Tetrahedral Zinc Research Articles

Synthesis and Structural Characterization of 2,2’-Bipyridine Zinc Formate: Analysis of Formate Bonding and Hydrosilylation of CO2 and Carbonyl Compounds

The zinc formate compound (bipy)Zn(O2CH)2 is obtained via the reaction of Zn(O2CH)2 with 2,2’-bipyridine (bipy). In addition, (bipy)Zn(O2CH)2 may be formed from zinc hydride via addition of bipy followed by addition of (i) HCO2H and (ii) CO2. The molecular structure of (bipy)Zn(O2CH)2 has been determined by X-ray diffraction, thereby demonstrating that it exists as a monomeric species with a distorted tetrahedral zinc center and κ1-monodentate formate ligands. As such, the coordination environment of the zinc provides a contrast to the octahedral sites in the isomeric 4,4’-bipyridine counterpart, (bipy4,4’)Zn(O2CH)2, and the aqua derivative, (bipy)Zn(O2CH)2(OH2)•H2O, both of which feature bridging formate ligands. Analysis of the bonding within the formate ligand indicates that the zinc–formate moiety is not best represented by a Zn–O–C(=O)H resonance structure, but instead possesses a significant ionic component that reduces the C=O bond order and increases the C–O bond order. The formate compound (bipy)Zn(O2CH)2 participates in hydrosilylation transformations involving CO2 and carbonyl compounds, including (i) the reaction of CO2 with (MeO)3SiH to afford HCO2Si(OMe)3 and (ii) insertion of Ph2CO, PhC(O)Me, Me2CO and PhCHO into the Si–H bonds of PhSiH3 to afford PhSi[OCH(R)R’]3via PhSiH2[OCH(R)R’] and PhSiH[OCH(R)R’]2.

Mutant-selective AKT inhibition through lysine targeting and neo-zinc chelation.

Somatic alterations in the oncogenic kinase AKT1 have been identified in a broad spectrum of solid tumours. The most common AKT1 alteration replaces Glu17 with Lys (E17K) in the regulatory pleckstrin homology domain1, resulting in constitutive membrane localization and activation of oncogenic signalling. In clinical studies, pan-AKT inhibitors have been found to cause dose-limiting hyperglycaemia2-6, which has motivated the search for mutant-selective inhibitors. We exploited the E17K mutation to design allosteric, lysine-targeted salicylaldehyde inhibitors with selectivity for AKT1 (E17K) over wild-type AKT paralogues, a major challenge given the presence of three conserved lysines near the allosteric site. Crystallographic analysis of the covalent inhibitor complex unexpectedly revealed an adventitious tetrahedral zinc ion that coordinates two proximal cysteines in the kinase activation loop while simultaneously engaging the E17K-imine conjugate. The salicylaldimine complex with AKT1 (E17K), but not that with wild-type AKT1, recruits endogenous Zn2+ in cells, resulting in sustained inhibition. A salicylaldehyde-based inhibitor was efficacious in AKT1 (E17K) tumour xenograft models at doses that did not induce hyperglycaemia. Our study demonstrates the potential to achieve exquisite residence-time-based selectivity for AKT1 (E17K) by targeting the mutant lysine together with Zn2+ chelation by the resulting salicylaldimine adduct.

A tetrahedral zinc(II) coordination polymer: Synthesis, characterisation, and application in ascorbic Acid fluorescence sensing

A new coordination polymer (CP), {[Zn(HL)₂(bib)]ₙ.0·25H2O} (1), was synthesized and characterized for its structural, thermal, and luminescence properties. The compound was obtained by reacting H3L= 3-(4-carboxyphenoxy)-5-methylbenzoic acid, bib = 1,4-bis(1-imidazoly)benzene, and Zn(ClO₄)₂·6H₂O in aqueous solution, followed by hydrothermal treatment at 120 °C for 72 h. Single-crystal X-ray diffraction revealed a 1D polymeric chain with zinc centres in a distorted tetrahedral geometry, coordinated by carboxylate and imidazole-based ligands. Infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) confirmed the bonding environment and thermal stability. CP 1 exhibited strong luminescence, peaking at 205 nm upon excitation at 285 nm, and demonstrated selective sensing of ascorbic acid (AA) with a high quenching efficiency (Ksv = 4.35 × 10² M⁻¹) and a detection limit of 3.15 × 10⁻4 M The luminescence was pH-dependent, with optimal fluorescence near neutral pH. These findings highlight the potential of CP 1 as a sensitive probe for AA detection, offering applications in environmental monitoring and chemical sensing.

