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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Synthesis of luminescent core/shell α-Zn 3 P 2 /ZnS quantum dots

Metal chalcogenide nanoparticles offer vast control over their optoelectronic properties via size, shape, composition, and morphology which has led to their use across fields including optoelectronics, energy storage, and catalysis. While cadmium and lead-based nanocrystals are prevalent in applications, concerns over their toxicity have motivated researchers to explore alternate classes of nanomaterials based on environmentally benign metals such as zinc and tin. The goal of this research is to identify material systems that offer comparable performance to existing metal chalcogenide systems from abundant, recyclable, and environmentally benign materials. With band gaps that span the visible through the infrared, II–V direct band gap semiconductors such as tetragonal zinc phosphide (α-Zn 3 P 2 ) are promising candidates for optoelectronics. To date, syntheses of α-Zn 3 P 2 nanoparticles have been hindered because of the toxicity of zinc and phosphorus precursors, surface oxidation, and defect states leading to carrier trapping and low photoluminescence quantum yield. Here, we report a colloidal synthesis of quantum confined α-Zn 3 P 2 nanoparticles from common phosphorus precursor tris(trimethylsilyl)phosphine and environmentally benign zinc carboxylates. Shelling of the nanoparticles with zinc sulfide is shown as a method of preventing oxidation and improving the optical properties of the nanoparticles. These results show a route to stabilizing α-Zn 3 P 2 nanoparticles for optoelectronic device applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Circulating levels of micronutrients and risk of osteomyelitis: a Mendelian randomization study

Background Few observational studies have investigated the effect of micronutrients on osteomyelitis, and these findings are limited by confounding and conflicting results. Therefore, we conducted Mendelian randomization (MR) analyses to evaluate the association between blood levels of eight micronutrients (copper, selenium, zinc, vitamin B12, vitamin C, and vitamin D, vitamin B6, vitamin E) and the risk of osteomyelitis. Methods We performed the two-sample and multivariable Mendelian randomization (MVMR) to investigate causation, where instrument variables for the predictor (micronutrients) were derived from the summary data of micronutrients from independent cohorts of European ancestry. The outcome instrumental variables were used from the summary data of European-ancestry individuals ( n = 486,484). The threshold of statistical significance was set at p < 0.00625. Results We found a significant causal association that elevated zinc heightens the risk of developing osteomyelitis in European ancestry individuals OR = 1.23 [95% confidence interval (CI) [1.07, 1.43]; p = 4.26E-03]. Similarly, vitamin B6 showed a similar significant causal effect on osteomyelitis as a risk factor OR = 2.78 (95% CI [1.34, 5.76]; p = 6.04E-03; in the secondary analysis). Post-hoc analysis suggested this result (vitamin B6). However, the multivariable Mendelian randomization (MVMR) provides evidence against the causal association between zinc and osteomyelitis OR = 0.98(95% CI [−0.11, 0.07]; p = 7.20E-1). After searching in PhenoScanner, no SNP with confounding factors was found in the analysis of vitamin B6. There was no evidence of a reverse causal impact of osteomyelitis on zinc and vitamin B6. Conclusion This study supported a strong causal association between vitamin B6 and osteomyelitis while reporting a dubious causal association between zinc and osteomyelitis.

