X-ray absorption spectroscopic studies on model compounds for biological iodine and bromine

Bromine contamination and risk management in terrestrial and aquatic ecosystems

Bromine (Br) is widely distributed through the lithosphere and hydrosphere, and its chemistry in the environment is affected by natural processes and anthropogenic activities. While the chemistry of Br in the atmosphere has been comprehensively explored, there has never been an overview of the chemistry of Br in soil and aquatic systems. This review synthesizes current knowledge on the sources, geochemistry, health and environmental threats, remediation approaches, and regulatory guidelines pertaining to Br pollution in terrestrial and aquatic environments. Volcanic eruptions, geothermal streams, and seawater are the major natural sources of Br. In soils and sediments, Br undergoes natural cycling between organic and inorganic forms, with bromination reactions occurring both abiotically and through microbial activity. For organisms, Br is a non-essential element; it is passively taken up by plant roots in the form of the Br- anion. Elevated Br- levels can limit plant growth on coastal soils of arid and semi-arid environments. Br is used in the chemical industry to manufacture pesticides, flame retardants, pharmaceuticals, and other products. Anthropogenic sources of organobromine contaminants in the environment are primarily wastewater treatment, fumigants, and flame retardants. When aqueous Br- reacts with oxidants in water treatment plants, it can generate brominated disinfection by-products (DBPs), and exposure to DBPs is linked to adverse human health effects including increased cancer risk. Br- can be removed from aquatic systems using adsorbents, and amelioration of soils containing excess Br- can be achieved by leaching, adding various amendments, or phytoremediation. Developing cost-effective methods for Br- removal from wastewater would help address the problem of toxic brominated DBPs. Other anthropogenic organobromines, such as polybrominated diphenyl ether (PBDE) flame retardants, are persistent, toxic, and bioaccumulative, posing a challenge in environmental remediation. Future research directives for managing Br pollution sustainably in various environmental settings are suggested here.

Iodine speciation in deep eutectic solvents

Iodine has been shown to act as a good electrocatalyst for metal digestion in deep eutectic solvents (DESs) but little is known about its speciation or reactivity in these high chloride containing media. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements were made at the iodine K-edge in a range of DESs with different glycolic or acidic hydrogen bond donors (HBDs), along with examining the effect of iodine concentration between 0.01 and 0.5 mol dm^-3. Three groups of speciation were detected: mixed I₂Cl^-/I₃^- (glycol and lactic acid systems), mixed I₃^-/I₂ (oxalic acid and urea systems), and singular I₃^- (levulinic acid system). UV-vis spectroscopy was used to confirm the speciation. Electrochemistry showed that iodine redox behaviour was unaffected by the changing speciation. Leaching data showed that metal oxidation was related not only to changing iodine speciation, but also the reactivity and coordination ability of the HBD.

Local environment of iodine dissolved as iodate in high-pressure aluminoborosilicate glasses: A I K-edge X-ray Absorption Spectroscopic study

The use of high-pressure synthesis conditions to produce I-bearing aluminoborosilicate represent a promising issue for the immobilization of 129I radioisotope. Furthermore, iodine appears to be more solubilized in glasses under its iodate (I5+) form rather than its iodide (I-) form. Currently, the local atomic environment for iodine is poorly constrained for I- and virtually unknown for I5+ or I7+. We used I K-edge X-ray Absorption Spectroscopy conducted at 20 K for determining the local atomic environment of iodine dissolved as I-, I5+, I7+ in a series of aluminoborosilicate glasses. We determined that I- is surrounded by either Na+ or Ca2+ in agreement with previous works. The signal collected from EXAFS reveals that I5+ is surrounded invariably by three oxygen atoms forming a IO3- cluster charge compensated by Na+ and/or Ca2+. The I-O distance in iodate dissolved in glass is comparable to the I-O distance in crystalline compounds at ~1.8 Å. The distance to the second nearest neighbor (Na+ or Ca2+) is also constant at ~3.2 Å. This derived distance is identical to the distance between I- and Na+ or Ca2+ in the case of iodide local environment. For one sample containing iodate and periodate, the distinction between the local environment of I5+ and I7+ could not be made suggesting that both environments have comparable EXAFS signal.

