Mercury(II) oxide/tetrafluoroboric acid. An unusual behavior in the oxidation of alkenes. Synthesis of trans-cinnamylethers

The synthesis of $\text{trans}$-cinnamylethers by oxidation of allylbenzene is described. The reaction cannot be explained by formation of an allylic mercurial. A new type of mechanism in the oxidation of alkenes by mercury(II) salts is proposed.     

Gabriel Dimension for Graded Rings

Using techniques of localization for Grothendieck categories with a family of projective generators, we show that for a graded ring R = ⊕ _σ∈G R _σ with finite support if R _e has Gabriel dimension then has Gabriel dimension. Moreover, adding some lattice results, we prove that if has Gabriel dimension then also has Gabriel dimension. This research has been supported by grant MTM2005-3227 from MEC.     

Cyclopalladation of N-phenyl-4-ferrocenylmethylpyrazoles: Crystal structure of [Pd{κ-C,N-C6H4-1-[(3,5-Me2-C3N2)-CH2-(η-C5H4)Fe(η-C5H5)]}Cl(PPh3)] · CH2Cl2

The synthesis and characterization of pyrazole derivatives of general formula [C₆H₄-4-R-1-{(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}] [R = OMe (1a) or H (1b)] with a ferrocenylmethyl substituent are described.The study of the reactivity of compounds 1 with palladium(II) acetate has allowed the isolation of complexes (μ-AcO)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (2) [R = OMe (2a) or H (2b)] that contain a bidentate [C(sp², phenyl), N]⁻ ligand and a central “Pd(μ-AcO)₂Pd” unit.Furthermore, treatment of 2 with LiCl produced complexes (μ-Cl)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (3) [R = OMe (3a) or H (3b)] that arise from the replacement of the acetato ligands by the Cl⁻.Compounds 2 and 3 also react with PPh₃ giving the monomeric complexes [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}X(PPh₃)] {X⁻ = AcO⁻ and R = OMe (5a) or H (5b) or X⁻ = Cl⁻ and R = OMe (6a) or H (6b)}, where the phosphine is in a cis-arrangement to the metallated carbon atom. Treatment of 3 with thallium(I) acetylacetonate produced [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}(acac)] (7) [R = OMe (7a) or H (7b)]. Electrochemical studies of the free ligands and the cyclopalladated complexes are also reported. The dimeric complexes 3 also react with MeO₂C-CC-CO₂Me (in a 1:4 molar ratio) giving [Pd{(MeO₂C-CC-CO₂Me)₂C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}Cl] (8) [R = OMe (8a) or H (8b)], which arise from the bis(insertion) of the alkyne into the σ{Pd-C(sp², phenyl)} bond of 3.     

Capillary electrochromatography and nano‐liquid chromatography coupled to nano‐electrospray ionization interface for the separation and identification of estrogenic compounds

Nano‐LC and CEC were coupled to MS through a nanospray or a pressurized liquid‐junction interface for the simultaneous separation and determination of 11 estrogenic compounds. Different stationary phases, that is, phenyl, C18, and C18 bidentate silica hydrate, were studied. For both techniques, the phenyl stationary phase was the best option, considering separation efficiency, selectivity, and resolution. Under the optimized conditions, the baseline separation of the target compounds (including estradiol and zearalanol epimers) was achieved in less than 20 min in nano‐LC‐MS and less than 13 min in CEC‐MS. Molecular imprinted polymer SPE was used for extracting the target compounds from mineral water samples with the analysis of nano‐LC‐MS. The whole molecular imprinted polymer SPE nano‐LC‐MS method was validated through a recovery study at two levels of concentration. Sensitivity was improved by on‐column focusing technique obtaining LODs in the range 1.4–55.4 ng/L.     

The pattern of distribution of amino groups modulates the structure and dynamics of natural aminoglycosides: implications for RNA recognition

Aminoglycosides are clinically relevant antibiotics that participate in a large variety of molecular recognition processes involving different RNA and protein receptors. The 3-D structures of these policationic oligosaccharides play a key role in RNA binding and therefore determine their biological activity. Herein, we show that the particular NH2/NH3(+)/OH distribution within the antibiotic scaffold modulates the oligosaccharide conformation and flexibility. In particular, those polar groups flanking the glycosidic linkages have a significant influence on the antibiotic structure. A careful NMR/theoretical analysis of different natural aminoglycosides, their fragments, and synthetic derivatives proves that both hydrogen bonding and charge-charge repulsive interactions are at the origin of this effect. Current strategies to obtain new aminoglycoside derivatives are mainly focused on the optimization of the direct ligand/receptor contacts. Our results strongly suggest that the particular location of the NH2/NH3(+)/OH groups within the antibiotics can also modulate their RNA binding properties by affecting the conformational preferences and inherent flexibility of these drugs. This fact should also be carefully considered in the design of new antibiotics with improved activity.     

Oppenauer oxidation of secondary alcohols with 1,1,1-trifluoroacetone as hydride acceptor

1,1,1-Trifluoroacetone (2a) reacts as a hydride-acceptor in the Oppenauer oxidation of secondary alcohols (1) in the presence of diethylethoxyaluminum. The oxidant allows for selective oxidation of secondary alcohols in the presence of primary alcohols.     

New insights into alpha-GalNAc-Ser motif: influence of hydrogen bonding versus solvent interactions on the preferred conformation

The structural features of the mucin-type simplest model, namely, the glycopeptide alpha-O-GalNAc-l-Ser diamide, have been investigated by combining NMR spectroscopy, molecular dynamics simulations, and DFT calculations. In contrast to previous reports, the study reveals that intramolecular hydrogen bonds between sugar and peptide residues are very weak and, as a consequence, not strong enough to maintain the well-defined conformation of this type of molecule. In fact, the observed conformation of this model glycopeptide can be satisfactorily explained by the presence of water pockets/bridges between the sugar and the peptide moieties. Additionally, DFT calculations reveal that not only the bridging water molecules but also the surrounding water molecules in the first hydration shell are essential to keep the existing conformation.