Binding of copper(II) to carnosine: Raman and IR spectroscopic study

A comparative Raman and FTIR study of carnosine, a dipeptide present in several mammalian tissues, and its complexes with copper(II) at different pH values was carried out. The neutral imidazole ring gives rise to some bands that appear at different wavenumbers, depending on whether the imidazole ring is in the tautomeric form II or I. At pH 7 and 9 the molecule exists in equilibrium between the two tautomeric forms; tautomer I is predominant. Metal coordination is a factor that affects the tautomeric equilibrium, and the copper(II) coordination site can be monitored by using some Raman marker bands such as the vC(4)=C(5) band. On the basis of the vibrational results, conclusions can be drawn on the functional groups involved in the Cu(II) chelation and on the species existing in the Cu(II)-carnosine system. At neutral and basic pH the most relevant species formed when the Cu(II)/carnosine molar ratio is not very different from unity is a dimer, [Cu(2)L(2)H(-2)](0). In this complex the ligand coordinates the metal via the N (amino), O (carboxylate), and N (amide) donor atoms while the N(tau) nitrogen atoms of the imidazole rings (tautomer II) bridge the copper(II) ions. At a slightly acidic pH the two monomeric complexes [CuLH](2+) and [CuL](+) were present. In the former the imidazole ring takes part in the Cu(II) coordination in the tautomeric I form whereas in the latter it is protonated and not bound to Cu(II).     

Anticancer activity, structure, and theoretical calculation of N-(1-phenyl-3-methyl-4-propyl-pyrazolone-5)-salicylidene hydrazone and its copper(II) complex

The pyrazolone derivative N-(1-phenyl-3-methyl-4-propyl-pyrazolone-5)-salicylidene hydrazone (H₂L) and its copper(II) complex [Cu₂L₂CH₃OH]·2CH₃OH have been both synthesized and characterized by elemental analyses, IR spectroscopy, X-ray crystallography, theoretical calculation and pharmacological testing. It’s found that the Cu(II) complex possesses more powerful anticancer effectivity than that of the ligand. In order to make its anticancer principium clearly, we investigate their structures. In ligand there are several coordination spots, such as N, O atoms, which are close to biological environment. The crystallographic structural analysis of the complex reveals that the two Cu centers display two different coordination patterns. O1, O2, N3, and N4 from the ligand take part in the coordination with Cu atoms, resulting in the formation of the double-nuclear complex. The pharmacological testing results show that the coordination effect improves the antitumor activity of the ligand. The calculated Fukui function for H₂L and its deprotonated form L²⁻ predicts that the most probable reactive sites for electrophilic attack are oxygen atoms. The result is agreement well with the experimental data of the crystal structure analyses.     

Raman and IR study on copper binding of histamine

A comparative Raman and FTIR study of histamine (Hm), a small hormone present in a wide selection of living organisms, and its complexes with copper(II) at different pH values was carried out. Both the Raman and IR spectra present some marker bands useful for the identification of the structure of the species predominating in the Cu(II) aqueous and alcoholic systems. In particular, Raman spectroscopy appears to be a useful tool for analyzing the tautomeric equilibrium of the imidazole ring of Hm, because some bands (i.e., nuC(4)dbond;C(5)) appear at different wavenumbers, depending on whether the imidazole moiety is in the N(tau)-H (tautomer I) or N(pi)-H (tautomer II) protonated form. In aqueous solutions the manner in which Hm binds to Cu(II) depends on the pH. At basic pH the most relevant species formed are a dimer, [Cu(2)L(2)H(-2)](2+), and a monomeric complex, [CuL](2-) or [CuL(2)](+). On the contrary, by decreasing the pH, Hm acts as a mono- or bidentate ligand, giving rise to two types of monomeric complexes, [CuLH](2-) and [CuL](2-) or [CuL(2)](+). With respect to the Cu(II)-Hm alcoholic system, both the aminic group and the imidazole ring (tautomer I) take part in the Cu(II) coordination, leading to the formation of the [CuL](2-) or [CuL(2)](+) monomeric complex.     

