Coordination Of Zinc Ion Research Articles

A facile route to unlock the high capacity of molecular organic cathode for aqueous zinc-ion battery

The small-molecule organic materials have become promising candidates for aqueous zinc-ion batteries (AZIBs). However, the capacity output of these molecular organic cathodes still remains far from their theoretical values. Herein, we present a facile route by integrating a small amount of porous carbon (ketjen black, KB) into phenazine (PNZ) organic cathode by a facile route, which significantly improves the specific capacity for aqueous zinc-ion storage. Specifically, the PNZ/KB based battery delivers a high specific capacity of 179 mAh g−1 at 50 mA g−1 and still remains a high-rate capacity of 81 mAh g−1 at 1000 mA g−1. Additionally, the battery demonstrates stable cycling performance, retaining 70.6% of the initial capacity after 1000 charge-discharge cycles at 500 mA g−1. The spectroscopic analyses show that the zinc-ion coordination process of PNZ/KB cathode is highly reversible. The good performance of PNZ/KB cathode is ascribed to the unique branched chain shape of KB, which can give full access to active material of PNZ and generate more conductive paths for zinc-ion. The theoretical computation demonstrates that the intermolecular coordination between zinc-ion and PNZ molecule is more stable than that through the intramolecular interaction. This work provides a facile and effective strategy to boost the high capacity of organic cathode materials for aqueous zinc-ion batteries.

In Situ Grown Coordination-Supramolecular Layer Holding 3D Charged Channels for Highly Reversible Zn Anodes.

Dynamic reversible noncovalent interactions make supramolecular framework (SF) structures flexible and designable. A three-dimensional (3D) growth of such frameworks is beneficial to improve the structure stability while maintaining unique properties. Here, through the ionic interaction of the polyoxometalate cluster, coordination of zinc ions with cationic terpyridine, and hydrogen bonding of grafted carboxyl groups, the construction of a 3D SF at a well-crystallized state is realized. The framework can grow in situ on the Zn surface, further extending laterally into a full covering without defects. Relying on the dissolution and the postcoordination effects, the 3D SF layer is used as an artificial solid electrolyte interphase to improve the Zn-anode performance. The uniformly distributed clusters within nanosized pores create a negatively charged nanochannel, accelerating zinc ion transfer and homogenizing zinc deposition. The 3D SF/Zn symmetric cells demonstrate high stability for over 3000 h at a current density of 5 mA cm-2.

Tannic acid and zinc ion coordination of nanase for the treatment of inflammatory bowel disease by promoting mucosal repair and removing reactive oxygen and nitrogen species

Colon mucosal overexpression of reactive oxygen and nitrogen species (RONS) accelerates the development of inflammatory bowel disease (IBD) and destroys the mucosa and its barrier. IBD can be alleviated by removing RONS from the inflamed colon. The preparation of strong and efficient nanoantioxidants remains a challenge despite the development of numerous nanoantioxidants. In this paper, Zn-TA nanoparticles with fine hollow microstructure (HZn-TA) were successfully prepared and could be effectively used to treat IBD. In the first step, ZIF-8 nanoparticles were synthesized by a one-pot method. On this basis, HZn-TA nanoparticles were etched by TA, and a multifunctional nanase was developed for the treatment of IBD. RONS, including reactive oxygen species (ROS) and nitric oxide (NO), can be eliminated to increase cell survival following Hydrogen peroxide (H2O2) stimulation, including reactive oxygen species (ROS) and nitric oxide (NO with hydrogen peroxide (H2O2). In a model for preventing and delaying acute colitis, clearance of RONS has been shown to reduce intestinal inflammation in mice by reducing colon damage, proinflammatory cytokine levels, the spleen index, and body weight. Intestinal mucosal healing can be promoted by HZn-TA nanoparticles, which can upregulate zonula occludens protein 1 (ZO-1) and claudin-1 expression. Based on the results of this study, HZn-TA nanoparticles were able to effectively treat IBD with minimal adverse effects by being biocompatible, multienzyme active, and capable of scavenging RONS. Therefore, we pioneered the application of HZn-TA nanoparticles for the treatment of IBD, which are capable of clearing RONS without significant adverse effects. Statement of significance➢ HZn-TA nanoparticles were successfully prepared and could be effectively used to treat IBD.➢ Intestinal mucosal healing can be promoted by HZn-TA nanoparticles, which can upregulate ZO-1 and claudin-1 expression.➢ HZn-TA nanoparticles were able to effectively treat IBD with minimal adverse effects by being biocompatible, multienzyme active, and capable of scavenging RONS.