Zinc Nanoparticles and Nanocomposite Membrane Synthesized Using Leaves of Cinnamomum Tamala(Tejpatta) and Packaging Potential in Food Sector

ABSTRACT: Zinc oxide nanoparticles were synthesized using leaves of Tejpatta (Cinnamomum tamala) readily available as local herb in India. First confirmation was made by change of color of plant extract into cream color solution for zinc nanoparticle synthesis. The plant used as capping and reducing agent showed absorption peak of 329.4nm for zinc nanoparticle. While FESEM analysis further validated the nature of nano-particle synthesized of tetrahedral and crystalline zinc nanoparticles. The plant parts can be exploited for drug development as the plant is available in plenty growing all over arid region. Nanobiotech has served in recent years and utilized natural polymers or polymeric films, which have overcome the side effects of synthetic packaging films available commercially. The safety assessment should be in agreement with scientific advisory committee before permitting to packaging industries. The texture, flavor, processing, shelf life and transport of foods will become economical to meet the demand of food safety for future generations. Generally regarded as safe, packaging materials can be considered for globalization and revolution in food packaging sector. The present investigation reports zinc nanoparticle synthesis where potent zone of inhibition were reported against standard pathogen S. aureus and nanocomposite membranes were synthesized using different polymeric components available in reach like gelatin, sodium alginate and agarose instead of cellulose. The research will be further supplemented with application of biomembrane synthesized in antimicrobial resistance offered to food products.

Anti-toxoplasma activity and DNA-binding of copper(II) and zinc(II) coordination compounds with 5-nitroimidazole-based ligands.

Tetrahedral copper(II) and zinc(II) coordination compounds from 5-nitroimidazole derivatives, viz. 1-(2-chloroethyl)-2-methyl-5-nitroimidazole (cenz) and ornidazole 1-(3-chloro-2-hydroxypropyl)-2-methyl-5-nitroimidazole (onz), were synthesized and spectroscopically characterized. Their molecular structures were determined by X-ray diffraction studies. The complexes [Cu(onz)2X2], [Zn(onz)2X2], [Cu(cenz)2X2] and [Zn(cenz)2X2] (X- = Cl, Br), are stable in solution and exhibit positive LogD7.4 values that are in the range for molecules capable of crossing the cell membrane via passive difussion. Their biological activity against Toxoplasma gondi was investigated, and IC50 and lethal dose (LD50) values were determined. The ornidazole copper(II) compounds showed very good antiparasitic activity in its tachyzoite morphology. The interaction of the coordination compounds with DNA was examined by circular dichroism, fluorescence (using intercalating ethidium bromide and minor groove binding Hoechst 33258) and UV-Vis spectroscopy. The copper(II) compounds interact with the minor groove of the biomolecule, whereas weaker electrostatic interactions take place with the zinc(II) compounds. The spectroscopic data achieved for the two series of complexes (namely with copper(II) and zinc(II) as metal center) agree with the respective DNA-damage features observed by gel electrophoresis.

Mechanisms of Zn removal from water by amorphous geopolymer: Molecular-level insights from X-ray absorption spectroscopy, isotope fractionation, and surface complexation modeling

Porous geopolymers have attracted widespread attention as promising heavy metal adsorbents that can be synthesized from aluminosilicate solid wastes. However, the precise microstructural evidence for adsorbed heavy metals on geopolymers remains unclear due to the insensitivity of conventional characterization techniques on minerals with amorphous structure and surface disorder. Batch adsorption and column experiments coupled with X-ray absorption spectroscopy (XAS), Zn stable isotope, and surface complexation model (SCM) were employed to reveal the Zn removal mechanisms with coal fly ash porous geopolymer (CFAPG) at a molecular scale. The macroscopic kinetic and isothermal adsorption of Zn on CFAPG were well described by the pseudo-second-order model and Bi_Langmuir equation, respectively, indicating the presence of abundant heterogeneous active sites on the CFAPG surface. Two types of active sites on the CFAPG surface were identified by XAS coupled with Zn isotopes in batch experiments at pH ≤ 6.0: one is pH-dependent and associated with tetrahedral zinc coordination, and the other is pH-insensitive and associated with octahedral zinc coordination; these sites were confirmed by the bidentate SCM as the variable charge site (surface complexation, >S-OH) and the permanent negative charge site (cation exchange, >X–), respectively. Furthermore, the important contribution of surface co-precipitation besides surface complexation and cation exchange to the Zn adsorption on CFAPG was identified by XAS coupled with SCM in a flow-through column experiment at pH >6.0. These investigations provide a systemic understanding of the Zn adsorption mechanisms on CFAPG and an SCM reference for the application and prediction of geopolymers in heavy metal-contaminated water remediations.