Spectroscopic,structural and antibacterial properties of copper(II) complexes with bio-relevant 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone

The coordination behaviour of the title ligand, 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone(HMPz4BM), is reported with solid state isolation of copper(II) complexes, [Cu(HMPz4BM)X₂] (X = Cl, Br, NO₃, ClO₄ and BF₄) which have been spectroscopically and structurally characterised. I.r. data for the free ligand and its Cu(II) complexes indicate that HMPz4BM exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen(tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a square pyramidal environment for the seemingly pentacoordinated Cu(II) species. E.s.r parameters (RT and LNT) of the reported copper(II) complexes are indicative of a dx_x2–y2 ground state for the reported species. Cyclic voltammograms of Cu(II) complexes show a quasireversible Cu^II/Cu^III couple and also an irreversible Cu^II/Cu^I couple. X-ray crystallography of a representative species, [Cu(HMPz4BM)(NO₃)₂] (C2/c, monoclinic ), has unambiguously documented the conjectural findings from i.r. data that coordinating sites of the title ligand are pyrazolyl (tertiary)nitrogen, azomethine nitrogen and the thione sulphur (NNS); and the oxygen of one of the nitrate ions has occupied the basal plane; the fifth coordination position has been occupied by the oxygen of another nitrate ion in a square pyramidal geometry. The antibacterial properties of the ligand and its copper(II) complexes studied on microorganism, Staphylococcus aureus have pointed out that most of the complexes have higher activities than that of the free ligand.     

Binding of copper(II) to thyrotropin-releasing hormone (TRH) and its analogs

Spectroscopy (UV-Vis, ¹H NMR, ESR) and electrochemistry revealed details of the structure of the Cu(II)-TRH (pyroglutamyl-histidyl-prolyl amide) complex. The ¹H NMR spectrum of TRH has been assigned. NMR spectra of TRH in the presence of Cu(II) showed that Cu(II) initially binds TRH through the imidazole. TRH analogs, pGlu-His-Pro-OH, pGlu-(1-Me)His-Pro-amide, pGlu-His-(3,4-dehydro)Pro-amide, pGlu-His-OH, pGlu-Glu-Pro-amide, and pGlu-Phe-Pro-amide provided comparison data. The stoichiometry of the major Cu(II)-TRH complex at pH 7.45 and greater is 1:1. The conditional formation constant (in pH 9.84 borate with 12.0 mM tartrate) for the formation of the complex is above 10⁵ M⁻¹. The coordination starts from the 1-N of the histidyl imidazole, and then proceeds along the backbone involving the deprotonated pGlu-His amide and the lactam nitrogen of the pGlu residue. The fourth equatorial donor is an oxygen donor from water. Hydroxide begins to replace the water before the pH reaches 11. Minority species with stoichiometry of Cu-(TRH)_x (x = 2-4) probably exist at pH lower than 8.0. In non-buffered aqueous solutions, TRH acts as a monodentate ligand and forms a Cu(II)-(TRH)₄ complex through imidazole nitrogens. All the His-containing analogs behave like TRH in terms of the above properties.     

Synthesis, characterization and copper chemistry of a non-symmetric phenanthroline ligand: 2-Methyl-9-(3,5-dimethyl-N-pyrazolylmethyl)-1,10-phenanthroline

The synthesis of an unsymmetrical phenanthroline-based ligand, 2-methyl-9-(3,5-dimethylpyrazolylmethyl)-1,10-phenanthroline (L), and its cupric [Cu(II)] (1) and cuprous [Cu(I)] (2) complexes, are reported. The X-ray structures of each of these Cu complexes show distinct changes in coordination environments consistent with the geometrical preferences of the two oxidation states. In the solid-state, the Cu(II) complex (1) adopts a geometry best described as trigonal bipyramidal, while the Cu(I) complex (2) consists of a single dicationic dimer in which the ligand bridges between two copper ions, separated by 4.26 Å. The two Cu(I) coordination sites differ in 2 with one copper center complexed in a trigonal planar geometry and the other copper in a distorted tetrahedral environment; the latter coordination results from an additional CH₃CN ligand. Complex 1 exhibits a reversible redox process at −0.34 V versus Fc/Fc⁺ in CH₃CN, attributable to the Cu²⁺/Cu⁺ couple, while the dimeric Cu(I) complex (2) does not display this redox couple on the CV timescale. Over minutes however, complex 1 does oxidize in the presence of dioxygen to 2 in CH₃CN.     