Long-lifespan Zinc-ion Capacitors Enabled by Anodes Integrated with Interconnected Mesoporous Chitosan Membranes through Electrophoresis-driven Phase Separation.

The advancement of highly secure and inexpensive aqueous zinc ion energy storage devices is impeded by issues, including dendrite growth, hydrogen evolution and corrosion of zinc anodes. It is essential to modify the interface of zinc anodes that homogenizes ion flux and facilitates highly reversible zinc planarized deposition and stripping. Herein, by coupling zinc ion coordination with acid-base neutralization under the driving of electrophoresis, manageable mesoscopic phase separation for constructing chitosan frameworks was achieved, thereby fabricating interconnected mesoporous chitosan membranes based heterogeneous quasi-solid-state electrolytes integrated with anodes. The framework is constructed by twisted chitosan nanofiber bundles, forming a three-dimensional continuous spindle-shaped pore structure. With this framework, the electrolyte provides exceptional ion conductivity of 25.1 mS cm-1 , with a puncture resistance strength of 2.3 GPa. In addition, the amino groups of chitosan molecule can make the surface of the framework positively charged. Thus, reversible zinc planarized deposition is successfully induced by the synergistic effect of stress constraint and electrostatic modulation. As a result, as-assembled zinc ion capacitor has an excellent cycle life and sustains the capacity by over 95 % after 20000 cycles at a current density of 5 A g-1 . This research presents a constructive strategy for stable electrolytes-integrated zinc anodes.

Long‐lifespan Zinc‐ion Capacitors Enabled by Anodes Integrated with Interconnected Mesoporous Chitosan Membranes through Electrophoresis‐driven Phase Separation

AbstractThe advancement of highly secure and inexpensive aqueous zinc ion energy storage devices is impeded by issues, including dendrite growth, hydrogen evolution and corrosion of zinc anodes. It is essential to modify the interface of zinc anodes that homogenizes ion flux and facilitates highly reversible zinc planarized deposition and stripping. Herein, by coupling zinc ion coordination with acid‐base neutralization under the driving of electrophoresis, manageable mesoscopic phase separation for constructing chitosan frameworks was achieved, thereby fabricating interconnected mesoporous chitosan membranes based heterogeneous quasi‐solid‐state electrolytes integrated with anodes. The framework is constructed by twisted chitosan nanofiber bundles, forming a three‐dimensional continuous spindle‐shaped pore structure. With this framework, the electrolyte provides exceptional ion conductivity of 25.1 mS cm−1, with a puncture resistance strength of 2.3 GPa. In addition, the amino groups of chitosan molecule can make the surface of the framework positively charged. Thus, reversible zinc planarized deposition is successfully induced by the synergistic effect of stress constraint and electrostatic modulation. As a result, as‐assembled zinc ion capacitor has an excellent cycle life and sustains the capacity by over 95 % after 20000 cycles at a current density of 5 A g−1. This research presents a constructive strategy for stable electrolytes‐integrated zinc anodes.

Achieving high-performance peptide-based foam via moderate hydrolysis and zinc coordination of oat proteins

Currently, developing natural macromolecule-based liquid foam with high foaming performance remains a challenge. This study demonstrated that zinc ion coordination (16:1 mass ratio of peptide to ZnSO4) considerably improved the foaming performance of oat peptides (OP), a 75-min hydrolysate of oat globulin. In particular, the coordination complex (OM–Zn; 10 mg/mL) of the 3–10 kDa peptides (OM) and zinc ion exhibited foaming ability and half-life (t1/2) of 190.3% and 30.6 h, respectively, with its t1/2 15.7-fold longer than that of OP. Further investigations revealed that zinc coordination induced OM assembling into high-amphiphilic (88.5°of θo/w) and low-surface charge (−6.5 mV) supramolecules through the formation of coordinate and hydrogen bonds, allowing the OM–Zn particles to have high apparent viscosity (64.7 Pa s), shearing resistance, and interface absorption capacity (30.2 nN of adhesion). Compared to egg white (11% protein), OM–Zn (1% protein) had (a 1.3-fold) larger foaming volume and stronger foaming fabricability. Meanwhile, the OM–Zn foam could also absorb and release hydrophobic and hydrophilic molecules, and the rifampicin-loaded OM–Zn foam effectively released the drug to 62% in 30 h, superior to currently drug-loaded nano-systems. These findings implied the potential of OM–Zn as a foam for food and drug delivery and established a groundwork for using green peptide-based functional foam as a substitute for their synthesized counterparts.

