Equivalents Of Cu Research Articles

Aggregation of [Cu${{\bf }{{{\bf II}\hfill \atop \bf 4\hfill}}}$] Building Blocks into [Cu${{\bf }{{{\bf II}\hfill \atop \bf 8\hfill}}}$] Clusters or a [Cu${{\bf }{{{\bf II}\hfill \atop \bf 4\hfill}}}$]∞ Chain through Subtle Chemical Control

AbstractCoordination complexes of the ligand H3L [1,3‐bis(3‐oxo‐3‐phenylpropionyl)‐2‐hydroxy‐5‐methylbenzene] with CuII are reported. Clusters showing various nuclearities or modes of supramolecular organization have been prepared by slightly changing the reaction conditions and have been crystallographically characterized. The reaction of H3L with one equivalent of Cu(OAc)2 in DMF yields the dinuclear complex [Cu2(HL)2(dmf)2] (1). Reaction in MeOH of H3L with an increased amount of metal, in the form of Cu(NO3)2, and excess strong base (nBu4NOH) affords the cluster [Cu8(L)2(OMe)8(NO3)2] (2). Complex 2 is a dimer of two linear [Cu4] arrays bridged by methoxide ligands, where the polynucleating ligand is fully deprotonated. The [Cu4]2 clusters are linked to each other by NO3− bridges to form one‐dimensional coordination polymers. The link between [Cu8] units and their relative spatial positioning can be modified by changing the anion of the CuII salt, as demonstrated by the synthesis of the cluster polymers [Cu8(L)2(OMe)8Cl2] (3) and [Cu8(L)(OMe)7.86Br2.14] (4), where only NO3− has been replaced by Cl− or Br−, respectively. Similarly, when ClO4− is used, compound [Cu8(L)2(OMe)8(ClO4)2(MeOH)4] (5) can be isolated. It contains independent [Cu8] units. A slight change in the stoichiometry of the reaction leading to 2 affords the related complex catena‐[Cu4(L)(OMe)3(NO3)2(H2O)0.36] (6). This polymer contains essentially the same [Cu4] moiety as 2, albeit organized in a completely different arrangement. Each [Cu4] unit in 6 is linked by OMe− ligands to two such equivalent groups to form an infinite chain. Magnetic susceptibility measurements reveal weak antiferromagnetic exchange between CuII centers in 1 (J = −0.73 cm−1) and strong antiferromagnetic coupling within [Cu4] chains in 2, 5, and 6 (most negative J values of −113.8 and −177.3 cm−1 for 2 and 6, respectively).

A peptide model of the copper-binding region of lysyl oxidase

The copper-binding site of lysyl oxidase remains extremely poorly characterized and although models have been suggested for copper(II) coordination by three histidine ligands, as has been found for other copper-containing amine oxidases, there has been no experimental confirmation of these suggestions. In this work, two synthetic peptides with 24 and 34-amino acid residues, respectively, were chosen from the highly conserved histidine-rich sequence previously suggested as the copper-binding region of lysyl oxidase. These peptides each bind one equivalent of Cu(II), at the same site in the two peptides. Spectroscopic (NMR, electron paramagnetic resonance (EPR), CD, visible absorption and fluorescence) techniques were employed to investigate the nature of the resulting complexes. The results indicate that at neutral pH three histidine ring nitrogen atoms and one carboxylate oxygen atom coordinate as the in-plane ligands of the copper, which is in an approximately tetragonally-distorted octahedral geometry. Modeling of the copper-peptides using the consistent force field (CFF91) produces a minimum energy configuration with three histidines and one water molecule as the copper ligands. CD, EPR and fluorescence results are reported for lysyl oxidase and compared with results for the peptides.

Co-ordination chemistry of amino pendant arm derivatives of 1,4,7-triazacyclononane.