Zhang, Xu↗
DOE OSTI2021

Material Failure Mechanisms of Alkaline Zn Rechargeable Conversion Electrodes

Zinc (Zn) alkaline electrodes hold great importance and promise in the battery technology community, yet their behavior in real-world applications is still poorly understood. Here, we report a study of failure mechanisms and material evolution during cycling of 27 zinc–manganese dioxide (Zn–MnO 2 ) cells wherein the percent utilization of the Zn electroactive material is systematically varied between 1 and 16%. Cell fabrication is kept typical of the prevailing industrial cell design. The cycle life ranges from 2800 to 60, depending inversely on the Zn utilization. In all cases, the Zn material microstructure sheds the polytetrafluoroethylene (PTFE) binder and forms zinc oxide (ZnO) rods, with longer rods formed by lower current per Zn mass. Irreversible side reactions such as the hydrogen evolution reaction (HER), short circuits, or gas crossover cause the Zn anode’s charging efficiency to average 92% (as low as 86%), which in turn causes the baseload of metallic Zn to gradually disappear. Cell failure occurs after the baseload of metallic Zn is exhausted. The total lifetime discharge capacity remains constant near 12 ± 5 Ah/g Zn invariant of Zn utilization, which suggests that the aforementioned processes of Zn microstructural evolution and side-reaction destruction of baseload metallic zinc both progress linearly with cell capacity throughput. Manual reproduction of individual Zn failure mechanisms is performed in 22 fresh cells. Tight packing of the microstructure can lead to poor mass transfer, which causes supersaturation of soluble Zn and finally produces a high overvoltage during discharge. Here, the low charging current density yields poor coulombic efficiency due either to the competitive HER or soft short circuits.

25 ENERGY STORAGE↗
DOE OSTI2023

Structural Characterization of TRAF6 N-Terminal for Therapeutic Uses and Computational Studies on New Derivatives

Tumor necrosis factor receptor-associated factors (TRAFs) are a protein family with a wide variety of roles and binding partners. Among them, TRAF6, a ubiquitin ligase, possesses unique receptor binding specificity and shows diverse functions in immune system regulation, cellular signaling, central nervous system, and tumor formation. TRAF6 consists of an N-terminal Really Interesting New Gene (RING) domain, multiple zinc fingers, and a C-terminal TRAF domain. TRAF6 is an important therapeutic target for various disorders and structural studies of this protein are crucial for the development of next-generation therapeutics. Here, we presented a TRAF6 N-terminal structure determined at the Turkish light source “Turkish DeLight” to be 3.2 Å resolution at cryogenic temperature (PDB ID: 8HZ2). This structure offers insight into the domain organization and zinc-binding, which are critical for protein function. Since the RING domain and the zinc fingers are key targets for TRAF6 therapeutics, structural insights are crucial for future research. Separately, we rationally designed numerous new compounds and performed molecular docking studies using this template (PDB ID:8HZ2). According to the results, 10 new compounds formed key interactions with essential residues and zinc ion in the N-terminal region of TRAF6. Molecular dynamic (MD) simulations were performed for 300 ns to evaluate the stability of three docked complexes (compounds 256, 322, and 489). Compounds 256 and 489 was found to possess favorable bindings with TRAF6. These new compounds also showed moderate to good pharmacokinetic profiles, making them potential future drug candidates as TRAF6 inhibitors.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

The electrolyte comprising more robust water and superhalides transforms Zn-metal anode reversibly and dendrite-free

A great challenge for all aqueous batteries, including Zn-metal batteries, is the parasitic hydrogen evolution reaction on the low-potential anode. Herein, we report the formula of a highly concentrated aqueous electrolyte that mitigates hydrogen evolution by transforming water molecules more inert. The electrolyte comprises primarily ZnCl 2 and LiCl as an additive, both of which are inexpensive salts. The O–H covalent bonds in water get strengthened in a chemical environment that has fewer hydrogen bonding interactions and a greater number of Zn–Cl superhalides, as suggested by integrated characterization and simulation. As a result, the average Coulombic efficiency of zinc-metal anode is raised to an unprecedented >99.7% at 1 mA cm –2 . In the new electrolyte, the plating/stripping processes leave the zinc-metal anode dendrite-free, and the zinc-metal anode delivers stable plating/stripping cycles for 4000 hours with an areal capacity of 4 mAh cm –2 at 2 mA cm –2 . Furthermore, the high Coulombic efficiency of zinc-metal anode in the ZnCl 2 -LiCl mixture electrolyte is demonstrated in full cells with a limited anode. The V 2 O 5 ·H 2 O| |Zn full cell with an N/P mass ratio of 1.2 delivers a stable life of more than 2500 cycles, and the LiMn 2 O 4 | |Zn hybrid cell with an N/P mass ratio of 0.6 exhibits 1500 cycles in its stable life.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Highly Coupled Heterobicycle‐Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C 60