Novel Fluorescent Tetrahedral Zinc (II) Complexes Derived from 4-Phenyl-1-octyl-1H-imidazole Fused with Aryl-9H-Carbazole and Triarylamine Donor Units: Synthesis, Crystal Structures, and Photophysical Properties.

We present here the design, synthesis, and photophysical properties of two novel fluorescent zinc (II) complexes, ZnCl2(ImL1)2 and ZnCl2(ImL2)2, containing 4-(1-octyl-1H-imidazol-4-yl)-N,N-diphenyl-[1,1-biphenyl]-4-yl)-4-amine ImL1 and 9-(4-(1-octyl-1H-imidazol-4-yl)-[1,1-biphenyl]-4-yl)-9H-carbazole ImL2 ligands. The newly synthesized free ligands and their zinc (II) complexes were characterized using several spectroscopic techniques; their structures were identified by single-crystal X-ray diffraction; and their photophysical properties have been studied in the context of their chemical structure. The ZnCl2(ImL1)2 and ZnCl2(ImL2)2 complexes showed good thermal stability at 341 °C and 365 °C, respectively. Photophysical properties, including UV-Vis absorption spectra in ethanol solution and photoluminescence (PL) in both solid state and ethanol solution, were determined. UV-Vis adsorption data indicated that both free ligands had similar UV-Vis absorption properties, while their Zn (II) complexes had distinctive absorption characteristics. The fluorescence spectra show that both ligands and their corresponding Zn (II) complexes emit violet to cyan luminescence in the solid state at room temperature, while in ethanol solution at the same temperature, they exhibit efficient photoluminescence properties in the UV-A emission spectral region. Because of these photophysical properties, the synthesized ligands and their cognate Zn (II) complexes can be used as scaffolds for the potential development of optoelectronic materials.

In Situ Synthesis of Multivariate Zeolitic Imidazolate Frameworks for C2 H4 /C2 H6 Kinetic Separation.

Herein, a new approach for the in situ synthesis of zeolitic imidazolate framework (ZIF) nanoparticles with triple ligands, referred to as Sogang ZIF-8 (SZIF-8), is reported for enhanced C2 H4 /C2 H6 kinetic separation. SZIF-8 consists of tetrahedral zinc metals coordinated with tri-butyl amine (TBA), 2,4-dimethylimidazole (DIm), and 2-methylimidazole (MIm). SZIF-8(x) with different DIm contents in x (up to 23.2 mol%) are synthesized in situ because TBA preferably deprotonates DIm ligands due to the much lower pKa of DIm over MIm, allowing for the Zn-DIm coordination. The Zn-DIm coordination reduces the window size of ZIF-8 with suppressed linker flipping motion due to bulky DIm ligands and simultaneously enhances the interfacial interaction between 6FDA-DAM polyimide (6FDA) and SZIF-8 via electron donor-acceptor interactions. Consequently, 6FDA/SZIF-8(13) mixed matrix membrane exhibits an excellent C2 H4 permeability of 60.3 Barrer and C2 H4 /C2 H6 selectivity of 4.5. The temperature-dependent transport characterization reveals that such excellent C2 H4 /C2 H6 kinetic separation is attained by the enhancement in size discrimination-based energetic selectivity. Our hybrid multi-ligand approach can offer a useful tool for the fine-tuning of molecular structures and textural properties of other metal organic frameworks.

