Donor–Acceptor Mechanism of Complex Formation

The gas-phase van der Waals complexes formed in the course of donor–acceptor interaction are shown to become coordination compounds only in the crystalline state. With close lengths of the covalent-ionic and coordination bonds, their energies differ by 100 kJ. This energy difference is due to the work spent to overcome van der Waals forces during the formation of complex ions from interacting molecules.     

Carbon–Carbon Bond Formation via Catalytically Generated Aminocarbene Complexes: Rhodium-Catalyzed Hydroaminative Cyclization of Enynes with Secondary Amines

We report a hydroaminative cyclization of enynes using phosphine-quinolinolato rhodium catalysts. The hydroaminative cyclization of 2-vinylphenylacetylene derivatives with secondary amines gives 2-aminoindenes in good yields. The reaction is considered to proceed through carbon–carbon bond formation on a catalytically generated aminocarbene ligand.     

Use of Iodosobenzene in Combination with Vilsmeier–Haack Reagent in Carbon–Carbon Bond Cleavage of Dehydroacetic Acid and Its Analogue

The reaction of dehydroacetic acid with iodosobenzene in combination with Vilsmeier–Haack reagent offers a new and convenient method for C‐C bond cleavage with the formation of 3‐chloro‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one.     

Simulation of the Carbon Synthesis Process in Atmospheric-Pressure Microwave Discharge in an Argon–Ethanol Gas Mixture

High Energy Chemistry - A self-consistent model has been formulated that describes microwave discharge in an argon/ethanol gas mixture. On the basis of this model, two-dimensional numerical...     

Nitrogen–Carbon Bond Formation by Reactions of a Titanium–Potassium Dinitrogen Complex with Carbon Dioxide,tert-Butyl Isocyanate,and Phenylallene

Nitrogen–carbon bond-forming reactions at coordinated dinitrogen in a bifunctional titanium–potassium system are reported. A titanium atrane complex with a tris(aryloxide)methyl ligand ( 1 ) was treated with two equivalents of potassium naphthalenide under N₂ atmosphere to generate a bifunctional complex ( 2 ) in which N₂ binds end-on to two titanium centers and side-on to three potassium cations. Dinitrogen complex 2 reacted with carbon dioxide, tert-butyl isocyanate, and phenylallene, forming nitrogen–carbon bonds and affording diverse N-functionalized products. The reaction of 2 with CO₂ followed by addition of Me₃SiCl resulted in the formation of the starting complex 1 with concomitant release of silylated carboxyl hydrazines while the reaction with two equivalents of tert-butyl isocyanate proceeded by insertion into the Ti−N bonds. Treatment of 2 with phenylallene afforded vinyl-substituted hydrazido complexes.     

Hypervalent-Iodine-Mediated Carbon–Carbon Bond Cleavage and Dearomatization of 9H-Fluoren-9-ols

A transition-metal-free synthesis of spiro compounds from 9H-fluoren-9-ols mediated by hypervalent iodine is reported. In this reaction, an unprecedented β-carbon elimination of tertiary alkoxyliodine(III) to form new diaryliodonium salts is proposed. The obtained phenol intermediates undergo oxidative dearomatization to furnish a class of oxo-spiro compounds. This domino reaction significantly increases the complexity of these molecules and shows excellent regio- and stereoselectivity.     

Promotion of the Direct Electron Transfer of Hemoglobin by the Carbon Nanotube

It is reported that the direct electron transfer of hemoglobin (Hb) can be effectively promoted by carbon nanotubes when Hb was immobilized on the surface of the carbon nanotubes modified electrode. The results indicated that the conversion of Hb-Fe(Ⅲ)/Hb-Fe(Ⅱ) is a one-electron coupled one-proton reaction process. The method presented can be easily extended to study the direct electrochemistry of other proteins or enzymes,     

Formation of the layering boundary in the water–benzene–perfluorobenzene system

The dynamics of the interface between liquid phases in the water–benzene–perfluorobenzene system was studied in a natural experiment. The interfacial tension was found to depend on the density of the organic layer. The range of interfacial tensions in which inversion of the organic and aqueous phases takes place was determined, and the working range of a separating flask as an element of the separation scheme for the mixture was revealed.     

Carbon Deposits Formed on the Surface of Ru–Ni Catalysts During the Mixed Reforming of Methane Process

Monometallic nickel and bimetallic ruthenium–nickel catalysts supported onto aluminum oxide without additives and aluminum oxide modified with MgO and CaO were prepared by an impregnation method. The catalysts were tested in the process of the mixed reforming of methane, and their properties were characterized by thermogravimetry, scanning electron microscopy, and X-ray diffractometry. The total organic carbon content of the catalysts was also measured. The promoting effect of ruthenium and structural promoters on the catalytic activity of Ni/Al₂O₃ was confirmed. The Ru–Ni/MgO–Al₂O₃ catalyst exhibited the highest stability and activity; this fact can be explained by the increased adsorption of methane on the surface of ruthenium–nickel clusters.     

