Conditional Stability Constants Research Articles

Electronic Spectroscopies Combined with Quantum Chemistry Calculations: Study of the Interactions of 3-Hydroxyflavone with Copper Ions.

The current study aims at obtaining a better understanding of the mechanisms involved in the complexation of copper ions by 3-hydroxyflavone (3HF), which is one of the most studied compounds of the flavonoid family. To achieve this goal, quantum chemistry calculations combined with electronic spectroscopies, including absorption, fluorescence emission, and excitation, have been used. The formation of successive complexes of stoichiometry (metal/ligand) 1:2, 1:1, and 3:2 has been highlighted. Even under acidic conditions (pH = 4.0), the α-hydroxy-keto function of the molecule presents a high complexing power with regard to copper ions, insofar as a stable complex of 1:2 stoichiometry is obtained with a large conditional stability constant (log β = 8.7). The formation of this predominant species induces a quenching of the dual fluorescence of 3HF, whereas the second complex of stoichiometry 1:1 presents a fluorescence emission.

Ternary Zn(II) Complexes of FluoZin-3 and the Low Molecular Weight Component of the Exchangeable Cellular Zinc Pool.

Knowledge of the nature of exchangeable (labile) intracellular Zn(II) is increasingly important for biomedical research. The detection and quantitative determination of Zn(II) ions is usually performed by using Zn(II)-specific fluorescent sensors, among which 2-[2-[2-[2-[bis(carboxylatomethyl)amino]-5-methoxyphenoxy]ethoxy]-4-(2,7-difluoro-3-oxido-6-oxo-4a,9a-dihydroxanthen-9-yl)anilino]acetate (FluoZin-3) has been used most widely. Selectivity of this sensor for Zn(II) over other divalent cations was demonstrated, but possible interference in its performance by other compounds has not been investigated. Many potential low molecular weight ligands for Zn(II) ions (LMWLs) are abundant in the cell. In this study we demonstrate that FluoZin-3 is susceptible to competition for Zn(II) from LMWLs and also forms strong ternary complexes with some of them. We determined the set of conditional stability constants C Ktern for ternary Zn(FluoZin-3)(LMWL) complexes using fluorescence titrations and applied it to model the response of exchangeable zinc to FluoZin-3. We found that competition and formation of ternary complexes with LMWLs together strongly affect (net reduce) the Zn(FluoZin-3) fluorescence. This effect may cause a significant underestimation of exchangeable Zn(II). We also demonstrated a strong pH dependence of this effect. Reduced glutathione (GSH) emerged as the most important Zn(II) partner among the LMWLs, characterized with Ktern = 2.8 ± 0.2 × 106 M-1. Our experiments and calculations suggest that Zn(LMWL) complexes contribute to the exchangeable cellular zinc pool.

Organic complexation of copper in estuarine waters: An assessment of the multi-detection window approach

Abstract Speciation of dissolved Cu in seawater is mainly dominated by organic complexation . However, the analysis is complicated by the presence of many different classes of naturally-occurring organic ligands. In this study, we successfully determined the total dissolved Cu concentrations, Cu-complexing ligand concentrations and their conditional stability constants in Japanese estuarine waters using competitive ligand exchange adsorptive stripping voltammetry (CLE-AdCSV) coupled with a multi detection window approach. The Cu speciation parameters were calculated using ProMCC software. The use of the 5 μM SA detection window was sufficient and effective in detecting two ligand classes in the waters of Otsuchi Bay. The concentrations of the strong ligands (L 1) were between 1.95 and 4.21 nM, while the concentrations of the weak ligand (L2) were in the range of 6.3–33 nM. The conditional stability constants of the strong ligand were around 1015, while those of the weak ligands averaged around 1013. In all of the samples, the L1 concentrations exceeded the total dissolved Cu concentrations, and the two parameters were strongly correlated. Free Cu2+ concentrations were between 10−13 and 10−15 M, a range that is not toxic for most phytoplankton .

Complexation of Trivalent Lanthanides (Eu) and Actinides (Cm) with Aqueous Phosphates at Elevated Temperatures.

