Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

Vanadium(V) 8-quinolinolate—monomer or dimer?

Extraction of vanadium(V) with 8-quinolinol into chlorobenzene is discussed. Three dimeric species are shown to be responsible for the extraction: 2VO₃^- + 4(HOx)_o α (V₂O₃Ox₄)_o + 2OH^-; log K_ex,1 = -1.60 ± 0.10 2VO₃^- + 4(HOx)_o + H⁺ + ClO₄^- α (V₂O₃H(Ox)₄ · ClO₄)_o + 2OH^-; log K_ex,2 = 1.55 ± 0.10 2VO₃^- + 4(HOx)_o + 2H⁺ + 2ClO₄^- α (V₂O₂Ox₄ · 2ClO₄)_o + 2OH^-; log K_ex,3 = 2.65 ± 0.10 The vanadium(V) complex of 8-quinolinol has also been studied by thermogravimetry and i.r. and visible spectroscopy; an oxo-bridged dimeric structure is postulated. In contrast to 8-quinolinol, 2-methyl-8-quinolinol gives a monomeric vanadium(V) complex under the usual experimental conditions.     

Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

The kinetics and mechanism by which monochloramine is reduced by hydroxylamine in aqueous solution over the pH range of 5–8 are reported. The reaction proceeds via two different mechanisms depending upon whether the hydroxylamine is protonated or unprotonated. When the hydroxylamine is protonated, the reaction stoichiometry is 1:1. The reaction stoichiometry becomes 3:1 (hydroxylamine:monochloramine) when the hydroxylamine is unprotonated. The principle products under both conditions are Cl^–, NH⁺₄, and N₂O. The rate law is given by ?[d[NH₂Cl]/dt] = k₊[NH₃OH⁺][NH₂Cl] + k₀[NH₂OH][NH₂Cl]. At an ionic strength of 1.2 M, at 25°C, and under pseudo‐first‐order conditions, k₊= (1.03 ± 0.06) ×10³ L · mol^?1 · s^?1 and k₀=91 ± 15 L · mol^?1 · s^?1. Isotopic studies demonstrate that both nitrogen atoms in the N₂O come from the NH₂OH/NH₃OH⁺. Activation parameters for the reaction determined at pH 5.1 and 8.0 at an ionic strength of 1.2 M were found to be ΔH? = 36 ± 3 kJ · mol^–1 and Δ S? = ?66 ± 9 J · K^?1 · mol^?1, and Δ H? = 12 ± 2 kJ · mol^?1 and Δ S? = ?168 ± 6 J · K^?1 · mol^?1, respectively, and confirm that the transition states are significantly different for the two reaction pathways. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 124–135, 2006     

Kinetic Studies on the Oxidation of Germanium(II) with Chlorate by Polarographic Analysis

The rate of oxidation of Ge(II) chloride by large excess of ClO₂^? ions in HCl, NaCl and Na₂SO₄ mixed solutions was polarographically observed at various H₂O⁺ and Cl^? ion concentrations. The observed rate constant, k_obs, is expressed by k_o=K_obs/(ClO₃^?)={k₁,(H⁺)+k₂K₁(Cl^?)²+ K₃K₂(SO₄^2?)} (H⁺)/{(H⁺)¹+K₁(Cl^-)2 +K₂(SO₄^2?)} for the following reaction processes, The values were obtained aa k₁=1.5410^-3liter² mole^2? sec^-1, k₂=5.00×10^-2liter² mole^2? sec^-2 and k₂=4.30×10^-3liter² mole^2? sec^-2, K₁=1.80× 10^-2, K₂= 2.43×10^-2 mole liter^-1 at constant ionic strength I=0.50 M at 30°C.     

