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This study explores key features of bromine and iodine metabolism in the filamentous brown alga and genomics model Ectocarpus siliculosus. Both elements are accumulated in Ectocarpus, albeit at much lower concentration factors (2-3 orders of magnitude for iodine, and

Despite its paramount role in the functioning of coastal ecosystems, relatively little is known about halogen metabolism in giant kelp (Macrocystis pyrifera). This is an important shortcoming given the potential implications for marine and atmospheric chemical processes in the wide distribution range of Macrocystis. The work presented here constitutes the first in depth investigation of the uptake, efflux, and of the physiological function of iodide in this important kelp species. Iodide uptake and efflux rates were measured in adult sporophytes of Macrocystis under normal and stressed (exogenous hydrogen peroxide and an elicitor-triggered oxidative burst) conditions. Kelp tissue took up iodide according to Michaelis-Menten type kinetics when incubated in seawater enriched with various concentrations of iodide. Upon the addition of exogenous hydrogen peroxide, simulating oxidative stress, a marked efflux of iodide occurred. In situ generation of hydrogen peroxide was elicited in Macrocystis upon the addition of oligomeric degradation products of alginate as well as arachidonic acid and methyl jasmonate constituting a defensive oxidative burst that could be linked to iodine accumulation. H2O2 was detected at the single cell level using dichlorohydrofluorescein diacetate, a fluorogenic probe capable of detecting intracellular H2O2. When assayed for vanadium haloperoxidase activity, several bromoperoxidase isoforms were detected as well as a single iodoperoxidase. Altogether, the results of this study show that Macrocystis has an elaborate iodine metabolism, which is likely significant for impacting iodine speciation in seawater around kelp beds and for volatile halogen emissions into the coastal atmosphere.

It is well known that bacteria and fungi have evolved sophisticated systems for acquiring the abundant but biologically inaccessible trace element iron. These systems are based on high affinity Fe(III)-specific binding compounds called siderophores which function to acquire, transport, and process this essential metal ion. Many hundreds of siderophores are now known and their numbers continue to grow. Extensive studies of their isolation, structure, transport, and molecular genetics have been undertaken in the last three decades and have been comprehensively reviewed many times. In this review we focus on a unique subset of siderophores that has only been recognized in the last 20 years, namely those whose iron complexes display photoactivity. This photoactivity, which typically results in the photooxidation of the siderophore ligand with concomitant reduction of Fe(III) to Fe(II), seemingly upsets the siderophore paradigm of forming and transporting only extremely stable Fe(III) complexes into microbial cells. Here we review their structure, synthesis, photochemistry, photoproduct coordination chemistry and explore the potential biological and ecological consequences of this photoactivity.

While polycarboxylates and hydroxyl-acid complexes have long been known to be photoactive, simple carboxylate complexes which lack a significant LMCT band are not typically strongly photoactive. Hence, it was somewhat surprising that a series of reports demonstrated that materials synthesized from iron(III) and polysaccharides such as alginate (poly[guluronan-co-mannuronan]) or pectate (poly[galacturonan]) formed photoresponsive materials that convert from hydrogels to sols under the influence of visible light. These materials have numerous potential applications in areas such as photopatternable materials, materials for controlled drug delivery, and tissue engineering. Despite the near-identity of the functional units in the polysaccharide ligands, the reactivity of iron(III) hydrogels can depend on the configuration of some chiral centers in the sugar units and in the case of alginate the guluronate to mannuronate block composition, as well as pH. Here, using temperature- and field-dependent transmission Mössbauer spectroscopy, we show that the dominant iron compound detected for both the alginate and pectate gels displays features typical of a polymeric (Fe

Bacteria use small diffusible molecules to exchange information in a process called quorum sensing (QS). An important class of quorum sensing molecules used by Gram-negative bacteria is the family of N-acylhomoserine lactones (HSL). It was recently discovered that a degradation product of the QS molecule 3-oxo-C(12)-homoserine lactone, the tetramic acid 3-(1-hydroxydecylidene)-5-(2-hydroxyethyl)pyrrolidine-2,4-dione, is a potent antibacterial agent, thus implying roles for QS outside of simply communication. Because these tetramic acids also appear to bind iron with appreciable affinity it was suggested that metal binding might contribute to their biological activity. Here, using a variety of spectroscopic tools, we describe the coordination chemistry of both the methylidene and decylidene tetramic acid derivatives with Fe(III) and Ga(III) and discuss the potential biological significance of such metal binding.

