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The dinoflagellate Alexandrium catenella is a well-known paralytic shellfish toxin producer that forms harmful algal blooms (HABs) worldwide. Blooms of this species have repeatedly brought severe ecological and economic impacts to Chile, especially in the southern region, where the shellfish and salmon industries are world-famous. The mechanisms of such HABs have been intensively studied but are still unclear. Nutrient overloading is one of the often-discussed drivers for HABs. The present study used the A. catenella strain isolated from southern Chile to investigate how iron conditions could affect their growth and toxin production as related to HAB. Our results showed that an optimum concentration of iron was pivotal for proper A. catenella growth. Thus, while excess iron exerted a toxic effect, low iron media led to iron insufficiency and growth inhibition. In addition, the study shows that the degree of paralytic shellfish toxin production by A. catenella varied depending on the iron concentration in the culture media. The A. catenella strain from southern Chile produced GTX1-4 exclusively in the fmol cell−1 scale. Based on these findings, we suggest that including iron and paralytic shellfish toxin measurements in the fields can improve the current HAB monitoring and contribute to an understanding of A. catenella bloom dynamics in Chile.

Many marine algae are strong accumulators of halogens. Commercial iodine production started by burning seaweeds in the 19th century. The high iodine content of certain seaweeds has potential pharmaceutical and nutritional applications. While the metabolism of iodine in brown algae is linked to oxidative metabolism, with iodide serving the function of an inorganic antioxidant protecting the cell and thallus surface against reactive oxygen species with implications for atmospheric and marine chemistry, rather little is known about the regulation and homoeostasis of other halogens in seaweeds in general and the ecological and biological role of marine algal halogenated metabolites (except for organohalogen secondary metabolites). The present review covers these areas, including the significance of seaweed-derived halogens and of halogens in general in the context of human diet and physiology. Furthermore, the understanding of interactions between halogenated compound production by algae and the environment, including anthropogenic impacts, effects on the ozone layer and global climate change, is reviewed together with the production of halogenated natural products by seaweeds and the potential of seaweeds as bioindicators for halogen radionuclides.

Phytoplankton blooms can cause acute effects on marine ecosystems due either to their production of endogenous toxins or to their enormous biomass leading to major impacts on local economies and public health. Despite years of effort, the causes of these Harmful Algal Blooms are still not fully understood. Our hypothesis is that bacteria that produce photoactive siderophores may provide a bioavailable source of iron for phytoplankton which could in turn stimulate algal growth and support bloom dynamics. Here we correlate iron concentrations, phytoplankton cell counts, bacterial cell abundance, and copy numbers for a photoactive siderophore vibrioferrin biosynthesis gene in water samples taken from 2017 cruises in the Gulf of California, and the Pacific Ocean off the coast of northern Baja California as well as during a multiyear sampling at Scripps Pier in San Diego, CA. We find that bacteria producing the photoactive siderophore vibrioferrin, make up a surprisingly high percentage of total bacteria in Pacific/Gulf of California coastal waters (up to 9%). Vibroferrin's unique properties and the widespread prevalence of its bacterial producers suggest that it may contribute significantly to generating bioavailability of iron via photoredox reactions.

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

Brown algae include the strongest accumulators of iodine known among living systems. This paper reviews the current state of bioinorganic research in the field, focusing on the models Laminaria digitata, Macrocystis pyrifera and Ectocarpus siliculosus, and covering uptake and efflux, localization and biological significance of storage, as well as marine and atmospheric chemistry of iodine.

Heteroscorpionate-based [(L10O)MoO2Cl] and [(L3S)MoO2Cl] complexes containing an interchangeable third heteroatom donor have been utilized for the systematic investigation of oxygen atom transfer (OAT) reactivity. The detection of phosphoryl intermediates and products in the reaction pathway were probed by UV–Vis, mass spectrometry, and 31P NMR spectroscopy. The OAT reactivity of the metal complexes toward PPh3 were monitored by UV–Vis spectroscopy under pseudo-first order conditions. The sterically encumbered (L10O) ligand gives rise to isolable trans and cis isomers of [(L10O)MoO2Cl] allowing investigation into the role of geometry on OAT reactivity. The OAT reactivity of the cis isomer of (L10O)MoO2Cl demonstrated a dramatic solvent dependence, in which the reaction proceeded at a measureable rate only in pyridine. However, the trans counterpart reacted in all solvents and at much faster rates. The catalytic oxidation of PPh3 to OPPh3 by trans-[(L10O)MoO2Cl] and cis-[(L3S)MoO2Cl] complexes using DMSO as an oxygen donor was monitored by 31P NMR in DMF at 30 °C with rates, kcat = 4.26 × 10−5 s−1 and 5.28 × 10−5 s−1, respectively.

