Biomedical subjects

Brent J. Hamstra

Publications and source records attributed to Brent J. Hamstra.

2 recordsLinked to original sources

PubMed1999

Molybdenum(V) on an Oxide String. Synthesis and Structure of the Novel Linear Trinuclear Complex {[MoO(TPP)][O-Mo(TPP)-O][MoO(TPP)]}ClO(4).

The syntheses and crystallographic characterization of the linear trinuclear complex [Mo(3)O(4)(TPP)(3)]ClO(4) and the monomeric precursors [MoO(TPP)(OClO(3))] and [MoO(TPP)(OH(2))]ClO(4) are described. The crystallographic analyses of [MoO(TPP)(OClO(3))] and [MoO(TPP)(OH(2))]ClO(4) show that these similar complexes are typical oxomolybdenum(V)-porphyrin complexes whose only significant structural differences are related to their respective axial ligands. [Mo(3)O(4)(TPP)(3)]ClO(4) is obtained by the controlled hydrolysis of [MoO(TPP)(OClO(3))] or by the direct reaction of [MoO(TPP)(OClO(3))] with {[MoO(TPP)](2)O}. This hydrolysis product contains the novel [Mo(3)O(4)(TPP)(3)](+) ion, which has an unprecedented linear [O=Mo-O-Mo-O-Mo=O](7+) unit and three nearly parallel 24-atom porphyrin mean planes. The central porphyrin is found to be rotated 29.3 degrees and 29.7 degrees with respect to the two terminal porphyrin ligands, which are nearly eclipsed (twist angle 0.44 degrees ). The formation of [Mo(3)O(4)(TPP)(3)]ClO(4) instead of the &mgr;-hydroxo-bridged binuclear complexes obtained from the hydrolysis of analogous mononuclear metalloporphyrin complexes is rationalized on the basis of the greater pi-acceptor ability of Mo(V). Crystal data for [MoO(TPP)(OClO(3)).0.9CH(2)Cl(2): a = 11.437(2) Å, b = 13.567(6) Å, c = 13.764(4) Å, alpha = 89.15(1) degrees, beta = 108.86(1) degrees, gamma = 103.96(2) degrees, triclinic, space group P&onemacr;, Z = 2, T = 293(2) K. Crystal data for [MoO(TPP)(OH(2))ClO(4).1.5C(7)H(8): a = 13.2138(7) Å, b = 13.5959(12) Å, c = 14.6676(11) Å, alpha = 74.292(8) degrees, beta = 69.114(8) degrees, gamma = 69.030(5) degrees, triclinic, space group P&onemacr;, Z = 2, T = 127(2) K. Crystal data for [Mo(3)O(4)(TPP)(3)]ClO(4).C(6)H(1)(4).3.4CH(2)Cl(2).4H(2)O: a = 26.428(6) Å, b = 18.683(6) Å, c = 28.692(4) Å, beta = 113.98(2) degrees, monoclinic, space group P2(1)/c, Z = 4, T = 127(2) K.

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PubMed1997

Structural and Solution Characterization of Mononuclear Vanadium(IV) Complexes That Help To Elucidate the Active Site Structure of the Reduced Vanadium Haloperoxidases.

The complexes [VO(H(2)O)ada] (1), [VO(H(2)O)Hheida] (2), and [VO(H(2)O)aeida] (3) (H(2)ada, N-(carbamoylmethyl)iminodiacetic acid; H(3)heida, N-(2-hydroxyethyl)iminodiacetic acid; H(2)aeida, N-(2-aminoethyl)iminodiacetic acid) were synthesized and crystallographically characterized. Crystallographic parameters for 1.2H(2)O: monoclinic, space group P2(1)/c (No. 14), a = 7.327(2) Å, b = 23.386(7) Å, c = 7.258(3) Å, alpha = 90 degrees, beta = 110.95(2) degrees, gamma = 90 degrees, V = 1204.6(7) Å(3), Z = 4, R1 = 0.0353, and wR(2)() = 0.0848. Crystallographic parameters for 2.H(2)O: orthorhombic, space group Pbca (No. 61), a = 10.512(2) Å, b = 11.727(2) Å, c = 16.719(5) Å, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, V = 2060.6(8) Å(3), Z = 8, R1 = 0.0297, and wR(2)() = 0.0758. Crystallographic parameters for 3: monoclinic, space group P2(1)/c (No. 14), a = 6.785(1) Å, b = 9.714(2) Å, c = 14.959(2) Å, alpha = 90 degrees, beta = 95.12(1) degrees, gamma = 90 degrees, V = 982.2(3) Å(3), Z = 4, R1 = 0.0298, and wR(2)() = 0.0762. In each structure, the tetradentate ligand is disposed so that the tertiary nitrogen is bound trans to the vanadyl oxo, and the rest of the donors occupy equatorial coordination positions. In solution, the structural integrity of these compounds is maintained as observed by UV/visible and EPR spectroscopies, and axial ligation by nitrogen is inferred on the basis of ESEEM spectroscopy. The implications of this study with respect to understanding the coordination environment of VO(2+) in the reduced, inactive form of vanadium bromoperoxidase (VBrPO) are discussed, and it is proposed that significant changes in the coordination environment of vanadium in VBrPO occur upon its reduction, which may provide a plausible explanation for its irreversible inactivation.

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