Dicopper Center Research Articles

A new unsymmetrical polyamine macrocycle incorporating two phenolic functions: synthesis, basicity and coordination behavior toward copper(II)

A new 26-membered macrocyclic ligand: 3,6,10,18,22,25-hexaaza-31,32-dihydroxy-14,29-dimethyl-tricyclo[25,3,1,1 11,17]dotriaconta-1(30),12,14,16(32),27,28-hexaene (L or BTBP) and a homodinuclear copper complex have been synthesized and characterized with elemental analysis, NMR, FAB MS and X-ray. The ligand maintains dinuclear integrity for copper(II) complexes, while facilitating the formation of non-bridged dicopper centers. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear complexes are formed with Cu(II) from pH 2 to 12 in aqueous solution. The stability constants and species distribution, as a function of the pH of the 1:1 and 1:2 [ligand/Cu(II)] complexes, were determined in KCl supporting electrolyte ( μ=0.100 M) at 25 °C. The neutral homodinuclear complex [Cu 2C 28H 44N 6O 2Br 2)]·2(CHCl 3)·2(CH 3OH) forms monoclinic crystals, of space group P2 1/ c, with a=14.319(3), b=21.801(4), c=7.0417(14) Å, β=100.893(4)°, and Z=2. Each copper is complexed by half of the coordination sites of the dinucleating macrocycle, and the anionic bromide enters into the coordination sphere and occupies an axial position to complete a square-pyramidal polyhedron.

Synthesis, structure, and H2O2-dependent catalytic functions of disulfide-bridged dicopper(I) and related thioether-copper(I) and thioether-copper(II) complexes.

A disulfide-bridged dicopper(I) complex, [Cu2(Py2SSPy2)](ClO4)2 (1) (Py2SSPy2 = bis(2-[N,N-bis(2-pyridylethyl)-amino]-1,1- dimethylethyl)disulfide), a thioether-copper(I) complex, [Cu(iPrSPy2)](ClO4) (2) (iPrSPy2 = N-(2-isopropylthio-2-methyl)propyl-N,N-bis-2-(2-pyridyl)ethylamine, and a thioether-copper(II) complex, [Cu-(PheSPy2)(H2O)](ClO4)2 (3) (PheSPy2 = N-(2-methyl-2-phenethylthio)propyl-N,N-bis-2-(2- pyridyl)ethylamine), were newly synthesized by the reactions of Cu(ClO4)2.6H2O with a thiol ligand of Py2SH (N,N-bis[2-(2-pyridyl)-ethyl]-1,1-dimethyl-2- mercaptoethylamine) and thioether ligands of iPrSPy2 and PheSPy2, respectively. For complexes 1 and 2, X-ray analyses were performed. Complex 1 crystallizes in the triclinic space group P1, and complex 2 crystallizes in the orthorhombic space group Pbca with the following unit cell parameters: for 1, a = 15.165 (3) A, b = 22.185 (4) A, c = 14.989 (3) A, alpha = 105.76 (1) degrees, beta = 90.82 (2) degrees, gamma = 75.23 (1) degrees, and Z = 2; for 2, a = 17.78 (2) A, b = 17.70 (1) A, c = 15.75 (1) A, and Z = 8. Complex 1 is the first structurally characterized example obtained by the redox reaction Cu(II) + RSH-->Cu(I) + RSSR and has two independent structures (1a, 1b) which mainly differ in S-S bond distances, Cu(I)...Cu(I) separations, and C-S-S-C dihedral angles of the disulfide units. The S-S bond distances of 2.088(7) A in 1a and 2.070(7) A in 1b are indicative of significant activation of the S-S bonds by the dicopper centers. Fragment molecular orbital (FMO) analyses and molecular orbital overlap population (MOOP) analyses based on the extended Hückel method clarify the preferable formation of the disulfide S-S bond in 1 rather than the formation of a thiolate-copper(II) complex within the Py2S- ligand framework. Catalytic functions of complexes 1-3 were investigated with peroxides (H2O2 and tBuOOH) as oxidants. Complex 1 catalyzed the selective oxidation of cyclohexane to cyclohexanol and mediated the cyclohexene epoxidation in the presence of H2O2. A transient dark green intermediate observed in the reaction of 1 with H2O2 is characterized by UV-vis, EPR, and resonance Raman spectroscopies, identifying it as a Cu(II)-OOH species, 1(OOH). The resonance Raman features of the nu(O-O) bands at 822 and 836 cm-1, which are red-shifted to 781 and 791 cm-1, respectively, upon introduction of H2(18)O2, are indicative of formation of two kinds of Cu-OOH species rather than the Fermi doublet and the significant weakening of the O-O bonds. These mechanistic studies demonstrate that by virtue of the electron-donating ability of the disulfide unit the Cu-OOH species can be actually activated for one-electron oxidation, which has been reported so far unfavorable for other vibrationally characterized Cu-OOH species.

