Conditional Stability Constants Research Articles

The molecular binding sequence transformation of soil organic matter and biochar dissolved black carbon antagonizes the transport of 2,4,6-trichlorophenol

Dissolved organic matter (DOM) and dissolved black carbon (DBC) are significant environmental factors that influence the transport of organic pollutants. However, the mechanisms by which their molecular diversity affects pollutant transport remain unclear. This study elucidates the molecular binding sequence and adsorption sites through which DOM/DBC compounds antagonize the transport of 2,4,6-trichlorophenol (TCP) using column experiments and modelling. DBC exhibits a high TCP adsorption rate (kn = 5.32 × 10−22 mol1–n∙Ln–1∙min−1) and conditional stability constant (logK = 5.19–5.74), indicating a strong binding affinity and antagonistic effect on TCP. This is attributed to the high relative content of lipid/protein compounds in DBC (25.65 % and 30.28 %, respectively). Moreover, the small molecule lipid compounds showed stronger TCP adsorption energy (Ead = −0.0071 eV/−0.0093 eV) in DOM/DBC, combined with two-dimensional correlation spectroscopy model found that DOM/DBC antagonized TCP transport in the environment through binding sequences that transformed from lipid/protein small molecule compounds to lignin/tannin compounds. This study used a multifaceted approach to comprehensively assess the impact of DOM/DBC on TCP transport. It reveals that the molecular diversity of DOM/DBC is a critical factor affecting pollutant transport, providing important insights into the environmental trend and ecological effects of pollutants.

Ocean alkalinity enhancement using sodium carbonate salts does not lead to measurable changes in Fe dynamics in a mesocosm experiment

Abstract. The addition of carbonate minerals to seawater through an artificial ocean alkalinity enhancement (OAE) process increases the concentrations of hydroxide, bicarbonate, and carbonate ions. This leads to changes in the pH and the buffering capacity of the seawater. Consequently, OAE could have relevant effects on marine organisms and in the speciation and concentration of trace metals that are essential for their physiology. During September and October 2021, a mesocosm experiment was carried out in the coastal waters of Gran Canaria (Spain), consisting on the controlled variation of total alkalinity (TA). Different concentrations of carbonate salts (NaHCO3 and Na2CO3) previously homogenized were added to each mesocosm to achieve an alkalinity gradient between Δ0 to Δ2400 µmol L−1. The lowest point of the gradient was 2400 µmol kg−1, being the natural alkalinity of the medium, and the highest point was 4800 µmol kg−1. Iron (Fe) speciation was monitored during this experiment to analyse total dissolved iron (TdFe, unfiltered samples), dissolved iron (dFe, filtered through a 0.2 µm pore size filter), soluble iron (sFe, filtered through a 0.02 µm pore size filter), dissolved labile iron (dFe′), iron-binding ligands (LFe), and their conditional stability constants (KFeL′) because of change due to OAE and the experimental conditions in each mesocosm. Observed iron concentrations were within the expected range for coastal waters, with no significant increases due to OAE. However, there were variations in Fe size fractionation during the experiment. This could potentially be due to chemical changes caused by OAE, but such an effect is masked by the stronger biological interactions. In terms of size fractionation, sFe was below 1.0 nmol L−1, dFe concentrations were within 0.5–4.0 nmol L−1, and TdFe was within 1.5–7.5 nmol L−1. Our results show that over 99 % of Fe was complexed, mainly by L1 and L2 ligands with kFe′L′ ranging between 10.92 ± 0.11 and 12.68 ± 0.32, with LFe ranging from 1.51 ± 0.18 to 12.3 ± 1.8 nmol L−1. Our data on iron size fractionation, concentration, and iron-binding ligands substantiate that the introduction of sodium salts in this mesocosm experiment did not modify iron dynamics. As a consequence, phytoplankton remained unaffected by alterations in this crucial element.

