The copper chelator methanobactin from Methylosinus trichosporium OB3b binds copper(I)

The oxidation state of copper bound to methanobactin, a small siderophore-like molecule from the methanotroph Methylosinus trichosporium OB3b, was investigated. Purified methanobactin loaded with Cu(II) exhibits a weak EPR signal probably due to adventitious Cu(II). The EPR signal intensity increases significantly upon addition of the strong oxidant nitric acid. Features of the X-ray absorption near edge spectrum, including a 1s --> 4p transition at 8985 eV, further indicate the presence of Cu(I). EXAFS data were best fit using a multiple scattering model generated from previously reported crystallographic parameters. These results establish definitively that M. trichosporium OB3b methanobactin binds Cu(I) and suggest that methanobactin itself reduces Cu(II) to Cu(I).     

Copper trafficking mechanism of CXXC-containing domains: insight from the pH-dependence of their Cu(I) affinities

Copper is trafficked to cellular destinations by homeostatic proteins that also prevent adverse reactivity of the metal. The copper metallochaperone HAH1 (human Atx1) binds Cu(I) via a CXXC motif on loop1/α1 of a βαββαβ ferredoxin-like structure. A similar fold constitutes each of the six metal-binding domains (MBDs) of the two P-type ATPases (Menkes and Wilson disease proteins), the destination for copper bound to HAH1. In this work we have investigated the influence of pH on copper trafficking between HAH1 and the first MBD of the Menkes protein (MNK1). Cu(I) affinities of 5.6 × 10(17) and 3.6 × 10(17) M(-1) have been determined at pH 7.0 for HAH1 and MNK1, respectively, from competition titrations with the chromophoric Cu(I) ligand bathocuproine disulfonate. The mutation of Lys60 on loop5 of HAH1 to Ala (the corresponding residue is Phe67 in MNK1) results in a 3-fold lowering of the affinity for Cu(I) at pH 7.0. The Cu(I) affinity of WT HAH1 exhibits a different pH-dependence compared to MNK1 and Lys60Ala HAH1. This arises because the pK(a) of the second Cys ligand in the CXXC motif of HAH1 is 1.5 pH units lower due to stabilization of the thiolate via a hydrogen-bonding interaction with the side chain of Lys60. The thermodynamic gradient for Cu(I) transfer between HAH1 and MNK1 depends on pH. The decrease in the pK(a) of the Cys ligand in HAH1 can also influence the kinetics of Cu(I) transfer.     

Role of iron and copper in particulate methane monooxygenase of Methylosinus trichosporium OB3b

The role of iron and copper in particulate methane monooxygenase (pMMO) of Methylosinus trichosporium OB3b is described, and an overview of the enzyme's properties is presented. The pMMO from M. trichosporium OB3b was solubilized in the detergent n-dodecyl--D-maltoside and purified by chromatographic techniques. The enzyme consists of 0.9 iron atoms and 12.8 copper atoms per molecule. The iron site in pMMO may be mononuclear non-heme iron. Copper exists as either copper ion coupled to four nitrogen atoms and/or trinuclear copper cluster wherein copper ions are ferromagnetically coupled.     

Exploring the Structural Details of Cu(I) Binding to α-Synuclein by NMR Spectroscopy

The aggregation of α-synuclein (AS) is selectively enhanced by copper in vitro, and the interaction is proposed to play a potential role in vivo. In this work, we report the structural, residue-specific characterization of Cu(I) binding to AS and demonstrate that the protein is able to bind Cu(I) with relatively high affinity in a coordination environment that involves the participation of Met1 and Met5 residues. This knowledge is a key to understanding the structural-aggregation basis of the copper-catalyzed oxidation of AS.     