In this brief review we focus on a few examples of how a family of homo- and heteroscorpionate ligands allow us to examine how changes in reactivity, structure, or physical/chemical properties around biologically interesting N2X coordinated metal centers vary as a function of donor atom, charge, hydrophobicity, hydrogen bonding, etc., in a way previously unavailable. Such a family of ligands is the bioinorganic chemists answer to site-directed mutagenesis. Here we focus on two bioinorganic examples i.e. models for molybdoenzymes and zinc metalloproteins.

In contrast to the generally boron-poor terrestrial environment, the concentration of boron in the marine environment is relatively high (0.4 mM) and while there has been extensive interest in its use as a surrogate of pH in paleoclimate studies in the context of climate change-related questions, the relatively depth independent, and the generally non-nutrient-like concentration profile of this element have led to boron being neglected as a potentially biologically relevant element in the ocean. Among the marine plant-like organisms the brown algae (Phaeophyta) are one of only five lineages of photosynthetic eukaryotes to have evolved complex multicellularity. Many of unusual and often unique features of brown algae are attributable to this singular evolutionary history. These adaptations are a reflection of the marine coastal environment which brown algae dominate in terms of biomass. Consequently, brown algae are of fundamental importance to oceanic ecology, geochemistry, and coastal industry. Our results indicate that boron is taken up by a facilitated diffusion mechanism against a considerable concentration gradient. Furthermore, in both Ectocarpus and Macrocystis some boron is most likely bound to cell wall constituent alginate and the photoassimilate mannitol located in sieve cells. Herein, we describe boron uptake, speciation, localization and possible biological function in two species of brown algae, Macrocystis pyrifera and Ectocarpus siliculosus.

The iron uptake and storage systems of terrestrial/higher plants are now reasonably well understood with two basic strategies being distinguished: Strategy I involves the induction of an Fe(III)-chelate reductase (ferrireductase) along with Fe(II) or Fe(III) transporter proteins while strategy II plants have evolved sophisticated systems based on high-affinity, iron specific, binding compounds called phytosiderophores. In contrast, there is little knowledge about the corresponding systems in marine, plant-like lineages. Herein we report a study of the iron uptake and storage mechanisms in the harmful algal bloom dinoflagellate Lingulodinium polyedrum. L. polyedrum is an armored dinoflagellate with a mixotrophic lifestyle and one of the most common bloom species on Southern California coast widely noted for its bioluminescent properties and as a producer of yessotoxins. Short term radio-iron uptake studies indicate that iron is taken up by L. polyedrum in a time dependent manner consistent with an active transport process. Based on inhibitor and other studies it appears that a reductive-oxidative pathway such as that found in yeast and the green alga Chlamydomonas reinhardtii is likely. Of the various iron sources tested vibrioferrin, a photoactive and relatively weak siderophore produced by potentially mutualistic Marinobacter bacterial species, was the most efficient. Other more stable and non-photoactive siderophores such as ferrioxamine E were ineffective. Several pieces of data including long term exposure to 57Fe using Mossbauer spectroscopy suggest that L. polyedrum does not possess an iron storage system but rather presumably relies on an efficient iron uptake system, perhaps mediated by mutualistic interactions with bacteria.

Kelps have a major role in marine and atmospheric iodine cycling in the coastal zone of temperate regions, with potential wide-ranging impacts on ozone destruction in the coastal marine boundary layer. However, little is known about the impact of kelp forests on iodine speciation in coastal sea water. To address this, we examined iodide and iodate concentrations in seawater in and around a giant kelp forest near San Diego, CA, USA, and a nearby site that was not influenced by kelp biology. Our data shows that while both iodide and iodate concentrations remained unchanged during the year at the nearby site, these concentrations changed significantly in and around the kelp forest, and were strongly related to changes in kelp canopy biomass. In particular, iodide reached its highest concentration and iodate reached its lowest concentration during the summer when the kelp canopies were near their maximum, while the opposite pattern was observed during the winter and spring when the kelp canopies were near their minimum. Further, comparisons of these changes with corresponding changes in seawater temperature and wind speed indicated that these relationships were relatively small compared to those with changes in kelp biomass. Together, our data show a strong relationship between kelp biomass and iodine metabolism.