Spectroscopic insights into the influence of oxidation on the binding properties of Cu(II) onto biochar-derived dissolved organic matter

The oxidation may change the composition, content, and structure of biochar-derived dissolved organic matter (BDOM) that influences the geochemical behavior of heavy metals (HMs) when biochar is applied. Herein, the binding characteristics of Cu(II) onto BDOM and oxidized BDOM (OBDOM) were investigated using synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) spectroscopy in combination with two-dimensional correlation spectroscopy (2D-COS). The results showed that the content of BDOM300 and BDOM600 decreased by 30.21% and 13.67% respectively after oxidation. Humic-like substances are dominated in the BDOM, which can be preferentially oxidized. Meanwhile, humic-like substances (e.g. 412 nm in the BDOM300, 490 nm in the OBDOM300, 525 nm in the BDOM600, and OBDOM600) can preferentially react with Cu(II). The functional groups, at 1712 cm−1 in the BDOM300, 1631 and 1290 cm−1 in the OBDOM300, 1515 cm−1 in the BDOM600, 1740 cm−1 in the OBDOM600, played important roles in the complexation between humic-like substances and Cu(II). The logarithmic conditional stability constant (Log K) of the complexes is higher in the OBDOM300 than those in the BDOM300, and higher in the OBDOM600 than those in the BDOM600. The results also indicated that the presence of BDOM promoted the adsorption of Cu(II) by BC300 and BC600, and inhibited the adsorption of Cu(II) by OBC300 and OBC600. Therefore, it is particularly important to insight into the effect of oxidation on the binding properties of Cu(II) and BDOM. This study can provide scientific guidance for the use of biochar in the remediation of HMs.

Didactic experiment for voltametric determination the complexing capacity of natural waters

The titration method can be applied to determine the complexation capacity between metal ions and ligands in natural water samples. The process involves the incremental addition of the metal to the sample containing a specific ligand, resulting in a titration curve that reflects the formation of complexes. The change in the curves slope indicates the saturation of the complexation capacity. In this study, the copper (II) ion was used due to its stability with organic ligands. The titration curve was analyzed to determine the complexation capacity (CC) and conditional formation constant (K) of the complex. Different mathematical treatments are proposed for this analysis. In the described experiment, differential pulse anodic stripping voltammetry was used to determine the complexation capacity of humic substances in natural waters. Experimental parameters such as pH, supporting electrolyte concentration, and volume of additions were previously optimized for the voltammetry technique. The obtained data were processed and analyzed, resulting in titration curves and voltammograms. The analysis of the curves allowed for the calculation of the complexation capacity and conditional stability constant of the formed complex. The results demonstrate the feasibility of the method as a didactic experiment for the voltammetric determination of natural water complexation capacity.

Experimental and computational evidence of U(VI)–OH–Si(OH)4 complexes under alkaline conditions: Implications for cement systems

The complexation of uranyl hydroxides with orthosilicic acid was investigated by experimental and theoretical methods. Spectroluminescence titration was performed in a glovebox under argon atmosphere at pH 9.2, 10.5 and 11.5, with [U(VI)] = 10−6 and 5 × 10−6 mol kgw−1. The polymerization effects of silicic acid were minimized by ruling out samples with less than 90 % monomeric silicic acid present, identified via UV–Vis spectrometry using the molybdate blue method. Linear regression analysis based on time-resolved laser-induced fluorescence spectroscopy (TRLFS) results yielded the conditional stepwise formation constants of U(VI)–OH–Si(OH)4 complexes at 0.05 mol kgw−1 NaNO3. The main spectroscopic features – characteristic peak positions and decay-time – are reported for the first time for the UO2(OH)2SiO(OH)3− species observed at pH 9.2 and 10.5 and UO2(OH)2SiO2(OH)22− predominant at pH 11.5. Quantum chemical calculations successfully computed the theoretical luminescence spectrum of the complex UO2(OH)2SiO(OH)3− species, thus underpinning the proposed chemical model for weakly alkaline systems. The conditional stability constants were extrapolated to infinite dilution using the Davies equation, resulting in log10β°(UO2(OH)2SiO(OH)3−) and log10β°(UO2(OH)2SiO2(OH)22−). Implications for U(VI) speciation in the presence and absence of competing carbonate are discussed for silicate-rich environments expected in certain repository concepts for nuclear waste disposal.

