Induced heterogeneity,a novel technique for the study of gas-phase reactions. 2. Direct study of C?C bond scission in ethane

Deliberate activation of the reaction vessel surface leads to the domination of chain termination in ethane pyrolysis by the reaction As a result, chains are dramatically reduced in length, methane yields are entirely primary and larger in proportion to other products, and values of k₁ can be directly determined from methane yield data without ambiguity. Experiments carried out in the temperature range of 841–913K at initial ethane pressures of 1–20 torr, without and with added nitrogen, yield the infinite pressure Arrhenius equation It is shown that most previously published data can be combined with those of this study to yield Fall-off curves for k₁ as a function of pressure are in good agreement with those from other laboratories. From these the relevant data for k_?1 can be extracted for use in other kinetic studies.     

Induced heterogeneity,a novel technique for the study of gas-phase reactions. Part I. Determination of the arrhenius parameters for C?C bond scission in propane

It is shown that, by deliberate activation of the reaction vessel, heterogeneous reaction at the wall can be made to dominate chain termination in a complex gas-phase reaction. For a homogeneous process, characterized, as is often the case, by multiple terminations, this has the effect of simplifying the mechanism and allowing explicit solution of the relevant steady-state equations so that the rate constants of some individual steps can be evaluated without assumption as to the values of those of others. The pyrolysis of propane, in the vicinity of 500°C, has been used as an example of this approach. Enhancement of the wall activity leads to the reaction (1) providing, almost exclusively, chain termination. As a result, rate constants for the initiation step (2) can be directly determined. The results of this study provide the Arrhenius equation In combination with current thermochemical values this result gives k_?1 = 10^13.40 cm³/mol·s which, in turn, implies, via the geometric mean rule, k_Et-Et = 10^12.9 cm³/mol·s for ethyl–ethyl recombination, in good accord with the most recent determinations and compatible with the newly proposed value of the enthalpy of formation of ethyl. The first-order wall constant k₈ has been evaluated as k₈<10^4.2 s^?1. This appears to be the first occasion on which a wall constant has been evaluated from data for a high-temperature complex gas reaction.     

The Duality Property of Positive R-Compact Operators

We study the duality of r-compact operator. We establish if an operator ${T:E\rightarrow F}$ is r-compact, then its adjoint ${T^{\prime}: F^{\prime }\rightarrow E^{\prime }}$ is also r-compact. We also provide some sufficient condition on the pair of Banach lattices E and F which guarantees that a regular operator ${T:E\rightarrow F}$ such that ${T^{\prime }:F^{\prime }\rightarrow E^{\prime }}$ is r-compact, must itself be r-compact.     

Investigation of beta-CD-derivatized erythromycin as chiral selector in CE

A novel water-soluble beta-CD-derivatized erythromycin (EM) was synthesized and used as an effective chiral selector for the resolution of chiral compounds in CZE. The purpose of substitution at the primary hydroxyl site of beta-CD with 1-oxygen-2,3-epoxypropane is to produce a compound having functions of both beta-CD and EM. beta-CD-derivatized EM exhibited excellent enantioselectivities compared with single beta-CD and EM for chiral separation in CE. We also investigated the influence of pH and concentration of BGE, concentration of chiral selector, applied potential, and organic modifier on chiral compounds' separation.     

Structural characterization and NMR study of NaNbWO(6) and its proton-exchanged derivatives

The structural characterization of NaNbWO(6), prepared by the ceramic route, has been performed. Electron diffraction has shown the presence of two related phases in a 1:1 ratio, whose lattice parameters correspond to those of the well-known tetragonal tungsten bronzes (TTB) and those of a monoclinically distorted phase. In addition to basic unit cells, the morphology of the two phases has been found to be similar, but they present a slight difference in the W/Nb ratio. (1)H and (23)Na magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectra of NaNbWO(6) and its proton-exchanged derivatives have been interpreted on the basis of the ideal TTB structure. The average structure and the morphology remain unchanged in Na(1-x)H(x)NbWO(6) derivatives. (1)H and (23)Na MAS-NMR spectroscopies have been used to monitor changes produced during exchange processes. It has been shown that the exchange of Na ions is mainly produced, but not exclusively, at tetragonal channels. However, a large amount of Na ions at the pentagonal channels do not exchange with protons, suggesting that these ions are needed to stabilize the TTB-like structure. A tentative distribution of sodium ions in the most-exchanged oxide, deduced from NMR results, approximately (Na(0.46))(p)(Na(0.08))(s)H(0.46)NbWO(6), has been proposed. NMR spectra of Na(1-x)H(x)NbWO(6) indicate that two different OH groups are formed upon exchanging. The study of samples hydrated with D(2)O allowed us to conclude that deuterons of adsorbed water exchange with protons of the two OH groups. The proton-deuteron exchange is slow at room temperature but is strongly enhanced at 90 degrees C. This observation relates to the proton conductivity displayed by exchanged products under a humid atmosphere.     