Thermodynamic Model for ThO<Subscript>2</Subscript>(am) Solubility in Isosaccharinate Solutions

Extensive studies on ThO₂(am) solubility were carried out as functions of a wide range of isosaccharinate concentrations (0.0002 to 0.2 mol⋅kg⁻¹) at fixed pH values of about 6 and 12, and varying pH (ranging from 4.5 to 12) at fixed aqueous isosaccharinate concentrations of 0.008 mol⋅kg⁻¹ or 0.08 mol⋅kg⁻¹, to determine the aqueous complexes of isosaccharinate with Th(IV). The samples were equilibrated over periods ranging up to 69 days, and the data showed that, in most cases, steady-state concentrations were reached in <15 days. The data were interpreted using the SIT model, and required the inclusion of mixed hydroxy-ISA complexes of Th(IV) [Th(OH)ISA²⁺, Th(OH)₃(ISA)₂^-_{2}^{-}, and Th(OH)₄(ISA)₂^2-]_{2}^{2-}] with log ₁₀ K ⁰=12.5±0.5,4.4±0.5 and −3.2±0.5 for the reactions:

Effects of the ancillary ligands of polypyridyl cobalt(II) complexes on pH-induced spectral properties and DNA binding properties

Abstract  

Two new Co(II) complexes [Co(ipH)₂(bdipH)]²⁺ and [Co(8-HQ)₂(bdipH)] (ipH = imidazo[4,5-f][1,10]phenanthroline, bdipH = 2-(benzo[d][1,3]dioxol-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, 8-HQ = 8-hydroxyquinoline) were synthesized and characterized in detail by elemental analysis, IR, and UV–Vis spectroscopic techniques. The effects of pH on the UV–Vis absorption and emission spectra of the complex were studied. The interaction of the two complexes with calf thymus DNA was explored by using viscosity measurements, electronic absorption titration, competitive binding experiments, and cyclic voltammetry. The experimental results show that complex [Co(ipH)₂(bdipH)]²⁺ exhibits pH-sensitive emission, the two complexes can bind to DNA in an intercalation mode, and the DNA binding affinity of complex [Co(ipH)₂(bdipH)]²⁺ (K _b = 2.11 × 10⁵ M⁻¹) is greater than that of complex [Co(8-HQ)₂(bdipH)] (K _b = 1.76 × 10⁵ M⁻¹). The results show that the size and shape of the ancillary ligand have significant effects on the binding affinity of DNA and complexes.     

Phase diagrams and physicochemical properties of Li<Superscript>+</Superscript>,K<Superscript>+</Superscript>(Rb<Superscript>+</Superscript>)//borate–H<Subscript>2</Subscript>O systems at 323 K

The phase and physicochemical properties diagrams of Li⁺,K⁺(Rb⁺)//borate–H₂O systems at 323 K were constructed using the experimentally measured solubilities, densities, and refractive indices. The Schreinemakers’ wet residue method and the X-ray diffraction were used for the determination of the compositions of solid phase. Results show that these two systems belong to the hydrate I type, with no solid solution or double salt formation. The borate phases formed in our experiments are RbB₅O₆(OH)₄ · 2H₂O, Li₂B₄O₅(OH)₄ · H₂O, and K₂B₄O₅(OH)₄ · 2H₂O. Comparison between the stable phase diagrams of the studied system at 288, 323, and 348 K show that in this temperature range, the crystallization form of salts do not changed. With the increase in temperature, the crystallization field of Li₂B₄O₅(OH)₄ · H₂O salt at 348 K is obviously larger than that at 288 K. In the Li⁺,K⁺(Rb⁺)//borate–H₂O systems, the densities and refractive indices of the solutions (at equilibrium) increase along with the mass fraction of K₂B₄O₇ (Rb₂B₄O₇), and reach the maximum values at invariant point E.     

