Stereospecific reactions of copper(II) complexes of serine and threonine with formaldehyde

Summary Condensations of Cu(L-ser)₂ and Cu(L-thr)₂ (where L-ser=L-serinato anion and L-thr=L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products:bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)₂ and Cu(D-thr)₂ also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)₂ and Cu(DL-thr)₂, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)₂ with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The compexes have been characterized by analytical and by i.r. electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible Cu^II/Cu^I redox process in aqueous media at –0.18 Vversus s.c.e.; complex (3) exhibits irreversible Cu^II/Cu^I reduction at –0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system.     

Kinetics and mechanism of ninhydrin reaction with copper(II) complexes of glycine and α-alanine. Elucidation of the template mechanism

Ninhydrin has been found to react with Cu(glycine)⁺ and Cu(alanine)⁺ in the ratio of 1:1. The kinetic studies of the reaction were carried out at different concentrations of the reactants at 80°C (pH = 5.0). The reaction proceeds through the formation of a ternary labile complex of ninhydrin with Cu(II) complexes of glycine and alanine. The kinetics were found to follow pseudo-first-order reaction path with respect to Cu(II)-complex in presence of excess [Ninhydrin]. Formation of a ternary labile complex indicates a template reaction mechanism based on the reactions with coordinated ligands. The variation of pseudo-first-order rate constants with [ninhydrin] was found to be in good agreement with equation where B₁ and B₂ are the unknown empirical parameters. The [acetate ion] has no significant effect on the rate constants. On the basis of observed data a probable mechanism has been proposed. © 1993 John Wiley & Sons, Inc.     

Pt(II) stereoisomeric complexes with serine

There have been synthesized Pt(II) stereoisomeric complexes with hydroxy-α-amino acid serine (SerH = NH₂CH(CH₂OH)COOH is α-amino-β-hydroxypropionic acid): trans-[Pt(S-SerH)₂Cl₂], trans-[Pt(R-SerH)(S-SerH)Cl₂] with monodentately (through NH₂ group ) bound SerH and cis-, trans-[Pt(R-Ser)(S-Ser)], trans-[Pt(S-Ser)₂] with bidentately bound (through groups NH₂ and COO) ligands (R, S is the absolute configuration of asymmetric carbon atom). The successive phases in the synthesis of Pt(II) stereoisomeric complexes with serine were studied by ¹⁹⁵Pt NMR spectroscopy. To identificate the compounds synthesized the method of elemental analysis, IR and NMR (¹⁹⁵Pt, ¹³C, ¹H) spectroscopy were used. For trans-[Pt(R-Ser)(S-Ser)] the X-ray diffraction data were obtained.     

Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and NiL₂ (L^?=diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL₂, DTG 250–350°, DTA 300–320° and for NiL₂, DTG 290–390°, DTA 360–400°. Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

     

Thermal decomposition kinetics of Schiff base complexes of copper(II) and palladium(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and Pd(LH)₂Cl₂ (LH=salicylidene-2-aminofluorene and 2-hydroxy-1-naphthalidene-2-aminofluorene) in air are studied. Mass loss considerations at the main decomposition stages indicate conversion of the complex to oxides. Mathematical analysis of TG data shows that first order kinetics are applicable in all cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.     

