A representative set of vanadium(IV and V) compounds in varying coordination environments has been tested in the concentration range 1 to 10(-6) mM, using transformed mice fibroblasts (cell line SV 3T3), with respect to their short-term cell toxicity (up to 36 hours) and their ability to stimulate glucose uptake by cells. These insulin-mimetic tests have also been carried out with non-transformed human fibroblasts (cell line F26). The compounds under investigation comprise established insulin-mimetic species such as vanadate ([H(2)VO(4)](-)), [VO(acetylacetonate)(2)], [VO(2)(dipicolinate)](-) and [VO(maltolate)(2)], and new systems and coordination compounds containing OO, ON, OS, NS and ONS donor atom sets. A vitality test assay, measuring the reduction equivalents released in the mitochondrial respiratory chain by intracellular glucose degradation, is introduced and the results are counter-checked with (3)H-labelled glucose. Most compounds are toxic at the 1 mM concentration level, and most compounds are essentially non-toxic and about as effective as or more potent than insulin at concentrations of 0.01 mM and below. V(V) compounds tend to be less toxic than V(IV)compounds, and complexes containing thio functional ligands are somewhat more toxic than others. Generally, ON ligation is superior in insulin-mimetic efficacy to OO or O/ NS coordination, irrespective of the vanadium oxidation state. There is, however, no striking correlation between the nature of the ligand systems and the insulin-mimetic potency in these cell culture tests, encompassing 41 vanadium compounds, the results on 22 of which are reported in detail here. The syntheses and characteristics of various new compounds are provided together with selected speciation results. The crystal and molecular structures of [[VO(naph-tris)](2)] [where naph-tris is the Schiff base formed between o-hydroxynaphthaldehyde and tris(hydroxymethyl)amine] are reported. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-001-0311-5.

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Speciation in the molybdophosphate system has been studied by a combination of potentiometric (glass electrode) and 31P NMR measurements at 25 °C in 3.0 M Na(C104) medium. Data cover the acidity range 5.5 > -lg [H+] > 0.5.la The total concentrations of molybdate, Mo, and phosphate, P, were varied within the limits 0.010 < Mo < 0.480 M and 0.005 < P < 0.040 M. By using the NMR data qualitatively and quantitatively, by adjusting formation constants to minimize deviations in both emf and NMR data, and by taking results from earlier complementary studies into consideration, we have now established the existence of 18 molybdophosphate complexes and been able to determine compositions and formation constants for the 14 different species that are formed in significant amounts (>0.05/'). Four series of homonuclear molybdophosphate complexes exist. Besides the Mo5P2 and ,, series there are two isomeric Mo9P series. In acid solutions (-lg [H+] 5 1.8) and at high Mo/P ratios (>9) an Mo12P complex is present. Equilibria are rapid, except for -lg [H+] < 3, where the dimer Mo18P2 is slowly formed, the slower the higher the Mo/P ratio. This species takes up to 1 month to be formed in full amount. Equilibrium constants and NMR characteristics of the complexes formed are given. The equilibrium conditions for "fresh" and "aged" solutions are illustrated in distribution diagrams. Known and proposed structures of the main complexes are discussed.

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A systematic study of the physiologically interesting vanadium-maltol (V-MaH) system has been performed in 0.150 M Na(Cl) at 25 degrees C, using NMR, ESR, and potentiometric techniques. Complexation occurs within a wide pH range, from around 1 up to 10.5. However, a pH-, concentration-, and time-dependent spontaneous reduction of vanadium(V) to vanadium(IV) occurs. From ESR spectra the conditions for this reduction are evaluated and discussed. From potentiometric (glass electrode) and quantitative (51)V NMR measurements, the full speciation in the H(+)-H(2)VO(4)(-)-MaH system was determined in the pH range 5-10.5. Data were evaluated with the computer program LAKE, which is able to treat combined emf and NMR data. The pK(a) value for MaH was determined to be 8.437 +/- 0.005. In the ternary system, three complexes are formed: VMa(2)(-), VMa(-), and VMa(2)(-), having log beta(0,1,2) = 7.02 +/- 0.03, log beta(0,1,1) = 2.66 +/- 0.05, and log beta(-)(1,1,1) = -7.37 +/- 0.21. The errors given are 3sigma. The VMa(2)(-) complex appears as the main species in a pH range from 4.5 to 8.5, whereas both mononuclear monoligand species are minor. Equilibrium conditions are illustrated in distribution diagrams, and the structures of the complexes formed are proposed.