Hypoglycemic effect of copper(II) acetate imidazole complexes

The effect of copper(II) complexes on glucose metabolism was studied in normal and streptozotocin-induced diabetic rats. The copper(II) complexes used were bis(acetato)tetrakis(imidazole) copper (II), [Cu(OAc)₂(Im)₄], bis(acetato)bis(2-methylimidazole) copper(II), [Cu(OAc)₂(1,2dmIm)₂], and bis)acetato)bis(μ-acetato)tetrakis(N-methylimidazole) copper(II) hexaaquo, [Cu₂(OAc)₄-(NmIm)₄]·6H₂O. Intramuscular administration of various doses of Cu(OAc)₂(Im)₄ ranging from 10 to 100 mg/kg body mass to overnight fasted rats decreased blood glucose levels in a dose-dependent manner. Maximum hypoglycemic effect was observed 3 h after administration and lasted for at least 6 h. Treatment with 100 mg/kg body mass of Cu(OAc)₂(Im)4 caused hypoglycemic shock, which was irreversible and even lethal. Blood insulin levels were reduced sharply during this hypoglycemic shock. Similar changes in blood glucose level were achieved using Cu(OAc)₂)2mIm)₂. The same pattern of hypoglycemia, although less pronouned, was observed for Cu₂(OAc)₄(NmIm)₄·6H₂O and Cu (OAc)₂(1,2dmIm)₂. Binary copper(II) acetate complex, the ligand imidazole, and the inorganic form of copper, such as copper(II) chloride, had no significant effect on blood glucose level. These results indicate that the hypoglycemic activity of these complexes varies with the imidazole ligand and structure of the complex. Intramuscular administration of Cu(OAc)₂(Im)₄ to diabetic rats caused a reduction in blood glucose levels and improved their tolerance for glucose.     

Coordination abilities of neurokinin A and its derivative and products of metal-catalyzed oxidation

The classical tachykinins, substance P, neurokinin A and neurokinin B are predominantly found in the nervous system where they act as neurotransmitters and neuromodulators. Significantly reduced levels of these peptides were observed in neurodegenerative diseases and it may be suggested that this reduction may also result from the copper(II)-catalyzed oxidation. The studies of the interaction of copper(II) with neurokinin A and the copper(II)-catalyzed oxidation were performed. Copper(II) complexes of the neurokinin A (His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH₂) and acetyl-neurokinin A (Ac-His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH₂) were studied by potentiometric, UV-Vis (UV-visible), CD (circular dichroism) and EPR spectroscopic methods to determine the stoichiometry, stability constants and coordination modes in the complexes formed. The histidine residue in first position of the peptide chain of neurokinin A coordinates strongly to Cu(II) ion with histamine-like {NH₂, N_Im} coordination mode. With increasing of pH, the formation of a dimeric complex Cu₂H₂L₂ was found but this dimeric species does not prevent the deprotonation and coordination of the amide nitrogens. In the Ac-neurokinin A case copper(II) coordination starts from the imidazole nitrogen of the His; afterwards three deprotonated amide nitrogens are progressively involved in copper coordination. To elucidate the products of the copper(II)-catalyzed oxidation of the neurokinin A and Ac-neurokinin A, liquid chromatography-mass spectrometry (LC-MS) method and Cu(II)/hydrogen peroxide as a model oxidizing system were employed.Oxidation target for both studied peptides is the histidine residue coordinated to the metal ions. Both peptides contain Met and His residues and are very susceptible on the copper(II)-catalyzed oxidation.     

Metal coordination core of bleomycin : comparison of metal complexes between bleomycin and its biosynthetic intermediate.

On the basis of electron spin resonance results, the 1:1 Cu(II), Co(II), Co(II)-O₂, and Ni(III) complexes of bleomycin(BLM) have been compared with the corresponding metal complexes of its biosynthetic intermediate(P-3A). The present study suggests that (1) P-3A is an useful ligand for the clarification of metal-binding sites of BLM; (2) the secondary amine, pyrimidine ring nitrogen, deprotonated peptide nitrogen of histidine residue, and histidine imidazole groups as planar ligand donors, and the α-amino group as axial donor, are substantially important for metal-coordination of BLM; and (3) the sugar and bithiazole portions of BLM probably contribute to stabilization of Co(II)-O₂ adduct complex and axial sixth coordination of Cu(II) and Ni(III) complexes.     

