Coordination Geometry Research Articles

Quasi-open Cu(I) sites for efficient CO separation with high O2/H2O tolerance.

Carbon monoxide (CO) separation relies on chemical adsorption but suffers from the difficulty of desorption and instability of open metal sites against O2, H2O and so on. Here we demonstrate quasi-open metal sites with hidden or shielded coordination sites as a promising solution. Possessing the trigonal coordination geometry (sp2), Cu(I) ions in porous frameworks show weak physical adsorption for non-target guests. Rational regulation of framework flexibility enables geometry transformation to tetrahedral geometry (sp3), generating a fourth coordination site for the chemical adsorption of CO. Quantitative breakthrough experiments at ambient conditions show CO uptakes up to 4.1 mmol g-1 and CO selectivity up to 347 against CO2, CH4, O2, N2 and H2. The adsorbents can be completely regenerated at 333-373 K to recover CO with a purity of >99.99%, and the separation performances are stable in high-concentration O2 and H2O. Although CO leakage concentration generally follows the structural transition pressure, large amounts (>3 mmol g-1) of ultrahigh-purity (99.9999999%, 9N; CO concentration < 1 part per billion) gases can be produced in a single adsorption process, demonstrating the usefulness of this approach for separation applications.

Deformation of pairs and Noether–Lefschetz loci in toric varieties

We continue our study of the Noether–Lefschetz loci in toric varieties and investigate deformation of pairs (V, X) where V is a complete intersection subvariety and X a quasi-smooth hypersurface in a simplicial projective toric variety PΣ2k+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathbb {P}_{\\Sigma }^{2k+1}$$\\end{document}, with V⊂X\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V\\subset X$$\\end{document}. The hypersurface X is supposed to be of Macaulay type, which means that its toric Jacobian ideal is Cox–Gorenstein, a property that generalizes the notion of Gorenstein ideal in the standard polynomial ring. Under some assumptions, we prove that the class λV∈Hk,k(X)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda _V\\in H^{k,k}(X)$$\\end{document} deforms to an algebraic class if and only if it remains of type (k, k). Actually we prove that locally the Noether–Lefschetz locus is an irreducible component of a suitable Hilbert scheme. This generalizes Theorem 4.2 in our previous work (Bruzzo and Montoya 15(2):682–694, 2021) and the main theorem proved by Dan (in: Analytic and Algebraic Geometry. Hindustan Book Agency, New Delhi, pp 107–115, 2017).

Cu(II) coordination polymers based on 1,3,5-tris(triazol-1-ylmethyl)-2,4,6-trimethylbenzene: synthesis, structure, and biological properties

Two new Cu(II)-based coordination polymers, [Cu(TTTMB)(Hbtrc2−)]n (1) and {[Cu(TTTMB)2(H2O)2](NO3)2(H2O)4}n (2), were synthesized under hydrothermal conditions (TTTMB = 1,3,5-tris(triazol-1-ylmethyl)-2,4,6-trimethylbenzene; H3btrc = 1,3,5-trimesic acid). The structures of these polymers were established by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Polymer 1 displays a three-dimensional (3-D) structure with the Schläfli symbol (4·62)(4·67·82) and crystallizes in the monoclinic space group P2(1)/n. Each Cu(II) in 1 is five-coordinate in a slightly distorted rectangular pyramid geometry. Polymer 2 has a 2-D network structure with (4,4) topology and each Cu(II) ion has a slightly distorted octahedral coordination geometry. The antidiabetic activity against α-amylase and antioxidant activity against DPPH of the two Cu(II)-based complexes were evaluated in vitro. Polymers 1 (IC50 = 1.43 mg/mL) and 2 (IC50 = 2.45 mg/mL) exhibited more effective inhibition on α-amylase than the standard drug acarbose (IC50 = 2.94 mg/mL). The results of the antioxidant studies revealed that 2 demonstrated a potent scavenging effect on DPPH with IC50 values of 2.59 mg/mL, slightly lower than that of vitamin E (2.67 mg/mL).

Point Defects in Silicon-Doped β-Ga2O3: Hybrid-DFT Calculations.