A hierarchical porous N-doped carbon material as catalyst derived from the folic acid-Zn/KBr hydrogel: Reaction network and kinetics and mechanism for the oxidation of furfural to maleic acid

A novel hydrogel (named FA-Zn/KBr) was prepared, by taking advantage of the hydrogen-bonding and π-π stacking interactions between the pterin heterocycles of the folic acid (FA) molecules. The hydrogel is composed of highly dispersed KBr, coordinated zinc ions, and stacked arrays of folate tetramers. Due to the presence of KBr, a hierarchical porous nitrogen-doped carbon (PNC-800) material with a specific surface area 2807.9 m2/g can be formed through the calcination of the FA-Zn/KBr xerogel under N2. PNC-800 is used to catalyze the oxidation of furfural to maleic acid in the presence of H2O2. Representative nine reactions constitute the reaction network. The reaction rate constants and apparent activation energy were obtained for each reaction. Based on the kinetics parameters, the simulated results are in good agreement with the experimental data. The mechanism of the reaction catalyzed by PNC-800 is proposed based on ample experimental evidence. The graphitic nitrogen species in PNC-800 are the active sites. PNC-800 catalyzes the decomposition of hydrogen peroxide to generate hydroxyl radical (HȮ), which oxidizes furfural to furfural radical, and the furfural radical is subsequently converted to 5-hydroxy-furan-2(5H)-one (HFONE). The conversion of furfural to maleic acid via the formation of HFONE is the main reaction pathway. In addition, the hierarchical porous structure with a high specific surface area facilitates the interaction of reactant with the active sites. PNC-800 has been shown an excellent catalytic activity for the production of maleic acid from furfural. For the oxidation of 1000 mM furfural using 50 mg PNC-800 at 80 °C within 9 h, the conversion of furfural is 100 % with a maleic acid yield 67.5 %.

Shear-Responsive Sol-Gel Transition of Phase Change Material Emulsions for an Injectable Thermal Insulation Platform.

Phase change materials (PCMs) have attracted significant attention as promising insulating materials. However, they often suffer from the simple yet critical problem of leakage in practical applications. Therefore, in this study, an injectable PCM emulsion insulation platform is developed. For this, n-hexadecane, as a PCM, emulsion droplets are armored with a metal-organic membrane (MOM) through the coordination of zinc ions and phytic acid. The MOM layer not only provides a rigid interfacial modulus but also allows the emulsion to exhibit viscoelastic behavior by shear stress-induced interdrop association. This MOM-enveloped PCM emulsion (PCMEMOM ) exhibited typical sol-gel transition behavior in response to applied shear stress, indicating the injectable characteristic of the PCMEMOM . After observing the rheological hysteresis and thermal stability of the PCMEMOM under repetitive heating and cooling cycles, the thermal insulation performance of PCMEMOM is quantitatively and visually demonstrated. These findings suggest an efficient method to exploit high-performance insulation systems.

Protein@PP-Zn nanocomplex assembled by coordination of zinc ions used for intracellular protein delivery

Protein@PP-Zn nanocomplex assembled by coordination of zinc ions used for intracellular protein delivery

A pH‐Activatable Prodrug and Metal Prodrug Conjugate of Gossypol: Synthesis, Emergent Photophysical, Nanoscopic, Computational, and in‐Vitro Cellular Studies

AbstractThe major hurdle to the success of many potent chemotherapeutic drugs is the lack of stability of their active form suited for a particular mode of action. Efforts are needed to stabilize such functionalities by employing new and novel strategies to overcome challenges. In this study, tumor‐environment‐specific, pH‐activatable prodrug and metal‐prodrug conjugate has been developed to ameliorate the side effects of chemotherapeutic drugs bearing reactive functionalities. As a proof of concept, a pre‐clinically tested natural compound, gossypol, was modified to form a pH‐responsive prodrug by incorporating an imine linkage amenable to form confined molecular structures through coordination with a bio‐relevant and nontoxic zinc metal ion. Detailed photophysical, computational, and nanoscopic studies revealed the unique zinc ion coordination behavior and its effect on molecular confinement. Computational studies demonstrated that an increasing degree of complexation, with Zn‐N−Py coordination, gradually turns off fluorescence by reducing the band gap that allows nonradiative decay. In‐vitro prodrug activation and release of gossypol from gossyzid and gossyzid‐Zn were assessed by ESI‐MS and RP‐HPLC studies. The gossyzid and gossyzid‐Zn demonstrated pH‐specific cytotoxicity validated by the number of in‐vitro cellular assays. Such a strategy can essentially be adapted to strengthen many chemotherapeutic drugs to enhance their efficacy and reduce side effects.

