Oxidation of tetraaza macrocyclic complexes of nickel(II) with peroxobisulfate ions

Spectrophotometry has been used to study the kinetics of oxidation of some tetraaza macrocyclic complexes of nickel (II) with peroxobisulfate ions in perchloric and sulfuric acid solutions. A scheme of the processes taking place has been proposed and the activation parameters of the reactions determined. The influence of different factors (pH value, ionic strength of the solution, temperature) on the kinetic parameters of the oxidation reactions has been studied. A significant influence of the conformations of the macrocyclic ligands in the complexes on the rate of the processes has been noticed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 577–583, September–October, 1988.     

Dissociation processes and factors causing the stabilization of complexes in solutions

The factors causing the thermodynamic and kinetic stability of complexes of metal ions in various media have been discussed. It has been shown in the case of the protolytic dissociation reactions of the porphyrin, tetraazaporphyrin, and phthalocyanine complexes of magnesium, zinc, and copper that the decisive role in the kinetic stabilization of these compounds is played by the rigid structure and the extensive system of conjugation in the macrocyclic ligand.The material was presented at the 17th Chugaev Conference on the Chemistry of Complex Compounds, Minsk, 1990.Ivanovo Chemical-Engineering Institute. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 3, pp. 270–278, May–June, 1991. Original article submitted February 25, 1991.     

Influence of substituents in the ligand on the properties of macrocyclic complexes of zinc

The synthesis of complexes of zinc with saturated 14-member tetraazamacrocyclic ligands is described; the compounds obtained were characterized by the of elementary analysis and IR spectroscopy. The distribution of electron density in the coordination mode of complexes of zinc with macrocycles differing in number and mutual arrangement of the substituents was investigated by the XES method. The kineties of reactions of replacement of zinc ions by copper ions in complexes with saturated macrocycles and an analogous noncyclic ligand was investigated; the influence of substituents on the kinetic parameters of these reactions was established.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 21, No. 4, pp. 424–431, July–August, 1985.     

Three-dimensional structures in oscillating reactions of oxidation of nickel and copper tetraazamacrocyclic complexes and influence of surface on their course

The formation on three-dimensional structures in systems containing a bromate and nickel and copper tetraazamacrocyclic complexes has been described. The reasons influencing their formation and course of oscillating chemical reactions with the participation of macrocyclic complexes is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 234–236, March–April, 1987.     

Kinetic stability of complexes of conjugated macroheterocycles with metals in a proton-donor medium

The rate of decomposition of conjugated macroheterocyclic ligands containing isoindole and 1,2,4-thiadiazole residues has been studied together with the rate of dissociation of their complexes with copper, cobalt, and zinc in a proton-donor medium at three temperatures. Rate constants and activation parameters have been determined for the decomposition of the macrocyclic ligands and the dissociation of their complexes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 268–271, February, 1990.     

Oscillatory Briggs-Rauscher reactions involving macrocyclic transition-metal complexes

New forms have been observed for oscillatory Briggs-Rauscher reactions catalyzed by macrocyclic nickel complexes. The number of oscillations in the reaction increases in the presence of cobalt complexes. Suggestions are made on how the catalysts act in these systems.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 167–171, May–June, 1994.     

Mass spectrometric study of products and intermediate compounds in oscillating chemical reactions of oxidation of macrocyclic copper and nickel complexes by a bromate

Products and intermediate compounds formed in oscillating chemical reactions of oxidation of copper and nickel tetraazamacrocyclic complexes were studied by the method of desorption field mass spectrometry. It was shown that a cascadelike oxidation of the macrocyclic ligand takes place and its hydrolysis with rupture of the macrocyclic ring at the azomethine bonds. Products of bromination of oxygen- and nitrogen-containing compounds, participants in the reactions, were discovered.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 221–225, March–April, 1987.     

Complexes of copper with 14–18-membered macrocyclic tetraaza ligands and their participation in oscillating chemical reactions

A number of copper complexes have been synthesized with 14–18-membered tetraaza macrocyclic ligands having six methyl groups and two double bonds located in the cis position relative to the metal ion. These compounds have been investigated by means of ESR spectrometry and electronic and IR spectroscopy. It has been shown that the size of the macroring does not have any great influence on the magnitudes of the spectral parameters. It has been found that these copper complexes can be oxidized by potassium bromate in an oscillatory regime.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 59–64, January–February, 1986.     

