Reaction of vanadate ion with chlorpromazine,formation of vanadyl ion and chlorpromazine free radical

The red colored product, which was identified as a chlorpromazine (CPZ) free radical, was observed in the reaction of CPZ with the vanadate ion (+5 oxidation state). The product and the mechanism for the reaction were characterized from optical and EPR spectrometries. Optimal conditions for generation of the free radical were determined as reaction time within one minute of pH 6 and free radical stabilizing time of 30 minutes by acidifying with HCl. Under these conditions, the stoichiometry for the reaction was found to be 1:1, indicating the involvement of one electron transfer from CPZ to the vanadate ion to form the free radical and vanadyl ion (+4 oxidation state). A possible reaction scheme was proposed:

The implications of this reaction were discussed with regard to the pharmacological action of the vanadate ion and CPZ.     

Hydrogen peroxide release by rat peritoneal macrophages in the presence and absence of tumor cells

The ability of mineral oil-elicited rat peritoneal macrophages to release hydrogen peroxide (H₂O₂) to the extracellular medium was measured in the presence and absence of rat lymphoma cells grown in tissue culture, and in the presence of phorbol myristate acetate (PMA). Horseradish peroxidase (HRP)-catalyzed oxidation of scopoletin or phenol red was used to measure H₂O₂ release during incubation of cells in monolayer culture for periods up to 24 h. Macrophages appeared to release H₂O₂ with or without PMA, although PMA greatly increased the amount of H₂O₂ released in short (1 to 4 h) incubations. Tumor cells did not replace PMA as a triggering agent for H₂O₂ release. Instead, tumor cells inhibited H₂O₂ release. The probable basis for inhibition was competition between macrophages and tumor cells for the supply of oxygen (O₂). Tumor cells did not inhibit H₂O₂ release when the O₂ concentration was held constant. The rates at which macrophages took up O₂ and released H₂O₂ were proportional to the O₂ concentration, as measured with the O₂ electrode. Rates of H₂O₂ release could be calculated from the difference in the rate constants for O₂ uptake measured in the presence of two different extracellular H₂O₂-consuming systems (HRP-scopoletin vs catalase). PMA-stimulated uptake of O₂ and release of H₂O₂ were highest in a small subpopulation of macrophages, obtained at the lowest-density position on gradients of bovine serum albumin. These cells also released H₂O₂ in the absence of PMA. Tumor cells had no effect on the rate constants for O₂ uptake and H₂O₂ release by the unfractionated macrophages or the macrophage subpopulations.     

Stability constants for,and structural investigation of,divalent metal ion complexes with polyene antibiotics

The stability constants for the formation of complexes between Ca(II), Mg(II), Cu(II), Zn(II) and Ni(II) with nystatin and amphotericin-B (polyene antibiotics) have been determined by both a potentiometric and a solubility method. The structures of the complexes have been investigated by NMR, ESR and CD spectroscopy. The transition metal stability constants are consistent with the Irving- Williams series. The structural results are discussed and related to the importance of such complexes in mode of action theories.     

The determination of the binding constant of metalloenzymes for their active site metal ion from ligand inhibition data: Theoretical analysis and application to the inhibition of thermolysin by 1,10-phenanthroline

An equation is found relating the fractional activity, (v/v₀), of an enzyme assay mixture to the total concentrations of metalloenzyme, active site metal ion, metal-binding ligand and substrate and the stability constants of the complexes present. When (v/v₀) is measured as a function of the total ligand concentration, this equation offers a way of data-plotting which yields straight lines and permits the calculation of the metal-binding constant K_ME from either the slope or the intercept, provided that mixed complexes (enzyme-metal ion-ligand) do not contribute significantly to the change in (v/v₀). Since deviations from linearity occur in the latter case, the proposed inhibition plot serves as a diagnostic tool for the recognition of such complexes. Application to the inhibition of thermolysin by 1,10-phenanthroline gives a value of 2.1 × 10¹¹m⁻¹ for K_ZnE, the binding constant of the active site zinc ion, at pH 7.50, 25°C and ionic strength 0.1. The equation also allows the rapid calculation of the ligand concentration necessary to attain a desired degree of inhibition when the total enzyme and active site metal ion concentrations of the solution are known.     

