Biochar-derived dissolved black carbon (DBC) varies in chemical composition and significantly affects the environmental fate of metal ions. However, the intrinsic molecular composition of DBC ...fractions and their molecular interaction mechanisms with metal ions remain unclear. We propose a novel, molecular-level covariant binding mechanism to comparatively interpret the heterogeneities, active sites, and sequential responses of copper binding with molecular compounds in DBC and natural dissolved organic matter (DOM). Relatively large proportions of lipid/aliphatic/peptide-like compounds with low mass distributions and lignin-like compounds with oxidized/unsaturated groups existed in acidic- and alkaline-extracted DBC, respectively. A larger percentage of tannin-like/condensed aromatic compounds and higher average conditional stability constants (logK̅ Cu) of visible fluorescent components were found for DOM than for DBC. Overall, 200–320 Da and 320–480 Da molecular components contributed significantly to the logK̅ Cu values of UVA and visible fluorescent components, respectively, in DBC/DOM. Nitrogenous groups likely exhibited stronger binding affinities than phenolic/carboxylic groups. The sequential copper-binding responses of molecular compounds in DBC/DOM generally followed the order lipid/aliphatic/peptide-like compounds → tannin-like compounds → condensed aromatic compounds. These insights will improve the prediction of the potential effects of DBC on various contaminants and the risks of biochar application to ecosystems.
Fe(II) has been extensively studied due to its importance as a reductant in biogeochemical processes and contaminant attenuation. Previous studies have shown that ligands can alter aqueous Fe(II) ...redox reactivity but their data interpretation is constrained by the use of probe compounds. Here, we employed mediated electrochemical oxidation (MEO) as an approach to directly quantify the extent of Fe(II) oxidation in the absence and presence of three model organic ligands (citrate, nitrilotriacetic acid, and ferrozine) across a range of potentials (E H) and pH, thereby manipulating oxidation over a broad range of fixed thermodynamic conditions. Fe(III)-stabilizing ligands enhanced Fe(II) reactivity in thermodynamically unfavorable regions (i.e., low pH and E H) while an Fe(II) stabilizing ligand (ferrozine) prevented oxidation across all thermodynamic regions. We experimentally derived apparent standard redox potentials, E H ϕ, for these and other (oxalate, oxalate2, NTA2, EDTA, and OH2) Fe-ligand redox couples via oxidative current integration. Preferential stabilization of Fe(III) over Fe(II) decreased E H ϕ values, and a Nernstian correlation between E H ϕ and log(K Fe(III)/K Fe(II)) exists across a wide range of potentials and stability constants. We used this correlation to estimate log(K Fe(III)/K Fe(II)) for a natural organic matter isolate, demonstrating that MEO can be used to measure iron stability constant ratios for unknown ligands.
•Overview of zinc fingers (ZFs) discovery; biophysical and structural study.•Division of ZF classes according to their structural fold and coordination mode.•Methods and approaches used for ...determination of ZFs stability constants.•Structural and sequential factors that affect thermodynamic stability and metal-coupled folding.•Coordination properties of diverse ZFs and their reactivity.
Zinc fingers (ZFs) are among the most structurally diverse protein domains. They interact with nucleic acids, other proteins and lipids to facilitate a multitude of biological processes. Currently, there are more than 10 known classes of ZFs, with various architectures, metal binding modes, functions and reactivity. The versatility, selectivity and stability of these short amino acid sequences is achieved mainly by (i) residues participating in Zn(II) coordination (mostly Cys and His), (ii) hydrophobic core and ZF structure formation, and (iii) variable residues responsible for inter- and intramolecular interactions. Since their discovery, ZFs have been extensively studied in terms of their structure, stability and recognition targets by the application of various methodologies. Studies based on interactions with other metal ions and their complexes have contributed to the understanding of their chemical properties and the discovery of new types of ZF complexes, such as gold fingers or lead fingers. Moreover, due to the presence of nucleophilic thiolates, ZFs are targets for reactive oxygen and nitrogen species as well as alkylating agents. Interactions with many reactive molecules lead to disturb the native Zn(II) coordination site which further result in structural and functional damage of the ZFs. The post-translational modifications including phosphorylation, acetylation, methylation or nitrosylation frequently affect ZFs function via changes in the protein structure and dynamics. Even though the literature is replete with structural and stability data regarding classical (ββα) ZFs, there is still a huge gap in the knowledge on physicochemical properties and reactivity of other ZF types. In this review, metal binding properties of ZFs and stability factors that modulate their functions are reviewed. These include interactions of ZFs with biogenic and toxic metal ions as well as damage occurring upon reaction with reactive oxygen and nitrogen species, the methodology used for ZFs characterization, and aspects related to coordination chemistry.
