Coordination Of Cu Research Articles

Spectroscopic and Electronic Structure Studies of Copper(II) Binding to His111 in the Human Prion Protein Fragment 106−115: Evaluating the Role of Protons and Methionine Residues

The prion protein (PrP(C)) is implicated in the spongiform encephalopathies in mammals, and it is known to bind Cu(II) at the N-terminal region. The region around His111 has been proposed to be key for the conversion of normal PrP(C) to its infectious isoform PrP(Sc). The principal aim of this study is to understand the role of protons and methionine residues 109 and 112 in the coordination of Cu(II) to the peptide fragment 106-115 of human PrP, using different spectroscopic techniques (UV-vis absorption, circular dichroism, and electron paramagnetic resonance) in combination with detailed electronic structure calculations. Our study has identified a proton equilibrium with a pK(a) of 7.5 associated with the Cu(II)-PrP(106-115) complex, which is ascribed to the deprotonation of the Met109 amide group, and it converts the site from a 3NO to a 4N equatorial coordination mode. These findings have important implications as they imply that the coordination environment of this Cu binding site at physiological pH is a mixture of two species. This study also establishes that Met109 and Met112 do not participate as equatorial ligands for Cu, and that Met112 is not an essential ligand, while Met109 plays a more important role as a weak axial ligand, particularly for the 3NO coordination mode. A role for Met109 as a highly conserved residue that is important to regulate the protonation state and redox activity of this Cu binding site, which in turn would be important for the aggregation and amyloidogenic properties of the protein, is proposed.

A gold nanorod based colorimetric probe for the rapid and selective detection of Cu2+ ions

A gold nanorod (AuNR) based colorimetric probe was reported for the rapid and selective detection of Cu(2+) ions. The probe was fabricated by functionalizing cysteine (Cys) onto AuNR (Cys-AuNR) with an aspect ratio of 2.3. The strong coordination of Cu(2+) with cysteine resulted in a stable Cys-Cu-Cys complex, and induced the aggregation of the colloidal nanorods along with a rapid colour change from blue-green to dark gray. Potential factors affecting the performance of the probe for the detection of Cu(2+) were carefully optimized, including the pH value of the buffer media, the concentration of cysteine, and the kinetics for the coordination of Cu(2+) with Cys-AuNR. Under optimal conditions, the developed colorimetric method gave a linear range of 1-100 μM for Cu(2+), and a detection limit (3s) of 0.34 μM. Moreover, the developed method exhibited excellent selectivity for Cu(2+), and quantitative spike-recoveries from 90% to 107% in environmental water samples. The proposed colorimetric approach can in principle be used to detect other metal ions by functionalizing various specific ligands onto the AuNR that can selectively bind the other target metal ions.

One to chelate them all: investigation of a versatile, bifunctional chelator for 64Cu, 99mTc, Re and Co

We describe the synthesis of the dip (di-picolyl-carboxylate) bifunctional chelator system, capable of fast coordination of Cu(2+), (64)Cu(2+) and Co(2+), as well as the [M(CO)(3)](+)-core (M = (99m)Tc, Re); it displays a variety of binding modes--tridentate when protected, tetradentate when deprotected. Syntheses of both the benzyl-nitro derivative and the benzyl-amino derivatives are described. The latter was coupled to biotin to show the viability of the system for functionalization with biomolecules. Besides coordination chemistry with stable isotopes, we also present labelling data with (64)Cu and (99m)Tc, as well as in vitro stability studies.

Synthesis, characterization, and DFT studies of thione and selone Cu(i) complexes with variable coordination geometries

Coordination of Cu(I) halides with N,N'-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu(4)(μ-dmise)(4)(μ-X)(2)X(2) copper complexes with average Cu-Se bond lengths of 2.42 Å and a Cu(2)(μ-X)(2) core (X = I (1) or Br (6)) that's in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)(2)X (3a, 3b, 4, and 7) or Cu(dmise)(2)X (2, 5, and 8) with average Cu-S and Cu-Se bond lengths of 2.23 Å and 2.34 Å, respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular π-π interactions, and short contact interactions between X-H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV.

A BODIPY-based fluorescent chemodosimeter for Cu(ii) driven by an oxidative dehydrogenation mechanism

A boradiazaindacene (BODIPY) derivative containing a simple NO bidentate ligand shows a Cu(2+)-selective fluorescence in aqueous media. This is promoted via a coordination of Cu(2+) followed by oxidative dehydrogenation of an amine moiety, leading to a formation of a fluorescent Cu(+)-Schiff base complex.