Electron-transfer kinetics of copper(II/I) tripodal ligand complexes

The electron-transfer kinetics for each of three copper(II/I) tripodal ligand complexes reacting with multiple reducing and oxidizing counter reagents have been examined in aqueous solution at 25 degrees C, mu = 0.10 M. For all of the ligands studied, an amine nitrogen serves as the bridgehead atom. Two of the ligands (PMMEA and PEMEA) contain two thioether sulfurs and one pyridyl nitrogen as donor atoms on the appended legs while the third ligand (BPEMEA) has two pyridyl nitrogens and one thioether sulfur. Very limited kinetic studies were also conducted on two additional closely related tripodal ligand complexes. The results are compared to our previous kinetic study on a Cu(II/I) system involving a tripodal ligand (TMMEA) with thioether sulfur donor atoms on all three legs. In all systems, the Cu(II/I) electron self-exchange rate constants (k(11)) are surprisingly small, ranging approximately 0.03-50 M(-)(1) s(-)(1). The results are consistent with earlier studies reported by Yandell involving the reduction of Cu(II) complexes with four similar tripodal ligand systems, and it is concluded that the dominant reaction pathway involves a metastable Cu(II)L intermediate species (designated as pathway B). Since crystal structures suggest that the ligand reorganization accompanying electron transfer is relatively small compared to our earlier studies on macrocyclic ligand complexes of Cu(II/I), it is unclear why the k(11) values for the tripodal ligand systems are of such small magnitude.     

On the complexation of copper (II) ion with 2-hydroxybenzamide

The complexation of the Cu2+ ion with 2-Hydroxybenzamide (salicylamide, HL) has been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in NaCIO4 media for ionic strength ranging from 0.5 to 3 mol/dm3. The data are consistent with the formation of the complexes CuH(-1)(HL)+, CuH(-2)(HL)2, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL). The minor species, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL), amount to at least 20% of the total copper. Elaboration of the data according to the Specific Interaction Theory yields the constants valid in the infinite dilution reference state: [formulas: see text] and the interaction coefficients (kg/mol) of complex species with medium ions: b(L-,Na+) = 0.11 +/- 0.03; b(CuH(-1)(HL)+,NaClO4) = 0.17 +/- 0.05; b(CuH(-2)(HL)2,NaClO4) = 0.11 +/- 0.05; b(Cu2H(-2)(HL)2(2+),NaClO4) = 0.2(7) +/- 0.1; b(CuH(-2)(HL),NaClO4) = -0.0(3) +/- 0.1.     

The nonisothermal decomposition kinetics of copper(II) complexes with phthalanilic acids and amino acids

Fifteen new kinds of mixed ligand complexes Cu(x‐P)A [P = 2‐(COO)C₆H₄CONH‐C₆H₄; x = H, 2‐Cl, 2‐CH₃, 2‐OCH₃, 4‐OCH₂CH₃; A = dehydronium Met, Leu, Phen] were synthesized. The thermal decomposition behavior of each complex is studied by TG. Coats‐‐Redfern, MacCallum‐‐Tammer, and Zsako methods are adopted to estimate the values of the apparent activation energy E_a, the activation entropy δS^≠, the reaction order n, and the frequency factor A. The results showed that the reaction order is 2/3 for each of the complex. Studies on the mechanism of the thermal decomposition reactions suggested that these reactions all fit the kinetic equation 1 ? (1 ? α)^1/3 = © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 623–628, 2003     

Kinetic study of copper(II) complexation with 9-ethyl-3-carbazolecarboxaldehyde-thiosemicarbazone and kinetic-spectrophotometric determination of copper(II)

The kinetics of complexation reaction of Cu(II) with 9-ethyl-3-carbazolecarboxaldehyde-thiosemicarbazone (ECCAT) has been examined spectrophotometrically. The ligand was synthesized for the first time. The complexation reaction was carried out in a DMF-water medium at 35°C. The complex has maximum absorbance at 393 nm. Kinetic and activation parameters of the complexation reaction were calculated by the Arrhenius and Eyring equations using the data obtained from investigating the effect of temperature on reaction rates under the specified conditions. We also proposed reaction rate equations. Based on the studied complexation reaction, a simple kinetic method for the spectrophotometric determination of copper(II) has been developed. The calibration graphs are linear in the concentration range 0.2–1.9 μg/mL. The species that caused interference were investigated. The text was submitted by the authors in English.     