The solubility of cooperite PtS(cr) was measured in aqueous sulfide solutions at 25 °C/1 bar, 75 °C/1 bar, and 450 °C/1000 bar. The concentration of Pt increases with an increase of temperature from ...10–10.2 to 10–7.4m (mol⋅(kg H2O)−1) in solutions which contain 0.06–0.07 m of total reduced sulfur. The experimental solubility data are accurately described by the reactionsPtScr+H2S˚aq=PtHS2˚aqKs˚PtHS2.PtScr+2H2S˚aq=PtHS3−+H+Ks˚PtHS3−..
The charged complex Pt(HS)3− dominates in low-temperature near-neutral solutions but was not detected at 450 °C where the only hydrosulfide complex was Pt(HS)2°(aq). The effect of NaCl on the PtS(cr) solubility is negligible which implies that mixed Pt-HS-Cl complexes can be neglected. The PtS(cr) solubility constant, Ks°(Pt(HS)2), was determined as log Ks° = −9.09 ± 0.17 (25 °C/1 bar), −9.50 ± 0.35 (75 °C/1 bar), and − 6.68 ± 0.10 (450 °C/1000 bar). The PtS(cr) solubility constant, Ks°(Pt(HS)3−), was determined as log Ks° = −14.43 ± 0.31 (25 °C/1 bar), and − 13.15 ± 0.23 (75 °C/1 bar). The PtS(cr) solubility constants together with the literature data were fitted to a simple density modellogKSoPtHS2o=−7.30−638.9∙TK−1−5.98∙logdwlogKSoPtHS3−=0.633−4522.6∙TK−1+43.03∙logdw
where d(w) is the pure water density. The Ks°(Pt(HS)2) increases with an increase of temperature, but Ks°(Pt(HS)3−) has a maximum at ca. 200 °C. Accordingly, at higher temperatures the role of the latter complex decreases and its contribution to the dissolved Pt concentration becomes negligible at t > 300 °C. Thermodynamic calculations show that in natural hydrothermal fluids, which contain up to 0.1 m of total reduced sulfur, the concentration of Pt-HS complexes can reach a few ppb. Higher solubility of Pt-bearing minerals can be attained in chloride-bearing fluids due to the formation of PtCl42−, which plays the dominant role in high-temperature hydrothermal transport of Pt.
