CuII Ions Research Articles

A bis-chelate o-vanillin-2-ethano-lamine copper(II) complex bearing both imine and amine forms of the ligand.

The mol-ecular bis-chelate complex (2-{[(2-hy-droxy-ethyl-κO)amino-κN]meth-yl}-6-meth-oxy-phenolato-κO)(2-{[(2-hy-droxy-eth-yl)imino-κN]meth-yl}-6-meth-oxy-phenolato-κO)copper(II), [Cu(C10H14NO3)(C10H12NO3)] or [Cu(HL im)(HL am); HL im = C10H14NO3; HL am = C10H12NO3, represents the first compound containing a salicyl-idene-2-ethano-lamine type ligand in both imino HL im (Schiff base) and amino HL am (reduced Schiff base) forms that has been structurally characterized on the basis of X-ray data. Two mol-ecules of the monodeprotonated ligands coordinate the CuII ion in an (N,O phen)-bidentate and an (N,O phen,O alc)-tridentate fashion in the case of the imino and amino forms, respectively. The shape of the CuN2O3 coordination polyhedron is a distorted square-pyramid (geometry index τ5 = 0.26). Inter-molecular N-H⋯O and O-H⋯O hydrogen bonds, involving H atoms of the amino and hy-droxy-ethyl groups, create a two-dimensional supra-molecular array extending parallel to (010).

Homo- and heterometallic oxalate-based complexes obtained using [Cr(C2O4)3]3− building block – Two polymorphs of a solvate

Two heterometallic complex salts, as polymorphs of a solvate, consisting of three different mononuclear units, [CuCl(phen)2][Cu(H2O)(phen)2][Cr(C2O4)3]·nH2O [n = 5 (1) and n = 8 (2); phen = 1,10-phenanthroline] were obtained in reactions in which [Cr(C2O4)3]3− was used as a building unit. The polymorphs of a solvate are obtained in crystalline forms that differ in type or stoichiometry of included solvent molecules, mostly obtained under different conditions. In this [CuIICrIII] system, the used solvents and crystallization method influence the final product, i.e., the formation of a specific solvatomorph. From the reaction of an aqueous solution of K3[Cr(C2O4)3]·3H2O and acetonitrile solutions containing phen and CuCl2·2H2O, compound 1 was formed when the layering technique is used; and compound 2 can be obtained from the mixture of these reactants, but using methanol instead of acetonitrile. Based on the index parameter for the degree of trigonality, τ, the geometry of copper(II) atoms of the [Cu(H2O)(phen)2]2+ cations in 1 and 2 are distorted from square pyramidal toward trigonal bipyramidal conformation, while those of [CuCl(phen)2]+ have a trigonal bipyramidal geometry. Interestingly, in the presence of [NBu4]+ cations, and applying slow liquid diffusion, partial decomposition of the building block [Cr(C2O4)3]3− occurred and the homobinuclear oxalate-bridged complex [{Cu(bpy)Cl}2(µ-C2O4)]·CH3OH (3; bpy = 2,2′-bipyridine) was formed. Consequently, the oxalate ligand released from the coordination sphere of CrIII was coordinated to CuII ions during the crystallization process. The obtained oxalate-based compounds 1–3 were characterized by IR spectroscopy and single-crystal X-ray diffraction.

Structural and Spectroscopic Characteristics of NiII and CuII Complexes with Poly (Vinyl Alcohol-Nicotinic Acid) Copolymers for Photocatalytic Degradation of Indigo Carmine Dye

Poly-vinyl-alcohol (PVA) has been cross-linked chemically with nicotinic-acid (NA) in an aqueous medium. The copolymers were complexed with NiII and CuII ions. The complexes and copolymers were analyzed using FT-IR and UV–Visible spectroscopy, XRD and TGA, but copolymers were extra analyzed with nuclear magnetic resonance (1H NMR). FT-IR spectra of copolymer revealed the presence of C=O & C–N groups due to the esterification of PVA-NA. The Cu/NA-PVA formed via bidentate interaction of the pyridinyl and carboxyl of NA. EPR/UV-vis data shows the square-planar geometry for NiII and CuII complexes. The adsorption of IC dye onto CuII/NA-PVA complex was noticeably greater (90%) in 35 min than NiII/NA-PVA. The DFT\B3LYP with 6- 311G* quantum chemical calculations were carried out for tested compounds. The DFT was conducted to examine an interaction mode of the target compounds with the reaction system. The QSPR was calculated as: optimization geometries, (FMOs), chemical-reactivities and NLO for the copolymers. The (MEPs) were figured to predict the interaction behavior of the ligand and its complexes.