Unexpected formation of two different coordination polymers from the reaction of Zn(HCOO)2·2H2O with 1,2-bis(4-pyridyl)ethylene

Zn(HCOO)2·2H2O reacts with 1,2-bis(4-pyridyl)ethylene (bpe) yielding two new coordination polymers [Zn4(HCOO)8(bpe)2(H2O)]∞ (1) and [Zn2(HCOO)4(bpe)]∞ (2) which were structurally characterized by IR spectroscopy and single crystal X-ray diffraction study. The hydrate species 1 is a 3D polymer where four different zinc sites are present, the first of them, four-coordinated, being linked by three bridging formate and one bridging bpe, the second six-coordinated, with a ZnNO5 coordination environment, almost regular, due to three bridging formate groups and one monodentate formate, one water molecule and one bpe. The third zinc center in 1 is always tetrahedral with three bridging formate ligands and one bridging bpe whereas the fourth Zn site is coordinated by five bridging formate ligands and one bridging bpe. The anhydrous species 2, obtained upon recrystallisation from DMF at 278 K is a zig-zag 1D polymer with a tetrahedral N2O2 zinc coordination environment due to two monodentate formate groups and two bridging bpe. Thermal analysis of 1 show a weight loss due to water elimination followed by formate and bpe decomposition, whereas in the case of 2 only a decomposition between 210 and 240 °C was observed.

Crystallographic snapshots of ternary complexes of thermophilic secondary alcohol dehydrogenase from Thermoanaerobacter pseudoethanolicus reveal the dynamics of ligand exchange and the proton relay network.

Three-dimensional structures of I86A and C295A mutant secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter pseudoethanolicus were determined by x-ray crystallography. The tetrameric structure of C295A-SADH soaked with NADP+ and dimethyl sulfoxide (DMSO) was determined to 1.85 Å with an Rfree of 0.225. DMSO is bound to the tetrahedral zinc in each subunit, with ligands from SG of Cys-37, NE2 of His-59, and OD2 of Asp-150. The nicotinamide ring of NADP is hydrogen-bonded to the N of Ala-295 and the O of Val-265 and Gly-293. The O of DMSO is connected to a network of hydrogen bonds with OG of Ser-39, the 3'-OH of NADP, and ND1 of His-42. The structure of I86A-SADH soaked with 2-pentanol and NADP+ contains (R)-2-pentanol bound in each subunit, ligated to the tetrahedral zinc, and connected to the proton relay network. The structure of I86A-SADH soaked with 3-methylcyclohexanol and NADP+ has alcohol bound in three subunits. Two of the sites have the alcohol ligated to the zinc in an axial position, with OE2 of Glu-60 in the other axial position of a trigonal bipyramidal complex. One site has 3-methylcyclohexanol bound noncovalently, with the zinc in an inverted tetrahedral geometry with Glu-60. The fourth site also has the zinc in a trigonal bipyramidal complex with axial Glu-60 and water ligands. These structures demonstrate that ligand exchange of SADH involves pentacoordinate and inverted zinc complexes with Glu-60. Furthermore, we see a network of hydrogen bonds connecting the substrate oxygen to the external solvent that is likely to play a role in the mechanism of SADH.

Micro to Nano: Multiscale IR Analyses Reveal Zinc Soap Heterogeneity in a 19th-Century Painting by Corot.

Formation and aggregation of metal carboxylates (metal soaps) can degrade the appearance and integrity of oil paints, challenging efforts to conserve painted works of art. Endeavors to understand the root cause of metal soap formation have been hampered by the limited spatial resolution of Fourier transform infrared microscopy (μ-FTIR). We overcome this limitation using optical photothermal infrared spectroscopy (O-PTIR) and photothermal-induced resonance (PTIR), two novel methods that provide IR spectra with ≈500 and ≈10 nm spatial resolutions, respectively. The distribution of chemical phases in thin sections from the top layer of a 19th-century painting is investigated at multiple scales (μ-FTIR ≈ 102 μm3, O-PTIR ≈ 10-1 μm3, PTIR ≈ 10-5 μm3). The paint samples analyzed here are found to be mixtures of pigments (cobalt green, lead white), cured oil, and a rich array of intermixed, small (often ≪ 0.1 μm3) zinc soap domains. We identify Zn stearate and Zn oleate crystalline soaps with characteristic narrow IR peaks (≈1530-1558 cm-1) and a heterogeneous, disordered, water-permeable, tetrahedral zinc soap phase, with a characteristic broad peak centered at ≈1596 cm-1. We show that the high signal-to-noise ratio and spatial resolution afforded by O-PTIR are ideal for identifying phase-separated (or locally concentrated) species with low average concentration, while PTIR provides an unprecedented nanoscale view of distributions and associations of species in paint. This newly accessible nanocompositional information will advance our knowledge of chemical processes in oil paint and will stimulate new art conservation practices.