Studies of solid-state ion-selective electrodes prepared from semiconducting organic radical-ion salts

The primary redox reactions for solid-state ion-selective electrodes prepared from electronically semiconducting salts of 7,7,8,8-tetracyanoquinodimethane (tcnq) can be identified by considering the redox properties of their constituent ions or molecules. Three different processes involving the couples, Mⁿ⁺/M⁰, 2tcnq^o/(tcnq^-)₂ and (tcnq^-)₂/2tcnq^2- are possible depending on salt composition. Ionic product values determined by potentiometric and atomic absorption methods are in excellent agreement for several such salts; K_s(K₂tcnq₂)=5.8±1.2·10^-11(pot.), 1.7±1·10^-11 (a.a.s.); K_s(Cdtcnq₂) = 3.0±0.5·10^-9 (pot.), 2.9±0.3·10^-9(a.a.s.); K_s(Pbtcnq₂) = 1.3±0.3·10^-10 (pot.), 0.96±0.2·10^-10(a.a.s.); and indicate that the lower activity limit for electrode response is controlled by the solubility of the sensor material itself. Comparisons of predicted and observed standard electrode potentials provide quantitative support for an ion-exchange mechanism of interference. The behaviour of electrodes prepared from Cu₂tcnq₂ (copper(I)) and Cutcnq₂ (copper(II)) is explained on the basis of an interference mechanism and considerations of solid-state equilibria.     

Syntheses,crystal structures,and magnetic properties of a series of double end-on azido-bridged dinuclear manganese(II) complexes

Four azido-bridged dinuclear Mn(II) complexes, [Mn₂(phen)₄ μ-₁,₁-N₃)₂][Fe^III(bpmb)(CN)₂]₂·H₂O (1), [Mn₂(phen)₄(μ-₁,₁-N₃)₂][Fe^III(bpClb)(CN)₂]₂·H₂O (2), and [Mn₂(phen)₄(μ-₁,₁-N₃)₂][M^III(bpdmb)(CN)₂]₂·3H₂O [M = Fe (3) or Cr (4); phen = 1,10-phenanthroline, bpmb^2– = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate, bpClb^2– = 1,2-bis(pyridine-2-carboxamido) 4-chloro-benzenate, bpdmb^2– = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate], have been synthesized using the synthetic strategy of large anion inducement. Single-crystal X-ray diffraction analysis reveals that all four complexes are doubly end-on (EO) azido-bridged binuclear Mn(II) complexes with two large [M(L)(CN)₂]^– (L = bpmb^2?, bpClb^2?, or bpdmb^2?) building blocks acting as charge-compensating anions. The magnetic properties of the complexes have been investigated, and the results indicate that the magnetic coupling between two Mn(II) centers through the EO azide bridges is ferromagnetic, with J = 0.64(1) cm^?1 for 1, 0.43(1) cm^?1 for 2, 0.50(1) cm^?1 for 3, and 0.66(2) cm^?1 for 4. The magneto-structural relationships of EO azido-bridged Mn(II) systems are discussed.     

Zur Bedeutung von V2O3(OH)4(g) für den chemischen Transport von V2O5(s) in Anwesenheit von Wasser. Nachweis des Gasteilchens,thermodynamische Daten und Modellrechnungen

V₂O₃(OH)₄(g), Proof of Existence, Thermochemical Characterization, and Chemical Vapor Transport Calculations for V₂O₅(s) in the Presence of Water By use of the Knudsen-cell mass spectrometry the existence of V₂O₃(OH)₄(g) is shown. For the molecules V₂O₃(OH)₄(g), V₄O₁₀(g), and V₄O₈(g) thermodynamic properties were calculated by known Literatur data. The influence of V₂O₃(OH)₄(g) for chemical vapor transport reactions of V₂O₅(s) with water ist discussed. Δ_BH°(V₂O₃(OH)₄(g), 298) = –1920 kJ · mol^–1 and S°(V₂O₃(OH)₄(g), 298) = 557 J · K^–1 · mol^–1, Δ_BH°(V₄O₁₀(g), 298) = –2865,6 kJ · mol^–1 and S°(V₄O₁₀(g), 298) = 323.7 J · K^–1 · mol^–1, Δ_BH°(V₄O₈(g), 298) = –2465 kJ · mol^–1 and S°(V₄O₈(g), 298) = 360 J · K^–1 · mol^–1.     