Synthesis, structure and magnetic behavior of a di-μ-chloro-di-μ-imidazolato-tetracopper(II) complex with two dinucleating macrocycles

The synthesis, crystal structure and magnetic behavior of the di-μ-chloro-di-μ-imidazolato-tetracopper(II) complex [L 2Cu 4(Im) 2Cl 2](ClO 4) 4(CH 3OH), where Im is imidazole and L is 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1 11,13]triaconta-1(29),11(30),12,14,25(26),27-hexaene, have been studied. X-ray structure analysis shows that the compound crystallizes in monoclinic and space group P2(1)/ c, with a=13.716(3), b=11.165(2), c=27.340(6) Å, β=98.43(3)° and Z=2. The cation consists of two imidazolate bridged dicopper(II) centers encapsulated within two macrocycles, respectively, which are linked by a pair of chloride atoms. In each imidazolate bridged dicopper(II) center, both copper atoms are five-coordinated by four basal nitrogen atoms (three from the macrocycle and one from the imidazolate) and one axial chloride atom shared with another copper atom in the other imidazolate bridged dicopper(II) center in the molecule. pH-dependent ESR studies of the title complex in frozen 50% aqueous DMSO solution show that the bridged cation [LCu 2(Im)] 3+ exists as a major species in solution over the range 7.00≤pH≤11.5, and the μ-Im bridge is broken in the pH range of 7.00–5.20. The molar conductance of the title complex indicates that the μ-Cl bridge is almost entirely dissociated when dissolved in 1:1 DMSO aqueous solution. However, when Cl − ions were gradually added to the solution, a complex with a CuN 4Cl chromophore was successively formed. Magnetic measurement studies on the powder sample reveal that antiferromagnetic interactions are mediated through both μ-Im ( J 1=−26.78 cm −1) and μ-Cl ( J 2=−9.52 cm −1) bridges.

The syntheses, crystal structure and magnetic behavior of μ-imidazolato-dicopper(II) complexes with the dinucleating hexaazamacrocycles

The synthesis, crystal structure and magnetic properties of the imidazolate-bridged dinuclear copper(II) complex [LCu2(Im)](ClO4)3(H2O) ·1/2(MeCN), (ImH=imidazole, L=bis-p-xylylBISDIEN) have been studied. Single crystal X-ray diffraction determination reveals the distorted square planar geometries of the imidazolate bridged dicopper(II) center are incorporated within the dinucleating macrocycle. The Cu—Cu separation in the complex is 6.005A. Magnetic measurements reveal an antiferromagnetic exchange interaction with a coupling constant of J=−26.52cm−1. The enzymatic activity of the title complex is 5.9 percent of that of the protein.

Crystal structure of a plant catechol oxidase containing a dicopper center.

Catechol oxidases are ubiquitous plant enzymes containing a dinuclear copper center. In the wound-response mechanism of the plant they catalyze the oxidation of a broad range of ortho-diphenols to the corresponding o-quinones coupled with the reduction of oxygen to water. The crystal structures of the enzyme from sweet potato in the resting dicupric Cu(II)-Cu(II) state, the reduced dicuprous Cu(I)-Cu(I) form, and in complex with the inhibitor phenylthiourea were analyzed. The catalytic copper center is accommodated in a central four-helix-bundle located in a hydrophobic pocket close to the surface. Both metal binding sites are composed of three histidine ligands. His 109, ligated to the CuA site, is covalently linked to Cys 92 by an unusual thioether bond. Based on biochemical, spectroscopic and the presented structural data, a catalytical mechanism is proposed in which one of the oxygen atoms of the diphenolic substrate binds to CuB of the oxygenated enzyme.

Extended metal environments of cytochrome c oxidase structures.

