Four new metal complexes with the amino acid deoxyalliin

The solid complexes [Co(C6H10NO2S) 2], [Ni(C6H10NO2S)2], [Cu(C6H10NO2S)2] and [Fe(C 6H10NO2S)2] were obtained from the reaction of cobalt(II), nickel(II), copper(II) and iron(II) salts with the potassium salt of the amino acid deoxyalliin (S-allyl-L-cysteine). Electronic absorption spectra of the complexes are typical of octahedral structures. Infrared spectroscopy confirms the ligand coordination to the metal ions through (COO-) and (NH2) groups. EPR spectrum of the Cu(II) complex indicates a slight distortion of its octahedral symmetry. Mössbauer parameters permitted to identify the presence of iron(II) and iron(III) species in the same sample, both of octahedral geometry. Thermal decomposition of the complexes lead to the formation of CoO, NiO, CuO and Fe2O3 as final products. The compounds show poor solubility in water and in the common organic solvents. ©2005 Sociedade Brasileira de Química.

Synthesis, Characterization and Biological Activities of a Bidentate Schiff Base Ligand: N,N '-Bis(1-phenylethylidene)ethane-1,2-diamine and its Transition Metals (II) Complexes

Schiff base ligand: N,N'-bis(1-phenylethylidene)ethane-1,2-diamine (L), was derived from acetophenone and ethylenediamine by condensation and its complexes (1-5) were prepared with Pb2+, Ni2+, Co2+, Cu2+ and Cd2+ metal ions. Their structures were characterized by FAB-MS, IR spectra, elemental analyses and molar conductance. The octahedral geometry of the complexes was proposed by electronic spectra and magnetic moment data. The conductivity data showed that the complexes have non-electrolytic nature. The complexes (1-5) have higher in vitro antimicrobial activity than the Schiff base ligand (L). In the nuclease activity, the complexes cleave DNA as compared to control DNA in the presence of H2O2.

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)2]n (where M=Cu (1), Zn (2), Co (3); Pht2−=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)6](HPht)2 · 2H2O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1–3 (2 is isostructural to 3) consist of [M(1-MeIm)2] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N2O2 type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N2O2) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C–H⋯O contacts. In contrast to polymers 1–3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)6]2+ cation, two hydrogen phthalate anions (HPht−) and two H2O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C–H⋯O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co2+ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and 1H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures.

Molecular physiology of nickel and cobalt homeostasis in Rhizobium leguminosarum.

Transition metals such as Fe, Cu, Mn, Ni, or Co are essential nutrients, as they are constitutive elements of a significant fraction of cell proteins. Such metals are present in the active site of many enzymes, and also participate as structural elements in different proteins. From a chemical point of view, metals have a defined order of affinity for binding, designated as the Irving-Williams series (Irving and Williams, 1948) Mg2+ menor que Mn2+ menor que Fe2+ menor que Co2+ menor que Ni2+ menor que Cu2+mayor queZn2+ Since cells contain a high number of different proteins harbouring different metal ions, a simplistic model in which proteins are synthesized and metals imported into a ?cytoplasmic soup? cannot explain the final product that we find in the cell. Instead we need to envisage a complex model in which specific ligands are present in definite amounts to leave the right amounts of available metals and protein binding sites, so specific pairs can bind appropriately. A critical control on the amount of ligands and metal present is exerted through specific metal-responsive regulators able to induce the synthesis of the right amount of ligands (essentially metal binding proteins), import and efflux proteins. These systems are adapted to establish the metal-protein equilibria compatible with the formation of the right metalloprotein complexes. Understanding this complex network of interactions is central to the understanding of metal metabolism for the synthesis of metalloenzymes, a key topic in the Rhizobium-legume symbiosis. In the case of the Rhizobium leguminosarum bv viciae (Rlv) UPM791 -Pisum sativum symbiotic system, the concentration of nickel in the plant nutrient solution is a limiting factor for hydrogenase expression, and provision of high amounts of this element to the plant nutrient solution is required to ensure optimal levels of enzyme synthesis (Brito et al., 1994).

Isolation of a myoglobin molten globule by selective cobalt(III)-induced unfolding

Reaction of the Schiff-base complex [Co(acetylacetonate-ethylenediimine)(NH3)2]+ with metmyoglobin at pH 6.5 yields a partially folded protein containing six Co(III) complexes. Although half of its α-helical secondary structure is retained, absorption and CD spectra indicate that the tertiary structure in both B-F and AGH domains is disrupted in the partially folded protein. In analogy to proton-induced unfolding, it is likely that the loss of tertiary structure is triggered by metal-ion binding to histidines. Cobalt(III)-induced unfolding of myoglobin is unique in its selectivity (other proteins are unaffected) and in allowing the isolation of the partially folded macromolecule (the protein does not refold or aggregate upon removal of free denaturant).

Embracing ligands. Synthesis, characterisation and the correlation between 59Co NMR and ligand field parameters of Co(III) complexes with a new class of nitrogen-thioether multidentate ligand

The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN(4)S(2)amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN(4)S(2)amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN(4)S(2)amp) are reported and the complexes [Co(RN(4)S(2)amp)](3+) (R = Pr, Bu, Xy) characterised by single crystal X-ray study. The low-temperature (11 K) absorption spectra have been measured in Nafion films. From the observed positions of both spin-allowed (1)A(1g) --> T-1(1g) and (1)A(1g) --> T-1(2g) and spin forbidden (1)A(1g) --> T-3(1g) and (1)A(1g) --> T-3(2g) bands, octahedral ligand-field parameters (10D(q), B and C) have been determined. DFT calculations suggest that significant interaction between the d-d and CT excitations occurs for the complexes. The calculations offer an explanation for the observed deviations from linearity of the relationship between Co-59 magnetogyric ratio and beta(DeltaE)(-1) (beta = the nephelauxetic ratio; DeltaE the energy of the (1)A(1g) --> T-1(1g) transition) for a series of amine and mixed amine/thioether donor complexes.

The preparation and characterization of seven-coordinate tin(IV) complexes of the 2,6-diacetylpyridine Schiff bases of S-alkyl/aryl-dithiocarbazates and the X-ray crystal structure of the [Sn(dapsme)I-2] complex (dapsme=doubly deprotonated form of the 2,6

New tin(IV) complexes of empirical formula, Sn(SNNNS)I-2 (SNNNS = anionic form of the 2,6-diacetylpyridine Schiff bases of S-methyl- or S-benzyldithiocarbazate) have been prepared and characterized by a variety of physico-chemical techniques. The structure of Sn(dapsme)I-2 has been determined by single crystal X-ray crystallographic structural analysis. The complex has a seven-coordinate distorted pentagonal-bipyramidal geometry with the Schiff base coordinated to the tin(IV) ion as a dinegatively charged pentadentate chelating agent via the pyridine nitrogen atom, the two azomethine nitrogen atoms and the two thiolate sulfur atoms. The ligand occupies the equatorial plane and the iodo ligands are coordinated to the tin(IV) ion at axial positions. The distortion from an ideal pentagonal bipyramidal geometry is attributed to the restricted bite size of the pentadentate ligands. (C) 2004 Elsevier Ltd. All rights reserved.

Oxidation of mixed-valence CoIII/FeII complexes reversed at high pH: A kinetico-mechanistic study of water oxidation

The outer-sphere oxidation of Fell in the mixed-valence complex trans-[(LCoNCFeII)-Co-14S-N-III(CN)(6)](-), being L-14S an N3S2 macrocylic donor set on the cobalt(III) center, has been studied. The comparison with the known processes of N-5 macrocycle complexes has been carried out in view of the important differences occurring on the redox potential of the cobalt center. The results indicate that the outer-sphere oxidation reactions with S2O82- and [Co(ox)(3)](3-) involve a great amount of solvent-assisted hydrogen bonding that, as a consequence from the change from two amines to sulfur donors, are more restricted. This is shown by the more positive values found for DeltaS(double dagger) and DeltaV(double dagger). The X-ray structure of the oxidized complex has been determined, and it is clearly indicative of the above-mentioned solvent-assisted hydrogen bonding between nitrogen and cyanide donors on the cobalt and iron centers, respectively. trans-[(LCoNCFeIII)-Co-14S-N-III(CN)(6)], as well as the analogous N-5 systems trans-[(LCoNCFeIII)-Co-14-N-III(CN)(6)], trans-[(LCoNCFeIII)-Co-15-N-III-(CN)(6)], and cis-[(LCoNCFeIII)-Co-n-N-III(CN)(6)], Oxidize water to hydrogen peroxide at pH > 10 with a rather simple stoichiometry, i.e., [(LCoNCFeIII)-Co-n-N-III(CN)(5)] + OH- - [(LCoNCFeII)-Co-n-N-III(CN)(5)](-) + 1/2H(2)O(2). In this way, the reversibility of the iron oxidation process is achieved. The determination of kinetic and thermal and pressure activation parameters for this water to hydrogen peroxide oxidation leads to the kinetic determination of a cyanide based OH- adduct of the complex. A second-order dependence on the base concentration is associated with deprotonation of this adduct to produce the final inner-sphere reduction process. The activation enthalpies are found to be extremely low (15 to 35 kJ mol(-1)) and responsible for the very fast reaction observed. The values of DeltaS(double dagger) and DeltaV(double dagger) (-76 to -113 J K-1 mol(-1) and -5.5 to -8.9 cm(3) mol(-1), respectively) indicate a highly organized but not very compressed transition state in agreement with the inner-sphere one-electron transfer from O2- to Fe-III.

Tuning the metal-to-metal charge transfer energy of cyano-bridged dinuclear complexes

The metal-to-metal charge transfer (MMCT) transitions of a series of Class II mixed valence dinuclear complexes bearing cyano bridging ligands may be varied systematically by variations to either the hexacyanometallate(II) donor or Co-III acceptor moieties. Specifically, the new dinuclear species trans-[(LCoNCFe)-Co-14S(CN)(5)](-) (L-14S = 6-methyl-1,11-diaza-4,8-dithia- cyclotetradecane-6-amine) and trans-[(LCoNCRu)-Co-14(CN)(5)]-(L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecane-6-amine) have been prepared and their spectroscopic and electrochemical properties are compared with the relative trans-[(LCoNCFe)-Co-14(CN)(5)](-). The crystal structures of Na{trans-[(LCoNCFe)-Co-14S(CN)(5)]}.51/2H(2)O.1/2EtOH, Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.3H(2)O and Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.8H(2)O are also reported. The ensuing changes to the MMCT energy have been examined within the framework of Hush theory, and it was found that the free energy change between the redox isomers was the dominant effect in altering the energy of the MMCT transition.

Molecular mixed-valence cyanide bridged Co-III-Fe-II complexes

Cyano-bridged mixed-valence compounds have been known for a long time, i.e., Prussian Blue polymeric solids. Nevertheless, the interest in discrete complexes having a well-defined molecular nuclearity has emerged more recently. There are numerous examples of cyano-bridged mixed-valence complexes in the recent literature, as they show promising and useful applications in electrochromism, molecular magnetism and molecular electronics. In this paper, the reactivity, synthetic and structural chemistry, as well as some physical and chemical properties, of a series of discrete dinuclear mixed-valence cyano-bridged complexes of general formulae [LnCoIII(mu NC)Fe-II(CN)(5)](-) (L = pentadentate macrocyclic ligand) are reviewed. Special emphasis is given to the synthetic strategy, redox properties and metal-to-metal-charge-transfer (MMCT) band energy. Tuning the MMCT transition energy has been possible by changing the redox potential of the metal centers, both through structural and outer-sphere changes. The redox processes that involve the appearance and disappearance of these MMCT bands in the visible region have been dealt with in relation to the possible uses of the complexes. (c) 2004 Elsevier B.V. All rights reserved.

Time-resolved spectroscopy of the metal-to-metal charge transfer excited state in dinuclear cyano-bridged mixed-valence complexes

Visible pump-probe spectroscopy has been used to identify and characterize short-lived metal-to-metal charge transfer (MMCT) excited states in a group of cyano-bridged mixed-valence complexes of the formula [(LCoNCMII)-N-III(CN)(5)](-), where L is a pentadentate macrocyclic pentaamine (L-14) or triamine-dithiaether (L-14S) and M is Fe or Ru. Nanosecond pump-probe spectroscopy on frozen solutions of [(LCoNCFeII)-Co-14-N-III(CN)(5)](-) and [(LCoNCFeII)-Co-14S-N-III(CN)(5)](-) at 11 K enabled the construction of difference transient absorption spectra that featured a rise in absorbance in the region of 350-400 nm consistent with the generation of the ferricyanide chromophore of the photoexcited complex. The MMCT excited state of the Ru analogue [(LCoNCRuII)-Co-14-N-III(CN)(5)](-) was too short-lived to allow its detection. Femtosecond pump-probe spectroscopy on aqueous solutions of [(LCoNCFeII)-Co-14-N-III(CN)(5)](-) and [(LCoNCFeII)-Co-14S-N-III(CN)(5)](-) at room temperature enabled the lifetimes of their Co-II-Fe-III MMCT excited states to be determined as 0.8 and 1.3 ps, respectively.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Dinuclear cyano-bridged Co-III-Fe-II complexes as precursors for molecular mixed-valence complexes of higher nuclearity

