Keywords: Zirconium / Zirconium oxo cluster / Hafnium oxo cluster / Metal carboxylate / Ligand exchange 12 ] 2 is also reported for comparison. The Zr12 clusters are structurally related to the Zr6 clusters since they are composed of two Zr6 sub-units which are bridged by four carboxylate ligands. In each compound, carboxylic acid molecules interact with the cluster by hydrogen bonding to part of the µ 3 -OH ligands. The clusters are highly dynamic in solution, due to site exchange of the

The glycan chain repeats of the S-layer glycoprotein of

Hydrothermal polymerization (HTP) yields highly crystalline polyimides. A general picture of the mechanisms leading to crystallinity and morphology is provided.

No abstract

An opening for CO: An iron PNP pincer complex self‐assembles in the solid state through intermolecular FeCl⋅⋅⋅HN hydrogen bonds to form a 3D supramolecular network. This compound reacts readily with gaseous CO in the solid state and in solution to stereospecifically give the octahedral complexes cis‐ and trans‐[Fe(PNP‐iPr)(CO)(Cl)2], respectively. In the solid‐state process the supramolecular connectivities between individual molecules are maintained without loss of crystallinity.

Sacculi of Bacillus sphaericus CCM 2177 contain a secondary cell wall polymer which was completely extracted with 48% hydrofluoric acid. Nuclear magnetic resonance analysis showed that the polymer is composed of repeating units, as follows: →3)-[4,6-O-(1-carboxyethylidene)]∼0.5-β-d-ManpNAc-(1→4)-β-d-GlcpNAc-(1→. The N-terminal part of the S-layer protein carrying S-layer homologous motifs recognizes this polymer as a binding site.

Several new iron(II) complexes of the types [Fe(PNP)X 2 ] (X = Cl, Br) containing tridentate PNP pincer-type ligands based on 2,6-diaminopyridine and 2,6-diaminopyrimidine have been prepared. They all exhibit intermolecular Fe-X 3 3 3 H-N hydrogen bonds, forming supramolecular networks in the solid state. In the case of X = Cl these compounds react readily with gaseous CO both in the solid state and in solution to give selectively the octahedral complexes cis-and trans-[Fe(PNP)(CO)-(Cl) 2 ], respectively, whereas with X = Br mixtures of cis and trans isomers are obtained. These transformations are accompanied by color and spin-state changes. CO binding is fully reversible in all cases, and heating solid samples of either cis-or trans-[Fe(PNP)(CO)(X) 2 ] leads to complete regeneration of analytically pure [Fe(PNP)(X) 2 ]. M€ ossbauer spectroscopy confirmed the high-spin nature of the parent five-coordinate Fe(II) complex (δ = 0.80(1) mm s -1 ) and the shift to two different low-spin octahedral species after reaction with CO in the solid (δ = 0.13(1) mm s -1 ) or in solution (δ = 0.15(1) mm s -1 ). Magnetization studies led to a magnetic moment close to 4.9 μ B , reflecting the expected four unpaired d-electrons in [Fe(PNP)Cl 2 ], which were confirmed by DFT calculations. The DFT study of the reaction pathway for CO capture led to low energy barriers (e3.4 kcal mol -1 ). The cis-trans isomerization reaction was found to take place with a low energy barrier (10.8 kcal mol -1 ), after initial loss of chloride, and involves also spin-state changes.

The glycan repeats of the surface layer glycoprotein of Aneurinibacillus thermoaerophilus L420-91 T contain Drhamnose and 3-acetamido-3,6-dideoxy-D-galactose, both of which are also constituents of lipopolysaccharides of Gram-negative plant and human pathogenic bacteria. The two genes required for biosynthesis of the nucleotide-activated precursor GDP-D-rhamnose, gmd and rmd, were cloned, sequenced, and overexpressed in Escherichia coli. The corresponding enzymes Gmd and Rmd were purified to homogeneity, and functional studies were performed. GDP-D-mannose dehydratase (Gmd) converted GDP-D-mannose to GDP-6-deoxy-D-lyxo-4-hexulose, with NADP ؉ as cofactor. The reductase Rmd catalyzed the second step in the pathway, namely the reduction of the keto-intermediate to the final product GDP-D-rhamnose using both NADH and NADPH as hydride donor. The elution behavior of the intermediate and end product was analyzed by high performance liquid chromatography. Nuclear magnetic resonance spectroscopy was used to identify the structure of the final product of the reaction sequence as GDP-␣-D-rhamnose. This is the first characterization of a GDP-6-deoxy-Dlyxo-4-hexulose reductase. In addition, Gmd has been shown to be a bifunctional enzyme with both dehydratase and reductase activities. So far, no enzyme catalyzing these two types of reactions has been identified. Both Gmd and Rmd are members of the SDR (short chain dehydrogenase/reductase) protein family.