Search results for "SELECTIVITY"
showing 10 items of 1148 documents
Enthalpies of formation of isoprene’s major oxidation byproducts
2005
Abstract The theoretical enthalpies of formation ( Δ f H 298 . 15 ∘ ) of methyl vinyl ketone (MVK, CH 2 CHC(O)CH 3 ), methacrolein (MACR, CH 2 C(CH 3 )CHO), and the radical products formed in their corresponding OH radical oxidations have been calculated with DFT (MPW1K/6-31+G(d,p)) and multilevel (MCCM-UT-CCSD(T)//MPW1K/6-31+G(d,p)) methods. The bond dissociation energies ( BDE , DH 298 . 15 0 ) of the H-atoms that can be abstracted from the MVK and MACR molecules, and the C–O forming bonds of the OH addition products are also calculated. The regioselectivity of the global reaction is discussed in terms of bond strength.
An Efficient Synthesis of γ-Aminoacids and Attempts to Drive Its Enantioselectivity
2008
Addition of carboxylic acid dianions to bromoacetonitrile lead, in good yields,to the corresponding gamma-cyanoacids, which on hydrogenation yielded gamma-amino acids. This two step methodology improves upon previously described results. Poor e.e's resultedfrom our attempts to drive the enantioselectivity of this transformation by chiral amide induction.
A simple synthesis of γ-aminoacids
2007
The addition of dianions of carboxylic acids to bromoacetonitrile, leads, in good yields, to the corresponding γ-cyanoacids that give γ-aminoacids on hydrogenation. This two-step methodology improves the results previously described.
CO2 Reduction in Photocatalytic Membrane Reactor: Products Selectivity Study
2018
CO2 Reduction in Photocatalytic Membrane Reactor: Products Selectivity Study
Optical mercury sensing using a benzothiazolium hemicyanine dye.
2006
[structure: see text] The selectivity and sensitivity of a benzothiazolium hemicyanine dye toward mercury(II) in aqueous solutions are described. Mercury ions coordinate to the dye forming a 1:1 complex. This interaction induces a color change in the dye at micromolar concentrations of mercury. Furthermore, the color change and quenching of the dye emission are selective for mercury when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II).
Conformationally regulated fluorescent sensors. Study of the selectivity in Zn 2+ versus Cd 2+ sensing
2004
Abstract The Zn 2+ and Cd 2+ complexing properties of four ligands containing a 4,4′-substituted biphenyl moiety are described. Ligands 1 and 3 , containing only one 1-aza-18-crown-6 cavity, lead to selective complexation of Cd 2+ versus Zn 2+ . Ligand 4 , with two crown cavities linked to a tetramethylbenzidine unit, is able to form 1:1 complexes with Zn 2+ and Cd 2+ , showing a higher complexing constant with Zn 2+ than with Cd 2+ , probably due to enthalpic factors. Several complementary experiments suggest that the 1:1 complexes formed by ligand 4 involve both crown cavities acting together to give rise to clamp structures. The formation of this type of zinc complex gives rise to red sh…
CARCINOGENESIS: Glutathione S-transferase A1–1-catalysed conjugation of bay and fjord region diol epoxides of polycyclic aromatic hydrocarbons with g…
1996
the fjord region diol epoxides a similar substrate enantioselectivity was noted, i.e. the enantiomer with the corresponding R configuration was again preferentially conjugated. In contrast, for the bay region syn -diol epoxides this substrate selectivity was reversed, resulting in a preference for the enantiomer with the S configuration. The chemically more reactive syn diastereomers were in general better substrates for GST Al-1 than the corresponding anti diastereomers. However, a comparison between different diol epoxide diastereomers revealed no obvious correlation between chemical reactivity of the compounds and catalytic efficiencies. Furthermore, no significant correlation between di…
Tumor-initiating activity of the (+)-(S,S)- and (−)-(R,R)-enantiomers of trans-11,12-dihydroxy-11,12-dihydrodibenzo[a,l]pyrene in mouse skin
1999
Abstract A single administration of enantiomerically pure 11,12-dihydrodiols of dibenzo[ a,l ]pyrene (DB[ a,l ]P) on the back of NMRI mice and subsequent chronic treatment with 12- O -tetradecanoylphorbol 13-acetate (TPA) (initiation/promotion assay) revealed strikingly different carcinogenic activities of both enantiomers. Tumor-initiating activity of (−)-(11 R ,12 R )-DB[ a,l ]P-dihydrodiol, which is the metabolic precursor of the (−)- anti -(11 R ,12 S )-dihydrodiol (13 S ,14 R )-epoxide, was exceptionally higher than the corresponding effect of (+)-(11 S ,12 S )-DB[ a,l ]P-dihydrodiol, the metabolic precursor of (+)- syn -(11 S ,12 R )-dihydrodiol (13 S ,14 R )-epoxide. After topical ap…
Detoxification of optically active bay- and fjord-region polycyclic aromatic hydrocarbon dihydrodiol epoxides by human glutathione transferase P1-1 e…
1998
Dihydrodiol epoxides (DEs) are important carcinogenic metabolites of polycyclic aromatic hydrocarbons (PAHs). The metabolic formation of four stereoisomeric DEs (a pair of optically active diastereomers termed as syn- and anti-form) is possible. Glutathione tranferases (GSTs) have been demonstrated to catalyze the detoxification of DEs. Purified GSTs display remarkable differences in catalytic efficiencies towards bay- and fjord-region DEs along with a high degree of regio- and stereoselectivity. Here we determined to which extent heterologously expressed human GSTP1-1, a major GST isoform in lung, affects the mutagenicity of stereoisomeric bay-region DEs of benzo[a]pyrene in Chinese hamste…
Origin and significance of the production of carbon dioxide during the ozonization of 13C-labeled D-glucose at different pH values.
2001
Abstract [1- 13 C], [2- 13 C] and [6- 13 C] d -glucose were, respectively, ozonized in a semi-batch reactor in acidic and basic conditions. The composition of the gas phase was evaluated by on-line mass spectrometry measurements. The quantitative and isotopic analyses of the carbon dioxide formed during ozonization are presented and discussed. The data, correlated with previous literature results, clearly show that at pH 2.5 the production of carbon dioxide from C-6 and C-1 carbon atoms is nearly equivalent. Conversely, at higher pH values, CO 2 is released with a greater selectivity from the reducing end. The importance of the decarboxylation reaction in the formation of by-products with f…