The metals of the cytochrome c oxidase structures of the bovine heart mitochondrion (PDB code 1occ) and of the soil bacterium Paracoccus denitrificans (1arl) include a dicopper center (CuA), magnesium, two proximal hemes, a copper (CuB) atom, and a calcium. The mitochondrial structure also possesses a bound distant zinc ion. The extended environments of the metal sites are analyzed emphasizing residues of the second shell in terms of polarity, hydrophobicity, secondary structure, solvent accessibility, and H-bonding networks. A significant difference in the CuA metal environments concerns D-51 I in 1occ, absent from 1arl. The D-51 I appears to play an important role in the proton pumping pathway. Our analysis uncovers several statistically significant residue clusters, including a cysteine-histidine-tyrosine cluster overlapping the CuA-Mg complex; a histidine-acidic cluster enveloping the environment of Mg, the two hemes, and CuB; and on the protein surface a mixed charge cluster, which may help stabilize the quaternary structure and/or mediate docking to cytochrome c. These clusters may constitute possible pathways for electron transfer, for O2 diffusion, and for H2O movement. Many hydrogen bonding relations along the interface of subunits I and II demarcate this surface as a potential participant in proton pumping.

The synthesis, structure and SOD-like behaviors of a μ-imidazolato-dicopper(II) complex with a binucleating hexaazamacrocycle

The synthesis, crystal structure and magnetic properties of the imidazolate-bridged dinuclear copper(II) complex [LCu 2(Im)(DMSO) 2](ClO 4) 3(DMSO), where ImH is imidazole, and L is 3, 6, 9, 17, 20, 23-hexaazatricyclo[23.3.1.1 11,13]triaconta-1(29), 11(30), 12, 14, 25(26), 27-hexaene, have been studied. Single crystal X-ray diffraction determination reveals the distorted tetragonal pyramid geometries of the imidazolate bridged dicopper(II) center are incorporated within the binucleating macrocycle. Both copper atoms are five-coordinated by four basal nitrogen atoms (three from the macrocycle and one from the imidazolate) and one oxygen atom from the DMSO molecule. Two coordinated DMSO molecules are situated at the same side of the macrocycle. The Cu–Cu separation in the complex is 5.93 Å. Magnetic measurements and ESR spectroscopy studies exibit an antiferromagnetic exchange interaction with a coupling constant of J= − 26.94 cm −1. Investigations on the pH-dependent ESR of the title compound in frozen 50% aqueous DMSO solution confirm the existence of the bridged cation [LCu 2(Im)] 3+ as a major species in solution mainly in the range 5.2⩽pH⩽11.5. The imidazolate bridge is broken in the pH range of 5.2–3.3, which is close to that for the native enzyme.

Proton NMR Spectroscopy as a Probe of Dinuclear Copper(II) Active Sites in Metalloproteins. Characterization of the Hyperactive Copper(II)-Substituted Aminopeptidase from Aeromonas proteolytica

Proton NMR spectra of the hyperactive Cu(II)-substituted aminopeptidase from Aeromonas proteolytica (AAP) were recorded in both H2O and D2O buffered solution at pH 6.7. Several remarkably sharp, well resolved hyperfine shifted 1H NMR signals were observed in the 70 to −20 ppm chemical shift range. That hyperfine shifted signals were observed is due to spin-coupling of the two Cu(II) ions. Comparison of the spectra recorded in H2O and D2O buffered solutions indicated that the signals at 44.6, 43.3, and 17.7 ppm were solvent exchangeable. The two most strongly downfield shifted signals were assigned to imidazole N−H protons of the two coordinated histidine residues, while the remaining exchangeable signal was assigned to a peptidyl N−H proton that is in close proximity to the dicopper(II) center. One-dimensional NOE studies at pH 6.7 revealed two Y−CH2−CH< moieties that were assigned to coordinated aspartic acid and histidine residues. In addition, a Y−CH2−CH2−CH< moiety was also identified and was assigned to the coordinated glutamic acid residue, Glu152. All of the hyperfine shifted signals for [CuCu(AAP)] sharpened and shifted toward the diamagnetic region as the temperature was increased following Curie behavior. Fits of these data and those of a series of magnetically diverse μ-phenoxo and μ-alkoxo dicopper(II) model complexes to the population distribution of the ground and first excited states, provided information on the magnetic properties of dicopper(II) clusters. These fits indicated that the two Cu(II) ions in AAP are ferromagnetically coupled with a 2J value of 50 + 40 cm-1. These data provide the first structural information regarding the hyperactive [CuCu(AAP)] enzyme and are discussed in terms of the previously proposed mechanism of action for AAP.