Although the iron uptake and storage mechanisms of terrestrial/higher plants have been well studied, the corresponding systems in marine algae have received far less attention. Studies have shown that while some species of unicellular algae utilize unique mechanisms of iron uptake, many acquire iron through the same general mechanisms as higher plants. In contrast, the iron acquisition strategies of the multicellular macroalgae remain largely unknown. This is especially surprising since many of these organisms represent important ecological and evolutionary niches in the coastal marine environment. It has been well established in both laboratory and environmentally derived samples, that a large amount of iron can be 'non-specifically' adsorbed to the surface of marine algae. While this phenomenon is widely recognized and has prompted the development of experimental protocols to eliminate its contribution to iron uptake studies, its potential biological significance as a concentrated iron source for marine algae is only now being recognized. This study used an interdisciplinary array of techniques to explore the nature of the extensive and powerful iron binding on the surface of both laboratory and environmental samples of the marine brown alga Ectocarpus siliculosus and shows that some of this surface-bound iron is eventually internalized. It is proposed that the surface-binding properties of E. siliculosus allow it to function as a quasibiological metal ion 'buffer', allowing iron uptake under the widely varying external iron concentrations found in coastal marine environments.

Iron is an essential element for all living organisms due to its ubiquitous role in redox and other enzymes, especially in the context of respiration and photosynthesis. Although the iron uptake and storage mechanisms of terrestrial/higher plants have been well-studied, the corresponding systems in marine algae have received far less attention. While the iron many marine algae take up from the environment, irrespective of its detailed internalization mechanism, arrives at the cell surface by diffusion, there is growing evidence for more “active” means of concentrating this element prior to uptake. It has been well established in both laboratory and environmentally derived samples, that a large amount of iron can be “non-specifically” adsorbed to the surface of marine algae. While this phenomenon is widely recognized and has prompted the development of experimental protocols to eliminate its contribution to iron uptake studies, its potential biological significance as a concentrated iron storage source for marine algae is only now being recognized. In this study, using an interdisciplinary array of techniques, we show that the giant kelp Macrocystis pyrifera also displays significant cell surface bound iron although less than that seen with the related brown alga Ectocarpus siliculosus. The iron on the surface is likely bound to carboxylate groups and once inside the iron is found to localize differently depending on cell type. Iron appears to be stored in an as yet undefined mineral phase.

The iron uptake and storage systems of terrestrial/higher plants are now reasonably well understood with two basic strategies being distinguished: strategy I involves the induction of a Fe(III)-chelate reductase (ferrireductase) along with Fe(II) or Fe(III) transporter proteins while strategy II plants have evolved sophisticated systems based on high-affinity, iron specific, binding compounds called phytosiderophores. In contrast, there is little knowledge about the corresponding systems in marine, plant-like lineages. Herein we report a study of the iron uptake and storage mechanisms in the green alga Tetraselmis suecica. Short term radio-iron uptake studies indicate that iron is taken up by Tetraselmis in a time and concentration dependent manner consistent with an active transport process. Based on inhibitor and other studies it appears that a reductive-oxidative pathway such as that found in yeast and the green alga Chlamydomonas reinhardtii is likely. Upon long term exposure to (57)Fe we have been able, using a combination of Mössbauer and X-ray absorption spectroscopies, to identify three metabolites. The first exhibits Mössbauer parameters typical of a [Fe(4)S(4)](2+) cluster and which accounts for approximately 10% of the total intracellular iron pool. The second displays a spectrum typical of a [Fe(II)O(6)] system accounting for approximately 2% of the total pool. The largest component (ca. 85+%) consists of polymeric iron-oxo mineral species with parameters between that of the crystalline ferrihydrite core of animal ferritins and the amorphous hydrated ferric phosphate of bacterial and plant ferritins.

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.

