Space-time chaos in reactions of NADH with atmospheric oxygen in the presence of copper(II) complexes

In the oxidation of aqueous solutions of NADH by atmospheric oxygen in the presence of certain copper(II) compounds, an irregularly oscillating timewise change has been observed in the potential of a point platinum electrode (PPE), relative to either a silver chloride electrode or a second PPE located in the same solution. Phase portraits have been constructed on the basis of experimental data for all of the systems that have been investigated. It has been shown that the existence of chaotic oscillations, and also the form of the phase portrait of the systems, depend on the magnitude of the redox potential of the CuL²⁺/CuL⁺ pair. For compounds with E₀=0.60–0.64 V, the phase portrait has the form of a screw-type chaos, which then changes over to Lorentz-type chaos. Only for this group of complexes is chaotic behavior observed when the solution is stirred. For compounds with E₀=0.15–0.41 V, screw-type chaos is observed; and for compounds with E₀<0, no chaotic behavior has been detected.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 175–184, March–April, 1990.     

Volt-amperometry of 1,4-dihydropyridine derivatives

It was found that compounds of the 3,5-dicarbonyl-1,4-dihydropyridine series are oxidized on a rotating platinum microelectrode in acetonitrile at potentials that are accessible for electrochemical investigation (from 0.8 to 1.4 V relative to a saturated calomel electrode). The electrochemical oxidation potentials of 41 compounds were determined, and the influence of electronic effects of substituents introduced into various positions of the dihydropyridine ring on E_p and E_1/2 was revealed. The potentials obtained were compared with the peculiarities of the chemical and enzymatic oxidation of-the corresponding compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 84–87, January, 1972.     

Study of Adsorption, Condensation, Orientation, and Reduction of Quinoline Molecules on a Pure Mercury Electrode Using Raman Microprobe Spectroscopy

Quinoline is known to adsorb on a mercury electrode surface with several differentorientations and it sometimes blocks other electrochemical reactions. The Ramanmicroprobe technique has been applied successfully to observe reorientations ofquinoline adsorbed on the mercury surface from neutral and basic aqueoussolutions. The orientation-distance profile from the mercury surface was also studied.A Raman band intensity of quinoline (1373 cm^–1) relative to the intensity ofperchlorate ion (931 cm^–1) was measured. The peak positions did not shift evenwhen the applied potential was altered, but the relative peak intensity changed.It was concluded that the adsorbed quinoline changes its orientation from a flatat –0.1 > E > –0.3V, to a standing at E < –0.5 V, passing through a mixtureof the two orientations when –0.3 > E > –0.5 V.     

Electrochemical analysis of the coordination sphere of ruthenium(ii) as electron transfer mediator in glucose oxidase catalysis in aqueous solutions

The redox potentials of the cis-[Ru(LL)₂XY]ⁿ⁺ complexes (LL = 2,2"-bipyridyl (bpy), 1,10-phenanthroline (phen), and 4,4"-dimethyl-2,2"-bipyridyl (Me₂bpy); X, Y = Cl^–, Br^–, CO₃ ^2–, NO₂ ^–, SCN^–, N₃ ^–, H₂O, and DMSO) in aqueous buffer solutions were measured and analyzed in the framework of the Lever theory on the additivity of contributions of ligands (E _L) to the apparent redox potential of the complex (E ^o"). The complexes manifest the properties of reversible or quasireversible redox systems, whose formal redox potentials lie in the 0.2—0.5 V range. The complexes are efficient electron transfer mediators between the active center of glucose oxidase (GO) from Aspergillus niger and an electrode.     

Electrochemical and FTIR studies of -phenylalanine adsorption at the Au(111) electrode

The adsorption of -phenylalanine (Phe) at the Au(111) electrode surface has been studied using electrochemical techniques and subtractively normalized interfacial Fourier transform infrared (SNIFTIR) techniques. The electrochemical measurements of cyclic voltammetry, differential capacity and chronocoulometry were used to determine Gibbs energies of adsorption and the reference (E₁) and sample (E₂) potentials to be used in the spectroscopic measurements. The vibrational spectra have been used to determine: (i) the orientation of the molecule at the surface as a function of potential; (ii) the dependence of the band intensity on the surface coverage; (iii) the character of surface coordination, and (iv) the oxidation of adsorbed Phe molecules at positive potentials. The adsorption of Phe is characterized by ΔG values ranging from −18 to −37 kJ mol⁻¹ that are characteristic for a weak chemisorption of small aromatic molecules. The electrochemical and SNIFTIR measurements indicated that adsorbed Phe molecules change orientation as a function of applied potential. At the negatively charged surface Phe is predominantly adsorbed in the neutral form of the amino acid. At potentials positive to the pzc, adsorption occurs predominantly in the zwitterionic form with the ---COO⁻ group directed towards the surface and the ammonium group towards the solution. At more positive potentials electrocatalytic oxidation of Phe occurs and is marked by the appearance of the CO₂ asymmetric stretch band in the FTIR spectrum. Thus, relative to pzc, Phe is weakly chemisorbed at negative potentials, changes orientation at potentials close to the pzc and is oxidized at positive potentials.     