Recommendations for best practice for iron speciation by competitive ligand exchange adsorptive cathodic stripping voltammetry with salicylaldoxime

The method of competitive ligand exchange followed by adsorptive cathodic stripping voltammetry (CLE-AdCSV) allows for the determination of dissolved iron (DFe) organic speciation parameters, i.e., ligand concentration (LFe) and conditional stability constant (log KFe′Lcond). Investigation of DFe organic speciation by CLE-AdCSV has been conducted in a wide range of marine systems, but aspects of its application pose challenges that have yet to be explicitly addressed. Here, we present a set of observations and recommendations to work toward establishing best practice for DFe organic speciation measurements using the added ligand salicylaldoxime (SA). We detail conditioning procedures to ensure a stable AdCSV signal and discuss the processes at play during conditioning. We also present step-by-step guidelines to simplify CLE-AdCSV data treatment and interpretation using the softwares ECDSoft and ProMCC and a custom spreadsheet. We validate our application and interpretation methodology with the model siderophore deferoxamine B (DFO-B) in a natural seawater sample. The reproducibility of our application and interpretation methodology was evaluated by running duplicate titrations on 19 samples, many of which had been refrozen prior to the duplicate analysis. Nevertheless, 50% of the duplicate analyses agreed within 10% of their relative standard deviation (RSD), and up to 80% within 25% RSD, for both LFe and log KFe′Lcond. Finally, we compared the sequential addition and equilibration of DFe and SA with overnight equilibration after simultaneous addition of DFe and SA on 24 samples. We found a rather good agreement between both procedures, with 60% of samples within 25% RSD for LFe (and 43% of samples for log KFe′Lcond), and it was not possible to predict differences in LFe or log KFe′Lcond based on the method applied, suggesting specific association/dissociation kinetics for different ligand assemblages. Further investigation of the equilibration kinetics against SA may be helpful as a potential way to distinguish natural ligand assemblages.

Natural copper-binding ligands in the Arctic Ocean. The influence of the Transpolar Drift (GEOTRACES GN04)

The Arctic Ocean is a unique biogeochemical environment characterized by low salinity surface waters, extensive sea-ice coverage, high riverine inputs, large shelf extension and the long residence time of deep waters. These characteristics determine the distribution of dissolved bio-essential trace metals, such as copper (Cu), and the dissolved organic-binding ligands capable of complexing it. This work reports the concentrations and conditional stability constants of dissolved Cu-binding ligands (LCu and log KcondCu2+L) measured in samples from the Polarstern (PS94) expedition, as part of the international GEOTRACES program (cruise GN04). Full-depth profile stations from the Barents Sea, Nansen Basin, Amundsen Basin and Makarov Basin were analysed by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV). The basins and water masses presented a wide range of LCu concentrations (range: 1.40 – 7.91 nM) and log KcondCu2+L values (range: 13.83 – 16.01). The highest variability of Cu-binding ligand concentrations was observed in surface waters (≤200 m), and mean concentrations increased from the Barents Sea and Nansen Basin (2.15 ± 0.31 nM and 1.93 ± 0.35 nM, respectively) to the Amundsen (3.84 ± 1.69 nM) and Makarov Basins (4.40± 2.03 nM). The influence of the Transpolar Drift (TDP) flow path was observed in the Amundsen and Makarov Basins, especially on Cu-binding ligand concentrations (LCu range: 3.96 – 7.91 nM). In contrast, deep waters (>200 m) showed no significant differences between basins and water masses in terms of LCu concentrations (range: 1.45 – 2.78 nM) and log KcondCu2+L (range: 14.02 – 15.46). The presence of strong Cu-binding ligands (log KcondCu2+L>13) in surface waters stabilises the excess of dissolved copper (dCu) transported in the TPD and favours its export to the Fram Strait and Nordic Seas.