Efficient Covalent Bond Formation in Gas-Phase Peptide–Peptide Ion Complexes with the Photoleucine Stapler

Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* _n L _m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N₂ from the L* diazirine rings underwent insertion into X?H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific ¹³C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)⁺ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]⁺ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide–peptide ion interactions in the gas phase.

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Impedance Characterization of the Film Formation Process at the Graphite Anodes

A passive SEI (Solid electrolyte interface) film had been suggested to be formed on the graphite anodes with the irreversible capacity loss at ca. 1.20V in the first charge process by Fong et al. And the capacity loss at ca. 0.75V was originated from the electrolyte decomposition on the new surface created by the exfoliation of the graphite structure for solvent co-intercalation1. Aurbach et al studied the surface chemistry of the insulating film on the graphite electrodes in different elect…     

A Kinetic Evidence for the Nitroxyl Radicals Recycling Mechanism in the Photostabilizing Process of HALS

The photoinduced bulk polymerization of a reactive-hindered amine fight stabilizers(r-HALS), 4-acryloyl-2, 2, 6, 6-tetramethylpiperidinyl (ATMP), was performed at 80℃ by using a DPC technique. An unique periodic exponential attenuation-type oscillating curve was found when the polymerization was carried out in air, but this phenomenon was not found in nitrogen.It is supposed that this unique kinetic performance may be attributed to nitroxyl radicals that are produced in situ from the oxidation of ATMP. ATMP polymer with narrow polydispersity (d =1.03) can be obtained by photoinduced solution polymerization of ATMP. The signal detected in ESR may be assigned to the nitroxyl radicals in the matrix of ATMP polymer. Since this kind of recycling of nitroxyl radicals is well documented for the photostabilizing mechanism of HALS, the present results may serve as a kinetic evidence for this mechanism.     

Carbon–Carbon Bond Formation by Radical Cyclization: Regioselective Synthesis of Spiro Heterocyclic Compounds by n Bu3SnH‐Mediated Reaction

Several spiro heterocyclic compounds have been regioselectively synthesized in excellent yield by ⁿ Bu₃SnH‐AIBN‐mediated radical cyclization of 4‐(2′‐bromoaryloxymethyl)‐1‐methylquinolin‐2(1H)‐ones in refluxing benzene under nitrogen for 4 h.     

TEM Study on the Formation Process of TiO2 Nanotubes

The process,that the polycrystalline TiO2 powders were converted into TiO2 nanotubes,was observed with transmission electron microscope.The results obtained indicated that in concentrated NaOH aqueous solution,anisotroplc swelling appears on the polycrystalline TiO2 granula at first,and then the nanotubes are formed.     

Studies on the Mechanism of the Direct Synthesis of Styrene form Benzene and Ethylene

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The Role of Iron–Carbon Galvanic Contact in the Formation of Dispersed Iron Hydr(oxides) in Water and Electrolyte Solutions

The comparative analysis of phase formation on the iron surface in aqueous medium in the presence and absence of iron–carbon (coke) galvanic contact was carried out. The role of galvanic contact in phase formation processes was determined. It was shown that, in the presence of galvanic contact almost complete oxidation of iron ions on the surface of an iron half-element and a rather efficient stationary formation of dispersed phases serving as sorbents of heavy metals from solutions take place. The effect of anionic composition of solution on the parameters of phase formation was studied. It was established that maximal amount of iron–oxygen-containing phases is formed in zinc chloride solution. The presence of sulfate and nitrate ions in solution decreased significantly the rate of phase formation in iron–carbon galvanic contact.     

Induced Collapse in the Formation of Alternating Langmuir–Blodgett Films

Two compounds whose molecules have large dipole moments, strereoregular perfluorinated alkylmethacrylate-co-methacrylic acid (A) and p-octadecylaminoazobenzene-p"-sulfamide (B), were used to assemble Langmuir–Blodgett polar films by the alternating method to achieve high polarization. According to estimates, the dipole moment of the dimeric unit of copolymer A is equal to about 4 D, the dipole moment of compound B, to 12 D. Unusually high (several units) transfer ratio was observed for the monolayer B when preparing the structures of (AB) _n type. The monolayers were stable during their formation process. Upon the pause of a substrate when passing through the monolayer B, the monolayer area remained strictly constant. According to the model proposed, the monolayer looses its stability and locally collapses in the meniscus zone at the contact line of the monolayer B and substrate due to an increase in the electrostatic repulsion between the dipoles of molecules B. The validity of this model is confirmed by the data of small-angle X-ray diffraction and atomic force microscopy for various alternating Langmuir–Blodgett films.     

Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate

Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev…     

Mechanism of the molecular mobility of water in the temperature range 298–359 K

The Raman spectra of liquid water in the region of O-H stretching vibrations were obtained in the temperature range 298–359 K. The Raman spectra were decomposed into the components using the XPSPEAK-4.1 program, and their temperature dependence was evaluated. The number of bifurcate hydrogen bonds and the percentage of rotational conformers containing bifurcate bonds were shown to increase with temperature. The defect mechanism of the molecular mobility of water on the hydrogen bond network in the temperature range 298–359 K was proposed.