A naphthalimide fluorophore with efficient intramolecular PET and ICT Processes: Application in molecular logic

A novel 4-amino-1,8-naphthalimide (NDI) with two different metal cation receptors connected at 4-amino or imide nitrogen positions respectively was designed and prepared. Significant internal charge transfer (ICT) as well as photoinduced electron transfer (PET) from the receptors to NDI is revealed by the shifted UV-vis absorption spectra and significant fluorescence quenching. Both Zn(2+) and Cu(2+) can coordinate selectively with the two cation receptors in this molecule with different affinities. The coordination of Zn(2+) with the receptor at imide nitrogen hindered the PET process and accordingly restored the quenched fluorescence of NDI. But the coordination of Zn(2+) at 4-amino position blocked the ICT process and caused significant blue-shift on the absorption peak with the fluorescence intensity unaffected. Similarly, coordination of Cu(2+) with the receptor at imide nitrogen can block the PET process, but can not restore the quenched fluorescence of compound 3 due to the paramagnetic properties of Cu(2+), which quench the fluorescence significantly instead. With Cu(2+) and Zn(2+) as two chemical inputs and absorption or fluorescence as output, several logic gate operations, such as OR, NOR and INHIBIT, can be achieved.

Chiral and Extended π‐Conjugated Bis(2‐pyridyl)phospholes as Assembling N,P,N Pincers for Coordination‐Driven Synthesis of Supramolecular [2,2]Paracyclophane Analogues

Chiral, π-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole derivatives 1a(2,2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan-Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu(I) and formation of chiral supramolecular assemblies with π-conjugated ditopic dicyano ligands was investigated. Chiral C(2)-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2)·2 HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis(aza[4]helicene)phosphole 1a(4) was synthesized and displays extended π conjugation. A supramolecular rectangle was obtained by coordination to Cu(I) and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of π-π stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole.

Low-temperature X-ray diffraction study of [CuII(1,10-C12H8N2)3]2+{CoIII[η5-(3)-1,2-C2B9H11]2} 2 − ·CH3CN

Single crystal XRD is used to study the crystal structure of a new compound containing the dicarbollyl cluster anion Co(III) with the composition [CuPhen3][Co(C2B9H11)2]2·CH3CN, where Phen is 1,10-phenanthroline. The crystallographic data: C46H71B36N7Co2Cu, M = 1292.66, monoclinic system, P21/c space group, unit cell parameters a = 14.7178(2) A, b = 19.5640(4) A, c = 22.8663(5) A, β = 106.6601(7)°, V = 6307.75(33) A3, Z = 4, dx = 1.361 g/cm3, T = 100 K, μ = 0.90 mm−1. The structure is solved by the direct method and refined by the full-matrix LSM in an anisotropic-isotropic (for H atoms) approximation up to the final agreement factors R1 = 0.0370, wR2 = 0.0869 for 13,807 Ihkl ≥ 2 σI out of 18,295 measured Ihkl. The structure consists of [CuPhen3] cations, Co(C2B9H11)2 anions, and acetonitrile molecules MeCN. The central Cu atom in the cation in the general position, and its coordination geometry is a distorted extended octahedron formed by six nitrogen atoms of the three bidentate Phen ligands. The coordination of Cu(II) in the cation is (2+2+2) with two long axial and four shorter equatorial Cu-N bonds, whose average lengths are 2.239(2) A and 2.077(1) A respectively. Each anion has its own position of the -C2-groups; for Co(1), it is a quasi-gauche-configuration; for Co(2), a quasi-trans-configuration.

A unique, rigid porous coordination polymer with 1,4,5-triazanaphthalene and mixed-valence Cu as the bridging metal

Abstract A novel mixed-valence Cu(I)/Cu(II) compound with the bridging ligand 1,4,5-triazanaphthalene (tan) is reported, having the overall formula [Cu2(tan)4](ClO4)3. The synthesis, X-ray crystal structure and preliminary spectroscopic properties are presented. The coordination of Cu(I) is tetrahedral, and that of Cu(II) is square planar. The packing of the units generates a 3D network with spaces in the cavities, available for the counter anions and accessible for small solvent molecules.

Synthesis, Characterisation and Photophysical Study of Alkynylrhenium(I) Tricarbonyl Diimine Complexes and Their Metal-Ion Coordination-Assisted Metallogelation Properties

A series of alkynylrhenium(I) tricarbonyl diimine complexes has been synthesized and characterized. A blue shift of the intense low-energy MLCT absorption band in the visible region was observed upon coordination of Cu(I) or Ag(I). This class of complexes has been found to show rich thermotropic gelation behaviour upon Cu(I) or Ag(I) coordination with their morphology characterized by SEM. Their variable-temperature UV/Vis absorption and emission properties have also been studied. A blue shift in the MLCT absorption band and the switching on of luminescence were observed upon sol-gel transition.