The binding properties of 1,4,7-triazacyclononane ([9]aneN3) to metal cations can be adapted through sequential functionalisation of the secondary amines with aminoethyl or aminopropyl pendant arms to generate ligands with increasing numbers of donor atoms. The new amino functionalised pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN3), L1, has been synthesised and its salt [H2L1]Cl2 characterised by X-ray diffraction. The protonation constants of the ligands L1-L4 having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with CuII and ZnII have been investigated by potentiometric measurements in aqueous solutions. In order to discern the protonation sites of ligands L1-L4, 1H NMR spectroscopic studies were performed in D2O as a function of pH. While the stability constants of the CuII complexes increase on going from L1 to L2 and then decrease on going from L2 to L3 and L4, those for ZnII complexes increase from L1 to L3 and then decrease for L4. The X-ray crystal structures of the complexes [Cu(L1)(Br)]Br, [Zn(L1)(NO3)]NO3, [Cu(L2)](ClO4)2, [Ni(L2)(MeCN)](BF4)2, [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O have been determined. In both [Cu(L1)(Br)]Br and [Zn(L1)(NO3)]NO3 the metal ion is five co-ordinate and bound by four N-donors of the macrocyclic ligand and by one of the two counter-anions. The crystal structures of [Cu(L2)](ClO4)2 and [Ni(L2)(MeCN)](BF4)2 show the metal centre in slightly distorted square-based pyramidal and octahedral geometry, respectively, with a MeCN molecule completing the co-ordination sphere around NiII in the latter. In both [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O the metal ion is bound by all six N-donors of the macrocyclic ligand in a distorted octahedral geometry. Interestingly, and in agreement with the solution studies and with the marked preference of CuII to assume a square-based pyramidal geometry with these types of ligands, the reaction of L4 with one equivalent of Cu(BF4)2.4H2O in MeOH at room temperature yields a square-based pyramidal five co-ordinate CuII complex [Cu(L6)](BF4)2 where one of the three propylamino pendant arms of the starting ligand has been cleaved to give L6.

Methods for Characterizing TPQ-Containing Proteins

Publisher Summary The standard 20 amino acid side chains define a repertoire of chemical function rich in potent nucleophiles but notably electrophile poor. Nature overcomes this deficiency by either supplying an exogenous cofactor to an enzyme, such as pyridoxal phosphate (PLP), pyrroloquinoline quinine (PQQ), or a metal ion, or by modifying the existing amino acid side chains in situ to supply an active site with reactive carbonyls. The latter strategy has certain advantages, because it obviates the need for transport and insertion of a reactive species across cellular space and into an enzyme. In 1990, the first of what has been shown to be a series of covalently linked, side chain–derived cofactors was discovered and definitively described as 2,4,5 trihydroxyphenylalanine quinone (topaquinone, or TPQ). TPQ is generated post-translationally in a spontaneous process that depends only on the active site Cu and O 2 . Two observations first indicated that this was true. First, Hansenula polymorpha (HPAO) heterologously expressed in S. cerevisiae , a host with no endogenous copper amine oxidases (CAOs), has fully processed and functional TPQ, suggesting that special host-produced factors are not necessary for TPQ formation. Second, CAO expressed in hosts without adequate Cu(II) supplementation in the growth medium is purified with less than an equivalent of Cu(II) per subunit. Work with CAOs has progressed to the stage where these enzymes can be used as virtual laboratories for exploring detailed mechanistic questions. Such a detailed understanding will complement efforts to understand broader questions about CAOs, their roles in nature, and their place in the wider family of quinoproteins.

Serotonin–Cu(II)-mediated DNA cleavage: mechanism of copper binding by serotonin

It has been proposed that considerable DNA damage may be caused by endogenous metabolites produced during the body's normal metabolic processes. 5-hydroxytryptamine (serotonin) is an important neurotransmitter in brain and spinal cord. We have previously shown that serotonin induces oxidative cleavage of DNA strands in the presence of copper ions. In the present paper we have examined the mechanism of copper binding by serotonin using absorption spectroscopy, Cu(II)-mediated lipid peroxidation and by determining the oxidation of the serotonin molecule. Addition of increasing concentrations of Cu(II) to serotonin leads to a progressive enhancement in the absorption band and is accompanied by a shift towards a lower wavelength indicative of the formation of an oxidised species of serotonin. Studies with the structurally related molecules tryptophan and melatonin showed that only serotonin is able to reduce Cu(II) to Cu(I). Similarly, only serotonin was found to be able to abolish the copper-mediated peroxidation of mitochondria. These results suggested the involvement of the phenolic group in copper binding. Further, it was also shown that the binding of copper to serotonin leads to the formation of a quinone in the absence of molecular oxygen. Based on these results, a model has been proposed in which serotonin reduces two molar equivalents of Cu(II) to Cu(I) through a reaction involving two electron oxidation of the phenolic ring to a quinone methide.

Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "roof-shaped" Cu2X2 dimers with hydroxide, methoxide, and azide bridges.

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.