Key aspects of the iodine metabolism in brown algae: a brief critical review

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.

Emission of volatile halogenated compounds, speciation and localization of bromine and iodine in the brown algal genome model Ectocarpus siliculosus

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 < 1 order of magnitude for bromine) than e.g. in the kelp Laminaria digitata. Iodide competitively reduces the accumulation of bromide. Both iodide and bromide are accumulated in the cell wall (apoplast) of Ectocarpus, with minor amounts of bromine also detectable in the cytosol. Ectocarpus emits a range of volatile halogenated compounds, the most prominent of which by far is methyl iodide. Interestingly, biosynthesis of this compound cannot be accounted for by vanadium haloperoxidase since the latter have not been found to catalyze direct halogenation of an unactivated methyl group or hydrocarbon so a methyl halide transferase-type production mechanism is proposed.

Uptake and distribution of organo-iodine in deep-sea corals

Understanding iodine concentration, transport, and bioavailability is essential in evaluating iodine's impact to the environment and its effectiveness as an environmental biogeotracer. While iodine and its radionuclides have proven to be important tracers in geologic and biologic studies, little is known about transport of this element to the deep sea and subsequent uptake in deep-sea coral habitats. Results presented here on deep-sea black coral iodine speciation and iodine isotope variability provides key information on iodine behavior in natural and anthropogenic environments, and its geochemical pathway in the Gulf of Mexico. Organo-iodine is the dominant iodine species in the black corals, demonstrating that binding of iodine to organic matter plays an important role in the transport and transfer of iodine to the deep-sea corals. The identification of growth bands captured in high-resolution scanning electron images (SEM) with synchronous peaks in iodine variability suggest that riverine delivery of terrestrial-derived organo-iodine is the most plausible explanation to account for annual periodicity in the deep-sea coral geochemistry. Whereas previous studies have suggested the presence of annual growth rings in deep-sea corals, this present study provides a mechanism to explain the formation of annual growth bands. Furthermore, deep-sea coral ages based on iodine peak counts agree well with those ages derived from radiocarbon (¹⁴C) measurements. These results hold promise for developing chronologies independent of ¹⁴C dating, which is an essential component in constraining reservoir ages and using radiocarbon as a tracer of ocean circulation. Furthermore, the presence of enriched ¹²⁹I/¹²⁷I ratios during the most recent period of skeleton growth is linked to nuclear weapons testing during the 1960s. The sensitivity of the coral skeleton to record changes in surface water ¹²⁹I composition provides further evidence that iodine composition and isotope variability captured in proteinaceous deep-sea corals is a promising geochronometer as well as an emerging tracer for continental material flux.

Reduction of hypervalent iodine by coordination to iron(iii) and the crystal structures of PhIO and PhIO2

Iodine L₃-edge XANES spectra using reference compounds with formal iodine oxidation states spanning −1 to +7 show that iodine in an Fe(iii) coordinated iodosylbenzene (PhIO) is reduced compared to parent hypervalent PhIO which has been structurally characterized.

A phase-space beam position monitor for synchrotron radiation

The stability of the photon beam position on synchrotron beamlines is critical for most if not all synchrotron radiation experiments. The position of the beam at the experiment or optical element location is set by the position and angle of the electron beam source as it traverses the magnetic field of the bend-magnet or insertion device. Thus an ideal photon beam monitor would be able to simultaneously measure the photon beam's position and angle, and thus infer the electron beam's position in phase space. X-ray diffraction is commonly used to prepare monochromatic beams on X-ray beamlines usually in the form of a double-crystal monochromator. Diffraction couples the photon wavelength or energy to the incident angle on the lattice planes within the crystal. The beam from such a monochromator will contain a spread of energies due to the vertical divergence of the photon beam from the source. This range of energies can easily cover the absorption edge of a filter element such as iodine at 33.17 keV. A vertical profile measurement of the photon beam footprint with and without the filter can be used to determine the vertical centroid position and angle of the photon beam. In the measurements described here an imaging detector is used to measure these vertical profiles with an iodine filter that horizontally covers part of the monochromatic beam. The goal was to investigate the use of a combined monochromator, filter and detector as a phase-space beam position monitor. The system was tested for sensitivity to position and angle under a number of synchrotron operating conditions, such as normal operations and special operating modes where the photon beam is intentionally altered in position and angle at the source point. The results are comparable with other methods of beam position measurement and indicate that such a system is feasible in situations where part of the synchrotron beam can be used for the phase-space measurement.