A first estimation of the role of penguin guano on copper cycling and organic speciation in Antarctic coastal waters

Cu is a vital micronutrient, but free Cu ions (Cu2+) in seawater, even at subnanomolar concentrations, can impede phytoplankton growth. Natural Cu complexation with organic ligands regulates Cu acquisition and, in most instances, reduces Cu2+ concentrations below toxic thresholds. Along the Antarctic coast, the sources and sinks of Cu and its associated ligands remain poorly defined. Despite the high productivity in the area, there are no studies on the role of trophic transfer in Cu cycling.This study explores penguin guano release of Cu and Cu ligands and its potential in neutralizing copper toxicity along the Antarctic coast. We collected guano in a Chinstrap penguin nesting location in the West coast of Deception Island and extracted its components into aqueous solution imitating natural processes. Copper concentration in guano was 0.4 mg (dry weight g)−1 constituting a potential toxic threat and showed biomagnification with respect to krill. Surface seawater samples collected from various locations varying in penguin activity, were analyzed to assess the potential influence of guano on the area. Visual examination and elevated levels of Al suggested that a substantial portion of guano was lithogenic. Consequently, only a modest 16 % of the total Cu present in guano could be extracted using mechanical methods. Notably, the concentrations of the extracted organic ligands were approximately 23 times higher than the concentrations of the extracted Cu. This significant presence of ligands effectively nullifies any potential toxicity that could have arisen from free Cu2+ ions. Guano ligands' conditional stability constants were lower than those in surface seawater suggesting phytoplankton exudation was the main ligand source in the area. Overall, guano acts as a key node for Cu cycling in coastal Antarctic waters but its deleterious potential is neutralized by ligands from krill digestion and the high background concentration of phytoplankton exudates.

Distribution of copper-binding ligands in Fram Strait and influences from the Greenland Shelf (GEOTRACES GN05)

The Fram Strait represents the major gateway of Arctic Ocean waters towards the Nordic Seas and North Atlantic Ocean and is a key region to study the impact of climate change on biogeochemical cycles. In the region, information about trace metal speciation, such as copper, is scarce. This manuscript presents the concentrations and conditional stability constants of copper-binding ligands (LCu and log KcondCu2+L) in the water column of Fram Strait and the Greenland shelf (GEOTRACES cruise GN05). Cu-binding ligands were analysed by Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using salicylaldoxime (SA) as competitive ligand. Based on water masses and the hydrodynamic influences, three provinces were considered (coast, shelf, and Fram Strait) and differences were observed between regions and water masses. The strongest variability was observed in surface waters, with increasing LCu concentrations (mean values: Fram Strait = 2.6 ± 1.0 nM; shelf = 5.2 ± 1.3 nM; coast = 6.4 ± 0.8 nM) and decreasing log KcondCu2+L values (mean values: Fram Strait = 15.7 ± 0.3; shelf = 15.2 ± 0.3; coast = 14.8 ± 0.3) towards the west. The surface LCu concentrations obtained above the Greenland shelf indicate a supply from the coastal environment to the Polar Surface Water (PSW) which is an addition to the ligand exported from the central Arctic to Fram Strait. The significant differences (in terms of LCu and log KcondCu2+L) between shelf and coastal samples were explained considering the processes which modify ligand concentrations and binding strengths, such as biological activity in sea-ice, phytoplankton bloom in surface waters, bacterial degradation, and meltwater discharge from 79NG glacier terminus. Overall, the ligand concentration exceeded those of dissolved Cu (dCu) and kept the free copper (Cu2+) concentrations at femtomolar levels (0.13–21.13 fM). This indicates that Cu2+ toxicity limits were not reached and dCu levels were stabilized in surface waters by organic complexes, which favoured its transport to the Nordic Seas and North Atlantic Ocean and the development of microorganism.