Synergistic role of carbon quantum dots in the activity and stability of Candida rugosa lipase encapsulated within metal–organic frameworks (ZIF-8)

Carbon quantum dots (CQDs) are particularly attractive in biosensing, bioimaging and drug delivery applications due to their luminescent properties, water dispersibility and favorable biocompatibility. In the study, by combining CQDs derived from edible mushroom Agaricus bisporus and zeolitic imidazolate frameworks (ZIFs) crystals, a new support material was prepared for encapsulation of Candida rugosa lipase. The study aimed to shed light on the activity, thermal and storage stability, and reusability of physically adsorbed or in-situ encapsulated enzyme. The enzyme loading efficiency of the in-situ encapsulation method was 3.11-fold higher (371 mg g−1). Also, catalytic activities were 119.8 U/g (CQDs@ZIF- 8@CRLenc) and 34.2 U/g (CQDs@ZIF-8@CRLads). The CQDs@ZIF-8@CRLenc with the biocatalytic activity was 3.5-folds higher than that of the CQDs@ZIF-8@CRLads. In the in-situ encapsulation, the CQDs and the enzyme were physically entrapped within three-dimensional structures of ZIF-8 that were constructed from tetrahedral zinc ions bridged by imidazolate. The structural, morphological, and spectrophotometric analyses were performed using TEM, SEM-EDX, FT-IR, XRD, UV–vis, fluorescence, and confocal microscopy. The effects of pH (4.0–9.0) and temperature (30–60 °C) on the enzymatic activity were studied and optimized. The coexistence of the CQDs and ZIF-8 crystals remarkably enhanced the activity, reusability, thermal resistance, and storage stability of the enzyme encapsulated within ZIF-8 crystals (the relative enzyme activity; after 6 re-uses: 73%, 2-hour-incubation at 60 °C: 70%, 5-week-storage at 4 °C: 70%). The CQDs from A. bisporus entrapped within ZIF-8 can synergistically enhance the catalytic performance and thermal/storage stability of immobilized C. rugosa lipase.

Evaluation of the Anticancer and DNA-Binding Characteristics of Dichloro(diimine)zinc(II) Complexes

Several metal diimine complexes have been reported to possess anticancer properties. To evaluate the anticancer properties of tetrahedral zinc(II) diimine complexes, six complexes were synthesized with the general formula M(N^N)Cl2 {where M = Zn, Pt and N^N = 2,2’-biquinoline (1), 2,2’-dipyridylketone (2) and 4-((pyridine-2-ylmethylene)amino)phenol (3)}. In general, the intrinsic DNA-binding constants for the different compounds exhibited values within close proximity; the changes in the viscosity of the CT-DNA upon binding to the compounds suggest intercalation-binding mode. Molecular docking study predicted that complexes containing the highly planar ligand 2,2’-biquinoline are capable to establish π–π interactions with nucleobases of the DNA; the other four complexes engaged in donor–acceptor interactions with DNA nucleobases. The six complexes and two reference drugs (cisplatin and sunitinib) were tested against two cancer cell lines (COLO 205 and RCC-PR) and one normal cell line (LLC-MK2), highlighting the better performance of the zinc(II) complexes compared to their platinum(II) analogues. Moreover, zinc(II) complexes have higher selectivity index values than the reference drugs, with promising anticancer properties.

A Water Molecule Triggers Guest Exchange at a Mono-Zinc Centre Confined in a Biomimetic Calixarene Pocket: a Model for Understanding Ligand Stability in Zn Proteins.