In this study, the complexation of Eu(III) and Cm(III) with aqueous phosphates was investigated using laser-induced luminescence spectroscopy. Experiments at 25 °C and different ionic strengths (0.6-3.1 mol·L-1 NaClO4) established the formation of EuH2PO42+ and CmH2PO42+. From the conditional stability constants, the respective values at infinite dilution as well as the ε(Me(H2PO4)2+;ClO4-) (Me = Eu or Cm) ion interaction coefficients (using the specific ion interaction theory - SIT) were derived. Further experiments (at constant ionic strength of 1.1 mol·L-1) showed that upon increasing the temperature (25-80 °C), the formation of both EuH2PO42+ and CmH2PO42+ was favored. Using the van't Hoff equation, the molal enthalpy Δ R H m° and molal entropy Δ R S m° of these reactions were derived, corroborating an endothermic and entropy driven complexation process. This work contributes to a better understanding of the coordination chemistry of both trivalent lanthanides and actinides with phosphate ions.

Interaction of Arsenous Acid with the Dithiol-Type Chelator British Anti-Lewisite (BAL): Structure and Stability of Species Formed in an Unexpectedly Complex System.

British anti-Lewisite (2,3-dimerkaptopropan-1-ol, dimercaprol, BAL) is one of the best-known chelator-type therapeutic agents against toxic metal ions and metalloids, especially arsenicals. Surprisingly, the mechanisms of action at the molecular level, as well as the coordination features of this traditional drug toward various arsenicals, are still poorly revealed. The present study on the interaction of arsenous acid (H3AsO3) with BAL, involving UV and NMR titrations, electrospray ionization mass spectrometry, and 2D NMR experiments combined with MP2 calculations, demonstrates that the reaction of H3AsO3 with BAL at pH = 7.0 results in a more complex speciation than was assumed before. The three reactive hydroxyl groups of H3AsO3 allow for interaction with three thiol moieties via condensation reaction, leading to the observed AsBAL2 and As2BAL3 complexes besides the AsBAL species. This indicates the strong propensity of inorganic As(III) to saturate its coordination sphere with thiolate groups. The alcoholic hydroxyl group of the ligand may also directly bind to As(III) in AsBAL. Compared to dithiothreitol or dithioeritritol, the preference of BAL to form complexes with such a tridentate binding mode is much lower owing to the more strained bridged bicyclic structure with an αAsSC < 90° bond angle and an unfavorable condensed boat-type six-membered ring. On the basis of the NMR data, the predominating, bidentately bound AsBAL species, including a five-membered chelate ring, exists in rapidly interconverting envelope forms of E and Z stereoisomers. The conditional stability constants calculated for the three macrospecies from a series of UV data [log βpH=7.0 = 6.95 (AsBAL), 11.56 (AsBAL2), and 22.73 (As2BAL3)] reflect that BAL is still the most efficient, known, dithiol-type chelator of H3AsO3.

Binding of Cu, Co, and Cs to fluorescent components of natural organic matter (NOM) from three contrasting sites.

Aqueous natural organic matter (NOM) contains different types of functional groups (carboxylic, phenolic, sulfidic, etc.), and hence could change the speciation of metals in environmental systems. This work is a proof-of-concept study on the interaction of three metals (Cu, Co, and Cs) with NOM using fluorescence spectroscopy. The specific aim was to determine the conditional stability constants for these three metals with NOM optical components, obtained from the quenching of fluorescence signals. Three contrasting water types were sampled in Northern Ontario: a pristine source (Cross Rd.), an urban-impacted source (Junction Creek), and an industrially impacted creek (Copper Cliff creek). In this investigation, Cu2+ was used as a benchmark, whereas Co2+ and Cs+ analyses were novel applications of this technique. Humic-like (H-like; terrestrial and microbial), fulvic-like (F-like), and protein-like (P-like) fluorescence components were found in various proportions at the three sampling sites. For these samples, the fluorescence signals of the H-, F-, and P-like components were quenched upon additions of Cu2+. The computed conditional stability constants (as log Kc) ranged from 4.46 to 6.06. In contrast, Kc values with Co2+ were measurable only for the two H-like components of the pristine sample (log Kc 3.02-4.05). Cesium (Cs+) induced quenching only for the P-like component at the industrial-impacted site (log Kc 4.82-5.03). While this study corroborates earlier reports that Cu2+-NOM interactions can be measured by fluorescence, we are showing for the first time a direct chemical interaction of Co2+ and Cs+ with specific NOM components, as reported by fluorescence quenching.

