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.     

Aryl- and alkenyllithium preparations and copper-catalyzed reaction between the derived magnesium reagents and the monoacetate of 4-cyclopentene-1,3-diol

[reaction: see text] Aryl- and alkenyllithiums, prepared by halogen-lithium exchange with lithium, exchange with n-(or t-)BuLi, stannane-lithium exchange with n-BuLi, and direct lithiation with n-BuLi, were transformed into magnesium reagents with MgCl2 and subjected to CuCN-catalyzed reaction with the title monoacetate. Except for the halogen-lithium exchange with n-BuLi, the other preparations of the lithium anions were found to be compatible with the CuCN-catalyzed reaction to afford S(N)2-type products efficiently.     

Effective 1,5-, 1,6- and 1,7-remote stereocontrol in reactions of alkoxy- and hydroxy-substituted allylstannanes with aldehydes

Alk-2-enylstannanes with 4-, 5- and 6-alkoxy- or -hydroxy-substituents are transmetallated stereoselectively with tin(iv) halides to generate allyltin trihalides which react with aldehydes to give (Z)-alk-3-enols with useful levels of 1,5-, 1,6- and 1,7-stereocontrol. Alk-2-enylstannanes with a stereogenic centre bearing a hydroxy or alkoxy group at the 4-, 5- or 6-position, react with overall (Z)-1,5-, 1,6- and 1,7-syn-stereoselectivity with respect to the hydroxy and alkoxy substituents. The analogous reactions of alkoxy- and -hydroxyalk-2-enylstannanes with a methyl bearing stereogenic centre at the 4- or 5-position react with overall (Z)-1,5- and 1,6-anti-stereoselectivity with respect to the hydroxy and methyl substituents.     

Probing metabolic alterations in breast cancer in response to molecular inhibitors with Raman spectroscopy and validated with mass spectrometry

Rapid and accurate response to targeted therapies is critical to differentiate tumors that are resistant to treatment early in the regimen. In this work, we demonstrate a rapid, noninvasive, and label-free approach to evaluate treatment response to molecular inhibitors in breast cancer (BC) cells with Raman spectroscopy (RS). Metabolic reprogramming in BC was probed with RS and multivariate analysis was applied to classify the cells into responsive or nonresponsive groups as a function of drug dosage, drug type, and cell type. Metabolites identified with RS were then validated with mass spectrometry (MS). We treated triple-negative BC cells with Trametinib, an inhibitor of the extracellular-signal-regulated kinase (ERK) pathway. Changes measured with both RS and MS corresponding to membrane phospholipids, amino acids, lipids and fatty acids indicated that these BC cells were responsive to treatment. Comparatively, minimal metabolic changes were observed post-treatment with Alpelisib, an inhibitor of the mammalian target of rapamycin (mTOR) pathway, indicating treatment resistance. These findings were corroborated with cell viability assay and immunoblotting. We also showed estrogen receptor-positive MCF-7 cells were nonresponsive to Trametinib with minimal metabolic and viability changes. Our findings support that oncometabolites identified with RS will ultimately enable rapid drug screening in patients ensuring patients receive the most effective treatment at the earliest time point.

Rapid and accurate response to targeted therapies is critical to differentiate tumors that are resistant to treatment early in the regimen.     

Studies with 1‐functionally substituted alkyl azoles: Novel synthesis of functionally substituted azolylbenzimidazoles and functionally substituted azolyl‐1,2,4‐triazoles

ω‐Azolylacetophenones 1 and 2 react with dimethylformamide dimethylacetal to yield enaminones 7,8 that were converted into azolylazoles via reaction with hydrazine and with hydroxylamine. Compounds 1,2 also coupled with aromatic diazonium salts to yield arylhydrazones and reacted with nitrous acid to yield corresponding oximes.     

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.     

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.     

Networking particles over distance using oligonucleotide-based devices

Microparticles covered with DNA-based computing elements that sense inputs and release oligonucleotides as outputs could be used to construct autonomous networks with increasingly complex functions. We demonstrate cascades of particles with up to three layers and a nonlinear network with an AND gate hub. In order to establish functional networks, particles do not have to be in direct physical contact.     

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.     

Oxidation of Hydrogen by Metal Complexes of Platinum and Palladium Immobilized on Silica

The thermal stability of metal complexes immobilized on the surface of silica and its connection with the catalytic activity in the oxidation of hydrogen were investigated. High catalytic activity was exhibited by heterogenized platinum and palladium acetylacetonate near room temperatures in the initial state and by γ-aminopropylsilicas treated with platinum and palladium complexes. The catalytic activity of the metal complexes correlates with their thermal stability and with the ability to undergo oxidation to a metal state with high valence. This revised version was published online in August 2006 with corrections to the Cover Date.     

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 .     

Excited-state structure and dynamics of 1,3,5-tris(phenylethynyl)benzene as studied by Raman and time-resolved fluorescence spectroscopy

Excited-state structure and dynamics of 1,3,5-tris(phenylethynyl)benzene (TPB) have been studied in n-hexane and n-heptane solutions. Time-resolved fluorescence spectra, fluorescence anisotropy, and lifetime of TPB were recorded with femtosecond to nanosecond time resolution. Raman depolarization ratio was also measured to elucidate a nonplanar structure of the ground state. Two fluorescence components, the short-lived component with 150 fs lifetime and the long-lived component with 10 ns lifetime, were observed. The analysis of the fluorescence anisotropy values combined with the Raman depolarization data has led to a conclusion that TPB is primarily excited to a short-lived excited singlet state with a nonplanar structure, and then it relaxes to a long-lived excited singlet state with a 3-fold axis. A rapid structural change from a nonplanar to a planar structure is suggested to take place in the process of relaxation.     

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.     

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.     

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.     

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.     

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...     

Supramolecular hydrogels based on short peptides linked with conformational switch

Short peptides appropriately linked with an azobenzene conformational switch were found to be motif and pH dependant supramolecular hydrogelators. The hydrogelation properties of the short peptides linked with the conformational switch were studied in detail with respect to dependence on amino acid residue, pH and salt effect. The presence of amino acids with aromatic side chains such as Phe and Tyr was found to be favorable for the short peptides to gel water at an appropriate pH range. Cationic amino acid residues such as Arg and Lys in the short peptides were found to be unfavorable for hydrogelation. pH and salt effect were also found to be important factors for the hydrogelation properties of the short peptides. A series of short peptides with bioactive sequences were linked with the conformational switch and their hydrogelation properties were investigated. Photoresponsive supramolecular hydrogels were realized based on the E-/Z- transition of the conformational switch upon light irradiation. Proper combination of amino acid residues in the short peptides resulted in smart supramolecular hydrogels with responses to multiple stimuli.