Coordination Sphere Of Metal Ion Research Articles

Synthesis and evaluation of bifunctional DFO2K: a modular chelator with ideal properties for zirconium-89 chelation.

The synthesis and evaluation of the newest generation of our DFO2 chelator family-DFO2K-is described. DFO2K was designed with a simple synthetic route to access different bifunctional derivatives, with each derivative having similar metal ion coordination spheres and high denticity (up to 12 coordinate) to ensure stable coordination of zirconium-89. The high denticity could potentially enhance stability with other large oxophilic radiometals. Zirconium-89 is the most popular radionuclide to pair with large macromolecules such as antibodies (immunoPET) for positron emission tomography applications. Although clinically successful, the stability of the "gold standard" chelator desferrioxamine B (DFO) can be improved as significant bone uptake is observed in animal models, despite no obvious stability issues in humans. Following the synthesis of DFO2K we assessed its radiolabeling efficiency with zirconium-89 and compared with DFO, which revealed rapid and nearly identical radiolabeling kinetics to DFO. The resultant [89Zr]Zr-DFO2K complex showed improved stability over [89Zr]Zr-DFO in different in vitro stability assays such as hydroxyapatite and 1000-fold molar excess EDTA challenges. Furthermore, biodistribution studies of the non-bifunctional chelators in healthy mice showed that [89Zr]Zr-DFO2K had a similar distribution profile and clearance to [89Zr]Zr-DFO. The bifunctional derivative p-SCN-Ph-DFO2K was conjugated to a non-specific human IgG antibody and evaluated after 2 weeks circulating in healthy female CD1 mice. Mice administered [89Zr]Zr-DFO2K-IgG showed substantially lower bone uptake in PET-CT images than [89Zr]Zr-DFO-IgG, with PET ROI data and ex vivo biodistribution revealing a statistically significantly lower bone uptake for DFO2K. Overall, owing to its high denticity, ease of synthesis, improved solubility over DFO2 and DFO2p, and stable chelation of zirconium-89, DFO2K appears to be an improved alternative chelator to DFO for zirconium-89 chelation.

Outer-sphere effects on the O2 sensitivity, catalytic bias and catalytic reversibility of hydrogenases.

The comparison of homologous metalloenzymes, in which the same inorganic active site is surrounded by a variable protein matrix, has demonstrated that residues that are remote from the active site may have a great influence on catalytic properties. In this review, we summarise recent findings on the diverse molecular mechanisms by which the protein matrix may define the oxygen tolerance, catalytic directionality and catalytic reversibility of hydrogenases, enzymes that catalyse the oxidation and evolution of H2. These mechanisms involve residues in the second coordination sphere of the active site metal ion, more distant residues affecting protein flexibility through their side chains, residues lining the gas channel and even accessory subunits. Such long-distance effects, which contribute to making enzymes efficient, robust and different from one another, are a source of wonder for biochemists and a challenge for synthetic bioinorganic chemists.

Equipping 1,4,7-Triazacyclononane with Substituents via Solid-Phase Synthesis.

Metal ion complexes frequently show substituted 1,4,7-triazacyclononane (tacn) as the ligand. Besides providing donor atoms for complex formation, tacn serves as a scaffold for equipping the complex with further functional units that are needed for the complementation and electronic tuning of the metal ion coordination sphere and/or add other features, e.g., light-absorbing antennas and groups for bioconjugation. To exploit the full potential of substituted tacn, strategies for directed syntheses of NO(R1,R1,R2) and NO(R1,R2,R3), i.e., tacn with two and even three different substituents R, are needed. Herein, we report a strategy that takes advantage of solid-phase synthesis in the assembly of the precursors NO(R1,R1,H) and NO(R1,R2,H). The assembly of NO(R1,R2,H) is based on a highly selective formation of NO(Cbz,tfAc,H), with Cbz being the link between tacn and solid phase. For this, tacn was loaded onto (4-nitrophenyl carbonate)-resin, thereby forming resin-bound (rb)-tacn, which corresponds to NO(Cbz,H,H) bound to the solid phase. Treatment of rb-tacn with ethyl trifluoroacetate gave rb-NO(tfAc,H), which corresponds to NO(Cbz,tfAc,H). With rb-tacn and rb-NO(tfAc,H) in hand, a variety of NO(R1,R1,H) and NO(R1,R2,H) were prepared, showing the broad applicability of the strategy with respect to the type of substituents and of reactions (nucleophilic substitution, reductive amination, aza-Michael addition, addition to epoxides, acylation). The study also identified limitations and points for improvement.