Extraction of certain actinide and lanthanide elements from different acidic media by polyurethane foams loaded with di-(2-ethylhexyl)phosphoric acid (HDEHP)

The extraction of cerium(III) from weakly acidic chloride solutions by HDEHP-nitrobenzene-loaded polyurethane foams could be analyzed quantitatively in terms of the equation: log(9.056 D_c)=log K_c+2.14 log (C_d?6C_c)+3 pH+log f_c where D_c is the distribution ratio of cerium(III) between the foam and aqueous phases, C_d and C_c are the total HDEHP and Ce(III) concentrations on the foam, respectively, log f_c=[Ce³⁺]_(sq)/[ΣCe(III)]_(aq), and K_c is the equilibrium constant of the equation: Ce _(aq) ³⁺ +2.14(HX)_2.8(o) ? ? CeX₆·H_3(o)+3H _(aq) ⁺ . Values of K_c under the different extraction conditions tested are given.     

Rare earth element complexation by fluoride ions in aqueous solution

Rare earth fluoride stability constants for Ce, Eu, Gd, Tb and Yb at 25°C have been determined by examining the influence of fluoride ions on the distribution of rare earths between tributyl phosphate (TBP) and 0.68M NaClO₄. Our results indicate that rare earth mono and difluoro complexation constants show a steady increase as a function of atomic number from La to Tb but remain relatively constant after Dy. This behavior is similar to that which has been observed for dicarboxylic acids. Stepwise stability constant ratios, K₂/K₁, obtained in our work (where K₁=[MF²⁺][M³⁺]^–1[F^–]^–1 and K₂=[MF ₂ ⁺ ]^–1[MF²⁺]^–1[F^–]^–1) indicated that, for all rare earths, K₂/K₁=0.09±0.03.     

Co(en)3[B4O5(OH)4]Cl·3H2O和[Ni(en)3][B5O6(OH)4]2·2H2O的合成、结构以及热力学性质

利用水热法合成了两种过渡金属配合物为模板剂的含水硼酸盐晶体Co(en)3[B4O5(OH)4]Cl·3H2O(1) 和 [Ni(en)3][B5O6(OH)4]2·2H2O (2),并通过元素分析、X射线单晶衍射、红外光谱及热重分析对其进行了表征。化合物1晶体结构的主要特点是在所有组成Co(en)33+, [B4O5(OH)4]2–, Cl– 和 H2O之间通过O–H…O、O–H…Cl、N–H…Cl和N–H…O四种氢键连接形成网状超分子结构。化合物2晶体结构的特点是[B5O6(OH)4]–阴离子通过O–H…O氢键连接形成沿a方向有较大通道的三维超分子骨架,模板剂[Ni(en)3]2+阳离子和结晶水分子填充在通道中。     

K2[Te4O8(OH)10]: synthesis,crystal structure and thermal behavior

Dipotassium octaoxodecahydroxotetratellurate, K₂[Te₄O₈(OH)₁₀], has been prepared hydrothermally in acidic medium under autogenous pressure. It crystallizes in space group P2₁/c of the monoclinic system with Z=2 in a cell of dimensions a=5.592(1) Å, b=8.283(2) Å, c=16.255(3) Å, and β=99.62(3)°. The outstanding feature of the structure is a tetrameric [Te₄O₈(OH)₁₀]^2– anion built up from edge and corner sharing TeO₆ octahedra. These anions and K⁺ cations are held together by electrostatic interactions and by hydrogen bonds. The compound decomposes in two steps at 350 and 420 °C, corresponding to a water and an oxygen loss, respectively, and affording the mixed valence oxide K₂Te^VI₃Te^IVO₁₂.     

