Hybrid polyoxotungstates as second-generation POM-based catalysts for microwave-assisted H2O2 activation

[structure: see text] Organic-inorganic hybrids synthesized from lacunary polyoxotungstates (POMs) have been screened as oxidation catalysts with H2O2 under MW irradiation. Yields up to 99% have been obtained in 25-50 min depending both on the POM structure and on the organic moiety. The reaction scope, optimized with the best performing catalyst [gamma-SiW10O36(PhPO)2]4-, includes epoxidation of terminal and internal double bonds, alcohol oxidation, and sulfoxidation, as well as oxygen transfer to electron-deficient substrates as chalcone, ketones, and sulfoxides.     

Surface behavior and molecular recognition in DNA microarrays from N,N-dimethylacrylamide terpolymers with activated esters as linking groups

A series of terpolymers made of DMA, NAS and MAPS were synthesized by free radical copolymerization and used as functional coatings for the fabrication of glass slide DNA microarrays. The surface properties of coated glass slides were investigated through contact angle measurements, ellipsometry and atomic force microscopy. The terpolymer molecular weight showed a moderate effect on surface tension (gamma(s) = 56-62 mN x m(-1)), but no clear effect on polymeric layer thickness (5-8 nm) and roughness. Hybridization experiments with amine-functionalized oligonucleotides gave the best fluorescence intensity results for microarrays coated with intermediate-molecular-weight terpolymers. Finally, an accelerated ageing test of the microarray in a humidity chamber showed a nice relationship between decay curves of contact angle against water and fluorescence intensity.     

Total synthesis of anthocyanidins via Heck reaction

Anthocyanidin moiety was obtained by cyclization of a 2-hydroxychalcone prepared by the Heck approach to the synthesis of flavonoids. 1-(3,4-dimethoxyphenyl)-prop-2-en-1-one has been used as a coupling partner along with o-acetoxyiodobenzene in the Heck reaction.     

Use of peptide nucleic acid probes for detecting DNA single-base mutations by capillary electrophoresis

Peptide nucleic acid (PNA) oligomers can be used as probes in pre-gel hybridization experiments, as an alternative to Southern hybridization. In this technique, the PNA probe is hybridized to a cyanine-5 labeled DNA sample denatured at low ionic strength, and the mixture is directly injected for size separation into a capillary electrophoresis (CE) system equipped with laser-induced fluorescence (LIF) detector. The neutral backbone of PNA allows hybridization to occur at low ionic strength and assures an efficient CE separation of the PNA/DNA hybrids from both double-stranded and single-stranded DNA. We have used as a model system the cystic fibrosis R553X and R1162X single-base mutations and we have assessed the influence of various factors, such as temperature and denaturants concentration on DNA/PNA hybrid stability in order to achieve the high specificity required for a single base pair discrimination.     

Selective generation and reactivity of 5'-adenosinyl and 2'-adenosinyl radicals

The reaction of hydrated electrons (e(-)(aq) with 8-bromoadenosine 7 has been investigated by radiolytic methods coupled with product studies. Pulse radiolysis revealed that one-electron reductive cleavage of the C-Br bond gives the C8 radical 8 followed by a fast radical translocation to the sugar moiety. The reaction is partitioned between C5' and C2' positions in a 60:40 ratio leading to 5'-adenosinyl radical 9 and 2'-adenosinyl radical 11. This radical translocation from C8 to different sites of the sugar moiety has also been addressed computationally by means of DFT B3LYP calculations. In addition, ketone 21 was prepared and photolyzed providing an independent generation of C2' radical 11. Both C5' and C2' radicals undergo unimolecular reactions. Radical 9 attacks adenine with a rate constant of 1.0 x 10(4) s(-1) and gives the aromatic aminyl radical 10, whereas C2' radical 11 liberates adenine with a rate constant of 1.1 x 10(5) s(-1).     

Proton‐conducting electrolytes based on silylated and sulfonated polyetheretherketone: Synthesis and characterization

A derivative of polyetheretherketone (PEEK) having sulfonic acid groups and silicon‐containing substituents covalently bound to the aromatic backbone has been prepared as proton‐exchange membrane material. The polymer 4 (PhSiSPEEK) has been synthesized via (i) sulfonation of PEEK up to 0.9 degree of sulfonation (DS, the number of sulfonic groups per repeat unit), (ii) conversion of sulfonated PEEK 1 (SPEEK09) into sulfonyl chlorinated derivative 2 (PEEKSO₂Cl), (iii) lithiation of 2 and subsequent addition of PhSiCl₃, followed by hydrolysis. The chemical structure of the synthesized polymers has been investigated by ¹H NMR and ¹³C NMR and ATR/FTIR spectroscopy and their thermal stability has been evaluated by thermogravimetric analysis. The presence of inorganic moieties increases the thermal stability of 4 with respect to the sulfonated and not silylated product. Despite its very high DS, PhSiSPEEK is insoluble in water but does not possess the plastic properties needed to be used as an electrolyte membrane. Blend membranes made of SPEEK05 (DS = 0.5) and containing 10 and 25 wt % of 4 (DS = 0.9, degree of silylation DSi = 0.1) have been prepared and characterized by water uptake measurements and electrochemical impedance spectroscopy. The combination of the two functionalized polymers having different properties allows to obtain proton‐conducting electrolytes that are potential candidates for fuel cells applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2178–2186, 2010     