Solid State Characterization of One‐ and Two‐Electron Oxidized CuII‐salen Complexes with para‐Substituents: Geometric Structure‐Magnetic Property Relationship

AbstractOne‐ and two‐electron oxidized CuII complexes of Schiff base ligands with para‐substituted phenolate moieties were synthesized and characterized. The crystal structure of the one‐electron oxidized methylthio‐substituted complex [Cu(MeS‐salen)]SbCl6 revealed the intermolecular π‐π stacking interaction of the two phenolate moieties with those of the neighboring complex cations to form the one‐dimensional chain. Such a π‐π stacking interaction could not be detected in the two‐electron oxidized complex [Cu(MeS‐salen)](SbCl6)2 and the oxidized methoxy‐substituted complexes [Cu(MeO‐salen)](SbF6)n (n=1, 2). Magnetic study of [Cu(MeO‐salen)]SbF6 showed a weak antiferromagnetic interaction between the CuII ion and phenoxyl radical unpaired electron spins, while [Cu(MeS‐salen)]SbCl6 showed a ferromagnetism. Both of the two‐electron oxidized complexes exhibited a relatively strong magnetic interaction between the two radical electrons, while the signs of the electron spins are different.

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation.

The development of long-wavelength photoinduced copper-catalyzed azide–alkyne click (CuAAC) reaction routes is attractive for organic and polymer chemistry. In this study, we present a novel synthetic methodology for the photoinduced CuAAC reaction utilizing exfoliated two-dimensional (2D) few-layer black phosphorus nanosheets (BPNs) as photocatalysts under white LED and near-IR (NIR) light irradiation. Upon irradiation, BPNs generated excited electrons and holes on its conduction (CB) and valence band (VB), respectively. The excited electrons thus formed were then transferred to the CuII ions to produce active CuI catalysts. The ability of BPNs to initiate the CuAAC reaction was investigated by studying the reaction between various low molar mass alkyne and azide derivatives under both white LED and NIR light irradiation. Due to its deeper penetration of NIR light, the possibility of synthesizing different macromolecular structures such as functional polymers, cross-linked networks and block copolymer has also been demonstrated. The structural and molecular properties of the intermediates and final products were evaluated by spectral and chromatographic analyses.

Mono- and oligonuclear complexes based on a o-vanillin derived Schiff-base ligand: Synthesis, crystal structures, luminescent and electrochemical properties

A new synthetic approach for homo- and heteronuclear complexes, based on N,N′-bis[(3-methoxysalicylideneamino)-propyl]-piperazine (H2L) Schiff-base ligand, has been developed. The ligand has been crystallized in the form H2L·2DMSO and its structure has been solved. Using this ligand, the following complexes have been synthesized: [CoL](ClO4) (1), [Zn2L(CH3COO)2]·2H2O (2), [Cu3L2(NO3)2] (3) and [LaCu6L4(H2O)2(NO3)2](NO3)5·15H2O (4). The 1–4 complexes were characterized by elemental analysis, X-ray crystallography, infrared and diffuse reflectance spectroscopy. The crystallographic investigations revealed that H2L presents the stable chair conformation of the piperazine ring, while its coordination mode changes according to the nature of the metal ion and counterion, respectively, allowing the formation of mono- (1) and oligonuclear (2–4) complexes. Compound 1 consists of a mononuclear complex cation, where the double-deprotonated ligand (L2−) encapsulates the trivalent cobalt ion. In compound 2, L2− acts as a symmetrical binucleatig ligand through the two N2O sets disposed on each side of the piperazine ring and coordinates two zinc(II) ions. Compounds 3 and 4 contain trinuclear units where two ligand molecules coordinate unsymmetrically three CuII ions, with the N3O donor set wrapped around the peripheral CuII and the remaining NO sets bound to the central CuII ion. Two such trinuclear moieties coordinate the LaIII ion in crystal 4. Electrochemical behavior of compounds 1 and 3 and luminescent properties of compound 2 are discussed.