Concomitant role of metal clusters and ligands in the synthesis and control of porosity in Metal-Organic Frameworks: A literature review

A clossal increase in the number of research articles on metal–organic frameworks (MOFs) have recently been anticipated as next-generation functional materials. The characteristic coordination behavior between metal ion and organic linker in MOFs provide them hydrid functional features of both the moieties. For the substantial improved performance of MOFs and to achieve widespread applications of MOFs in diverse fields, it is essential to develop effective synthetic strategies and understand the role of metal ion cluster or coordination sphere or secondary building units (SBU’s) and organic linker in detail. The augmentation in porosity and large surface area with multitude in diverse topologies provide a boost for the application of these materials in diverse allied fields. This review article provides a detailed introduction of the porous MOF materials; encompassing the role of secondary building units or metal cluster and organic linkers in defining the porosity of MOF materials. Detailed investigations about the role of metal ion clusters and expanded organic linkers that lead to MOFs with ultrahigh porosity have been done and portrayed carefully. The structural aspects of zirconium, zinc and copper cluster based porous MOFs and organic linkers (porphyrin and pyrene based) have been thoroughly portrayed owing to their various application in various fields. This review article will provide better understanding about the various factors involved in synthesis and controll of the porosity toward desired applications.

Can bacteria F. nucleatum be actively involved in colon cancer progression via a radical mediated mechanism?

Outer membrane proteins of Fusobacterium nucleatum, a cancer‑leading bacteria, are considered as the factors responsible for its pathogenicity. Among them, homotrimeric autotransporter protein YadA (Yersinia adhesin A) is an important virulence factor also found in the outer membrane of pathogenic Yersinia species. In this paper, the structure and stability of certain Cu(II) complexes with YadA fragments were investigated using both, experimental and theoretical methods. Potentiometry, UV–Vis, CD, EPR, and calculations at the density functional theory (DFT) level were applied to determine the metal ion coordination sphere. Moreover, the complexes ability to DNA cleavage and reactive oxygen species (ROS) production was studied. We have shown that copper(II) complexes can cleave DNA by 1O2, O2•− and •OH, which are formed in the studied systems. However, the results of electrophoretic experiments revealed that complexes cleave DNA less effectively than free copper(II) ions. Therefore, the presence of studied peptides may prevent DNA from a Cu(II)-induced damage to some extent.

Effect of solvent and auxiliary ligand on catecholase activities of Mn(III) complexes: A comparative study

A mononuclear Mn(III) complex with composition [MnIIIL(Cl)] (1) has been utilized to prepare two new complexes, [MnIIIL(N3)(CH3OH)] (2) and [MnIIIL(μ1,3-NCS)]n (3), by substitution of the auxiliary ligand. The ligand utilized for preparation of 1 is a Schiff base (H2L), obtained by 2:1 condensation of 3-Chlorosalicylaldehyde and ethylene diamine in methanol. The chloride anion, present in the coordination sphere of the central metal ion in 1 has been replaced by two other auxiliary ligands, azide and thiocyanate, in 2 and 3, respectively. All of the three complexes behaved as bio-functional models of catechol oxidase toward oxidation of 3,5-di-tert butyl catechol (3,5-DTBC). A detailed kinetic investigations were carried out for 2 and 3 in methanol, acetonitrile and N,N′-Dimethyl formamide (DMF) separately and the corresponding turn-over numbers have been determined. The ESI-MS spectra of the substrate-catalyst mixtures in acetonitrile and methanol confirmed formation of catecholate bound Mn(III) intermediate in the mass spectral time scale. The progress of the catechol oxidation was monitored by 1H-NMR spectroscopy with the reaction mixtures containing complex-substrate ratio at 1:20 after stirring in acetonitrile as well as methanol at room temperature in open air. NMR spectral data confirmed completion of the process in 90 minutes and 45 minutes for 2 and 3, respectively. Notably, in absence of any of these complexes, aerobic oxidation of 3,5-DTBC to the corresponding quinone is negligible even after twenty four hours of mixing in the same solvent. This observation is a clear indicative of high catalytic efficiencies of the prepared complexes.