Thermodynamic stabilization of nickel(III) by amide-containing ligands: Electrochemical study of complexes with 13- and 14-membered dioxotetraazamacrocycles

It was shown that the values of the redox potentials of Ni^IIIL/Ni^IIL complexes of nickel with 13- and 14-membered dioxotetraazamacrocycles accepted in the literature pertain to the redox transition of the metal ion in complexes with azomethine derivatives of the original ligands, the actual values of E_1/2 for the given compounds being considerably lower.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 29, No. 4, pp. 343–349, July–August, 1993.     

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.     

Voltamperometric determination of uranium and plutonium in alkaline solutions

The simultaneous determination of U(VI), Pu(VI), Pu(V) in 0.5–4.0 M NaOH has been elaborated by means of classical and differential pulse voltamperometry. U(VI) is determined with a dropping mercury electrode (DME) at the half-wave potential of E_1/2=–0.89 V vs. Ag/AgCl reference electrode due to reduction to U(V). The limiting current or peak heights are proportional to uranium(VI) concentration in the range of 1.3.10^–7–3·10^–4 M U(VI). Deviation from proportionality is observed for higher concentrations due to polymerization of uranates. Pu(VI) and Pu(V) are determined with a platinum rotating electrode at E_1/2=–0.02 V due to the reaction Pu(VI)+e^–»Pu(V) and with DME at E_1/2=–1.1 V due to the reduction to Pu(III). The limiting currents of both Pu(VI) and Pu(V) are proportional to their concentrations in the range of 4·10^–6–1.2·10^–3 M Pu. The determination of U(VI), Pu(VI), Pu(V) is not interfered by the presence of the following salts: 2M NaNO₃, 2M NaNO₂, 1.5M NaAlO₂, 0.5M NaF and ions of Mo(VI), W(VI), V(V), Cu(II). The presence of CrO ₄ ^2– and FeO ₂ ^– ions disturbs the determination of U(VI) in 1–4M NaOH, however, contribution of the reaction Fe(III)+e^–»Fe(II) to uranium reduction peak can be calculated from the height of the second peak Fe(II)+2 e^–»Fe(0).     

Analysis of the interaction energy in the Cu+-H2O and Cl−-H2O systems,with CP corrections to the BSSE of the separate terms,and MC simulations of the aqueous systems with and without CP corrections

The interaction energyE of the systems Cu⁺-H₂O and Cl^–-H₂O has been computed over a wide range of distances and orientations with the MINI-1 basis set in the SCF approximation. The interaction energy has been decomposed according to the Kitaura-Morokuma scheme, with and without counterpoise (CP) corrections to the basis set superposition error. The importance of this correction is analysed by its effect upon Monte Carlo calculations of the Cu⁺-water and Cl^–-water systems, using two-body potentials without and with CP corrections. The effect of CP corrections on theE analysis is similar to that found in other systems of analogous composition (of the general type ion plus neutral ligands), but with significant differences in the details. The effect of the CP corrections to the interaction potential, and then on the results of the Monte Carlo simulations, is small for the Cu⁺ ion, but remarkable for the Cl^– ion.     

