Metal Ion Transfer Research Articles

Mechanistic insights into uptake, transfer and exchange of metal ions by the three-metal clusters of a metalloprotein.

Metallothioneins (MTs) are small proteins that coordinate d-block metal ions in sulfur-metal clusters to control metal ion concentrations within the cell. Here we study metal cluster formation in the MT of the periwinkle Littorina littorea (LlMT) by nuclear magnetic resonance (NMR). We demonstrate that the three Cd2+ ions in each domain are taken up highly cooperatively, that is, in an all-or-none fashion, with a four- to six-fold higher affinity for the C-terminal domain. During the transfer of metal ions from Cd2+-loaded MT to apo MT, Cd2+ is most efficiently transferred from the metalated protein to the apo C-terminal domain. This behavior might be connected to unique structural motifs in the C-terminal domain, such as two double-CXC motifs and an increased proportion of positively charged residues. In Cd2+/Zn2+ metal exchange experiments, the N-terminal domain displayed the most efficient inter-molecular metal exchange. Amide hydrogen exchange reveals fewer protected amides for the N-terminal domain, suggesting the structure might more easily "open up" to facilitate metal exchange. Experiments with a physical separation of donor and acceptor species demonstrate that metal exchange and transfer require protein-protein contacts. These findings provide insights into the mechanism of metal uptake and metal transfer, which are important processes during metal detoxification in snail MTs.

Effects of carrier surface hydrophilic modification on sludge granulation: From sludge characteristics, extracellular polymeric substances, and microbial community

Aerobic granular sludge (AGS) is a powerful biotechnological tool capable of treating multiple pollutants simultaneously. However, the granulation process and pollutant removal efficiency still need to be further improved. In this study, Fe2O3- and MnO2-surface-modified straw foam-based AGS (Fe2O3@SF-AGS and MnO2@SF-AGS), with an average particle size of 3 mm, were developed and evaluated. The results showed that surface modification reduced the hydrophobic groups of carriers, facilitating the attachment and proliferation of microorganisms. Notably, MnO2@SF-AGS showed excellent granulation performance, reaching a stable state about one week earlier than the unmodified SF-AGS. The polymeric substance content of MnO2@SF-AGS was found to be 1.28 times higher than that of the control group. Furthermore, the removal rates for NH4+-N, TN, and TP were enhanced by 27.28%, 12.8%, and 32.14%, respectively. The bacterial communities exhibited significant variations in response to different surface modifications of AGS, with genera such as Saprospiraceae, Terrimonas, and Ferruginibacter playing a crucial role in the formation of AGS and the removal of pollutants specifically in MnO2@SF-AGS. The charge transfer of metal ions of MnO2@SF promotes the granulation process and pollutant removal. These results highlight that MnO2@SF-AGS is an effective strategy for improving nitrogen and phosphorus removal efficiency from wastewater.

Enhanced separation via confined shear flow in microchannel: A novel insight into the role of confined hydrogen bonds in microfluid and its effect on competitive mass transfer of hydrated ions

Microfluidic extraction and separation have demonstrated enormous potential in the field of purification and separation, but the essence of its enhanced separation has always been a focus of debate in the academic community. This study reveals that the interaction between extractant molecules and ions in the process of microfluidic extraction exhibits some significant differences from conventional liquid–liquid two phase stirring dispersed droplet extraction. The interaction between extractant molecules and metal ions through the hydrogen bonds (H-bonds) bridged by water molecules around the hydration shell of metal ions exhibits a noticeable change in confined flow in microchannel. It was demonstrated that in our experiments that the strength difference of this interaction is subjected to the ability of different metal ions to bind water molecules. Therefore, the differences in the interaction between extractant molecules and ions through the hydrogen bonding “water-bridge” are easier to be distinguished within the confined fluid, due to the different effects from the confined environment on mass transfer of metal ions with different abilities to bind water molecules. The confined fluid environment strengthened the difference in the interaction, leading to an amplification of difference in ion diffusion rates, thereby achieving enhanced separation of target rare earth Er3+ ions from the coexisting background ions. Hydrophilic coexisting background ions can be separated by reducing the microchannel width, so that the βEr/Al increases from 2.95 to 49.78. However, the relatively hydrophobic background ions can be separated by increasing flow rates, so that the βEr/Mg increases from 75.32 to 299.06. This work provides a new insight into the essence of microfluidic enhanced separation from the perspective of confined H-bonds.

