Reaction of hydrogen peroxide with hexaaquacobalt(III) perchlorate

The reaction of with H₂O₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 26.4 ± 0.5 s⁻¹. The rate law shows a simple inverse dependence on [H⁺] that is consistent with a rapidly maintained equilibrium between and its hydrolyzed form Co(H₂O)₅(OH)²⁺, followed by the rate controlling step, i.e. oxidation of H₂O₂ by Co(H₂O)₅(OH)²⁺.     

Decarboxylation kinetics for the carbonatotris(pyridine)cobalt(III) ion in perchloric acid solutions

The kinetics of the decomposition reactions of the CO(py)₃(CO₃)(H₂O)⁺ ion have been investigated in aqueous perchloric acid solutions over a range of hydrogen ion concentrations (0.10 to 5.0 M) and at two ionic strengths (I = 1.0 and 5.0 M). At the lower ionic strength, plots of ln (A_t–A_∞ versus time show a nonlinearity that is consistent with that expected for consecutive first-order reactions. The rates of the faster reaction are similar to those reported for the spontaneous reduction of aquopyridine-cobalt(III) cations. At the higher ionic strength, the above noted curvature is not apparent and the decarboxylation kinetics of the title complex may be described by a pseudo-first-order rate constant: k_obs = k[H₃O⁺]. At 20°C, k = (1.75−+0.09) s⁻¹ M⁻¹ with activation parameters ofΔH^‡ = (97 −+ 4) kJ mol⁻¹ and ΔS^‡ = −(54 −+ 32) J deg⁻¹ mol⁻¹. These kinetic parameters are compared with those previously reported for the similar complexes, Co(py)₄CO₃⁺ and Co(py)₂(CO₃)(H₂O)₂⁺.     

Kinetics and mechanism of Ru(III) and Hg(II) co-catalyzed oxidation of D-galactose and D-ribose by N-bromoacetamide in perchloric acid

Kinetics of oxidation of reducing sugars D-galactose (Gal) and D-ribose (Rib) by N-bromoacetamide (NBA) in the presence of ruthenium(III) chloride as a homogeneous catalyst and in perchloric acid medium, using mercuric acetate as a scavenger for Br(minus sign) ions, as well as a co-catalyst, have been investigated. The kinetic results indicate that the first-order kinetics in NBA at lower concentrations tend towards zero order at its higher concentrations. The reactions follow identical kinetics, being first order in the [sugar] and [Ru(III)]. Inverse fractional order in [H(+)] and [acetamide] were observed. A positive effect of [Hg(OAc)(2)] and [Cl(minus sign)] was found, whereas a change in ionic strength (mu) has no effect on oxidation velocity. Formic acid and D-lyxonic acid (for Gal) and formic acid and L-erythronic acid (for Rib) were identified as main oxidation products of reactions. The various activation parameters have been computed and recorded. A suitable mechanism consistent with experimental findings has been proposed.     

Mn(III)-containing acid phosphatase: Properties of Fe(III)-substituted enzyme and function of Mn(III) and Fe(III) in plant and mammalian acid phosphatases

The function of Mn(III) in plant acid phosphatase has been investigated by a metal-substitution study, and some properties of the Fe(III)-substituted enzyme were compared with those of the native Mn(III) enzyme and mammalian Fe(III)-containing acid phosphatases. ¹⁹F nuclear magnetic resonance (NMR) and proton relaxation rate measurements showed that inhibitors such as F⁻ and nitrilotriacetic acid interact with paramagnetic Mn(III) active site. The ³¹P-NMR signal of the enzyme-phosphate complex was also broadened by the paramagnetic effect of Mn(III). In the metal-substitution experiments of the Mn(III)-acid phosphatase with Fe(III), Zn(II) and Cu(II), only the iron gave satisfactory substitution. The Fe(III)-substituted plant acid phosphatase exhibited an absorption maximum at 525 nm (ε = 3000), typical high spin ferric ESR signal at g = 4.39, and lower pH optimum (pH 4.8) than the native Mn(III)-enzyme (pH 5.8). The phosphatase activity of the Fe(III)-substituted enzyme was reduced to about 53% of that of the native enzyme. The substrate specificities of both metallophosphatases were remarkably similar, but different from that of the Fe(III)-containing uteroferrin. The present results indicate that Mn(III) and Fe(IIII) in the acid phosphatase play an important role on effective binding of phosphate and acceleration of hydrolysis of phosphomonoesters at pH 4–6.     

