Joseph A. Bonadies

The molecular structure and magnetic properties of the dimeric N,N'-ethylenebis (salicylamine) Fe(III)-μ-methoxo-N,N'-ethylene(o-hydroxylphenylglycine) salicylamine Fe(III): a complex with a μ-monodentate acetato bridge

Abstract We have prepared and characterized a dimeric complex of the formula Fe 2 L(OCH 3 )L′·solvent where L = N,N′ -ethylenebis(salicylamine) and L′ = N,N′ -ethylene( o -hydroxylphenylglycine)salicylamine. Crystals of the methanol solvate were found to be orthorhombic, space group P 2 nb , with a = 13.748 (5), b = 22.426(9), c = 11.762(6) A and d calc = 1.41 g/cm 3 . Least squares refinement of 966 reflections gave a final R factor of 0.066. The structure shows that the two iron atoms are coordinated to two different ligands and are bridged by a methoxide ion and a μ-monodentate acetate oxygen from the pendant arm of L′. The magnetic susceptibility was measured over the range 2–300 K and gave a spin coupling constant J = −8.3 cm −1 . The significance of acetate bridges to the exchange coupling pathway is discussed.

Evaluation of Structural Possibilities for the Mn Centers of the OEC

The great diversity of structural proposals for metal association in the OEC can be organized in three broad categories as single, dual or multiple centers. In the single center proposal, a tetranuclear assembly of manganese accumulates oxidizing equivalents and oxidizes water directly. The cubane proposal of Brudvig (1) and the double pivot mechanism of Christou (2) are two examples. These models have structural analogy to the Fe4S4 clusters. The multiple center idea (3) invokes a mononuclear Mn(IV) in an electron transfer equilibrium with a dinuclear center and a fourth, redox inactive manganese segregated from the other metal atoms. This is reminiscient of cytochrome oxidase where a dinuclear center reduces oxygen to water and two single site metal ions (copper and heme iron) contribute reducing equivalents. Two dual center possibilities are are two sets of dimers or, what we suggested (4), a monomer/trimer organization. The latter is consistent with Fe3S4 centers. A possible trinuclear structure is shown in figure 1. Three manganese are arranged in a distorted triangular orientation with the terminal manganese separated from the central manganese ion by 2.7 A. The two terminal manganese ions are separated by either 3.3 A or 4.3 A. A mononuclear center is located at a distance >5 A.

Transport properties of N-acyl derivatives of the coprogen and ferrichrysin classes of siderophores inNeurospora crassa

Several derivatives of the coprogen and ferrichrysin classes of siderophores were synthesized as potential affinity labels of the iron uptake system inNeurospora crassa. While only one of these compounds has proved useful as an affinity label, all were recognized and transported byNeurospora crassa. One derivative, chloroacetyl-ferrichrysin, proved to be an unexpectedly potent reversible inhibitor (K1=0.4 μM) of both ferrichrysin and coprogen uptake, similar to the natural siderophore, ferrirubin. The reported results provide further understanding of the steric and electronic requirements of siderophores for the iron uptake system inNeurospora crassa.

Models for the active sites in the manganese catalase, oxygen evolving complex and vanadium bromoperoxidase

LO81 MODELS FOR THE ACTIVE SITES IN THE MANGANESE CATALASE, OXYGEN EVOLVING COMPLEX AND VANADIUM BROMOPEROXIDASE. V.L. Pecoraro, X. Li, J.A. Bonadies, MS. Lab, E. Larson and S. Saadeh, Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-I 055, USA. Schiff Base and a-hydroxy acid complexes of manganese will be presented as models for the spectroscopic and reactivity behavior of oxygen metabolising manganese enzymes. Specific emphasis will be placed on evaluating the active site cluster nuclear@ and the role of calcium ion in the photosynthetic oxygen evolving enzyme. Vanadium (IV) and (V)complexes of alkoxy Schiff base ligands will be examined as models for the vanadium bromoperoxidase active site. The solution chemistry of Vanadium monomers and dimers will be presented.

The acid promoted disproportionation of a vanadium(IV) phenolate: implications for vanadium uptake in tunicates

Under anaerobic conditions VIVO(salen)(salen =N,N′-ethylenebis-salicylideneaminato) undergoes an acid promoted disproportionation to yield a VIII(salen) species and VVO(salen)+ which upon addition of chloride ion react via back electron transfer to yield VIVO(salen) and VIVCl2(salen).