Heterobimetallic 21,23-dimetallaporphyrin: activation of metal-metal interactions within the porphyrinoid macrocycle.

Two core-modified porphyrins containing metal atoms, namely platinum(II) or platinum(IV) and rhodium(III), in place of two NH units, have been obtained by a post-synthetic modification of the 21,23-ditelluraporphyrin. The products of the tellurium-to-metal exchange, 21-platina-23-rhodaporphyrins, incorporate rhodacyclopentadiene and platinacyclopentadiene units with the metal atoms facing each other. The two molecules exhibit different degrees of metal-metal interaction depending on the oxidation state of platinum, with the NBO bond order being 0.04 for platinum(IV) and 0.15 for platinum(II). Consistently, the Quantum Theory of Atoms in Molecules analysis revealed the presence of the bond determinant, the bond critical point, in the platinum(II) species, in contrast to the platinum(IV) congener. The two porphyrinoids are interconvertible in redox reactions. They both exhibit fluxional behaviour in solution, studied by 1H NMR, involving alteration in the metal ion coordination sphere accompanied by the macrocyclic skeleton conformation change.

Probing the Influence of Anions on Charge Transfer in Redox Couples for Flow Battery Applications

Integrating intermittent renewables like solar and wind to meet rising energy demand has necessitated the development of low-cost energy storage technologies like flow batteries for ensuring grid reliability. Aqueous redox flow batteries (RFBs) are a promising technology for storing energy on a large scale and releasing it based on demand. RFBs store energy in different oxidation states of species dissolved in electrolytes, which undergo charge transfer by accepting or donating electrons on the electrodes’ surface to store and release electricity. Several aqueous RFBs based on 3d transition metal ion redox couples have been demonstrated. Most of these RFBs employ acidic electrolytes and use porous carbon felts as electrodes due to their high surface area.1 The anions in these electrolytes affect the structure of the reactive species in solution by altering the metal ion coordination sphere. Additionally, these anions influence the charge transfer process either by getting adsorbed on the electrode surface and changing the number of available sites for the reaction, or changing the energy of the adsorbed intermediate. However, there is a lack of systematic study that identifies these structures and simultaneously looks at the adsorbed intermediates to understand the reaction mechanism in the presence of anions, hindering the design of novel electrolytes and electrocatalysts to control the charge transfer.In this work, we study the influence of anions on the V2+/V3+ redox couple by identifying the structures of V2+ and V3+ complexes and conducting kinetic measurements on a controlled glassy carbon surface in various acidic electrolytes (HClO4, H2SO4, HCl, HBr, and HI) to get mechanistic insights of V2+/V3+ charge transfer. We choose V2+/V3+ because of its enormous potential as negative electrode in aqueous vanadium-based RFBs and the similarity in the observed kinetic enhancement in the presence of chloride anions, as also seen for Cr2+/Cr3+, Fe2+/Fe3+, and Cu+/Cu2+ redox couples,2 suggesting the possible similarity in the reaction mechanism. Using a combination of extended X-ray absorption fine structure, UV-Vis spectroscopy, and density functional theory calculations, we show that V2+ exists as [V(H2O)6]2+ in all electrolytes, while V3+ exists as a mixture of [V(H2O)6]3+ and [V(H2O)5SO4]+ in H2SO4, and [V(H2O)6]3+, [V(H2O)5X]2+, and [V(H2O)4X2]+ (X = Cl, Br, and I) in HCl, HBr, and HI. We evaluate the exchange current densities (io ) and apparent activation energies (Ea ) in these electrolytes using a rotating disk electrode setup. We show that the io follows the order H2SO4 < HCl < HClO4 < HBr < HI, while the Ea follows the order of H2SO4 > HClO4 > HCl > HBr > HI. This difference in orders of io and Ea for HCl and HClO4 