Solution structural studies of molybdate-nucleotide polyanions

Spontaneous Assembly of an Organic-Inorganic Nucleic Acid Z-DNA Double-Helix Structure

Herein, we report a hybrid polyoxometalate organic-inorganic compound, Na₂ [(HGMP)₂ Mo₅ O₁₅ ]⋅7 H₂ O (1; where GMP=guanosine monophosphate), which spontaneously assembles into a structure with dimensions that are strikingly similar to those of the naturally occurring left-handed Z-form of DNA. The helical parameters in the crystal structure of the new compound, such as rise per turn and helical twist per dimer, are nearly identical to this DNA conformation, allowing a close comparison of the two structures. Solution circular dichroism studies show that compound 1 also forms extended secondary structures in solution. Gel electrophoresis studies demonstrate the formation of non-covalent adducts with natural plasmids. Thus we show a route by which simple hybrid inorganic-organic monomers, such as compound 1, can spontaneously assemble into a double helix without the need for a covalently connected linear sequence of nucleic acid base pairs.

Structural characterization and reactivity of gamma-octamolybdate functionalized by proline

The reaction of molybdate and dl-proline at pH 3.4 results in the formation of a Na(4)[Mo(8)O(26)(proO)(2)] x 22H(2)O complex (pro=proline) in which two proline ligands are attached to molybdenum(VI) ions via monodentate coordination of the carboxylate groups. The structure of the complex was determined by single crystal X-ray diffraction and by combination of (1)H, (13)C and (95)Mo NMR spectroscopy techniques in solution. The structure of the complex is strongly dependent on the pH. At native pH 3.4 the octamolybdate-type structure seems to be present in solution, but the increase of pH to 5.8 resulted in a rearrangement of the structure to a heptamolybdate-type structure. At physiological pH, the polyoxometalate framework was completely dissociated into the monomeric MoO(4)(2-) unit. The reactivity of the Na(4)[Mo(8)O(26)(proO)(2)] x 22H(2)O towards the hydrolysis of ATP was tested at different pH values. While in solution at pH 3.4 the hydrolysis proceeded to yield AMP (adenosine monophosphate) and ADP (adenosine diphosphate) in nearly equal amounts, reaction mixture at pH 5.8 gave ADP as the only product of hydrolysis after 24h of reaction. At neutral pH, the hydrolysis of ATP was slower, but it proceeded to yield 75% of ADP after 48 h of reaction.

Reactivity of potential anti-diabetic molybdenum(VI) complexes in biological media: A XANES spectroscopic study

The application of Mo(VI) complexes as anti-diabetic agents is a subject of considerable recent interest. The stability and speciation of [Mo(VI)O(4)](2-) and three analogs of known anti-diabetic V(IV) complexes ([Mo(VI)O(2)L(2)]; where LH=2,4-pentanedione, l-cysteine ethyl ester or N,N-diethyldithiocarbamic acid) in natural and simulated biological fluids (including blood and its components, cell culture media, and artificial digestion systems) were studied using MoK-edge XANES (X-ray absorption near-edge structure) spectroscopy of freeze-dried samples at 20K. All of the studied [MoO(2)L(2)] complexes decomposed extensively under simulated gastric and intestinal digestion conditions (3 h at 310 K), as well as in blood plasma or in cell culture medium (24 h at 310 K). The reaction products of [MoO(4)](2-) and [MoO(2)L(2)] with biological fluids could be satisfactorily modelled (using multiple linear regression analyses) as mixtures of tetrahedral and octahedral Mo(VI) species (with O-donor ligands) in various ratios, which were dependent on the nature of the medium rather than that of the initial Mo(VI) compounds. Red blood cells take up Mo(VI) predominantly in the form of [MoO(4)](2-). Implications of these results to the development of Mo(VI)-based anti-diabetics and to the mechanisms of natural uptake and metabolism of Mo(VI) are discussed.