Heterobimetallic metallacrown of EuIIICuII5 with 5-methyl-2-pyrazinehydroxamic acid: Synthesis, crystal structure, magnetism, and the influence of CuII ions on the photoluminescent properties

A 3d-4f heterobimetallic metallacrown with the formula of [EuCu5(5mpzHA)5(NO3)3/2(H2O)6]2·3NO3·4H2O·5CH3OH (MC1) has been prepared using the stirring method from a mixture of 5-methyl-2-pyrazinehydroxamic acid (5mpzHA), Cu(AcO)2·H2O, and Eu(NO3)3·5H2O salts in methanol under reflux, which yielded single crystals after slow solvent evaporation. Single crystal X-ray diffraction analysis shows a crown-like [EuCu5(5mpzHA)5] core with the 15-MC-5 system, with five CuII and one EuIII ions occupying the rim and the dome of the crown, respectively. Water molecules oxygen atoms and one nitrate anion fill the coordination sphere around the EuIII ion, which exhibits a MFF-9 shape. The MC1 is made up of two [EuCu5(5mpzHA)5(NO3)3/2(H2O)6] metallacrown units connected by one coordinated nitrate ion, where intramolecular hydrogen bonding interactions generate aR86(18) supramolecular macrocycle leading a two-dimensional supramolecular network. The emission and excitation spectra of MC1 show the absence of EuIII emission and f-f transitions, probably due to the paramagnetic nature of the CuII ions which play a key role in quenching the fluorescence in MC1. The observed magnetic properties are attributed to antiferromagnetic interactions among the CuII ions within the metallacrown rim plus the depopulation of EuIII excited Stark sublevels. This magnetic behavior was also supported by the EPR spectroscopy which presents a superposition of signals of the termally populated state 7F1 of EuIII and CuII ions at room temperature and a sole signal of CuII ion at 4 K.

Interaction of the potent antitumoral compounds Casiopeinas® with blood serum and cellular bioligands

Casiopeinas® are among the few CuII compounds patented for their antitumor activity, but their mode of action has not been fully elucidated yet. One of them, Cas II-gly, is formed by 4,7-dimethyl-1,10-phenanthroline (Me2phen) and glycinato (Gly). In blood and cells, Cas II-gly can keep its identity or form mixed species with serum or cytosol bioligands (bL or cL) with composition CuII–Me2phen–bL/cL, CuII–Gly–bL/cL, or CuII–bL/cL. In this study, the binding of Cas II-gly with low molecular mass bioligands of blood serum (citric, L-lactic acid, and L-histidine) and cytosol (reduced glutathione (GSH), reduced nicotinamide adenine dinucleotide (NADH), adenosine triphosphate (ATP), and l-ascorbic acid) was examined through the application of instrumental (ElectroSpray Ionization-Mass Spectrometry and Electron Paramagnetic Resonance) and computational (Density Functional Theory) methods. The results indicated that mixed species CuII–Me2phen–bL/cL are formed, with the bioligands replacing glycinato. The formation of these adducts may participate in the copper transport toward the target organs and facilitate the cellular uptake or, in constrast, preclude it. In the systems with GSH, NADH and L-ascorbate, a redox reaction occurs with the partial oxidation of cL to the corresponding oxidized form (GSSG, NAD+ and dehydroascorbate) which interact with CuII. Formed CuI ion does not give complexation reactions with reduced or oxidized form of bioligands for its ‘soft’ character and low affinity for oxygen and nitrogen donors compared to CuII. However, CuI could promote Fenton-like reactions with production of reactive oxygen species (ROS) related to the antitumor activity of Casiopeinas®.

The Copper Chaperone NosL Forms a Heterometal Site for Cu Delivery to Nitrous Oxide Reductase.

The final step of denitrification is the reduction of nitrous oxide (N2O) to N2, mediated by Cu‐dependent nitrous oxide reductase (N2OR). Its metal centers, CuA and CuZ, are assembled through sequential provision of twelve CuI ions by a metallochaperone that forms part of a nos gene cluster encoding the enzyme and its accessory factors. The chaperone is the nosL gene product, an 18 kDa lipoprotein predicted to reside in the outer membrane of Gram‐negative bacteria. In order to better understand the assembly of N2OR, we have produced NosL from Shewanella denitrificans and determined the structure of the metal‐loaded chaperone by X‐ray crystallography. The protein assembled a heterodinuclear metal site consisting of ZnII and CuI, as evidenced by anomalous X‐ray scattering. While only CuI is delivered to the enzyme, the stabilizing presence of ZnII is essential for the functionality and structural integrity of the chaperone.

Loading Linear Arrays of CuII Inside Aromatic Amide Helices.

