction of the untreated membrane with DTNB or NEM had little or no effect on the specific binding of insulin. It is suggested that initially, part of the thiols responsible for the exchange reaction may not be available for reaction with DTNB and reduction with DTT generates further thiols leading to increased specific binding in general and increased insulin binding to the receptor through covalent disulfide linkages in particular.     

Chemistry of Substituted Quinolinones. Part 8. Synthesis and Cyclization Reactions of Ethyl 5-Amino-1-(1-methyl-2-oxoquinolin-4-YL)-3-methylsulfanylpyrazole-4-carboxylate

The synthesis of the titled amino-ester 3 is described and its hydrolysis and chloroacetylation led to the acid 5 and acetamide 7 , which were cyclized to the pyrazolopyridones 6 and 8 , respectively. Condensation of 3 with 2,5-dimethoxytetrahydrofuran afforded the pyrrolylpyrazole 9 , which underwent cyclization by action of PPA to give pyrazolopyrrolizine 10 . Treating 3 with thiophosgene gave the pyrazolyl isothiocyanate 11 , which added aniline to yield the thiourea derivative 12 , and cyclized to give pyrazolopyrimidinethiones 13-15 . Condensation of 3 with formamide furnished pyrazolopyrimidine 16 , while with triethyl orthoformate produced the ethoxymethyleneaminopyrazole 18 , which condensed with hydrazine to give the aminopyrazoloprimidine 19 . Reaction of 3 with Lawesson's reagent resulted in the pyrazolothiazaphosphinine 21 . Also the cyclization reaction of the compound 3 with malononitrile and its mixtures with carbon disulfide, phenyl isothiocyanate, or benzaldehyde led to the formation of a variety of polyfunctional substituted pyrazolopyrimidines 23 and 26 , pyrazolothiazine 24 and pyrazolopyridine 28 .     

Phototoxic and photochemical properties of sanguinarine.

Sanguinarine, a commercial drug exhibiting antimicrobial and antitumor properties, was studied with respect to its basic photochemical characteristics and also with regard to its phototoxicity to mosquito larvae (Aedes atropalpus). Sanguinarine proved to be clearly phototoxic to larvae, with an LD50 of 0.096 mg/mL with near UV exposure as compared with 23.3 mg/mL without. Flash photolysis experiments enabled the study of the triplet state of sanguinarine to be undertaken. Quenching by oxygen occurs with a rate constant of 6 x 10(9) M-1s-1 and time-resolved emission studies indicate that sanguinarine produces a significant amount of singlet oxygen (phi delta = 0.16) as does the isoquinoline alkaloid, berberine (phi delta = 0.25). These values represent the first direct quantitative measurements of photosensitization parameters of these compounds. Additionally, sanguinarine exhibits efficient electron donation properties, undergoing reaction with methyl viologen with a rate constant greater than 10(10) M-1s-1, but is a poor electron acceptor. Phototoxicity of sanguinarine can thus be explained in terms of its photosensitization properties.     

Ion-exchange properties of ammoniated lignin

The oxidative ammonolysis of hydrolysis lignin from sunflower husks has given ion-exchange materials with amphoteric properties. The greatest total exchange capacity of the sample with respect to 0.1 N caustic soda solution amounted to 11.5 meq/g, and with respect to 0.1 N hydrochloric acid solution to 0.6 meq/g. The processes of ion exchange with heavy-metal cations are accompanied by complex formation. The bond of the metal cations with the lignin in the complexes is effected through nitrogen and the oxygen of a nonalcoholic group.