In this work, hybrid density functional theory calculations are used to evaluate the structural and electronic properties and formation energies of Si-doped β-Ga2O3. Overall, eight interstitial (Sii) and two substitutional (SiGa) positions are considered. In general, our results indicate that the formation energy of such systems is significantly influenced by the charge state of the defect. It is confirmed that it is energetically more favorable for the substitution process to proceed under Ga-poor growth conditions than under Ga-rich growth conditions. Furthermore, it is confirmed that the formation of SiGaI with a tetrahedral coordination geometry is more favorable than the formation of SiGaII with an octahedral one. Out of all considered interstitial positions, due to the negative formation energy of the Si +3 charge state at i8 and i9 interstitial positions over the wide range of Fermi energy, this type of defect can be spontaneously stable. Finally, due to a local distortion caused by the presence of the interstitial atom as well as its charge state, these systems obtain a spin-polarized ground state with a noticeable magnetic moment.

Syntheses and characterizations of two-dimensional heteronuclear tetracyanonickelate(II) complexes with 4-ethylpyridine and investigation of the catalytic activity of [Cd(4epy)2Ni(µ-CN)4

Three new 2D heteronuclear tetracyanonickelate(II) complexes with 4-ethylpyridine (4epy), [Cu(4epy)2Ni(µ-CN)4]n (1), [Zn(4epy)2Ni(µ-CN)4]n (2) and [Cd(4epy)2Ni(µ-CN)4]n (3), were synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, elemental and thermal analyses, single crystal (SC-XRD) and powder X-ray diffraction (PXRD) techniques. The single crystal X-ray analysis reveals that each metal ion (Cu(II), Zn(II), and Cd(II)) is coordinated by two nitrogen atoms from 4epy ligands and four nitrogen atoms from cyanide ligands and Ni(II) ions are coordinated by four carbon atoms from cyanide ligands showing a distorted octahedral and square planar coordination geometries, respectively. The most outstanding features of the complexes are the weak intermolecular C–H⋅⋅⋅Ni interactions between the Ni(II) ion and hydrogen atom of the ethyl group of the 4epy ligand. Adjacent 2D structures are further combined by these C–H⋅⋅⋅Ni interactions, generating a 3D network. The heterogeneous catalytic activity of 3 was investigated for oxidation of some primary and secondary aliphatic or aromatic alcohols; no acid formation was observed in some aromatic alcohols after 24 h and 100% aldehyde selectivity was determined.

Syntheses, Structures, Structural Transformation, and Properties of Neodymium Sulfate Based Inorganic Networks

AbstractTwo neodymium sulfate based purely inorganic networks, [NH4][Nd(SO4)2(H2O)3] ⋅ H2O (1) and [Nd2(SO4)3(H2O)4] ⋅ H2O (2) have been synthesized at different reaction temperatures and pH values. The structure of 1 features a two‐dimensional (2D) anionic corrugated sheet with an sql topological net built up by linking NdO8 units and μ2‐SO42− anions, in which the NH4+ charge‐compensating/templating cations occupy the intersheet layers. While 2 possesses a 3D neutral framework with an unprecedented (3,42,7‐c) net constructed by NdO9 units and μ4‐ and μ6‐SO42− linkers. They exhibit thermally induced irreversible structural transformation associated with the dehydration and the changes in coordination geometry and dimensionality. Both compound 1 and 2 display typical antiferromagnetic interactions between the Nd3+ centres. In addition, the CO2 adsorption isotherms of the desolvated samples 1 and 2 were also investigated.

MESPEUS: a database of metal coordination groups in proteins.

MESPEUS is a freely accessible database which uses carefully selected metal coordination groups found in metalloprotein structures taken from the Protein Data Bank. The database contains geometrical information of metal sites within proteins, including 40 metal types. In order to completely determine the metal coordination, the symmetry-related units of a given protein structure are taken into account and are generated using the appropriate space group symmetry operations. This permits a more complete description of the metal coordination geometry by including all coordinating atoms. The user-friendly web interface allows users to directly search for a metal site of interest using several useful options, including searching for metal elements, metal-donor distances, coordination number, donor residue group, and structural resolution. These searches can be carried out singly or in combination. The details of a metal site and the metal site(s) in the whole structure can be graphically displayed using the interactive web interface. MESPEUS is automatically updated monthly by synchronizing with the PDB database. An investigation for the Mg-ATP interaction is given to demonstrate how MESPEUS can be used to extract information about metal sites by selecting structure and coordination features. MESPEUS is available at http://mespeus.nchu.edu.tw/.