occurs because io has a contribution from both apparent frequency factor and Ea , highlighting the need to consider both apparent frequency factor and Ea independently to infer mechanistic insights.We show that anions influence the V2+/V3+ kinetics by changing the energetics of the adsorbed intermediate. This is identified by the decreasing Ea with increasing adsorption energy of the *[anion-V3+] intermediate. Because the adsorption energy of the intermediate follows the same order as anion polarizability,3 it also explains the use of anion polarizability to explain the kinetic behavior of these redox couples in previous studies. The apparent frequency factor follows the order opposite to the coverage of anions on glassy carbon, indicating the coverage is not responsible for the observed trends in V2+/V3+ activity in these acidic electrolytes. We compare the trends in adsorption energy of similarly forming intermediates during charge transfer for these other kinetically similar behaving redox couples (Cr2+/Cr3+, Fe2+/Fe3+, and Cu+/Cu2+) to rationalize trends in their inner-sphere charge transfer behavior. Further, we highlight how our findings show that electrocatalyst and electrolyte engineering to tune the intermediate’s energy is a viable strategy to control the charge transfer by comparing V2+/V3+ kinetic measurements on various metal electrocatalysts.REFERENCES: Dunn, B. et al. Sci. Mag. 334, 928–935 (2011).Agarwal, H. et al. ACS Energy Lett. 4, 2368–2377 (2019).Anbar, M. et al. J. Phys. Chem. 69, 973–977 (1965).

Structural modifications on nickel dithiolene complexes lead to increased metal participation in the electrocatalytic hydrogen evolution mechanism

In this work we present the electrocatalytic activity of alkylated nickel bis-dithiolene complexes toward hydrogen evolution from protons (TFA) in organic media (DMF). The hydrogen evolving mechanism is discussed and the complexes are compared to their non-alkylated analogs using DFT calculations. The findings support increased metal participation in the hydrogen evolving mechanism due to the structural and electronic modifications imposed by the alkyl-bridge on the sulfur atoms. Typically for this class of compounds, the coordinated sulfur atoms act as internal proton relays that facilitate transfer of protons to the metal ion during the catalytic cycle, highlighting the importance of modifying the coordination sphere of metal ions in the design of homogeneous hydrogen evolving catalysts.

Zinc Fingers.

Zinc finger (ZF) domains, that represent the majority of the DNA-binding motifs in eukaryotes, are involved in several processes ranging from RNA packaging to transcriptional activation, regulation of apoptosis, protein folding and assembly, and lipid binding. While their amino acid composition varies from one domain to the other, a shared feature is the coordination of a zinc ion, with a structural role, by a different combination of cysteines and histidines. The classical zinc finger domain (also called Cys2His2) that represents the most common class, uses two cysteines and two histidines to coordinate the metal ion, and forms a compact ββα architecture consisting in a β-sheet and an α-helix. GAG-knuckle resembles the classical ZF, treble clef and zinc ribbon are also well represented in the human genome. Zinc fingers are also present in prokaryotes. The first prokaryotic ZF domain found in the transcriptional regulator Ros protein was identified in Agrobacterium tumefaciens. It shows a Cys2His2 metal ion coordination sphere and folds in a domain significantly larger than its eukaryotic counterpart arranged in a βββαα topology. Interestingly, this domain does not strictly require the metal ion coordination to achieve the functional fold. Here, we report what is known on the main classes of eukaryotic and prokarotic ZFs, focusing our attention to the role of the metal ion, the folding mechanism, and the DNA binding. The hypothesis of a horizontal gene transfer from prokaryotes to eukaryotes is also discussed.

