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1. Crystallographic characterization of a tri-Asp metal-binding site at the three-fold symmetry axis of LarE

   https://doi.org/DOI: 10.1038/s41598-020-62847-6  

   Fellner, M; Huizenga, KG; Hausinger, RP; Hu, J. (April 2020, Scientific reports)

   Abstract Detailed crystallographic characterization of a tri-aspartate metal-binding site previously identified on the three-fold symmetry axis of a hexameric enzyme, LarE from Lactobacillus plantarum, was conducted. By screening an array of monovalent, divalent, and trivalent metal ions, we demonstrated that this metal binding site stoichiometrically binds Ca2+, Mn2+, Fe2+/Fe3+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+, but not monovalent metal ions, Cr3+, Mg2+, Y3+, Sr2+ or Ba2+. Extensive database searches resulted in only 13 similar metal binding sites in other proteins, indicative of the rareness of tri-aspartate architectures, which allows for engineering such a selective multivalent metal ion binding site into target macromolecules for structural and biophysical characterization. 

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2. Nanopore Detection of Metal Ions: Current Status and Future Directions

   https://doi.org/10.1002/smtd.202000266  

   Roozbahani, Golbarg Mohammadi; Chen, Xiaohan; Zhang, Youwen; Wang, Liang; Guan, Xiyun (August 2020, Small Methods)

   Abstract In this review, recent research efforts that aimed at developing nanopore sensors for detection of metal ions, which play a crucial role in environmental safety and human health, are highlighted. Protein pores use three stochastic sensing‐based strategies for metal ion detection. The first strategy is to construct engineered nanopores with metal ion binding sites, so that the interaction between the target analytes and the nanopore can slow the movement of metal ions in the nanochannel. Second, large molecules such as nucleic acids and especially peptides can be utilized as external selective molecular probes to detect metal ions based on the conformational change of the ligand molecules induced by the metal ion–ligand chelation/coordination interaction. Third, enzymatic reactions can also be used as an alternative to the molecule probe strategy in the situation that a sensitive and selective probe molecule for the target analyte is difficult to obtain. On the other hand, by taking advantage of steady‐state analysis, synthetic nanopores mainly use two strategies (modification and modification‐free) to detect metals. Given the advantages of high sensitivity and selectivity, and label‐free detection, nanopore‐based metal ion sensors should find useful application in many fields, including environmental monitoring, medical diagnosis, and so on. 

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3. 1,2,3-Triazoles: Controlled Switches in Logic Gate Applications

   https://doi.org/10.3390/s23157000  

   Ghosh, Debanjana; Atkinson, Austin; Gibson, Jaclyn; Subbaiahgari, Harini; Ming, Weihua; Padgett, Clifford; Aiken, Karelle S.; Landge, Shainaz M. (August 2023, Sensors)

   A 1,2,3-triazole-based chemosensor is used for selective switching in logic gate operations through colorimetric and fluorometric response mechanisms. The molecular probe synthesized via “click chemistry” resulted in a non-fluorescent 1,4-diaryl-1,2,3-triazole with a phenol moiety (PTP). However, upon sensing fluoride, it TURNS ON the molecule’s fluorescence. The TURN-OFF order occurs through fluorescence quenching of the sensor when metal ions, e.g., Cu2+, and Zn2+, are added to the PTP-fluoride ensemble. A detailed characterization using Nuclear Magnetic Resonance (NMR) spectroscopy in a sequential titration study substantiated the photophysical characteristics of PTP through UV-Vis absorption and fluorescence profiles. A combination of fluorescence OFF-ON-OFF sequences provides evidence of 1,2,3-triazoles being controlled switches applicable to multimodal logic operations. The “INH” gate was constructed based on the fluorescence output of PTP when the inputs are F− and Zn2+. The “IMP” and “OR” gates were created on the colorimetric output responses using the probe’s absorption with multiple inputs (F− and Zn2+ or Cu2+). The PTP sensor is the best example of the “Write-Read-Erase-Read” mimic. 