Kinetics of the destruction of cyclic complexes of nickel(III) and their participation in oscillating chemical processes

A spectrophotometric method has been used to study in sulfuric acid solutions the chelate reduction of nickel(III) compounds Ni^IIIL, where L are l4-membered tetraazamacrocyclic ligands with a different number of substitutents (from 0 to 0) and double bonds (from U to 4). Based on the comparison of the kinetic characteristics of the redox reactions of the nickel complexes with data on the participation of such compounds in oscillating chemical reactions in the systems NiLBrO^– ₃-H₂SO₄ it was concluded that a necessary condition for the creation of OCR in this case is, besides the autocatalytic regime of the oxidation of the [NiL]²⁺ complex with bromate, the ability of nickel(III) to undergo rapid reduction (k > 10^–4 sec^–1) by the oxidation of the coordinated macrocyclic ligand.L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of Ukrainian SSR, Kiev. Translated from Teoretichesakaya i ÉksperimentaI'naya Khimiya, Vol. 27, No. l pp. 51–55, January–February, 1991. Original article submitted May 29, 1990.     

Effect of the coordination number of the nickel(II) ion on the kinetic characteristics of the oxidation of its macrocyclic complexes by peroxodisulfate ions

A study of the kinetics of the oxidation by peroxodisulfate of macrocyclic complexes of nickel(II) with a pH-regulatable position of the thermodynamic equilibrium between the tetra- and hexacoordinated forms showed that the square-planar form is substantially more reactive than the hexacoordinated form. The observed effect may be a consequence of different mechanisms of the redox processes: intraspheral in the first case and extraspheral in the second.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, Nos. 5–6, pp. 442–447, September–December, 1992.     

Electronic structure and redox properties of macrocyclic complexes [M(TAAB)]n+ (M = Ni,Cu)

The SCF-LCAO-MO method in the CNDO approximation has been used in calculating the electronic structure of complexes of nickel and copper with the macrocyclic ligand TAAB, complexes with the general formula [M(TAAB)]ⁿ⁺ (n=0–3). From an analysis of the distribution of electron density and populations of the AOs of the central ion in these complexes, it has been established that the process of reduction of nickel compounds is accompanied by an increase in electron density on the carbon atoms of the macrocyclic ligand, whereas in the reduction of [Cu(TAAB)]²⁺ a substantial increase is observed in the populations of the 3d AOs of the central ion, i.e., it is reduced. The difference in behavior of the complexes upon reduction is due to differences in the electronic configuration of the central ion. The structure and orbital composition of the frontier MOs have been analyzed, and it has been shown that in the reduced complexes of nickel [Ni(TAAB)], which have strong nucleophilic properties, not only the central ion may act as a nucleophilic center, but also the carbon atoms of the macrocyclic ligand.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 421–428, July–August 1987.     

Sorption of metal ions by technical lignins and their derivatives

Atomic absorption analysis has been used to study the sorption of lead, zinc, and iron ions by technical lignins and their derivatives. The capacity of technical lignins and some of their derivatives for forming complexes can be used for nature-protecting purposes and for the enterosorption of heavy-metal ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 362–363, May–June, 1998.     

Formation Constants of Complexes of Monovalent Cations with Benzocrown Ethers in Nitromethane

The complexation reactions between the macrocyclic polyethers dibenzo-18-crown-6, benzo-18-crown-6, benzo-15-crown-5 and polyethers bearing a stilbene unit with alkali metal and silver cations have been studied conductometrically in nitromethane. The formation constants of 1 : 1 and 1 : 2 (metal : ligand) complexes were determined and found to decrease with increasing cation diameter. The stability of the stilbene crown – metal cation complexes is lower than for complexes of other investigated crown ethers with analogous cations. There seem to be some effects of double bond-silver ion interactions.     

Magnetic Properties and Structure of Polynuclear Compounds Based on Macrocyclic Azacyclam Complexes of Nickel(II) and Bridging Oxalate Ions

By X-ray diffraction analysis, we have established the structure of a binuclear complex of nickel(II) with an azacyclam ligand and a bridging oxalate ion. Study of the magnetic properties of a series of complexes of this type with related macrocyclic ligands has allowed us to observe antiferromagnetic coupling between the metal ions and a magnitude of the exchange integral J that varies in the range from –11.8 cm^–1 to –25.6 cm^–1. We have shown that, despite the close structural parameters of the macrocyclic ligands, the complexes are characterized by different magnetochemical behavior.     