Cyclic metal-radical complexes based on 2-[4-(1-imidazole)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide: Syntheses, crystal structures and magnetic properties

Using new nitronyl nitroxide radical ligand 2-[4-(1-imidazole)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITPhIm), three new complexes [M(hfac)₂(NITPhIm)]₂ (M = Cu(II) 1, Mn(II) 2, Co(II) 3; hfac = hexafluoroacetylacetonate) have been prepared. Three complexes possess cyclic dimer structure in which each NITPhIm radical links two different metal ions through the oxygen of nitroxide group and the nitrogen of imidazole. The magnetic studies show the copper(II) ion interacts ferromagnetically with the directly bonding nitronyl nitroxide while manganese(II) and cobalt(II) ions strong antiferromagnetically interact with the directly coordinated nitroxide groups. There is a weak antiferromagnetic coupling between the metal ion and the nitroxide through phenyl and imidazole rings of the radical ligand, which is agreement with spin polarization mechanism. The results show that the minor changes in the structure of radical ligand can change the magnetic behavior of radical-metal complex.     

Effects of imidazole and zinc on the interaction of some amino acid compounds of copper(II) with hydrogen peroxide

A novel effect of the inhibition of the decomposition of amino acids to carbonates on addition of imidazole (HIm) to a reacting system containing equimolar amounts of copper and zinc metal powders, an amino acid [glycine (Hgly), aspartic acid (H₂Asp) or glycylglycine (H₂gg)] (1:1:2) and excess hydrogen peroxide (H₂O₂) resulting in formation of a mixed metal mixed ligand peroxo complex compound was observed, because in the absence of imidazole the corresponding reaction system yields only a mixed metal peroxo carbonate. For the resulting complex compounds, the homogeneity, i.e. [Cu(Zn)(O₂ ^2–)(Gly)₂(HIm)(H₂O)], [Cu(Zn)(O₂ ^2–)(Asp)(HIm)(H₂O)₂] or [Cu(Zn)₂(O₂ ^2–)₂(gg)(HIm)(H₂O)₄], molecular formula, presence of peroxo group and coordination environment were established by combined physicochemical evidence from elemental and thermogravimetric analysis in air and argon atmospheres, electron spin resonance and electronic and IR spectral data. It is noteworthy to mention that the corresponding carboxylic acids of the above-mentioned amino acids, i.e. acetic and succinic acids, either do not decompose to carbonates in the absence of imidazole or form novel homogeneous peroxo mixed metal mixed ligand complex compounds as described above in the presence of imidazole. This suggests an important and significant mutual influence (in vitro) of biologically active chromophores like peroxo ions, imidazole and amino groups in the above-mentioned chemical reactions containing bioactive metals such as copper and zinc.     

Investigations into some aryl substituted bis(thiosemicarbazones) and their copper complexes

The synthesis of three bis(thiosemicarbazone) compounds formed by the reaction of benzil with either thiosemicarbazide, 4-methyl-3-thiosemicarbazide or 4-phenyl-3-thiosemicarbazide are reported. The compounds were characterised by NMR spectroscopy, mass spectrometry and in the case of benzil bis(4-methyl-3-thiosemicarbazone) and benzil bis(4-phenyl-3-thiosemicarbazone) by X-ray crystallography. Attempts to purify benzil bis(thiosemicarbazone) and benzil bis (4-methyl-3-thiosemicarbazone) by recrystallisation resulted in the isolation of cyclised products that were characterised by X-ray crystallography. The 3 bis(thiosemicarbazone) compounds were used to synthesise both Cu(II) and Cu(I) complexes. The copper(II) complexes were formed by the reaction of the proligands with copper(II) acetate which gave neutral copper(II) complexes in which the thiosemicarbazone is doubly deprotonated, acting as a dianionic ligand. The copper(II)-benzil bis(4-phenyl-3-thiosemicarbazonato) complex was characterised by X-ray crystallography to show the copper in an essentially square planar N₂S₂ environment. The copper(I) complexes were synthesised by reacting the bis (thiosemicarbazone) ligands with [Cu(CH₃CN)₄]PF₆ to give cationic complexes. The copper(I)-benzil-bis(thiosemicarbazone) complex was characterised by X-ray crystallography which revealed that the complex was a dimeric dication. Each of the benzil bis(thiosemicarbazone) ligands act as a bidentate N,S donor to each copper(I) atom, forming an overall helical structure in which each copper atom is in a strongly distorted tetrahedral N₂S₂ environment. Electrochemical measurements show that the copper(II)-benzil bis(thiosemicarbazonato) complex undergoes a reversible reduction at biologically accessible potentials.     