Estimation of stability constants of Fe(III) with antibiotics and dissolved organic matter using a novel UV–vis spectroscopy method

Determining conditional stability constant (Kcond) is paramount in assessing complex stability, particularly in Fe(III) complexes that are prevalent in actual surface water and wastewater matrices. In this study, existing methods of Kcond determination were evaluated and a novel UV–Vis spectroscopy method was proposed based on the evaluation of these approaches. Model ligands (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and oxalic acid (OA)), as well as common antibiotics (kanamycin (Kana) and tetracycline (TTC)), were employed to determine the Kcond of the Fe(III)-ligand complexes under neutral conditions (pH 6.5). The obtained fitting results revealed that the logKcond were in the order of Fe(III)-EDTA (7.08) > Fe(III)-NTA (4.67) > Fe(III)-OA (4.32) > Fe(III)-TTC (4.28) > Fe(III)-Kana (3.07). In addition to these single ligands, the methodology was extended to the Fe(III) complexation with humic acid (HA), a complex mixture of organic components, where the fitting result indicated a logKcond of 5.02 M−1. The method's application domain was analyzed by numerical analysis and combined with experimental results. The findings demonstrate that the proposed methodology possesses satisfactory measurement capability for Kcond ranging from 103 to 107 M−1, suggesting its broad applicability to the majority of complexes. This method can provide valuable insights into the impact of Fe(III) complexes within the water matrix.

Surface modification of typical calcium-containing minerals by aluminum ion and its effect on adsorption of citric acid

In this study, aluminum ion surface modification was used to improve the depressive performance of citric acid on calcite. The micro-flotation experiment showed that the mixed depressant of aluminum ion and citric acid displayed a higher separation effect on the two minerals than the single citric acid, the recovery of scheelite was 90.6 %, but that of calcite was 4.3 % using the mixed depressant. The artificial mixed mineral experiment confirmed that the mixed depressant exhibited an efficient separation effect, and an excellent scheelite enrichment index with WO3 grade of 67.36 % and scheelite recovery of 83.95 % was obtained using 1.0 × 10−4 mol/L aluminum ion and 1.0 × 10−4 mol/L citric acid. The surface characterization methods indicated that the aluminum ion complex was selectively adsorbed on the CO32- sites of the calcite surface in the form of aluminum citrate and monohydrogen aluminum citrate radical. The calculation result of thermodynamic and conditional stability constants revealed that the aluminum species complex aluminum citrate was more easily formed and more stable than monohydrogen aluminum citrate radical. Atomic force microscopy images showed that aluminum ion complexes were selectively adsorbed on the calcite surface in the form of clusters and sheets with higher adsorption height and density than scheelite. This study provides an excellent reagent system using for enriching scheelite.

Removal of residual benzohydroxamic acid-lead complex from mineral processing wastewater by metal ion combined with gangue minerals

Benzohydroxamic acid-lead (BHA-Pb) complex reagent is a commonly used collector for the flotation of oxidized ores such as tungsten ore, cassiterite, and ilmenite, but the BHA-Pb complex remaining in the mineral processing wastewater (MPW) after flotation is economically and efficiently difficult to remove. At present, the treatment technology usually starts from the treatment of MPW at a wastewater treatment station. However, the treatment cost is inevitably high due to the huge amount of MPW. In this study, a new process of removing residual BHA-Pb complex reagent from MPW in one-step using metal ions combined with gangue minerals in tailings pulp was proposed. It started from tailings pulp treatment and taking tailings reservoir as the main reaction site. The basic issues related to the new process were mainly studied. The concentration of BHA was characterized using chemical oxygen demand (COD). The results show that when Ca2+, Fe3+, or Al3+ was added to the BHA-Pb solution, only Fe3+ could effectively remove the COD of the BHA-Pb solution, while Ca2+ and Al3+ could not. This is because the BHA-Pb complex can be preferentially transformed into the BHA-Fe complex, and the COD of the BHA-Fe complex solution is most easily removed. However, BHA-Fe complex systems have dark colors and are difficult to settle. When gangue minerals are added to the BHA-Fe complex system, gangue minerals can play the role of coarse particles carrying fine particles settling, which is helpful to the sedimentation of the BHA-Fe complex system. The transformation mechanism between BHA-Pb and BHA-Fe complexes was explained by the conditional stability constants and Gibbs free energy changes analysis. In addition, the sedimentation mechanism of the BHA-Fe complex system was analyzed by zeta potential and scanning electron microscope-energy dispersive spectrometer. This study provides a new idea for removing residual organic flotation reagents from MPW starting from tailings pulp treatment.

