Evidence for involvement of cationic intermediate in epoxidation of chiral allylic alcohols and unfunctionalised alkenes catalysed by MnIII(quinazolinone) complexes

A pair of Mn^III(quinazolinone) complexes was prepared and evaluated in the catalytic epoxidation of the chiral allylic alcohols and unfunctionalised alkenes with iodosylbenzene. Epoxidation of chiral allylic alcohols with 1,3-allylic strain proceeded chemo- and diastereoselectively to give threo-epoxy alcohol (up to 99% d.r). Epoxidation of unfunctionalised alkenes by the proposed catalyst system proceeded nonselectively, as evidenced by the formation of isomerization and rearrangement products in the epoxidation of (Z)-stilbene. A three-step pathway involving a cationic intermediate is proposed for the formation of isomerization and rearrangement products. The fact that only products resulting from the cationic intermediate were detected in the oxidation of a mechanistic probe, (2-methoxy-3-vinylcyclopropyl)benzene, with Mn^III(quinazolinone) and PhIO substantiated the cationic oxygen transfer mechanism.     

Synthesis of aromatic acids via catalysed methyl formate-chloroarene reactions

Chlorobenzene and more generally, chloroarenes, can be converted into aromatic acids via catalytic reaction with aqueous methyl formate under biphasic conditions. The only efficient catalyst is [PdCl₂(PCy₃)₂] (Cy = cyclohexyl). [RU₃(CO)₁₂] and ammonium formate improve yield and selectivity. The mechanism should involve oxidative addition of the C---Cl bond to a zero-valent Pd species followed by CO insertion. The palladium catalyst may also directly activate methyl formate. The procedure is convenient (no solvent, no initial pressurization) and at least as efficient as previously described methods.     

Lighting-up the dynamics of telomerization and DNA replication by CdSe-ZnS quantum dots

CdSe-ZnS core-shell quantum dots (QDs) act as photochemical centers for lighting-up the dynamics of telomerization or DNA replication.     

Synergistic effects in multicomponent electrocatalysts: the Pb-Ir-O system

The ionic interactions were studied in aqueous solutions of Na(3)IrCl(6) + Pb(NO(3))(2) in order to develop a facilitated electrosynthesis of iridium-based catalytic surfaces. Spectroscopic studies indicated that ion pair charge-transfer complexes [IrCl(6)(3-)]-Pb(II) (K = 6 x 10(3)) and [Ir(H(2)O)Cl(5)(2-)]-Pb(II) (K = 2 x 10(3)) were formed in fresh and aged solutions, respectively. Electrochemical studies showed that interactions between the Ir(H(2)O)Cl(5)(2-) and Pb(II) species lead to synergistic lowering of the overpotential that was necessary for nucleation and growth of mixed metal oxide PbIrOx on the surface of glassy carbon electrodes. The Ir:Pb stoichiometry of the PbIrOx surface films was the same (1:1) as that of the high-temperature phase of Pb-Ir-O pyrochlore. Compared to IrOx, the PbIrOx films displayed enhanced catalytic activity toward the electrooxidation of carbohydrates. This was ascribed to synergism that involved retention of carbohydrate molecules at the Pb(II) sites of a PbIrOx film and oxidation at the adjacent Ir(IV) sites. The synergistic electroplating utilizing interactions between the partially aquated transition metal complex and posttransition metal ion represents a new synthetic route to highly homogeneous and reactive films of mixed metal oxides.     

Direct copper(I) iodide dimethyl sulfide catalyzed conjugate addition of alkenyl groups from vinylzirconocene reagents

[reaction: see text] CuI.0.75DMS complex is an excellent catalyst for the direct conjugate addition of alkenyl groups from vinylzirconocene reagents to alpha,beta-unsaturated aldehydes and ketones. The presence of the catalyst with an alkenylzirconocene, at +40 degrees C in THF, circumvents the need for making discrete alkenylcopper reagents. The catalyst is superior in terms of product yields and alkene flexibility in comparison to other copper(I) sources as well as the nickel(II)-catalyzed conjugate addition. This simple one-pot procedure shows that only 1 equiv of the vinylzirconocene is needed.     

