Proteomics of bovine myelin sheath: Characterization of a truncated form of P0 by MALDI-TOF/TOF mass spectrometry

The glycoprotein P0, the major structural protein of the peripheral nerve myelin, plays a critical role in holding myelin lamellae together via interaction of both extracellular and cytoplasmic domains. Mutations in the human P0 gene give rise to severe and progressive forms of dominantly inherited peripheral neuropathies like CMT1B. Here we report on the characterization of a bovine P0-derived protein of nearly 26 kD that corresponds to the P0 protein truncated in its cytoplasmic domain. Matrix assisted laser desorption ionization (MALDI)-time-of-flight/time-of-flight (TOF/TOF) mass spectrometry (MS) analysis on its tryptic digest has provided a peptide mapping, the main difference of which from the normal P0 analog was represented by the absence of the cluster of peaks at m/z 1513.7501, 1530.7701, and 1546.7651. The latter corresponds to the P0 fragment QTPVLYAMLDHSR and to its pyroglutamic and methionine-oxidized derivatives. The species at 1530.7701 covering the sequence 186-198 of P0 is not an artifact and might have a functional role in the myelin architecture.     

Salt and solvent effects on the kinetics of the oxidation of the excited state of the [Ru(bpy)3]2+ complex by S2O8(2-)

The title reaction was studied in different reaction media: aqueous salt solutions (NaNO3) and water-cosolvent (methanol) mixtures. The observed rate constants, k(obs), show normal behavior in the solutions containing the electrolyte, that is, a negative salt effect. However, the solvent effect is abnormal, because a decrease of the rate constant is observed when the dielectric constant of the reaction medium decreases. These effects (the normal and the abnormal) can be explained using the Marcus-Hush treatment for electron transfer reactions. To apply this treatment, the true, unimolecular, electron-transfer rate constants, k(et), have been obtained from k(obs) after calculation of the rate constants corresponding to the formation of the encounter complex from the separate reactants, k(D), and the dissociation of this complex, k(-D). This calculation has been carried out using an exponential mean spherical approach (EMSA).     

Electron paramagnetic resonance of three-spin nitroxide-copper(II)-nitroxide clusters coupled by a strong exchange interaction

The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides represents an unusual exchange-coupled three-spin system. The antiferromagnetic exchange coupling, which already atT < 150 K is larger than the thermal energy kT, induces the transition from a total spin state S = (3)/(2) to a state S = (1)/(2) and produces static spin polarization. Anomalous electron paramagnetic resonance (EPR) spectra of an S = (1)/(2) state were detected experimentally and described theoretically. The effective g factor of the three-spin system is smaller than 2, despite the fact that all the individual components have g > 2. The observed signals with g < 2 are highly informative and can be employed for determination of the sign and value of the exchange interaction in three-spin nitroxide-copper-nitroxide clusters.     

Oxidations catalyzed by osmium compounds. Part 1: Efficient alkane oxidation with peroxides catalyzed by an olefin carbonyl osmium(0) complex

A carbonyl osmium(0) complex with π-coordinated olefin, (2,3-η-1,4-diphenylbut-2-en-1,4-dione)undecacarbonyl triangulotriosmium (1), efficiently catalyzes oxygenation of alkanes (cyclohexane, cyclooctane, n-heptane, isooctane, etc.) with hydrogen peroxide, as well as with tert-butyl hydroperoxide and meta-chloroperoxybenzoic acid in acetonitrile solution. Alkanes are oxidized to corresponding alcohols, ketones (aldehydes) and alkyl hydroperoxides. Thus, heating cyclooctane with the 1-H₂O₂ combination at 70 °C gave products with turnover number as high as 2400 after 6 h. The maximum obtained yield of all products was equal to 20% based on cyclohexane and 30% based on H₂O₂. The oxidation of linear and branched alkanes exhibits very low regio- and bond-selectivity parameters and this testifies that the reaction proceeds via attack of hydroxyl radicals on C-H bonds of the alkane. The oxygenation products were not formed when the reaction was carried out under argon atmosphere and it can be thus concluded that the oxygenation occurs via the reaction between alkyl radicals and atmospheric oxygen. In summary, the Os(0) complex is much more powerful generator of hydroxyl radicals than any soluble derivative of iron (which is an analogue of osmium in the Periodic System).     

A hyphenated flow-through analytical system for the study of the mobility and fractionation of trace and major elements in environmental solid samples

A flow-through hyphenated analytical method has been tested that enables not only the accelerated and efficient fractionation of trace elements (TE) species in environmental solids to be achieved but allows real-time studies on the leaching process to be made. Rotating coiled columns (RCC), earlier used mainly in countercurrent chromatography, have been successfully applied to the dynamic fractionation of heavy metals in soil, sediment, and sludge samples. A ground solid sample (about 0.5 g) was retained in a PTFE rotating column as the stationary phase whereas different aqueous eluents, chosen according to recent data on the selectivity of leachants, were continuously pumped through. Elements were determined in the effluent on-line by inductively coupled plasma atomic emission spectrometry (ICP-AES). Since the flow rates used in the RCC are in good agreement with those needed for cross-flow nebulization in the ICP-AES spectrometer, both devices were coupled directly without any additional interface systems. Simultaneous investigation of the elution profiles of trace and major elements has made it possible to study the elements association in separated fractions and hence to prove the efficacy of extractants and their selectivity toward targeted mineralogical phases of samples. The close association of heavy metals with Mn oxides in the sediment and sludge samples was confirmed. The time-resolved dissolution of different organic complexes of metals was observed for the sediment sample. It was found that in sediment and sludge samples the dynamics of iron release under the action of Tamm's reagent is somewhat different from that of aluminium. In addition, the proposed method can also be applied to develop effective leaching schemes and in the analysis of environmental solids for risk assessment of their contaminants addressed to water quality and bioavailability.     

