One octarepeate expansion to the human prion protein alters both the Zn2+ and Cu2+ coordination environments within the octarepeate domain

The influence of a single octarepeat expansion on the Cu(II) and Zn(II) coordination environments within the octarepeat domain of the human prion protein is examined. Using X-ray absorption spectroscopy and diethyl pyrocarbonate labeling studies, we find that at low copper concentrations the "normal" octarepeat domain (four PHGGGWGQ repeats) coordinates Zn(II) in an (N/O)(6) coordination environment with two histidine residues and Cu(II) in a redox-inactive (N/O)(4) coordination environment using one imidazole residue. Expansion of the octarepeat region by one repeat (five PHGGGWGQ repeats) yields a three-histidine (N/O)(6) coordination environment for Zn(II) and a two-histidine (N/O)(4) coordination environment for Cu(II) at low copper concentrations. This Cu(II)[(N/O)(2)-histidine(2)] coordination motif is redox-active and capable of generating H(2)O(2) under reducing aerobic conditions.     

Metal uptake by a novel bidentate thiosemicarbazide chelating polymer

1-Cyanoethanoyl-4-acryloyl thiosemicarbazide (CEATS) has been prepared and polymerized by a free radical mechanism. The polymer PCEATS has chelating affinity, and metal-uptake capacities were determined for the chlorides of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) in the pH range 1.04–6.0. The extraction experiments show high capacity for Cu(II), (0.26?mmol/g) at pH 5.34 and lower uptake capacities for the other divalent metal ions around pH 5 in buffered solutions, under noncompetitive conditions. However, competitive experiments, performed with solutions containing a mixture of metal chloride salts and acetate buffer, showed a high selectivity for Cu(II) and Cd(II) over other cations. Distribution coefficients determined for the polymer and the metal ions indicate that the Cu(II) complex is more stable than the Cd(II) are and suggest that the stability of the complex decreases rapidly with decreasing pH. Kinetic experiments have shown that uptake of Cu(II), is slow, with t _0.5?=?10?h. Ligand regeneration experiments for Cu(II)-loaded PCEATS performed with 2.00?M H₂SO₄ have shown that the capacity for Cu(II) stays at the same level after several cycles of consecutive loading and stripping, indicating that the polymer is chemically stable. ESR spectra of Cu(II)–CEATS resin show that there are two different coordination complexes present in the polymer. IR spectra of the Cu(II) complex confirms the bidentate behavior (S, O; N, O) of CEATS and PCEATS (it is supposed that the cations bridge vicinal CEATS ligands through S, O and N, O atoms); the acetate group completes the octahedral coordination. The obtained data suggest that the polymer behaves as a bidentate ligand via the thiocarbonyl, carbonyl and imide groups. PCEATS and its complexes have an inhibitory effect on both the bacterium Azotobacter and the fungus Fusarium oxysporium. The effect on the microorganisms is proportional to the amount of free ligand in the complex.     

Cu(II)-脱乙酰壳聚糖配位聚合物的配位数

IR,ESR和XPS的测试结果表明,脱乙酰壳聚糖(简记CS)膜在铜氨水溶液浸渍过程中Cu(II)既与CS发生配位反应形成Cu(II)-CS配位聚合物,也产生吸附作用。ESR谱示出CuCl~2.2H~2O与Cu(II)-CS膜中的Cu(II)均含有一个单电子,可以利用XPS的Shake-up效应研究Cu(II)-CS配位聚合物的配位数,所得结果为4。又以同样的方法研究Cu(II)-聚乙烯醇(简记PVA)配位聚合物的配位数,发现Cu(II)是以低自旋状态的dsp^2杂化空轨道与PVA的羟基氧配位,其配位数也是4,这与资料所报道的一致,从而间接地验证了此方法研究Cu(II)-CS配位聚合物配位数的可靠性。     

Cu(Ⅱ)脱乙酰壳聚精配位聚合物的配位数

IR,ESR和XPS的测试结果表明,脱乙酰壳聚糖(简记CS)膜在铜氨水溶液浸渍过程中Cu(Ⅱ)既与CS发生配位反应形成Cu(Ⅱ)-CS配位聚合物,也产生吸附作用.ESR谱示出CuCl_2·2H_2O与Cu(Ⅱ)-CS膜中的Cu(Ⅱ)均含有一个单电子,可以利用XPS的Shake-up效应研究Cu(Ⅱ)-CS配位聚合物的配位数,所得结果为4.又以同样的方法研究Cu(Ⅱ)-聚乙烯醇(简记PVA)配位聚合物的配位数,发现Cu(Ⅱ)是以低自旋状态的dsp~2杂化空轨道与PVA的羟基氧配位,其配位数也是4,这与资料所报道的一致,从而间接地验证了此方法研究Cu(Ⅱ)-CS配位聚合物配位数的可靠性.     