New binuclear complexes of Co(II), Zn(II), and Ni(II) derived from a diatopic heteroscorpionate ligand, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR, UV-vis spectroscopy, and magnetic susceptibility. These building blocks have been subsequently used for the construction of higher order metallosupramolecular architectures.

Reaction of [Os3(CO)11(NCMe)] with bis-diphenylphosphanylethylene sulfide, {Ph2PCH2CH2}2S (PSP), leads to the formation of [Os3(CO)11(PSP)] and [{Os3(CO)11}2(-PSP)] in good yield. Similarly, treatment of [Os3(CO)10(NCMe)2] with PSP affords the cluster [Os3(CO)10(-PSP)], in which the two phosphanes of the PSP ligand coordinate to different osmium atoms of the same triosmium unit. Reaction of [Os3(CO)11(PSP)] with [Os3(CO)10(NCMe)2] yields the compound 1,2-[{Os3(CO)11}(3-PSP){Os3(CO)10}] in which the thioether moiety and one of the phosphane groups of the PSP ligand are coordinated equatorially to the {Os3(CO)10} subunit. The cluster 1,2-[{Os3(CO)11}(3-PSP){Os3(CO)10}] is also formed when [Os3(CO)11(PSP)] is oxidatively decarbonylated by reaction with trimethylamine N-oxide. The metastable cluster 1,2-[{Os3(CO)11}(3-PSP){Os3(CO)10}] undergoes slow isomerisation at room temperature to form 1,1-[{Os3(CO)11}(3-PSP){Os3(CO)10}] in which the thioether and phosphane moieties coordinate in a chelating mode to one of the {Os3(CO)10} subunits with the thioether moiety in an axial position. The dynamic behaviour of these clusters has been investigated by variable-temperature 13C{1H} and 13P{1H} NMR spectroscopy. The solid-state structures of [{Os3(CO)11}2(-PSP)] and [Os3(CO)10(-PSP)] are reported.

Three new N2O heteroscorpionate ligands designated L6OH, L7OH and L9OH, containing either appended hydrogen bond donating or accepting residues have been synthesized and characterized. Metal complexes of these ligands with Co(II) and Ni(II) have been characterized by X-ray crystallography. A facile decomposition pathway leading to C–N bond cleavage and isolation of metal pyrazole complexes was also identified.

As models for the labile water ligands so ubiquitous in zinc metalloprotein active sites, aquo and hydroxo complexes of zinc with the ester substituted trispyrazolylborate ligand, [(TpCO2Et,Me) have been isolated and crystallographically characterized. These complexes are stabilized by internal hydrogen bonding between the water or hydroxide and the ester carbonyls of the ligand. The dinuclear hydroxo complex, which maintains its structure in solution, appears to catalyze self-transesterification reactions in alcoholic solvents. However, the expansion of the coordination sphere from four- to five-coordinate in 2 or the dimerization that occurs with 3 suggest that a more sterically restrictive ester substituted ligand will be needed to enforce the desired mononuclear four-coordinate pseudotetetrahedral geometry most commonly seen in zinc metalloenzyme active sites.

The hydrogen-bond accepting ligand K[TpCO2Et,Me] was prepared and its complexes with divalent Ni, Co, Mn and Cu reveal a stabilization of penta- or hexa-coordinate metal aquo complexes of the general form [TpCO2Et,MeM(H2O)x] (x = 2 or 3) which are unprecedented for the alkyl substituted Tp analogs. These complexes make good structural models for many of the enzymes of the vicinal oxygen chelate superfamily.

A series of pseudotetrahedral and octahedral zinc(II) complexes of the heteroscorpionate ligand bis(3,5-dimethylpyrazolyl)(1-methyl-1-sulfanylethyl)methane (L3SH) have been synthesized and most characterized by X-ray crystallography. Pseudotetrahedral complexes isolated include [Zn(L3S)(CH3)], [Zn(L3S)(Cl)], [Zn(L3S)(OAc)], [Zn(L3S)(SPhF5)], [Zn(L3S)(SBz)] (Bz = CH2Ph), [Zn(L3S)(OPhp-NO2)], and [Zn(L3S)2]. In addition, the octahedral complex [Zn2{(L3S)2Zn}{O2P(OPh)2}4] was also synthesized. Comparisons between these complexes and those of the corresponding tris(pyrazolyl)borate, Tp−, or aromatic phenol or benzenethiolate ligands (L1O)− and (L2S)− reveal significant differences. Among these is a change in binding of acetate from pure unidentate to anisobidentate as the ligand donor is changed from S to N to O. Trends such as these may aid in understanding how the donor set affects the structure and reactivity at pseudotetrahedral zinc centers in metalloproteins.