Influence of solvent and weak C-H...O contacts in the self-assembled [Pt2M4{CC(3-OMe)C6H4}8] (M = Cu, Ag) clusters and their role in the luminescence behavior

New alkynyl complexes [Pt2M4{CC(3-OMe)C6H4}8] (M = Ag 1, Cu 2) have been synthesized and their structures and properties compared to those of related [Pt2M4(CCPh)8] compounds. For the Pt-Ag derivatives, the X-ray structures of the discrete yellow solvate monomer, [Pt2Ag4{CC(3-OMe)C6H4}8].2THF ([1.2THF]), and the dark garnet unsolvated polymeric form, [Pt2Ag4{CC(3-OMe)C6H4}8](infinity) ([1](infinity)), are presented. The yellow form ([1.2THF]) exhibits a distorted octahedral geometry of the metal centers with the platinum atoms mutually trans and the four silver atoms in the equatorial plane. Pairs of Ag atoms are weakly bridged by THF molecules [mu-Ag2...O(THF)]. The garnet form ([1](infinity)) has an unprecedented infinite stacked chain of octahedral clusters linked by short Pt...Pt bonds (3.1458(8) A). In both forms, different types of weak C-H...O (OMe) hydrogen bonds are observed. For comparative purposes, we have also provided the crystal structures of the yellow monomer form, [Pt2Ag4-(CCPh)8].CHCl3, and the red dimer form, [Pt2Ag4(CCPh)8]2 (Pt-Pt 3.221(2) A). These clusters display intense photoluminescence in both solution and the solid state, at room temperature and 77 K. The emission observed for the yellow form [1.2THF] in the solid state is assigned to a 3MLM'CT [Pt(d)/pi(CCR) --> Pt(p(z))/Ag(sp)/pi(CCR)] state modified by Pt...Ag, Ag...Ag, and Ag...(THF) contacts. However, in the garnet form [1](infinity) and in 2, the emissions are related to the axial Pt-Pt bonds and are assigned as phosphorescence from a metal-metal-to-ligand charge-transfer (3MMLCT) excited state ([1](infinity)), or an admixture of a metal-metal (Pt-Pt) centered 3(dsigmap(z)sigma) and 3MMLCT excited state (2). For 1, a remarkable quenching and a shift to higher energies in the emission is observed on changing from CH2Cl2 to THF, and for both 1 and 2, the emission spectra at 77 K varies with the concentration, showing their tendency to stack even in glass.     

Synthesis of indoles by intermolecular cyclization of unfunctionalized nitroarenes and alkynes, catalyzed by palladium-phenanthroline complexes

Palladium-phenanthroline complexes efficiently catalyze the reaction of nitroarenes with arylalkynes and CO to give 3-arylindoles by an ortho-C-H functionalization of the nitroarene ring. Both electron-withdrawing and electron-donating substituents are tolerated on the nitroarene, except for bromide and activated chloride. Nitroarenes bearing electron-withdrawing substituents react faster, but the selectivity of the reaction depends on both polar and radical stabilization effects. Among those tested, only arylalkynes afforded indoles under the investigated conditions. The reaction mechanism was partly investigated. The kinetics is first order in nitroarene concentration and the rate-determining step of the cycle is the initial nitroarene reduction. No primary isotope effect is observed on either rate or selectivity, implying that the cyclization step is fast.     

The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study

The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H...pi interaction, present in solution.     

Energy barriers of proton transfer reactions between amino acid side chain analogs and water from ab initio calculations

Proton transfer reactions were studied in all titratable pairs of amino acid side chains where, under physiologically reasonable conditions, one amino acid may function as a donor and the other one as an acceptor. Energy barriers for shifting the proton from donor to acceptor atom were calculated by electronic structure methods at the MP2/6-31++G(d,p) level, and the well-known double-well potentials were characterized. The energy difference between both minima can be expressed by a parabola using as argument the donor-acceptor distance R(DA). In this work, the fit parameters of the quadratic expression are determined for each donor-acceptor pair. Moreover, it was found previously that the energy barriers of the reactions can be expressed by an analytical expression depending on the distance between donor and acceptor and the energy difference between donor and acceptor bound states. The validity of this approach is supported by the extensive new data set. This new parameterization of proton transfer barriers between titratable amino acid side chains allows us to very efficiently estimate proton transfer probabilities in molecular modelling studies or during classical molecular dynamics simulation of biomolecular systems.     

Effect of photonic crystal structure on the nonlinear optical anisotropy of birefringent porous silicon

Anisotropic photonic crystal structures consisting of birefringent porous silicon layers with alternating porosity were fabricated. The in-plane birefringence formed as a result of anisotropic etching in Si(110) results in unique multilayered structures with two distinct photonic bandgaps for orthogonal light polarizations. Nonlinear optical studies based on the third-harmonic generation from these structures demonstrate variation in the symmetry of the nonlinear optical response.