The effect of pressure on the photochemistry of tris(bipyridyl)chromium(III) ion

The quantum yield for the photoaquation of Cr(bpy)₃³⁺ in basic medium decreases with increasing pressure, with an apparent volume of activation of 3.8 ± 1.0 ml mol⁻¹. From this value and that associated with the phosphorescence lifetime, the volumes of activation for non-radiative decay to the ground state and for formation of photoproduct are derived as −1.6 and +2.9 ml mol⁻¹, respectively. The latter value is consistent with either an associative process with water entering from pockets between the ligands or a dissociative process involving one or both bonds to a bipyridyl ligand.     

Metal chelates of heterocyclic nitrogen-containing ketones. XIV. Metal ion,anion and substituent effects on the enolization of mono-keto compounds

A number of new complexes of iron(II), cobakt(II), nickel(II), copper(II) and palladium(II) containing 2-picolyl-p-nitrophenyl- or 2-picolyl-p-tolyl ketone, L and L′, respectively, and various anions (Cl^?, Br^?, NSC^?, BF₄^? or ClO₄^?) have been synthesized and characterized by elemental analyses, magnetic susceptibility, ESR, IR and reflectance spectral measurements. The stereochemistry and the nature of the complexes are markedly dependent upon the molar of the reactants, the anions and the ligand substituents. In all complexes the ligands are cheated to the metal ion via the pryridine nitrogen and the carbonyl oxygen atoms, whereby in the case of [ML₂]X₂, M = iron(II) and [ML₃]X₂, M = cobalt(II) or nickel(II) and X = ClO₄^? or BF₄^?, the 2-picolyl-p-nitrophenyl ketone exists in its enol form which is only deprotonated in the presence of palladium(II). The ligand field parameters (Dq, B′, λ and β) are calculated and related to the electronic environment and the basicity of the ligands.     

The copper(II) catalyzed reaction of L-ascorbinc acid with tris(oxalato)cobaltate(III) ion in aqueous solution

The kinetics of the reaction between tris(oxalato)cobaltate(III) ion and L-ascorbic acid were studied in aqueous solution over a range of copper(II) ion concentrations, ascorbic acid concentrations, pH values and temperatures. A rate law of the type rate = k[HA^?][Cu²⁺][Co³⁺], where HA^? = ascorbate, is suggested by the experimental results. A mechanism involving a copper-ascorbate complex is proposed.     

The effect of cupric ion on the reoxidation pathway of an IgG1 immunoglobulin

The addition of a 5–10μM of cupric ion to the reoxidation medium of a partially reduced IgG protein results in an altered pathway for covalent reassembly of the molecule. The formation of HL is favored over that of H₂ and H₂L.     

Effects of solvent and ionic medium on the kinetics of axial ligand substitution in vitamin B12. Part IV. The reaction between aquocobalamin and the thiocyanate ion in acetonitrile-water mixtures

The rate constants for the reaction of aquocobalamin with the thiocyanate ion were measured as a function of ionic strength and solvent composition in acetonitrile-water mixtures. The reaction is described by a two-step mechanism: the ligation reaction, where the most stable isomer (S-bonded) is formed and the isomerisation reaction (S-bonded to N-bonded thiocyanate). For the ligation reaction a full quantitative analysis of solvent effects could be performed, whereas for the isomerisation reaction only qualitative observations were made. The equilibrium constant for the isomerisation (S-bonded/N-bonded) is large and does not change with the solvent composition. It is found that the transfer Gibbs energies of activation for the ligation reaction are the same as found for the ligand thiourea. The absence of a solvent effect on the isomerisation reaction is a further example of the ability of vitamin B₁₂ to create its own micro environment.     

Coordination chemical studies on metalloenzymes. Measurement of binding constant between apo-tyrosinase and copper ion

The behavior of complexing agents for the copper removal reaction was studied by the equilibrium dialysis method. In the copper removal reaction, complexing agents are divided into two types: those that are reducing agents and those that are not. Sodium cyanide and sodium thiosulfate are of the first type, and 8-hydroxyquinoline-5-sulfonic acid, 2,2′-bipyridyl, and picolinic acid are of the second type. From equilibrium dialysis with the first type of complexing agent, the apparent binding constant (pH 6.0) between cuprous ions and apotyrosinase was calculated to be 10¹⁵m^?1. Similarly, the apparent binding constant (pH 6.0) between cupric ions and apo-tyrosinase was about 10¹³m^?1, which was calculated from equilibrium dialysis with the second type of complexing agent. The apparent binding constant between cuprous ions and apo-tyrosinase was larger than that between cupric ions and apo-tyrosinase.     