Structural Systematics of Lanthanide(III) Picrate Solvates: Hexamethylphosphoramide and Octamethylpyrophosphoramide Adducts

Crystalline products of the reactions of lanthanide picrates, Ln(pic)3 (pic=2,4,6-trinitrophenoxide), with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) have been characterised by single-crystal X-ray diffraction studies. With hmpa and lighter lanthanides (La, Sm, Eu), isomorphous species (monoclinic, P21/c, Z 4) of stoichiometry [Ln(pic)3(hmpa)3]·0.5H2O, have been defined where the molecular units in the lattice contain 9-coordinate Ln with tricapped trigonal-prismatic coordination geometry. The picrate ligands are bidentate through phenoxide-O and 2-nitro-O, with the latter occupying the capping positions, while the hmpa ligands are singly O-bound to one trigonal face. Heavier lanthanides (Gd, Lu) and Y have been found to give isomorphous (monoclinic, P21/n, Z 4) species of stoichiometry [Ln(pic)3(hmpa)2], with 8-coordinate Ln of an irregular geometry best considered as close to that of a bicapped trigonal-prism. The picrate ligands chelate in the same manner as in the lighter Ln complexes but with one spanning a trigonal edge, and the hmpa-O donors occuping two apices of the other trigonal face. The ligand ompa has been found to act as a bidentate chelate in all isolated species, displacing one picrate from the metal ion coordination sphere to give ionic complexes. For La, Nd, and Gd, isomorphous (monoclinic, P21/n, Z 4) complexes of stoichiometry [Ln(pic)2(ompa)2(OH2)](pic)·0.5H2O containing 9-coordinate, tricapped trigonal-prismatic Ln with a single aqua ligand have been defined, while for Er, Yb, Lu, and Y, both the coordinated and lattice water molecules are lost in isomorphous (monoclininc, P21/c, Z 8) 8-coordinate, square-antiprismatic species of stoichiometry [Ln(pic)2(ompa)2](pic). For Er, further polymorphs, one monoclinic, P21/c, and the other triclinic, , have also been characterised.

Exploring Soft Donor Character of the N-2-Pyrazinylmethyl Group by Coordinating Trivalent Actinides and Lanthanides Using Aminopolycarboxylates.

The trivalent f-element coordination chemistry of a novel aminopolycarboxylate complexant was investigated. The novel reagent is an octadentate complexant that resembles diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA), but a single N-acetate pendant arm was substituted with a N-2-pyrazinylmethyl functional group. Thermodynamic studies of ligand protonation and trivalent lanthanide, americium and curium, complexation by N-2-pyrazinylmethyldiethylenetriamine-N,N',N″,N″-tetraacetic acid (DTTA-PzM) emphasize the strong electron withdrawing influence of the N-2-pyrazinylmethyl group. Specifically, DTTA-PzM is more acidic compared to a N-2-pyridinylmethyl-substituted structural equivalent, DTTA-PyM, with a substantial lowering of pK7, corresponding to the protonation of a second aliphatic amine site. The participation of the pyrizyl nitrogen in the metal ion coordination sphere is evident from the fluorescence lifetime decay measurements of metal hydration and the interpretation of the stability constants for ML- and MHL(aq) complexes. The overall conditional stability constants for the trivalent f-element complexation by DTTA-PzM complexes decrease, relative to DTTA-PyM, as expected based on the lower basicity of pyrazine in water relative to pyridine. Replacement of the N-2-pyridinylmethyl group with N-2-pyrazinylmethyl, while enhancing the total acidity of DTTA-PzM, also reduces its softness, as manifested by a small lowering of β101Am/Nd and liquid-liquid separation of trivalent lanthanides from trivalent americium. Despite this, the 4f/5f separation is doubled when DTTA-PzM replaces DTPA as an aqueous complexant in solvent extraction.