Highly selective recovery of yttrium from mining wastewater using biosynthetic iron sulfide nanoparticles

The selective recovery of rare earth elements (REEs) from mining wastewater has become a hot research topic due to the increasing industrial value of REEs. Herein, biosynthetic iron sulfide nanoparticles (nFeS) were deployed as a superior adsorbent to selectively recover Y(Ⅲ) from mining wastewater. The maximum adsorption efficiency achieved for of Y(Ⅲ) by nFeS was 81.2 % compared to only 38.7 % for Eu(Ⅲ) and 20.8 % for Mn(Ⅱ), demonstrating that nFeS had a high selective adsorption for Y(Ⅲ). To understand the origins of the high selectivity of nFeS, the removal of REEs by the capping layer and the FeS-core were separately investigated. Specifically, given the hard and soft acid base principle (HASB) and the square antiprism coordination geometry of Y(Ⅲ), the adsorption of Y(Ⅲ) by the capping layer was predominantly attributed to CO and –NH2 serving as a monodentate ligand to strongly chelate with Y(Ⅲ), while Y(Ⅲ) interacted with Fe–O on the FeS-core and –COOH more via ion-exchange with Y(Ⅲ). Collectively, cooperative interactions between the capping layer and FeS-core resulted in the overall highly selective adsorption of Y(Ⅲ) by nFeS, suggest this approach has significant potential for future practical remediation and recovery applications to Y(Ⅲ) rich mining wastewaters.

Fundamental understanding on cyclability behaviors of ammonium vanadate nanoarchitectures as cathode materials for Li-ion batteries: A comparative insight of dual modification of precursor and morphology

Development of high-performance Li-ion battery electrodes has emerged as an important issue for satisfying good rate capability and long cycle life during electrochemical lithium (de) intercalation. As cathode materials, vanadium-based compounds are very appealing for energy-storage applications owing to their multiple valence states and coordination geometries. However, they still face bottlenecks such as less stable layered structure and intrinsically low ionic/electronic conductivity. This investigation records on two main parts of new strategic design and electrochemical lithium storage for NH4V4O10 (NHV) cathode nanostructures. NHV structures with diverse motifs (i.e. mat-like sheet, square-sheet microflowers, belt-based microflowers, and nano-belt) were systematically fabricated by tailoring the combined reducing agents (H2C2O4 + KSCN and K2C2O4 + HCl), and its concentrations under controlled hydrothermal protocol. Benefiting from H2C2O4 + KSCN as a mixed precursor in different molar ratios (2,1, 1,1, and 1:2), the electrode materials with various shapes such as mat-like sheet, square-sheet microflowers, belt-based microflowers achieved high specific capacities of 132.02, 162.54 and 172.02 mAh g−1, respectively. From results, the nanobelt-like NHV synthesized by the reducing environment of K2C2O4 + HCl with molar ratio of 1:2 at 180 °C for 24 h delivered an extraordinary discharge capacity of 196.76 mAh g−1 at a current density of 30 mA g−1 in a potential region of 1.8–4.0 V, which reach 87.28 % capacity retention over 50 cycles. However, in the process of using K2C2O4 + HCl, the change in hydrothermal conditions led to a decrease in the storage capacity and cyclability behavior. Such results will potentially help in engineering a novel strategy toward developing electrochemically appropriate constructions, which offer efficient vanadate-based nanostructures via modifying the structure and morphology with improved pathway for rapid electron transfer.

Effect of Metal Environment and Immobilization on the Catalytic Activity of a Cu Superoxide Dismutase Mimic

The Cu(II)/Cu(I) conversion involves variation in the coordination number and geometry around the metal center. Therefore, the flexibility/rigidity of the ligand plays a critical role in the design of copper superoxide dismutase (SOD) mimics. A 1,3-Bis[(pyridin-2-ylmethyl)(propargyl)amino]propane (pypapn), a flexible ligand with an N4-donor set, was used to prepare [Cu(pypapn)(ClO4)2], a trans-Cu(II) complex whose structure was determined by the X-ray diffraction. In DMF or water, perchlorate anions are exchanged with solvent molecules, affording [Cu(pypan)(solv)2]2+ that catalyzes O2•− dismutation with a second-order rate constant kMcF = 1.26 × 107 M−1 s−1, at pH 7.8. This high activity results from a combination of ligand flexibility, total charge, and labile binding sites, which places [Cu(pypapn)(solv)2]2+ above other mononuclear Cu(II) complexes with more favorable redox potentials. The covalent anchoring of the alkyne group of the complex to azide functionalized mesoporous silica through “click” chemistry resulted in the retention of the SOD activity and improved stability. A dicationic Cu(II)-N4-Schiff base complex encapsulated in mesoporous silica was also tested as an SOD mimic, displaying higher activity than the free complex, although lower than [Cu(pypapn)(solv)2]2+. The robustness of covalently attached or encapsulated doubly charged Cu(II) complexes in a mesoporous matrix appears as a suitable approach for the design of copper-based hybrid catalysts for O2•− dismutation under physiological conditions.