Oxime-containing acetylcholinesterase reactivators and their complexes with Pd(II) and Pt(II) ions: recent developments

The ability of oxime-containing acetylcholinesterase reactivators BT-07 (K005), BT-08 (K033), BT-07-4M (K074), and obidoxime (H$_{2}$LX$_{2}$, X = Cl$^{-}$, Br$^{-})$ to bind palladium(II) or platinum(II) cations was evaluated in aqueous solutions (pH 7.4) at metal-to-ligand molar ratio varying from 1:10 to 10:1. Spectral changes were monitored within a week after mixing the reagents in the range from 220 nm to 500 nm. Results showed that depending on chemical structure and reaction time, oximes form two complex species of composition, [MHL]$^{3+}$ or [M$_{2}$L]$^{4+}$ (M = Pd(II), Pt(II)). It was also found that complexation of platinum(II) ions proceeds slower as compared to palladium(II). Conditional stability constants of new complex species were determined spectrophotometrically using an advanced chemometric procedure, based on the resolution of overlapping bands technique.

Influence of organic complexation on dissolved iron distribution in East Antarctic pack ice

Abstract Since Antarctic sea ice covers an area larger than the Antarctic continent itself, the discovery that it can fertilize the Southern Ocean with iron (Fe) has fostered a new breadth of research in recent years. In order to test the hypothesis that Fe-binding organic ligands control the distribution of dissolved iron (DFe) in Antarctic pack ice, iron organic speciation was investigated in samples collected during the Sea Ice Physics and Ecosystem eXperiment-2 (SIPEX-2) voyage in Austral winter/spring 2012. Dissolved Fe was measured using sector field inductively coupled plasma mass spectrometry, and iron organic speciation parameters were determined by competitive ligand equilibration - adsorptive cathodic stripping voltammetry method, using 1-nitroso-2-naphthol (NN) as the added ligand. The concentration of Fe-binding organic ligands (Lt) ranged from 4.9 nM to 41 nM (average of 14.9 ± 8.4 nM, n = 34), and was always higher than the corresponding DFe (average of 7.5 ± 4.5 nM, n = 34). Conditional stability constants (log K′ Fe’L = 11.7–13.0) were similar to those previously observed in land-fast ice. Concentrations of DFe and Lt displayed similar depth profiles; their strong correlation (Spearman's ρ = 0.80, p 1). Estimates showed that pack ice would have released 0.45 μmol/m 2 /d of Lt during spring melt, 0.21 μmol/m 2 /d of which are free from Fe binding, and hence available for further complexation. Therefore, it is suggested that this excess of Fe-free ligands may play a key role in controlling the solubility of free or newly formed Fe in surface waters before the peak of primary production, outcompeting the Fe-binding organic ligands already present in seawater.

The copper complexation ability of a synthetic humic-like acid formed by an abiotic humification process and the effect of experimental factors on its copper complexation ability.

Humic acids have an important impact on the distribution, toxicity, and bioavailability of hazardous metals in the environment. In this study, a synthetic humic-like acid (SHLA) was prepared by an abiotic humification process using catechol and glycine as humic precursors and a MnO2 catalyst. The effect of physico-chemical conditions (ionic strength from 0.01 to 0.5M NaNO3, pH from 4 to 8, temperature from 25 to 45°C, and humic acid concentration from 5 to 100mg/L) on the complexation ability of SHLA for Cu2+ were investigated. A commercial humic acid (CHA, CAS: 1415-93-6) from Sigma-Aldrich was also studied for comparison. The results showed that for pH4 to 8, the conditional stability constants (log K) of SHLA and CHA were in the range 5.63-8.62 and 4.87-6.23, respectively, and complexation capacities (CC) were 1.34-2.61 and 1.42-2.31mmol/g, respectively. The Cu complexation ability of SHLA was higher than that of the CHA due to its higher number of acidic functional groups (SHLA 19.19mmol/g; CHA 3.87mmol/g), extent of humification and aromaticity (AL/AR: 0.333 (SHLA); 1.554 (CHA)), and O-alkyl functional groups (SHLA15.56%; CHA 3.45%). The log K and complexation efficiency (fraction of metal bound to SHLA) of SHLA were higher at higher pH, lower ionic strength, higher temperature, and higher SHLA concentration. Overall, SHLA was a good and promising complexation agent for copper in both soil washing of copper contaminated soil and the treatment of copper-containing wastewater.