Characterization of the Structural and Electronic Properties of Spin-Coupled Dinuclear Copper(II) Centers by Proton NMR Spectroscopy

The 1H NMR spectra of a series of well-characterized μ-phenoxo and μ-alkoxo spin-coupled dicopper(II) complexes have been investigated. The complexes studied were [Cu2(BPMP)(OH)]2+ (1) (BPMP = 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol), [Cu2(CH3HXTA)(OH)]2- (2) (CH3HXTA = N,N ‘-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-carboxymethylglycine), [Cu2(m-XYL)(OH)]2+ (3) (m-XYL = 2,6-bis[[bis(2-pyridylethyl)amino]methyl]phenol), and [Cu2(TBHP)(OAc)]2+ (4) (TBHP = N,N,N ‘,N ‘-tetrakis[(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane). The magnetic interactions of these complexes range from strongly antiferromagnetically to weakly ferromagnetically coupled. Both one- and two-dimensional (COSY) 1H NMR methods were used to facilitate the assignment of the hyperfine shifted 1H NMR signals of each complex. COSY experiments provide clear cross signals for resonances <200 Hz wide. These data have facilitated the assignment of the hyperfine shifted 1H NMR signals and have verified that the solid state structures exist in solution for each system studied. Assuming a paramagnetic dipolar relaxation mechanism, the crystallographically determined Cu−H distance (r) is proportional to T11/6. All calculated Cu−H distances for 1−4 are within ca. 20% of the Cu−H distances derived from X-ray crystallography. These data indicate that a paramagnetic dipolar relaxation mechanism is the dominant proton relaxation pathway for spin-coupled dicopper(II) centers. Our results indicate that 1H NMR spectroscopy is an excellent tool with which to probe the solution structures of spin-coupled dicopper(II) centers in model complexes as well as biological systems.

Autoxidation of a dicopper(I) macrocyclic complex: evidence for a mixed-valence intermediate

Interaction of O2 with dicopper(I) complexes of 20-membered N4 macrocycles L1 and L2{23,24-dioxa-3,7,14,18-tetra-azatricyclo[18.2.1.1 9,12]tetracosa-1 (22),2,7,9,11,13,18,20-octaene and its 5,5,16,16-tetramethyl derivative} proceeds via an intermediate red-brown species, whose electronic and e.s.r. spectra suggest a mixed-valence formulation. This red-brown species can also be generated by conproportionation between dicopper(I) and dicopper(II) complexes of these macrocycles. The mixed-valence product cannot be isolated in the solid state, as concentration of the solutions leads to disproportionation with precipitation of a solid [Cu4L12(OH)]3+ cluster. Cyclic voltammetry revealed that all redox processes associated with the copper centres in these complexes are irreversible, probably due to a chemical process such as transfer of the hydroxo bridging ligand at each redox stage. It is believed that the pair of irreversible reduction waves observed in the cyclic voltammogram of the di-µ-hydroxo-dicopper(II) complex of L1 correspond to sequential one-electron reductions of the dicopper centre.

Thiocyanate cleaves the imidazolate-bridged dicopper(II) center in a binucleating macrocycle to form the copper(II) thiocyanate complex [Cu2(SCN)4 .cntnd. A]. Model chemistry for superoxide dismutase

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThiocyanate cleaves the imidazolate-bridged dicopper(II) center in a binucleating macrocycle to form the copper(II) thiocyanate complex [Cu2(SCN)4 .cntnd. A]. Model chemistry for superoxide dismutaseAndrea E. Martin and Stephen J. LippardCite this: J. Am. Chem. Soc. 1984, 106, 9, 2579–2583Publication Date (Print):May 1, 1984Publication History Published online1 May 2002Published inissue 1 May 1984https://doi.org/10.1021/ja00321a015RIGHTS & PERMISSIONSArticle Views101Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (621 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Peroxide coordination to a dicopper(II) center. Dioxygen binding to a structurally characterized phenoxide-bridged binuclear copper(I) complex

Etude RX du monocation [Cu 2 (C 36 H 39 N 6 O)] avec le coordinat octadente dimethyl-1,3 phenol portant des substituants (bis[pyridyl-2]-2 ethyl) amino sur les groupes methyl: cristallisation dans P2 1 /n avec Z=2; affinement jusqu'a R=0,059

A monohydroxobridged, strongly antiferromagnetically coupled dicopper(II) center in a binucleating macrocycle. Comparisons with binuclear copper sites in biology

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA monohydroxobridged, strongly antiferromagnetically coupled dicopper(II) center in a binucleating macrocycle. Comparisons with binuclear copper sites in biologyPeter K. Coughlin and Stephen J. LippardCite this: J. Am. Chem. Soc. 1981, 103, 11, 3228–3229Publication Date (Print):June 1, 1981Publication History Published online1 May 2002Published inissue 1 June 1981https://doi.org/10.1021/ja00401a058RIGHTS & PERMISSIONSArticle Views184Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (307 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts