The DMSO reductase family of microbial molybdenum enzymes; Molecular properties and role in the dissimilatory reduction of toxic elements

The dimethylsulfoxide (DMSO) reductase family of molybdenum enzymes is a large and diverse group that is found in bacteria and archaea. These enzymes are characterised by a bis(molybdopterin guanine dinucleotide)Mo form of the molybdenum cofactor, and they are particularly important in anaerobic respiration including the dissimilatory reduction of certain toxic oxoanions. The structural and phylogenetic relationship between the proteins of this family is discussed. High-resolution crystal structures of enzymes of the DMSO reductase family have revealed a high degree of similarity in tertiary structure. However, there is considerable variation in the structure of the molybdenum active site and it seems likely that these subtle but important differences lead to the great diversity of function seen in this family of enzymes. This diversity of catalytic capability is associated with several distinct pathways of electron transport.

Electrolytic properties and nanostructural features in the La2O3-CeO2 system

Doped ceria (CeO2) compounds are fluorite-type oxides which show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in applications of these materials for low or intermediate temperature operation of solid-oxide fuel cells (SOFCs). In this study, the effective index was suggested to maximize the ionic conductivity in La2O3-CeO2 based oxides. The index considers the fluorite structure, and combines the expected oxygen vacancy level with the ionic radius mismatch between host and dopant cations. Using this approach, the ionic conductivity of this system has been optimized and tested under operating conditions of SOFCs. LaxCe1-xO2-delta (x = 0.125, 0.15, 0.175, and 0.20), (LaxSr1-x)(0.175)Ce0.825O2-delta (x = 0.1, 0.2, and 0.4), and (La1-xSr0.2Bax)(0.175)Ce0.825O2-delta (x 5 0.03, 0.05, and 0.07) were prepared and characterized as the specimens with low, intermediate, and high index, respectively. The ionic conductivity was increased with increasing suggested index. The transmission electron microscopy analysis suggested that partial substitution of alkaline earth elements in place of La into Ce site contributes to a decrease of microdomain size and an improvement of conductivity. (La0.75Sr0.2Ba0.05)(0.175)Ce0.825O1.891 with high index and small microdomains exhibited the highest conductivity, wide ionic domain, and good performance in SOFCs. (C) 2003 The Electrochemical Society.

Synthesis and complexation properties of some novel lariat-crown ethers

Several new lariat-crown ethers bearing either bridged bisdioxine or tetraoxaadamantane units as chiral substituents are prepared by reacting the corresponding amino-crown ether derivatives with the dimeric alpha-oxoketene, the latter obtained by flash vacuum pyrolysis of a furan-2,3-dione precursor. Complexation properties towards differently charged metal ions are investigated by H-1 NMR titration to obtain complexation constants (K-c-values for potassium/ sodium rhodanides: 480-1100 mol dm(-3)), as well as extraction experiments to explore the metal ion transportation abilities of the new lariat crown derivatives. In particular, a significantly increased ability to transport metal ions from water into chloroform was found with spherical tetraoxaadamantyl derivatives when compared with the free amino-benzocrown ethers.