Manipulating Spin Transition To Achieve Switchable Multifunctions.

The spin transition of metal ions involves interconversion between electron configurations exhibiting considerably different functions and plays a substantial role in the chemical, physical, and biological fields. The photoinduced spin transition offers a promising approach to tune various physical properties with high spatial and temporal resolutions for producing smart multifunctional materials not only to explore their basic science but also to satisfy the demands of the next-generation photoswitchable-molecule-based devices. Therefore, it is attracting considerable interest to utilize photoinduced spin transition to simultaneously tune multifunctions. However, two issues are challenging in obtaining reversible and swift manipulation of functions: (1) the interconversion between different electron configurations of photoresponsive units should be reversibly switched via photoinduced spin transition; (2) effective coupling should be built between the photoresponsive and functional units to produce photoswitchable functions utilizing photoinduced spin transition. In this Account, we will review our recent advances in the usage of spin transition of metal ions as actuators for tuning the magnetic, dielectric, fluorescence, and mechanical properties, wherein the role of a photoswitchable spin transition is highlighted. We mainly focus on the study of two spin-transition categories, including spin-crossover (SCO) of one metal ion and metal-to-metal charge transfer (MMCT). Initially, we will describe a strategy for developing photoinduced reversible SCO and MMCT. The role of flexible intermolecular interactions, in particular, π···π interactions, is discussed with respect to a photoinduced reversible MMCT. Then, the SCO and MMCT units were assembled using metallocyanate building blocks to form a chain, wherein the spin states, anisotropy, and magnetic coupling interactions can be photoswitched to tune the single-chain magnet behavior. Besides magnetic properties, the photoinduced spin transition that is associated with the concomitant changing of charge distribution, bond lengths, and absorption spectra can be utilized to tune the multifunctions. Therefore, the transfer of an electron from a central cobalt site to one of the two iron sites in linear trinuclear Fe2Co compounds resulted in the transformation of a centrosymmetric nonpolar molecule into an asymmetric polar molecule, and the molecular electric dipole and dielectric properties can be reversibly switched. Moreover, the spin transition usually involved significant expansion or contraction of the coordination sphere of metal ions because of the population/depopulation of the antibonding eg orbitals. Therefore, colossal positive and negative thermal expansion behaviors were achieved in a layered compound by manipulating the spin-transition process and the rotation of the functional units, thereby providing a strategy for synthesizing phototunable nanomotors. Photoinduced spin transition can also be used to modulate the fluorescence properties by controlling the energy transfer between the fluorescent ligands and the metal sites showing SCO. Finally, we will provide a perspective and detail the remaining challenges that are associated with this research area. We believe that an increasing number of fascinating photoswitchable SCO and MMCT systems will emerge in the near future and that the materials exhibiting various properties and functions that can be manipulated using photoinduced spin transition will provide novel opportunities for the development of smart multifunctional materials and devices.

Irreversible exchange of potassium with thallium in coordination polymer nanostructures upon solid-state Mechanochemical process

Solid-state conversion of three-dimensional KI coordination polymer [K2(μ8–1,5-nds)(H2O)2]n (1) nanostructures, [1,5-H2nds = 1,5-naphthalenedisulfonic acid], prepared by sonochemical procedure, to three-dimensional [Tl2(μ12–1,5-nds)]n (2) coordination polymer nanoparticles was studied by mechanochemical reaction. During this solid-state cation exchange process, in addition to removal of two coordinated water molecules from 1, the coordination mode of 1,5-nds2¯ and coordination sphere of metal ion in 1 changed from μ8- and KO8 to μ12- and O9Tl⋯Tl3 in 2, respectively. IR spectroscopy, X-ray powder diffraction (XRD) and thermo gravimetric and differantial thermal analyses (TG-DTA), indicated that this conversion is irreversible.