Coordination and metalation bifunctionality of Cu with 5,10,15,20-tetra(4-pyridyl)porphyrin: toward a mixed-valence two-dimensional coordination network

We investigated the coordination self-assembly and metalation reaction of Cu with 5,10,15,20-tetra(4-pyridyl)porphyrin (2HTPyP) on a Au(111) surface by means of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. 2HTPyP was found to interact with Cu through both the peripheral pyridyl groups and the porphyrin core. Pairs of pyridyl groups from neighboring molecules coordinate Cu(0) atoms, which leads to the formation of a supramolecular metal-organic coordination network. The network formation occurs at room temperature; annealing at 450 K enhances the process. The interaction of Cu with the porphyrin core is more complex. At room temperature, formation of an initial complex Cu(0)-2HTPyP is observed. Annealing at 450 K activates an intramolecular redox reaction, by which the coordinated Cu(0) is oxidized to Cu(II) and the complex Cu(II)TPyP is formed. The coordination network consists then of Cu(II) complexes linked by Cu(0) atoms; that is, it represents a mixed-valence two-dimensional coordination network consisting of an ordered array of Cu(II) and Cu(0) centers. Above 520 K, the network degrades and the Cu atoms in the linking positions diffuse into the substrate, while the Cu(II)TPyP complexes form a close-packed structure that is stabilized by weak intermolecular interactions. Density functional theory investigations show that the reaction with Cu(0) proceeds via formation of an initial complex between metal atom and porphyrin followed by formation of Cu(II) porphyrin within the course of the reaction. The activation barrier of the rate limiting step was found to be 24-37 kcal mol(-1) depending on the method used. In addition, linear coordination of a Cu atom by two CuTPyP molecules is favorable according to gas-phase calculations.     

Lumenal loop M672-P707 of the Menkes protein (ATP7A) transfers copper to peptidylglycine monooxygenase

Copper transfer to cuproproteins located in vesicular compartments of the secretory pathway depends on activity of the copper-translocating ATPase (ATP7A), but the mechanism of transfer is largely unexplored. Copper-ATPase ATP7A is unique in having a sequence rich in histidine and methionine residues located on the lumenal side of the membrane. The corresponding fragment binds Cu(I) when expressed as a chimera with a scaffold protein, and mutations or deletions of His and/or Met residues in its sequence inhibit dephosphorylation of the ATPase, a catalytic step associated with copper release. Here we present evidence for a potential role of this lumenal region of ATP7A in copper transfer to cuproenzymes. Both Cu(II) and Cu(I) forms were investigated since the form in which copper is transferred to acceptor proteins is currently unknown. Analysis of Cu(II) using EPR demonstrated that at Cu:P ratios below 1:1 (15)N-substituted protein had Cu(II) bound by 4 His residues, but this coordination changed as the Cu(II) to protein ratio increased toward 2:1. XAS confirmed this coordination via analysis of the intensity of outer-shell scattering from imidazole residues. The Cu(II) complexes could be reduced to their Cu(I) counterparts by ascorbate, but here again, as shown by EXAFS and XANES spectroscopy, the coordination was dependent on copper loading. At low copper Cu(I) was bound by a mixed ligand set of His + Met, whereas at higher ratios His coordination predominated. The copper-loaded loop was able to transfer either Cu(II) or Cu(I) to peptidylglycine monooxygenase in the presence of chelating resin, generating catalytically active enzyme in a process that appeared to involve direct interaction between the two partners. The variation of coordination with copper loading suggests copper-dependent conformational change which in turn could act as a signal for regulating copper release by the ATPase pump.     