Direct demonstration that ferrous ion complexes of di- and triphosphate nucleotides catalyze hydroxyl free radical formation from hydrogen peroxide

Utilizing an electron paramagnetic resonance (EPR) spin-trapping technique it was demonstrated that the di- and triphosphate nucleotides of adenosine, cytidine, thymidine, and guanosine in the presence of Fe(II) catalyze hydroxyl free radical formation from H₂O₂. The triphosphate nucleotides in general were about 20% more effective than the diphosphate nucleotides. The amount of ?H produced from H₂O₂ as a function of nucleotide level tended to increase in a sigmoidal fashion beginning at a nucleotide/Fe(II) ratio of 2 but then rose rapidly up to a ratio of 5 at which point the increase became more gradual. The monophosphate nucleotides did not cause an increase in the amount of hydroxyl free radical produced from H₂O₂ over the low level obtained in the buffer system only. The cations, Mg²⁺ and Ca²⁺, even at much higher than physiological levels and much higher than the level of added Fe(II), did not cause a substantial diminution of the Fe(II)-nucleotide-catalyzed breakdown of H₂O₂ to yield ?H. A study of the time course of the effectiveness of Fe(II)-nucleotide-mediated ?H formation from H₂O₂ demonstrated that Fe(II) in the presence of nucleotides remained in an effective catalytic state with a halftime of about 160 s whereas in the absence of the nucleotides the halftime was 7.5 s. All observations indicate that Fe(II) ligates with di- and triphosphate nucleotides and remains in the ferrous state which is then capable of catalyzing ?H formation from H₂O₂; but with time, oxidation of the metal ion to the ferric state occurs, which either ligated to the nucleotide or to buffer ions, is ineffective in H₂O₂ catalysis to yield ?H. Iron-nucleotide complexes may be of importance in mediating oxygen free radical damage to biological systems. The observations presented here indicate that hydroxyl free radicals will be produced when H₂O₂ is present with ferrous-nucleotide complexes.     

Effects of phenoxide ligation: Synthesis and characterization of the [Mo2Fe6S8(SEt)3(OPh)6]3− ion

Reaction of phenol with an alkylthiolate-ligated double cubane complex effects phenolate substitution at the terminal positions; the product can be isolated as its benzyltriethylammonium salt. The phenolate cluster possesses unaltered magnetic properties and blue shifted optical spectra, and undergoes ligand exchange reactions with electrophiles as expected for terminal phenolate substitution. Increased isotropic proton NMR shifts and large negative shifts in corresponding first and second reduction potentials are consistent with increased donation of electron density to the [MoFe₃S₄]³⁺ cores for phenolate versus thiophenolate terminal ligands to iron. Similar behavior has been observed for Fe₄S₄, Fe₂S₂ and MoS₂Fe systems.     

Light-induced electron-transfer reactions. Part 2. Kinetics of the intra-molecular redox decomposition of tris(oxalato)-cobaltate(III) by irradiation with visible light of aqueous solution containing tris(2,2′-bipyridine)ruthenium(II) ion

The rate of the intra-molecular redox decomposition of the tris(oxalato)cobaltate(III) ion [Co(Ox)₃]^3? is greatly accelerated by irradiation with visible light of aqueous acidic solutions containing the tris(2,2′-bipyridine)ruthenium(II) ion [Ru(bpy)₃]²⁺. The rate of the light-induced reaction in hydrochloric acid with an acidity range 0.05–0.18 mol dm^?3 is of zero-order with respect to the [Co(Ox)₃]^3? ion concentration and is proportional to the light-intensity irradiated and also essentially to the [Ru(bpy)₃]²⁺ ion concentration. Moreover, the rate is independent not only of the oxalate ion concentrations, but also of the acidity over the range 0.05–0.18 mol dm^?3 hydrochloric acid. The ionic-strength dependence, as well as temperature dependence, were extremely small. The [Ru(bpy)₃]²⁺ concentration does not change during the occurrence of the reaction and the tris(2,2′-bipyridine)ruthenium(II) ion acts as a homogeneous catalyzer. However, a dramatic indication that the situation was rather different was found in the stronger acid solutions of 0.5 or 1.0 mol dm^?3 hydrochloric acid, in which the [Ru(bpy)₃]²⁺ concentration decreased greatly immediately after the initiation of reaction and then increased up to the initial concentration. Such a decrease at the initial stage of the reaction disappeared by addition of oxalate before the start of the reaction. A chain mechanism of reaction is proposed to account for these results.     

