Carl J. Carrano

Binding of Vanadate to Human Serum Transferrin

Human serum transferrin specifically and reversibly binds 2 equiv of vanadate at the two metal-binding sites of the protein. The vanadium(V)-transferrin complex can be formed either by the addition of vanadate to apotransferrin or by the air oxidation of the vanadyl(IV)-transferrin complex. The formation of the vanadium complex can be blocked by loading the apotransferrin with iron(III), and bound vanadium can be displaced from the protein by the subsequent addition of either gallium(III) or iron(III). The binding constant for the second equiv of vanadate is 10(6.5) in 0.1 M hepes, pH 7.4 at 25 degrees C. The binding constant for the first equiv of vanadate is probably very similar, although no quantitative value could be determined. Although transferrin reacts with the vanadate anion, studies on the transferrin model compound ethylenebis(o-hydroxyphenylglycine) indicate that at pH 9.5, the vanadium is binding at the metal-binding site as a dioxovanadium(V) cation coordinated to two phenolic residues at each binding site. This bound cation appears to be protonated over the pH range 9.5-6.5, as shown by changes in the difference uv spectrum of the transferrin complex, to produce an oxohydroxo species. Further decreases in the pH lead to dissociation of the vanadium-transferrin complex.

Synthesis and structure of two tris(pyrazolyl)boratotin(II) compounds

Abstract The reaction of SnCl 2 with 2 or 1 equivalents of [HB(pz * ) 3 ]K in CH 2 Cl 2 affords [HB(pz * ) 3 ] 2 Sn (I) or [HB(pz * ) 3 ]SnCl (II) (pz * = 3,5-dimethyl-1-pyrazolyl), respectively. The structures of I and II have been established by X-ray crystallography; I possesses a novel geometry. Compound I crystallizes in the P 1 − space group with a 10.975(1), b 11.067(2), c 14.578(3) A, α 88.64(1), β 85.71(1), and γ 83.74(1)°. Compound II crystallizes in the P 1 − space group with a 8.148(1), b 8.827(1), c 13.546(2) A, α 77.81(1), β 90.02(1), and γ 80.50(1)°.

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.

A photoaffinity label for the siderophore-mediated iron transport system in Neurospora crassa

Abstract A photoaffinity derivative of the coprogen class of siderophores, p -azidobenzoylcoprogen B, has been synthetized. In the dark it is recognized and taken up by the iron transport system in Neurospora crassa ( arg -5, ota, aga ) in a concentration-dependent manner ( K m = 6 μ M, V max = 0.2 nmol·min −1 ·mg −1 ). It is also a competitive inhibitor of coprogen uptake, K I ≈ 5 μ M. Photolyssis of cells with near-ultraviolet light during transport in the presence of the photoaffinity label results in approx. 50% irreversible inhibition of both coprogen and ferrichrysin uptake. Uptake of p -azidobenzoylcoprogen B itself is also inhibited upon illumination. It is proposed that this affinity label be used in isolation of the iron receptor protein(s) in N. crassa .

An affinity label for the anion binding site in ovotransferrin: Implications for iron release to reticulocytes

Bromopyruvate has been found to be an affinity label for the anion binding site in ovotransferrin. Spectral and radioactive labeling studies indicate that the bromopyruvate first forms a reversible ternary complex with ovotransferrin and iron and then reacts to yield the covalently bound product. This derivative is partially resistant to iron loss by protonation and suggests that protonation and loss of anion is a requisite first step for iron release to reticulocytes.

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.

Mössbauer spectroscopy on high‐spin d5 iron complexes: Crystal field calculations

Mossbauer spectra of high‐spin ferric Fe(EHPG) compounds in frozen solution have been recorded at 4.2 K in a small applied field. The spectra have been analyzed in terms of a spin Hamiltonian with S=5/2 used as an intermediate step for generating a crystal field model that has the ground sextet 6A1 and three excited quartet states appropriately spaced in energy. The model has been found to be appropriate for g=4.3 high‐spin ferric complexes with spin Hamiltonian D values in the range 0.6–1.7 cm−1. It is shown that the model can provide a three‐way correlation of the relevant data obtained by Mossbauer, EPR, and optical absorption spectroscopy.

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).