Spectroscopic and thermal studies on the decomposition of l,3,5-triamino-2,4,6-trinitrobenzene (TATB)

The kinetics of the thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in condensed state has been investigated by high temperature infrared spectroscopy (IR) and thermogravimetry (TG) in conjunction with pyrolysis gas analysis, differential thermal analysis (DTA) and hot stage microscopy. The decomposition proceeds in two main stages under isothermal conditions and the initial stage involving about 24% loss in weight obeys Avrami-Erofe'ev equation (n= 1), and is governed by an activation energy (E) of 150.58 kJ·mol^–1 and log(A in s^–1) 12.06. The second stage corresponding to 24 to 90% loss in weight gave best fit for Avrami-Erofe'ev equation,n=2, withE=239.56 kJ·mol^–1 and log(A in s^–1) 19.88 by isothermal TG. The effect of additives, on the initial thermolysis of TATB has also been studied. Evolved gas analysis by IR showed that NH₃, CO₂, NO₂, HCN and H₂O are produced in the initial stage of decomposition. The decomposition in KBr matrix in the temperature range 272 to 311.5°C shows relative preferential loss in the -NH₂ to -NO₂ band intensity which indicates that the rupture of C-NH₂ bond, weakened also by the interaction of the NH₂ with the neighbouring NO₂ group, appears to be the primary step in the thermolysis of TATB.     

Investigations of TsVM zeolite acidities with different degrees of exchange of Na+ by H+

The method of programmed thermal desorption of ammonia has been used to establish that on the surface of the sodium form of type TsVM zeolite having a modulus SiO₂/Al₂O₃= 34.5 there are two types of acidic centers having ammonia desorption activation energies E_d equal to 40–45 and 80–100 kJ/mole. Replacement of Na⁺ by H⁺ leads to the appearance of a third type of center with a value E_D=130–150 kJ/mole. In this case in the IR spectra of specimens saturated with ammonia a band appears at 1410 cm_–1, which is evidence for the presence of NH ₄ ⁺ ions. Increasing the degree of Na⁺ replacement by H⁺ leads to a nonproportional rapid increase in the concentration of highly energetic centers, which may be explained by the partial transfer of aluminum into cationic positions with the formation of additional acidic centers.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 752–755, November–December, 1986.     

Rapid determination of telmisartan in pharmaceuticals and serum by the parallel catalytic hydrogen wave method

The polarographic characteristics of telmisartan have been investigated in 0.8 mol L^–1 NH₃.H₂O–NH₄Cl (pH 8.9)–0.01 mol L^–1 H₂O₂ as supporting electrolyte. The results demonstrate that the polarographic reduction wave at ca. –1.30 V in the absence of H₂O₂ is a catalytic hydrogen wave, and the reduction wave enhanced by H₂O₂ is a so-called parallel catalytic hydrogen wave. The analytical sensitivity of the parallel catalytic hydrogen wave is ca. 60 times higher than that of the corresponding catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave a novel method has been developed for determination of telmisartan by linear sweep polarography. The calibration curve is linear in the range 2.0×10^–8–2.0×10^–6 mol L^–1 and the detection limit is 1.0×10^–8 mol L^–1. The precision is excellent with relative standard deviations of 2.6% at a concentration of 1.0×10^–7 mol L^–1 telmisartan. The proposed method has been applied to the direct determination of the telmisartan in capsule forms and biological samples. The proposed method has been proved to be advantageous over existing CZE and MEKC methods in simplicity, rapidity, and reproducibility.     

Polarographische Bestimmung der 2,2′-Dicinchoninsäure

Zusammenfassung Eine polarographische Methode zur Bestimmung der 2,2-Dicinchoninsäure in 15%iger Ammoniumacetatlösung als Grundelektrolyt wurde ausgearbeitet. Der zweistufigen Reduktion entsprechen zwei polarographische Stufen, deren Halbstufenpotentiale gegen die gesättigte KalomelelektrodeE _1/2=–0,74 V undE _1/2=–1,28 V betragen.Die charakteristischen zwei Maxima wurden mit 0,5%iger Gelatinelösung beseitigt und der Sauerstoff mit elektrolytisch hergestelltem Wasserstoff entfernt.Die lineare Abhängigkeit des Diffusionsstromes für beide Stromstufen der Säure in zwei Konzentrationsbereichen —von 1·10^–4- bis 3·10^–4-m und von 0,5·10^–3-bis 3·10^–3-m —wurde festgestellt.

---

Summary A polarographic method has been developed for the determination of 2,2-dicinchonic acid in 15% ammonium acetate solution as fundamental electrolyte. The two-stage reduction is shown by two polarographic stages, whose half-stage potentials as referred to the saturated calomel electrode amount toE _1/2=–0.74 V andE _1/2=–1.28 V.The two characteristic maxima were removed by 0.05% gelatin solution and the oxygen was eliminated by means of hydrogen produced electrolytically. The linear dependence of the diffusion current for both current stages of the acid were established in two concentration ranges —from 1·10^–4 to 3·10^–4 M and from 0.5·10^–3 to 3·10^–3 M.