Calculation of protein volumes: An alternative to the Voronoi procedure

All the methods that have been applied to assessing local volume occupation or packing in proteins have particular defects. For example, the Voronoi method used by Richards (method A) and by Finney misallocates both non-bonded and covalent contacts in a geometrically rigorous, though chemically inconsistent, manner. Richards' method B, in which covalent and non-bonded contacts are partitioned in chemically sensible ways, is unfortunately not completely rigorous, in that every polyhedron vertex has associated with it a small vertex-error polyhedron, which is not allocated to any atom.We present here a generalization of the Voronoi method that is particularly suited to multicomponent assemblies such as proteins. This radical plane partitioning of volume is completely rigorous; it gives rise to no vertex error, and handles the more numerous non-bonded contacts realistically. Its application to RNAase-S is described and the results compared with both Voronoi's method and Richards' method B. A particular advantage of both the radical plane and Richards' methods is a relative insensitivity to the treatment of the surface, a problem that has plagued other approaches to describing packing in proteins. Although the radical plane is seen to misallocate volume chemically between covalently-bonded neighbours, this problem vanishes when groups of atoms in side-chain residues are considered.     

Kinetics of azide attack on organonitriles coordinated to pentaamminecobalt(III)

Four new 5-substituted tetrazole complexes of pentaamminecobalt(III) have been synthesized. The N-1 bonded complexes of 5-(p-methylphenyl)tetrazole, 5-(p-chlorophenyl)tetrazole, 5-(p-nitrophenyl)tetrazole and the N-2 bonded complex of 5-(m-formylphenyl)tetrazole. Kinetic studies of the complex formation reaction, wherein azide ion attacks coordinated organonitrile ligands, have been shown to follow a second order rate law, first order in nitrile complex and azide. Rate constants and activation parameters have been determined for five organonitrile complexes and a Hammett type correlation has been established for the formation reaction described by the equation log k = 2.42σ – 2.44 at 25 °C and ionic strength 1.0 M. Two mechanisms are proposed for complex formation which are consistent with our observations.     

The reactivity of imidazole nitrogens in histidine to alkylation

Copper(II)-histidine complex was allowed to react at pH 6.0–6.1 at 22°C with bromoacetic acid. The reaction was followed by means of amino acid analysis of the histidine and N^im-carboxymethylhistidine derivatives. The results of the alkylation study indicate that the nucleophilic, active histidine molecule is coordinated to the copper(II) ion through the amino nitrogen and a carboxylate oxygen with the imidazole group turned away from the copper. This model of copper-bound histidine permitted the determination of the intrinsic nucleophilic activity of the imidazole nitrogens through their respective rate constants for alkylation. The tele-nitrogen is three times more reactive than the pros-nitrogen in the histidine and in the pros-carboxymethylhistidine-tele-carboxymethylhistidine systems. The carboxymethylation of copper(II)-histidine and bovine pancreatic ribonuclease have some analogies, which suggest that in pros-carboxymethylhistidine-119 ribonuclease the carboxylate unit of the alkylated histidine residue points into the active site.     

The oxidative addition of methyl iodide to β-diketonecarbonyltriphenylphosphinerhodium(I) complexes

The kinetics and mechanism of the reaction [Rh(β-diketone)(CO)(PPh₃)] + CH₃I → [Rh(β-diketone)(CH₃)(I)(CO)(PPh₃)] where β-diketone = acac, TFDMAA, TFAA and HFAA, were studied with the aid of i.r. and visible spectrophotometry. The reaction proceeds by two consecutive steps through a postulated ionic intermediate. The influence of phosphine dissociation, solvent polarity, alkyl group variation and different electronegative β-diketone substituents on the reaction rate were investigated. The rate constant for a methyl-acyl → metal-alkyl conversion (CH₃ migration) was determined.     

Hydride transfer from transition metal hydrides to dihapto acyl ligands

The dihapto acyl ligand in Cp₂Zr[C(O)R]X, (R = Me, Ph; X = Me, Cl) is subject to hydrogen transfer from Cp₂MH₂ (M = Mo, W), Cp₂ReH and CpReH₄(PMe₂Ph). The initial products are bimetallic dimers of the type Cp₂XZrOCH(R)ML_n. The fate of this bimetallic species is highly dependent upon the Group VIB metal when Cp₂MH₂ is the hydride source. For M = Mo, a second hydrogen migrates to the acyl carbon, yielding Cp₂Zr(OEt)Me and products derived from Cp₂Mo. For M = W, CO bond scission occurs with retention of the WC bond, to yield the carbene complexes Cp₂WC(C)R along with various oxyzirconium products. Filled d orbitals are not necessary on the hydride source; Cp₂NbH₃ also readily reduces the acyl in Cp₂Zr[C(O)Me]Me.