Substantial contribution of the two imidazole rings of the His13-His14 dyad to Cu(II) binding in amyloid-β(1-16) at physiological pH and its significance

The interaction of amyloid-β (Aβ) peptide with Cu(II) appears to play an important role in the etiology of Alzheimer's disease. At physiological pH, the Cu(II) coordination in Aβ is heterogeneous, and there exist at least two binding modes in which Cu(II) is coordinated by histidine residues. Electron spin resonance studies have revealed a picture of the Cu(II) binding at a higher or lower pH, where only one of the two binding modes is almost exclusively present. We describe a procedure to directly examine the coordination of Cu(II) to each histidine residue in the dominant binding mode at physiological pH. We use nonlabeled and residue-specifically (15)N-labeled Aβ(1-16). For quantitative analysis, the intensities of three-pulse electron spin-echo envelope modulation (ESEEM) spectra are analyzed. Spectral simulations show that ESEEM intensities provide information about the contribution of each histidine residue. Indeed, the ESEEM experiments at pH 6.0 confirm the dominant contribution of His6 to the Cu(II) coordination as expected from the work of other researchers. Interestingly, however, the ESEEM data obtained at pH 7.4 reveal that the contributions of the three residues to the Cu(II) coordination are in the order of His14 ≈ His6 > His13 in the dominant binding mode. The order indicates a significant contribution from the simultaneous coordination by His13 and His14 at physiological pH, which has been underappreciated. These findings are supported by hyperfine sublevel correlation spectroscopy experiments. The simultaneous coordination by the two adjacent residues is likely to be present in a non-β-sheet structure. The coexistence of different secondary structures is possibly the molecular origin for the formation of amorphous aggregates rather than fibrils at relatively high concentrations of Cu(II). Through our approach, precise and useful information about Cu(II) binding in Aβ(1-16) at physiological pH is obtained without any side-chain modification, amino acid residue replacement, or pH change, each of which might lead to an alteration in the peptide structure or the coordination environment.     

Mechanism of change in enantiomer migration order of enantioseparation of tartaric acid by ligand exchange capillary electrophoresis with Cu(II) and Ni(II)-D-quinic acid systems

The mechanism of change in the enantiomer migration order (EMO) of tartarate on ligand exchange CE with Cu(II)- and Ni(II)-D-quinic acid systems was investigated thoroughly by circular dichroism (CD) spectropolarimetry. The (13) C NMR spectra of solutions containing D-quinate (pH 5.0) with Cu(II) or Ni(II) revealed the coordination of carboxylate and hydroxyl groups on D-quinate. The D-quinic acid concentration dependence of the CD spectra at a fixed Cu(II) concentration at pH 5.0 indicates that the 1:1, 1:2 and 1:3 Cu(II)-D-quinate complexes were formed with an increase in the concentration of D-quinic acid. The CD spectral behavior revealed that D-tartarate is selectively coordinated to the 1:1 complex to give the 1:1:1 Cu(II)-D-quinate-D-tartarate ternary complex while L-tartarate is selectively bound to the 1:2 and 1:3 complexes to form the 1:2:1 ternary complex. In the Ni(II)-D-quinic acid system, it became apparent that the 1:2 Ni(II)-D-quinate complex is mainly formed in the wide range of D-quinic acid concentration at pH 5.0 and D-tartarate is selectively coordinated to the 1:2 complex to form the 1:2:1 ternary complex. The change in EMO of tartarate on ligand exchange CE was explainable by the change in coordination selectivity for D- and L-tartarates in the Cu(II)- and Ni(II)-D-quinic acid systems depending on the compositions of the complexes formed in BGE.     

Nature of metal binding sites in Cu(II) complexes with histidine and related N-coordinating ligands, as studied by EXAFS

