Metal Ion Coordination Research Articles

Ground- and Excited-State Properties of Iron(II) Complexes Linked to Organic Chromophores.

Two new bichromophoric complexes, [Fe(bim-ant)2]2+ and [Fe(bim-pyr)2]2+ ([H2-bim]2+ = 1,1'-(pyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium); ant = 9-anthracenyl; pyr = 1-pyrenyl), are investigated to explore the possibility of tuning the excited-state behavior in photoactive iron(II) complexes to design substitutes for noble-metal compounds. The ground-state properties of both complexes are characterized thoroughly by electrochemical methods and optical absorption spectroscopy, complemented by time-dependent density functional theory calculations. The excited states are investigated by static and time-resolved luminescence and femtosecond transient absorption spectroscopy. Both complexes exhibit room temperature luminescence, which originates from singlet states dominated by the chromophore (1Chrom). In the cationic pro-ligands and in the iron(II) complexes, the emission is shifted to red by up to 110 nm (5780 cm-1). This offers the possibility of tuning the organic chromophore emission by metal-ion coordination. The fluorescence lifetimes of the complexes are in the nanosecond range, while triplet metal-to-ligand charge-transfer (3MLCT) lifetimes are around 14 ps. An antenna effect as in ruthenium(II) polypyridine complexes connected to an organic chromophore is found in the form of an internal conversion within 3.4 ns from the 1Chrom to the 1MLCT states. Because no singlet oxygen forms from triplet oxygen in the presence of the iron(II) complexes and light, efficient intersystem crossing to the triplet state of the organic chromophore (3Chrom) is not promoted in the iron(II) complexes.

Elucidating the role of metal ions in carbonic anhydrase catalysis

Why metalloenzymes often show dramatic changes in their catalytic activity when subjected to chemically similar but non-native metal substitutions is a long-standing puzzle. Here, we report on the catalytic roles of metal ions in a model metalloenzyme system, human carbonic anhydrase II (CA II). Through a comparative study on the intermediate states of the zinc-bound native CA II and non-native metal-substituted CA IIs, we demonstrate that the characteristic metal ion coordination geometries (tetrahedral for Zn2+, tetrahedral to octahedral conversion for Co2+, octahedral for Ni2+, and trigonal bipyramidal for Cu2+) directly modulate the catalytic efficacy. In addition, we reveal that the metal ions have a long-range (~10 Å) electrostatic effect on restructuring water network in the active site. Our study provides evidence that the metal ions in metalloenzymes have a crucial impact on the catalytic mechanism beyond their primary chemical properties.

Improving flame retardancy and self-cleaning performance of cotton fabric via a coating of in-situ growing layered double hydroxides (LDHs) on polydopamine

In order to improve flame retardancy and soiling resistance of cotton fabric, a safe coating was fabricated on its surface. At first dopamine was polymerized on the cotton surface to be polydopamine (PDA), and then layered double hydroxides (LDHs) grew in situ on the platform of PDA by the coordination of catechol groups and metal ions. Cone calorimetry test results showed the coating reduced heat and smoke release during burning. Most important, more than 94% smoke was suppressed by the PDA-LDHs coating. Little cotton left after combustion but more than 10.2% of char was remained for the treated fabric by PDA-LDHs. On the other hand further covered by polydimethylsiloxane (PDMS), the treated cotton exhibited enhanced resistance to soiling and became more durable. For more than 96% oil/water separation efficiency, the treated cotton fabric can be expected to be an ideal filtration material.

Salen–Mg‐doped NH2–MIL‐101(Cr) for effective CO2 adsorption under ambient conditions

A novel metal‐doped metal–organic framework (MOF) was developed by incorporating salen–Mg into NH2–MIL‐101(Cr) structure under ambient conditions. The Schiff base complex was successfully prepared by condensing salicylaldehyde with a free amino group and then coordinating metal ions. Such a structure can endow the sample with higher CO2 adsorption performance. At 0°C and 1 bar, the salen–Mg‐modified sample achieves the maximum adsorption capacity of 2.18 mmol g−1 for CO2, which was 5.8% higher than the pristine salen–MOF under the same conditions. Notably, the Freundlich model indicates that the CO2 adsorption process of all samples conforms to reversible adsorption. However, the correlation coefficients (R2) of the Mg‐doped sample are lower than that of the pristine sample. Besides, the CO2/N2 adsorption selectivity and isosteric heat also show a similar trend. These results indicate that the salen–Mg can enhance the interaction between the material and CO2 molecules.

Cationic Bola Form Metallosurfactants Based on Isothiouronium, Synthesis and Anti-Microbial Activity

Abstract Two series of well-defined dimeric metallo-bolaamphiphiles (bola surfactants) with the coordinated metal ions (Cu, Co, Zn) were prepared. These oligomeric surfactants consist of simple monomeric cationic surfactant fragments which are coupled via the hydrophilic ammonium chloride head groups by C6 and C12 spacer groups of different lengths. FTIR and 1HNMR identification techniques confirmed the obtained products. Measurements of surface tensions showed that the synthesized Bola amphiphiles have the desired, relatively low critical micelle formation concentrations (CMC). Bola amphiphiles with long spacer groups (C12) have a pronounced surface activity. The properties of these cationic surfactant oligomers in aqueous solution such as micellization and surface activity were discussed in relation to spacer group. In addition, the synthesized compounds were examined for their anti-microbial activity using the agar diffusion technique.

Synthesis, characterisation and biological investigation of some third-row elements with halo- substituted coumarin schiff base with N and O as donors

The present work involves in the synthesis, spectral characterisation and the biological analysis of the metal complexes which were derived from 3-Chloro-8-formyl-7-hydroxy-4-methylcoumarin and benzylamine. The molar conductivity values indicated that the complexes are non-electrolytes. Elemental analysis was carried out to assign the [ML2(H2O)2] stoichiometry to the metal complexes, where M=Co (II), Ni (II) and Cu(II) and L=deprotonated ligand. The IR data confirmed coordination of metal ions to the ligand. The presence of a coordinated water molecule was investigated by thermal studies and the electronic spectral results were helpful in assigning the geometry to synthesised complexes. The both Schiff base and the derived metal complexes were subjected various biological activities to check their potency.

A Phosphine Functionalized β-Diketimine Ligand for the Synthesis of Manifold Metal Complexes.

A bis(diphenyl)‐phosphine functionalized β‐diketimine (PNac‐H) was synthesized as a flexible ligand for transition metal complexes. The newly designed ligand features symmetrically placed phosphine moieties around a β‐diketimine unit, forming a PNNP‐type pocket. Due to the hard and soft donor atoms (N vs. P) the ligand can stabilize various coordination polyhedra. A complete series ranging from coordination numbers 2 to 6 was realized. Linear, trigonal planar, square planar, tetrahedral, square pyramidal, and octahedral coordination arrangements containing the PNac‐ligand around the metal center were observed by using suitable metal sources. Hereby, PNac‐H or its anion PNac− acts as mono‐, bi‐ and tetradendate ligand. Such a broad flexibility is unusual for a rigid tetradentate system. The structural motifs were realized by treatment of PNac‐H with a series of late transition metal precursors, for example, silver, gold, nickel, copper, platinum, and rhodium. The new complexes have been fully characterized by single crystal X‐ray diffraction, NMR, IR, UV/Vis spectroscopy, mass spectrometry as well as elemental analysis. Additionally, selected complexes were investigated regarding their photophysical properties. Thus, PNac‐H proved to be an ideal ligand platform for the selective coordination and stabilization of various metal ions in diverse polyhedra and oxidation states.

Tying different knots in a molecular strand.

The properties of knots are exploited in a range of applications, from shoelaces to the knots used for climbing, fishing and sailing1. Although knots are found in DNA and proteins2, and form randomly in other long polymer chains3,4, methods for tying5 different sorts of knots in a synthetic nanoscale strand are lacking. Molecular knots of high symmetry have previously been synthesized by using non-covalent interactions to assemble and entangle molecular chains6-15, but in such instances the template and/or strand structure intrinsically determines topology, which means that only one type of knot is usually possible. Here we show that interspersing coordination sites for different metal ions within an artificial molecular strand enables it to be tied into multiple knots. Three topoisomers-an unknot (01) macrocycle, a trefoil (31) knot6-15, and a three-twist (52) knot-were each selectively prepared from the same molecular strand by using transition-metal and lanthanide ions to guide chain folding in a manner reminiscent of the action of protein chaperones16. We find that the metal-ion-induced folding can proceed with stereoinduction: in the case of one knot, a lanthanide(III)-coordinated crossing pattern formed only with a copper(I)-coordinated crossing of particular handedness. In an unanticipated finding, metal-ion coordination was also found to translocate an entanglement from one region of a knotted molecular structure to another, resulting in an increase in writhe (topological strain) in the new knotted conformation. The knot topology affects the chemical properties of the strand: whereas the tighter 52 knot can bind two different metal ions simultaneously, the looser 31 isomer can bind only either one copper(I) ion or one lutetium(III) ion. The ability to tie nanoscale chains into different knots offers opportunities to explore the modification of the structure and properties of synthetic oligomers, polymers and supramolecules.

The research progress on CO<sub>2</sub> absorption and conversion by metal coordination-based (chelate-based) ionic liquids

<p indent=0mm>Metal coordination-based ionic liquids (ILs) are a type of low-temperature molten salts formed by the coordination of metal ions and organic or inorganic ligands. Among them, when the metal ion and the ligand have a multidentate coordination site, it is called metal chelate-based ILs. At present, metal coordination-based (chelate-based) ILs have been widely used in gas absorption and organic catalysis, showing excellent performance. In this paper, the research progresses on CO₂ absorption and conversion by metal coordination-based (chelate-based) ILs in recent years have been reviewed, focusing on the effects of metal ions and ligand types on CO₂ absorption and chemical conversion performance. Generally, the metal anion-coordination-based ILs absorb CO₂ through physical interaction, while the metal cation-chelate-based ILs with alcohol amine or amine ligand can react with CO₂ through chemical interaction. Therefore, the CO₂ absorption capacity of the former is lower than that of the latter. The stronger the chelation interaction between the central metal ion and the ligand, the greater the CO₂ absorption capacity of the metal cation-chelate-based ILs. The chelation interaction between the ligand and the central metal ion can be adjusted by changing the type of the central metal ion and the number of ligand coordination atoms. Increasing the central metal ion empty orbital and the number of ligand coordination atoms will enhance the chelation interaction of the metal cation-chelate-based ILs. In addition, the introduction of functionalized anion groups such as [Im]⁻, [Pyr]⁻, [Pro]⁻, [PhO]⁻, etc. is beneficial to improve the carbon capture ability of the metal cation-chelate-based ILs. In this way, the anion and cation of the metal cation-chelate-based ILs can react with CO₂, thereby increasing the CO₂ absorption capacity. Although the high viscosity of the metal cation-chelate-based ILs will affect its absorption performance, the mixed system obtained by mixing the metal cation-chelate-based ILs with other ILs can not only effectively reduce the viscosity of the system in the process of absorbing CO₂, but also can effectively improve the absorption performance of the mixed system. Considering the good thermal stability, excellent carbon capture ability and recycling performance of the metal cation-chelate-based ILs, it is a good solvent suitable for CO₂ absorption at high temperature. Besides the excellent carbon capture performance, the metal coordination (chelate-based) ILs can also effectively catalyze the reaction of CO₂ with the different substrates such as epoxy compounds (such as ethylene oxide, propylene oxide, styrene oxide, etc.), terminal alkynes, propargyl alcohol with mild reaction conditions and high product yields. The catalytic performance is mainly related to the types of central metal ions and ligands. Metal ions can effectively stabilize the reaction substrate and intermediates, thereby reducing the activation energy of the reaction. The chemical conversion of CO₂ catalyzed by the metal coordination (chelate-based) ILs can be achieved at room temperature and under atmospheric pressure, which provides a new idea for the resource utilization of carbon dioxide. Finally, present issues, challenges, and opportunities faced by metal coordination-based (chelate-based) ILs in the absorption and conversion of CO₂ are also discussed.

Physicochemical profile of Os (III) complexes with pyrazine derivatives: From solution behavior to DNA binding studies and biological assay

New series of osmium(III) complexes with pyrazinamide (PZA) and its analogues (PTCA, PAOX) were synthesized. The physicochemical features in the solid phase have been identified and confirmed using elemental analysis, mass spectrometry, spectroscopic techniques (FT-IR, 1H NMR) and thermogravimetric analysis. Based on the studies we confirmed bidentate nature of selected pyrazine derivatives and proven involvement azomethine and amine nitrogen atoms in coordination of metal ion. In particular, complex (2) is more stable than (1) and (3), retaining thermal stability up to 120 °C. After one stage dehydration process, the simultaneous destruction of Os(III) complexes architecture was observed with immediate decomposition and elimination of pyrazine derivatives. The acid-base equilibria studies of newly synthesized Os(III) complexes were carried out by combined pH-metric-spectrophotometric and potentiometric titrations in the aqueous solution. Os(III) complexes exhibited rich redox chemistry as demonstrated by cyclic voltammetry. The cyclic voltammograms revealed a well-defined redox couples which correspond to reversible, single-electron OsIII → OsII reduction within ‐1.152 to ‐1.374 V vs Ag/AgCl and OsIII → OsIV oxidation within 0.460–0.831 V vs Ag/AgCl. The binding ability of bioactive ligand and their Os(III) complexes with Calf Thymus DNA (CT-DNA) were investigated by spectrophotometric titration. The observed hypsochromic and bathochromic shifts with simultaneous hyperchromic effect confirmed mixed mode of interaction with biological target. Biological activity of Os(III) complexes, i.e. antimicrobial, cytotoxic, haemolytic and photodynamic potential were studied.

Macromolecular Chiral Amplification through a Random Coil to One-Handed Helix Transformation Induced by Metal Ion Coordination in an Aqueous Solution

Many inspiring achievements have been made in inducing chiral amplification in helical polymers; however, the induction of helical chirality in random coil polymers by the intermolecular noncovalen...

Comparison of structural, spectroscopic, theoretical and thermal properties of metal complexes (Zn(II), Mn(II), Cu(II), Ni(II) and Co(II)) of pyridazine-3-carboxylic acid and pyridazine-4-carboxylic acids

In our present work, we studied complexes of 3d-transition metals with pyridazine-3-carboxylic and pyridazine-4-carboxylic acids. The synthesis of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with pyridazinecarboxylic acids was performed. The effect of selected 3d-transition metal ions on the electronic system of ligands and the thermal properties of the complexes by the use of TG-FTIR were studied. The products of dehydration and decomposition processes of studied compounds were determined from the TG (thermogravimetric) and DSC (differential scanning calorimetry) curves. The crystal structures of manganese(II) pyridazine-3-carboxylate acid and pyridazine-4-carboxylate were analysed by the use of single-crystal X-ray analysis. The geometries, NBO atomic charges, energy of HOMO and LUMO orbitals were calculated in the B3LYP/6-311++G(d,p) level. The aromaticity of ligands and complexes were discussed on the basis of HOMA and Bird’s indices. The influence of the type of metal ion coordination and the location of the carboxylate anion in the pyridazine ring on the aromaticity of complexes were discussed. The comparison of the effect of metal ions on the electronic charge distribution and aromaticity of pyridazynecarboxylic and pyridinecarboxylic acids (i.e. nicotinic and picolinic acids) was done.

Complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with ligand formed by condensation reaction of isatin with glutamic acid

The complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with ligand (H2L=C13H12N2O5) formed by condensation reaction of isatin and glutamic acid were synthesized. Their physico-chemical properties were characterized using elemental analysis, XRF, XRD, FTIR, TG–DSC and TG–FTIR methods and magnetic measurements (Gouy’s and SQUID-VSM methods). The complexes were obtained in crystalline forms (monoclinic or triclinic) with the formulae: M(LH)2·nH2O for Mn(II), Ni(II) and Zn(II) and ML·nH2O for Co(II) and Cu(II), where LH=C13H11N2O5–, L-=C13H10N2O52–, n = 1 for Mn(II), Cu(II) and Zn(II), n = 2 for Co(II) and n = 3 for Ni(II). In air at 293–1173 K they decompose in three steps forming finally the oxides of the appropriate metals. The gaseous decomposition products were identified as: H2O, CO2, CO, hydrocarbons and N2O. The magnetic moment values for complexes (except Zn(II) complex) show their paramagnetic properties with the ferro- and antiferromagnetic interactions between central ions. The compounds of Mn(II) and Co(II) are high spin complexes with weak ligand field. In Co(II) and Cu(II) complexes two carboxylate groups take part in the metal ion coordination while in those of Mn(II), Ni(II) and Zn(II) only one carboxylate anion coordinates to central ion.

Sol–Gel Transitions of Comb‐Like Polymethacrylate Copolymers by Mechano‐Thermal Stimuli in Water

AbstractSonogelation by supramolecular gelators is highlighted as a paradigm shift for their potential applications in material and biomedical sciences. Yet, these materials require organic solvents and low‐frequency ultrasound, limiting their utility. Here, a comb‐like polymethacrylate copolymer is synthesized with 2,6‐bis(1‐methylbenzimidazolyl)‐4‐oxypyridine tridentate ligand randomly distributed on poly(ethylene glycol) side chains. Upon addition of zinc perchlorate salt, this copolymer rapidly forms a hydrogel after exposure to either mechanical (i.e., ultrasound) or thermal stimuli. Spectroscopic analysis, to elucidate the mechanism, indicates metal ion coordination to ligand as well as the carbonyl and ethylene glycol units; interestingly, 1H‐NMR suggests that the coordination between tridentate ligand moiety and Zn2+ is unexpectedly weaker in water than in acetonitrile. Investigations by dynamic light scattering indicates that the copolymer forms nanodispersions in excess salt, which coalesces to form a hydrogel by either heating or high intensity focused ultrasound (HIFU). Rheological quantification of these gels suggests stronger crosslinking by HIFU compared to heating.

HD-[HD-GYP] Phosphodiesterases: Activities and Evolutionary Diversification within the HD-GYP Family.

Cyclic dinucleotides are signaling molecules that modulate many processes, including immune response and virulence factor production. Their cellular levels in bacteria are fine-tuned by metal-dependent phosphodiesterases, namely, the EAL and HD-GYP proteins, with HD-GYPs belonging to the larger HD domain superfamily. In this study, we first focus on the catalytic properties and the range of metal ions and substrates of the HD-[HD-GYP] subfamily, consisting of two HD domains. We identified SO3491 as a homologue of VCA0681 and the second example of an HD-[HD-GYP]. Both proteins hydrolyze c-di-GMP and 3'3'c-GAMP and coordinate various metal ions, but only Fe and to a lesser extent Co support hydrolysis. The proteins are active only in the diferrous form and not in the one-electron more oxidized FeIIFeIII state. Although the C-terminal HD-GYP domain is essential for activity, the role of the N-terminal HD domain remains unknown. We show that the N-terminal site is important for protein stability, influences the individual apparent kcat and KM (but not kcat/KM), and cannot bind c-di-GMP, thus precluding its involvement in cyclic dinucleotide sensing. We proceeded to perform phylogenetic analyses to examine the distribution and functional relationships of the HD-[HD-GYP]s to the rest of the HD-GYPs. The phylogeny provides a correlation map that draws a link between the evolutionary and functional diversification of HD-GYPs, serving as a template for predicting the chemical nature of the metallocofactor, level of activity, and reaction outcome.

Two hundred times enhancement of emission intensity of a heptadentate acyclic sensor coordinated with Zn2+ ion: synthesis, crystal structure and emission properties

A heptadentate N4O3 coordinated dinuclear zinc complex was synthesized. The sensor functioned as a “turn-on” fluorescence receptor only to Zn2+ ion in 3:2 v/v MeOH/water in HEPES buffer at pH 7.2 at 25 °C. A huge increase in emission intensity (approximately 200 times) of the ligand was observed in the presence of Zn2+ which was accounted for by the formation of a metal-ligand complex and thus could be used as zinc ion-selective luminescent probe, continuously emitting blue light in the presence of a UV lamp. The theoretically optimized geometry in solution state gives an idea about bond relaxation as well as change the geometric scenario of the coordinated metal ion from trigonal bipyramidal to square pyramidal.