Synthesis and Characterization of a Novel Calix[4]arene-Based Two-Coordinate Copper(I) Complex That Is Unusually Resistant to Dioxygen

The ligand X4Me2Imme2 was synthesized from p-tert-butylcalix[4]arene. Upon reaction with one equivalent of Cu(NCMe)4PF6, it led to the new two-coordinate copper(I) complex [Cu(X4Me2Imme2)]PF6 that was characterized by X-ray diffraction analysis. This complex revealed itself to be totally inert towards dioxygen in the solid state as well as in coordinating or protic solvents.

Synthesis and Characterization of a Novel Calix[4]arene-Based Two-Coordinate Copper(I) Complex That Is Unusually Resistant to Dioxygen

The ligand X4Me2Imme2 was synthesized from p-tert-butylcalix[4]arene. Upon reaction with one equivalent of Cu(NCMe)4PF6, it led to the new two-coordinate copper(I) complex [Cu(X4Me2Imme2)]PF6 that was characterized by X-ray diffraction analysis. This complex revealed itself to be totally inert towards dioxygen in the solid state as well as in coordinating or protic solvents.

Total Syntheses of (±)-Isosteviol and (±)-Beyer-15-ene-3β,19-diol by Manganese(III)-Based Oxidative Quadruple Free-Radical Cyclization

Tetraene 1 was prepared in nine steps from the known propargylic alcohol 7 in 17% overall yield or as a 2:1 E/Z mixture in only five steps in 7% overall yield. Oxidative cyclization of 1 with 2 equiv of Mn(OAc)3·2H2O and 1 equiv of Cu(OAc)2 in MeOH at 25 °C provided 35% of tetracycle 2. Further elaboration provided (±)-isosteviol (3) in six steps in 51% yield and (±)-beyer-15-ene-3β,19-diol in four steps in 17% yield.

Oxidative modification of aldose reductase induced by copper ion. Factors and conditions affecting the process.

Bovine lens aldose reductase (ALR2) is inactivated by copper ion [Cu(II)] through an oxygen-independent oxidative modification process. A stoichiometry of 2 equiv of Cu(II)/enzyme mol is required to induce inactivation. While metal chelators such as EDTA or o-phenantroline prevent but do not reverse the ALR2 inactivation, DTT allows the enzyme activity to be rescued by inducing the recovery of the native enzyme form. The inactive enzyme form is characterized by the presence of 2 equiv of bound copper, at least one of which present as Cu(I), and by the presence of two lesser equivalents, with respect to the native enzyme, of reduced thiol residues. Data are presented which indicate that the Cu-induced protein modification responsible for the inactivation of ALR2 is the generation on the enzyme of an intramolecular disulfide bond. GSH significantly interferes with the Cu-dependent inactivation of ALR2 and induces, through its oxidation to GSSG, the generation of an enzyme form linked to a glutathionyl residue by a disulfide bond.

Stoichiometry and cluster specificity of copper binding to metallothionein: homogeneous metal clusters

Experiments were done to define the stoichiometry of binding of Cu(I) to metallothionein (MT) and to determine its sites of binding in mixed-metal species. Spectrophotometric titrations of rabbit liver Cd7-MT 2, apoMT, and Cd4-alpha-domain with Cu(I) revealed endpoints of 3-4, 4 and 8, and 4 and 6-7 added Cu(I)/mol of MT for the three species respectively. Observed endpoints depended on conditions of the titration and the wavelength chosen for absorbance measurement. Nevertheless, from metal and sulphydryl analyses of titrated proteins that were pretreated with Chelex-100 to remove metal ions from solution, almost all of the cadmium was displaced from Cd7-MT by the addition of 7 Cu(I)/mol of MT. Similarly, 4 Cu(I)/mol of Cd4-alpha-domain completely displaced bound cadmium. The Cu4-alpha-domain was converted into a Cu6-alpha species upon addition of two equivalents of Cu(I)/mol of alpha-domain. Reaction of Cd7-MT with 7, 12 and 20 Cu/mol of MT, followed by reaction with Chelex resin, generated protein samples in each case with about 7 Cu/mol of MT. 111Cd-NMR analysis of the reaction of 111Cd7-MT with Cu(I) showed that nearly co-operative one-for-one replacement of 111Cd occurred and that the beta-domain cluster reacted before the alpha-domain cluster. Two mixed-metal MTs with Cu to Zn ratios approximating 3 to 4 and 6 to 4 were isolated from calf liver. After substitution of Zn with 111Cd, NMR spectra of each protein showed that 111Cd was confined almost completely to the alpha-domain. By inference, about 3 or 6 Cu were bound in the beta-domain of these proteins. Supporting this segregation of metal ions into domains, reaction of Cu6, Zn4-MT with nitrilotriacetate removed zinc exclusively, whereas reaction of Cu6,Cd4-MT with 4,7-phenylsulphonyl-2,9-dimethyl-1,10-phenanthroline extracted only Cu(I). Proteolytic digestion of both products followed by gel filtration demonstrated that Cu(I) and Cd were bound to fragments of the intact protein. Finally, reaction of rabbit liver 111Cd7-MT 2 with Cu10-MT 2 resulted in interprotein metal exchange in which 111Cd-moved from the beta- to the alpha-domain according to NMR analysis. In contrast with the prevalent view that six Cu(I) bind to each domain of MT, the present results show that Cu(I) binds to MT with a minimum stoichiometry of about 7 Cu(I)/mol of MT and can bind to the alpha-domain with stoichiometries of 4 or 6 Cu(I)/mol of MT. Although MTs interacting with 12 or 20 Cu(I)/mol of MT are less stable than that binding about 7 Cu(I)/mol, it appears that MT can bind Cu(I) in multiple stoichiometries.