Empowering nuclear reactor analysis: OpenNode for accurate 3D core simulation through nodal expansion neutron diffusion equations solving

OpenNode is a sophisticated reactor core simulation tool, meticulously designed for educational purposes. Its main function is to solve the complex partial differential equation governing multi-group neutron diffusion in a Cartesian geometry. OpenNode relies on the second- and fourth-order Nodal Expansion Method (NEM) to provide accurate solutions to three-dimensional steady-state problems, encompassing both the direct and adjoint modes. At the heart of this method, the neutron balance equation serves as the fundamental framework for calculating the nodal neutron flux and the effective multiplication factor, enabling the complex evaluation of neutron flux distributions within individual nodes.The NEM methodology, carefully programmed in Fortran-90 in OpenNode, meticulously decomposes the reactor core into nodes of reasonable size. This approach balances computational efficiency and accuracy, achieving outstanding precision even when using a reduced number of computational meshes. To further increase the number of equations while maintaining the balance between unknowns, OpenNode judiciously incorporates two essential approximations: the Weighted Residual Method (WRM) and the Quadratic Transverse Leakage (QTL) approximation.OpenNode transcends simple computational prowess by adopting an intuitive Graphical User Interface (GUI), meticulously developed by combining Python 3, Qt Designer, and Blender software. This Python-powered graphical interface offers users a seamless, user-friendly experience, facilitating tasks such as data entry, execution of complex simulations, calculation of results, data visualization, 3D design of nuclear core geometry, and in-depth analysis of results. One of OpenNode’s key features is its innate flexibility, enabling it to solve problems in both 2D and 3D Cartesian geometries. This adaptability makes it a versatile tool suitable for a wide range of research and power reactor applications, offering users the ability to model and design reactors with unrivaled ease.To substantiate OpenNode’s reliability, comprehensive criticality calculations are carried out in various scenarios, including single-cell verification, BIBLIS, KOEBERG cores in two dimensions (2D), and IAEA cores in three dimensions (3D). The results clearly demonstrate OpenNode’s robustness and reliability in multidimensional criticality analysis. In particular, OpenNode adheres to an open-source philosophy, making it readily available for download. This commitment to open access fosters collaboration and paves the way for wider adoption within the education and research communities, nurturing a thriving ecosystem of shared knowledge and exploration.

Synthesis, X-ray Structures and Hirshfeld Analysis of Two Novel Thiocyanate-Bridged Ag(I) Coordination Polymers

Two novel silver(I) coordination polymers, [Ag(4BP)(SCN)]n (1) and {(4BPH)+[Ag(SCN)2]−}n (2) (4BP = 4-benzoyl pyridine), have been synthesized. The two complexes were prepared using almost the same reagents, which were AgNO3, 4BP and NH4SCN. The only difference was the presence of 1:1 (v/v) HNO3 in the synthesis of 2. In the two complexes, the Ag(I) has distorted tetrahedral coordination geometry. The structure of both complexes and the involvement of the thiocyanate anion as a linker between the Ag(I) centers were confirmed using single-crystal X-ray diffraction. 4BP participated as a monodentate ligand in the coordination sphere of complex 1, while in 2 it is found protonated (4BP-H)+ and acts as a counter ion, which balances the charge of the anionic [Ag(SCN)2]− moiety. The thiocyanate anion shows different coordination modes in the two complexes. In complex 1, the thiocyanate anion exhibits a µ1,1,3 bridging mode, which binds three Ag(I) ions to build a boat-like ten-membered ring structure leading to a two-dimensional coordination polymer. In 2, there are mixed µ1,1 and µ1,3 bridging thiocyanate groups, which form the one-dimensional polymeric chain running in the a-direction. Several interactions affected the stability of the crystal structure of the two complexes. These interactions were examined using Hirshfeld surface analysis. The coordination interactions (Ag-S and Ag-N) have a great impact on the stability of the polymeric structure of the two complexes. Additionally, the hydrogen-bonding interactions are crucial in the assembly of these coordination polymers. The O…H (10.7%) and C…H (34.2%) contacts in 1 as well as the N···H (15.3%) and S···H (14.9%) contacts in 2 are the most significant. Moreover, the argentophilic interaction (Ag…Ag = 3.378 Å) and π- π stacking play an important role in the assembly of complex 2.