A thermodynamical study on the complex formation of Cm(III) with methacrylate

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to investigate the complexation of Cm(III) with methacrylate in NaCl solution as a function of the temperature (20–60 °C), ionic strength (0–2.5 mol/kg) and ligand concentration (0–0.2 mol/kg). The aqueous speciation of Cm(III) is obtained by deconvolution of the experimental emission spectra using pure component spectra of all Cm(III) species involved under the given experimental conditions. By applying the specific ion interaction theory (SIT), the temperature-dependent thermodynamic stability constants (log K0n(T), n = 1,2) are determined by extrapolating the conditional stability constants to zero ionic strength. Additionally, the binary ion interaction coefficients (ε(i,j)) for the interaction between Cl− and the complex species [Cm(Meth)n]3−n (n = 1,2) are calculated. The temperature dependency of log K0n in combination with the integrated Van't Hoff equation provides the molal standard reaction enthalpies and entropies (ΔrH0m, ΔrS0m) of the respective complexation reactions confirming that both, the formation of [CmMeth]2+ and [Cm(Meth)2]+ are endothermic and entropy driven. At temperatures ≥70 °C, an additional Cm(III) species is formed that is attributed to the thermically induced polymerization of methacrylate.

Distinct Siderophores Contribute to Iron Cycling in the Mesopelagic at Station ALOHA

The distribution of dissolved iron (Fe), total organic Fe-binding ligands, and siderophores were measured between the surface and 400 m at Station ALOHA, a long term ecological study site in the North Pacific Subtropical Gyre. Dissolved Fe concentrations were low throughout the water column and strong organic Fe-binding ligands exceeded dissolved Fe at all depths; varying from 0.9 nmol L-1 in the surface to 1.6 nmol L-1 below 150 m. Although Fe does not appear to limit microbial production, we nevertheless found siderophores at nearly all depths, indicating some populations of microbes were responding to Fe stress. Ferrioxamine siderophores were most abundant in the upper water column, with concentrations between 0.1-2 pmol L-1, while a suite of amphibactins were found below 200 m with concentrations between 0.8-11 pmol L-1. The distinct vertical distribution of ferrioxamines and amphibactins may indicate disparate strategies for acquiring Fe from dust in the upper water column and recycled organic matter in the lower water column. Amphibactins were found to have conditional stability constants (log ) ranging from 12.0-12.5, while ferrioxamines had much stronger conditional stability constants ranging from 14.0-14.4, within the range of observed L1 ligands by voltammetry. We used our data to calculate equilibrium Fe speciation at Station ALOHA to compare the relative concentration of inorganic and siderophore complexed Fe. The results indicate that the concentration of Fe bound to siderophores was up to two orders of magnitude higher than inorganic Fe, suggesting that even if less bioavailable, siderophores were nevertheless a viable pathway for Fe acquisition by microbes at our study site. Finally, we observed rapid production of ferrioxamine E by particle-associated bacteria during incubation of freshly collected sinking organic matter. Fe-limitation may therefore be a factor in regulating carbon metabolism and nutrient regeneration in the mesopelagic.

Binding of proton and iron to lignite humic acid size-fractions in aqueous matrix

The bioavailability of trivalent iron (Fe3+) to plants can be enhanced using fertilizer solutions containing humic acids (HA) as manifested from the increased crop yield at an iron stress conditions. The lignite-derived HA (HAlignite) facilitates higher diffusion of Fe3+ between the soil layers as attributable to more number of reactive sites in the assemblage compared to those from other origins. In the current work, the proton-binding of HAlignite size-fractions (5–10, 10–30, 30–100, and >100 kDa), as segmented based on the molecular weight distribution, and their complexation with Fe3+ have been studied at varying pH ranging from low to high. The protonation or formation of Fe3+-complexes exhibited a comparable pattern despite the differences in the conformational distribution of HAlignite size-fractions. The protonation behavior specified that the behavior of HAlignite size-fractions has similarity with that of a dibasic acid. The results are interpreted using reactive structural units (RSU) concept to show that the carboxyl and phenolic-hydroxyl groups in the HAlignite size-fractions simultaneously available as the Fe3+-binding sites. The stability constants for larger MW fractions of HAlignite (>100 kDa) was the lowest, as attributed to the increased aggregation rate in an aqueous matrix. The trend in conditional stability constants of HAlignite-size fractions and other Fe-chelators point to a better Fe-binding capability of HAlignite (30–100 kDa) size-fraction than the biodegradable alternatives (GLDA, HIDS, EDDS, IDSA, or NTA), while the Fe-interaction was stronger with classical synthetic chelators (EDTA, DTPA, or EDDHA).