Distribution and speciation of bromine in mammalian tissue and fluids by X-ray fluorescence imaging and X-ray absorption spectroscopy

Bromine is one of the most abundant and ubiquitous trace elements in the biosphere and until recently had not been shown to perform any essential biological function in animals. A recent study demonstrated that bromine is required as a cofactor for peroxidasin-catalysed formation of sulfilimine crosslinks in Drosophila. In addition, bromine dietary deficiency is lethal in Drosophila, whereas bromine replenishment restores viability. The aim of this study was to examine the distribution and speciation of bromine in mammalian tissues and fluids to provide further insights into the role and function of this element in biological systems. In this study we used X-ray fluorescence (XRF) imaging and inductively coupled plasma-mass spectrometry (ICP-MS) to examine the distribution of bromine in bovine ovarian tissue samples, follicular fluid and aortic serum, as well as human whole blood and serum and X-ray absorption spectroscopy (XAS) to identify the chemical species of bromine in a range of mammalian tissue (bovine, ovine, porcine and murine), whole blood and serum samples (bovine, ovine, porcine, murine and human), and marine samples (salmon (Salmo salar), kingfish (Seriola lalandi) and Scleractinian coral). Bromine was found to be widely distributed across all tissues and fluids examined. In the bovine ovary in particular it was more concentrated in the sub-endothelial regions of arterioles. Statistical comparison of the near-edge region of the X-ray absorption spectra with a library of bromine standards led to the conclusion that the major form of bromine in all samples analysed was bromide.

Different speciation for bromine in brown and red algae, revealed by in vivo X-ray absorption spectroscopic studies

Members of various algal lineages are known to be strong producers of atmospherically relevant halogen emissions, that is a consequence of their capability to store and metabolize halogens. This study uses a noninvasive, synchrotron-based technique, X-ray absorption spectroscopy, for addressing in vivo bromine speciation in the brown algae Ectocarpus siliculosus, Ascophyllum nodosum, and Fucus serratus, the red algae Gracilaria dura, G. gracilis, Chondrus crispus, Osmundea pinnatifida, Asparagopsis armata, Polysiphonia elongata, and Corallina officinalis, the diatom Thalassiosira rotula, the dinoflagellate Lingulodinium polyedrum and a natural phytoplankton sample. The results highlight a diversity of fundamentally different bromine storage modes: while most of the stramenopile representatives and the dinoflagellate store mostly bromide, there is evidence for Br incorporated in nonaromatic hydrocarbons in Thalassiosira. Red algae operate various organic bromine stores - including a possible precursor (by the haloform reaction) for bromoform in Asparagopsis and aromatically bound Br in Polysiphonia and Corallina. Large fractions of the bromine in the red algae G. dura and C. crispus and the brown alga F. serratus are present as Br(-) defects in solid KCl, similar to what was reported earlier for Laminaria parts. These results are discussed according to different defensive strategies that are used within algal taxa to cope with biotic or abiotic stresses.