Introduction to non-convex fuzzy geometry

This study is an extension of the recently developed theory on analytical fuzzy geometry with fuzzy numbers and fuzzy points. In the existing study, both the fuzzy numbers and fuzzy points are convex and normal fuzzy sets in nature. However, in reality, considering fuzzy objects as convex and normal sets is an oversimplified assumption. Here, the nature of non-convex and non-normal fuzzy sets is studied. In the first part of this paper, the concept of same points has been extended for non-convex and non-normal fuzzy sets. A computationally efficient method for extended addition, subtraction, multiplication, and division of two generalized fuzzy sets is proposed using the extended concept of same points. The proposed procedure drastically reduces the computational complexity of extended arithmetic operations on two generalized fuzzy sets drastically.In the second part of this paper, the genesis and morphology of fuzzy points are studied. The conjunction of non-convex fuzzy sets generates a new class of study which is termed as non-convex or generalized fuzzy geometry where the generalized fuzzy point is the key concept. The effect of different t-norms as a conjunction operator on fuzzy sets is studied with geometrical visualization. The extended arithmetic operations between generalized fuzzy points have been defined using the extended concept of same points developed here. The formation of the locus of a non-convex fuzzy point as a fuzzy line segment has also been introduced.

New binuclear copper(I) complexes with dual bioactivity: Synthesis, structural characterization and biological assays against bacteria and cancer

Novel binuclear heteroleptic copper(I) complexes based on mixed DPPE /thiocarbamoyl-pyrazoline ligands were synthesized and structurally characterized. Accordingly, the X-ray studies the three prepared complexes belong to the monoclinic crystalline system. All complexes 1, 2, and 3 possess similar structural behavior around the Copper(I) atoms which presented a distorted tetrahedral coordination geometry determined by using the τ4 (tau four) parameter analysis. The complete characterization of the prepared compounds also included HRMS-ESI(+), NMR and elemental analyses, MID infrared, and UV–Vis spectroscopies. TD-DFT studies were also performed to support the assignments and interpretation of the main absorption bands observed in the UV–Vis experiments. The binuclear CuI complexes were assayed against a panel of antibiotic-resistant (MDR) bacteria (S. aureus) and S. pseudointermedius (MDR isolated from dog skin) showing promising MIC (7.8 to 62.5 µg/mL) and MBC (15.6 to 62.5 µg/mL) values. Additionally, the binuclear complexes were also tested as anticancer agents against tumoral cells B16F10 and 4 T1 (metastatic murine melanoma and murine mammary carcinoma respectively) showing very low IC50 (0.16 to 0.6 µM) values.

Why the Golden Spiral is Golden

Summary It is shown that there is a logarithmic spiral that segments a straight line through its pole in the golden ratio ϕ . This is the same spiral that is often referred to in the literature as the “Golden Spiral” Using the tools of analytic geometry and parametric vector equations, it is shown that the golden spiral is actually a member of a family of spirals defined by a generalized equation. The spirals exist as a continuum defined by a real number q > 1. When q = ϕ , the spiral segments a line through its pole in the golden ratio. That is the characteristic feature that sets it apart from all the other spirals in the continuum.

Crystal structure and Hirshfeld surface analysis of poly[[tetra-aqua-(μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-[8.8.4.13,17.18,12]tetra-cosane-5,6,14,15,20,21-hexaonato)iron(IV)dilithium] tetra-hydrate

The title compound, [FeLi2(C12H12N12O6)(H2O)4]·4H2O, consists of iron complex anions, lithium cations and water mol-ecules. The complex anion shows a clathrochelate topology. The coordination geometry of the FeIV centre is inter-mediate between a trigonal prism and a trigonal anti-prism. In the crystal, the complex anions are connected through two Li cations into dimers, which are connected by Li-O bonds, forming infinite chains along the b-axis direction.

Insights into molecular mechanisms of metallodrugs using metallomic studies

Metal ions are the center of an important class of therapeutics, i.e. metallodrugs for their unique coordination geometries and redox states. Many cellular functions depend on the interaction of metal ions with proteins, as well as the transport and uptake of metals into cells, storage and secretion which are regulated by peculiar control systems. The cellular redox homeostasis is regulated by a plethora of factors including metal ions that can produce reactive radicals and its dysregulation can lead to oxidative stress as observed in pathological conditions in many diseases as cancer, cardiovascular disease, diabetes, atherosclerosis, neurological disorders (Alzheimer’s, Parkinson’s disease) and chronic inflammation. Omics approaches can provide in-depth insights into the mechanisms of action (MOAs) of metallo-therapeutic compounds and metallomics is a proteomic tool that allows to investigate MOAs of metallodrugs, including their physiological metabolism (e.g., cellular distribution and biotransformation) and their molecular targets. Herein, we review the most recent and significant metallomic studies concerning metallodrugs in pathological cellular conditions including oxidative stress.