Metal transport capabilities of anticancer copper chelators

In the present study, several Cu chelators [2,2′-biquinoline, 8-hydroxiquinoline (oxine), ammonium pyrrolidinedithiocarbamate (APDTC), Dp44mT, dithizone, neocuproine] were used to study Cu uptake, depletion and localization in different cancer cell lines. To better understand the concentration dependent fluctuations in the Cu intracellular metal content and Cu-dependent in vitro antiproliferative data, the conditional stability constants of the Cu complex species of the investigated ligands were calculated. Each investigated chelator increased the intracellular Cu content on HT-29 cells causing Cu accumulation depending on the amount of the free Cu(II). Copper accumulation was 159 times higher for Dp44mT compared to the control. Investigating a number of other transition metals, intracellular accumulation of Cd was observed only for two chelators. Intracellular Zn content slightly decreased (cca. 10%) for MCF-7 cells, while a dramatic decrease was observed on MDA-MB-231 ones (cca. 50%). A similar decrease was observed for HCT-116, while Zn depletion for HT-29 corresponded to cca. 20%. The IC50 values were registered for the investigated four cell lines at increasing external Cu(II) concentration, namely, MDA-MB-231 cells had the lowest IC50 values for Dp44mT ranging between 7 and 35 nM. Thus, Zn depletion could be associated with lower IC50 values. Copper depletion was observed for all ligands being less pronounced for Dp44mT and neocuproine. Copper localization and its colocalization with Zn were determined by μ-XRF imaging. Loose correlation (0.57) was observed for the MCF-7 cells independently of the applied chelator. Similarly, a weak correlation (0.47) was observed for HT-29 cells treated with Cu(II) and oxine. Colocalization of Cu and Zn in the nucleus of HT-29 cells was observed for Dp44mT (correlation coefficient of 0.85).

Toxic metals (Ni2+, Pb2+, Hg2+) binding affinity of dissolved organic matter (DOM) derived from different ages municipal landfill leachate

Solid waste production is rapidly increasing in Bangladesh and landfill leachate is the consequence of the decomposition of this waste. These leachates contain heavy metals and significant amount of dissolved organic matter (DOM). DOM is known to have considerable role in heavy metals speciation. Hence, it is important to characterize DOM/leachate and evaluate toxic metals binding affinity of DOM. The objectives of this study were to characterize the DOM in landfill leachate through physico-chemical and optical analyses and to investigate the toxic metals (Ni2+, Pb2+ and Hg2+) binding affinity of three different ages (fresh sample L-1, young sample L-2 and mature sample L-3) DOM samples. Results suggested that leachate is a potential pollutant which contained very high organic pollutant load. Conditional stability constant (LogK) and percentages of fluorophores that correspond to metal binding (%f) values indicated that young DOM sample (L-2) had the highest binding affinity to all the three metals ions. In general, DOM samples showed the following order affinity to the metal ions; Ni2+ binding affinity: L-2 > L-3 > L-1, Pb2+ binding affinity: L-2 > L-3 > L-1 and Hg2+ binding affinity: L-2 > L-1 > L-3.

Solubility and hydrolysis of U(VI) in 0.5 mol/kg NaCl solutions at T = 22 and 80 °C