The very stable helices of 8‐amino‐2‐quinolinecarboxylic acid oligoamides are shown to uptake CuII ions in their cavity through deprotonation of their amide functions with minimal alteration of their shape, unlike most metallo‐organic structures which generally differ from their organic precursors. The outcome is the formation of intramolecular linear arrays of a defined number of CuII centers (up to sixteen in this study) at a 3 Å distance, forming a molecular mimic of a metal wire completely surrounded by an organic sheath. The helices pack in the solid state so that the arrays of CuII extend intermolecularly. Conductive‐AFM and cyclic voltammetry suggest that electrons are transported throughout the metal‐loaded helices in contrast with hole transport observed for analogous foldamers devoid of metal ions.

Loading Linear Arrays of CuII Inside Aromatic Amide Helices

AbstractThe very stable helices of 8‐amino‐2‐quinolinecarboxylic acid oligoamides are shown to uptake CuII ions in their cavity through deprotonation of their amide functions with minimal alteration of their shape, unlike most metallo‐organic structures which generally differ from their organic precursors. The outcome is the formation of intramolecular linear arrays of a defined number of CuII centers (up to sixteen in this study) at a 3 Å distance, forming a molecular mimic of a metal wire completely surrounded by an organic sheath. The helices pack in the solid state so that the arrays of CuII extend intermolecularly. Conductive‐AFM and cyclic voltammetry suggest that electrons are transported throughout the metal‐loaded helices in contrast with hole transport observed for analogous foldamers devoid of metal ions.

Benchmark C2 H2 /CO2 Separation in an Ultra-Microporous Metal-Organic Framework via Copper(I)-Alkynyl Chemistry.

Separation of acetylene from carbon dioxide remains a daunting challenge because of their very similar molecular sizes and physical properties. We herein report the first example of using copper(I)-alkynyl chemistry within an ultra-microporous MOF (CuI @UiO-66-(COOH)2 ) to achieve ultrahigh C2 H2 /CO2 separation selectivity. The anchored CuI ions on the pore surfaces can specifically and strongly interact with C2 H2 molecule through copper(I)-alkynyl π-complexation and thus rapidly adsorb large amount of C2 H2 at low-pressure region, while effectively reduce CO2 uptake due to the small pore sizes. This material thus exhibits the record high C2 H2 /CO2 selectivity of 185 at ambient conditions, significantly higher than the previous benchmark ZJU-74a (36.5) and ATC-Cu (53.6). Theoretical calculations reveal that the unique π-complexation between CuI and C2 H2 mainly contributes to the ultra-strong C2 H2 binding affinity and record selectivity. The exceptional separation performance was evidenced by breakthrough experiments for C2 H2 /CO2 gas mixtures. This work suggests a new perspective to functionalizing MOFs with copper(I)-alkynyl chemistry for highly selective separation of C2 H2 over CO2 .

Two-Dimensional Nitronyl Nitroxide–Cu Networks Based on Multi-Dentate Nitronyl Nitroxides: Structures and Magnetic Properties

Two multi-dentate nitronyl nitroxide radicals, namely, bisNITPhPy ([5-(4-pyridyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene) and NIT-3Py-5-4Py (2-{3-[5-(4-pyridyl)]pyridyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were assembled with CuII ions to obtain two-dimensional heterospin 2p–3d coordination polymers [Cu7(hfac)14(bisNITPhPy)2]n (1) and [Cu2(hfac)4(NIT-3Py-5-4Py)]n (2) (hfac: hexafluoroacetylacetonate). In both compounds, the bisNITPhPy and NIT-3Py-5-3Py radicals acted as pentadentate and tetradentate ligands, respectively, to connect with CuII ions, generating a 2D layer structure. The analysis of the magnetic behavior indicated that strong antiferromagnetic coupling and ferromagnetic interaction (J = 17.1 cm−1) coexisted in 1. For 2, there were ferromagnetic couplings between the CuII ion and NO group, as well as the CuII ion and radical via the pyridine ring with J1 = 32.8 and J2 = 2.2 cm−1, respectively.

Oxidase Reactivity of CuII Bound to N-Truncated Aβ Peptides Promoted by Dopamine.