Dissociation of Zinc Complexes in a Series of Phenyltetrabenzoporphyrins with Varying Macrocycle Rigidity

Kinetic stability of zinc complexes with meso-phenyltetrabenzoporphyrins in DMSO–HOAc mixture and in glacial acetic acid was studied. The stability of complexes was found to decrease with reduction in their macrocyclic effect and with increasing polarization of their macrocycles. The stability of nonplanar and nonsymmetrically substituted complexes was determined to be lower than that of the more planar and symmetrically substituted complexes.     

Kinetic features of the hydrolysis of the hemicelluloses of sunflower seed husks

A kinetic analysis has been made of the hydrolysis reactions of sunflower seed husks. The presence of six kinetically homogeneous fractions in the hemicellulose complex has been shown. The kinetic characteristics and the amounts of each fraction have been determined.St. Petersburg Academy of Wood Technology. Translated from Khimiya Prirodnykh Soedeninii, No. 1, pp. 136–141, January–February, 1993.     

Influence of the nature of an organic solvent on the kinetic parameters of the thermal homolysis of five-coordinate complexes of alkylcobalt

By the spectrophotometric method in solvents of different natures a study was made of the kinetics of the homolytic breakage of the axial cobalt-carbon bond in five-coordinate complexes with dianionic tetradentate equatorial ligands. The negative values obtained for the activation entropies of the processes investigated are explained by the existence of interaction between the components of the primary radical pair and the solvent molecules. The kinetic parameters of the redox-interaction reactions of some macrocyclic complexes of cobalt(II) with chloroform and carbon tetrachloride were determined. A scheme in which the autocatalytic homolysis of the Co-CH ₃ bond in the presence of chlorine-containing solvents is proposed.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev 252028. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 838–844, April, 1992.     

The coordination of the catalytic zinc ion in alcohol dehydrogenase studied by combined quantum-chemical and molecular mechanics calculations

Summary The coordination number of the catalytic zinc ion in alcohol dehydrogenase has been studied by integrated ab initio quantum-chemical and molecular mechanics geometry optimisations involving the whole enzyme. A four-coordinate active-site zinc ion is 100–200 kJ/mol more stable than a five-coordinate one, depending on the ligands. The only stable binding site for a fifth ligand at the zinc ion is opposite to the normal substrate site, in a small cavity buried behind the zinc ion. The zinc coordination sphere has to be strongly distorted to accommodate a ligand in this site, and the ligand makes awkward contacts with surrounding atoms. Thus, the results do not support proposals attributing an important role to five-coordinate zinc complexes in the catalytic mechanism of alcohol dehydrogenase. The present approach makes it possible also to quantify the strain induced by the enzyme onto the zinc ion and its ligands; it amounts to 42–87 kJ/mol for four-coordinate active-site zinc ion complexes and 131–172 kJ/mol for five-coordinate ones. The four-coordinate structure with a water molecule bound to the zinc ion is about 20 kJ/mol less strained than the corresponding structure with a hydroxide ion, indicating that the enzyme does not speed up the reaction by forcing the zinc coordination sphere into a structure similar to the reaction intermediates.     

Kinetics of the reaction of cobalt(II) phthalocyanine complexes with functionalized organosilicas

The kinetics of the reaction of cobalt(II) phthalocyanine complexes with functionalized aminoorganosilicas was studied. Comparison of the kinetic parameters of the reactions studied provided additional information on the reaction mechanism and structure of the supported metal complexes, permitting delineation between the diffusion and kinetic regions of the reaction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 5, pp. 303–307, September–October, 1995.     

Inorganic particulates in removal of toxic heavy metal ions

Adsorption behavior of zinc ions on hydrous zirconium oxide (HZO) in aqueous solution has been studied as a function of concentration (10^–2–10^–8M), temperature (303–333 K) and pH 3–8 of adsorptive solution applying radiotracer technique. The kinetics of adsorption follows first order rate law and agrees well with the classical Freundlich isotherm in the entire range of adsorptive concentration. The removal was found to be increasing with pH of the adsorptive solution while it was suppressed in the presence of acid concentrations. The overall process is found to be endothermic and irreversible in nature.