Kinetic and mechanistic study of oxidation of l-methionine by Waugh-type enneamolybdomanganate(IV) in perchloric acid

The reaction between methionine and enneamolybdomanganate(IV) in perchloric acid was carried out under pseudo-first-order conditions keeping large excess of methionine. The orders in oxidant and substrate were found to be unity and 0.91, respectively. The reaction proceeds with rapid formation of complex between the reactants followed by its decomposition in a rate determining step. The accelerating effect of hydrogen ions on the reaction is due to the formation of active hexaprotonated oxidant species. The product of the reaction was found to be methionine sulfoxide. The reaction involves direct two-electron transfer step without any free radical intervention. The effect of ionic strength, solvent polarity and the activation parameters were also in support of the mechanism proposed.     

Kinetics and mechanism of oxidation of some aldoses by vanadium(v) in perchloric acid medium

The kinetics of oxidation of some aldoses by vanadium(V) in perchloric acid media have been investigated. Each reaction is first order with respect to both [Vanadium(V)] and [Aldose]. The reactions are catalysed by acid. The addition of sodium perchlorate accelerates the rate of reaction. Kinetic evidence for the formation of an intermediate compound between vanadium(V) and aldoses is insignificant, and a mechanism is suggested in which vanadium(V) reacts with the aldoses by a fast step to form a transition state, followed by the decomposition of the latter to give the products of reaction in a slow step. The formation of free-radical intermediates has been demonstrated, and one-electron reduction of vanadium(V) by aldoses seems to be the most plausible mechanism. The oxidation rates follow the order: xyloses arabinose galactose mannose. The activation parameters are reported.     

Kinetics and mechanism of oxidation of -glucose and -ribose by chromium(VI) and vanadium(V) in perchloric acid medium

The kinetics of oxidations of -glucose and -ribose by chromium(VI) and vanadium(V) in perchloric acid medium have been studied. Each reaction was first order with respect to [oxidant] and [substrate]. The reactions were catalysed by acid, but their dependence on acidity was complex. Sodium perchlorate accelerated the rate of reaction. The rate of oxidation of ribose was greater than that of glucose. Mechanisms for these oxidations are suggested. An attempt has also been made to correlate rate constants and activation parameters for the oxidations of different aldoses by these two oxidants.     

Reaction between iron(III) and pyrazoic acid

In the reaction of [Fe(H₂O)₆]³⁺ with pyrazoic acid, reduction of iron(III) to iron(II) is observed. When an excess of iron is present, the reaction involves a transfer of four electrons per mole of acid. At room temperature the redox reaction, which is dependent on hydrogen ion, iron(III) and pyrazoic acid concentrations, is rather slow and is the rate-determining step. The kinetic study was carried out at 50.0 ± 0.1 °C. The redox reaction is followed by a fast reaction of the iron(II) with an excess of ligand, resulting in the production of well-known complexes, where the acid acts as a chelating ligand through the nitrogen and oxygen atoms.     

Reaction of trans-dichlorobis(ethylenediamine)nickel(III) in aqueous hydrochloric acid

Both EPR and electronic absorbance spectroscopy have been used to follow the disappearance of [Ni^III(en)₂Cl₂]⁺ in aqueous HCI solutions. The rate of Ni(III) reduction is influenced by both the H⁺ and Cl^? concentrations, although the rate is not linear with respect to the concentration of either species. A mechanism is proposed in which the first step in the reaction is the proton-induced chelate ring opening which is followed by the reduction of Ni(III) by chloride ions. In the presence of H₂SO₄ the coordinated Cl^? ions are rapidly replaced by HSO_4^? ions and the resulting complex is much more stable, even in a 6 N acid solution.     