Toward the detection of cellular copper(II) by a light-activated fluorescence increase.

A new type of Cu2+ fluorescent sensor, coucage, has been prepared with a photosensitive nitrophenyl group incorporated into the backbone of a coumarin-tagged tetradentate ligand. Coucage provides a selective fluorescence response for Cu2+ over other biologically relevant metal ions. Coordination of Cu2+ dims the fluorescence output until irradiation with UV light cleaves the ligand backbone, which relieves the copper-induced quenching to provide a turn-on response. Experiments in live MCF-7 cells show that coucage can be used for detecting changes in intracellular Cu2+ upon the addition of excess exogenous copper. If improvements can be made to increase its affinity for copper, this new type of turn-on sensor could be used as a tool for visualizing the cellular distribution of labile copper to gain insight into the mechanisms of copper trafficking.

Structure of selected basic copper(II) sulphate minerals based upon spectroscopy – Implications for hydrogen bonding

The application of near-infrared and infrared spectroscopy has been used for identification and distinction of basic Cu-sulphates that include devilline, chalcoalumite and caledonite. Near-infrared spectra of copper sulphate minerals confirm copper in divalent state. Jahn–Teller effect is more significant in chalcoalumite where 2B 1g → 2B 2g transition band shows a larger splitting (490 cm −1) confirming more distorted octahedral coordination of Cu 2+ ion. One symmetrical band at 5145 cm −1 with shoulder band 5715 cm −1 result from the absorbed molecular water in the copper complexes are the combinations of OH vibrations of H 2O. One sharp band at around 3400 cm −1 in IR common to the three complexes is evidenced by Cu OH vibrations. The strong absorptions observed at 1685 and 1620 cm −1 for water bending modes in two species confirm strong hydrogen bonding in devilline and chalcoalumite. The multiple bands in ν 3 and ν 4(SO 4) 2− stretching regions are attributed to the reduction of symmetry to the sulphate ion from T d to C 2V. Chalcoalumite, the excellent IR absorber over the range 3800–500 cm −1 is treated as most efficient heat insulator among the Cu–sulphate complexes.

Investigation of binary polymer/surfactant or ternary polymer/surfactant/Cu2+complexes in aqueous solution through Nile red probing

The optical properties (absorption and emission) of Nile red have been widely used for staining or probing purposes in diverse aqueous systems. However, the applications of Nile red for the determination of the critical aggregation concentration of polymer/surfactant complexes or for the investigation of ternary polymer/surfactant/Cu2+ systems are very limited. The interactions between anionic polyelectrolytes and the oppositely charged surfactant N,N,N,N-dodecyltrimethylammonium chloride were investigated in dilute aqueous solution, exploiting the optical properties of Nile red. It is shown that the emission properties of Nile red present better sensitivity than its absorption properties, concerning the detection of the hydrophobic polymer/surfactant complexes formed in aqueous solution. Moreover, it is found that the formation of ternary polymer/surfactant/Cu2+ complexes leads to a pronounced quenching of the luminescence of Nile red. The corresponding Stern–Volmer plots indicate that quenching is more favourable when coordination of Cu2+ ions with poly(sodium acrylate) takes place, as compared to simple electrostatic binding of these ions with poly(sodium styrene sulfonate). Nile red is a sensitive and accurate tool, as an alternative to pyrene, for the characterization of binary polymer/surfactant complexes or for obtaining information on the local arrangement of ternary polymer/surfactant/Cu2+ systems in aqueous solution. Copyright © 2010 Society of Chemical Industry

Binding and Inhibition of Copper Ions to RecA Inteins from Mycobacterium tuberculosis

Protein splicing is a unique post-translational process in which an intein excises itself from a precursor with the concomitant ligation of flanking sequences. The binding of zinc to intein inhibits protein splicing reversibly and EDTA relieves the inhibition. Copper was found to inhibit protein trans splicing; however, the recovery of intein splicing required both EDTA and TCEP, suggesting a different inhibition mechanism for copper compared to zinc. In this work, we have investigated the binding properties and inhibition effects of copper ions on the RecA intein from Mycobacterium tuberculosis. Both Cu(+) and Cu(2+) exhibited high binding affinity to inteins, while different binding sites were identified. Cu(2+) coordinates to Cys1, the key residue involved in the mechanism of protein splicing, however, Cu(+) does not coordinate to cysteine. An in vitro inhibition assay indicated that monovalent Cu(+) demonstrates reversible inhibition to protein splicing, and the inhibitory efficiency is comparable to Zn(2+). Redox reaction between Cu(2+) and cysteine in inteins were observed and the rate constants were determined. The results suggested a dual role for Cu(2+) in the inhibition of intein splicing: strong coordination of Cu(2+) to key residues (including Cys1) in the intein, and subsequent oxidation of Cys1, the residue required for the N-->S acyl shift step in protein splicing. A kinetic study suggested that the coordination could be the major cause of inhibition effect of Cu(2+) initially, whereas the redox reaction could play an additional role in inhibition at a later stage.