Kelps have a major role in marine and atmospheric iodine cycling in the coastal zone of temperate regions, with potential wide-ranging impacts on ozone destruction in the coastal marine boundary layer. However, little is known about the impact of kelp forests on iodine speciation in coastal sea water. To address this, we examined iodide and iodate concentrations in seawater in and around a giant kelp forest near San Diego, CA, USA, and a nearby site that was not influenced by kelp biology. Our data shows that while both iodide and iodate concentrations remained unchanged during the year at the nearby site, these concentrations changed significantly in and around the kelp forest, and were strongly related to changes in kelp canopy biomass. In particular, iodide reached its highest concentration and iodate reached its lowest concentration during the summer when the kelp canopies were near their maximum, while the opposite pattern was observed during the winter and spring when the kelp canopies were near their minimum. Further, comparisons of these changes with corresponding changes in seawater temperature and wind speed indicated that these relationships were relatively small compared to those with changes in kelp biomass. Together, our data show a strong relationship between kelp biomass and iodine metabolism.

The reaction of H2Re2(CO)8 (1) with Cp*Rh(CO)2 (2) in refluxing hexane affords the mixed-metal clusters H2RhRe2Cp*(CO)9 (4, major product), HRh2ReCp*2(CO)6 (5), and HRhRe3Cp*(CO)14 (6). 4 and 5 are electron-precise 48e clusters and display triangular metallic cores, while 6 contains 64 valence electrons and exhibits a spiked-triangular core having a pendant Re(CO)5 moiety. Heating 1 with Cp*2Rh2(CO)2 (3) gives 4 and 5 as the principal products, in addition to H2Rh2Re2Cp*2(CO)8 (7) in low yield. Cluster 7 possesses 60e and contains a tetrametallic core with two face-capping CO and hydride groups. Heating 4 under CO leads to cluster fragmentation and formation of Re2(CO)10 and 2 in essentially quantitative yield, as assessed by IR spectroscopy. The kinetics for the fragmentation of 4 in toluene under CO have been investigated over the temperature range 325−349 K by UV−vis spectroscopy. On the basis of the first-order rate constants and the Eyring activation parameters (ΔH⧧ = 25.0(8) kcal/mol; ΔS⧧ = −2.6(3) ...

The coordination of iron(III) to the marine amphiphilic marinobactin and aquachelin siderophores, as well as to petrobactin, an unusual 3,4-dihydroxybenzoyl siderophore is reported. Potentiometric titrations were performed on the apo siderophore to determine the ligand pK(a) values, as well as the complex formed with addition of 1 equiv of Fe(III). The log K(ML) values for Fe(III)-marinobactin-E and Fe(III)-aquachelin-C are 31.80 and 31.4, respectively, consistent with the similar coordination environment in each complex, while log K(ML) for Fe(III)-petrobactin is estimated to be about 43. The pK(a) of the beta-hydroxyaspartyl hydroxyl group was determined to be 10.8 by (1)H NMR titration. (13)C NMR and IR spectroscopy were used to investigate Ga(III) coordination to the marinobactins. The coordination-induced shifts (CIS) in the (13)C NMR spectrum of Ga(III)-marinobactin-C compared to apo-marinobactin-C indicates that the hydroxamate groups are coordinated to Ga(III); however, the lack of CISs for the carbons of the beta-hydroxyamide group suggests this moiety is not coordinated in the Ga(III) complex. Differences in the IR spectrum of Ga(III)-marinobactin-C and Fe(III)-marinobactin-C in the 1600-1700 cm(-1) region also corroborates Fe(III) is coordinated to the beta-hydroxyamide moiety, whereas Ga(III) is not coordinated.

The reactivity of the labile cluster Os3(CO)10(MeCN)2 (1) with the monofunctionalized heterocyclic ligands 6-R-2,2′-bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2′-bipyridine reacts with 1 in refluxing CH2Cl2 to give an isomeric mixture of HOs3(CO)9(N2C12H11) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs3(CO)9(N2C10H6-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2′-bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6′ ortho site of the unsubstituted bipyridine ring, as verified by 1H NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs3(CO)9(N2C10H6-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2′-bipyridine. The reaction between the labile cluster Os3(CO)10(MeCN)2 (1) and the monofunctionalized heterocyclic ligand 6-Et-2,2′-bipyridine proceeds readily at room temperature to furnish an isomeric mixture of the cyclometalated and ortho-metalated hydride-bridged clusters HOs3(CO)9(N2C12H11) (2 and 3). Treatment of 1 with 6-Ph-2,2′-bipyridine also yields two distinct hydride-containing clusters that result from independent ortho-metalation paths involving the 6-phenyl substituent and unsubstituted bipyridine group. The bipyridine-derived ortho metalation attendant in the new clusters HOs3(CO)9(N2C10H6-6-Et) (3) and HOs3(CO)9(N2C10H6-6-Ph) (5) has been established by X-ray crystallography.

Textural, mineralogical, and X-Ray fluorescence (XRF) analyses are used as a cost effective method to distinguish for the first time ancient Egyptian and Nubian-style ceramics found in Nubia. Textural and mineralogical data suggest that Nubian-style sherds are mixtures of sand, silt, and clay sediment that is generally finer grained and poorer in quartz than is the sediment mixture used to produce Egyptian-style pottery. Chemical data also establish a significant difference in the amount of chemical variation found within each style population, but nonetheless supports a considerable overlap in the possible provenance of both styles. Observations and data obtained during this study indicate that standardized, Egyptian-style manufacturing was introduced into Nubia under colonialism, without substantially altering the diversity of native methods of production.

Eight coordination polymers of silver Ag(I) derived from bidentate coordinating heteroscorpionate ligands, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L3c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR spectroscopy, and elemental analysis. By varying the solvent polarity, the protonation state of the uncoordinated carboxylate groups and hence their solid-state interactions can be controlled. While the silver monomers (tectons) possess chirality due to the asymmetric coordination of the achiral ligands to the silver ion, all of the solid-state materials were isolated as racemic mixtures.

Treatment of Os3(CO)10(MeCN)2 (1) with the heterocyclic ligand 6-methyl-2,2′-bipyridine (6-Me-2,2′-bpy) at room temperature leads to the formation of the isomeric hydride-bridged clusters HOs3(CO)9...

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.

Twelve new dioxo W(VI) complexes of a family of heteroscorpionate ligands of the type [(L)WO2Y], where L = N2X ligand and Y = Cl or OR, have been synthesized and characterized. With the more sterically bulky ligands we show that these complexes exist as isolable cis and trans isomers and compare the rate of such isomerization with their corresponding dioxo Mo(VI) analogs. � 2006 Elsevier B.V. All rights reserved.

Complexes of Cu(II) derived from two new nonfacially coordinating heteroscorpionate ligands, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L3c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR, and UV-vis spectroscopy, electrochemistry, and magnetic susceptibility. The use of these new complexes as building blocks for the construction of supramolecular architectures is discussed.

We have successfully prepared a series of vanadyl complexes with N2O heteroscorpionate ligands and have characterized their cis and trans geometrical isomers both in solution and the solid state. The major difference between the isomers, and between the various oxygen atom donors of the N2O scorpionate ligands, is in their redox potentials which can span almost a volt for this ostensively similar set of compounds. Such data may be useful in screening vanadium complexes for potential biological activity. � 2006 Elsevier B.V. All rights reserved.

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.

UV photolysis of the ferric aerobactin complex results in decarboxylation of the alpha-hydroxy carboxylic acid group of the central citrate moiety of aerobactin. The structure determination of the photooxidized ligand shows that decarboxylation occurs at the citrate moiety forming a 3-ketoglutarate moiety. Proton and carbon-13 NMR establish the presence of keto and enol tautomers of the apo-photoproduct, with the enol form prevailing in water. The photoproduct retains the ability to coordinate iron(III). The values of the ligand protonation constants, the pKa of the Fe(III)-ligand complex, and the Fe(III) stability constant of the photoproduct of aerobactin are all close to those of aerobactin. CD spectroscopy suggests that the chirality of the ferric complexes of aerobactin and its photoproduct are similar. Like aerobactin, the photoproduct promotes iron acquisition by the source bacterium, Vibrio sp. DS40M5.

A series of zinc complexes containing the tripodal heteroscorpionate ligand bis(3,5-dimethylpyrazol-2-yl)diphenylmethanol (L2H) have been synthesized and characterized by X-ray crystallography. The L2H/Zn complexes were designed to model the N2OX coordination (with the zinc-bound O being a reactive nucleophile) that is characteristic of many protease and amidase zinc enzymes. The pseudotetrahedral mononuclear complexes characterized include [(L2)ZnI] (1), [(L2)Zn(CH3)] (2), and [(L2)Zn(SPh)] (3). Alkylation of (1) with methyl iodide has revealed a modest nucleophilicity of the chelated zinc-bound alkoxide, and produces the penta-coordinate [(L2OCH3)ZnI2] (4) which contains a weakly bound ether in the fifth coordination site. However, when the coordination sphere also includes a thiolate sulfur as in (3), reaction with methyl iodide produces exclusive alkylation at the sulfur to produce thioanisole and (1). The coordination of the ether in the neutral (4) can be strengthened by reaction with various silver salts, Ag+X−, to produce other penta-coordinate complexes [(L2OCH3)ZnI(Tf)] (5) and [(L2OCH3)ZnI(H2O)]BF4 (6) which show enhanced coordination of the ether.

Full length recombinant iron regulatory protein, Fur, has been isolated and characterized from the algal-associated marine bacterium Marinobacter algicola DG893. Under nondenaturing conditions the Fur protein behaves on size exclusion chromatography as a dimer while it is monomeric under SDS PAGE conditions. ICP-MS and fluorescence quenching experiments show that Mb-Fur binds a single metal ion (Zn, Mn, or Co) per monomer. Electrophoretic mobility shift assays were used to probe the interaction of Mb-Fur with the purported Fur box in the promoter region upstream of the vibrioferrin biosynthetic operon. Interaction of Mb-Fur with a 100 bp DNA fragment containing the Fur box in the presence of 10 µM Mn, Co or Zn(II) resulted in decreased migration of DNA on a 7.5 % polyacrylamide gel. In the absence of the Fur protein or the metal, no interaction is seen. The presence of EDTA in the binding, loading or running buffers also abolished all activity demonstrating the importance of the metal in formation of the promoter-repressor complex. Based on a high degree of similarity between Mb-Fur and its homolog from Pseudomonas aeruginosa (PA) whose X-ray structure is known we developed a structural model for the former which suggested that only one of the several metal binding sites found in other Fur’s would be functional. This is consistent with the single metal binding stoichiometry we observed. Since the purported metal binding site was one that has been described as “structural” rather than “functional” in PA and yet the monometallic Mb-Fur retains DNA Fur box binding ability it reopens the question of which site is which, or if different species have adapted the sites for different purposes.

It is shown in model complexes designed to mimic the binding site of zinc-thiolate proteins that a single hydrogen bond between an amide N-H and a Zn-coordinated thiolate reduces its reactivity toward electrophiles by up to 2 orders of magnitude. In addition, we show that a single N-H...S hydrogen bond is sufficient to achieve near 100% regiospecificity of reaction between a strong, and hence inherently indiscriminate, alkylating agent like trimethyloxonium tetraflouroborate and a single sulfur in a dithiolate construct. The importance of these results in understanding how systems such as the zinc fingers of the GATA family and the E. coli DNA repair protein Ada, which share the same pseudotetrahedral structure and tetracysteinyl ligation around the zinc, can fulfill such widely divergent (structural vs reactive) roles and how specificity of reaction in such multi-thiolate containing systems can be achieved is discussed.

Four new Mo(VI)-dioxo complexes of a family of N2X heteroscorpionate ligands are reported which, together with data already available for (TpR)-, provide a unique example of a comprehensive set of isostructural, isoelectronic complexes differing only in one biologically relevant donor atom. A study of these complexes allows for a direct comparison of structural, spectroscopic, and oxygen atom transfer reactivity properties of the Mo(VI)-dioxo center (of relevance to various families of molybdoenzymes) as a function of donor atom identity.

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.

Deconvoluting the different contributions of thiolate and ene-1,2-dithiolate donors to the underlying electronic structure of the Mo site in sulfite oxidase (SO) has proven to be a difficult task. One way in which these differences might be illuminated is by selectively substituting Se for S in model complexes which possess multiple sulfur donor ligand environments. Here we report the synthesis and structures of new oxo-Mo(V) complexes as effective models for the one-electron reduced active site of SO. We have used the tridentate heteroscorpionate ligand (2-dimethylethanethiol)bis(3,5-dimethylpyrazolyl)methane (L3SH) in order to model the constrained cysteinyl sulfur (S(Cys)) ligand environment observed in the crystal structure of the enzyme, and benzene-1,2-dithiol (bdt) as a mimic of the ene-1,2-dithiolate chelate. [(L3S)MoO(bdt)] and [(L3S)MoO(SPh)(2)] have been structurally characterized by X-ray crystallography, and as such, [(L3S)MoO(bdt)] is only the second known model compound that closely approximates the active site structure of reduced forms of SO. Additionally, benzenethiol (SPh) and benzeneselenol (SePh) have been used to perturb the equatorial ligand environment of [(L3S)MoO(bdt)].) This has provided much needed insight into the electronic structure of the one-electron reduced SO site and has allowed for increased understanding of the individual roles played by these different thiolate donors in the oxidative half-reaction of the enzyme. Interestingly, the EPR spectra of [(L3S)MoO(bdt)], [(L3S)MoO(SPh)(2)], and [(L3S)MoO(SePh)(2)] closely resemble that of both high pH (hpH) and low pH (lpH) SO, except for the fact that the magnitude of g(1) is found to be consistently higher in the model spectra compared to that of the enzyme. It is suggested that this derives from an increase in Mo-S covalency in the models relative to hpH and lpH SO.

We have previously demonstrated that the complex [(L1O)MoOCl(2)], where L1OH = (2-hydroxy-3-tert-butyl-5-methylphenyl)bis(3,5-dimethylpyrazolyl)methane, exists as both cis and trans isomers (Kail, B.; Nemykin, V. N.; Davie, S. R.; Carrano, C. J.; Hammes, B. S.; Basu, P. Inorg. Chem. 2002, 41, 1281-1291). Here, the cis isomer is defined as the geometry with the heteroatom in the equatorial position, and the trans isomer is designated as the geometry with the heteroatom positioned trans to the terminal oxo group. The trans isomer represents the thermodynamically more stable geometry as indicated by its spontaneous formation from the cis isomer. In this report, we show that for complexes of [(LO)MoOCl(2)], where LOH is the sterically less restrictive (2-hydroxyphenyl)bis(3,5-dimethylpyrazolyl)methane, only the trans isomer could be isolated, while in the corresponding thiolate containing ligand (2-dimethylethanethiol)bis(3,5-dimethylpyrazolyl)methane (L3SH) only the cis isomer could be observed. In addition, we have isolated and structurally characterized the complex [(L1O)MoO(OPh)(Cl)], a rare example of a species possessing both cis and trans phenolates. Using DFT calculations, we have investigated the origins of the differences in stability between the cis and trans isomers in these complexes and suggest that they are related to the trans influence of the oxo-group. Crystal data for [(LO)MoOCl(2)] (1) include that it crystallizes in the triclinic space group P(-)1 with cell dimensions a = 8.9607 (12) A, b = 10.596 (4) A, c = 13.2998 (13) A, alpha = 98.03 (2) degrees, beta = 103.21 (2) degrees, gamma = 110.05(2) degrees, and Z = 2. [(L1O)MoO(OPh)Cl].2CH(2)Cl(2) (2.2CH(2)Cl(2)) crystallizes in the triclinic space group P(-)1 with cell dimensions a = 12.2740 (5) A, b = 13.0403 (5) A, c = 13.6141 (6) A, alpha = 65.799 (2) degrees, beta = 64.487 (2) degrees, gamma = 65.750 (2) degrees, and Z = 2. [(L3S)Mo(O)Cl(2)] (3) crystallizes in the orthorhombic space group Pna2(1), with cell dimensions a = 13.2213 (13) A, b = 8.817 (2) A, c = 15.649 (4) A, and Z = 4. The implications of these results on the function of mononuclear molybdoenzymes such as sulfite oxidase, and the DMSO reductase, are discussed.

The syntheses and characterization of a series of zinc complexes containing the tripodal ligand bis(5-tert-butyl-3-methylpyrazol-2-yl)acetic acid (H2) which is designed to model the 2-His-1-carboxylate facial triad observed in the active sites of various metalloenzymes such as carboxypeptidase A (CPA) and thermolysin (TLN) are reported. Pseudotetrahedral complexes isolated include [Zn2(CH3)], [Zn2(Cl)], [Zn2(SPh)], [Zn2(OAc)], [Zn2(NCS)] and [Zn2(AH)]. In addition, a four (solution) or five-coordinate (solid state) cationic zinc aqua complex, [Zn2(OH2)]+ and a 5-coordinate zinc acetohydroxamate complex, [Zn2(AH)] were synthesized and structurally characterized. The former represents a structural mimic of the resting state while the latter depicts the inhibited state of zinc enzymes CPA and TLN. Crystal data: [Zn2(CH3)] crystallizes in the triclinic space group , with cell dimensions a=6.638(6) A, b=12.249(10) A, c=13.327(12) A, α=82.862(15)°, β=76.811(15)°, γ=88.988(17)° and Z=2; [Zn2(Cl)] crystallizes in the triclinic space group , with cell dimensions a=8.9933(7) A, b=9.7985(8) A, c=12.1536(9) A, α=94.0420(10)°, β=105.3950(10)°, γ=95.6490(10)° and Z=2; [Zn2(SPh)]·0.5CH2Cl2 crystallizes in the triclinic space group , with cell dimensions a=12.1273(15) A, b=12.9073(16) A, c=17.824(2) A, α=87.194(2)°, β=78.769(3)°, γ=76.027(2)° and Z=4; [Zn2(OH2)]ClO4 crystallizes in the monoclinic space group P21/n, with cell dimensions a=12.620(2) A, b=11.1416(18) A, c=19.315(3) A, β=101.883(2)°, and Z=4; [Zn2(AH)]·3.25CH2Cl2 crystallizes in the orthorhombic space group Pccn, with cell dimensions a=23.7791(6) A, b=14.1675(3) A, c=22.1213(5) A, α=β=γ=90° and Z=8. The 1H NMR spectra of these diamagnetic zinc complexes suggests that all complexes retain their overall symmetry in solution.