Analysis of the fatty acid components in a perchloric acid-soluble protein

We had previously found that a perchloric acid-soluble protein (PSP1) occurs in rat liver, and that this novel protein inhibits protein synthesis in a rabbit reticulocyte lysate system (T. Oka, H. Tsuji, C. Noda, K. Sakai, Y.-H. Hong, I. Suzuki, S. Mu?oz, Y. Natori, J. Biol. Chem. 270 (1995) 30060-30067). In the present study, we analyzed lipid components bound to PSP1. Native PSP1 was purified from rat liver using Sephadex G-75, DE-52 cellulose and IgGPSP-affinity chromatography, and the lipid components were extracted. The components obtained from the purified PSP1 were shown to be free fatty acids by thin-layer chromatography. By GC-MS, six major fatty acids were identified as 14:0, 16:0, 18:0, 18:1, 18:2 and 20:4. 1 mol of PSP1 contained 1.26 mol of total fatty acid components. The fatty acid-binding assay of PSP1 showed that the Bmax was 1.25 mol fatty acid/mol PSP1 and the Kd value for palmitic acid was 6.03 microM. The concentration of PSP1 mRNA in rat liver increased 2.3-fold by the administration of peroxisome proliferator, bezafibrate. These findings show that PSP1 is a fatty acid-binding protein-like protein, which is involved in the intracellular metabolism of fatty acid and is quite different from the known fatty acid-binding proteins.     

Mode of enhancement in ribonucleic acid synthesis directed by chromium (III)-bound deoxyribonucleic acid

By forming a complex with calf thymus DNA, Cr(III), i.e., CrCl3 and Cr(NO3)3, significantly enhanced its template activity for in vitro RNA synthesis as assayed by 3H incorporation from [5-3H]uridine triphosphate (UTP). The extent of the augmentation in RNA synthesis was proportional to the binding ratio of Cr(III) to the template DNA. K2CrO4, on the other hand, neither bound to DNA nor enhanced its template activity. Experiments using rifampicin and heparin suggested that incorrect and nonviable initiation sites for RNA synthesis became functional in Cr(III)-bound DNA. The incorporation of [gamma-32P]adenosine triphosphate (ATP) into RNA synthesized on Cr(III)-bound DNA was 8 to 9 times greater than that on control DNA. This value was much higher than that of the 3H incorporation form [5-3H]UTP, i.e., the incorporation of 32P on Cr(III) bound DNA was 8 to 9 times greater that of 3H and less than twice that on control DNA. These results suggest that Cr(III) possibly induces the abnormal synthesis of RNA of a very low molecular weight, for most if not all the molecules, by binding to the template DNA.     

Complexes of vanadium(III) with L-alanine and L-aspartic acid

The equilibria of the complexation processes of V(3+) with L-alanine and L-aspartic acid in aqueous solution over a wide pH range (2-10) were studied by potentiometric and spectroscopic (UV-Vis, CD) methods. The results show that alanine forms complexes with V(3+) in the metal ion concentration range and at the ligand-to-metal ratios investigated, giving mononuclear species only. In ML(2) species, which dominate in the range pH 4-8, alanine acts as a bidendate ligand through O and N atoms. The complexation processes of V(3+) with aspartic acid are more complicated. In acidic solution (up to pH approximately 4) they are similar to those for alanine. In the higher pH region, however, there are complicated equilibria among mono- and various dinuclear species. These dinuclear species consist of carboxylic or mu-oxo bridges and differ from each other by the number of coordinated ligands and OH(-) groups. The solid phase of the V(III) complex with aspartic acid could be isolated from nonaqueous solution only. Spectroscopic (UV-Vis-IR) measurements and magnetic susceptibility data confirm the coordination of vanadium(III) by two carboxylic groups. Both V(III)-L-aspartic acid and V(III)-L-alanine complexes have a significant apoptotic effect on Hepatoma Morris 5123 cells.     