Complete Models of p53 Better Inform the Impact of Hotspot Mutations

Mutations in tumor suppressor genes often lead to cancerous phenotypes. Current treatments leverage signaling pathways that are often compromised by disease-derived deficiencies in tumor suppressors. P53 falls into this category as genetic mutations lead to physical changes in the protein that impact multiple cellular pathways. Here, we show the first complete structural models of mutated p53 to reveal how hotspot mutations physically deviate from the wild-type protein. We employed a recently determined structure for the p53 monomer to map seven frequent clinical mutations using computational modeling approaches. Results showed that missense mutations often changed the conformational structure of p53 in the DNA-binding site along with its electrostatic surface charges. We posit these changes may amplify the toxic effects of these hotspot mutations by destabilizing an important zinc ion coordination region in p53 to impede proper DNA interactions. These results highlight the imperative need for new studies on patient-derived proteins that may assist in redesigning structure-informed targeted therapies.

Self-Healing Solid Polymer Electrolyte with High Ion Conductivity and Super Stretchability for All-Solid Zinc-Ion Batteries.

The zinc-ion battery (ZIB) is a novel energy storage device, an attractive alternative to the lithium-ion battery. The frequently used aqueous electrolyte suffers from many problems such as zinc dendrites and leakage, which prompts hydrogel electrolytes and solid electrolytes as good replacements. However, hydrogel electrolytes are usually unstable, owing to water volatilization. Herein, a novel solid polymer electrolyte (SPE) utilizing coordination of zinc ions is designed and then introduced into an all-solid ZIB. Benefiting from the unique coordination structure between the polymer and zinc ions, the SPE shows outstanding flexibility, high ion conductivity, and self-healing properties. In addition, the imine bonds in the polymer allow the electrolyte to degrade in acid environments, endowing its recyclability. More importantly, solid-state ZIBs based on the polymer electrolytes exhibit an impressive cycling stability (125% capacity retention after 300 cycles) and a high coulombic efficiency (94% after 300 cycles). The results demonstrate the promising potentials of the developed SPEs that can be used in all-solid ZIBs.

Elucidation and control of low and high active populations of alkaline phosphatase molecules for quantitative digital bioassay

Alkaline phosphatase (ALP), a homo‐dimeric enzyme has been widely used in various bioassays as disease markers and enzyme probes. Recent advancements of digital bioassay revolutionized ALP‐based diagnostic assays as seen in rapid growth of digital ELISA and the emerging multiplex profiling of single‐molecule ALP isomers. However, the intrinsic heterogeneity found among ALP molecules hampers the ALP‐based quantitative digital bioassays. This study aims quantitative analysis of single‐molecule activities of ALP from Escherichia coli and reveals the static heterogeneity in catalytic activity of ALP with two distinct populations: half‐active and fully‐active portions. Digital assays with serial buffer exchange uncovered single‐molecule Michaelis–Menten kinetics of ALP; half‐active molecules have halved values of the catalytic turnover rate, k cat, and the rate constant of productive binding, k on, of the fully active molecules. These findings suggest that half‐active ALP molecules are heterogenic dimers composed of inactive and active monomer units, while fully active ALP molecules comprise two active units. Static heterogeneity was also observed for ALP with other origins: calf intestine or shrimp, showing how the findings can be generalized across species. Cell‐free expression of ALP with disulfide bond enhancer and spiked zinc ion resulted in homogenous population of ALP of full activity, implying that inactive monomer units of ALP are deficient in correct disulfide bond formation and zinc ion coordination. These findings provide basis for further study on molecular mechanism and biogenesis of ALP, and also offer the way to prepare homogenous and active populations of ALP for highly quantitative and sensitive bioassays with ALP.

