Ab initio molecular orbital study of the reactivity of active alkyl groups. V. Nitrosation mechanism of acetone with syn-form of methyl nitrite

The mechanisms of nitrosation of acetone through sodium enolate [CH3CO1CH2]-Na+ (1) or naked enolate [CH3CO1CH2]- (2) with methyl nitrite CH3O3NO2 (3), and the reactivity of the syn-form of 3 (syn-3) during the C-N bond formation process were investigated using ab initio molecular orbital (MO) methods. Our results have demonstrated the predominant formation of E-1-hydroxyimino-2-oxo-propane CH3COCH=NOH (4E) when the complex [CH3CO1CH2NO2(O3CH3)]-Na+ was produced kinetically via a metal-chelated pericyclic transition state (TS(CHELATED)), in which the O3 atom of syn-3 was coordinated to the Na+ atom of 1.     

A regiocontrolled synthesis of substituted indoles by palladium-catalyzed coupling of 2-bromonitrobenzenes and 2-bromoacetanilides

The palladium-catalyzed cross-coupling reaction of 2-bromonitrobenzenes or 2-bromoacetanilides with ethylene has been used to produce a variety of substituted indoles. The mild reaction conditions and selectivity inherent in the coupling reaction have been utilized to produce regiochemically pure 4-, 5-, 6-, and 7-substituted indoles.     

Natural products and Chagas' disease: a review of plant compounds studied for activity against Trypanosoma cruzi

Here, we review studies that have investigated the activity of plant-derived compounds against Trypanosoma cruzi, the etiologic agent of Chagas’ disease. In the last decade, more than 300 species belonging to almost 100 families have been evaluated for activity, and here we describe the compounds isolated; 85 references are cited.     

Acceleration of the reaction OH + CO → H + CO2 by vibrational excitation of OH

The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO.     

Reversible Chain Transfer Catalyzed Polymerizations (RTCPs) of Styrene and Methyl Methacrylate with Phosphorus Catalysts

Summary : Phosphorus compounds were employed as catalysts in Reversible Chain Transfer Catalyzed Polymerization (RTCP), a novel class of living radical polymerization (LRP) which we had recently developed. Low-polydispersity polystyrene and poly(methyl methacrylate) with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. These catalysts are particularly featured by their high reactivity hence small amounts being required, low toxicity, and low cost. Some phosphorus catalysts used in this work are among the least expensive catalysts/mediators of LRP developed so far.     

Kinetics of hydrogen bonding between anthracene urea derivatives and anions in the excited state

Urea compounds are useful anion sensors due to their hydrogen-bonding capabilities. We investigated the emissive properties of complexes consisting of urea-anthracene (nPUA, n = 1, 2) host compounds and acetate anions held as guests through intermolecular hydrogen bonding. The kinetics of a new emission band formed by conformational changes in the excited singlet state were revealed. The new band is thought to arise from a charge-transfer interaction between the anthracene and urea moieties after intermolecular hydrogen-bond reconfiguration in the excited state, with rate constants of 2.4 × 10(9) and 4.0 × 10(7) s(-1) for 1PUA and 2PUA, respectively.     

Real-space observation of local anisotropic correlation between buckled dimers on Si(100) induced by a bidentate adsorbed molecule

The anisotropic correlation between buckled dimers on Si(100) was investigated by scanning tunneling microscopy. A bidentate ligand molecule was used to pin two neighboring dimers at 300 K. The chemically pinned dimer induces antiferromagnetic interaction along the dimer rows. Observed results agree well with Monte-Carlo simulations semi-quantitatively.     

Direct measurement of interactions between stimulation-responsive drug delivery vehicles and artificial mucin layers by colloid probe atomic force microscopy

A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed.     

pH-responsive aqueous foams stabilized by hairy latex particles

Polystyrene (PS) latex particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA) hair (PDEA-PS particles) were synthesized by dispersion polymerization and characterized in terms of diameter, diameter distribution, morphology, chemical composition, surface chemistry, and pH-response using scanning electron microscopy (SEM), elemental microanalysis, (1)H nuclear magnetic resonance spectroscopy, the laser diffraction method, and zeta potential measurements. The hairy particles can act as pH-responsive stabilizers of aqueous foams by adsorption at the air-water surface. Above pH 8.0, where particles have nonprotonated PDEA hair, which is relatively hydrophobic, particle-stabilized foams are stable for at least 1 month. Optical microscopy and SEM confirmed that flocculated PDEA-PS latex particles were adsorbed at the air-water interface and stabilized the aqueous foams. At pH 6.1 and 7.1, relatively stable foams can be prepared that remain stable for at least 24 h. SEM studies indicated that the PDEA-PS particles were adsorbed at the air-water interface as a monolayer at pH 6.1. At pH 5.1 and 3.1, where the particles have cationic water-soluble PDEA hairs with hydrophilic character, no foam was formed. Rapid defoamation can be induced by lowering the solution pH; the addition of acid caused the in situ protonation of 2-(diethylamino)ethyl methacrylate residues, which impart water-soluble hydrophilic character to the PDEA hair, and the PDEA-PS particles desorbed from the air-water interface. The foaming and defoaming cycles could be repeated at least five times.