6.1.2. Aqueous V(III) Chemistry 877 6.1.3. Oxidation State of Vanadium in Tunicates 878 6.1.4. Uptake of Vanadate into Tunicates 879 6.1.5. Vanadium Binding Proteins: Vanabins 879 6.1.6. Model Complexes and Their Chemistry 880 6.1.7. Catechol-Based Model Chemistry 880 6.1.8. Vanadium Sulfate Complexes 881 6.2. Fan Worm Pseudopotamilla occelata 883 7. Vanadium Nitrogenase 883 7.1. Nitrogenases 883 7.2. Biochemistry of Nitrogenase 884 7.3. Clusters in Nitrogenase and Model Systems: Structure and Reactivity 885

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The chemistry and biochemistry of vanadium and the biological activities exerted by vanadium compounds.

Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous pow...

The perovskite structure—a review of its role in ceramic science and technology

Calcium oxalate (CaOx) crystals are distributed among all taxonomic levels of photosynthetic organisms from small algae to angiosperms and giant gymnosperms. Accumulation of crystals by these organisms can be substantial. Major functions of CaOx crystal formation in plants include high-capacity calcium (Ca) regulation and protection against herbivory. Ultrastructural and developmental analyses have demonstrated that this biomineralization process is not a simple random physical-chemical precipitation of endogenously synthesized oxalic acid and environmentally derived Ca. Instead, crystals are formed in specific shapes and sizes. Genetic regulation of CaOx formation is indicated by constancy of crystal morphology within species, cell specialization, and the remarkable coordination of crystal growth and cell expansion. Using a variety of approaches, researchers have begun to unravel the exquisite control mechanisms exerted by cells specialized for CaOx formation that include the machinery for uptake and accumulation of Ca, oxalic acid biosynthetic pathways, and regulation of crystal growth.

CALCIUM OXALATE IN PLANTS: Formation and Function

I. Introduction A FUNCTIONAL relationship between cell growth and the initiation and progression of events associated with differentiation has been a fundamental question challenging developmental biologists for more than a century. In the case of bone, as observed with other cells and tissue, the relationship of growth and differentiation must be maintained and stringently regulated, both during development and throughout the life of the organism, to support tissue remodeling. For many years, bone was defined anatomically and examined largely in a descriptive manner by ultrastructural analysis and by biochemical and histochemical methods. These studies provided the basis for our understanding of bone tissue organization and orchestration of the progressive recruitment, proliferation, and differentiation of the various cellular components of bone tissue. Now, complemented by an increased knowledge of molecular mechanisms that are associated with and regulate expression of genes encoding phenotypic compone...

Molecular mechanism mediating proliferation, defferentiation interralationships during progressie development of the osteoblast phenotype

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

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Application of Spectroscopic Methods for Structural Analysis of Chitin and Chitosan

Crystallographic data on ammonium uranyl phosphate trihydrate

The crystal structure of pyridinium thiosaccharinate thiosaccharin, [HNC5H5]+ [(tsac)(Htsac)]− (Htsac = C7H5NO2S2, the thiosaccharin molecule), was determined by single-crystal X-ray diffraction. Both, the thiosaccharinate anion, the corresponding neutral molecule and the pyridinium cation are nearly planar and arranged in the solid state in an almost parallel fashion, hence giving rise to a layered supramolecular structure. The anion shows small but significant modifications in the bonding of the thioamide group as compared with the neutral molecule. The crystal is further stabilized by an extensive H-bonding network. The FTIR spectrum of the compound is briefly commented.

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A New Supramolecular Assembly Obtained by Reaction Between Thiosaccharin and Pyridine

Recently, Braunstein and Clark1 described the synthesis and vibrational spectra of complexes containing the AuCl2, AuBr2 and AuI2 ions. In order to obtain a deeper insight into the vibrational properties of these anions it seems interesting to calculate, using the available spectroscopic data, values for the mean amplitudes of vibration and some related quantities.

Enrique J. Baran

Papers

Crystallographic data on ammonium uranyl phosphate trihydrate

A New Supramolecular Assembly Obtained by Reaction Between Thiosaccharin and Pyridine

Mean Amplitudes of Vibration for Some Linear Gold(I) Complexes

Neue Beweise über die Wechselwirkung des Vanadyl(IV)-Kations mit Nucleotiden: 31P-NMR- und IR-Messungen in Lösung

Mittlere Schwingungsamplituden von Chromylfluorid