Abstract In this study, the solubility and hydrolysis of U(VI) was investigated at elevated temperature. Experiments were performed in solutions of NaCl 0.51 mol/kg of water in the pHm range 4–13.4 (with pHm = –log[H+]) at T = 22 ± 3 and 80 ± 5 °C under N2/Ar atmosphere. Two solid phases were used as starting U(VI) materials: UO3·2H2O(cr) equilibrated in solutions with 4 ≤ pHm ≤ 5 and Na2U2O7·H2O(cr) (a synthetic clarkeite-like phase) equilibrated in solutions with 7 ≤ pHm ≤ 13.4. The solubility of UO3·2H2O(cr) at T = 80 °C in the acidic pHm-range is decreased by a factor of ten with respect to the U(VI)-phase studied at room temperature. Solid phase characterization by XRD, SEM–EDS and quantitative chemical analysis indicate that this decrease is correlated to the transformation of UO3·2H2O(cr) into a sodium-containing U(VI) solid phase. The solubility of Na2U2O7·H2O(cr) in the alkaline pHm-range is drastically enhanced at T = 80 °C. The main contribution to this effect results from the increased acidity of water at elevated temperature, although an enhanced hydrolytic activity of U(VI) or a decreased stability of Na2U2O7·H2O(cr) are also considered, in order to explain the solubility data under these experimental conditions. Solid phase characterization after completing the solubility experiments confirms that Na2U2O7·H2O(cr) retains its stoichiometry and structure at T = 80 °C within the timeframe of the study (t ≤ 290 days). A thermodynamic model, comprising conditional stability constants and enthalpy data has been developed, describing reliably the processes of hydrolytic dissolution of Na2U2O7·H2O(cr) in alkaline NaCl solutions up to 0.51 mol/kg and their temperature dependence in the range 22–80 °C. This work represents the first comprehensive study on U(VI) solubility and hydrolysis at elevated temperatures extending to alkaline pHm conditions relevant in the context of nuclear waste disposal. It provides robust solubility upper limits to be considered in source term estimations, but also thermodynamic data for both solid phases and aqueous species that can be implemented in thermodynamic databases and related geochemical calculations.

Electrochemical recovery of copper complexed by DTPA and C12‐DTPA from aqueous solution using a membrane cell

AbstractBACKGROUNDThe electrochemical recovery of copper from diethylenetriaminepentaacetic acid (DTPA) and C12–DTPA (a surface‐active derivative of DTPA) complex solutions was investigated in a membrane flow cell. Electrolysis time, solution flow rate, applied current density, and solution pH were evaluated.RESULTSThe chelating surfactant C12‐DTPA can promote the kinetics of copper electrodeposition more than DTPA depending on the experimental conditions. At a current density of 30 A m–2, a solution flow rate of 0.6 L min–1, and pH 10 after 180 min treatment, the copper recovery and current efficiency were 50% and 43.3%, respectively, in the Cu(II)‐DTPA system and about 65% and 53.6%, respectively, in the Cu(II)‐C12‐DTPA system. The differences in the amount of recovery could be explained in terms of differences in the diffusion of copper complexes with DTPA and C12‐DTPA to the cathode, as well as their solution behavior and pH‐dependent conditional stability constants (log10 K'CuDTPA3‐).CONCLUSIONElectrochemical methods could be effectively combined with foam flotation for the chelating surfactant C12‐DTPA, to recover copper and C12‐DTPA. This makes the overall treatment more sustainable, and can be helpful in complying with the increasingly stringent environmental regulations. © 2017 Society of Chemical Industry

On the nature of dissolved copper ligands in the early buoyant plume of hydrothermal vents

Environmental contextCopper released by deep-sea hydrothermal vents has been recognised to be partly stabilised against precipitation by its complexation with strong Cu binding ligands. Yet, the sources and nature of these compounds in such environments are still not fully understood. This study shows that the Cu ligands detected are hydrothermally sourced and could be mainly inorganic sulfur species. AbstractThe apparent speciation of Cu in the early buoyant plume of two black smokers (Aisics and Y3) from the hydrothermal vent field Lucky Strike (Mid-Atlantic Ridge) was investigated using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE–AdCSV). We have assessed the apparent Cu-binding ligand concentration ([L]) and the corresponding conditional stability constant (log K′) for 24 samples. At the smoker Aisics, [L] ranged from 18.2 to 2970 nM. Log K′CuL ranged from 12.4 to 13.4. At Y3, the binding capacity of natural ligands was from 32.5 to 1020 nM, with Log K′CuL ranging from 12.5 to 13.1. Total dissolved Cu ranged from 7.0 to 770 nM and from 12.7 to 409 nM at Aisics and Y3, respectively. Our results show that the amount of ligand L increases with dissolved Mn (dMn) concentrations, suggesting a hydrothermal origin of the Cu-binding ligands detected. In addition, such high concentrations of Cu-binding ligands can only be explained by an additional abiotic source differing from organic processes. Based on the massive in situ concentrations of free sulfides (up to 300 µM) and on the striking similarities between our log K′CuL and the log K′Cu(HS) previously published, we infer that the Cu-binding ligands could be predominantly inorganic sulfur species in the early buoyant plume of the two vent sites studied.