Soil amendments alter cadmium distribution and bacterial community structure in paddy soils

Soil amendments play a pivotal role in ensuring the safety of food production by inhibiting the transfer of heavy metal ions from soils to crops. Nevertheless, their impact on soil characteristics and the microbial community and their role in reducing cadmium (Cd) accumulation in rice remain unclear. In this study, pot experiments were conducted to investigate the effects of three soil amendments (mineral, organic, and microbial) on the distribution of Cd speciation, organic components, iron oxides, and microbial community structure. The application of soil amendments resulted in significant reductions in the soil available Cd content (16 %–51 %) and brown rice Cd content (16 %–78 %), facilitating the transformation of Cd from unstable forms (decreasing 10 %–20 %) to stable forms (increasing 77 %–150 %) in the soil. The mineral and organic amendments increased the soil cation exchange capacity (CEC) and plant-derived organic carbon (OC), respectively, leading to reduced Cd accumulation in brown rice, while the microbial amendment enhanced OC complexity and the abundances of Firmicutes and Bacteroidota, contributing to the decreased rice Cd uptake. The synchrotron radiation–based Fourier transform infrared (SR-FTIR) spectroscopy indicated that soil amendments regulated soil Cd species by promoting iron oxides and OC coupling. Moreover, both organic and microbial amendments significantly reduced the diversity and richness of the bacterial communities and altered their compositions and structures, by increasing the relative abundances of Bacteroidota and Firmicutes and decreasing those of Acidobacteria, Actinobacteria, and Myxococcota. Soil microbiome analysis revealed that the increase of Firmicutes and Bacteroidota associated with Cd adsorption and sequestration contributed to the suppression of soil Cd reactivity. These findings offer valuable insights into the potential mechanisms by which soil amendments regulate the speciation and bioavailability of Cd, and improve the bacterial communities, thereby providing guidance for agricultural management practices.

Preparing carbonated water-bio-heavy oil emulsions via membrane emulsification for efficient interphase mass transfer desalination

Bio-heavy oil with high oxygen content and combustion calorific value has attracted lots of attention as a green and sustainable fuel to cope with the increasingly severe energy shortages. However, the high salt content limits its combustion utilization due to potential risks such as equipment corrosion and wear blockage. The traditional desalination method using sulfuric acid causes a large amount of wastewater, Herein, we propose an assisted metal-ion interphase mass transfer desalination strategy by preparing carbonated water-in-bio-heavy oil (CW/O) emulsions with continuous membrane emulsification. α-Al2O3 membrane with an average pore size of 600 nm was selected as the emulsification medium. Saturated carbonic acid solutions as a dispersed phase were pressed through the membrane pores into bio-heavy oil to form uniform micron-sized CW/O emulsions. The prepared CW/O droplets provide a large interphase mass transfer interface which assists the hydrolysis of fatty acid salts of bio-heavy oil in the acidic environment and yields an efficient transfer of metal ions. As a result, the CW/O emulsion with an average droplet size (D3,2) of 4.29 μm and a specific surface area of 139.63 m2/m3 was prepared at a pressure of 0.5 MPa, achieving a salt removal efficiency of up to 85.62 %. This study provides a novel chemical-free and effective strategy for efficient oil product refining while utilizing CO2 through the continuous preparation of micron-sized CW/O droplets with sufficient interphase mass transfer area.