111Cd NMR studies of the domain specificity of Ag+ and Cu+ binding to metallothionein.

Metal displacement reactions of Cd7MT with Ag+ or Cu+ and interprotein metal exchange reactions between Cd7MT and Ag12MT or Cu12MT were studied by 111Cd NMR. Titration of 111Cd7MT with Ag+ indicates that Ag+ binds preferentially to the beta-domain of the protein to form the metal hybrid species, (Cd4)alpha(Ag6)beta MT. Once the beta-domain is filled, additional Ag+ ions displace Cd2+ from the alpha-domain to form (Ag6)alpha(Ag6)beta MT. The metal displacement reaction is cooperative and the two domains react independently of one another. The (Cd4)alpha(Ag6)beta MT hybrid protein is also formed as the major product of direct interprotein metal exchange between Cd7MT and Ag12MT. Cu+ reacts with Cd7MT in a manner similar to Ag+, with addition of 6 equiv of Cu+ leading to preferential formation of (Cd4)alpha(Cu6)beta-MT, and 12 equiv of Cu+ to formation of (Cu6)alpha(Cu6)beta MT. However, unlike Ag+, Cu+ appears to produce intermediate species that may contain mixed-metal clusters. Interprotein metal exchange between Cu12-MT and Cd7MT leads to the net transfer of Cd2+ into the alpha-domain and Cu+ into the beta-domain. The differential affinities of the two domains for monovalent and divalent metal ions plus the availability of facile pathways for metal exchange may be features that enable MT to function simultaneously in the metabolism of different metal ions.

Synthesis, Crystal Structure, and Solution Properties of a Hexacopper(II) Complex with Bridging Hydroxides, Pyrazolates, and Nitrates.

A reaction of [Cu(pzH)4(NO3)2] (pzH = pyrazole) (1) with 2 equiv of Cu(NO3)2·3H2O at pH 6 afforded the unusual hexacopper(II) complex [Cu3(μ3-OH)(μ-pz)3(μ4-NO3)(pzH)3]2(μ-NO3)2 (pz = pyrazolate) (2). Both 1 and 2 have been structurally characterized by X-ray diffraction. The intertrimer linkage in 2 is supported with two bridging nitrate ions. The behavior of 2 in aqueous media has been examined by means of electronic absorption spectroscopy and electric conductivity measurements.

Mn(III)-Based Oxidative Free-Radical Cyclizations of Unsaturated Ketones.

Mn(III)-based oxidative free-radical cyclization of unsaturated ketones is a versatile synthetic procedure with broad applicability. For example, oxidation of cyclopentanone 1a with 2 equiv of Mn(OAc)(3).2H(2)O and 1 equiv of Cu(OAc)(2).H(2)O in AcOH at 80 degrees C for 1.5 h affords 75% of bicyclo[3.2.1]oct-3-en-8-one 8a and 15% of bicyclo[3.2.1]oct-2-en-8-one 9a. Bridged bicyclic ketones that cannot enolize further are isolated in good yield. Monocyclic beta,gamma-unsaturated ketones that can enolize are oxidized further to give gamma-acetoxy enones. The formation of bicyclo[3.3.1]non-2-en-9-one (57a) in 52% yield from 2-allylcyclohexanone (56a) suggests that kinetically controlled enolization is the rate-determining step in alpha-keto radical formation. A wide variety of examples delineating the scope, limitations, and stereoselectivity of this reaction are presented.