Nine new pseudotetrahedral Zn(II) complexes of the heteroscorpionate ligands (3-tert-butyl-2-hydroxy(or thio)-5-methylphenyl)bis(3,5-dimethylpyrazolyl)methane, L1OH or L2SH, have been prepared and characterized (in most cases crystallographically). Complexes isolated include [(L1O)ZnCl], [(L1O)ZnI], [(L1OH)ZnI(2)], [(L1O)ZnCH(3)], [(L1O)ZnOAc], [(L1O)ZnSPh], [(L1O)ZnSBz], [(L2S)ZnCH(3)], [(L2S)ZnSPh], and [(L2S)(2)Zn]. In conjunction with the widely studied tris(pyrazolyl)borates this new series of heteroscorpionates provides a set of isolobal and isoelectronic ligands differing in donor set, i.e. N(3), N(2)O, and N(2)S. Preliminary reactivity studies with HX species, MeI, or trimethyl phosphate suggest differences between the three sets of ligands.

The synthesis of a trinuclear thiolate bridged NiII system, [Ni3(L5S)4]2+ [L5SH = (2-sulfanylphenyl)bis(pyrazolyl)methane] which contains a linear NiS2NiS2Ni moiety, is reported. Two octahedrally coordinated (L5S)2Ni complexes, in which the thiol sulfurs are mutually cis, constitute the two terminal positions while the central position contains a distorted tetrahedral, four-coordinate, Ni(II) ion. In the presence of alkyl- or aryl-nitriles, such as MeCN, the [Ni3(L5S)4]2+ cation undergoes cleavage and rearrangement reactions to give thiolate bridged dinuclear dications, either [Ni2(L5S)2(MeCN)4]2+ or [Ni2(L5S)2(MeCN)2(H2O)2]2+, in which MeCN ligand N-donors (and/or H2O O-donors) occupy the vacant coordination sites of each Ni2+ atom. An analogous Co(II) dimer is also reported. The trimer → dimer reaction can be reversed by desolvation of [Ni2(L5S)2(MeCN)4]2+ or [Ni2(L5S)2(MeCN)2(H2O)2]2+ by an appropriate non-nitrile solvent, such as MeNO2 resulting in reformation of the [Ni3(L5S)4]2+ cation. Variable temperature magnetic data indicate that the Ni atoms in the trimer are weakly antiferromagnetically coupled while they are weakly ferromagnetically coupled in the dimer.

F. Organisms that accumulate vanadium ......... (i) Amanita muscaria (ii) Tunicates G. Vanadium-protein interactions (i) Vanadium transferrin (ii) Vanadoenzymes (a) Vanadium bromoperoxidase (b) Vanadium nitrogenase H. Other systems (i) Vanadyl-substituted bleomycin (ii) Vanadyl-substituted dopamine /J-monooxygenase (iii) Vanadocene interaction with nucleic acids .... I. Summary and a look to the future Acknowledgements References

The photoreactivep-azidobenzoyl analog of ferrioxamine B was used to show that ferrioxamine-B-mediated iron transport is separate and distinct from coprogen-mediated iron transport inEscherichia coli. Photolysis of this analog inhibited uptake of [59Fe]ferrioxamine B but not [59Fe]coprogen or [59Fe]ferrichrome. Conversely, photolysis of thep-azidobenzoyl analog of coprogen B inhibited uptake of [59Fe]coprogen but not [59Fe]ferrioxamine B or [59Fe]ferrichrome. Photolabeling of outer membranes withp-azidobenzoyl-[59Fe]ferrioxamine B resulted in the labeling of two iron-regulated peptides with molecular masses of about 66 and 26 kDa. Expression of these peptides was increased when ferrioxamine B was the sole iron source. Both peptides were present in outer membrane preparations of thefhuF mutant H1717, but the 66 kDa peptide was not inducible. These results are evidence for an outer membrane receptor inE. coli unique for linear ferrioxamines.

The new ditopic heteroscorpionate ligand, (3-methoxy-4-hydroxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L5v), and four coordination polymers of silver Ag(I) derived therefrom, have been synthesized and characterized by X-ray diffraction, ESI-MS, IR spectroscopy and elemental analysis. The presence of different anions (i.e. BF4−, CF3SO3−, NO3−, or SbF6−) lead to different crystal packing schemes due to different H-bonding patterns that depend on the relative charge delocalization and/or shape of the anion.