In vivo speciation studies and antioxidant properties of bromine in Laminaria digitata reinforce the significance of iodine accumulation for kelps

The metabolism of bromine in marine brown algae remains poorly understood. This contrasts with the recent finding that the accumulation of iodide in the brown alga Laminaria serves the provision of an inorganic antioxidant - the first case documented from a living system. The aim of this study was to use an interdisciplinary array of techniques to study the chemical speciation, transformation, and function of bromine in Laminaria and to investigate the link between bromine and iodine metabolism, in particular in the antioxidant context. First, bromine and iodine levels in different Laminaria tissues were compared by inductively coupled plasma MS. Using in vivo X-ray absorption spectroscopy, it was found that, similarly to iodine, bromine is predominantly present in this alga in the form of bromide, albeit at lower concentrations, and that it shows similar behaviour upon oxidative stress. However, from a thermodynamic and kinetic standpoint, supported by in vitro and reconstituted in vivo assays, bromide is less suitable than iodide as an antioxidant against most reactive oxygen species except superoxide, possibly explaining why kelps prefer to accumulate iodide. This constitutes the first-ever study exploring the potential antioxidant function of bromide in a living system and other potential physiological roles. Given the tissue-specific differences observed in the content and speciation of bromine, it is concluded that the bromide uptake mechanism is different from the vanadium iodoperoxidase-mediated uptake of iodide in L. digitata and that its function is likely to be complementary to the iodide antioxidant system for detoxifying superoxide.

Modelling the site of bromide binding in vanadate-dependent bromoperoxidases

Treatment of Boc-protected (S)-serine (Ser) methyl ester with triphenylphosphine bromide Ph(3)PBr (intermittently generated from PPh(3) and N-bromosuccinimide) yields Boc-3-bromoalanine (R)-Boc-BrAlaMe and, after deprotection, bromoalanine methyl ester (R)-BrAlaMe in the form of its hydrobromide. Boc-BrAlaMe and BrAlaMe have been structurally characterised. The reaction between BrAlaMe, salicylaldehyde (sal) and VO(2+) results in the formation of Schiff base complexes of composition [VO(sal-BrAlaMe)solv](+) (solv = CH(3)OH: 3, THF: 5) and [VO(sal-BrAla)THF] 4. DFT calculations of the structures of 3, 4 and 5, based on the B3LYP functional and employing the triple zeta basis set 6-311++g(d,p), provide distances Br···V = 4.0 ± 0.1 Å, if some distortion of the dihedral angle ∠N-C-C-Br is allowed (affording a maximum energy of ca. 45 kJ mol(-1)), and thus model Br···V distances detected by X-ray methods in bromoperoxidases from the marine algae Ascophyllum nodosum and Corallina pilulifera. The DFT calculations have been validated by comparing calculated and found structures, including the new complex [V(V)O(Amp-sal)OMe(MeOH)] (1, Amp is the aminophenol moiety) and the known complex [VO(L-Ser-van)H(2)O] (van = vanillin). Additional validation has been undertaken by checking experimental against calculated (BHandHLYP) EPR spectroscopic hyperfine coupling constants. Complexes containing bromine as a substituent at the phenyl moiety of a Schiff base ligand do not allow for an appropriate simulation of the Br···V distance in peroxidases. The closest agreement, d(Br···V) = 4.87 Å, is achieved with [VO(3Br-salSer)THF] (6), where 3Brsal-Ser is the dianionic Schiff base formed between 3-Br-5-NO(2)-salicylaldehyde and serine.

Partition of iodine (¹²⁹I and ¹²⁷I) isotopes in soils and marine sediments

Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope ¹²⁹I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter. Due to its long half-life (15.7 million years), ¹²⁹I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of ¹²⁹I and ¹²⁷I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify ¹²⁹I in humic and fulvic acid and humin. The results show that 30-56% of the total ¹²⁷I and 42-60% of the total ¹²⁹I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, (¹²⁷I and ¹²⁹I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 ¹²⁹I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.

Inorganic iodine incorporation into soil organic matter: evidence from iodine K-edge X-ray absorption near-edge structure

The transformation of inorganic iodine (I(-) and IO(3)(-)) incubated in soils with varying amounts of organic matter (Andosols from the surface layer of an upland field and forest, as well as Acrisols from surface and subsurface layers of an upland field) was investigated by using the iodine K-edge X-ray absorption near-edge structure (XANES). After 60d of reaction, both I(-) and IO(3)(-) were transformed into organoiodine in surface soils containing sufficient amounts of organic matter, whereas IO(3)(-) remained unchanged in the subsurface soil of Acrisols with low organic matter contents. Transformation of IO(3)(-) into organoiodine was not retarded when the microbial activity in soil was reduced by gamma-ray irradiation, suggesting that microbial activity was not essential for the transformation of inorganic iodine into organoiodine. Soil organic matter has the ability to transform inorganic iodine into organoiodine.