---

Résumé Mise au point d'une méthode polarographique pour doser l'acide dicinchonine-2, 2 en solution dans l'acétate d'ammonium à 15% comme électrolyte support. La réduction en deux temps correspond à deux vagues polarographiques, dont les potentiels de demi-vague par rapport à l'électrode au calomel saturée s'élèvent àE _1/2= – 0,74 V etE _1/2=–1,28 V.On élimine les deux maximums caractéristiques par une solution de gélatine à 0,05% et l'oxygène par l'hydrogène préparé électrolytiquement. Mise en évidence d'un rapport linéaire entre le courant de diffusion pour les deux vagues de courant de l'acide dans les deux domaines de concentration: de 1·10^–4 à 3·10^–4 M et de 0,5·10^–3 à 3·10^–3 M.

     

Calorimetric study of cross-linking polymerization of methyl methacrylate in the presence of a multimonomer

The kinetics of free-radical cross-linking polymerization of methyl methacrylate (MM) in the presence of poly[2-(10-undecenoyloxy)ethyl methacrylate] (PUDEM) as a macromolecular cross-linker has been isothermally examined within the temperature range from 85–100°C using the differential scanning calorimetry (DSC). The activation energy found for this reaction, E _a=89.3 kJ mol^–1, exceeds slightly the literature values of activation energy obtained for the mass polymerization of MM without any cross-linking agent. The activation energy has been also determined by the isoconversion method. It has been found that E _a decreases with the increase in the conversion, which may indicate a change in the reaction mechanism.This work was partly supported by the Committee for Research (KBN) in the framework of project No. 7 T08E 026 20     

Instantaneous strain recovery elasticity and endothermic heat change in nylon-6 monofilaments and silicone rubbers

The instantaneous elastic moduli for a nylon-6 monofilament were derived on strain recoveries right after creep, stress relaxation, and rapid elongation,E _c ,E _s andE _e , respectively. It was found that during strain recoveryE _s (>E _e ) andE _e increase monotonically with increasing load,m ₁, on the sample. The extrapolated value of E_s atm ₁=0 g is almost equal to Young's modulus, 4.06 GPa. The value ofE _c also increased with increasingm ₁, and atm ₁=600 g (1.93 t cm^–2) reached about 14 GPa. The endothermic heat change right after creep, stress relaxation or rapid elongation,Q, was negligibly small. For comparison,E _s ,E _c andQ were also investigated for silicone rubber. It was found thatE _s (53.8 M Pa at the draw ratioD=1.2) decreased abruptly atD=1.3. In the range ofD=1.4–1.9,E _s was only 22.6 MPa. In the case of stress relaxation,Q increased with increasingD from 4 J mol^–1 (atD=1.2) to 56 J mol^–1 (atD=1.9). FurthermoreE _c (5.58 MPa atm ₁=133.8 g (429.4 kg cm^–2)) increased gradually with increasing m₁ and attained 16.6 MPa atm ₁=548.4 g (1.76 t cm^–2). In the case of creep,Q was in the range of 0–11.5 J mol^–1 and larger when larger loads,m ₂ were removed during the later stages of creep.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe author wishes to thank Mr. Keizi Igarashi and Mr. Tetsuya Yasui for helping in the experiments.     

A nonadiabatic lower bound calculation of H 2 + and D 2 +

Accurate nonadiabatic lower and upper bounds for groundstate energies of H ₂ ⁺ and D ₂ ⁺ are calculated with the linearized method of variance minimization. The results in a.u. are –0.59713906₃<E ₀(H ₂ ⁺ )<–0.59713899₄ –0.59878877₅<E ₀(D ₂ ⁺ )<–0.59877873₈ i.e. the values are determined with an absolute error smaller than 0.02 cm^–1 for H ₂ ⁺ and 0.01 cm^–1 for D ₂ ⁺ .     