Presence of a copper(I)-thiolate regulatory domain in the copper-activated transcription factor Amt1.

The Amt1 transcription factor from Candida glabrata is activated by the formation of a tetracopper-thiolate cluster. Recombinant Amt1 (residues 1-110) is isolated as a Cu,ZnAmt1 complex. Previous mapping studies [Farrell et al. (1996) Biochemistry 35, 1571-1580] revealed that the Zn(II) site is enfolded by an independent, N-terminal domain consisting of residues 1-40. One prediction from the mapping study is that the tetracopper cluster is enfolded by residues 41-110. A truncated Amt1 peptide consisting of residues 37-110 was expressed and isolated as a CuAmt1 complex with 4 mol equiv of Cu(I) bound. The bound Cu(I) ions in the truncated Amt1 complex were spectroscopically similar to Cu(I) ions bound in the 110-mer Amt1 molecule in the energies and intensities of the ultraviolet S-->Cu charge transfer transitions and luminescence. Copper K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) of the truncated CuAmt1 complex revealed the same 2.26 A mean Cu-S bond distance as in the Cu,ZnAmt1 complex. A diagnostic feature of the polycopper-thiolate cluster in Cu,-ZnAmtl1 is the short 2.7 A Cu-Cu distance determined by Cu K-edge EXAFS. The truncated CuAmt1 complex had the same short 2.7 A Cu-Cu distance. The truncated CuAmt1 complex bound DNA specifically and with high affinity consistent with residues 41-110 being an independent domain stabilized by the tetracopper cluster. Thus, Amt1 consists of three independent and contiguous domains, an N-terminal Zn module (residues 1-40), an adjacent Cu regulatory domain (residues 41-110), and a C-terminal transcriptional activation domain. Cu(I) activation of Amt1 appears to consist of conversion of the 70-residue Cu regulatory domain from an inactive conformer to a structure containing the tetracopper cluster.

Copper(I) and copper(II) dinuclear complexes of a macrocyclic ligand derived from the 2:2 condensation of pyridine-2,6-dicarboxaldehyde and 1,4,7-triazaheptane

The macrocyclic Schiff base ligand 3,6,9,17,20,23,28,29-octaazatricyclo[23.3.1.1 11,15]tridecanedeca-1(28),2,9,11,13,15(30),16,23,25(29),26-ene (PD) 2(DIEN) 2, 1, was prepared from the 2:2 condensation of diethylenetriamine and pyridine-2,6-dicarboxaldehyde. A copper(I) dinuclear complex 2 was formed by the reaction of 1 with two equivalents of Cu(CH 3CN) 4PF 6 in 3:1 methanol/acetonitrile solvent. The complex 2 was oxygenated at 25°C to the extent of a 1:1 molar ratio of dioxygen to complex and a copper(I)-dioxygen complex 3 was spectroscopically indicated as an initial species which degraded to a copper(II) complex, 4, of 1. A dinuclear copper(II) complex 5 was formed by the reaction of 1 with two equivalents of Cu(ClO 4) 2·7H 2O. The X-band EPR spectra of both 4 and 5 are characterized by axial signals with g ⊥ values of 2.076 and 2.085 respectively. Conductivity measurements have shown that 4 is a 3:1 electrolyte when dissolved in acetonitrile. EPR and ultraviolet-visible spectral parameters suggest that 4 and 5 have distorted pyramidal structures in solution.

Structure and properties of copper-(II) and -(I) complexes with 2,6-bis[2-(thiophen-2-ylmethylimino)ethyl]pyridine

Positive-ion FAB mass spectroscopy, elemental analysis, EPR spectroscopy and X-ray diffraction analysis have revealed the structure of the copper(II) complex of 1 : 2 (Cu : L) stoichiometry obtained by mixing in methanol 1 equivalent of Cu(ClO4)2·6H2O and 1 equivalent of 2,6-bis[2-(thiophen-2-ylmethylimino)ethyl]pyridine (L). The copper(II) ion is co-ordinated to six nitrogen atoms in an octahedral arrangement not involving the thiophene S atoms. The planes of the two trans pyridine subunits are perpendicular (94°); the Cu–N bond distances are 1.924 and 1.983 A for the pyridine, 2.098, 2.118 and 2.284, 2.330 A for the imine indicating slight distortion in the structure. Cyclic voltammetry in acetonitrile showed reversible behaviour for the [CuIIL2]2+-[CuIL2]+ couple, and the redox potential E was –0.61 V vs. 10 mmol dm–3 Ag–Ag+ in MeCN. Spectroscopic investigation of acetonitrile solutions having a 1 : 1 Cu : L molar ratio indicated the formation of species with 1 : 1 overall stoichiometry. The electrochemical measurements revealed that these complexes decompose during the electron transfer leading to the [CuIIL2]2+–[CuIL2]+ redox process.