Photothermal and magnetocaloric-stimulated shape memory and self-healing via magnetic polymeric composite with dynamic crosslinking

Multiple-stimulated shape-memory and self-healing materials can be employed in some covert circumstances and special system because of the flexible control manners, which shows great potential in practical application. In this work, Fe3O4 grafted copolymer, Fe3O4-g-P(TMA-co-LA-co-VI), with magnetic, near-infrared light and thermo multiple-stimulated shape memory and self-healing performance, was synthesized, where tetrahydrofurfuryl methacrylate (TMA), lauryl acrylate (LA) and 1-vinylimidazole (VI) were biomass derived monomers. Dynamic metal-ligand network in Fe3O4-g-P(TMA-co-LA-co-VI)/Zn was subsequently constructed via the coordination of VI and zinc ion. The mechanical properties of the nanocomposite could be simply regulated by varying the Fe3O4 content and the molar ratio of monomers. Among all the samples, Fe3O4-g-P(TMA-co-LA-co-VI)/Zn with Fe3O4 content of 1 wt % and TMA/LA/VI molar ratio of 8/2/2.5 showed a breaking stain of 300% and a maximum stress of 1.66 MPa, which also showed an excellent thermo stimulated shape memory and self-healing performance. As the Fe3O4 nanoparticles were uniformly dispersed in the nanocomposites, their photothermal and magnetocaloric transformation can efficiently stimulate the dynamic and reversible metal-ligand crosslinked process between VI and Zn2+. Therefore, this kind of effective stimulation can finally lead to excellent remote-controllable shape memory and self-healing performance. The integration of magnetic, near-infrared light and thermo multiple-stimulation for shape memory and self-healing also augurs well for their wide application potential in artificial intelligence materials and life science.

Dissolution and separation of non-metallic powder from printed circuit boards by using chloride solvent

Non-metallic components (NMC) in waste printed circuit boards (WPCBs) are made of the thermosetting epoxy resin and glass fiber, which has been a research concern in the waste recycling area. The recycling of thermosetting epoxy resin is a serious challenge due to their permanent cross-linked structure. An efficient approach to chemical recycling of epoxy resin for resource reutilization was developed in this research. ZnCl2/CH3COOH aqueous solution was selected as catalysts system to decompose epoxy resin under a mild reaction condition. The influence of reaction parameters such as reaction temperature, time, liquid-solid ratio and ZnCl2 amount on the decomposition efficiency of epoxy resin and reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent and decomposed products were analyzed using scanning electron microscope(SEM), Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography–mass spectrometry (GC–MS). Results showed that up to 81.85% of epoxy resin could be dissolved by using a temperature of 190 °C during 8 h with a mixture of acetic acid (15 wt%): ZnCl2 (5 g) 20 mL/g. Incompletely coordinated zinc ions enables the cleavage of CN, CBr and CO bonds in the thermosetting brominated epoxy resin, which was mainly converted to phenol, 2-Bromophenol and 2, 4-Dibromophenol with high resource value. And the functional groups of ethyl acetate and acetic acid maintained chemical structure before and after reaction. This research provided a practical approach to the dissolution and reutilization of NMC in WPCBs.

A type of dissoluble organosilicon elastomer with stretchable, self-healable and antibacterial properties

Bacterial resistance to antibiotics reduced the demand for antibiotics in the field of medical devices. Polymer antibacterial materials have shown great potential in the medical field. However, the treatment of materials after use is not environmentally friendly. Therefore, the development of dissoluble polymer antibacterial materials has become an urgent challenge. In this paper, an antibacterial polymer material with high self-healing ability and rapid dissolution is reported. The new material was formed by the Schiff base reaction and cross-linking of aldehyde group and amino in terephthalaldehyd (TA), 3,4-diaminofurazan (DAF) and α,ω-aminopropyl terminated polydimethylsiloxane (PDMS, Mn = 3000). The properties of the material were further enhanced by the coordination of zinc ion with nitrogen and oxygen atoms of 3,4-diaminofurazan. The antibacterial polymer material designed by us can be effectively repaired at 100 °C. The first repair efficiency was 89.5%. After repeated repair, its mechanical properties were not significantly reduced. E. coli and S.aureus were used to evaluate the antibacterial ability of the material. The antibacterial efficiency of the material was 99.9993% and 99.9997% respectively. This new idea solved the urgent problems in the current application, and provided guidance for the research of flexible antibacterial materials.