The preparation and characterization of a series of trinuclear mixed-valence cyano-bridged Co-III-Fe-II-Co-III compounds derived from known dinuclear [{LnCoIII(mu-NC)}Fe-II(CN)(5)](-) complexes (L-n = N-5 or N3S2 n-membered pendant amine macrocycle) are presented. All of the new trinuclear complexes were fully characterized spectroscopically (UV-vis, IR, and C-13 NMR). Complexes exhibiting a trans and cis arrangement of the Co-Fe-Co units around the [Fe(CN)(6)](4-) center are described (i.e., cis/trans-[{LnCoIII(mu-NC)}(2)Fe-II(CN)(4)](2+)), and some of their structures are determined by X-ray crystallography. Electrochemical experiments revealed an expected anodic shift of the Fe-III/II redox potential upon addition of a tripositively charged {(CoLn)-L-III} moiety. The Co-III/II redox potentials do not change greatly from the di- to the trinuclear complex, but rather behave in a fully independent and noncooperative way. In this respect, the energies and extinction coefficients of the MMCT bands agree with the formal existence of two mixed-valence Fe-II-CN-Co-III units per molecule. Solvatochromic experiments also indicated that the MMCT band of these compounds behaves as expected for a class II mixed-valence complex. Nevertheless, its extinction coefficient is dramatically increased upon increasing the solvent donor number.

Transition metal complexes as mediator-titrants in protein redox potentiometry

A selection of nine macrocyclic Fe-III/II and Co-III/II transition metal complexes has been chosen to serve as a universal set of mediator-titrants in redox potentiometry of protein samples. The potential range spanned by these mediators is approximately from +300 to -700 mV vs the normal hydrogen electrode, which covers the range of most protein redox potentials accessible in aqueous solution. The complexes employed exhibit stability in both their oxidized and their reduced forms as well as pH-independent redox potentials within the range 6 < pH < 9. The mediators were also chosen on the basis of their very weak visible absorption maxima in both oxidation states, which will enable (for the first time) optical redox potentiometric titrations of proteins with relatively low extinction coefficients. This has previously been impractical with organic mediators, such as indoles, viologens and quinones, whose optical spectra interfere strongly with those of the protein.

Studies on the thermal decomposition behaviour, kinetics and electrical conductivity of the non-isothermal decomposition of pyridine mono carboxylic acids and some of their transition metal complexes

The thesis is divided into four chapters. They are: introduction, experimental, results and discussion about the free ligands and results and discussion about the complexes. The First Chapter, the introductory chapter, is a general introduction to the study of solid state reactions. The Second Chapter is devoted to the materials and experimental methods that have been used for carrying out tile experiments. TIle Third Chapter is concerned with the characterisations of free ligands (Picolinic acid, nicotinic acid, and isonicotinic acid) by using elemental analysis, IR spectra, X-ray diffraction, and mass spectra. Additionally, the thermal behaviour of free ligands in air has been studied by means of thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) measurements. The behaviour of thermal decomposition of the three free ligands was not identical Finally, a computer program has been used for kinetic evaluation of non-isothermal differential scanning calorimetry data according to a composite and single heating rate methods in comparison with the methods due to Ozawa and Kissinger methods. The most probable reaction mechanism for the free ligands was the Avrami-Erofeev equation (A) that described the solid-state nucleation-growth mechanism. The activation parameters of the decomposition reaction for free ligands were calculated and the results of different methods of data analysis were compared and discussed. The Fourth Chapter, the final chapter, deals with the preparation of cobalt, nickel, and copper with mono-pyridine carboxylic acids in aqueous solution. The prepared complexes have been characterised by analyses, IR spectra, X-ray diffraction, magnetic moments, and electronic spectra. The stoichiometry of these compounds was ML2x(H20), (where M = metal ion, L = organic ligand and x = water molecule). The environments of cobalt, nickel, and copper nicotinates and the environments of cobalt and nickel picolinates were octahedral, whereas the environment of copper picolinate [Cu(PA)2] was tetragonal. However, the environments of cobalt, nickel, and copper isonicotinates were polymeric octahedral structures. The morphological changes that occurred throughout the decomposition were followed by SEM observation. TG, DTG, and DSC measurements have studied the thermal behaviour of the prepared complexes in air. During the degradation processes of the hydrated complexes, the crystallisation water molecules were lost in one or two steps. This was also followed by loss of organic ligands and the metal oxides remained. Comparison between the DTG temperatures of the first and second steps of the dehydration suggested that the water of crystallisation was more strongly bonded with anion in Ni(II) complexes than in the complexes of Co(II) and Cu(II). The intermediate products of decomposition were not identified. The most probable reaction mechanism for the prepared complexes was also Avrami-Erofeev equation (A) characteristic of solid-state nucleation-growth mechanism. The tempemture dependence of conductivity using direct current was determined for cobalt, nickel, Cl.nd copper isonicotinates. An activation energy (ΔΕ), the activation energy (ΔΕ ) were calculated.The ternperature and frequency dependence of conductivity, the frequency dependence of dielectric constant, and the dielectric loss for nickel isonicotinate were determined by using altemating current. The value of s paralneter and the value of'density of state [N(Ef)] were calculated. Keyword Thermal decomposition, kinetic, electrical conduclion, pyridine rnono~ carboxylic acid, cOlnplex, transition metal compJex.