Hydroxylase activity of Met471Cys tyramine beta-monooxygenase

A series of mutations was targeted at the methionine residue, Met471, coordinating the Cu(M) site of tyramine beta-monooxygenase (TbetaM). The methionine ligand at Cu(M) is believed to be key to dioxygen activation and the hydroxylation chemistry of the copper monooxygenases. The reactivity and copper binding properties of three TbetaM mutants, Met471Asp, Met471Cys, and Met471His, were examined. All three mutants show similar metal binding affinities to wild type TbetaM in the oxidized enzyme forms. EPR spectroscopy suggests that the Cu(II) coordination geometry is identical to that of the WT enzyme. However, substrate hydroxylation was observed for the reaction of tyramine solely with Met471Cys TbetaM. Met471Cys TbetaM provides the first example of an active mutant directed at the Cu(M) site of this class of hydroxylases. The reactivity and altered kinetics of the Met471Cys mutant further highlight the central role of the methionine residue in the enzyme mechanism. The sole ability of the cysteine residue to support activity among the series of alternate amino acids investigated is relevant to theoretical and biomimetic investigations of dioxygen activation at mononuclear copper centers.     

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.     

Model peptides provide new insights into the role of histidine residues as potential ligands in human cellular copper acquisition via Ctr1

Cellular acquisition of copper in eukaryotes is primarily accomplished through the Ctr family of copper transport proteins. In both humans and yeast, methionine-rich "Mets" motifs in the amino-terminal extracellular domain of Ctr1 are thought to be responsible for recruitment of copper at the cell surface. Unlike yeast, mammalian Ctr1 also contains extracellular histidine-rich motifs, although a role for these regions in copper uptake has not been explored in detail. Herein, synthetic model peptides containing the first 14 residues of the extracellular domain of human Ctr1 (MDHSHHMGMSYMDS) have been prepared and evaluated for their apparent binding affinity to both Cu(I) and Cu(II). These studies reveal a high affinity Cu(II) binding site (log K = 11.0 ± 0.3 at pH 7.4) at the amino-terminus of the peptide as well as a high affinity Cu(I) site (log K = 10.2 ± 0.2 at pH 7.4) that utilizes adjacent HH residues along with an additional His or Met ligand. These model studies suggest that the histidine domains may play a direct role in copper acquisition from serum copper-binding proteins and in facilitating the reduction of Cu(II) to the active Ctr1 substrate, Cu(I). We tested this hypothesis by expressing a Ctr1 mutant lacking only extracellular histidine residues in Ctr1-knockout mouse embryonic fibroblasts. Results from live cell studies support the hypothesis that extracellular amino-terminal His residues directly participate in the copper transport function of Ctr1.     

Optically activated uptake and release of Cu2+ or Ag+ ions by or from a photoisomerizable monolayer-modified electrode

Di-(N-butanoic acid-1,8-naphthalimide)-piperazine dithienylethene was covalently linked to a cysteamine monolayer associated with a Au surface to yield a photoisomerizable monolayer composed of the open or closed dithienylcyclopentene isomers (3a or 3b), respectively. Electrochemical and XPS analyses reveal that the association of metal ions to the monolayer is controlled by its photoisomerization state. We find that Cu(2+) ions reveal a high affinity for the open (3a) monolayer state, K(a) = 4.6 × 10(5) M(-1), whereas the closed monolayer state (3b) exhibits a substantially lower binding affinity for Cu(2+), K(a) = 4.1 × 10(4) M(-1). Similarly, Ag(+) ions bind strongly to the 3a monolayer state but lack binding affinity for the 3b state. The reversible photoinduced binding and dissociation of the metal ions (Cu(2+) or Ag(+)) with respect to the photoisomerizable monolayer are demonstrated, and the systems may be used for the photochemically controlled uptake and release of polluting ions. Furthermore, we demonstrate that the photoinduced reversible binding and dissociation of the metal ions to and from the photoisomerizable electrode control the wettability properties of the surface.     