In this study, the ligand exchange mechanism at a biomimetic ZnII centre, embedded in a pocket mimicking the possible constrains induced by a proteic structure, is explored. The residence time of different guest ligands (dimethylformamide, acetonitrile and ethanol) inside the cavity of a calix[6]arene-based tris(imidazole) tetrahedral zinc complex was probed using 1D EXchange SpectroscopY NMR experiments. A strong dependence of residence time on water content was observed with no exchange occurring under anhydrous conditions, even in the presence of a large excess of guest ligand. These results advocate for an associative exchange mechanism involving the transient exo-coordination of a water molecule, giving rise to 5-coordinate ZnII intermediates, and inversion of the pyramid at the ZnII centre. Theoretical modelling by DFT confirmed that the associative mechanism is at stake. These results are particularly relevant in the context of the understanding of kinetic stability/lability in Zn proteins and highlight the key role that a single water molecule can play in catalysing ligand exchange and controlling the lability of ZnII in proteins.

Structurally Modelling the 2-His-1-Carboxylate Facial Triad with a Bulky N,N,O Phenolate Ligand.

We present the synthesis and coordination chemistry of a bulky, tripodal N,N,O ligand, ImPh2NNO tBu (L), designed to model the 2‐His‐1‐carboxylate facial triad (2H1C) by means of two imidazole groups and an anionic 2,4‐di‐tert‐butyl‐subtituted phenolate. Reacting K‐L with MCl2 (M = Fe, Zn) affords the isostructural, tetrahedral non‐heme complexes [Fe(L)(Cl)] (1) and [Zn(L)(Cl)] (2) in high yield. The tridentate N,N,O ligand coordination observed in their X‐ray crystal structures remains intact and well‐defined in MeCN and CH2Cl2 solution. Reacting 2 with NaSPh affords a tetrahedral zinc thiolate complex, [Zn(L)(SPh)] (4), that is relevant to isopenicillin N synthase (IPNS) biomimicry. Cyclic voltammetry studies demonstrate the ligand's redox non‐innocence, where phenolate oxidation is the first electrochemical response observed in K‐L, 2 and 4. However, the first electrochemical oxidation in 1 is iron‐centred, the assignment of which is supported by DFT calculations. Overall, ImPh2NNO tBu provides access to well‐defined mononuclear, monoligated, N,N,O‐bound metal complexes, enabling more accurate structural modelling of the 2H1C to be achieved.

Asymmetric construction of tetrahedral chiral zinc with high configurational stability and catalytic activity

Chiral metal complexes show promise as asymmetric catalysts and optical materials. Chiral-at-metal complexes composed of achiral ligands have expanded the versatility and applicability of chiral metal complexes, especially for octahedral and half-sandwich complexes. However, Werner-type tetrahedral complexes with a stereogenic metal centre are rarely used as chiral-at-metal complexes because they are too labile to ensure the absolute configuration of the metal centre. Here we report the asymmetric construction of a tetrahedral chiral-at-zinc complex with high configurational stability, using an unsymmetric tridentate ligand. Coordination/substitution of a chiral auxiliary ligand on zinc followed by crystallisation yields an enantiopure chiral-only-at-zinc complex (> 99% ee). The enantiomer excess remains very high at 99% ee even after heating at 70 °C in benzene for one week. With this configurationally stable zinc complex of the tridentate ligand, the remaining one labile site on the zinc can be used for a highly selective asymmetric oxa-Diels-Alder reaction (98% yield, 87% ee) without substantial racemisation.

Synthesis and structures of tetrahedral zinc(II) complexes bearing indomethacin and nitrogen donor ligands

The interaction between imidazole (imi) linker with the selected non-steroidal anti-inflammatory drug indomethacin (indo) [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid)], and Zinc(II) acetate dihydrate resulted in the formation of a polymeric complex {[Zn(indo-O)(µ-indo-O,O’)(imi)].2.5H2O}nZI-1, (indo-O is monodentate indomethacin, µ-indo-O,O’ is bridging bidentate indomethacin, imi is imidazole, and n = 2). Also, two mononuclear Zn(II) carboxylate complexes with the general formula [Zn(indo-O)2(L)], synthesized from N, N'-donor ligands denoted by L, namely 2,2′-bipyridine (bpy) (ZI-2), and 1,10-phenanthroline (phen) (ZI-3), with indomethacin are reported. In a bid to understand the indomethacin ligand's binding mode, the three synthesized complexes have been characterized using elemental analysis, FT-IR, UV–Visible, 1H, and 13C NMR spectroscopies, as well as TG analysis. The results from single-crystal X-ray diffraction studies showed that ZI-1 is polymeric and consists of Zn(II) units having trans- ZnNO3 chromophore, in which one of the indomethacin ligands is coordinated in a monodentate mode to each of the Zn(II) ion, while two indomethacin ligands with the use of their carboxylate oxygen atoms, act as bridges between two tetrahedral Zn(II) centers. Also, three lattice water molecules present in the coordination sphere formed an interaction with the imidazole and indomethacin ligands. Structural analysis of the mononuclear complexes ZI-2 and ZI-3 confirmed the bidentate coordination of the N, N'-donor ligands, and a tetrahedral geometry around the Zn(II). The crystal packing of ZI-2 and ZI-3 complexes were dominated by C-H···O, C-H···N, C-H···Cl, π···π, and C-H···π interactions. FT-IR analysis of the three complexes provided evidence of monodentate coordination of the indomethacin ligand. 1H NMR result of the complexes in DMSO-δ6 confirmed the presence of proton signals corresponding to the indomethacin ligand and the nitrogen donor ligands. ZI-1 had the least stability, as observed in TG studies.