Novel water-soluble aromatic bisdiglycolamide masking agents for the separation of trivalent americium over lanthanides by NTAamide(n-Oct) extractant

Two novel water-soluble aromatic bisdiglycolamides (BisDGAs) of SO3-TEX(m)-BisDGA (sodium bis((2-(2-(diethylamino)− 2-oxoethoxy)acetamido)methyl)benzenesulfonate) and SO3-TEX(p)-BisDGA (sodium 2,5-bis((2-(2-(diethylamino)− 2-oxoethoxy)acetamido)methyl)benzenesulfonate) were synthesized and used as masking agents for the selective extraction and separation of Am3+ over Eu3+ in HNO3 solutions by N,N,N′,N′,N′′,N′′-hexaoctylnitrilotriacetamide (NTAamide(n-Oct)) in n-dodecane. Their influences on the separation effect of Am3+ over Eu3+ were investigated and compared with that of a water-soluble aliphatic bisdiglycolamide of N,N,N′′′,N′′′-tetraethyl-N′,N′′-ethidene bisdiglycolamide (TEE-BisDGA) reported by our previous work. SO3-TEX(m)-BisDGA and SO3-TEX(p)-BisDGA exhibit significantly better masking effects than TEE-BisDGA. The masking selectivity for Eu3+ over Am3+ follows the order of SO3-TEX(m)-BisDGA > SO3-TEX(p)-BisDGA > TEE-BisDGA. During the extraction process, the three BisDGA masking agents form the 1:2 complexes, while the NTAamide (n-Oct) extractant forms the 1:1 complexes with Am3+ and Eu3+. Meanwhile, the conditional stability constants (log β) for the three masking agents with Eu3+ were calculated using the least squares method, which are also in line with those obtained from fluorescence spectrometry (FS). By means of FS, time-resolved laser-induced fluorescence spectrometry (TRLFS), Fourier Transform infrared spectrometry (FT-IR), conductivity, and electrospray ionization mass spectrometry (ESI-MS) analyses, the composition of the complex of Eu3+ with water-soluble BisDGAs (L) was determined to be [Eu(NO3)2(H2O)∙2L](NO3). Furthermore, a batch simulation of multistage countercurrent extraction with 12-stage extraction, 4-stage scrubbing and 8-stage stripping was carried out and demonstrates a highly efficient separation of Am3+ over Lns3+ with the recovery rates above 99.9 % for all metal ions in the simulated feed solution, and with the decontamination factors more than 500 between Am3+ and most of the lanthanide ions.

Влияние катамина АБ на комплексообразование бромпирогаллолового красного с ионами скандия

The regularities of complexation of bromopyrogallol red with scandium ions in the dual system and in the presence of cationic surfactant catamin AB have been studied. The optimum pH interval of complexation was determined. The light absorption spectra of the dye and its complexes with scandium ions in dual systems and in the catamin AB presence at different pH values and surfactant concentrations were recorded. The ratio between metal ion and reagent in complexes without and in the presence of catamin AB was determined by saturation and isomolar series methods at pH 5,90 and 6,40. The conditional stability constants of the obtained complexes were determined by the Babko method, calibration graphs were constructed, and molar light absorption coefficients were calculated. The influence of interfering ions was studied at pH 6,40.