Monopicolinate cyclen and cyclam derivatives for stable copper(II) complexation

The syntheses of a new 1,4,7,10-tetraazacyclododecane (cyclen) derivative bearing a picolinate pendant arm (HL1), and its 1,4,8,11-tetraazacyclotetradecane (cyclam) analogue HL2, were achieved by using two different selective-protection methods involving the preparation of cyclen-bisaminal or phosphoryl cyclam derivatives. The acid-base properties of both compounds were investigated as well as their coordination chemistry, especially with Cu(2+), in aqueous solution and in solid state. The copper(II) complexes were synthesized, and the single crystal X-ray diffraction structures of compounds of formula [Cu(HL)](ClO(4))(2)·H(2)O (L = L1 or L2), [CuL1](ClO(4)) and [CuL2]Cl·2H(2)O, were determined. These studies revealed that protonation of the complexes occurs on the carboxylate group of the picolinate moiety. Stability constants of the complexes were determined at 25.0 °C and ionic strength 0.10 M in KNO(3) using potentiometric titrations. Both ligands form complexes with Cu(2+) that are thermodynamically very stable. Additionally, both HL1 and HL2 exhibit an important selectivity for Cu(2+) over Zn(2+). The kinetic inertness in acidic medium of both complexes of Cu(2+) was evaluated by spectrophotometry revealing that [CuL2](+) is much more inert than [CuL1](+). The determined half-life values also demonstrate the very high kinetic inertness of [CuL2](+) when compared to a list of copper(II) complexes of other macrocyclic ligands. The coordination geometry of the copper center in the complexes was established in aqueous solution from UV-visible and electron paramagnetic resonance (EPR) spectroscopy, showing that the solution structures of both complexes are in excellent agreement with those of crystallographic data. Cyclic voltammetry experiments point to a good stability of the complexes with respect to metal ion dissociation upon reduction of the metal ion to Cu(+) at about neutral pH. Our results revealed that the cyclam-based ligand HL2 is a very attractive receptor for copper(II), presenting a fast complexation process, a high kinetic inertness, and important thermodynamic and electrochemical stability.     

Molecular complexes of hydrazides with copper(II)

Summary The reaction of substituted hydrazides with copper(II) chloride was investigated in the solid state or in solution in order to account for substituent effects. Spectroscopic results and values of the formation constants indicate the occurrence of strong complexes.

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Molekulare Komplexe von Hydraziden mit Kupfer(II)

Zusammenfassung Die Reaktionen von substituierten Hydraziden mit Kupfer(II)chlorid wurden im Festzustand und in Lösung untersucht. Die spektroskopischen Ergebnisse und die Werte der Bildungskonstanten zeigen die Koordinierung zu starken Komplexen an.

     

Determination of copper(I) and copper(II) ions after complexation with bicinchoninic acid by CE

A facile, sensitive, and selective method was developed for the simultaneous separation and determination of copper(I) [Cu(+)] and copper(II) [Cu(2+)] ions using CE with direct UV detection. The copper ions were complexed with a 1.5 mM bicinchoninic acid disodium salt solution at pH 8.7 prior to analysis. Acetate buffer (2 mM) was used as the CE running buffer. Parameters affecting CE separation such as sample pH, applied voltage, concentration of complexing agent, nature of the buffer solution, and interferences by other metal ions, were evaluated. The LODs for Cu(+) and Cu(2+) were 3.0 and 2.5 microg/mL (S/N = 3), respectively. The developed method allows the simultaneous determination of Cu(+) and Cu(2+) in less than 5 min with RSDs of between 5.3 and 9.5% for migration time and between 3.4 and 9.7% for peak areas, respectively. At optimum conditions, the percentage recoveries of Cu(+) and Cu(2+) were found to be 99.4 and 99.5%.     

Dissociation and complexation ofN-m-tolyl-p-methoxybenzohydroxamic acid with manganese(II), nickel(II), copper(II) and zinc(II)

Summary The thermodynamic ionisation and formation constant at different ionic strengths of some divalent metal ions ofN-m-tolyl-p-methoxybenzohydroxamic acid at 25 and 35° were determined in several dioxanwater media. The solid complexes of Cu^II, Ni^II and Mn^II withN-m-tolylbenzo-,N-m-tolyl-p-methylbenzo- andN-m-tolyl-p-methoxybenzohydroxamic acids were prepared and their magnetic susceptibilities measured at room temperature.     