Die Kristallstruktur von Kalium-trithiowolframat-chlorid K3(WOS3)Cl

A recently prepared new thiotungstate has been characterized by three-dimensional X-ray structure analysis, to be a double salt, containing K₂WOS₃ and KCl in equimolar proportions: potassium trithiotungstate chloride, K₃(WOS₃)Cl. Space group: Pca2₁ with a = 12.507, b = 6.317, c = 12,371 Å, Z = 4. The compound represents a new structure type with stoichiometry M^I₂XY₄ · M^IZ. Besides isolated tetrahedral WOS₃^2- ions (bond lengths W–O 1.760 Å, W–S 2.208, 2.197, 2.196 Å) the structure contains Cl^? ions octahedrally co-ordinated by K⁺, the K⁺ ions having 5S + 10 + 2Cl as neighbours. The dimensions of the WOS₃^2? ions in this compound show that, as in other transition metal oxo-, thio- and selenoanions, strong π bonding is present, the W–S bonds taking part in the π bond system.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

Photosubstitution reactions in potassium octacyanomolybdate(IV) and octacyanotungstate(IV) in the presence of 1,10-phenanthroline and 2,2-́bipyridyl

Substitution reactions take place following the photonic excitation of aqueous K₄M(CN)₈ (where M = Mo or W) in the presence of 1,10-phenanthroline and 2,2$\text{-}\text{?}$bipyridyl. Changes in absorbance with time show that the overall reaction is dependent on photochemical activation of potassium octacyanomolybdate(IV) and -tungstate(IV). The species [K₂Mo(CN)₄(OH)₂(phen)], [K₂W(CN)₄(OH)₂(phen)], [K₂Mo(CN)₄(OH)₂(bipy)] and [K₂W(CN)₄(OH)₂(bipy)] exist in solution. The final photosubstitution products [Mo(OH)₃(CN)(phen)₂] · 2H₂O], [Mo(OH)₃(CN)(bipy)₂] · 3H₂O, [W(OH)₃(CN)(phen)₂] · 2H₂O and [W(OH)₃(CN)(bipy)₂] · H₂O have been isolated in the solid state. Their IR spectra have been discussed. The quantum yield of the photosubstitution reactions has been determined and its variation with change of concentration of the complex as well as the H⁺ ion concentration has been studied.     

Kinetics of oxidation of a 2-aminomethylpyridinechromium(III) complex by periodate

The oxidation kinetics of the 2-aminomethylpyridineCr^III complex with periodate in aqueous solution were studied and found to obey the rate law:Rate = [Cr^III]_T [IO₄ ^-]{k¹K² + k₂ K₁ K₃/[H⁺]}/{1+K₁/[H⁺] + k₂[IO₄ ^-]+K₁K₃/[H⁺][IO₄ ^-]} where K ₁, K ₂ and K ₃ are the deprotonation of [Cr(L)₂(H₂O)]³⁺ and pre-equilibrium formation constants for [(L)₂—Cr—OIO₃]²⁺ and [(L)₂—Cr—OH—OIO₃]⁺ precursor complexes respectively. An inner-sphere mechanism was proposed. The effect of Cu²⁺ on the oxidation rate was studied over the (1.0–9.0) × 10⁻⁵ mol dm⁻³ range. The reaction rate was found to be inversely proportional to the Cu²⁺ concentration over the range studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Experimental and theoretical study on the complexation of Ca2+ with beauvericin

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ca²⁺(aq) + 1·Sr²⁺(nb) ? 1·Ca²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex(Ca²⁺, 1·Sr²⁺) = 1.1 ± 0.1. Further, the stability constant of the 1·Ca²⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb(1·Ca²⁺) = 10.1 ± 0.2. Finally, by using quantum mechanical density functional level of theory calculations, the most probable structures of the non-hydrated 1·Ca²⁺ and hydrated 1·Ca²⁺·H₂O complex species were predicted.