A Mets motif peptide found in copper transport proteins selectively binds Cu(I) with methionine-only coordination

Mets motifs, which refer to methionine-rich sequences found in the high-affinity copper transporter Ctr1, also appear in other proteins involved in copper trafficking and homeostasis, including other Ctrs as well as Pco and Cop proteins isolated from copper-resistant bacteria. To understand the coordination chemistry utilized by these proteins, we studied the copper binding properties of a peptide labeled Mets7-PcoC with the sequence Met-Thr-Gly-Met-Lys-Gly-Met-Ser. By comparing this sequence to a series of mutants containing noncoordinating norleucine in place of methionine, we confirm that all three methionine residues are involved in a thioether-only binding site that is selective for Cu(I). Two independent methods, one based on mass spectrometry and one based on rate differences for the copper-catalyzed oxidation of ascorbic acid, provide an effective K(D) of approximately 2.5 microM at pH 4.5 for the 1:1 complex of Mets7-PcoC with Cu(I). These results establish that a relatively simple peptide containing an MX(2)MX(2)M motif is sufficient to bind Cu(I) with an affinity that corresponds well with its proposed biological function of extracellular copper acquisition.     

Templated Total Synthesis of Cu(I)-Methanobactin OB3b**

Methanobactin OB3b (Mbn-OB3b) is a unique natural product with stunning affinity for copper ions (K_a≈Cu(I) 10³⁴). Here, we report the first total synthesis of Cu(I)-bound methanobactin OB3b featuring as key transformations a cyclodehydration-thioacylation sequence, to generate the conjugated heterocyclic systems, and a copper-templated cyclization, to complete the caged structure of the very sensitive target compound.     

CopAb, the second N-terminal soluble domain of Bacillus subtilis CopA, dominates the Cu(I)-binding properties of CopAab

The Cu(I)-detoxifying P-type ATPase CopA from Bacillus subtilis contains two N-terminal soluble domains, CopAa and CopAb, connected by a short linker. This arrangement is extremely common in prokaryotic Cu(I) transporters and is also found amongst the multiple soluble domains of eukaryotic homologues. Previous studies of a protein containing only these domains (CopAab) revealed complex Cu(I)-binding properties: both domains are able to bind Cu(I) extremely tightly and, at levels of Cu(I) > 1 per CopAab, the protein undergoes dimerisation, yielding a highly luminescent multi-Cu(I) bound species (Singleton and Le Brun, Dalton Trans., 2009, 688-696). To investigate this complex Cu(I)-binding behaviour and, in particular, to determine the contributions of the two domains to the overall behaviour of the N-terminal part, we generated and purified each domain in isolation. Here, we report studies of the second domain, CopAb. The protein was found to bind Cu(I) with an extremely high affinity (K = ~1 × 10(18) M(-1)) and remained as a monomer up to a level of 1 Cu(I) per protein. Above this level, the protein dimerised, generating a weakly luminescent species. Studies of the acid-base properties of the binding motif Cys residues revealed pK(a) values of < ~5 and ~6.3, adding further support to the proposal that high Cu(I)-affinity is correlated with low proton affinity. Exchange of Cu(I) between the protein and a high affinity chelator was found to occur rapidly via Cu(I)-mediated association, a process that is relevant to in vivo Cu(I) trafficking. Overall, the Cu(I)-binding properties of CopAb are very similar to those of the two-domain protein CopAab, indicating that this domain plays a dominant role in determining the binding properties of CopAab.     

邻苯三酚红修饰碳糊电极吸附伏安法测定痕量铜

报道了采用邻苯三酚红修饰碳糊电极测定痕量铜的方法。通过在邻苯二甲酸氢钾 -氢氧化钠 (p H4.5)介质中富集 ,Cu2 +和邻苯三酚红形成络合物富集于电极表面 ,然后转换到 0 .0 50 mol· L-1的 H3PO4 中 ,经阴极还原后再进行阳极溶出伏安法测定。Cu2 +浓度在 1 .6× 1 0 -9～ 2 .8× 1 0 -7mol·L-1范围内与二次导数峰电流呈线性关系 ,检出限达 8× 1 0 -10 mol·L-1。同时 ,对电极反应机理进行了探讨。应用于合金样的测定 ,取得满意的结果。     