Formation d''etats triplets du biacetyle dans sa reaction en phase gazeuse avec un plasma froid d''azote

The behaviour of the biacetyl molecule (BA) in a cold plasma, obtained by extraction of reactive species from a nitrogen plasma generated in a microwave discharge, is discussed. When the partial pressures of nitrogen and biacetyl are approximately equal (p_N2 ≈ 0.60 Torr, p_BA ≈ 0.55 Torr), the emission of the ³A_u---¹A_g transition of biacetyl is observed with a vibrational structure. On reaction of biacetyl with nitrogen cold plasma preferentially enriched in N₂(A³Σ⁺_u), an enhancement of the emission intensity of the phosphorescence of biacetyl is observed. The initiator of this transition is the triplet state BA(³B_u) which originates from an isoenergetic transfer from N₂(A³Σ⁺_u) according to the overall mechanism

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Modification of the thermoresistance to spray-drying of a cold-adapted subtilisin by genetic engineering

The thermoresistance of a cold-adapted subtilisin dried by spray-drying was studied. Proteolytic activity of this enzyme was measured before and after spray-drying. Without chemical additives, spray-drying yields ranged from 2–13%. The use of arabic gum and lactose in the composition of the enzyme solutions allowed the strengthening of the enzyme structures and increased water mobility in the product. Increase of water mobility led to a shorter residence time of the product in the spray-drier and a net yield increase was obtained (yield higher than 50%). The effect of two selective mutations on the thermoresistance to spray-drying of the cold-adapted subtilisin was also investigated. Mutation T85D (introduction of an additional link with an ion Ca²⁺ necessary for enzyme activity, by substitution of Asp for Thr 85) had no effect on the thermoresistance of the subtilisin to spray-drying. Mutation H121W (introduction of an additional aromatic link by substitution of Trp for His 121) reduced the drying yield from 66% (not modified subtilisin) to 52%. This higher thermosensitivity could be explained by an increase of the hygroscopic character of the modified subtilisin (mutation H121W).     

Molecular modeling study of the aggregation behavior of nickel(II), cobalt(II), lead(II) and zinc(II) bis(2-ethylhexyl) phosphate complexes

The physiochemical nature of the metal-extractant species in organic solvent has been a matter of debate over liquid-liquid extraction of transition metals by bis(2-ethylhexyl) phosphate. The aggregation behavior of nickel(II), cobalt(II), lead(II), and zinc(II) bis(2-ethylhexyl) phosphate have been investigated using molecular modeling. The recently confirmed "open" water channels rodlike reversed micelles which is in contact with the nonaqueous solvent rather than in an inner core (or "closed" water channel) of the nickel-extractant species by Ibrahim and Neuman appears to be a unique structure for such species. Lead-, cobalt- and zinc-extractant species behave in a different manner. The cobalt-extractant species form rodlike reversed micelles, but does not show the formation of any open water channel. The zinc- and lead-extractant species form ellipsoidal (or deformed spherical) reversed micelles with fewer water molecules located at the core of the micelles which is in accord with the conventional view of reversed micelles. The structural variations of the reversed micelles for the metal extracted species are in accord with the known extraction behavior of such metals when using HDEHP.     

Raman microscopy for the chemometric analysis of tumor cells

Raman spectroscopy is recognized as a tool for chemometric analysis of biological materials due to the high information content relating to specific physical and chemical qualities of the sample. Thirty cells belonging to two different prostatic cell lines, PNT1A (immortalized normal prostate cell line) and LNCaP (malignant cell line derived from prostate metastases), were mapped using Raman microscopy. A range of spectral preprocessing methods (partial least-squares discriminant analyses (PLSDAs), principal component analyses (PCAs), and adjacent band ratios (ABRs)) were compared for input into linear discriminant analysis to model and classify the two cell lines. PLSDA and ABR were able to correctly classify 100% of cells into benign and malignant groups, while PLSDA correctly classified a greater proportion of individual spectra. PCA was used to image the distribution of various biochemicals inside each cell and confirm differences in composition/distribution between benign and malignant cell lines. This study has demonstrated that PLSDAs and ABRs of Raman data can identify subtle differences between benign and malignant prostatic cells in vitro.     

Synthesis and properties of isoviagra. A 2‐methyl‐2H‐pyrazolo[4,3‐d]pyrirnidin‐7‐one isomer of viagra®

The synthesis and spectral properties (ir, ms, nmr) of a substituted 2‐methyl‐2H‐pyrazolo[4,3‐d]‐pyrimidin‐7‐one ( 3 ), an isomer of Viagra^®, are described. The key synthon, 4‐amino‐1‐methyl‐5‐propyl‐3‐pyrazolecarboxamide ( 7 ), is prepared via the reaction of ethyl 2,4‐dioxoheptanoate with methylhydrazine, followed by cyclization, nitration, amidation, and nitro group reduction. Interaction of 7 with 2‐ethoxyben‐zoyl chloride yielded the respective bis‐amide ( 8 ) which was cyclized in polyphosphoric acid to the corresponding pyrazolo[4,3‐d]pyrimidin‐7‐one derivative 9 . Chlorosulfonylation of 9 , and subsequent treatment with 1‐methylpiperazine furnished iso Viagra ( 3 ).