Synthesis and reactivity of N,N′-bis [ o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthylene (Binap-P 2N 2). Crystal structure of [Ag(Binap-P 2N 2)][[BF 4

The condensation of a racemic mixture of 2,2′-diamino-1,1′-binaphthylene with two equivalents of o-(diphenylphosphino)benzaldehyde gives a racemic mixture of N, N′-bis[ o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthylene (Binap-P 2N 2) ( I) in good yield. The coordination behaviour of I towards Cu I and Ag I has been explored. The interaction of I with one equivalent of Cu(Ph 3P) 2Br and [Cu(CH 3CN) 4][PF 6] in CH 2Cl 2 gives Cu(Binap-P 2N 2)Br( II) and [Cu(Binap-P 2N 2)][PF 6] ( III) in 60% and 74% yield, respectively. In II the Binap-P 2N 2 ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Cu, whereas in III it acts in tetradentate chelating mode. A variable temperature 31P{ 1H} NMR study of II reveals that the coordinated and the uncoordinated imino groups of the tridentate Binap-P 2N 2 ligand undergo a facile intramolecular exchange even at −55°C. The interaction of I with one equivalent of AgBF 4 in CH 2Cl 2 gives [Ag(Binap-P 2N 2)][BF 4] ( IV) in 79% yield. In IV, the Binap-P 2N 2 ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Ag. The structure of IV has been established by an X-ray diffraction study. The distance between Ag and N(2) is 2.56(1) Å, and the non-bonding distance between Ag and N(1) is > 3.0 Å.

A novel cytochrome c oxidase from Rhodobacter sphaeroides that lacks CuA.

Rhodobacter sphaeroides contains at least two different cytochrome c oxidases. When these bacteria are grown with high aeration, the traditional aa3-type cytochrome c oxidase is present at relatively high levels. However, under microaerophilic growth conditions or when the bacteria are grown photosynthetically, the amount of the aa3-type oxidase is greatly diminished and an alternate cytochrome c oxidase is evident. This alternate oxidase has been purified and characterized. The enzyme consists of three subunits by SDS-PAGE analysis (Mapp 45, 35, and 29 kDa). Two of the three subunits (Mapp 35 and 29 kDa) contain covalently bound heme C. Metal and heme analyses indicate that the oxidase contains heme C, heme B (protoheme IX), and Cu in a ratio of 3:2:1. Cryogenic Fourier transform infrared (FTIR) difference spectroscopy of the CO adduct of the reduced enzyme shows that the oxidase contains a heme-copper binuclear center and, thus, is a member of the heme-copper oxidase superfamily. In contrast to other members of this superfamily, however, this oxidase does not contain either heme O or heme A as a component of the binuclear center, but has heme B at this site. The single equivalent of Cu found in the oxidase is accounted for by the CuB component at the binuclear center. This suggests that this oxidase does not contain CuA, which is found in all other well-characterized cytochrome c oxidases. Both EPR and optical spectroscopic studies are consistent with this conclusion, also indicating that this oxidase does not contain CuA.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation of copper(I) binap-P 2N 2 complexes; crystal and molecular structure of [Cu(Binap-P 2N 2)Br

The interaction of a racemic mixture of N,N′-bis[ o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthyl (Binap-P 2N 2) ( I) with 1 equivalent of Cu(Ph 3P) 2Br and [Cu(CH 3CN) 4]PF 6 in CH 2Cl 2 gave Cu(Binap-P 2N 2)Br ( II) and [Cu(Binap-P 2N 2)]PF 6 ( III) in 60 and 74% yield, respectively. The structure of II was established by X-ray diffraction and can be described as distorted tetrahedral with the bromide ion and the two phosphino groups and one of the two imino groups of I coordinated to the copper. Variable temperature 31P { 1H} NMR study of II shows that the coordinated and the uncoordinated imino groups of the tridentate Binap-P 2N 2 ligand undergo a facile intramolecular exchange even at −55°C.