Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Compounds Exhibiting Coördination Number Eight. The Potassium Tetraoxalatometallates of Zirconium(IV), Hafnium(IV), Thorium(IV), and Uranium(IV)

Abstract: Conditions for the preparation of the tetraoxalatometallates of zirconium (IV), hafnium (IV), thorium(IV), and uranium (IV), free of hydrolysis products, were studied. The zirconium and hafnium compounds are monoclinic with four molecules in the unit cell. The crystals belong to the space group P2/sub 1/ /a, which permits the existence of mirror images in the solid state. Attempts to resolve the possible racemic pairs of these anions were unsuccessful. Oxalate exchange studies with C/sup 14/ containing oxalic acid showed that complete exchange occurred withth a few minutes time of the experiment. It is shown that the anions lose oxalate by hydrolysis and/or aquation. The infrared spectra have frequencies for O-C-O vibrations about half way between those for the oxalate ion and a covalent oxalate molecule. (auth)

Iron(III) complexes of fluorescent hydroxamate ligands: preparation, properties, and cellular processing

Abstract: Iron(III) complexes containing hydroxamic acid fluorophores were investigated as models of hypoxia selective prodrugs in vitro. Two complexes were synthesised, [Fe(c343haH)3] and [Fe(salen)(c343haH)]. The fluorescence of the hydroxamate coumarin fluorophore was almost completely quenched on coordination to the iron(III) centre in [Fe(c343haH)3]. However, quenching was minimal for [Fe(c343haH)(salen)] in aqueous media and we propose that the fluorescence results from structural rearrangements that occur because of the inherent strain in the iron-salen structure. Fluorescence was also measured in the presence of the cellular reductants ascorbic acid and cysteine. Fluorescence intensity increased over time, with the most rapid return of fluorescence occurring over a two hr period. The rapid fluorescence return indicates that the complexes undergo ligand release, either via reduction followed by aquation, or via direct ligand exchange with the reductants. Electrochemical studies demonstrated that both complexes have very negative reduction potentials. Furthermore, [Fe(c343haH)(salen)] was shown to exhibit quasi-reversibility of reduction. The distribution of the free hydroxamate ligand and the complexes were monitored in A2780 cells. The free ligand displayed non-specific distribution, which differed from the nucleolar distribution of [Fe(c343haH)3] and the lysosomal accumulation of [Fe(c343haH)(salen)] over time. Thus the results of the present study show that iron(III) complexes present a viable model for monitoring hydroxamate fluorophore displacement in vitro to determine the fate of prodrugs.

Micellar inhibition of the aquation of tris-(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) by sodium dodecyl sulphate in aqueous acid medium

Abstract: The inhibition of the aquation of Fe(Me4phen)2+3 by sodium dodecyl sulphate (SDS) in aqueous acid media has been investigated and a mechanism which explains the pronounced inhibition and pre-micellar activity at low [SDS]T has been proposed. Inhibition is due to favourable thermodynamic-/hydrophobic/electrostatic binding between the FeII complex and SDS monomer aggregates. The bound FeII complex is stabilised with respect to dissociation and binding takes place between the ridges of the Stern layer. The partitioning of the substrate between the bulk-water phase and the micellar phase is in favour of the latter at low [H+]T and low [SDS]T. From the rate law obtained and the observed kinetic data, the micelle–complex binding constant (K1) and micelle–acid binding constant (K3) were calculated to be (2.81 ± 0.08)× 105 and (13.80 ± 0.16) dm3 mol–1, respectively, in acid media. Using the Scatchard method, K1 values of (3.95 ± 0.08)× 105 and (3.04 ± 0.16)× 105 dm3 mol–1 were calculated for the binding in neutral medium (distilled water) and 2 × 10–5 mol dm–3 H+, respectively. The decrease in K1 in acid media is attributed to competition between H+ and the complex ion for the binding sites on the micelle. The kψ–[SDS]T profiles are structured owing to the evolution (size, geometry, aggregation number, etc.) of the micelle. The inhibition of the aquation rate by HSO–4 and SO2–4 ions which form a negative field around the FeII complex is only significant at high acid concentrations. The micelle-bound complex and micelle-bound protons have opposing effects on the aquation rate. The degree of inhibition is therefore sensitive to the ratio of the concentration of these bound species.

Osmium(II) tethered half-sandwich complexes: pH-dependent aqueous speciation and transfer hydrogenation in cells

Abstract: Aquation is often acknowledged as a necessary step for metallodrug activity inside the cell. Hemilabile ligands can be used for reversible metallodrug activation. We report a new family of osmium(II) arene complexes of formula [Os(η6-C6H5(CH2)3OH)(XY)Cl]+/0 (1–13) bearing the hemilabile η6-bound arene 3-phenylpropanol, where XY is a neutral N,N or an anionic N,O− bidentate chelating ligand. Os–Cl bond cleavage in water leads to the formation of the hydroxido/aqua adduct, Os–OH(H). In spite of being considered inert, the hydroxido adduct unexpectedly triggers rapid tether ring formation by attachment of the pendant alcohol–oxygen to the osmium centre, resulting in the alkoxy tethered complex [Os(η6-arene-O-κ1)(XY)]n+. Complexes 1C–13C of formula [Os(η6:κ1-C6H5(CH2)3OH/O)(XY)]+ are fully characterised, including the X-ray structure of cation 3C. Tether-ring formation is reversible and pH dependent. Osmium complexes bearing picolinate N,O-chelates (9–12) catalyse the hydrogenation of pyruvate to lactate. Intracellular lactate production upon co-incubation of complex 11 (XY = 4-Me-picolinate) with formate has been quantified inside MDA-MB-231 and MCF7 breast cancer cells. The tether Os–arene complexes presented here can be exploited for the intracellular conversion of metabolites that are essential in the intricate metabolism of the cancer cell.