Multiple bond migration with participation of a protophilic agent

The pathways of migration of the double bond in the 1-methoxy-2-propene molecule with participation of a hydroxide ion were investigated by theab initio RHF/6-31+G^* and MP2/6-31+G^* methods. Stationary points corresponding to complexes between the molecule under study and the hydroxide ion and between the corresponding carbanion and a water molecule were found on the potential energy surfaces of the proton transfer reactions. As in the propene molecule, migration of the double bond in the 1-methoxy-2-propene molecule can occur in the gas phase by the mechanism of intramolecular proton transfer involving the proton of the hydroxide ion. Conformational isomerism of the initial molecule and reaction products was considered. The proposed mechanism of 1,3-hydrogen shift involving the proton-containing base suggests the formation of bothE- andZ-products with predominance of the latter irrespective of the nature of the substituent. In this case the direction of multiple bond migration will be completely determined by the energy difference between the initial reagents and final products.     

An ab initio quantum chemical study of reaction mechanisms in the C2H2/CH3OH/KOH/DMSO system

An ab initio quantum chemical study (MP2/6-311++G**//B3LYP/6-31+G*) of a number of possible interactions is performed for the gas phase system of acetylene—potassium hydroxide-dimethylsulfoxide(DMSO)—methanol and with regard to the solvent effect within the continuum model. Key structures in the vinylation reaction are shown to be methoxide ion complexes with the alkali metal hydroxide and acetylene molecules. The formation of these complexes results in the activation of the acetylene molecule and an increase in the nucleophilicity of the methoxide ion. In the C₂H₂/CH₃OH/KOH/DMSO reaction system, a proton exchange between the acetylene molecule and the anionic nucleophile ([OH]^- and [CH₃O]^-) is freely performed with the formation of systems with ethynideions, whereas the thermodynamically preferable formation of vinyl alcohol or methyl vinyl ether is determined by a barrier of 20 kcal/mol.     

Fabrication and properties of pH-sensitive nanostructured polyelectrolyte microparticles loaded with insulin

Thorough investigation and comparative study were conducted for insulin-loaded microparticles fabricated by consecutive adsorption of polyanions (dextran sulfate and chitosan sulfate) and polycations (chitosan and protamine) onto protein microaggregates. The possible regulation of insulin release from the particles by variation in polyelectrolyte pairs, in the number of their adsorption cycles and in pH of media was demonstrated. For all studied cases the microparticles showed protective action towards insulin inactivation at acid pH values and protein release at pH > 5, corresponding to human gastro-intestinal conditions.     

Interaction of methanol,methanthiol, and acetoxime with potassium and rubidium hydroxides in dimethyl sulfoxide

An ab initio quantum chemical study of the reaction profiles of the nucleophile particle formation in the interaction of methanol, methanthiol, and acetoxime with an undissociated molecule of alkali metal hydroxide is performed for the gas phase and also with the explicit inclusion of a dimethyl sulfoxide molecule into the calculation and with allowance made for solvation effects within the continuum model.     

New regio-selective method of combinatorial synthesis of substituted thiophenes,thieno[3,2-b]pyridines and other heterocycles via combination of ‘domino’-type reactions

We present a novel combinatorial multicomponent regio-selective approach towards the synthesis of thieno[3,2-b]pyridines and pyridine pyrans. The methodology is based on the ‘domino’-type reaction. The high regio-selectivity in this reaction is gained by the in situ generation of the mono-potassium salt of 2-cyano-1-mercaptoethenethiolate. We also demonstrate that the use of ethyl 2-cyanoacetate in this reaction as a CH-acid leads to the termination of the domino sequence at the Dieckmann condensation step and yields novel ethyl 3-(4-cyano-3-hydroxy-5-(alkylthio)thiophen-2-yl)-3-oxopropanoate.     

Synthesis of ethyl 3-(3-hydroxy-2-thienyl)-3-oxopropanoates

An approach to the synthesis of substituted ethyl 3-(3-hydroxy-2-thienyl)-3-oxopropanoates was developed based on the reaction of ethyl cyanoacetate, carbon disulfide, and ethyl 4-chloroacetoacetate. The reaction regioselectively involved the ester group, rather than the nitrile one like in the case when malononitrile or cyanacetamide were used.     

COMPOSITION OF INDOOR AEROSOLS AT EMPEROR QIN''''S TERRA-COTTA MUSEUM, XI''''AN, CHINA, DURING SUMMER, 2004

Particle samples were collected in August 2004 both inside and outside Emperor Qin's Terra-Cotta Museum in Xi'an, China. Mass and chemical composition of total suspended particles (JSP, particles with aerodynamic diameter less than-30μm), PM2.5(particles with aerodynamic diameter <2.5μm) were determined. The average levels of indoor PM2.5 and TSP were 108.4 and 172.4 μg·m-3, respectively, with PM2.5 constituting 62.9% of the TSP mass. Sulfate ((32.4±6.2)%), organics ((27.7±8.0)%), and geological material ((12.5±3.4)%) dominated indoor PM2.5, followed by ammonium ((8.9±2.8)%), nitrate ((7.0±2.9)%), and elemental carbon (EC, (3.9±1.5)%). Particle size distribution varied with the number of tourists in the museum. The size of sulfate, organics, EC, nitrate, and ammonium was found to vary in the range of 0.43 to 3.3 μm in fraction. Ion balance indicated that the aerosol was acidic, with insufficient ammonium ions to neutralize the sulfuric and nitric acids. High concentrations of acidic aerosols will erode the Terra-cotta warriors and horses especially in the summer season with high temperature (30℃) and relative humidity (70%) and undesirable solar radiation inside the museum. More attention should be paid to protecting these precious antiques made 2000 years ago.     

Ytterbocenes as one- and two-electron reductants in their reactions with diazadienes: YbIII mixed-ligand bent-sandwich complexes containing a dianion of diazabutadiene

Ytterbocene [Yb(C(5)MeH(4))(2)(thf)(2)] reacts with diazabutadiene 2,6-iPr(2)C(6)H(3)-N=CH-CH=N-C(6)H(3)iPr(2)-2,6 (DAD) as a one-electron reductant to afford a bis(cyclopentadienyl) Yb(III) derivative containing a DAD radical anion [Yb(C(5)MeH(4))(2)(dad(-.))]. However, ytterbocenes [YbCp*(2)(thf)(2)] (Cp*=C(5)Me(5), C(5)Me(4)H) coordinated by sterically demanding cyclopentadienyl ligands act as two-electron reductants in their reactions with DAD. These reactions occur by abstraction of one Cp* ring and result in the formation of novel Yb(III) mixed-ligand bent-sandwich complexes, [YbCp*(dad)(thf)], in which the dianion of DAD has an uncommon terminal eta(4)-coordination to the ytterbium atom. The variable-temperature magnetic measurements of complex [Yb(C(5)Me(5))(dad)(thf)] suggest the existence of redox tautomerism for this compound.