Abstract Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole‐fused porphyrin dimers and their mono‐ and bis−zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady‐state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free‐base and zinc porphyrin) reveals the occurrence of efficient singlet‐singlet energy transfer (>95 % efficiency and rate constant >10 12 s −1 ) within the dyad. Further, donor‐acceptor conjugates were formed by metal‐ligand axial coordination of phenyl imidazole functionalized C 60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge‐separated state was in the 30–40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π‐spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Chemistry↗
DOE OSTI2026

“Antenna-like” Light-Harvesting in Partially Metalated Porphyrin Hydrogen-Bonded Organic Frameworks

Arrays of light harvesting molecules with long-range order hold promise as materials capable of efficient collection of photons as well as rapid transport of captured solar energy to chemical catalysts. Hydrogen-bonded organic frameworks (HOFs) could be promising artificial light-harvesting platforms, due to their crystalline nature and their comparative ease of synthesis. In this work, mixed-linkers of either zinc-metallated or free base tetrakis(4-carboxyphenyl)porphyrin HOFs were examined and found to demonstrate ‘antenna-like’ light harvesting behavior. Using time-resolved emission spectroscopy, Förster resonance energy transfer from zinc porphyrin to free-base porphyrin was assessed. Based on changes in the emission peak profile as the ratio of zinc porphyrin to free-base porphyrin is varied, we find that, in the limit of 100% zinc porphyrin, a photogenerated exciton can sample ~48 chromophores. These findings suggest that stacked linkers within HOFs can act as light harvesting ‘antennae’ and with encapsulation of suitable catalysts, may offer prospective application as photochemical energy conversion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Water or Anion? Uncovering the Zn 2+ Solvation Environment in Mixed Zn(TFSI) 2 and LiTFSI Water-in-Salt Electrolytes

Applications of aqueous zinc batteries for grid-scale energy storage are limited by their poor reversibility and the competing water splitting reaction. The recent invention of a water-in-salt (WIS) electrolyte concept provides a new route enabling a stable and highly reversible aqueous zinc battery chemistry. In the present work, a mixed zinc bis(trifluoromethane sulfonyl)imide (Zn(TFSI) 2 ) and LiTFSI WIS electrolyte was studied using X-ray total scattering, X-ray absorption, and Fourier transform infrared spectroscopy in conjunction with classical molecular dynamics simulations. It was found that, in the highly concentrated WIS electrolyte consisting of 1 m Zn(TFSI) 2 and 20 m LiTFSI, Zn 2+ cations are mainly solvated by six waters in their first solvation shell, while the TFSI – anions are completely excluded. This ion solvation picture is fundamentally different from the previous understandings. The results suggest that additional studies are needed to fully understand the unusual stability and reversibility of zinc-WIS electrolyte-based batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Identity of the reversible hole traps in InP/ZnSe core/shell quantum dots

Density functional theory calculations are combined with time-resolved photoluminescence experiments to identify the species responsible for reversible trapping of holes following photoexcitation of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) having excess indium in the shell. Several possible assignments are considered, and a substitutional indium adjacent to a zinc vacancy, In 3+ /V Zn 2- , is found to be the most likely. This assignment is consistent with the observation that trapping occurs only when the QD has excess indium and is supported by experiments showing that the addition of zinc oleate or acetate decreases the extent of trapping, presumably by filling some of the vacancy traps. We also show that addition of alkyl carboxylic acids causes increased trapping, presumably by creation of additional zinc vacancies. The calculations show that either a single In 2+ ion or an In 2+ -In 3+ dimer is much too easily oxidized to form the reversible traps observed experimentally, while In 3+ is far too difficult to oxidize. Additional experimental data on InP/ZnSe/ZnS QDs synthesized in the absence of chloride demonstrates that the reversible traps are not associated with Cl - . Furthermore, a zinc vacancy adjacent to a substitutional indium is calculated to have its highest occupied orbitals about 1 eV above the top of the valence band of bulk ZnSe, in the appropriate energy range to act as reversible traps for quantum confined holes in the InP valence band. The associated orbitals are predominantly composed of p orbitals on the Se atoms adjacent to the Zn vacancy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synthesis and functionalization of electron-deficient perfluoroalkyl porphyrin building blocks for supermolecular systems