Computational studies of Cu(II)/Met and Cu(I)/Met binding motifs relevant for the chemistry of Alzheimer's disease

A systematic study of the binding motifs of Cu(II) and Cu(I) to a methionine model peptide, namely, N-formylmethioninamide 1, has been carried out by quantum chemical computations. Geometries of the coordination modes obtained at the B3LYP/6-31G(d) level of theory are discussed in the context of copper coordination by the peptide backbone and the S atom of a methionine residue in peptides with special emphasis on Met35 of the amyloid-beta peptide (Abeta) of Alzheimer's disease. The relative binding free energies in the gas phase, DeltaG(g), are calculated at the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d) level of theory, and the solvation affects are included by means of the COSMO model to obtain the relative binding energies in solution, DeltaG(aq). A free energy of binding, DeltaG(aq) = -19.4 kJ mol(-1), relative to aqueous Cu(II) and the free peptide is found for the most stable Cu(II)/Met complex, 12. The most stable Cu(I)/Met complex, 23, is bound by -15.6 kJ mol(-1) relative to the separated species. The reduction potential relative to the standard hydrogen electrode is estimated to be E degrees (12/23) = 0.41 V. On the basis of these results, the participation of Met35 as a low affinity binding site of Cu(II) in Abeta, and its role in the redox chemistry underlying Alzheimer's disease is discussed.     

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.     

Copper Binding and Oligomerization Studies of the Metal Resistance Determinant CrdA from Helicobacter pylori

Within this research, the CrdA protein from Helicobacter pylori (HpCrdA), a putative copper-binding protein important for the survival of bacterium, was biophysically characterized in a solution, and its binding affinity toward copper was experimentally determined. Incubation of HpCrdA with Cu(II) ions favors the formation of the monomeric species in the solution. The modeled HpCrdA structure shows a conserved methionine-rich region, a potential binding site for Cu(I), as in the structures of similar copper-binding proteins, CopC and PcoC, from Pseudomonas syringae and from Escherichia coli, respectively. Within the conserved amino acid motif, HpCrdA contains two additional methionines and two glutamic acid residues (MMXEMPGMXXMXEM) in comparison to CopC and PcoC but lacks the canonical Cu(II) binding site (two His) since the sequence has no His residues. The methionine-rich site is in a flexible loop and can adopt different geometries for the two copper oxidation states. It could bind copper in both oxidation states (I and II), but with different binding affinities, micromolar was found for Cu(II), and less than nanomolar is proposed for Cu(I). Considering that CrdA is a periplasmic protein involved in chaperoning copper export and delivery in the H. pylori cell and that the affinity of the interaction corresponds to a middle or strong metal–protein interaction depending on the copper oxidation state, we conclude that the interaction also occurs in vivo and is physiologically relevant for H. pylori.     

Reevaluation of copper(I) affinity for amyloid-β peptides by competition with ferrozine--an unusual copper(I) indicator

The association constant of ferrozine (5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine-4,4'-disulfonic acid) with Cu(I) to form the chromophoric [Cu(I)(Fz)(2)](3-) complex was determined by UV/Vis titration experiments in Hepes buffer (0.1 M, pH 7.4). An association constant close to 10(12) M(-2), which is significantly weaker than those of the well-known, water-soluble, Cu(I) chelators bicinchoninic acid and 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline disulfonic acid, was found. The [Cu(I)(Fz)(2)](3-) chromophore was used in UV/Vis competition experiments to determine Cu(I) binding affinity for the amyloid-β peptide involved in Alzheimer's disease and for a series of pertinent mutants. An association constant of approximately 10(7) M(-1) was found; this is much weaker than that reported for dithiothreitol and confirms that imidazoles are harder ligands than thiolates. Each His mutation (H6A, H13A, and H14A) impacts the peptide affinity for Cu(I). The native human amyloid-β peptide was found to be a fourfold-stronger Cu(I) ligand than the murine peptide, which differs by three point mutations (R5G, Y10F, and H13R) from the human one.     