The halogenated metabolism of brown algae (Phaeophyta), its biological importance and its environmental significance

Brown algae represent a major component of littoral and sublittoral zones in temperate and subtropical ecosystems. An essential adaptive feature of this independent eukaryotic lineage is the ability to couple oxidative reactions resulting from exposure to sunlight and air with the halogenations of various substrates, thereby addressing various biotic and abiotic stresses i.e., defense against predators, tissue repair, holdfast adhesion, and protection against reactive species generated by oxidative processes. Whereas marine organisms mainly make use of bromine to increase the biological activity of secondary metabolites, some orders of brown algae such as Laminariales have also developed a striking capability to accumulate and to use iodine in physiological adaptations to stress. We review selected aspects of the halogenated metabolism of macrophytic brown algae in the light of the most recent results, which point toward novel functions for iodide accumulation in kelps and the importance of bromination in cell wall modifications and adhesion properties of brown algal propagules. The importance of halogen speciation processes ranges from microbiology to biogeochemistry, through enzymology, cellular biology and ecotoxicology.

The iron-site structure of [Fe]-hydrogenase and model systems: an X-ray absorption near edge spectroscopy study

The [Fe]-hydrogenase is an ideal system for studying the electronic properties of the low spin iron site that is common to the catalytic centres of all hydrogenases. Because they have no auxiliary iron-sulfur clusters and possess a cofactor containing a single iron centre, the [Fe]-hydrogenases are well suited for spectroscopic analysis of those factors required for the activation of molecular hydrogen. Specifically, in this study we shed light on the electronic and molecular structure of the iron centre by XAS analysis of [Fe]-hydrogenase from Methanocaldococcus jannashii and five model complexes (Fe(ethanedithiolate)(CO)(2)(PMe(3))(2), [K(18-crown-6)](2)[Fe(CN)(2)(CO)(3)], K[Fe(CN)(CO)(4)], K(3)[Fe(III)(CN)(6)], K(4)[Fe(II)(CN)(6)]). The different electron donors have a strong influence on the iron absorption K-edge energy position, which is frequently used to determine the metal oxidation state. Our results demonstrate that the K-edges of Fe(II) complexes, achieved with low-spin ferrous thiolates, are consistent with a ferrous centre in the [Fe]-hydrogenase from Methanocaldococcus jannashii. The metal geometry also strongly influences the XANES and thus the electronic structure. Using in silico simulation, we were able to reproduce the main features of the XANES spectra and describe the effects of individual donor contributions on the spectra. Thereby, we reveal the essential role of an unusual carbon donor coming from an acyl group of the cofactor in the determination of the electronic structure required for the activity of the enzyme.

Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry

Brown algae of the Laminariales (kelps) are the strongest accumulators of iodine among living organisms. They represent a major pump in the global biogeochemical cycle of iodine and, in particular, the major source of iodocarbons in the coastal atmosphere. Nevertheless, the chemical state and biological significance of accumulated iodine have remained unknown to this date. Using x-ray absorption spectroscopy, we show that the accumulated form is iodide, which readily scavenges a variety of reactive oxygen species (ROS). We propose here that its biological role is that of an inorganic antioxidant, the first to be described in a living system. Upon oxidative stress, iodide is effluxed. On the thallus surface and in the apoplast, iodide detoxifies both aqueous oxidants and ozone, the latter resulting in the release of high levels of molecular iodine and the consequent formation of hygroscopic iodine oxides leading to particles, which are precursors to cloud condensation nuclei. In a complementary set of experiments using a heterologous system, iodide was found to effectively scavenge ROS in human blood cells.