Light-induced nicking of deoxyribonucleic acid by cobalt(III) bleomycins

The anticancer drug bleomycin is a glycopeptide that causes strand scission of DNA both in vivo and in vitro. Cleavage of DNA by bleomycin has been studied extensively in vitro, with the findings that ferrous ion and molecular oxygen must be present and that addition of reducing agents greatly enhances the reaction. To date, only iron has been shown to be an effective metal cofactor for the cleavage of DNA by bleomycin. Here it is reported that two stable cobalt(III) complexes of bleomycin are strikingly effective in causing single-strand breaks (nicks) in supercoiled DNA in the presence of ultraviolet or visible radiation. For example, 366-nm light from an 18-W long-wavelength mercury lamp for 1 h causes 10(-6) M cobalt(III) bleomycin to completely convert supercoiled phi X174 DNA (10(-8) M DNA, 10(-4) M phosphate) into the nicked circular form. Furthermore, numerous alkali-labile sites are produced on the DNA during this treatment. The observed reactions are not caused by adventitious iron, and they occur only in the presence of cobalt(III) bleomycin and light.     

Effect Of Sodium Hexanitrocobaltate (III) Decomposition On Its Staining Of Intracellular Potassium Ions

The effect was examined of the chemical decomposition of the potassium stain, sodium hexanitrocobaltate (III) (SHC), on its ability to produce stain granules of consistent size that could be used to estimate the K⁺ contents of stomafal guard cells. Stomata in detached epidermis from leaves of Vicia faba (fava bean) were stimulated to accumulate K⁺ by treating them with fusicoccin. Stomatal apertures and the fraction of guard cell area covered by K⁺ precipitate granules (K⁺ score) were measured by digitizing photographic enlargements, and K* scores were correlated with the age of stain that had been stored either in open or closed containers. The ability of stain aged in open containers to produce consistent fractional cell coverage was compared to 1) the ability of identically treated stain to precipitate K⁺ from solutions of KCl, and to 2) the kinetics of decomposition of SHC. It was found that the fractional coverage of guard cells of stomata opened to the same apertures decreased with a first order rate constant of 2.3 × 10^-8/sec. The mass of precipitate formed by treatment of KCl solutions was unchanged for 2 hr after initial preparation of the SHC, and decreased thereafter with a first order rate constant of 1.0 × 10^-5/sec. When stored in tightly sealed containers, nearly 100 hr were required for an occasionally opened bottle of SHC to decay to the same efficacy as a solution left open to the air for 8 hr.     

Enhancement of ribonucleic acid synthesis by chromium(III) in mouse liver

The effect of Cr(III) administration on hepatic RNA synthesis in mice was studied. It was found that Cr accumulated in mouse liver. Forty-eight hours after intraperitoneal injection of CrCl3 (0.005-5 mg Cr/kg body weight) approximately 10% of the administered dose per g of tissue remained. The accumulated Cr was still retained 64 days after administration (5 mg Cr/kg) with only a slight decrease. Approximately 20% of the hepatic Cr was detected in the nuclei. By administering CrCl3. RNA synthesis in mouse liver was markedly enhanced without altering the pool size of nucleotides. This enhancement was dose-dependent and statistically significant at doses of 0.05 (p less than 0.05), 0.5 (p less than 0.01), and 5 mg Cr/kg (p less than 0.01), and remained so for at least 16 days after administration of 5 mg Cr/kg. The synthesis of DNA and protein in mouse liver were not significantly changed by CrCl3 administration. On the other hand, Cr(VI) administration did not enhance but rather inhibited RNA synthesis in mouse liver. These results suggest that Cr(III) specifically enhances RNA synthesis in mouse liver.