Mechanism of Ni2+ and NiOH+ interaction with hydroxamic acids in SDS: evaluation of the contributions to the equilibrium and rate parameters in the aqueous and micellar phase

The equilibria and kinetics (stopped-flow) of the binding of Ni(II) to salicylhydroxamic acid (SHA) and phenylbenzohydroxamic acid (PBHA) have been investigated in aqueous solutions containing SDS micelles. The two ligands are fairly distributed between the two pseudophases present, so the binding reaction occurs in both phases. The contributions to the total reaction from each phase has been evaluated, following a procedure where use is made of the experimentally determined partition coefficients of the reactants involved. The mechanism of the reaction occurring on the micelle surface has been derived and comparison with the mechanism in water shows that the step Ni(2+) + HL ? NiHL(2+) is operative in both pseudophases, whereas the step Ni(2+) + L(-)? NiL(+), which is operative in water, is replaced in SDS by the step NiOH(+) + HL ? NiL(+). The analysis of the equilibrium and of the kinetic data enabled the evaluation of the equilibrium and the rate constants of the individual steps taking part in the binding process over the micelle surface. Interestingly, the first hydrolysis constant of the Ni(H(2)O)(6)(2+) ion in SDS is more than two orders of magnitude higher than in water. The agreement between the equilibrium constants derived from kinetics and those obtained by static measurements confirms the validity of the proposed mechanism.     

Obtaining new flavanones exhibiting antifungal activities by methyltrioxorhenium-catalyzed epoxidation-methanolysis of flavones

New 3-hydroxy-2-methoxyflavanones have been obtained through epoxidation-methanolysis of the corresponding flavone with urea-hydrogen peroxide (UHP)/methyltrioxorhenium (CH₃ReO₃, MTO) catalytic system in methanol as nucleophilic solvent. After acetylation of the reaction mixtures, the corresponding cis- and trans-3-acetoxy-2-methoxyflavanones have been isolated and characterized by spectroscopic analyses. Their antifungal activity has been tested in vitro against three fungal strains of common saprotrophic soil and seed fungi, such as Trichoderma koningii, Fusarium solani and Cladosporium herbarum, potentially pathogenic for humans. Some aspects of the structure-activity relationship of the most active compounds have been evaluated. The mycelial growth of T. koningii and C. herbarum has been totally inhibited from cis-3-acetoxy-2,6-dimethoxyflavanone 7c and cis-3-acetoxy-2,7-dimethoxyflavanone 13c at the lowest concentration (0.5×10⁻⁴ M).     

Mechanism of indium(III) exchange between NTA and transferrin: a kinetic approach

The equilibria and kinetics for the process of In(3+) exchange between nitrilotriacetic acid (NTA) and bovine serum transferrin (T) have been investigated in aqueous solution containing sodium bicarbonate. The metal exchange equilibria have been measured by difference ultraviolet spectroscopy at 25 degrees C, pH=7.4, and I=0.2 M (NaClO4). The acid dissociation constants of NTA and the binding constants of In(III) to NTA have also been measured. Kinetic experiments revealed that the process of In(3+) uptake by transferrin from [In(NTA)2](3-) is biphasic, the fast phase being completed in a few seconds, the slow phase lasting for hours. The fast phase has been investigated by the stopped-flow method and results in monoexponential kinetics. It involves rapid interaction of the 1:1 complex ML (M=In, L=NTA) with TB (T=transferrin, B=CO3(2-)) to give a quaternary intermediate MLTB which then evolves to an "open" MTB* ternary complex complex with expulsion of L. In turn, this complex interconverts to a "closed", more stable, form MTB. Neither the prevailing complex M2L nor the TB2 form of transferrin are directly involved in the exchange process but act as metal and protein reservoirs. The pH dependence of the reaction has been also investigated. The slow phase has not been investigated in detail; it takes several hours to go to the completeness, its slowness being ascribed to metal redistribution between the C-site and N-site of the protein, and/or metal release from polynuclear In(III) species.     

Time‐Resolved In Situ Synchrotron X‐ray Study and Large‐Scale Production of Magnetite Nanoparticles in Supercritical Water

A general solution : In situ synchrotron X‐ray scattering in a high‐pressure pulsed injection reactor (see picture) shows that magnetite nucleation and growth are temporally separated. Gram‐scale crystalline, pure phase, superparamagnetic magnetite nanoparticles were synthesized without surfactants in supercritical water in less than one hour using a laboratory‐scale continuous‐flow reactor.