F. Organisms that accumulate vanadium ......... (i) Amanita muscaria (ii) Tunicates G. Vanadium-protein interactions (i) Vanadium transferrin (ii) Vanadoenzymes (a) Vanadium bromoperoxidase (b) Vanadium nitrogenase H. Other systems (i) Vanadyl-substituted bleomycin (ii) Vanadyl-substituted dopamine /J-monooxygenase (iii) Vanadocene interaction with nucleic acids .... I. Summary and a look to the future Acknowledgements References

Two isomeric tunichrome model compounds have been prepared from spermidine and trihydroxybenzoic acid. The coordination chemistry of these ligands with V(III), (IV), and (V) are reported. Vanadium(V) is found to undergo rapid reduction to V(IV) in the presence of these ligands, Vanadium(IV) complexes were characterized by optical and EPR spectroscopy as well as elemental analysis and magnetic measurements. Vanadium(III) also reacts rapidly with these ligands, producing what is thought to be a VOV dimer in acidic solution. The biological implications of the coordination chemistry reported herein with respect to vanadium metabolism in ascidians is discussed.

The intramolecularly base-stabilized arylaluminum dihydride [2,6-(Me2NCH2)2C6H3]AlH2 (1) has been prepared by the metathesis reaction of the corresponding lithium aryl with AlH2Cl·NMe3. Alternative methods for the synthesis of 1 are transmetalation or reduction reactions of [2,6-(Me2NCH2)2C6H3]MCl2 (M = Al (2), Ga (3), In (4)) with LiAlH4. The x-ray crystal structures of 1 and 2 have been determined: 1, orthorhobic, Pbca, with a = 17.179(3), b = 9.014(20, c = 12.707(3) A, V = 2794(1) A3 and Z = 8; 2, monoclinic, C2c, with a = 8.2880(10), b = 17.022(2), c = 14.381(3) A, β = 99.46(1)°, V = 2001.2(5) A3, and Z = 4. Compounds 1 and 2 are monomeric in the solid state.

A series of zinc complexes using a new tripodal, N(2)S, heteroscorpionate ligand (L3SH) that is isostructural and isoelectronic with the well-known N(3) trispyrazolylborates have been methylated in solution and the coordination properties of the resulting thioether examined. This system models the reactivity of zinc-containing enzymes involved in alkyl group transfers such as the DNA repair protein Ada from E. coli, or farnasyl transferase where it has been shown that the thioether resulting from alkyl group transfer remains in the coordination sphere of the zinc. The following complexes have been structurally characterized: [(L3S)ZnI] (1), [(L3SCH(3))ZnI(2)] (2), [(L3SCH(3))ZnI]BF(4) (3), [(L3SCH(3))Zn-mu-bis-acetato-mu-hydroxo-Zn(L3SCH(3))]BF(4) (5), [(L3SCH(3))ZnSPh(F5)]ClO(4) (7), and [(L3SCH(3))(2)Zn](BF(4))(2) (8). Complexes 3, 4, 5, 7, and 8 all display thioether coordination. Thus in the absence of superior anionic ligands, thioethers are reasonably good donors to zinc in either a tetrahedral or octahedral geometry. The methylation of the complex [(L3S)ZnSPh(F5)], which contains two different thiols, produces a single product, 7, where only the aliphatic thiol has been alkylated. This observation validates the suggestion that reactivity in enzymes with multiple zinc-bound thiols could be controlled by differences in thiol pK(a) (Hammes, B. S.; Warthen, C. R.; Crans, D.; Carrano, C. J. J. Biol. Inorg. Chem. 2000, 6, 82. Compound 7 is also of interest in that it resembles the metal ion-binding site of the blue copper protein, azurin.

Eight scorpionate-zinc thiolate complexes, [(L1O)ZnSPh], [(L1O)ZnSPhF5], [(L1O)ZnSBz], [(L1O)ZnSPh2,6-Me], [(L1O)ZnSPh2,4-Me], $${\rm [(L1O)ZnSPh}^{{\rm 4 - NO}_{\rm 2} } {\rm ]}$$ , [(TpPh,Ph)ZnSPh], and [(L2S)ZnSPh], were reacted with methyl iodide in chloroform, liberating the corresponding methyl thioethers as determined by 1H NMR. Three of these complexes are new and their synthesis and structural characterization are reported here. Weak alkylating agents such as trimethyl phosphate failed to undergo methyl transfer to the zinc thiolates under these conditions. Analysis of kinetic data as a function of concentration, temperature, pK a of the exogenous thiolate, and donor atom of the tripodal ligand are consistent with a mechanism where the zinc-bound thiolate is the active nucleophile in an associative-type methyl transfer reaction. Our model studies also provide experimental evidence to support the hypothesis that some enzymes can use the charge of the metal coordination site to modulate catalytic activity.