The redox chemistry of copper(II) is strongly modulated by the coordination to amyloid-β peptides and by the stability of the resulting complexes. Amino-terminal copper and nickel binding motifs (ATCUN) identified in truncated Aβ sequences starting with Phe4 show very high affinity for copper(II) ions. Herein, we study the oxidase activity of [Cu–Aβ4−x] and [Cu–Aβ1−x] complexes toward dopamine and other catechols. The results show that the CuII–ATCUN site is not redox-inert; the reduction of the metal is induced by coordination of catechol to the metal and occurs through an inner sphere reaction. The generation of a ternary [CuII–Aβ–catechol] species determines the efficiency of the oxidation, although the reaction rate is ruled by reoxidation of the CuI complex. In addition to the N-terminal coordination site, the two vicinal histidines, His13 and His14, provide a second Cu-binding motif. Catechol oxidation studies together with structural insight from the mixed dinuclear complexes Ni/Cu–Aβ4−x reveal that the His-tandem is able to bind CuII ions independently of the ATCUN site, but the N-terminal metal complexation reduces the conformational mobility of the peptide chain, preventing the binding and oxidative reactivity toward catechol of CuII bound to the secondary site.

Measurement of Interpeptidic CuII Exchange Rate Constants of CuII-Amyloid-β Complexes to Small Peptide Motifs by Tryptophan Fluorescence Quenching.

The interpeptidic CuII exchange rate constants were measured for two Cu amyloid-β complexes, Cu(Aβ1-16) and Cu(Aβ1-28), to fluorescent peptides GHW and DAHW using a quantitative tryptophan fluorescence quenching methodology. The second-order rate constants were determined at three pH values (6.8, 7.4, and 8.7) important to the two Cu(Aβ) coordination complexes, components Cu(Aβ)I and Cu(Aβ)II. The interpeptidic CuII exchange rate constant is approximately 104 M-1 s-1 but varies in magnitude depending on many variables. These include pH, length of the Aβ peptide, location of the anchoring histidine ligand in the fluorescent peptide, number of amide deprotonations required in the tryptophan peptide to coordinate CuII, and interconversion between Cu(Aβ)I and Cu(Aβ)II. We also present EPR data probing the CuII exchange between peptides and the formation of ternary species between Cu(Aβ) and GHW. As the nonfluorescent GHK and DAHK peptides are important motifs found in the blood and serum, their ability to sequester CuII ions from Cu(Aβ) complexes may be relevant for the metal homeostasis and its implication in Alzheimer's disease. Thus, their kinetic CuII interpeptidic exchange rate constants are important chemical rate constants that can help elucidate the complex CuII trafficking puzzle in the synaptic cleft.

A mixed-valence CuII/CuI coordination polymer based on bridged thiocyanate and in situ formed di(N-heterocyclic) sulfide: Synthesis, structure, and magnetic properties

A mixed-valence CuII/CuI coordination polymer {CuIICuI2[S(PIP)2](μ-SCN)4}n (1) has been generated via the reaction of KSCN, CuCl2·2H2O, and 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (HPIP) under solvothermal conditions. The di(N-heterocyclic) sulfide ligand [S(PIP)2] (S(PIP)2 = bis(3-(pyridin-2-yl)imidazo[1,5-a]pyridin-1-yl)sulfane) was formed in situ by the reaction of HPIP and KSCN in the presence of CuCl2·2H2O. The structure of compound 1 was determined by X-ray single crystal diffraction. In the structure of 1, one CuII ion, which is chelated by one neutral [S(PIP)2] ligand, and two CuI ions are connected by end-to-end thiocyanates to generate an infinite 2D coordination polymer. Complex 1 was also characterized by IR, PXRD, XPS and ESR. The magnetic properties of 1 have been investigated.

1,4,7‐Triazacyclononane (tacn) with N,N′‐bridging methylene‐bis(phosphinic acid) group and its complexes

AbstractA bicyclic ligand, 1,4,7‐triazacyclononane 1,4‐bridged with methylene‐bis(phosphinate) and bearing benzyl substituent on the remaining amino group, was synthesized from N‐benzyl‐tacn and CH2(PO2H2)2 by two sequential Mannich‐type reactions in a high yield. Basicity of the macrocycle is high (pK1=12.25). Complexes with CuII and NiII ions show dimeric structures in the solid state. The structures exhibit distorted octahedral environment with two ring amino groups from one molecule and two oxygen atoms of chelating bis(phosphinate) anion from the other molecule in the equatorial plane, and with the apical positions occupied by the remaining macrocycle amino group and by one of the phosphinate oxygen atoms. The metal ions in the dimers are additionally bridged by one phosphinate group. Stability of the CuII complex is more than ten orders of magnitude lower than that of the [Cu(nota)]− complex due to a different number and different nature of the pendant arms, and inappropriate arrangement of donor atoms in the ligand bicyclic structure. Rigidity of the short P−C−P chain of the geminal methylene‐bis(phosphinate) does not allow simultaneous coordination of both phosphinate groups and the ring amines to the same metal ion. The low solubility of NiII and ZnII complexes disabled determination of their stability constants.