Knowledge of the complexes formed by N-coordinating ligands and Cu(II) ions is of relevance in understanding the interactions of this ion with biomolecules. Within this framework, we investigated Cu(II) complexation with mono- and polydentate ligands, such as ammonia, ethylenediamine (en), and phthalocyanine (Pc). The obtained Cu-N coordination distances were 2.02 A for [Cu(NH(3))(4)](2+), 2.01 A for [Cu(en)(2)](2+), and 1.95 A for CuPc. The shorter bond distance found for CuPc is attributed to the macrocyclic effect. In addition to the structure of the first shell, information on higher coordination shells of the chelate ligands could be extracted by EXAFS, thus allowing discrimination among the different coordination modes. This was possible due to the geometry of the complexes, where the absorbing Cu atoms are coplanar with the four N atoms forming the first coordination shell of the complex. For this reason multiple scattering contributions become relevant, thus allowing determination of higher shells. This knowledge has been used to gain information about the structure of the 1:2 complexes formed by Cu(II) ions with the amino acids histidine and glycine, both showing a high affinity for Cu(II) ions. The in-solution structure of these complexes, particularly that with histidine, is not clear yet, probably due to the various possible coordination modes. In this case the square-planar arrangements glycine-histamine and histamine-histamine as well as tetrahedral coordination modes have been considered. The obtained first-shell Cu-N coordination distance for this complex is 1.99 A. The results of the higher shells EXAFS analysis point to the fact that the predominant coordination mode is the so-called histamine-histamine one in which both histidine molecules coordinate Cu(II) cations through N atoms from the amino group and from the imidazole ring.     

银配合物与联氨定向反应的研究I

本文研究了银的不同配合物与N2H4的反应, 得出微量的Cu^2^+不仅能加快反应速度, 能有效地促进N2H4按反应(4)进行四电子定向反应的比率, 而且N2H4按四电子定向的反应率随银配合物稳4Ag^+(AgL^q^±2)+N2H4 4Ag+N2+4H^+(8L^{q±(-1)]/2) (4)Ag^+(AgL^q^±2)+N2H4 Ag+1/2N2+NH3+H^+(+2L[q±(-1)]/2) (5)定常数的增大而降低的结论。无Cu^2^+时, N2H4的四电子反应率与银配合物的logβ2成线性关系; Cu^2^+存在时, N2H4单电子反应率的对数与1/logβ2呈线性关系。     

Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions

This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion-dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2-4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH2 PAMAM dendrimers in aqueous solutions. At low metal ion-dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH2 and G5-NH2 PAMAM dendrimers at pH 7.0.     

离聚体的结构表征 Ⅲ.EXAFS法测定含氟的铜离聚体的精细结构

本文报道了用先进的EXAFS及ESR等方法研究了羧酸型含氟的铜(Ⅱ)离聚体离子微区的内部精细结构,结果表明,铜离聚体的离子微区主要由羧酸根桥键的双核配位结构单元及平面四方形的配位结构单元等聚集而成。在双核配位结构单元中第一层为Cu~(2+)—O配位,配位数为4,配位键键长为1.96A,第二配位层为Gu~(2+)—Cu~(2+)配位,Cu~(2+)—Gu~(2+)间距为2.64A。平面四方形的配位结构单元Cu~(2+)—O的配位数为4,配位键键长为1.96A。共聚物中羧基含量对离聚体的基本配位结构单元和离子微区的精细结构影响较小,但对微区大小有影响。     

Coordination-synchronized trans-cis photoisomerization of bipyridylazobenzene driven by a Cu(II)/Cu(I) redox change

The trans-cis photoisomerization behavior of azobenzene-bipyridine ligand (dmpAB) was synchronized with coordination of the bipyridine moiety to copper. The coordination reaction can be reversibly controlled with reversible redox reaction of copper, to afford [Cu(dmpAB)(2)](+) in Cu(I) state and free dmpAB in Cu(II) state. UV irradiations to Cu(I) and Cu(II) samples form trans-rich and cis-rich compositions, respectively. The results enable us to control the trans-cis isomerization reversibly through Cu(II)/Cu(I) redox and a single UV light.     

Copper(I/II) complexes of a bis(tetrathiafulvalene)-2,2'-bipyridine: synthesis, characterization, magnetic and electrochemical properties

The coordination ability of the electroactive TTF-based chelating ligand 5,5'-bis(4,5-bis(thiomethyl)-4'-carbamoyltetrathiafulvalene)-2,2'-bipyridine (L) has been tested with Cu(I) and Cu(II) centres. [(L)2Cu(I)](PF6), [(L)2Cu(II)](OTf)2 and [(L)Cu(II)(DMF)3](OTf)2 have been synthesized. A single-crystal X-ray analysis was performed on [(L)Cu(II)(DMF)3](OTf)2, showing a distorted octahedral geometry around the Cu(II) centre, and the formation of dimeric units in the solid state through weak coordination in apical position of an amide oxygen atom from a neighbouring complex. Magnetic data show that the paramagnetic metallic centres are isolated, in agreement with the solid-state structure. Electrochemical measurements were performed on the three complexes and in all cases the Cu(I)/Cu(II) and TTF/TTF+*/TTF2+ redox processes were observed.     

Coordination of thrombolytic Pro-Ala-Lys peptides with Cu (II): leading to nanoscale self-assembly, increase of thrombolytic activity and additional vasodilation

Vasodilation is one of the biologically important properties for thrombolytic agents because of it may help thrombolysis via dilating blood vessels. Aimed at discovering agents with the dual-action of vasodilative and thrombolytic activities, H-Pro-Ala-Lys (PAK, 3a) and five novel analogs H-Pro-Ala-AA ( 2b-f, AA = Val, Phe, Ser, Glu, and His) were coordinated with Cu(II) to form Cu(II)-Pro-Ala-AA [( 3a-f) -Cu(II)]. The coordination chemistry was confirmed by the d-d transition occurred in their UV and circular dichroism (CD) spectra and the molecular ion in their electrospray ionization mass spectrometry (ESI-MS) spectra. The particle size tests of their solution and powders revealed that the coordination generally resulted in nanoscale self-assembly. Zeta potential and half-peak width tests indicated that the formed nanoparticles were sufficiently stable during the monitored 8 days. The bioassays implied that comparing to the PAK peptides themselves and CuCl 2 the coordination led to a 3000-fold increase of the in vitro thrombolytic activity, a 10-fold increase of the in vivo thrombolytic activity, and especially an additional vasodilation. Thus Cu(II)-peptide coordination indeed is a way for thrombolytic peptide design.     

Tetraalkoxyaluminates of nickel(II), copper(II), and copper(I)

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2.2HOiPr, with nickel(II) in a distorted octahedral oxygen environment, or Ni[Al(OiPr)4]2.py, with nickel(II) in a square-pyramidal O4N coordination sphere, or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated complex is Ni[(iPrO)3AlOAl(OiPr)3].3py (with nickel(II) being sixfold-coordinated), which may also be described as a "NiO" species trapped by two Al(OiPr)3 Lewis acid-base systems stabilized at nickel by three pyridine donors. Copper(I) compounds have been isolated in three forms: [(iPrO)4Al]Cu.2py, [(tBuO)4Al]Cu.2py, and Cu2[(tBuO)4Al]2. In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell [Cu-Cu 2.687(1) A] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu.py (pentacoordinated copper similar to the nickel derivative). Finally, a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by dimerization, with the formula {[(tBuO)4Al]Cu(OH).py}2. The formation of all of these isolated products is not always straightforward because some of these compounds in solution are subject to decomposition or are involved in equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize the compounds.     

Cyano-bridged 2D Cu(II)-Cr(III) coordination polymers: structural evidence for formation of a polymeric macrocyclic metallic compound

Two unique cyano-bridged 2D coordination polymers have been synthesized and characterized structurally and magnetically. The complexes contain two polyaza Cu(II) units and one novel macromolecular Cu(II) moiety, which have been synthesized via one-pot metal template condensation reactions involving ethylenediamine (en) and formaldehyde. Self-assembly of the polyaza Cu(II) mixture with [Cr(CN)(6)](3)(-) gave rise to two layered complexes. One complex contains unprecedented covalently linked polymeric Cu(II) chains and cyano-bridged Cu(II)(-)Cr(III) coordination chains, which are interwoven to form a novel layer. The other complex shows intriguing encapsulation of [Cr(CN)(6)](3)(-) anions. Intermetallic ferromagnetic coupling is operative within the bridged 2D layer. The magnetic susceptibilities of both complexes were simulated using approximate models.     

Targeted guanine oxidation by a dinuclear copper(II) complex at single stranded/double stranded DNA junctions

A dinuclear copper(II) complex [Cu(II)2(PD'O-)(H2O)2](ClO4)3 (5) with terminal Cu(II)-H(2)O moieties and a Cu...Cu distance of 4.13 A (X-ray structure) has been synthesized and characterized by EPR spectroscopy (ferromagnetic coupling observed) and cyclic voltammetry. Dizinc(II) and mononuclear copper(II) analogues [Zn(II)2(PD'O-)(H2O)2]3+ (7) and [Cu(II)(mPD'OH)(H2O)]2+ (6), respectively, have also been synthesized and structurally characterized. Reacting 5/MPA/O(2) (MPA = 3-mercaptopropionic acid) with DNA leads to a highly specific oxidation of guanine (G) at a junction between single- and double-stranded DNA. Mass spectrometric analysis of the major products indicates a gain of +18 and +34 amu relative to initial DNA strands. The most efficient reaction requires G at the first and second unpaired positions of each strand extending from the junction. Less reaction is observed for analogous targets in which the G cluster is farther from the junction or contains less than four Gs. Consistent with our previous systems, the multinuclear copper center is required for selective reaction; mononuclear complex 6 is not effective. Hydrogen peroxide as a substitute for MPA/O2 also does not lead to activity. Structural analysis of a [Cu(II)2(PD'O-)(G)]3+ complex (8) and dizinc analogue [Zn(II)(2)(PD'O-)(G)](ClO4)3 (9) (G = guanosine) reveals coordination of the G O6 and N7 atoms with the two copper (or zinc) centers and suggests that copper-G coordination likely plays a role in recognition of the DNA target. The Cu2-O2 intermediate responsible for guanine oxidation appears to be different from that responsible for direct-strand scission induced by other multinuclear copper complexes; the likely course of reaction is discussed.     

beta-diketiminate ligand backbone structural effects on Cu(I)/O(2) reactivity: unique copper-superoxo and bis(mu-oxo) complexes

Copper(I) and -(II) complexes of beta-diketiminate ligands with identical flanking 2,6-diisopropylphenyl groups but divergent backbone substitution patterns were prepared and structurally characterized, and reactions of the Cu(I) species with O(2) at low temperature were explored. Despite being far removed from the coordinated metal ion, the different backbone patterns significantly influence the steric encumbrance exerted by the ligands, as revealed by differences in (a) the structural features of the Cu(I) and Cu(II) complexes and (b) the course of the oxygenation reactions of the Cu(I) compounds. With the less hindered ligand, a rare example of a neutral bis(mu-oxo)dicopper complex was identified on the basis of its diagnostic spectral features (UV-vis, resonance Raman, EPR) and the stoichiometry of O(2) uptake (Cu:O(2) = 2:1). In contrast, oxygenation of the Cu(I) complexes supported by the more hindered ligands yielded novel (superoxo)copper complexes, identified by a Cu:O(2) ratio of 1:1, a lack of an EPR signal, and O-isotope sensitive resonance Raman spectral features (nu(O)(-)(O) = 968 cm(-1), Delta(18)O(2) = 51 cm(-1)). Symmetric coordination of the superoxo ligand is proposed on the basis of Raman data acquired using (16)O(18)O (single peak at 943 cm(-1)).     

EPR characterisation of Cu(II) complexes of poly(propylene imine) dendromesogens: using the orienting effect of a magnetic field.

Liquid-crystalline derivatives of poly(propylene imine)dendrimers of the 0th, 1st and 2nd generations, complexed with copper(II) ions, were studied by EPR spectroscopy. The structures of copper (II) complexes with different Cu(II) loadings x per dendrimer ligand L (x = Cu/L) were determined. At the lowest concentration, the Cu(II) ions form monomeric complexes with approximately square-planar N2O2 coordination of both carbonyl oxygen and amido nitrogen atoms. At higher copper content, two kinds of Cu(II) complex sites with different geometries exist. The orienting effect of a high magnetic field was used to investigate the structure and magnetic properties of the copper(II) complexes. This effect, for the first time in dendrimers, allowed the resolution of five nitrogen super-hyperfine lines on g(z) components with the unusual coupling constant of a(Nz)= 35.9 x 10(-4) cm(-1). The combination of the magnetic parameters and the orienting effect indicates the presence of a monomeric complex with pseudotetrahedral N2O2 coordination of the Cu(II) ion, as well as a "dimer" structure with fivefold coordination, presumably due to an N3O2 environment. Higher copper loadings lead to increased exchange coupling between the complex sites.