Interfacial salt effect induced by competitive adsorption of coexisting ions: A new understanding of the mass transfer selectivity in the near-interface boundary layer

Specific ion effects are known to influence the interfacial behavior of ions in the aqueous phase and thus affect their extraction and separation. There are many studies on enhanced extraction and separation of the target ions based on the specific ion effects. A microscopic level understanding of the competitive mass transfer and selectivity of ions at the interface between heterogeneous phases is crucial importance for the precise control of numerous chemical reaction and separation processes. The conventional salt effect (i.e., background coexisting ions promoting the mass transfer of the target ions) are only observed at higher coexisting ion concentrations. However, the present work reveals an interesting phenomenon: the adsorption enrichment and competitive hydration of coexisting salt cations at the liquid–liquid interface can significantly influence the mass transfer rate of the target rare earth ions in the near-interface boundary layer. Notably, such a distinct interfacial salt effect can promote the separation between coexisting and target ions at lower coexisting ion concentrations, and it cannot be explained by the traditional theory for the salt effect. A thin-layer organic oil film extraction system was employed here as a simplified model experiment to investigate this new interfacial salt effect on the non-equilibrium extraction and separation of target rare earth ions. The results demonstrated that the diffusion rate of the target ions (Er3+) is subject to the local concentration gradient of coexisting salt cations (Mg2+) in the near-interface boundary layer. At the lower bulk concentrations, the Mg2+ ions enriched at the interface would compete for water molecules around the hydration shell of target Er3+ ions, resulting in the dehydration of Er3+ ions. Therefore, an enhanced diffusion rate of Er3+ ions and their adsorption affinity towards the interface were observed. However, at a higher bulk concentration of Mg2+ ions, the diffusion resistance of Er3+ ions increased due to the competitive adsorption and hydration of Mg2+ ions at the interface. The thickness of the organic oil film layer also plays an important role in the diffusion of Er3+ ions. In particular, a thinner oil layer makes it easier to perceive the interfacial salt effect, which enhances the separation between Er3+ and Mg2+ compared to the case of a thicker oil layer. A quantitative correlation between the diffusion rate of Er3+ ions and the concentration of coexisting Mg2+ ions was established to describe the interfacial salt effect. This work highlights the microscopic nature of the salt effect induced by the competitive adsorption kinetics of coexisting ions in the near-interface boundary layer on promoting the extraction and separation of target metal ions. The results will help the development of new approaches to control the separation selectivity and enhance the mass transfer of target metal ions in practical applications.

Mechanism of incorporation of carbon nanomaterial particles in composite electrolytic metal coating

The problem of joint electrolytic deposition of metal ions and ultradispersed diamond particles into a metal matrix is formulated. The mathematical model describing the mechanism and kinetics of the cathodic process, the mass transfer of metal ions and carbon nanomaterial particles is developed. It has been established that transfer of particles of the dispersed phase occurs mainly not by the diffusion mechanism but under the influence of an electric field. Keywords: ultradispersed diamond particles, electrodeposition, composite electrolytic coatings.

First-principles study on the adsorption of divalent heavy metal ions by black phosphorus in water

With the rapid development of electronics, the application and research of two-dimensional materials have been at the forefront of the world’s scientific research. Black phosphorus (BP) has the advantages of large specific surface area, anisotropy, band tunability, high electrical conductivity and high theoretical specific capacity, which make it very promising for research in the fields of medicine, aerospace and electrochemistry. This paper calculates the electronic structure and adsorption properties of BP in water for different heavy metal ions of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text], including adsorption energy, bandgap, electron density and Mulliken population analysis, based on the first-principles approach of density generalized theory. First principles are quantum mechanical calculations based on density functional theory (DFT), which is a dominant well-developed method in the field of materials simulations, with low errors and high efficiency, especially in systems containing metallic particles. The results showed that the Pb[Formula: see text] adsorption system in water was more stable than the Hg[Formula: see text] adsorption system and the Cd[Formula: see text] adsorption system. The bandgap values of 0.617, 0.785 and 0.715[Formula: see text]eV of BP after adsorption of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text] in water are smaller compared to 0.891[Formula: see text]eV of intrinsic BP, and its properties change from direct bandgap semiconductor to indirect bandgap semiconductor. The higher the stability of a system for the adsorption of different heavy metal ions by BP, the higher the internal electron activity of the adsorption system and the amount of electron transfer. Meanwhile, it is concluded that the electrons mainly transfer from P to heavy metal ions in all the adsorption systems. The electron transfer of the BP-Pb[Formula: see text], Hg[Formula: see text], and Cd[Formula: see text] adsorption system occurs mainly in the p, s, and s/p orbitals, respectively. The above content investigated the electronic structure changes and internal electron transfer of heavy metal ions adsorbed by black phosphorus in water, expecting to provide a new reference basis for the detection of heavy metal ions in industrial wastewater using black phosphorus.

On the Influence of Counter-Ion Nature on Properties of Perfluorosulfonic Acid Membranes with Long and Short Side Chain

In this work, the study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in H+, Li+, Na+, and K+ forms and solutions of inorganic electrolytes is presented. The properties of the commercial Aquivion E87-05S and Nafion 212 membranes, as well as the membranes prepared from the dispersions of Nafion 212 in the solvents of different nature (N,N-dimethylformamide, 1‑methyl-2-pyrrolidone, isopropyl alcohol–water mixtures in volume ratio of 80–20) were investigated. The influence of the number of functional groups, the length of the side chains of the polymer macromolecules, and the polymer morphology in the membranes on their equilibrium and transport properties depending on the counter-ion nature was revealed. The effect of the relaxation and electrophoretic factors on the alkali metal ion transfer through the system of pores and channels of the perfluorosulfonic acid membranes was discussed. The slope of the concentration dependencies of the Donnan potential for all highly hydrated membranes in the H+ form was close to the Nernstian one, while the selectivity to the alkali metal ions increased for the membranes with the highest ion-exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of the co-ions from the membrane phase.

Bismuth Metal–Organic Framework/Carbon Nanosphere Composites for Ultrasensitive Simultaneous Electrochemical Detection of Lead and Cadmium

An amino-functionalized bismuth metal–organic framework (Bi-BDC-NH2) composited with nitrogen-doped mesoporous carbon nanosphere (NMCS) was prepared to fabricate a Bi-BDC-NH2@NMCS electrochemical sensor for simultaneous determination of Pb(II) and Cd(II). The synthesized Bi-BDC-NH2 was granular, amorphous, and loosely aggregated to form a porous structural composition where NMCS was embedded. The large specific area and exposed sites of Bi-BDC-NH2@NMCS copromote the adsorption and electron transfer of metal ions on the electrode surface. Compared with the traditional bismuth film electrode, the Bi-BDC-NH2@NMCS electrode can improve the charge transfer, stability, and conductivity. The developed method exhibited superior stripping performance with a detection limit of 0.36 ng mL–1 for Pb(II) and 0.44 ng mL–1 for Cd(II), respectively, and a linear range of 1.0–1500 ng mL–1. It was applied to detect Pb(II) and Cd(II) in liver, fish, and shrimp samples with recoveries of 93.6–99.7% and 94.4–103.2%, respectively.

Microbial driving mechanism of soil conditioner on reducing cadmium uptake by rice and improving soil environment

Soil conditioners can reduce the transfer of heavy metal ions from the soil to crops and play a crucial role in safe food production. However, it remains unclear how soil conditioners reduce cadmium (Cd) accumulation in rice (Oryza sativa L.). In this study, five soil conditioners (U-, N-, T-, L-, and C-type) commonly used in China were selected, and the effects of soil conditioners on bacterial and fungal community diversity, soil enzyme activity, soil pH, and organic matter content were investigated through field experiments in two sites. The Cd content of rice was significantly reduced by 32.4–55.1 % in site I and 16.0–33.3 % in site II under the five soil conditioner treatments. The decrease in Cd content was related to the increase in soil pH, organic matter content, and Cd fixation-related flora caused by soil conditioner application. U-, N- and C-type conditioners increased soil pH, inducing an increase in the relative abundances of microbial populations related to Cd sorption and sequestration (Firmicutes, Nitrospirota, Actinobacteriota, and Methylomirabilota). U-, T-, and L-type conditioners increased soil organic matter, causing an increase in the relative abundance of microbial flora associated with macromolecule degradation, including bacteria (Acidobacteriota and Chloroflexi) and fungi (Ascomycota and Basidiomycota). Conditioner application reduced the availability of soil Cd; indirectly promoted the increased abundance of beneficial soil bacteria; and increased the activities of invertase, urease, dehydrogenase, catalase, and acid protease. In conclusion, soil conditioner reduces the effective soil Cd by adjusting soil pH and organic matter content, increasing Cd-passivating flora and Cd-tolerant flora. Soil conditioner also increases the abundance of other beneficial flora, enhances soil enzyme activity, promotes the microecological balance of soil under Cd stress, and finally reduces Cd accumulation in rice.

Soil conditioners improve Cd-contaminated farmland soil microbial communities to inhibit Cd accumulation in rice

The addition of silicon (Si) and organic fertilizers to soil conditioners can inhibit the transfer of heavy metal ions from soil to crops. However, it is not clear how Si and organic fertilizers affect soil properties and the micro-ecological environment and thereby reduce cadmium (Cd) accumulation in rice. In this study, the effects of L-type soil conditioners containing Si and organic fertilizers on bacterial and fungal community diversity, soil pH, organic matter, and available Si were analyzed with field experiments at two sites in Liuzhou City and Hezhou City, respectively, in Guangxi, China. With the increase of Si and organic fertilizer content in soil conditioner, rice yield respectively increased by 16.8–25.8 and 6.8–13.1%, and rice Cd content decreased significantly by 8.2–21.1 and 10.8–40.6%, respectively, at the two experimental sites. Soil microbiome analysis showed that the increase in abundance of Firmicutes and Actinobacteriota bacteria associated with Cd adsorption and sequestration, and Basidiomycota fungal populations associated with degradation of macromolecules favored the inhibition of soil Cd activity (soil exchangeable Cd decreased by 14.4–14.8 and 18.1–20.6%). This was associated with an increase in organic matter and Si content caused by applying soil conditioners. In conclusion, L-type soil conditioners, rich in Si and organic fertilizer, can reduce soil Cd bioavailability by regulating the dominant Cd passivating flora in the soil and ultimately reduce Cd accumulation in rice.

Sustainable treatment of sewage sludge via plasma-electrolytic liquefaction for bio-friendly production of polyurethane foam

Safe and green disposal or utilization of sewage sludge (SS) has attracted significant attention as SS is increasingly produced worldwide and emerges as an environmental burden if without proper treatment. In this study, efficient and sustainable treatment of SS was achieved using plasma-electrolytic liquefaction (PEL) with alkaline catalysts including sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and sodium acetate (NaAc) and renewable solvents including polyethylene glycol (PEG) 200 and glycerol. Furthermore, the obtained bio-oil with abundant hydroxyl groups could partially replace polyols derived from fossil energy to synthesize bio-based polyurethane foams (BPUFs) for oil adsorption. The results showed that the Na2CO3 catalyst exhibited better performance and yielded bio-oil with a higher heating value (HHV) of 26.26 MJ/kg, very low nitrogen content (0.14%) and metal ions, and a nearly neutral pH of 7.41, under the optimized conditions. Compared with conventional oil bath liquefaction, PEL can significantly improve the liquefaction efficiency, promote the transfer of metal ions in SS to the solid residue (SR), and facilitate the transfer of nitrogen to the gas phase and SR, thereby upgrading the bio-oil to a certain extent. The BPUFs showed excellent oil adsorption capacity, reusability, and desorption and can play an important role in combating oil spills. The PEL method may provide a green avenue for SS valorization and the comprehensive utilization of the obtained products.

A ternary mechanism for the facilitated transfer of metal ions onto metal—organic frameworks: implications for the “versatility” of these materials as solid sorbents

A ternary mechanism for the facilitated transfer of metal ions onto metal—organic frameworks: implications for the “versatility” of these materials as solid sorbents

Transport of Zn (Ⅱ) through matrix enhanced polymer inclusion membrane containing OHA and D2EHPA

Recovery of heavy metal ions from waste water has benefits both in terms of resources reuse and environmental protection. Polymer inclusion membrane (PIM) has received increasing attention as a gentle and simple method compared to other separation techniques for the removal and recovery of heavy metal ions. The extractant and matrix are the most important components of the PIM. In this paper, a novel matrix enhanced polymer inclusion membrane (ME-PIM) system containing both octyl hydroxamic acid (OHA) and di (2-ethylhexyl) phosphoric acid (D2EHPA) as the carriers as well as poly(vinyl) chloride (PVC) and poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) as the matrix was reported. The SEM results indicate that the PVC has excellent compatibility with OHA and D2EHPA, resulting in dense ME-PIM compared to PVDF-CTFE. The effects of OHA and D2EHPA with different carrier ratios on the transport and the stability of the membrane were examined using Zn (Ⅱ) as a representative of heavy metal ions. The optimal results of this work showed that the initial mass transfer flux value of Zn (Ⅱ) was as high as 4.73 μmol/(m2·s), corresponding to a permeability of 2.21 × 10−2 m/h, using the ME-PIM composed of 61 wt.% PVC and 22 wt.% OHA + 17 wt.% D2EHPA. All these results suggest that the ME-PIM has a much higher initial mass transfer flux than those of PIMs in literatures. The addition of OHA to PIM introduced extractive functional groups into the polymer chain, forming an efficient and progressive mass transfer path with the extractant D2EHPA. Utilizing two extractants with synergistic effects, this novel ME-PIM system provides a potential advantage in promoting the mass transfer of metal ions in a PIM.

Kinetic regularities of the formation of composite electrolytic coatings containing ultradispersed diamond particles

The paper formulates the problem of joint electrolytic co-deposition of metal ions and ultradispersed diamond particles into a metal matrix. It presents the developed mathematical model that describes the mechanism and kinetics of the cathode process, mass transfer of metal ions and ultradispersed diamond particles. A satisfactory correlation with experimental data was obtained. The contribution of the thermal action of laser radiation to the intensification of the process of co-deposition of dispersed particles and metal ions was determined. It was found that the more intense penetration of dispersed phase particles into the forming coating during the laser stimulation of the electrodeposition process is due to the presence of a temperature gradient, which provides an additional supply of metal ions in the irradiation region. Based on the theoretical and experimental studies, we established the regularities of the influence of the number and size of nanoparticles on the strengthening properties of composite metal coatings. It was found that an increase in the temperature of an aqueous electrolyte solution in the cathode region during a laser-stimulated deposition process leads to an increase in the flux density of ultradispersed diamond particles, and, as a result, to an increase in the concentration of the dispersed phase in nickel composite coatings, which contributes to the formation of a finer crystalline structure of coatings, an improvement in adhesion, strength properties and increased wear resistance of coatings.

Structural Studies of Copper‐Binding Proteins Encoded by the ycnOperon from Bacillus subtilis

Most living organisms encode an ensemble of protein transporters and chaperones to regulate copper levels. The ycn operon of the bacterium Bacillus subtilisis regulated in response to copper, suggesting that the three proteins it encodes may engage in direct interactions with copper ions to facilitate transport and homeostasis of this transition metal. Here, we use a combination of structural, biochemical, biophysical, and bioinorganic approaches to determine the structures of individual proteins and their interactions with copper and other binding partners. The YcnI protein encoded by the operon contains a domain of unknown function (DUF1775) at its N‐terminus. We determined the structure of this domain and characterized its interactions with copper ions, finding that it coordinates the metal using a unique “mono‐histidine brace” site that is highly conserved across other members of the DUF1775 family. Our data also suggest a potential role for this domain to serve as a chaperone to facilitate transfer of metal ions. Furthermore, we also identify potential copper binding sites within the transcriptional regulator encoded within the same operon. Together, these studies reveal new insights into the structure and copper‐binding properties of proteins encoded by the ycnoperon, providing additional perspectives on how they may work together to regulate copper homeostasis. As homologs of these proteins are shared by many other bacterial species, it is likely that analogous mechanisms exist for copper uptake and homeostasis beyond B. subtilis.

Innovative bio-acid leaching method for high recovery of critical metals from end-of-life light emitting diodes

The main objective of this work is to introduce a new green recycling process for recovering valuable metals from electronic waste. One of the fastest-growing electronic waste streams is end-of-life light emitting diodes (LEDs). Due to environmental risk and a worldwide shortage of metals, recycling and recovering their valuable metal is an urgent task. In this study, an innovative bio-hydrometallurgical method for the extraction of valuable metals from end-of-life LED lamps is proposed. The present study evaluated a direct multi-step regulation strategy of waste content to enhance the bio-acid leaching of LED at a high pulp density (40 g/L) using a culture of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans (A. thiooxidans). Through a step-wise feeding strategy (10 g/d), the extraction of the metal was further improved due to balancing of A. thiooxidans population and stabilization of pH, ORP, and sulfuric acid concentration in the bioleaching solution. By comparing the results of multi-step and one-stage contact bioleaching, with multi-step contact bioleaching, Cu, Ni, and Ga extraction yields increased from 67%, 92%, and 39% to 100%, 100%, and 75%. Furthermore, this study demonstrates that the presence/addition of EPS did not only adsorb metal ions but also increased diffusion barriers, thus diminishing metal ion transfer from LED into bioleaching solution for an extended period of time. The multi-step non-contact bio-acid leaching method enhanced strategic critical element leaching yields to 100% from end-of-life LEDs. The final product, enriched in Au and Ag, could be used as a secondary source of precious metals.

Regulation of zinc-dependent enzymes by metal carrier proteins.

Zn2+ ions are essential in many physiological processes, including enzyme catalysis, protein structural stabilization, and the regulation of many proteins. The affinities of proteins for Zn2+ ions span several orders of magnitude, with catalytic Zn2+ ions generally held more tightly than structural or regulatory ones. Metal carrier proteins, most of which are not specific for Zn2+, bind these ions with a broad range of affinities that overlap those of catalytic, structural, and regulatory Zn2+ ions and are thought to be responsible for distributing the metal through most cells, tissues, and fluid compartments. While little is known about how many proteins obtain or release these ions, there is now considerable experimental evidence suggesting that metal carrier proteins may be responsible for transferring metals to and from some Zn2+-dependent proteins, thus serving as a major regulatory factor for them. In this review, the biological roles of Zn2+ and structures of Zn2+ binding sites are examined, and experimental evidence demonstrating the direct participation of metal carrier proteins in enzyme regulation is discussed. Mechanisms of metal ion transfer are also offered, and the potential physiological significance of this phenomenon is explored.

Impacts of heavy metal pollution on the ionomes and transcriptomes of Western mosquitofish (Gambusia affinis)

Our understanding of the mechanisms mediating the resilience of organisms to environmental change remains lacking. Heavy metals negatively affect processes at all biological scales, yet organisms inhabiting contaminated environments must maintain homeostasis to survive. Tar Creek in Oklahoma, USA, contains high concentrations of heavy metals and an abundance of Western mosquitofish (Gambusia affinis), though several fish species persist at lower frequency. To test hypotheses about the mechanisms mediating the persistence and abundance of mosquitofish in Tar Creek, we integrated ionomic data from seven resident fish species and transcriptomic data from mosquitofish. We predicted that mosquitofish minimize uptake of heavy metals more than other Tar Creek fish inhabitants and induce transcriptional responses to detoxify metals that enter the body, allowing them to persist in Tar Creek at higher density than species that may lack these responses. Tar Creek populations of all seven fish species accumulated heavy metals, suggesting mosquitofish cannot block uptake more efficiently than other species. We found population-level gene expression changes between mosquitofish in Tar Creek and nearby unpolluted sites. Gene expression differences primarily occurred in the gill, where we found upregulation of genes involved with lowering transfer of metal ions from the blood into cells and mitigating free radicals. However, many differentially expressed genes were not in known metal response pathways, suggesting multifarious selective regimes and/or previously undocumented pathways could impact tolerance in mosquitofish. Our systems-level study identified well characterized and putatively new mechanisms that enable mosquitofish to inhabit heavy metal-contaminated environments.