Microchemical imaging of iodine distribution in the brown alga Laminaria digitata suggests a new mechanism for its accumulation

Brown algal kelp species are the most efficient iodine accumulators among all living systems, with an average content of 1.0% of dry weight in Laminaria digitata. The iodine distributions in stipe and blade sections from L. digitata were investigated at tissue and subcellular levels. The quantitative tissue mapping of iodine and other trace elements (Cl, K, Ca, Fe, Zn, As and Br) was provided by the proton microprobe with spatial resolutions down to 2 mum. Chemical imaging at a subcellular resolution (below 100 nm) was performed using the secondary ion mass spectrometry microprobe. Sets of samples were prepared by both chemical fixation and cryofixation procedures. The latter prevented the diffusion and the leaching of labile inorganic iodine species, which were estimated at around 95% of the total content by neutron activation analysis. The distribution of iodine clearly shows a huge, decreasing gradient from the meristoderm to the medulla. The contents of iodine reach very high levels in the more external cell layers, up to 191 +/- 5 mg g(-1) of dry weight in stipe sections. The peripheral tissue is consequently the main storage compartment of iodine. At the subcellular level, iodine is mainly stored in the apoplasm and not in an intracellular compartment as previously proposed. This unexpected distribution may provide an abundant and accessible source of labile iodine species which can be easily remobilized for potential chemical defense and antioxidative activities. According to these imaging data, we proposed new hypotheses for the mechanism of iodine storage in L. digitata tissues.

Bromide does not bind to the Mn4Ca complex in its S1 state in Cl(-)-depleted and Br(-)-reconstituted oxygen-evolving photosystem II: evidence from X-ray absorption spectroscopy at the Br K-edge

Chloride is an important cofactor in photosynthetic water oxidation. It can be replaced by bromide with retention of the oxygen-evolving activity of photosystem II (PSII). Binding of bromide to the Mn(4)Ca complex of PSII in its dark-stable S(1) state was studied by X-ray absorption spectroscopy (XAS) at the Br K-edge in Cl(-)-depleted and Br(-)-substituted PSII membrane particles from spinach. The XAS spectra exclude the presence of metal ions in the first and second coordination spheres of Br(-). EXAFS analysis provided tentative evidence of at least one metal ion, which may be manganese or calcium, at a distance of approximately 5 A to Br(-). The native Cl(-) ion may bind at a similar distance. Accordingly, water oxidation may not require binding of a halide directly to the metal ions of the Mn complex in its S(1) state.

Speciation of iodine in solid environmental samples by iodine K-edge XANES: application to soils and ferromanganese oxides

A method was developed for speciation of iodine in solid materials using X-ray absorption near-edge structure (XANES). This method was used to identify the iodine species (mainly inorganic iodine) in environmental samples. It was shown that the XANES spectra of iodide and iodate sorbed within solid materials can be simulated by the linear combination of the spectra of iodide and iodate ions in water. The distribution coefficient (Kd) between soil and water was obtained independently for iodide and iodate, based on iodine speciation both in the solid phase, by XANES, and in the aqueous phase, by HPLC-ICP-MS. It was found that the Kd of iodate is larger than that of iodide by a factor of more than six, showing the more soluble nature of iodide. It was suggested that iodate can form in soil even when iodide is injected into the soil-water system under conditions within the iodide-stable field of the Eh-pH diagram of iodine. This is caused by the much higher affinity of iodate for solid surfaces than iodide. In soil samples under various water saturation conditions, or various Eh conditions, the iodide fraction in water increases with decreasing Eh, which results in an increase in the dissolved total iodine fraction in soil water. The speciation method using XANES was also applied to iodine in a natural soil sample and marine ferromanganese oxides. It is suggested that iodine K-edge XANES is a promising tool for determining the iodide/iodate ratio in natural solid samples, which contributes to better understanding of the behavior of iodine at the Earth's surface.

Bromine is an endogenous component of a vanadium bromoperoxidase

On the basis of EXAFS and MS/MS experimental results and a reinterpretation of the electron density map obtained by X-ray crystallography, we describe a new post-translational modification, that is, a 3,5-dibromotyrosine residue that is incorporated in the polypeptide chain of a vanadium haloperoxidase.