Binding Selectivity of Methanobactin from <Emphasis Type="Italic">Methylosinus trichosporium</Emphasis> OB3b for Copper(I), Silver(I), Zinc(II), Nickel(II), Cobalt(II), Manganese(II), Lead(II), and Iron(II)

Methanobactin (Mb) from Methylosinus trichosporium OB3b is a member of a class of metal binding peptides identified in methanotrophic bacteria. Mb will selectively bind and reduce Cu(II) to Cu(I), and is thought to mediate the acquisition of the copper cofactor for the enzyme methane monooxygenase. These copper chelating properties of Mb make it potentially useful as a chelating agent for treatment of diseases where copper plays a role including Wilson’s disease, cancers, and neurodegenerative diseases. Utilizing traveling wave ion mobility-mass spectrometry (TWIMS), the competition for the Mb copper binding site from Ag(I), Pb(II), Co(II), Fe(II), Mn(II), Ni(II), and Zn(II) has been determined by a series of metal ion titrations, pH titrations, and metal ion displacement titrations. The TWIMS analyses allowed for the explicit identification and quantification of all the individual Mb species present during the titrations and measured their collision cross-sections and collision-induced dissociation patterns. The results showed Ag(I) and Ni(II) could irreversibly bind to Mb and not be effectively displaced by Cu(I), whereas Ag(I) could also partially displace Cu(I) from the Mb complex. At pH ≈ 6.5, the Mb binding selectivity follows the order Ag(I)≈Cu(I)>Ni(II)≈Zn(II)>Co(II)>>Mn(II)≈Pb(II)>Fe(II), and at pH 7.5 to 10.4 the order is Ag(I)>Cu(I)>Ni(II)>Co(II)>Zn(II)>Mn(II)≈Pb(II)>Fe(II). Breakdown curves of the disulfide reduced Cu(I) and Ag(I) complexes showed a correlation existed between their relative stability and their compact folded structure indicated by their CCS. Fluorescence spectroscopy, which allowed the determination of the binding constant, compared well with the TWIMS analyses, with the exception of the Ni(II) complex.

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Autoredox interconversion of two galactose oxidase forms GOase(ox) and GOase(semi) with and without dioxygen

Solutions of galactose oxidase stored in air give in 3-4 h a mix of GOase(ox)(Cu(II)-Tyr(*)) and GOase(semi)(Cu(II)-Tyr), as a result of processes involving the formation and decay of the Cu(II)-coordinated tyrosyl radical (Tyr(*)). In this work the two reactions have been studied by UV-vis spectrophotometry and separate rate laws defined. The first involves the "spontaneous" autoreduction of GOase(ox) to GOase(semi), which in air-free conditions is 100% complete. Rate constants (k(red)) are dependent on pH, and previously defined acid dissociation constants pK(1a) = 5.7 (exogenous H(2)O ligand), and pK(2a) = 8.0 (axial H(+)Tyr-495) apply. Values of k(red)(25 degrees C) range from 1.55 x 10(-4) s(-1) (pH 5.5) to 2.69 x 10(-4) s(-1) (pH 8.6), I = 0.100 M (NaCl). No reaction occurs with N(3)(-) or NCS(-) present in amounts sufficient to give >98% binding at the substrate binding (exogenous) site, while CH(3)CO(2)(-) and phosphate (less extensively bound) also inhibit the reaction. From such inhibition studies K(25 degrees C) is 161 M(-1) at pH 6.4 for acetate (previous value 140 M(-)(1)) and 46 M(-1) at pH 7.0 for phosphate. No reaction occurs when the disulfide Cys515-Cys518 (10.2 A from the Cu) is chemically modified with HSPO(3)(2-), and electron transfer via the disulfide and exogenous position is proposed (source of the electron not established). The conversion of GOase(semi) to GOase(ox) only occurs with O(2) present, when a first-order dependence on [O(2)] is observed, giving k(ox)(25 degrees C) = 0.021 M(-1) s(-1) at pH 7.5. This process is unaffected by NCS(-) or N(3)(-) bound at the exogenous site, and a mechanism involving outer-sphere reaction of O(2) to O(2)(-) followed by a fast step O(2) to H(2)O(2) is proposed. As GOase(ox) is formed, autoreduction back to GOase(semi) occurs, and at pH 7.5 with O(2) in large excess (1.13 mM) the maximum conversion to GOase(ox) is 69%. The k(ox) reaction proceeds to completion with >98% N(3)(-) bound at the exogenous site.     