Изучение реакции ионов Cu(II) с N-(бензоил)-N'-(фенилсульфонил)гидразином в аммиачных средах спектрофотометрическим методом

The reaction of complexation of N-(benzoyl)-N'-(phenylsulfonyl)hydrazine with Cu(II) ions in an ammonia medium has been studied. The absorption spectra of the reagent and its complex with Cu(II) ions have been recorded and analyzed. The optimal conditions for the formation of the complex compound were found: the pH range of complex formation; optimal time for color development; amount of photometric reagent. Under optimal conditions for the complex formation of BPSH with Cu(II) ions, a calibration graph was constructed. The Bouguer-Lambert-Beer law is fulfilled in the range from 0,5 to 1,75 mg Cu(II) in 25 ml of solution. The true (19389) and apparent (4708) molar light absorption coefficients were calculated. The methods of saturation, equilibrium shift, curve intersection, isomolar series, and conductometric titration were used to determine the molar ratios in a solution of a complex compound – [Сu(II)]:[BFSH] = 1:1 and 1:2. According to the Babko method, the conditional stability constant of the complex was calculated – 2,45∙1013. The convergence and correctness of the spectrophotometric technique were determined by the method of mathematical statistics.

Combining voltammetric and mass spectrometric data to evaluate iron organic speciation in subsurface coastal seawater samples of the Ross sea (Antarctica)

Iron (Fe) is the most important trace element in the ocean, as it is required by phytoplankton for photosynthesis and nitrate assimilation. Iron speciation is important to better understand the biogeochemical cycle and availability of this micronutrient, in particular in the Southern Ocean. Dissolved Fe (dFe) concentration and speciation were determined in 24 coastal subsurface seawater samples collected in the western Ross sea (Antarctica) during the austral summer 2017 as part of the CELEBeR (CDW Effects on glacial mElting and on Bulk of Fe in the Western Ross sea) project. ICP-DRC-MS was used for dFe determination, whereas CLE-AdSV was used to obtain the concentration of complexed and free dFe, of the ligands, and the values of the stability constants of the complexes. Dissolved Fe values ranged from 0.4 to 2.5 nM and conditional stability constant (logK’Fe’L) from 13.0 to 15.0, highlighting the presence of Fe-binding organic complexes of different stabilities. Principal component analysis (PCA) allowed us to point out that Terra Nova Bay and the neighboring area of Aviator and Mariner Glaciers were different in terms of chemical, physical, and biological parameters. A qualitative investigation on the nature of the organic ligands was carried out by HPLC–ESI–MS/MS. Results showed that siderophores represented a heterogeneous class of organic ligands pool.

Iron ligands and isotopes in hydrothermal plumes over backarc volcanoes in the Northeast Lau Basin, Southwest Pacific Ocean

Deep-sea hydrothermal venting is an important source of dissolved iron (dFe) to the oceans. Fe isotopes can be used as a potential tool to trace the dispersal of hydrothermal plumes. However, Fe isotope fractionation and its relation with Fe speciation as hydrothermal plumes disperse is still poorly constrained. In this study, we determined the Fe speciation and total and dissolved Fe isotope composition (δ56tFe, δ56dFe) for several hydrothermal plumes from backarc volcanoes in the Northeast Lau Basin. This combined approach provides important insights into the evolution of Fe isotopes in hydrothermal plumes. The results suggest δ56tFe variation in plumes is related to the loss of particulate Fe-sulfides or Fe-oxyhydroxides (FeOOH), both of which are dependant on the H2S concentrations and Fe/H2S in the source hydrothermal fluids. δ56dFe compositions in the hydrothermal plumes increase during plume dispersal/dilution and can be as high as 0.85 ‰, demonstrating that hydrothermal plumes can export dissolved Fe with a significantly heavier δ56dFe than hydrothermal fluids. The reasons may be ascribed to the organic Fe complexes (FeL) and colloidal FeOOH in the dissolved phase. Another interpretation might be associated with the low pH in volcanic arc hydrothermal systems rich in magmatic CO2 and SO2, which decreases the Fe(II) oxidation rate. Further, we demonstrate for the first time that the δ56dFe is positively correlated with the conditional stability constants of FeL (logKʹFeL). A Rayleigh distillation model is presented based on the mass balance of the determined FeL, and colloidal FeOOH in hydrothermal plumes, which can explain the observed Fe isotope compositions in hydrothermal plumes. Our data show how Fe isotopes are transformed within a hydrothermal plume above arc volcanoes and how these may differ from that of the original vent fluids. It adds to our understanding of the processes that have an impact on the Fe speciation and isotope composition in deep-sea hydrothermal plumes.