Synthesis,structure and electrochemistry of a copper(II) complex with 1,2-di{o-[o-hydroxy(naphthylideneimino)]phenoxy}ethane

The title Schiff base ligand, H₂L, and its complex [CuL] have been prepared and characterized by elemental analysis and i.r. spectroscopy. The electrochemical properties of the single crystal [CuL]·0.5C₂H₄Cl₂ have been investigated by cyclic voltammetry (c.v.). Upon scanning at negative and positive potentials, two reduction and two oxidation waves were observed at E _1/2 ⁰ = –0.47 and –0.77 V and E _1/2 ⁰ = 1.10 and 1.39 V, respectively. Two K _com values for the reduction and oxidation process are 1.2×10⁵ and 8.0×10⁴, respectively, and indicate that the deprotonated ligand, L, has the ability to stabilize the mixed valent states of both Cu^IICu^I and Cu^IICu^III. The crystal structure has been solved by X-ray diffraction, with a final R = 0.0653. Wound around a copper atom, the effectively tetradentate chain ligand, L, coordinates only via its two imino and two phenolate groups at both ends of the chain. The geometry, D _2d symmetry, is best described as trans 'N₂O₂' square-planar with slight tetrahedral distortion. The reason, why the mononuclear [CuL] unit can display two c.v. waves in each process, has been explained on the basis of configuration interchange between mono- and dinuclear units in c.v. electrolyte solution.     

Densities and Excess Molar Volumes of Binary and Ternary Mixtures of Aqueous Solutions of 2,2,2-Trifluoroethanol with Acetone and Alcohols at the Temperature of 298.15 K and Pressure of 101 kPa

Excess molar volumes V_m^E of the binary mixtures of (trifluoroethanol + 1-propanol), (trifluoroethanol + 2-propanol), (acetone + water), (methanol + water), (ethanol + water), (1-propanol + water), (2-propanol + water), and the ternary mixtures of (trifluoroethanol + methanol + water), (trifluoroethanol + ethanol + water), (trifluoroethanol~+ 1-propanol + water), (trifluoroethanol + 2-propanol + water) and (trifluoroethanol + acetone + water) were measured with a vibrating tube densimeter at the temperature of 298.15 K and the pressure 101 kPa. The extrema in V_m^E of trifluoroethanol mixtures occur at –0.690 cm³-mol^–1 for (trifluoroethanol + 1-propanol), at –0.990~cm³-mol^–1 for (trifluoroethanol + 2-propanol); at 0.562 and –0.973 cm³-mol^–1 for (trifluoroethanol + methanol + water), at 0.629 and –0.973 cm³-mol^–1 for (trifluoroethanol + ethanol + water), at 1.082 and –0.659 cm³-mol^–1 for (trifluoroethanol~+ 1-propanol + water), at 0.998 and –0.991 cm³-mol^–1 for (trifluoroethanol~+ 2-propanol + water), and at 0.515 and –1.472 cm³-mol^–1 for (trifluoroethanol + acetone + water). The experimental ternary V_m^E values were predicted by empirical expressions using binary solution data.     

Electronic absorption spectra,ESR spectra,and structure of coordination polyhedrons of titanium(III) in molten and “instantly cooled” systems of sodium phosphates and halides

The structure of Ti(III) coordination polyhedrons in both individual NaPO₃ and 70 mole % NaPO₃-30 mole % Na_nX mixtures (X=PO₃ ^3–, P₂O₇ ^4–, F^–, Cl^–) in the molten and solid states has been investigated on the basis of data from electronic absorption and ESR spectra. The formation of tetragonally distorted Ti(III) coordination polyhedrons with D_4h symmetry coordinated only by (PO₃ ^–)_n chains with the following values of the spectroscopic parameters for the molten (and solid) states has been established in all the phosphate systems investigated: 10Dq=17,300 (18,000) cm^–1 (Ds=50 cm^–1, Dt=5600, g=1.959, g₁=1.930, =93. cm^–1). It has been shown that the greater is the extent of depolymerization of the phosphate chains in the melt, the stronger is the Ti(III) coordination polyhedron formed; the following relative series of the depolymerizing strength of the anions has accordingly been established: PO₄ ^3–2O₇ ^4–––.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 610–614, September–October, 1989.     

Adsorbability of halide ions on metal electrodes

Klopman's scheme was used to estimate the relative changes in ionic energy (E_t) in the transition state: aquo complex-metal electrode surface, from the electronic constitutions of the aquo systems [NaHal·10H₂O] (where Hal = F^–, Cl^–, I^–) calculated by the LCAO MO method in the MVG form, and made self-consistent with respect to the charges on the atoms and configurations. It was shown that the experimental data for halide ion adsorption on electrodes are explained, in the model adopted, not by the Coulomb but by the exchange contribution to E_t. The adsorbability of the fluoride ions is small owing to the very small contribution made to E_t by the interaction between the aquo system [NaF·10H₂O] and the metal surface through the fluorine atom.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 732–737, November–December, 1990.The authors thank I. B. Bersuker and I. Ya. Ogurtsov for their interest in the work and participation in the discussion.