Regulation of the Central Dogma through Bioinorganic Events with Metal Coordination for Specific Interactions

The central dogma is the core aspect of biological system regulation, receiving much attention from the field of biological chemistry. One of the main regulators of transcription and translation processes is the zinc finger (ZF) proteins, one or more domains of which coordinate with a zinc ion to interact with their binding partner. ZFs are modular domains that function independently in the presence of Zn2+ through the generation of short secondary structures via zinc ion coordination, which generate hydrogen bonds, despite being considered structural domains. In this review, structural and functional characteristics of ZF domains will be presented from the perspective of inorganic biochemistry. The major role of ZF domains in the central dogma involves transcriptional regulation through interactions with DNA and translational regulation through the generation of complexes with RNA. These findings indicate that the triggering many biological events can be explained by the coordination and biophysical chemistry of ZFs.

An enzyme-loaded reactor using metal-organic framework-templated polydopamine microcapsule

Abstract Ultrathin polydopamine microcapsules with hierarchical structure and porosity were prepared for the immobilization of multienzymes using metal-organic framework (MOF) as the template. The multienzyme/MOF composite was first prepared using a “one-pot” co-precipitation approach via the coordination and self-assembly of zinc ions and 2-methylimidazole in the presence of enzymes. The obtained nanoparticles were then coated with polydopamine thin layer through the self-polymerization of dopamine under alkaline condition. The polydopamine microcapsules with an ultrathin shell thickness of ~ 48 nm were finally generated by removing the MOF template at acidic condition. Three enzymes were encapsulated in PDA microcapsules including carbonic anhydrase (CA), formate dehydrogenase (FateDH), and glutamate dehydrogenase (GDH). FateDH that catalyzed the main reaction of CO2 reduction to formic acid retained 94.7% activity of equivalent free FateDH. Compared with free multienzymes, the immobilized ones embedded in PDA microcapsules exhibited 4.5-times higher of formate production and high catalytic efficiency with a co-factor-based formate yield of 342%.

Non-native fold of the putative VPS39 zinc finger domain.

Background: The multi-subunit homotypic fusion and vacuole protein sorting (HOPS) membrane-tethering complex is involved in regulating the fusion of late endosomes and autophagosomes with lysosomes in eukaryotes. The C-terminal regions of several HOPS components have been shown to be required for correct complex assembly, including the C-terminal really interesting new gene (RING) zinc finger domains of HOPS components VPS18 and VPS41. We sought to structurally characterise the putative C-terminal zinc finger domain of VPS39, which we hypothesised may be important for binding of VPS39 to cellular partners or to other HOPS components. Methods: We recombinantly expressed, purified and solved the crystal structure of the proposed zinc-binding region of VPS39. Results: In the structure, this region forms an anti-parallel β-hairpin that is incorporated into a homotetrameric eight-stranded β-barrel. However, the fold is stabilised by coordination of zinc ions by residues from the purification tag and an intramolecular disulphide bond between two predicted zinc ligands. Conclusions: We solved the structure of the VPS39 C-terminal domain adopting a non-native fold. Our work highlights the risk of non-native folds when purifying small zinc-containing domains with hexahistidine tags. However, the non-native structure we observe may have implications for rational protein design.

Non-native fold of the putative VPS39 zinc finger domain

Background: The multi-subunit homotypic fusion and vacuole protein sorting (HOPS) membrane-tethering complex is involved in regulating the fusion of late endosomes and autophagosomes with lysosomes in eukaryotes. The C-terminal regions of several HOPS components have been shown to be required for correct complex assembly, including the C-terminal really interesting new gene (RING) zinc finger domains of HOPS components VPS18 and VPS41. We sought to structurally characterise the putative C-terminal zinc finger domain of VPS39, which we hypothesised may be important for binding of VPS39 to cellular partners or to other HOPS components. Methods: We recombinantly expressed, purified and solved the crystal structure of the proposed zinc-binding region of VPS39. Results: In the structure, this region forms an anti-parallel β-hairpin that is incorporated into a homotetrameric eight-stranded β-barrel. However, the fold is stabilised by coordination of zinc ions by residues from the purification tag and an intramolecular disulphide bond between two predicted zinc ligands. Conclusions: We solved the structure of the VPS39 C-terminal domain adopting a non-native fold. Our work highlights the risk of non-native folds when purifying small zinc-containing domains with hexahistidine tags. However, the non-native structure we observe may have implications for rational protein design.