Ditopic carboxylate containing zigzag chain polymers with tetrahedral Co(II) and Zn(II) nodes

Two 1D coordination polymers based on tetrahedral cobalt(II) and zinc(II) complex monomers involving terephthalate (1,4-benzenedicarboxylate) dianions as ligand bridges viz., [Co(ta)(DMP)2]n1 and [Zn(ta)(DMP)2.H2O]n2 (ta = terephthalate, DMP = 3,5-dimethylpyrazole) have been synthesized and characterized by elemental analysis, spectroscopic methods as well as by single crystal X-ray diffraction method. Compounds 1 and 2 are chain polymers wherein the polymeric zigzag chains remain linked through intermolecular hydrogen bonds to give rise to robust 3D network structures. Topological analysis of the structure of 2 reveals an underlying net that can be described as 2C1. While the solid state UV–vis–NIR spectrum 2 reflects the tetrahedral coordination geometry around Co(II), thermogravimetric studies indicate that this species retains its 3D network up to about 170 °C. The temperature dependence of the magnetic susceptibility of 1 indicates weak antiferromagnetic interaction among the unpaired spins.

A giant hybrid organic-inorganic octahedron from a narrow rim carboxylate calixarene.

Here we discovered an unprecedented giant octahedral coordination compound bearing 16 Zn2+, 12 Na+, 8 O2-, 4 OH-, 13 H2O and 6 L4- ligands [L4- = fully deprotonated tetra(carboxymethoxy)calix[4]arene]. Its structure was elucidated by single-crystal X-ray diffraction, wavelength-dispersive X-ray spectroscopy and MALDI-TOF mass spectrometry. This compound, Zn8Na6L6⊃Zn8Na6O8(OH)4(H2O)13 (external⊃internal), has eight tetrahedral zinc ions forming the coordination vertices of an outermost cube where carboxylate groups from the sodium calixarenes are anchored. Its core consists of eight Zn2+, six Na+, eight O2-, and four OH- distributed over three layers, besides thirteen coordinated H2O molecules.

Crystal structure of the C-terminal domain of DENR

The density regulated protein (DENR) forms a stable heterodimer with malignant T-cell-amplified sequence 1 (MCT-1). DENR-MCT-1 heterodimer then participates in regulation of non-canonical translation initiation and ribosomal recycling. The N-terminal domain of DENR interacts with MCT-1 and carries a classical tetrahedral zinc ion-binding site, which is crucial for the dimerization. DENR-MCT-1 binds the small (40S) ribosomal subunit through interactions between MCT-1 and helix h24 of the 18S rRNA, and through interactions between the C-terminal domain of DENR and helix h44 of the 18S rRNA. This later interaction occurs in the vicinity of the P site that is also the binding site for canonical translation initiation factor eIF1, which plays the key role in initiation codon selection and scanning. Sequence homology modeling and a low-resolution crystal structure of the DENR-MCT-1 complex with the human 40S subunit suggests that the C-terminal domain of DENR and eIF1 adopt a similar fold. Here we present the crystal structure of the C-terminal domain of DENR determined at 1.74 Å resolution, which confirms its resemblance to eIF1 and advances our understanding of the mechanism by which DENR-MCT-1 regulates non-canonical translation initiation and ribosomal recycling.