Synthesis, structure and computational study of 5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine (Pesta) and its heterometallic π,σ-complex [Cu2FeCl2(Pesta)4][FeCl4

Copper(I) π-coordination compounds with allyl derivatives of azoles are an interesting subject of current research, but CuI π-complexes with other transition-metal ions incorporated in the structure have been virtually uninvestigated. The present work is directed toward the synthesis and structural characterization of the novel heterometallic CuI/FeII π-complex di-μ2-chlorido-1:2κ2Cl;2:3κ2Cl-tetrakis[μ2-5-(prop-2-en-1-ylsulfanyl)-1,3,4-thiadiazol-2-amine]-1:2κ2N4:N3;1(η2),κN4:2κN3;2:3κ2N3:N4;2κN3:3(η2),κN4-dicopper(I)iron(II) tetrachloridoferrate(II), [Cu2FeCl2(C5H7N3S2)4][FeCl4] (1). The structure of the 5-[(prop-2-en-1-yl)sulfanyl]-1,3,4-thiadiazol-2-amine (Pesta, C5H7N3S2) ligand is also presented. The cationic substructure in 1 consists of one FeII and two CuI ions bridged by two chloride ions along with two σ,σ- and two π,σ-coordinated ligands, whereas the anionic part is built of isolated tetrahedral [FeCl4]2- ions. π-Coordination of the Pesta allyl group to the CuI ions prevents agglomeration of the inorganic Cu-Cl-Fe-Cl-Cu part into infinate chains. An energy framework computational analysis was performed for Pesta.

Study of interaction of metal ions with methylthymol blue by chemometrics and quantum chemical calculations

In this study, we determine the acidity constants of methylthymol blue (MTB) and association constants of its complexes with the ZnII, CuII, and FeII metal ions (MIs), through theoretical and experimental means. The complexes were characterized using UV–Visible absorption spectroscopy combined with soft/hard chemometrics methods and quantum chemical calculations. Quantum chemical calculations revealed that electronic transitions in the UV–Visible spectra of MTB have mixed n → π* and π → π* characters. The results of molar ratio and multivariate curve resolution alternating least squares (MCR-ALS) revealed the formation of successive 1:2 and 1:1 complexes (MI:MTB) for the ZnII and CuII systems. However, the formation of successive 1:1 and 2:1 complexes are suggested for FeII by the molar ratio and MCR-ALS. The majority of transitions observed in the UV–Visible spectra of the Zn(MTB) and Cu(MTB) complexes have ligand-to-ligand charge transfer (LLCT) characters. However, the transitions in the UV–Visible spectrum of the Fe(MTB) complex have LLCT and metal-to-ligand charge transfer (MLCT) characters. For the Fe2(MTB) complex, the lowest energy transition of has an LLCT character. However, its higher energy transitions are a mixture of LLCT, MLCT, and metal-to-metal charge transfer (MMCT) characters. The correlation between experimental and computed wavelengths revealed that the 1:1 complexes of ZnII and CuII prefer square pyramidal geometries. However, the FeII complexes always show octahedral geometry.

Ligand Induced CuII Transport Restricts Cancer and Mycobacterial Growth: Towards a Plug-and-Select Ion Channel Scaffold.

Synthetic channels with high ion selectivity are attractive drug targets for diseases involving ion dysregulation. Achieving selective transport of divalent ions is highly challenging due their high hydration energies. A small tripeptide amphiphilic scaffold installed with a pybox ligand selectively transports CuII ions across membranes. The peptide forms stable dimeric pores in the membrane and transports ions by a Cu2+ /H+ antiport mechanism. The ligand-induced excellent CuII selectivity as well as high membrane permeability of the peptide is exploited to promote cancer cell death. The peptide's ability to restrict mycobacterial growth serves as seeds to evolve antibacterial strategies centred on selectively modulating ion homeostasis in pathogens. This simple peptide can potentially function as a universal, yet versatile, scaffold wherein the ion selectivity can be precisely controlled by modifying the ligand at the C terminus.