Structural and electronic differences of copper(I) complexes with tris(pyrazolyl)methane and hydrotris(pyrazolyl)borate ligands

Copper(I) complexes with tripodal nitrogen-containing neutral ligands such as tris(3,5-diisopropyl-1-pyrazolyl)methane (L1') and tris(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3'), and with corresponding anionic ligands such as hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (L1-) and hydrotris(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)borate (L3-) were synthesized and structurally characterized. Copper(I) complexes [Cu(L1')Cl] (1), [Cu(L1')(OClO3)] (2), [Cu(L1')(NCMe)](PF6) (3a), [Cu(L1')(NCMe)](ClO4) (3b), [Cu(L1')(CO)](PF6) (4a), and [Cu(L1')(CO)](ClO4) (4b) were prepared using the ligand L1'. Copper(I) complexes [Cu(L3')Cl] (5) and [Cu(L3')(NCMe)](PF6) (6) with the ligand L3' were also synthesized. Copper(I) complexes [Cu(L1)(NCMe)] (7) and [Cu(L1)(CO)] (8) were prepared using the anionic ligand L1-. Finally, copper(I) complexes with anionic ligand L3- and acetonitrile (9) and carbon monoxide (10) were synthesized. The complexes obtained were fully characterized by IR, far-IR, 1H NMR, and 13C NMR spectroscopy. The structures of both ligands, L1' and L3', and of complexes 1, 2, 3a, 3b, 4a, 4b, 5, 6, 7, and 10 were determined by X-ray crystallography. The effects of the differences in (a) the fourth ligand and the counteranion, (b) the steric hindrance at the third position of the pyrazolyl rings, and most importantly, (c) the charge of the N3 type ligands, on the structures, spectroscopic properties, and reactivities of the copper(I) complexes are discussed. The observed differences in the reactivities toward O2 of the copper(I) acetonitrile complexes are traced back to differences in the oxidation potentials determined by cyclic voltammetry. A special focus is set on the carbonyl complexes, where the 13C NMR and vibrational data are presented. Density functional theory (DFT) calculations are used to shed light on the differences in CO bonding in the compounds with neutral and anionic N3 ligands. In correlation with the vibrational and electrochemical data of these complexes, it is demonstrated that the C-O stretching vibration is a sensitive probe for the "electron richness" of copper(I) in these compounds.     

1-(2-噻唑)-3-(8-(5-对磺酸基苯基偶氮)喹啉)-三氮烯的合成及其与铜(Ⅱ)的显色反应

合成了新试剂1-(2-噻唑)-3-(8-(5-对磺酸基苯基偶氮)喹啉-三氮烯(TCPQT),并研究了其与Cu2+的显色反应。结果表明:在pH 7.5的磷酸盐缓冲溶液中,TCPQT与Cu2+形成摩尔比为1:1的紫红色络合物,该络合物在606.5nm处有一最大吸收峰,其表观摩尔吸光系数为3.36×105L.mol-1.cm-1,Cu2+的质量浓度在0～0.4μg/mL范围内符合比尔定律,相关系数r=0.9993。方法已用于测定食品中的微量铜。