Luminescence properties of [Ru(bpy)2MDHIP]2+ modulated by the introduction of DNA, copper(II) ion and EDTA

The luminescence properties of [Ru(bpy)(2)MDHIP](2+) (bpy=2,2'-bipyridine, MDHIP=2,4-dihydrophenyl-imidazo[4,5-f][1,10]phenanthroline) in the absence and presence of DNA modulated by the introduction of Cu(2+) ion and EDTA have been investigated. It is found that the ruthenium(II) complex can insert and stack between the base pairs of calf thymus DNA with MDHIP ligand, and the intramolecular hydrogen bond is located inside of the DNA. The presence of DNA can enhance the luminescence intensities of [Ru(bpy)(2)MDHIP](2+) both in buffer solution and on an ITO surface. Moreover, the luminescence intensities of [Ru(bpy)(2)MDHIP](2+) and DNA-bound [Ru(bpy)(2)MDHIP](2+) are quenched by Cu(2+), and next recovered by the addition of EDTA. The repetitive luminescence-modulations have been achieved through the introduction of equimolar Cu(2+) and EDTA, respectively. In addition, it becomes evident that the number of luminescence-modulation cycles for [Ru(bpy)(2)MDHIP](2+) in the absence and presence of DNA is influenced by the cumulative concentrations of CuEDTA, generated successively by the strong coordination of Cu(2+) to EDTA.

Coordination of Cu2+and Ni2+ with the histone model peptide of H2B N-terminal tail (1-31 residues): A spectroscopic study

The interaction of Cu(2+) and Ni(2+) with the N-terminal tail of histone H2B, the 31 amino acid peptide H2B(1-31) (Ac-PEPAKSAPAPKKG(13)SKKAVTKAQKKD(25)GKKRKR-NH(2)), studied by various spectroscopic techniques (UV/Vis, CD, EPR and NMR) are described. The results showed the formation of Cu(2+)-H2B(1-31) complexes above pH 7.3 most probably through the beta-carboxylate group of D25. With the increase of the pH, a mixture of 3 N and 4 N species presenting {2N(-), CO, epsilonNH(2)} and {2N(-), OH(2), epsilonNH(2)}{epsilonNH(2)} coordination modes, respectively is formed, while at highly basic solutions the binding of an additional amide donor is suggested. NMR spectroscopy supported by CD spectroscopy indicated that Ni(2+) coordination takes place most likely through Q22-K23-K24-D25 peptide fragment. Direct coordination to Ni(2+), in a {4N(-)} coordination mode, with a severe conformation change in all residues from G13 to G26 was observed. Cu(2+) and Ni(2+) binding to the N-terminal tail of H2B causes a severe conformational change that might interfere with histone post-translational modifications, possibly leading to epigenetic changes.

Label-Free Femtomolar Detection of Target DNA by Impedimetric DNA Sensor Based on Poly(pyrrole-nitrilotriacetic acid) Film

An ultrahigh performance impedimetric DNA sensor is presented showing detection limits in the femtomolar range. This electrochemical setup was constructed initially by electrogeneration of poly(11-pyrrol-1-yl-undecanoic acid N(alpha'),N(alpha)-bis(carboxymethyl)-L-lysine amide) (poly(pyrrole-NTA)) film. The latter was then modified by the coordination of Cu(2+) ions onto the chelating NTA centers followed by the immobilization of the ssHIV-DNA previously modified by a polyhistidine tag by affinity binding. The immobilization of the DNA probe and hybridization with the complementary target ssHIV-DNA were investigated using fluorescence microscopy and quantified with quartz crystal microbalance experiments leading to DNA probe and duplex coverage of 1.7 x 10(-11) and 7.7 x 10(-12) mol cm(-2), respectively. The duplex formation was corroborated by amperometric measurements through the duplex labeling by a glucose oxidase. In the presence of hydroquinone as redox indicator, the DNA sensor was applied to the impedimetric detection of target DNA without a labeling step. A linear quantification of the HIV DNA target was carried out in the range 10(-15) to 10(-8) mol L(-1).