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X · xCH₃COCH₃ (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N₃, NCS, NO₃; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature μ_eff values for the complexes are in the range 1.75-2.1 μ_B typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N₃, NO₃, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO₃] · 0.5CH₃COCH₃}₂ and [Cu(mpsme)NCS]_n complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO₃] 0.5CH₃COCH₃}₂ complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N₂OS₂ coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)]_n complex has a novel staircase-like one dimensional polymeric structure in which the NCS⁻ ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other.     

Histamine modified 2′-deoxyriboadenosine - Potential copper binding site in DNAzymes

Copper(II) complexes of histamine modified 2′-deoxyriboadenosine (N-[(9-β-D-2′-deoxyribofuranosylpurin-6-yl)-carbamoyl]histamine) ligand were studied by potentiometric, UV-visible and EPR techniques. The imidazole residue of the ligand was described as the main binding site forming mono-, bis-(ligand) and dimer complexes, but the interactions between adenosine nitrogen N(1) and carbamoyl nitrogen atoms and the copper(II) ion also were detected. This is the first report evaluating the coordinating ability of such a modified adenosine ligand towards copper(II) ion. Our findings suggest that histamine modified 2′-deoxyriboadenosine could chelate efficiently copper(II) ions if it were incorporated into DNAzyme sequence.     

On the generation of OH<Superscript>·</Superscript> radical species from H<Subscript>2</Subscript>O<Subscript>2</Subscript> by Cu(I) amyloid beta peptide model complexes: a DFT investigation

According to different studies, the interaction between amyloid β-peptide (Aβ) and copper ions could yield radical oxygen species production, in particular the highly toxic hydroxyl radical OH^· that is suspected to contribute to Alzheimer’s disease pathogenesis. Despite intensive experimental and computational studies, the nature of the interaction between copper and Aβ peptide, as well as the redox reactivity of the system, are still matter of debate. It was proposed that in Cu(II) → Cu(I) reduction the complex Cu(II)–Aβ could follow a multi-step conformational change with redox active intermediates that may be responsible for OH^· radical production from H₂O₂ through a Fenton-like process. The purpose of this work is to evaluate, using ab initio Density Functional Theory computations, the reactivity of different Cu(I)–Aβ coordination modes proposed in the literature, in terms of OH^· production. For each coordination model, we considered the corresponding H₂O₂ adduct and performed a potential energy surface scan along the reaction coordinate of O–O bond dissociation of the peroxide, resulting in the production of OH^· radical, obtaining reaction profiles for the evaluation of the energetic of the process. This procedure allowed us to confirm the hypothesis according to which the most populated Cu(I)–Aβ two-histidine coordination is not able to perform efficiently H₂O₂ reduction, while a less populated three-coordinated form would be responsible for the OH^· production. We show that coordination modes featuring a third nitrogen containing electron-donor ligand (an imidazole ring of an histidine residue is slightly favored over the N-terminal amine group) are more active towards H₂O₂ reduction.     

Copper(II) complexes with an avian prion N-terminal region and their potential SOD-like activity

Potentiometric and spectroscopic (UV-Vis, CD and EPR) studies were carried out on copper(II) complexes with chicken prion protein N-terminal fragments, Ac-(PHNPGY)₄-NH₂, and the mutated residue, Ac-(PHNPGF)₄-NH₂, to assess the role of tyrosine in the copper coordination. Both thermodynamic and spectroscopic results indicate that chicken prion fragments are not able to bind more than two copper ions and only with the involvement of side chain tyrosine groups. The prevailing complex shows one copper ion bound to four imidazole nitrogen atoms in the 1:1 metal to ligand ratio systems. The superoxide dismutase (SOD)-like activity of copper(II) complexes with the avian peptides and mammal analogue, Ac-(PHGGGWGQ)₄-NH₂, was also investigated by means of Pulse radiolysis. The copper(II) complexes with avian peptides do not display SOD-like activity, while very low activity has been detected for the copper(II) complexes with mammalian tetraoctarepeat.     