Association between chemical and genetic variation of Vitex rotundifolia populations from different locations in China: its implication for quality control of medicinal plants

Vitex rotundifolia is a widely distributed plant species that has been extensively used in traditional Chinese medicine. Its fruits, Fructus Viticis, are recorded as Manjingzi in the Pharmacopoeia of the People's Republic of China. For the effective quality control of its medicinal values reflected by chemical variation patterns, in addition to the relationship with genetic diversity, analyses based on high-performance liquid chromatographic (HPLC) fingerprinting and inter simple sequence repeat (ISSR) molecular markers were carried out, involving 14 V. rotundifolia populations from different locations in China. The HPLC data showed considerable variation of chemical constituents among the V. rotundifolia populations. The hierarchical clustering analysis further revealed four major groups based on their chemotype variation. Abundant genetic diversity was detected among the V. rotundifolia populations that also were clustered into four groups based on their ISSR data. It is important to point out that the genetic variation pattern revealed by molecular markers was closely associated with that indicated by chemical constitutes in the fruits of V. rotundifolia. This finding provides a solid basis for the combined use of chemical and genetic fingerprints in efficiently evaluating qualities and choosing favourable chemotypes with appropriate pharmacological properties of V. rotundifolia, in addition to establishing good agricultural practices for medicinal plants.     

Frequency of CYP2C9 genotypes among Omani patients receiving warfarin and its correlation with warfarin dose

OBJECTIVES: This study was conducted to determine the frequency of CYP2C9 alleles in Omani patients receiving warfarin and to correlate genotyping data with warfarin dosage. The Omani population has Asian and African ethnicities. METHODS: CYP2C9 genotypes were determined by the polymerase chain reaction restriction fragment length polymorphism method. Non-parametric Kruskal-Wallis test was used to compare groups of continuous data for significance differences. RESULTS: Genotyping data showed that 12.7 and 5.8% of the samples were heterozygous for the CYP2C9*2 and CYP2C9*3 alleles, respectively. The CYP2C9*2 allele frequency was 0.074 in our population. It was 0.029 for CYP2C9*3. CONCLUSION: This is the first report on the presence of CYP2C9*2 allele homozygocity in any Asian or African population.     

Preparation and characterization of a reduced chromium complex via vinyl oxidative coupling: formation of a self-activating catalyst for selective ethylene trimerization

Reaction of the divalent [(t-Bu)NP(Ph)(2)N(t-Bu)]CrCl(2)Li(THF)(2) (1) with 1 equiv of vinyl Grignard (CH(2)=CH)MgCl reproducibly afforded the triangulo {π-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr}(2)(μ,μ',η(4),η(4)'-C(4)H(4)){σ-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr} (2) containing a σ-/π-bonded butadiene-diyl unit. The diene-diyl moiety was generated by an oxidative coupling and deprotonation of two vinyl anions. The crystal structure revealed that of the three chromium atoms, each bearing one NPN ligand, two are perpendicularly bonded to the two sides of the π-system of the butadiene-diyl residue in a sort of inverted sandwich type of structure. The third is instead coplanar with the doubly deprotonated C(4) unit and σ-bonded to the two terminal carbon atoms. Despite the appearance as a Cr(II)/Cr(I) mixed valence species, DFT calculations have revealed that the structure of 2 consists of three divalent chromium atoms, while the additional electron resides on the π-system of the bridging organic residue. Complex 2 behaves as a single component selective catalyst for ethylene trimerization.