Rhizoferrin is a member of a new class of siderophores (microbial iron transport compounds) based on carboxylate and hydroxy donor groups rather than the commonly encountered hydroxamates and catecholates. We have studied the coordination chemistry of rhizoferrin (Rf), as a representative of this group, with Fe(3+), Rh(3+), Cr(3+), Al(3+), Ga(3+), VO(2+), and Cu(2+). The metal complexes have been studied by UV-vis, CD, NMR, and EPR spectroscopies and mass spectrometry. The formation constants for the iron complex have also been measured and yield a log K(LFe) of 25.3. The Rh and Cr rhizoferrin complexes are unusual in that they appear to adopt a chirality about the metal center that is the opposite of the native iron analog. Several of the alternative metal ion complexes are found to have biological activity toward Morganella morganii in a plate type assay.

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.

LBL-11878 Preprint LIBFV·',RY ANL1 Submitted to the Journal of the American Chemical Society SIDEROPHILIN METAL COORDINATION. 1. COMPLEXATION OF THORIUM BY TRANSFERRIN: STRUCTURE-FUNCTION I:MPLI CATIONS Wesley R. Harris, Carl J. Carrano, Vincent L. Pecoraro, and Kenneth N. Raymond August 1980 TWO-WEEK LOAN COPY This is a Library which may borrowed For a personal Copy two weeks. Tech. Info. Divisiony Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48

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.

Etude de l'acidification aerobie par HCl du complexe du titre donnant V IV Cl 2 (SALEN). Voltammetrie cyclique. Structure cristalline de V V O(SALEN)ClO 4

Les complexes d'oxovanadium avec l'ethylene bis ([o-hydroxyphenyl] glycine), EHPG, sont isoles et caracterises comme contenant du vanadium (IV) et du vanadium (V). Les etudes d'oxydoreduction electrochimique permettant d'etablir une relation entre ces 2 etats d'oxydation

Separation des formes meso et racemique du complexe du titre et evaluation comme modeles. Les 2 isomeres subissent l'hydrolyse a pH eleve. Implications de ces resultats par rapport a l'environnement du fer dans la transferrine

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)°.

[Co(H 2 O) 6 ] [Co(EHPG)] 2 •4H 2 O(1) (EHPG-ethylene bis-[(θ-hydroxyphenyl) glycine]) cristallise dans P2 1 /n avec Z=2; affinement jusqu'a R=0,025. [Mg[H 2 O) 6 ] [Ga(EHPG)] 2 •3H 2 O (2) cristallise dans C2/c avec Z=4; affinement jusqu'a R=0,033•Na 2 [Cu(EHPG)]•5,5H 2 O cristallise dans Pbcn avec Z=8; affinement jusqu'a R=0,052

Coordination pseudooctaedrique autour de l'atome Fe realisee par les 2 atomes N, les deux atomes O phenolates, l'atome O carboxylate et l'atome O d'une molecule methanol coordinee. Electrochimie. Spectre RPE et Mossbauer

Bromopyruvate, a known alkylating agent, has previously been reported to function as an affinity label for the anion-binding site in the iron-binding protein ovotransferrin [Patch, M.G., & Carrano, C. J. (1982) Biochim. Biophys. Acta 700, 217-220]. However, the present results indicate that hydroxypyruvate also functions in an almost identical manner, which implies that alkylation of a susceptible nucleophile cannot be the mechanism responsible for the covalent attachment of the anion. Model complexes and amino acid analysis of labeled ovotransferrin suggest that initial Schiff base formation, followed by reduction of the imine bond between the affinity anion and a lysine within the locus of the anion-binding site, accounts for the irreversible labeling. As expected, the covalently attached anions render the iron in the ovotransferrin-iron-anion ternary complex much more resistant to loss at low pH. It is proposed that the covalently labeled protein be used to test the hypothesis that iron removal from transferrin occurs by protonation and loss of the anion in low-pH lysosomal vesicles.

The mechanism by which iron uptake is facilitated by the siderophore rhodotorulic acid (RA) in the yeast Rhodotorula pilimanae was investigated with radioactively labeled Fe and RA and kinetically inert, chromic-substituted RA complexes. The weight of the evidence supports a model in which RA mediates iron transport to the cell but does not actually transport iron into the cell. It is proposed that RA exchanges the ferric ion at the cell surface with a membrane-bound chelating agent that completes the active transport of iron into the cell. Uptake of 55Fe in ferric rhodotorulate was much more rapid than uptake of RA itself. Two exchange-inert chromic complexes of RA showed no uptake.