Synthetic strategies for electron-deficient meso-perfluoroalkylporphyrins bearing diverse functional groups are described. Scalable and efficient syntheses for 5-triisopropylsilylethynyl-10,15,20-tris(heptafluoropropyl)porphyrin and 5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphyrin that equip meso-ethynyl functional groups via the bilane route have been established, along with a refined route to [5,15-bis(heptafluoropropyl)porphinato]zinc(II). meso-Position halogenation of [5,15-bis(heptafluoropropyl)porphinato]zinc(II) was achieved by selective meso-nitration and subsequent reduction, diazonium salt formation, and iodination reactions. Computational data describe the low energy excited states of these chromophores and the electronic structural factors that control reactivity of these meso-perfluoroalkyl substituted porphyrin complexes. meso-Functionalized [5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphinato]zinc(II) and [5-iodo-10,20-bis(heptafluoropropyl)porphinato]zinc(II) building blocks lay the foundation for the construction of highly conjugated multiporphyrin arrays that feature electronic structural properties important for the development of n-type materials and high potential photooxidants.

Chemistry↗
DOE OSTI2024

Synthesis of (oxo)chlorin dimers chelated with thallium(III)

Two target dimers have been prepared for fundamental studies of hole/electron transfer. Metalation with thallium(III) enables clocking of the rate of hole/electron transfer between the two macrocycles. Each dimer contains a diphenylethyne linker joining two identical hydroporphyrins (chlorin or oxochlorin). The linker is substituted at the 4,4′-positions whereas each (oxo)chlorin is joined at the 10-position. Each (oxo)chlorin is equipped with a gem-dimethyl group at the 18-position to stabilize the hydroporphyrin chromophore toward adventitious dehydrogenation and a 3,5-di-tert-butyl group at the 5-position to achieve increased solubilization in organic media. The dimers parallel a prior set of diphenylethyne-linked (oxo)chlorin constructs containing zinc-free base, zinc-zinc, and copper-copper metalation states that have been examined in studies of electronic communication. The building block (oxo)chlorins for preparing the thallium-containing dimers have been prepared in quantities of 32–404 mg, a scale up to 14-fold larger than previously. Thallation of the free base (oxo)chlorin dimers was achieved with excess TlCl 3 ⋅4H 2 O in CH 2 Cl 2 /CH 3 OH (3–4:1) upon overnight reaction at room temperature. The long-wavelength (Q[Formula: see text] absorption band of (oxo)chlorins lies between that of the zinc(II) and free base counterparts. Absorption spectral comparisons are provided of the thallium(III) and free base (oxo)chlorin monomers and dimers.

Chemistry↗
DOE OSTI2021

Neutron computed tomography of B12W and M8N socket sections of the Arecibo telescope

From neutron user principal investigator: We kindly request the public release of three neutron imaging datasets through ONCat. All datasets were collected from two forensic specimens, B12W and M8N, sectioned from zinc-filled steel-wire sockets recovered from the collapsed Arecibo Telescope. The dataset titled “Neutron radiographs of B12W and M8N socket sections of the Arecibo telescope” contains normalized two-dimensional (2D) neutron radiographs of the specimens, showing the geometry and spatial distribution of the steel wires embedded within the zinc matrix, as well as internal features such as voids and cracks. The dataset titled “Neutron computed tomography of B12W and M8N socket sections of the Arecibo telescope” contains normalized 2D neutron projection images acquired over a range of specimen rotation angles for one selected region of each specimen. These projection images were used to reconstruct three-dimensional (3D) tomographic volumes that reveal the embedded-wire geometry and internal defects. The dataset titled “Bragg edge imaging (BEI) of B12W and M8N socket sections of the Arecibo telescope” contains six time-of-flight (TOF) neutron imaging datasets, three from each specimen, acquired at regions of interest selected based on the radiographs. The spatially resolved 2D TOF images show the zinc matrix and embedded steel wires, and the wavelength-dependent neutron transmission data were used to characterize crystallographic texture within the zinc. All components and their condition are in the public domain as they are the property of the National Science Foundation (NSF). The neutron imaging data, part geometries, and detailed forensic information have been widely published in the Arecibo Telescope Collapse Forensic Report by Thornton Tomasetti Engineers and others (NASA report and NASEM report).