Reaction of the Zn, Cd, or Co nitrate salts with the deprotonated ligand (2-hydroxy-3-t-butyl-methylphenyl)bis(3,5-dimethylpyrazolyl)methane (L1O−) in methanol produced the following complexes: [(L1OH)Zn(NO3)2] in two isomorphs, a = 40.983(8) A, b = 9.571(2) A, c = 15.667(8) A, α = 90○, β = 106.38(1)○, γ = 90○, C2/c, and a = 13.027(3) A, b = 14.781(4) A, c = 16.107(3) A, α = 90○, β = 105.30(1)○, γ = 90○, P21/n; [(L1OH)Cd(pz)(NO3)2] a = 14.7476(2) A, b = 13.5411(2) A, c = 16.7223(2) A, α = 90○, β = 110.3840(10)○, γ = 90○, P21/c; and [(L1O)Co(pz)(NO3)] a = 11.4240(2) A, b = 13.4498(2) A, c = 13.8056(2) A, α = 105.2080(10)○, β = 105.8130(10)○, γ = 112.7470(10)○, P\({\bar 1}\). The Zn adopts a pseudotetrahedral four-coordinate geometry where the potentially tridentate ligand is actually bidentate with a protonated and uncoordinated phenoxy arm. The Co complex is pseudooctahedral six-coordinate where the phenoxy arm is deprotonated and coordinated. Finally the Cd complex is seven-coordinate but the metal is not coordinated through the phenoxy group that is again protonated.

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 water molecules in complexes [TpCO2Et,MeM(H2O)3]+ where M = Ni, Co, Mn, or Cu(II) are easily displaced by neutral bidentate ligands, L to produce species of the type [TpCO2Et,MeM(L)H2O]+. Attempted deprotonation of the water molecules in the parent complexes gives rise to rearrangement products for M = Ni, Co and Mn but gives isolable dinuclear hydroxo-bridged species for Zn and Cu. A number of interesting secondary interactions between the H-bond accepting [TpCO2Et,Me] group and the other ligands in the metal coordination sphere are revealed by X-ray crystallography. The ester carbonyl CO stretching frequency of the ligand in the IR is seen to be diagnostic of the type of interaction (i.e. nonbonded, H-bonded or weakly complexed, and strongly complexed) between it and the cation, and can be used to provide valuable information in the absence of X-ray crystal structures.

Evidence is increasing for a mutualistic relationship between phytoplankton and heterotrophic marine bacteria. It has been proposed that bacteria producing photoactive iron binding compounds known as siderophores could play an important role in such mutualistic associations by producing bioavailable iron utilizable by phytoplankton and in exchange receive autotrophically derived DOM. In order to understand the potential role photoactive siderophores might be playing in bacterial–algal mutualism or marine biogeochemistry in general, it is important to be able to detect and quantify their presence in various environments. One approach to accomplish that end is to make use of high sensitivity genomics technology (qPCR) to search for siderophore biosynthesis genes related to the production of photoactive siderophores. In this way one can access their “biochemical potential” and utilize this information as a proxy for the presence of these siderophores in the marine environment. In this report we studied the correlation of the presence of bacteria producing one of the three photoactive siderophores relative to total bacterial and dinoflagellate numbers from surface water at the Scripps Pier before, during, and after fall bloom of the dinoflagellate Lingulodinium polyedrum. We believe that these findings will aid us in gauging the importance of photoactive siderophores in the marine environment and in harmful algal bloom dynamics in particular.