Substituent effect on the formation of organically-modified silicate-phosphate alternating copolymer through nonaqueous acid–base reaction

Organically-modified silicate-phosphate and silicate-phosphite copolymers were prepared through nonaqueous acid–base reaction. The inductive effect of the organic substituent of the starting materials such as organically-modified chlorosilane and phosphorous acid on the acid–base reaction was investigated by ³¹P NMR measurement and ab initio molecular orbital calculation. The condensation reaction takes place by nucleophilic addition of phosphate ion (or phosphite ion) to chlorosilane through S_N2 mechanism to form silicate-phosphate (or phosphite) network. The reactivity of the acid–base pair can be controlled by changing the inductive effect of the organic substituents on the starting materials.     

Direct Mass Spectrometric Study of the Ionic Species Content of a C<Subscript>2</Subscript>HCl<Subscript>3</Subscript>/He/O<Subscript>2</Subscript> Microwave Discharge Plasma

Direct on-line studies of a C₂HCl₃/He/O₂ microwave discharge plasma made possible the evolution and detection of many unfamiliar ionic species. Numerous ionic chlorocarbons, chlorohydrocarbons, oxygenated chlorohydrocarbons, oxygenated hydrocarbon radicals, and simple hydrocarbon species were identified mass spectrometrically as by-products: C _m Cl _n (m = 1–4, 6, 8; n = 1–8), C _m H _n Cl _x (m = 1–4, 6, 7, 10; n, x = 1–6), C _m H _n Cl _x O _y (m = 1–5, 12; n = 1–7; x = 1, 2, 4, 6; y = 1–3), C _n H_2n−1O (n = 2, 3), C _m H _n (m = 2, 4, 6, 8; n = 2, 4), and so on. The studies clearly showed the presence of various unfamiliar positive ionic O-containing species such as C₂ClO₂, CCl₃CO, C₂H₂Cl₄O₂, and C₄H₂Cl₆O₃. It is apparent that positive-ion reactions play a significant role in producing many ionic species in the chemistry of C₂HCl₃ plasmas.     

Two-dimensional hopping motion of encapsulated La atoms in silylated La(2)@C(80)

The (139)La NMR study of the exohedrally functionalized derivatives of La(2)@C(80) metallofullerene, La(2)@C(80)(Ar(2)Si)(2)CH(2) (: Ar = Mes, Mes = mesityl, : Ar = Dep, Dep = 2,6-diethylphenyl), reveal that the two La atoms hop between two sites along the equator of the C(80) cage.     

Electron-transfer reactions through the associated interaction between cytochrome c and self-assembled monolayers of optically active cobalt(III) complexes: molecular recognition ability induced by the chirality of the cobalt(III) units

Self-assembled monolayers (SAMs) of optically active Co(III) complexes ((S)-2/(R)-2) that contain (S)- or (R)-phenylalanine derivatives as a molecular recognition site were constructed on Au electrodes ((S)-2-Au/(R)-2-Au). Molecular recognition characteristics induced by the S and R configurations were investigated by measurements of electron-transfer reactions with horse heart cytochrome c (cyt c). The electrochemical studies indicate that the maximum current of cyt c reduction is obtained when the Au electrode is modified by 2 with a moderate coverage of approximately 4.0 x 10(-11) mol cm(-2). Since the Au electrode is not densely packed with the Co(III) units at this concentration, we conclude that the penetrative association process between cyt c and the Co(III) unit plays an important role in this electron-transfer system. The differences in the electron-transfer rates of (S)-2-Au and (R)-2-Au increase with increasing scan rates, a result indicating that the chiral ligand has an influence on the rate of association of the complexes with cyt c. 3-Au has a mixed monolayer composed of 2 and hexanethiol and exhibits electron-transfer behavior comparable to 2-Au. The difference in the association rates of (S)-3-Au and (R)-3-Au is larger than that between (S)-2-Au and (R)-2-Au, which indicates that the molecular recognition ability of 3-Au has been enhanced by filling the gap between molecules of 2 with hexanethiols. The differences in the oxidation rates of cyt c(II) between (S)-2-Au and (R)-2-Au and between (S)-3-Au and (R)-3-Au were larger than the differences in the rates of the reduction of cyt c(III); this suggests that the size of the heme crevice varies according to the oxidation state of cyt c.     

Theoretical study on the reaction mechanism for the hydrolysis of esters and amides under acidic conditions

The mechanisms underlying the hydrolysis of methyl acetate and acetamide under acidic conditions were investigated using the MP2/6-311+G(d,p)//MP2/6-31+G(d,p) level of theory. It was necessary to include two water molecules as reactants to obtain a tetrahedral (TD) intermediate for the A_AC2 mechanism that Ingold classified for the hydrolysis of methyl acetate. This mechanism includes two TS structures, one for the formation of the TD intermediate and the other for its decomposition. Since the activation energies were calculated to be 15.7 and 18.3 kcal mol⁻¹, the second step determines the rate of hydrolysis. The calculated value was close to that observed at ∼16 kcal mol⁻¹. It was confirmed that the A_AC2 mechanism had a barrier lower by 9.9 kcal mol⁻¹ than the A_AL2 mechanism. The A_AC2 mechanism is also applicable to the acid-catalyzed hydrolysis of acetamide. It is not the TD intermediate with which the NH₃⁺ moiety forms, but one further step is required to produce the final products, acetic acid and ammonium ion.     

Catalytic <Emphasis Type="Italic">N</Emphasis>-Alkylation of Amines with Primary Alcohols over Halide Clusters

Piperidine was reacted with methanol under a hydrogen stream in the presence of (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O supported on silica gel. When the temperature was raised above 200 °C, the catalytic activity of the cluster appeared. Piperidine N-methylation proceeded yielding N-methylpiperidine in 95% selectivity at 350 °C. The corresponding halide clusters of niobium, molybdenum, and tantalum supported on silica gel also catalyzed the reaction. Primary alcohols such as ethanol and 1-propanol produced the corresponding N-alkyl products of piperidine; however, secondary and tertiary alcohols did not. Selective N-methylation of pyrrolidine, hexamethyleneimine, butylamine, and aniline also proceeded. Thus, the clusters catalyzed alkylation of aliphatic, alicyclic, and aromatic amines with primary alcohols. A Brønsted acid site attributable to a hydroxo ligand, which is formed on the cluster complex by thermal activation, is proposed as the active site of the catalyst.     

Strength and elasticity of bimodal porous silica prepared from water glass

The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale macropores.     

Rhodium-catalysed substitutive arylation of cis-allylic diols with arylboroxines

Substitutive arylation of cis-allylic diols occurs upon treatment with arylboroxines in the presence of a rhodium(I) catalyst; the reaction proceeds through the addition of an intermediate arylrhodium(I) species across the carbon-carbon double bond and subsequent beta-oxygen elimination.