Bilheux, Hassina↗
DOE OSTI2022

ZnCr and ZnNb Cold Spray Coatings

Novel cold spray zinc-based alloy coatings have been investigated for corrosion protection of API 5L low carbon steel pipelines used in transporting natural gas. These different zinc alloy coatings are designed for use to help prevent internal corrosion and improve the lifespan of steel pipelines via sacrificial anodic protection. The corrosion behavior of these cold deposited zinc alloy coatings was investigated in CO2 saturated 3.5 wt.% NaCl solutions under simulated natural gas pipeline conditions. Electrochemical tests were conducted at 25 and 40 °C to determine the polarization resistance and galvanic current between each coating and the steel substrate in the galvanic couple. Tests were conducted at atmospheric, 1 bar, pressure. The results indicate that use of these coatings has the potential to increase the lifespan of steel pipelines above what a zinc coating alone could provide.

Teeter, Lucas↗
DOE OSTI2022

Desulfurization and sulfur tolerant hydrogenation processes of hydrocarbon feedstocks

The present invention relates to the use of adsorbents comprising zinc oxide nanowires decorated with catalytically active metal particles for the removal of sulfur from hydrocarbon feedstocks, including the desulfurization of diesel fuels and the deep desulfurization of natural gas, and to the use of decorated zinc oxide nanowire adsorbents for the hydrogenation of naphthalene selectively to tetralin in the presence of sulfur compounds. The adsorbent comprises nickel metal particles or nickel-zinc alloy particles deposited on zinc oxide nanowires.

Sunkara, Mahendra↗
DOE OSTI2022

Electroactive ZnO: Mechanisms, Conductivity, and Advances in Zn Alkaline Battery Cycling

Zinc oxide is of great interest for advanced energy devices because of its low cost, wide direct bandgap, non-toxicity, and facile electrochemistry. In zinc alkaline batteries, ZnO plays a critical role in electrode passivation, a process that hinders commercialization and remains poorly understood. Here, novel observations of an electroactive type of ZnO formed in Zn-metal alkaline electrodes are disclosed. The electrical conductivity of battery-formed ZnO is measured and found to vary by factors of up to 10 4 , which provides a first-principles-based understanding of Zn passivation in industrial alkaline batteries. Simultaneous with this conductivity change, protons are inserted into the crystal structure and electrons are inserted into the conduction band in quantities up to ≈10 20 cm –3 and ≈1 mAh gZnO –1 . Electron insertion causes blue electrochromic coloration with efficiencies and rates competitive with leading electrochromic materials. The electroactivity of ZnO is evidently enabled by rapid crystal growth, which forms defects that complex with inserted cations, charge-balanced by the increase of conduction band electrons. Furthermore, this property distinguishes electroactive ZnO from inactive classical ZnO. Knowledge of this phenomenon is applied to improve cycling performance of industrial-design electrodes at 50% zinc utilization and the authors propose other uses for ZnO such as electrochromic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Polymer infiltration synthesis of inorganic nanoporous coatings: Does polymer template affect their properties?