Gallium(III)-pyridoxal thiosemicarbazone derivatives as nontoxic agents against Gram-negative bacteria.

Many bacterial strains are developing mechanism of resistance to antibiotics, rendering last-resort antibiotics inactive. Therefore, new drugs are needed and in particular metal-based compounds represent a valid starting point to explore new antibiotic classes. In this study, we have chosen to investigate gallium(III) complexes for their potential antimicrobial activity against different strains of Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa which have developed different type of resistance mechanism, including the expression of β-lactamases (NDM-1, ESβL, or AmpC) or the production of biofilm. We studied a series of thiosemicarbabazones derived from pyridoxal, their related Ga(III) complexes, and the speciation in solution of the Ga(III)/ligand systems as a function of the pH. Proton dissociation constants and conditional stability constants of Ga(III) complexes were evaluated by UV/Vis spectroscopy, and the most relevant species at physiological pH were identified. The compounds are active against resistant Gram-negative strain with minimal inhibitory concentration in the μM range, while no cytotoxicity was detected in eukaryotic cells.

Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

The availability of iron (Fe) to marine microbial communities is enhanced through complexation by ligands. In Fe limited environments, measuring the distribution and identifying the likely sources of ligands is therefore central to understanding the drivers of marine productivity. Antarctic coastal marine environments support highly productive ecosystems and are influenced by numerous sources of ligands, the magnitude of which varies both spatially and seasonally. Using competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with 2-(2-thiazolylazo)-p-cresol (TAC) as a competing artificial ligand, this study investigates Fe-binding ligands (FeL) across the continental shelf break in the Mertz Glacier Region, East Antarctica (64 - 67°S; 138 - 154°E) during austral summer of 2019. The average FeL concentration was 0.86 ± 0.5 nM Eq Fe, with strong conditional stability constants (Log KFeL) averaging 23.1 ± 1.0. The strongest binding ligands were observed in modified circumpolar deep water (CDW), thought to be linked to bacterial Fe remineralisation and potential siderophore release. High proportions of excess unbound ligands (L’) were observed in surface waters, as a result of phytoplankton Fe uptake in the mixed layer and euphotic zone. However, FeL and L’ concentrations were greater at depth, suggesting ligands were supplied with dissolved Fe from upwelled CDW and particle remineralisation in benthic nepheloid layers over the shelf. Recent sea-ice melt appeared to support bacterial production in areas where Fe and ligands were exhausted. This study is included within our newly compiled Southern Ocean Ligand (SOLt) Collection, a database of publicly available Fe-binding ligand surveys performed south of 50°S. A review of the SOLt Collection brings attention to the paucity of ligand data collected along the East Antarctic coast and the difficulties in pinpointing sources of Fe and ligands in coastal environments. Elucidating poorly understood ligand sources is essential to predicting future Fe availability for microbial populations under rapid environmental change.

Critical evaluation of the interaction between fluorescent dissolved organic matter and Pb(II) under variable environmental conditions

Dissolved organic matter (DOM) can strongly influence the behavior and risk of metal pollutants in aquatic ecosystems. However, a comprehensive study on the effects of DOM level and environmental factors on the binding of DOM with Pb(II) is lacking. This study examined the DOM-Pb(II) interaction in the river water under variable DOM level, pH, and major ions, using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like component were identified, and the abundant humic-like components showed higher Pb(II)-binding fractions (f) than the protein-like component. The f of PARAFAC components decreased while the conditional stability constants (logKM) increased for the diluted DOM, indicating the influence of DOM level on its metal binding. The DOM-Pb(II) interaction was sensitive to changes in pH, with generally higher f and lower logKM at the alkaline condition due to changes in the DOM conformation. The addition of major ions significantly decreased the fluorescence quenching by Pb(II), due to competitive effects and potential DOM conformation changes at elevated ions. Overall, our results show that the DOM-Pb(II) complexation is highly dependent on both the DOM properties and environmental factors, which have implications for optimizing the experimental conditions and for comparing the results in different environments.