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4. The versatility of 1,4,8,11-tetraazacyclotetradecane (cyclam) in the formation of compounds of Co ²⁺ , Ni ²⁺ , Cu ²⁺ , and Zn ²⁺ with metal ions in and out of the cyclic ligand ring

   https://doi.org/10.1515/zkri-2023-0026  

   Noor, Mah; Chah, Hamza; Tresp, David; Bernal, Ivan; Lalancette, Roger A. (June 2023, Zeitschrift für Kristallographie - Crystalline Materials)

   Herein we report the results of preparing metal compounds (where the metal ions are Co2+, Ni2+, Cu2+, Zn2+) with the cyclic ligand 1,4,8,11-tetraazacyclotetradecane [cyclam] under a variety of conditions of metal-ligand ratios and solvent media. In all cases, we used metal Cl2 . nH2O salts (except for anhydrous CoCl2), as specified. Outcome: we isolated species with a four-coordinate metal in the N4 cavity of the ligand alone, and also with either one or two additional axial ligands. Those axial ligands can be (a) a single chloride, leading to penta-coordinated+ products; (b) two chlorides, leading to octahedral-neutral compounds; (c) two waters, giving rise to hexa-coordinated [(cyclam)metal(H2O)2]2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H2]2+ in the crystals. With such a variety of products, it is not surprising that since the metal coordination numbers vary, the cyclam ligand stereochemistries are thereby affected. Interestingly, the [(cyclam)metal] species are invariably hydrogen-bonded to one another in infinite strings of two kinds: (1) those for which the crystal’s Z’ = 1 have single strings; (2) when Z’ = 2, there is a pair of homogeneous strings attached to one another by a variety of hydrogen-bonding linkages. Finally, we observed an interesting pair of hydroxonium cations: the first is hydoxonium cations in a pleated 2-D sheet consisting of fused pentagons located between sheets of [(cyclam)metal] moieties; the second one is an infinite string of composition (H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+). 

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5. Efficient Sequestration of Heavy Metal Cations by [Mo2S12]2− Intercalated Cobalt Aluminum-Layered Double Hydroxide

   https://doi.org/10.3390/inorganics13020050  

   Roy, Subrata Chandra; Donley, Carrie L; Islam, Saiful M (February 2025, Inorganics)

   Heavy metal cations such as Ag+, Pb2+, and Hg2+ can accumulate in living organisms, posing severe risks to biological systems, including humans. Therefore, removing heavy metal cations from wastewater is crucial before discharging them to the environment. However, trace levels and high-capacity removal of the heavy metals remain a critical challenge. This work demonstrates the synthesis and characterization of [Mo2S12]2− intercalated cobalt aluminum-layered double hydroxide, CoAl―Mo2S12―LDH (CoAl―Mo2S12), and its remarkable sorption properties for heavy metals. This material shows high efficiency for removing over 99.9% of Ag+, Cu2+, Hg2+, and Pb2+ from 10 ppm aqueous solutions with a distribution constant, Kd, as high as 107 mL/g. The selectivity order for removing these ions, determined from the mixed ion state experiment, was Pb2+ < Cu2+ ≪ Hg2+ < Ag+. This study also suggests that CoAl―Mo2S12 is not selective for Ni2+, Cd2+, and Zn2+ cations. CoAl―Mo2S12 is an efficient sorbent for Ag+, Cu2+, Hg2+, and Pb2+ ions at pH~12, with the removal performance of both Ag+ and Hg2+ cations retaining > 99.7% across the pH range of ~2 to 12. Our study also shows that the CoAl―Mo2S12 is a highly competent silver cation adsorbent exhibiting removal capacity (qm) as high as ~918 mg/g compared with the reported data. A detailed mechanistic analysis of the post-treated solid samples with Ag+, Hg2+, and Pb2+ reveals the formation of Ag2S, HgS, and PbMoO4, respectively, suggesting the precipitation reaction mechanism. 

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