New Metal Complexes Derived from Guanidine-Containing Dialdehyde Cellulose

New metal-polymer complexes of iron-containing composites of dialdehyde cellulose with guanidine acrylate or methacrylate have been developed. The structure and properties of these materials have been established by physicochemical testing. The polymeric iron-containing complexes obtained by radical polymerization (in situ) are formed due to intra- and intermolecular coordination of the metal ions with carboxylate oxygen atoms, and amino group nitrogen atoms of the guanidine fragment as well as hydroxyl groups of dialdehyde cellulose. The complexes obtained by mixing the metal salt with polymers in aqueous solution are formed due to replacement of water molecules in the coordination sphere of the solvated metal ions by hydroxyl groups of dialdehyde cellulose and the reaction of metals with carboxylate ions and guanidine groups of the polymer located on the composite surface. Guanidine-containing cellulose composites were found to be effective matrices for stabilizing the size of the growing particles containing a new metallic phase and to form polymer complexes with a narrow size distribution of both micro- and nanoparticles. These results suggest that the synthesized compounds hold promise for reagent transport when using composites as catalysts for various chemical reactions or for targeted delivery of drugs.

Simulation of metal ion coordination sphere in crystals with fluorite structure

Using quantum-chemical methods, it has been found that the structure of fluorite coincides with the symmetry and coordination number of central calcium atom in the (Oh)-Ca7F14 cluster. The Ca–F and F–F interatomic distances in the cluster are 3–4% shorter than in the crystal. The symmetry of the (Oh)–(ScCa6F14)+ cluster mimicking the cationic defect after the β-decay of 45Ca does not correspond to the energy minimum. The increase in the cation charge from 1.79 to 2.80 a. u. reduces the radius of the first coordination sphere by 0.14 A. For ytterbium dihalides, the bond lengths Yb–F 2.344, Yb–Cl 2.897 A and the cation charges 1.81, 1.64 a. u., respectively, have been found.

In vitro structure-specific Zn(II)-induced adipogenesis and structure-function bioreactivity correlations

The advent of Zn(II) metallodrugs in metabolic syndrome pathologies generates a strong challenge toward synthetic endeavors targeting well-defined, atoxic and biologically active binary/ternary species of Zn(II). Proper formulation of that metal ion's coordination sphere sets the stage for construction of appropriately configured Schiff ligands based on tromethamine and variably modified vanillin core components. The arising Schiff ligands react with Zn(II) in a defined stoichiometry, thereby delivering new binary Zn(II)-L species with defined physicochemical properties. Analytical (elemental), spectroscopic (FT-IR, Thermogravimetric Analysis) and crystallographic techniques attest to the distinct nature of the derived binary-ternary materials, bearing defined Zn(II):L molecular stoichiometry, variable nuclearity, charge, bulk and balance mix of hydrophilicity-hydrophobicity, thereby providing the physicochemical profile based on which biological studies could ensue. The structurally based selection of species was applied onto in vitro 3T3-L1 cultures, essentially exploring toxicity, migration, morphology, cell differentiation and maturation. The systematic effort toward comparative work on appropriately defined Zn(II) species and insulin in inducing adipogenesis reveals the salient structural features in the Schiff family of ligands configuring Zn(II) so as to promote complex formation sufficient to engage biomolecular targets during the process of initiation and maturation. Molecular targets of importance in adipogenesis were examined under the influence of Zn(II) and their expression levels suggest the structural composition that a Zn(II) ion might have to optimally pursue cell differentiation. Thus, a well-defined selection of binary Zn(II)-L species is tightly associated with the incurred bioactivity, thereby setting the stage for the development of efficient Zn(II) metallodrugs to combat Diabetes mellitus II.