Polynuclear copper (II) complexes with aminoalcohol ligands

Copper complexes with aminoalcoholato ligands have attracted much attention recently because of their potential applications in ceramic materials. This review deals with polynuclear copper (II) complexes containing bidentate and triden-tate aminoalcoholato ligands. The focus of this article is on the synthesis, structure, and magnetic properties of polynuclear copper (II) complexes obtained recently by our group. Some relevant work reported previously by other researchers is also included.Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday.     

1,6-Bis(hydrazidomethylsulfinyl)hexane: the solution state and complexation with copper(II)

Russian Chemical Bulletin - The solution state of a new antituberculosis drug 1,6-bis(hydrazidomethylsulflnyl)hexane (L) and its complexation with copper(II) were investigated by spectrophotometry,...     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

Thermal decomposition kinetics of vanillidene anthranilic acid complexes of cobalt(II), nickel(II), copper(II) and zinc(II)

The thermal decomposition of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of the Schiff base vanillidene anthranilic acid was studied by TG. The chelates show somewhat similar TG plots when heated in an atmosphere of air. Thermoanalytical data (TG and DTG) of these chelates are presented in this communication. Interpretation and mathematical analysis of these data and evaluation of order of reaction, the energy and entropy of activation based on the differential method employing the Freeman-Carroll equation, the integral method using Coats-Redfern equation and the approximation method using the Horowitz-Metzger equation are also given. On the basis of experimental findings in the present course of studies, it is concluded that the relative thermal stability of vanillidene anthranilic acid chelates can be aligned as Co(II)Ni(II)>Zn(II)>Cu(II).

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Zusammenfassung Die thermische Zersetzung von Cobalt(II)-, Nickel(II)-, Kupfer(II)- und Zink(II)-Komplexen der Schiffschen Base Vanillidenanthranilsäure wurde thermogravimetrisch untersucht. Die Chelate zeigen in einer Luftatmosphäre ähnliche TG-Kurven. Thermoanalytische Daten (TG and DTG) dieser Chelate werden mitgeteilt, interpretiert und mathematisch analysiert. Ebenfalls werden die Reaktionsordnung und die Energie und Entropie der Aktivierung nach der von Freeman-Carroll angewandten differentiellen Methode, nach der auf der Coats-Redfern-Gleichung basierenden integralen Methode und nach der die Horowitz-Metzger Gleichung benutzenden Näherungsmethode bestimmt. Aus den Befunden wird geschlossen, dass die thermische Stabilität von Vanillidenanthranilsäure-Chelaten in der Reihenfolge Co(II)Ni(II)>Zn(II)> >Cu(II) abnimmt.

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, , . - . . , , - , , - . , Ni>Zn>u.

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We thank Dr. C. P. Savariar, Professor of Chemistry, University of Calicut for encouragement. We are also grateful to the University Grants Commission for the award of a Senior Research Fellowship to one of us (J. C).     

Steric effects in the complexation kinetics of copper(II) with rac-5,5,7,12,12,14-hexamethyl 1,4,8,11-tetraazacyclotetradecane in basic aqueous media

Copper(II) reacts with rac-5,5,7,12,12,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane (tet-b) in strongly basic aqueous media to give [Cu(tet-b) (OH) (blue)]⁺ which contains trigonal bipyramidally co-ordinated Cu²⁺ with the tet-b ligand in its most stable, folded form. The kinetics of formation of this blue complex have been studied at 25.0° ± 0.1°C using the stopped-flow technique. Second-bond formation is proposed as the rate-determining step for tet-b reaction with Cu(OH)^-₃ and Cu(OH)^2-₄. Possible mechanisms for the reaction and the steric effects resulting from the methyl groups on the alkyl backbone of the macrocyclic ligand are considered.