Nanostructural characterization of TiN–Cu films using EXAFS spectroscopy

We report on the modification of the local coordination of Cu in TiN–Cu films, as a function of the growth conditions. The films were deposited on Si (100) by pulsed laser deposition using either an intermetallic TiCu target or elemental Ti and Cu targets. During growth the partial nitrogen pressure (p(N 2)) took values in the range 0–150 ⋅ 10 − 3 mbar. The bonding environment of Cu is identified using Extended X-Ray Absorption Fine Structure Spectroscopy (EXAFS) measurements at the Cu- K-edge. It is disclosed that in the films grown under p(N 2) < 150⋅10 − 3 mbar, Ti partially substitutes Cu in the fcc Cu phase. However, both the Cu–Ti bondlength and the coordination of Cu in the 1st nearest neighbor shell change as a result of the different growth conditions. More specifically, in the films grown in N 2 ambient, the degree of incorporation of Ti in fcc Cu sites decreases as the p(N 2) increases. When growth occurs from elemental targets under p(N 2) = 150 ⋅ 10 − 3 mbar, only fcc Cu is detected. The changes in the coordination of Cu as a function of the p(N 2) are attributed to the formation of crystalline TiN. Finally, the Cu–Cu bondlength is equal to the respective bondlength in the Cu-foil, independent of the growth conditions while, on the contrary, the Cu–Ti bondlength depends on p(N 2).

Impacts of the Location and Number of [Cu(bpy)2]2+Cross-Links on the Emission Photodynamics of [Ru(bpy)3]2+with Pendant Oligo(aminoethylglycine) Chains

Multifunctional aminoethylglycine (aeg) derivatized [Ru(bpy)(3)](2+) complexes with pendant bipyridine (bpy) ligands coordinate Cu(2+) to form coordinative chain cross-links in a "hairpin loop" motif. In this paper, we report the synthesis and characterization of a series of Ru aeg hairpins in which the relative aeg chain length and number of pendant bpy ligands is varied. Reaction of each of these with Cu(2+) is monitored using spectrophotometric emission titrations to determine the binding stoichiometry. Coordination of Cu(2+) causes quenching of the emissive excited state Ru species; the degree of quenching efficiency depends on the location and number of coordinated Cu ions. The heterometallic structures are fully characterized, and using the quantum yields and time-resolved emission following excitation of the Ru complexes in deoxygenated solutions, the radiative (k(r)) and nonradiative (k(nr)) relaxation rates are compared. These data reveal only a shallow decrease in k(nr) with increasing distance between the Ru and Cu complexes. Activation energies, determined from temperature dependent studies of the time-resolved emission, also increase as the Ru-Cu separation increases, resulting in the smaller nonradiative rates. Together, these data are suggestive of excited state electron transfer as the quenching mechanism and demonstrate that metal coordination self-assembles structures made from modular artificial amino acids can provide controlled arrangements of chromophores, electron donors, and electron acceptors to shuttle electrons in a new approach for mimicking photosynthesis.

Dense-shell glycodendrimers: UV/Vis and electron paramagnetic resonance study of metal ion complexation

The development of dendritic metal ion carrier systems for use in a biological environment is a challenging task as the carrier system must possess multiple features (e.g. a protective shell for metal decomplexation, targeting functions, metal–intradendrimer complexes, etc.) to substitute for the function of metal proteins in processes such as copper metabolism. Thus, Cu(II) complexation by a series of poly(propyleneimine) glycodendrimers ranging up to the fifth generation that have either a dense maltose or maltotriose shell was investigated by UV/Vis spectroscopy and electron paramagnetic resonance (EPR). As a necessary step towards potential biological application, we elucidated the complexation capacity, location of the Cu(II)–dendrimer complexes and the Cu(II) coordination sphere in the dendritic environment. A generation-dependent Cu(II) complexation was found. Furthermore, analysis of the EPR spectra revealed that internal and external Cu(II) coordination and the symmetry (axial and rhombic) of the generated complexes depend on the oligosaccharide shell, dendrimer generation and the relative concentrations of Cu(II) and the dendrimers. Both axial and rhombic symmetries are generation dependent, but also distort with increasing generation number. External coordination of Cu(II) is supported by sugar groups and water molecules. Finally, a third-generation dendrimer with a maltose shell was used to explore the general complexation behaviour of the dendritic poly(propyleneimine) scaffold towards different metal ions [Cu(II), Ag(I), VO(IV), Ni(II), Eu(III) and UO 2 (VI)].