New examples of chelating triketone-like ligands that promote formation of binuclear complexes

The present work is to investigate of binding properties of chelating triketone-like ligands, which are able to forming of binuclear complexes. The studied compounds are able to exist in cyclic or ‘close form’ (phenyl substituted or unsubstituted 2-hydroxy-2-(trifluoromethyl)chroman-4-ones) as well as in their associated ‘open form’ (phenyl substituted or unsubstituted 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-diones). In this paper there is good evidence for the compounds are being in solid in ‘close form’ (pre-ligands), whereas in basic solutions and when involved in metal ion coordination sphere they are being in ‘open form’ (ligands). Protolytic equilibria of the compounds in aqueous ethylene glycol solutions were studied. Schemes of acid-base equilibria of these compounds were proposed. Apparent ionization constants of compounds containing electron-donor and electron-acceptor substituents in the benzene ring were determined using spectrophotometric method. The binding properties of 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-dione towards Cu(II), Ni(II) and Co(II) were studied. The formation of 2:2 metal–ligand complexes was observed. X-ray analysis gives evidence the formation of complexes in which the ratio metal to ligand can be 1:2 and 2:2. Similar to β-triketones the studied ligands tends to formation of binuclear complexes with transition metal ions.

Sterically-constrained tripodal phosphorus-bridged tris-pyridyl ligands.

Introducing substituents into the 6-position of the 2-pyridyl rings of neutral tris-pyridyl phosphanes of the type P(2-py')3 (where 2-py' is a substituted 2-pyridyl ring), has a marked impact on their coordination of transition metal ions, as revealed in the current study. Whereas the unsubstituted phosphorus-bridged tris-pyridyl ligand P(2-py)3 (1) forms the sandwich cation [{P(py)3}2Fe](2+) (4) with iron(II), coordinating via all of the donor nitrogen atoms, the reaction of the methyl-substituted counterpart P(6-Me-2-py)3 (2) and FeCl2 results in the half-sandwich arrangement [{P(6-Me-2-py)3}FeCl2]·toluene (5·toluene), in which only two N-atoms of the ligand coordinate to the metal. A similar half-sandwich type complex, [{P(6-Me-2-py)3}FeCl(OTf)]·2THF (6·2THF), is obtained from reaction of 2 with Fe(OTf)2 in the presence of LiCl, only now with all three of the N-atoms of the ligand coordinated to Fe(II). The formation of a half-rather than full-sandwich complex 2 with suggests that steric clashing of the Me groups prevents the formation of sandwich-type arrangements. The reaction of [Cu(MeCN)4]PF6 with P(6-Me-2-py) (2) gives the complex [(MeCN)3Cu{P(6-Me-2-py)3}Cu(MeCN)](PF6)2 (7), in which two Cu(I) atoms are coordinated by the bridgehead P-atom and by the three N-atoms of the tris-pyridyl ligand (a unique coordination mode in this area). Overall, the results indicate that 6-Me substitution results in a promising 6-electron capping ligand for organometallic synthesis and catalysis.

Coordination Polymers and Oligonuclear Systems Based on Oximate or Hydroxamate Building Blocks: Magnetic and Sorption Properties

The review covers structures and properties of compounds, possessing porous crystal lattices, or coordination polymers, which are assembled on the basis of polynuclear oximate or hydroxamate complexes of 3d metals. It is shown that magnetic properties of such systems are governed by the exchange interactions in the polynuclear building blocks and can be pre-determined by the appropriate choice of starting compound. In contrast, the structure and topology of the framework, obtained on the basis of polynuclear oximate or hydroxamate, do not correlate with the quantity of vacancies in coordination spheres of metal ions in the starting compound, as well as they do not correlate with the quantity of ligand donor atoms. Some of the compounds, considered in this review, show ability to absorb different substrates. Such absorption is different from "classical" filling of micropores; sorption capacity is governed by the energy of host-guest interactions rather than the volume of rigid micropores in crystal lattice. Keywords: Building block approach, coordination polymer, hydroxamate, magnetic properties, metallacrown, oxime, sorption properties.