Heterometallic complexes derived from ruthenocene-functionalized dipyrromethenes

A new ligand based on a ruthenocene moiety appended by a diyrromethene (Rc-dpm) was synthesized. Two copper complexes, Cu(Rc-dpm)₂ (3) and Cu(Rc-dpm)acac (4), and one cobalt complex, Co(Rc-dpm)₃, 5, were prepared from the ligand. These complexes were characterized by a combination of UV-Vis spectroscopy, elemental analysis, and X-ray crystallography. Copper(II) complex 3 was found to be coordinated by two dipyrromethene ligands in a distorted square planar environment around the copper while complex 4 had one dipyrromethene ligand and an acac coordinated in a nearly idealized square planar copper geometry. The cobalt(III) complex 5 has an octahedral geometry around the cobalt via the coordination of three dipyyromethene ligands.     

Reversed micelles to mimic the active site of metalloenzymes

The structure and reactivity of cobalt(II), nickel(II), and copper(II) halides have been investigated in 0.20 M CTAX (X = Cl, Br) |CHCl₃ reversed micelles. The former two metal ions adopt a tetrahedral configuration at low water concentrations in the micelle. The tetrahedral complexes are converted to octahedral aqua complexes by increasing the water concentration (solvochromism) or by lowering the temperature (thermochromism). Upon reaction with imidazole, the tetrahedral cobalt and nickel halide complexes also undergo a structural transformation into an octahedral configuration with imidazole coordination. At low water concentrations, copper halides form a polynuclear complex bridged by halide ions and these halogen bridges are easily broken upon addition of water or imidazole. The copper complexes produced by reaction with imidazole were deduced to be CuIm₂X₂ and CuIm₄X₂ at intermediate and high ligand concentrations, respectively. It was also found that the cupric ion in reversed micelles is readily reduced to the cuprous ion with 2-mercaptoethanol, and the cuprous ion is oxidized to the cupric ion by reaction with hydrogen peroxide.     

The Analysis of Cu(II)/Zn(II) Cyclopeptide System as Potential Cu,ZnSOD Mimic Center

In this paper are presented the features of copper (II) and zinc (II) heteronuclear complexes of the cyclic peptide—c(HKHGPG)₂. The coordination properties of ligand were studied by potentiometric, UV–Vis and CD spectroscopic methods. These experiments were carried out in aqueous solutions at 298 K depending on pH. It turned out that in a physiological pH dominates Cu(II)/Zn(II) complex ([CuZnL]⁴⁺) which could mimic the active center of superoxide dismutase (Cu,ZnSOD). In next step we performed in vitro research on Cu,ZnSOD activity for [CuZnL]⁴⁺ complex existing in 7.4 pH by the method of reduction of nitroblue tetrazolium (NBT). Also mono- and di-nuclear copper (II) complexes of this ligand were examined. The ability of inhibition free radical reaction were compared for all complexes. The results of these studies show that Cu(II) mono-, di-nuclear and Cu(II)/Zn(II) complexes becoming to new promising synthetic superoxide dismutase mimetics, and should be considered for further biological assays.     

Assignment of a ligand in stellacyanin by a pulsed electron paramagnetic resonance method.

The electron spin echo decay envelope for the blue copper protein, stellacyanin, and for a number of other Cu(II) complexes has been studied. Particular attention was given to the form of the "nuclear modulation" patterns, which show the effects of coupling between the electron spin and the neighboring nuclei. The envelopes for the hydrated cupric complex and for copper(II) glycylglycine were essentially the same and indicative of the coupling to protons. The peptide complex contains nitrogen nuclei coupled directly to Cu(II), but the coupling constant is so large for these nuclei that a modulation pattern ascribable to 14N is not seen. For copper(II) bovine serum albumin, on the other hand, a contribution due to the coupling of the remote nitrogen belonging to a histidyl imidazole ligand was observed. The modulation pattern for this complex and for stellacyanin closely resembled one another, strongly suggesting that an imidazole is ligated to the copper in this blue protein.