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.
(7) was prepared by the reaction of [VOCl 2 (thf) 2 ] with phen in a methanolic solution. The X-ray structure of 3 shows that the vanadium(iv) atom is ligated to a tridentate mpg 3À ligand at the S thiolato , N peptide and O carboxylato atoms. The X-ray structure of 7 is also reported. The optical, infrared, magnetic, electron paramagnetic resonance, and electrochemical properties of compounds 1 ± 5Ć H 3 OH and 7 were studied. Combination of the correlation plots of the EPR parameters g z versus A z , or the groundstate orbital population (b*) 2 versus A z , together with the additivity relationship, A z,calcd Sn i A zi /4, were shown to provide a powerful tool for probing the equatorial donor atoms in an oxovanadium(iv) compound and consequently in biomolecules. Thus, these methods provide valuable evidence for the assignment of the equatorial donor atoms for the V IV O 2 center of the V IV O 2 ± glutathione system at various pH values. Model NMR studies (interaction of vanadium(v) with H 3 mpg) showed that there is a possibility of vanadium(v) ligation to glutathione. The contribution of a deprotonated peptide(amide) nitrogen to A z is not a fixed quantity (it varies from 29 to 43 Â 10 À4 cm À1), but is influenced by the presence of the three other donor atoms in the equatorial plane and, in particular, their charge.
Two mixed-valence Mn(III)Mn(II) complexes and a homo-valence Mn(II) trinuclear manganese complex of stoichiometry Mn(III)Mn(II)Mn(III)(5-Cl-Hsaladhp)(2)(AcO)(4)(MeOH)(2).4CH(3)OH (1a), Mn(III)Mn(II)Mn(III) (Hsaladhp)(2)(AcO)(2)(5-Cl-Sal)(2)(thf)(2) (3a) and Mn(II)Mn(II)Mn(II) (AcO)(6)(pybim)(2) (1b) where H(3)saladhp is a tridentate Schiff base ligand and pybim a neutral bidentate donor ligand, have been structurally characterized by using X-ray crystallography. The structurally characterized mixed-valence complexes have strictly 180 degrees Mn(III)-Mn(II)-Mn(III) angles as required by crystallographic inversion symmetry. The complexes are valence trapped with two terminal Mn(III) ions showing Jahn-Teller distortion along the acetate or salicylate-Mn(III)-X axis. The Mn.Mn separation is 3.511 Å and 3.507 Å respectively. The mixed-valence complexes have S = (3)/(2) ground state and the homovalence complex S = (5)/(2), with small antiferromagnetic exchange J couplings, -5.6 and -1.8 cm(-1), respectively, while the powder ESR spectra at 4 K show a broad low field signal with g approximately 4.3 for Mn(III)Mn(II)Mn(III) and a broad temperature-dependent signal at g = 2 for Mn(II)Mn(II)Mn(II). Crystal data for 1a: [C(36)H(60)O(20)N(2)Cl(2)Mn(3)], triclinic, space group P&onemacr;, a = 9.272(7) Å, b = 11.046(8) Å, c = 12.635(9) Å, alpha = 76.78(2) degrees, beta = 81.84(2) degrees, gamma = 85.90(2) degrees, Z = 1. Crystal data for 3a: [C(48)H(56)O(18)N(2)Cl(2)Mn(3)], monoclinic, space group P2(1)/n, a = 8.776(3) Å, b = 22.182(7) Å, c = 13.575(4) Å, beta = 94.44(1) degrees, Z = 2. Crystal data for 1b: [C(36)H(36)O(12)N(6)Mn(3)], triclinic, space group P&onemacr;, a = 13.345(6) Å, b = 8.514(4) Å, c = 9.494(4) Å, alpha = 75.48(1) degrees, beta = 75.83(1) degrees, gamma = 76.42(1) degrees, Z = 1.
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