Enthalpy—entropy compensation upon metal ion coordination with porphyrins: generalization for the free bases and doubly deprotonated macrocycles

Enthalpy—entropy compensation upon the coordination of zinc ions by porphyrins with various structural organizations of peripheral substitution in solutions at 298 K was studied. The same compensation temperature Tc was found for both free bases and doubly deprotonated porphyrin macrocycles. The data obtained indicate that the coordination of the metal ion in the tetrapyrrole macrocycle core by the free bases and doubly coordinated forms of porphyrins is characterized by the same promoting vibrational modes.

Synthesis of 1,4-Biphenyl-triazole Derivatives as Possible 17β-HSD1 Inhibitors: An in Silico Study.

Triazoles occupy an important position in medicinal chemistry because of their various biological activities. The structural features of 1,2,3-triazoles enable them to act as a bioisostere of different functional groups such as amide, ester, carboxylic acid, and heterocycle, being capable of forming hydrogen bonds and π–π interactions or coordinate metal ions with biological targets. In this work, the synthesis of 1,2,3-triazole derivatives via copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) is reported. Overexpression of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) is often found in breast cancer cells. Molecular similarity and docking analysis were used to evaluate the potential inhibitory activity of 1,2,3-triazoles synthesized over 17β-HSD1 for the treatment of mammary tumors. Our in silico analysis shows that compounds 4c, 4d, 4f, 4g, and 4j are good molecular scaffold candidates as 17β-HSD1 inhibitors.

Dielectric barrier discharge plasma treatment affects stability, metal ion coordination, and enzyme activity of bacterial superoxide dismutases

AbstractA molecular‐level understanding of the effects of atmospheric‐pressure plasma on biological samples requires knowledge of the effects on proteins. Superoxide dismutases, which detoxify superoxide under oxidative stress conditions, play a key role in bacterial plasma resistance. Investigation of the impact of dielectric barrier discharge (DBD) treatment on purified superoxide dismutases SodA and SodB of Escherichia coli showed that DBD treatment caused a rapid protein degradation, with only 8% of protein remaining after 10 min. The affinity of SodA for the metal cofactor Mn2+ was reduced. Mass spectrometry, in conjunction with coupled‐cluster calculations, revealed that modifications of amino acid residues in the active site can explain the decreased metal affinity and a distortion of the coordination geometry responsible for the activity loss.

Metal ion coordination delays amyloid-β peptide self-assembly by forming an aggregation–inert complex

A detailed understanding of the molecular pathways for amyloid-β (Aβ) peptide aggregation from monomers into amyloid fibrils, a hallmark of Alzheimer's disease, is crucial for the development of diagnostic and therapeutic strategies. We investigate the molecular details of peptide fibrillization in vitro by perturbing this process through addition of differently charged metal ions. Here, we used a monovalent probe, the silver ion, that, similarly to divalent metal ions, binds to monomeric Aβ peptide and efficiently modulates Aβ fibrillization. On the basis of our findings, combined with our previous results on divalent zinc ions, we propose a model that links the microscopic metal-ion binding to Aβ monomers to its macroscopic impact on the peptide self-assembly observed in bulk experiments. We found that substoichiometric concentrations of the investigated metal ions bind specifically to the N-terminal region of Aβ, forming a dynamic, partially compact complex. The metal-ion bound state appears to be incapable of aggregation, effectively reducing the available monomeric Aβ pool for incorporation into fibrils. This is especially reflected in a decreased fibril-end elongation rate. However, because the bound state is significantly less stable than the amyloid state, Aβ peptides are only transiently redirected from fibril formation, and eventually almost all Aβ monomers are integrated into fibrils. Taken together, these findings unravel the mechanistic consequences of delaying Aβ aggregation via weak metal-ion binding, quantitatively linking the contributions of specific interactions of metal ions with monomeric Aβ to their effects on bulk aggregation.