Synthesis of all-inorganic metal oxide architectures using polymer templates offers control over their thickness, porosity, and composition. Here, in this study, we provide insights into the synthesis of nanoporous zinc oxide films as a model system via infiltration of polymers that have different mechanisms of interaction with metal oxide precursors such as a polymer of intrinsic microporosity (PIM-1) and representative of the block-copolymers family (polystyrene-polyvinyl pyridine block copolymer). We investigated polymer infiltration process with both gas (diethyl zinc, DEZ, and water vapors) and solution (zinc acetylacetonate, Zn(acac) 2 , dissolved in ethanol) phase precursors. Using quartz crystal microbalance (QCM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, we systematically studied the effect of polymer template and the form of the metal oxide precursors on the properties of synthesized metal oxide thin coatings. We demonstrate that the infiltration of polymer templates can be efficiently achieved using both gas phase and solution phase precursors. We show that the crystallinity of the synthesized 200 nm ZnO films is mainly affected by the state of the precursor (gas or solution phase) and does not depend on the polymer template type. In turn, the polymer type affects the surface termination of ZnO films. We demonstrate that the surface of porous ZnO coatings synthesized with BCP (here PS-P4VP) is more accessible than the surface of ZnO synthesized with PIM; however, despite the lower surface accessibility for ethanol molecules, ZnO synthesized via infiltration of PIM-1 with solution-phase precursors demonstrates the largest change in resistivity upon its exposure to ethanol vapor at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Non-TZF Protein AtC3H59/ZFWD3 Is Involved in Seed Germination, Seedling Development, and Seed Development, Interacting with PPPDE Family Protein Desi1 in Arabidopsis

Despite increasing reports on the function of CCCH zinc finger proteins in plant development and stress response, the functions and molecular aspects of many non-tandem CCCH zinc finger (non-TZF) proteins remain uncharacterized. AtC3H59/ZFWD3 is an Arabidopsis non-TZF protein and belongs to the ZFWD subfamily harboring a CCCH zinc finger motif and a WD40 domain. In this study, we characterized the biological and molecular functions of AtC3H59, which is subcellularly localized in the nucleus. The seeds of AtC3H59-overexpressing transgenic plants (OXs) germinated faster than those of wild type (WT), whereas atc3h59 mutant seeds germinated slower than WT seeds. AtC3H59 OX seedlings were larger and heavier than WT seedlings, whereas atc3h59 mutant seedlings were smaller and lighter than WT seedlings. Moreover, AtC3H59 OX seedlings had longer primary root length than WT seedlings, whereas atc3h59 mutant seedlings had shorter primary root length than WT seedlings, owing to altered cell division activity in the root meristem. During seed development, AtC3H59 OXs formed larger and heavier seeds than WT. Using yeast two-hybrid screening, we isolated Desi1, a PPPDE family protein, as an interacting partner of AtC3H59. AtC3H59 and Desi1 interacted via their WD40 domain and C-terminal region, respectively, in the nucleus. Taken together, our results indicate that AtC3H59 has pleiotropic effects on seed germination, seedling development, and seed development, and interacts with Desi1 in the nucleus via its entire WD40 domain. To our knowledge, this is the first report to describe the biological functions of the ZFWD protein and Desi1 in Arabidopsis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Microbial Type IA Topoisomerase C-Terminal Domain Sequence Motifs, Distribution and Combination

Type IA topoisomerases have highly conserved catalytic N-terminal domains for the cleaving and rejoining of a single DNA/RNA strand that have been extensively characterized. In contrast, the C-terminal region has been less covered. Two major types of small tandem C-terminal domains, Topo_C_ZnRpt (containing C4 zinc finger) and Topo_C_Rpt (without cysteines) were initially identified in Escherichia coli and Mycobacterium tuberculosis topoisomerase I, respectively. Their structures and interaction with DNA oligonucleotides have been revealed in structural studies. Here, we first present the diverse distribution and combinations of these two structural elements in various bacterial topoisomerase I (TopA). Previously, zinc fingers have not been seen in type IA topoisomerases from well-studied fungal species within the phylum Ascomycota. In our extended studies of C-terminal DNA-binding domains, the presence of zf-GRF and zf-CCHC types of zinc fingers in topoisomerase III (Top3) from fungi species in many phyla other than Ascomycota has drawn our attention. We secondly analyze the distribution and combination of these fungal zf-GRF- and zf-CCHC-containing domains. Their potential structures and DNA-binding mechanism are evaluated. The highly diverse arrangements and combinations of these DNA/RNA-binding domains in microbial type IA topoisomerase C-terminal regions have important implications for their interactions with nucleic acids and protein partners as part of their physiological functions.

59 BASIC BIOLOGICAL SCIENCES↗