Cu2+ selective chelators relieve copper-induced oxidative stress in vivo.

Copper ions are essential for biological function yet are severely detrimental when present in excess. At the molecular level, copper ions catalyze the production of hydroxyl radicals that can irreversibly alter essential bio-molecules. Hence, selective copper chelators that can remove excess copper ions and alleviate oxidative stress will help assuage copper-overload diseases. However, most currently available chelators are non-specific leading to multiple undesirable side-effects. The challenge is to build chelators that can bind to copper ions with high affinity but leave the levels of essential metal ions unaltered. Here we report the design and development of redox-state selective Cu ion chelators that have 108 times higher conditional stability constants toward Cu2+ compared to both Cu+ and other biologically relevant metal ions. This unique selectivity allows the specific removal of Cu2+ ions that would be available only under pathophysiological metal overload and oxidative stress conditions and provides access to effective removal of the aberrant redox-cycling Cu ion pool without affecting the essential non-redox cycling Cu+ labile pool. We have shown that the chelators provide distinct protection against copper-induced oxidative stress in vitro and in live cells via selective Cu2+ ion chelation. Notably, the chelators afford significant reduction in Cu-induced oxidative damage in Atp7a-/- Menkes disease model cells that have endogenously high levels of Cu ions. Finally, in vivo testing of our chelators in a live zebrafish larval model demonstrate their protective properties against copper-induced oxidative stress.

Chlorofullerene C60Cl6: A Precursor for Straightforward Preparation of Highly Water‐Soluble Poly‐hydroxypyridinone Fullerene Derivatives as Potential Radionuclide Chelators

AbstractRadionuclide internal contamination can induce chemical and radiological intoxication and produce harmful free radicals in vivo. Conventional studies on chelating agents have disregarded the damage of free radicals to the body. Therefore, novel poly‐hydroxypyridinone fullerene derivatives were designed and prepared by using chlorofullerene as precursor. The poor water solubility of fullerene was ameliorated by chemically modifying of hydrophilic hydroxypyridinone, and obtaining high Water‐soluble fullerene derivatives. The radical scavenging reaction kinetics of target products were studied. They all exhibited much higher rate constants than other fullerene polymer system. The CeIII ion was used as a simulated radionuclide for evaluating the binding ability of target products, and the values of conditional stability constants were about 5.15‐6.11. Thus, the bifunctional, Water‐soluble fullerene derivatives were successfully generated. The results provided basis for further study on the potential application of poly‐hydroxypyridinone fullerene derivatives as radionuclide chelators.

Organic complexation of iron in the eastern tropical South Pacific: Results from US GEOTRACES Eastern Pacific Zonal Transect (GEOTRACES cruise GP16)

Abstract Dissolved iron, organic iron-binding ligands, and organic carbon were determined in full water column depth profiles across the US GEOTRACES Eastern Pacific Zonal Transect (GEOTRACES cruise GP16) in late 2013. Dissolved iron concentrations exhibited subsurface maxima associated with the remineralization of organic matter at the Peru shelf and with hydrothermal inputs from the East Pacific Rise. Iron-binding organic ligands are described as ligand classes based on defined ranges in conditional stability constants. The stronger L1-type ligands were measured in large excesses in surface and intermediate waters, and these excesses were negatively correlated with Si*, a biogeochemical proxy for iron limited diatom growth. These data suggest sources of strong iron-binding ligands from iron limitation of diatom communities, both locally and in waters originating from the Southern Ocean. Benthic sources of strong ligands were associated with new iron inputs from hydrothermal activity at the East Pacific Rise and from bottom sediments. In contrast to most studies in the Atlantic basin but consistent with previous datasets from the Pacific, stronger L1 ligands in this dataset were generally restricted to the upper water column and did not show large excesses through the water column. At depth, iron-binding ligands on GP16 were instead best described as L2 and L3 ligands. Concomitant decreases in excess L1, excess total ligands and dissolved organic carbon suggest similar degradation pathways of these pools below the surface.