Photoluminescence and Radiation Luminescence in a Hybrid Cuprous (I) Halide: (4,4‐Difluoro‐bipiperidinium)3Cu2I5

AbstractCopper (I) based halide scintillators have received high attention due to their high light yield. At the same time, researchers are increasingly interested in exploring organic‐inorganic hybrid copper(I) based halides, due to the diversity and tunability of structures. Here, we describe high‐efficiency photoluminescence and X‐ray excited luminescence in (DFPD)3Cu2I5 (1) (DFPD=4,4‐difluoro‐bipiperidinium). 1 is comprised of a unique [Cu2I5]3− cluster, which have typical structure allowing high‐transition‐probability self‐trapped exciton emission (one Cu+ ion adopts the tetrahedral coordination geometry, the other trigonal planar coordination geometry, the Cu−Cu distance (2.574 Å) is short). Accordingly, 1 shows efficient yellow‐green photoluminescence with the maximum at 527 nm, a full‐width at half‐maximum of 99.2 nm, a large Stokes shift of 214 nm (1.6 eV) and a quantum yield of 77.15 %. Polycrystalline 1 can also convert high‐energy X‐ray photons into UV‐visible pulsed fluorescence with the light yield of 5000 photons/MeV. This finding plays a valuable role in the development of organic‐inorganic hybrid copper(I) based scintillators.

Co and Cu crystalline frameworks built with nitrogen heterocycle polycarboxylic acids and their catalytic property towards the reduction of p-nitrophenol

Nitrogen heterocyclic polycarboxylic acid is a type of ligands with excellent coordination ability and rich conformations. Two metal complexes, ([Co2(L1)2(CH3COO)(H2O)3]‧(CH3COO)‧H2O (1) (HL1 = 4-[2,6-bis(pyrazin-2-yl) pyrid-4-yl]benzoic acid)) and (Cu2(L2)(H2O) (2) (H4L2 = 5-[6-(3,5-dicarboxy phenylamino)pyrid-2-ylamino]benzene-1,3-dicarboxylic acid)) were synthesized with transition metal salts and nitrogen heterocycle polycarboxylic acid ligands by solvothermal method. Both complexes were characterized by infrared and ultraviolet spectroscopy, powder X-ray diffraction analysis, and thermogravimetric analysis. The X-ray single crystal structural analysis shows that complex 1 is a one-dimensional double-chain supramolecular structure built by intermolecular hydrogen bonds. While complex 2 is a three-dimensional framework with multiple channels, where the two independent Cu(II) metals are five-coordinated to form a square pyramidal coordination geometry. In addition, in order to investigate the functional properties of the two complexes, catalytic reduction experiments towards p-nitrophenol were carried out preliminarily. The reduction efficiency above 96 % demonstrates their potential as catalysts.

Differences in heavy metal binding to cysteine-containing coiled-coil peptides.

One third of all structurally characterised proteins contain a metal; however, the interplay between metal-binding and peptide/protein folding has yet to be fully elucidated. To better understand how metal binding affects peptide folding, a range of metals should be studied within a specific scaffold. To this end, we modified a histidine-containing coiled-coil peptide to create a cysteine-containing scaffold, named CX3C, which was designed to bind heavy metal ions. In addition, we generated a peptide named CX2C, which contains a binding site more commonly found in natural proteins. Using a combination of analytical techniques including circular dichroism (CD) spectroscopy, UV-Vis spectroscopy and size-exclusion chromatography coupled to multi-angle light scattering (SEC-MALS), we examined the differences in the metal-binding properties of the two peptides. Both peptides are largely unfolded in the apo state due to the disruption of the hydrophobic core by inclusion of the polar cysteine residues. However, this unfolding is overcome by the addition of Cd(II), Pb(II) and Hg(II), and helical assemblies are formed. Both peptides have differing affinities for these metal ions, a fact likely attributed to the differing sizes of the ions. We also show that the oligomerisation state of the peptide complexes and the coordination geometries of the metal ions differ between the two peptide scaffolds. These findings highlight that subtle changes in the primary structure of a peptide can have considerable implications for metal binding.