•Pt(HS)2(aq) and Pt(HS)3− are the main hydrosulfide complexes of Pt.•Stability of Pt(HS)3− decreases at t > 200 °C.•Pt(HS)2(aq) dominate in chloride-sulfide-bearing fluids at 200 < t < 500 °C.•Pt(HS)2(aq) concentration in natural ore-forming fluids is between ppt and a few ppb. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The binding ability of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) towards Ga3+ has been investigated by ISEH+ (Ion Selective Electrode, glass electrode) potentiometric and UV/Vis spectrophotometric ...titrations in KCl(aq) at I = 0.2 mol dm−3 and at T = 298.15 K. Further experiments were also performed adopting both the metal (with Fe3+ as competing cation) and ligand-competition approaches (with EDTA as competing ligand). Results gave evidence of the formation of the Ga(8-HQA)+, Ga(8-HQA)(OH), Ga(8-HQA)(OH)2− and Ga(8-HQA)2− species, the latter being so far the most stable, as also confirmed by ESI-MS analysis. Experiments were also designed to determine the stability constants of the Ga(EDTA)− and Ga(EDTA)(OH)2− in the above conditions. Due to the relevance of Ga3+ hydrolysis in aqueous systems, literature data on this topic were collected and critically analyzed, providing equations for the calculation of mononuclear Ga3+ hydrolysis constants at T = 298.15 K, in different ionic media, in the ionic strength range 0 < I / mol dm−3 ≤ 1.0. The synthesis and characterization (by ElectroSpray Ionization – Mass Spectrometry (ESI-MS), Attenuated Total Reflectance - Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and ThermoGravimetric Analysis (TGA)) of Ga3+/8-HQA complexes were also performed, identifying Ga(8-HQA)2− as the main isolated species, even in the solid state. Finally, the potential effects of 8-HQA and Ga3+/8-HQA complex towards human microbiota exposed to ionizing radiation were evaluated (namely Actinomyces viscosus, Streptococcus mutans, Streptococcus sobrinus, Pseudomonas putida, Pseudomonas fluorescens and Escherichia coli), as well as their anti-proliferative and anti-inflammatory properties. A radioprotective effect of Ga3+/8-HQA complex was observed on Actinomyces viscosus, while showing a potential radiosensitizing effect against Streptococcus mutans and Streptococcus sobrinus. No cytotoxicity on RAW264.7 murine macrophage cells was observed, neither for the free ligand or Ga3+/8-HQA complex. Nevertheless, Ga3+/8-HQA complex highlighted potential anti-inflammatory properties.
The chemical speciation of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) / Ga3+ system was studied in aqueous solution. Solid state complexes were also obtained and characterized. Their effect on microbiota radiosensitivity and their anti-inflammatory action were also evaluated. Display omitted
•The chemical speciation of Ga3+/8-HQA system was studied.•Stability constants of Ga3+/EDTA and Ga3+ hydrolysis constants were reported.•Ga(8-HQA)2− is the main species formed, both in aqueous solution and solid state.•Ga3+/8-HQA complex shows radioprotective effect towards A. viscosus.•Ga3+/8-HQA complex shows radiosensitizing effect towards Streptococcus spp..•Ga3+/8-HQA complex shows anti-inflammatory potential.
Development of efficient carbon capture‐and‐release technologies with minimal energy input is a long‐term challenge in mitigating CO2 emissions, especially via CO2 chemisorption driven by engineered ...chemical bond construction. Herein, taking advantage of the structural diversity of ionic liquids (ILs) in tuning their physical and chemical properties, precise reaction energy regulation of CO2 chemisorption was demonstrated deploying metal‐ion‐amino‐based ionic liquids (MAILs) as absorbents. The coordination ability of different metal sites (Cu, Zn, Co, Ni, and Mg) to amines was harnessed to achieve fine‐tuning on stability constants of the metal ion‐amine complexes, acting as the corresponding cations in the construction of diverse ILs coupled with CO2‐philic anions. The as‐afforded MAILs exhibited efficient and controllable CO2 release behavior with great reduction in energy input and minimal sacrifice on CO2 uptake capacity. This coordination‐regulated approach offers new prospects for the development of ILs‐based systems and beyond towards energy‐efficient carbon capture technologies.
You've got MAIL: Reaction energy regulation of CO2 chemisorption is achieved deploying metal‐ion‐amino‐based ionic liquids (MAILs) as absorbents. Taking advantage of the coordination ability of different metal sites (Cu, Zn, Co, Ni, and Mg) to amines, fine‐tuning on stability constants of the metal ion‐amine complexes leads to efficient CO2 release with great reduction in energy input and minimal sacrifice on CO2 uptake capacity.
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