Solvent free oxidation of primary alcohols and diols using thymine iron(III) catalyst

In this study, we developed an efficient and selective iron-based catalyst system for the synthesis of ketones from secondary alcohols and carboxylic acids from primary alcohol. In situ generated iron catalyst of thymine-1-acetate (THA) and FeCl(3) under solvent-free condition exhibits high activity. As an example, 1-octanol and 2-octanol were oxidized to 1-octanoic acid and 2-octanone with 89% and 98% yields respectively.     

Secreted fungal sulfhydryl oxidases: sequence analysis and characterisation of a representative flavin-dependent enzyme from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis>

Background  

Sulfhydryl oxidases are flavin-dependent enzymes that catalyse the formation of de novo disulfide bonds from free thiol groups, with the reduction of molecular oxygen to hydrogen peroxide. Sulfhydryl oxidases have been investigated in the food industry to remove the burnt flavour of ultraheat-treated milk and are currently studied as potential crosslinking enzymes, aiming at strengthening wheat dough and improving the overall bread quality.     

Exploring laccase-like multicopper oxidase genes from the ascomycete <Emphasis Type="Italic">Trichoderma reesei</Emphasis>: a functional,phylogenetic and evolutionary study

Background  

The diversity and function of ligninolytic genes in soil-inhabiting ascomycetes has not yet been elucidated, despite their possible role in plant litter decay processes. Among ascomycetes, Trichoderma reesei is a model organism of cellulose and hemicellulose degradation, used for its unique secretion ability especially for cellulase production. T. reesei has only been reported as a cellulolytic and hemicellulolytic organism although genome annotation revealed 6 laccase-like multicopper oxidase (LMCO) genes. The purpose of this work was i) to validate the function of a candidate LMCO gene from T. reesei, and ii) to reconstruct LMCO phylogeny and perform evolutionary analysis testing for positive selection.     

Heterolytic dihydrogen activation by B(C6F5)3 and carbonyl compounds

Aromatic carbonyl compounds in combination with B(C(6)F(5))(3) are able to activate H(2) heterolytically. The reactivity of the carbonyl-B(C(6)F(5))(3) adduct is initiated by its thermal dissociation into components. After H(2) addition, aromatic carbonyl compounds convert into aryl-substituted methanes or alcohols.     

Infrared characterization of the HCOOH···CO2 complexes in solid argon: stabilization of the higher-energy conformer of formic acid

The complexes of formic acid (HCOOH, FA) with carbon dioxide are studied by infrared spectroscopy in an argon matrix. Two trans-FA···CO(2) and one cis-FA···CO(2) complexes are experimentally identified while the calculations at the MP2(full)/6-311++G(2d,2p) level of theory predict one more minimum for the cis-FA···CO(2) complex. The complex of the higher-energy conformer cis-FA with CO(2) is prepared by vibrational excitation of the ground-state trans-FA conformer combined with thermal annealing. The lifetime of the cis-FA···CO(2) complex in an argon matrix at 10 K is 2 orders of magnitude longer than that of the cis-FA monomer. This big difference is explained by the computational results which show a higher stabilization barrier for the complex. The solvation effects in solid argon are theoretically estimated and their contribution to the stabilization barriers of the higher-energy species is discussed. The relative barrier transmissions for hydrogen tunneling in the cis-FA···CO(2) complex and cis-FA monomer are in good agreement with the experimental decay rates.     

Dimers of the higher-energy conformer of formic acid: experimental observation

We report on the first experimental observation of formic acid dimers composed of two molecules of the higher-energy cis conformer. The cis-cis formic acid dimers are prepared in an argon matrix by selective vibrational excitation of the ground state trans conformer (deuterated form HCOOD) combined with thermal annealing of the matrix at about 30 K. Five cis-cis formic acid dimers are predicted by ab initio calculations (interaction energies from -16.9 to -27.2 kJ mol(-1)), and these structures are used for the assignment of the experimental spectra. Selective vibrational excitation of the obtained cis-cis dimers leads to the formation of several trans-cis dimers, which supports the proposed assignments.     

On theoretical predictions of noble-gas hydrides

We discuss the present status and reliability of theoretical predictions of noble-gas hydride molecules. It is shown that the single-reference MP2 calculations can produce a rather inaccurate energy diagram for the formation of noble-gas hydrides, and this may mislead the theoretical predictions. We suggest that the computational dissociation energy of the HY precursors should always be compared with the experimental values as a checkpoint for the computational accuracy. The computational inaccuracy probably explains why some compounds that are stable with the single-reference MP2 method (HArC(4)H, HArC(3)N, and HArCN) did not appear in matrix-isolation experiments, whereas the corresponding compounds with Kr and Xe are known.     

Binding properties of HABA-type azo derivatives to avidin and avidin-related protein 4

The chicken genome encodes several biotin-binding proteins, including avidin and avidin-related protein 4 (AVR4). In addition to D-biotin, avidin binds an azo dye compound, 4-hydroxyazobenzene-2-carboxylic acid (HABA), but the HABA-binding properties of AVR4 are not yet known. Differential scanning calorimetry, UV/visible spectroscopy, and molecular modeling were used to analyze the binding of 15 azo molecules to avidin and AVR4. Significant differences are seen in azo compound preferences for the two proteins, emphasizing the importance of the loop between strands beta3 and beta4 for azo ligand recognition; information on these loops is provided by the high-resolution (1.5 A) X-ray structure for avidin reported here. These results may be valuable in designing improved tools for avidin-based life science and nanobiotechnology applications.     

Dynamic intensity model calculation of vibronic oscillator strengths for Cs2NaNdCl6: A molecular dynamics study

We present here a dynamic intensity model calculation of vibronic oscillator strengths for the Cs2NaNdCl6 compound by applying the method of molecular-dynamics simulation (MDS). The force field parameters used for the MDS reproduce the structure and several vibrational frequencies of Cs2NaNdCl6 very well. Both the static-coupling (SC) and dynamic-coupling (DC) mechanisms are taken into account for the intensity parameter calculations, in which the effective point charges and isotropic polarizabilities are optimized with respect to experimental energy levels. A comparison of intensity parameters and vibronic oscillator strengths between the two individual mechanisms indicates that the DC mechanism is operative. The calculated vibronic oscillator strengths for the combined SC and DC mechanism agree quite well with the available experimental values.     

Hole transport in UTB MOSFETs in strained-Si directly on insulator with strained-Si thickness less than 5 nm

Hole transport is studied in ultrathin body (UTB) MOSFETs in strained-Si directly on insulator (SSDOI) with a Si thickness down to 1.4 nm. In these Ge-free SSDOI substrates, the Si is strained in biaxial tension with strain levels equivalent to strained-Si on relaxed SiGe, with Ge contents of 30 and 40% Ge. The hole mobility in SSDOI decreases slowly for Si thicknesses above 4 nm, but drops rapidly below that thickness. Relative to silicon-on-insulator control devices of equal thickness, SSDOI displays significant hole mobility enhancement for Si film thicknesses above 3.5 nm. Peak hole mobility is improved by 25% for 40% SSDOI relative to 30% SSDOI fabricated by the same method, demonstrating the benefits of strain engineering for 3.1-nm-thick UTB MOSFETs.