Microcalorimetric study of DNA–Cu(II)TOEPyP(4) porphyrin complex

The influence of new water soluble cationic metalloporphyrin Cu(II)TOEPyP(4) (meso-tetra-(4-N-oxyethylpyridyl)), analogue of Cu(II)TMPyP(4), on thermodynamic stability of DNA at various molar ratios of r = porphyrin/DNA b.p. (0 < r < 0.12) has been studied. It has been shown that Cu(II)TOEPyP(4) is a strong stabilizing agent for calf thymus DNA increasing its melting temperature from 75.5 to 99.5 °C, in the range 0 < r < 0.06. The melting enthalpy (∆H _m) does not change in the range 0.002 < r < 0.06 and it equals to 11.6 ± 0.8 cal/g. At r > 0.07, ∆H _m and T _m decrease, and at r = 0.12 they equal to 6.4 ± 0.6 cal/g and 92.5 °C, accordingly. We suggest that such centers of binding are the well documented 5′CG3′ sites and G-quadruplex at r < 0.01, and negatively charged phosphate groups at r > 0.01. On the basis of ∆H _m invariability with simultaneous increase of T _m in the range 0.002 < r < 0.06, it is shown that the DNA-Cu(II)TOEPyP(4) complex melting is not of an enthalpic nature but of an entropic one. The two-phase helix–coil transition of DNA at r < 0.01 is considered as a result of porphyrin redistribution in the melting process.     

The surface oxidation behavior of Ni–45.16%Ti shape memory alloys at different temperatures

The isothermal oxidation behavior of Ni–45.16%Ti (composition in atomic percent) alloy was investigated by thermogravimetric analysis, and differential scanning calorimeter (DSC) methods. It was found that Ni-rich NiTi alloy exhibits a different oxidation behavior at temperatures above 400 °C in oxygen atmosphere. The alloy was exposed to oxygen atmosphere isothermally, i.e., between 400 and 800 °C, for 1 h. A gravimetric method was used to determine the oxidation kinetics and it was seen that the oxidation constant increases significantly with isothermal temperature. The activation energy of oxidation reaction for NiTi alloy was determined to be 65.47 kJ mol^?1. According to DSC measurements, the transformation temperature of alloy (M _s, M _f, A _s and A _f) was increased and also R phase disappeared above 500 °C. The formal oxides were determined by means of SEM–EDX measurements and obtained oxides are TiO and TiO₂ oxides.     

Quantum chemical calculations of stability constants: study of ligand effects on the relative stability of Pd(II)�Cpeptide complexes

Replacement of [Pd(H₂O)₄]²⁺ by cis-[Pd(en)(H₂O)₂]²⁺, [PdCl₄]^2?, and [Pd(NH₃)₄]²⁺ on the hydrolytic cleavage of the Ace-Ala-Lys-Tyr-Gly?CGly-Met-Ala-Ala-Arg-Ala peptide is theoretically investigated by using different quantum chemical methods both in the gas phase an in water solution. First, we carry out a series of validation calculations on small Pd(II) complexes by computing high-level ab initio [MP2 and CCSD(T)] and Density Functional Theory (B3LYP) electronic energies while solvent effects are taken into account by means of a Poisson-Boltzmann continuum model coupled with the B3LYP method. After having assessed the actual performance of the DFT calculations in predicting the stability constants for selected Pd(II)-complexes, we compute the relative free energies in solution of several Pd(II)?Cpeptide model complexes. By assuming that the reaction of the peptide with cis-[Pd(en)(H₂O)₂]²⁺, [Pd(Cl)₄]^2?, and [Pd(NH₃)₄]²⁺ would lead to the initial formation of the respective peptide-bound complexes, which in turn would evolve to afford a hydrolytically active complex [Pd(peptide)(H₂O)₂]²⁺ through the displacement of the en, Cl^?, and NH₃ ligands by water, our calculations of the relative stability of these complexes allow us to rationalize why [Pd(H₂O)₄]²⁺ and [Pd(NH₃)₄]²⁺ are more reactive than cis-[Pd(en)(H₂O)₂]²⁺ and [PdCl₄]^2? as experimentally found.     

Correlation of the extraction constants of the system Cd(II)–H3PO4/Cyanex 302–kerosene at different ionic strengths

Bromley's theory for calculating activity coefficients in order to correlate the values of cadmium extraction constant by Cyanex 302 from phosphoric acid solutions at different ionic strengths has been applied. A chemical model for the aqueous phase including the species H₃PO₄, H₂PO₄⁻, H₅P₂O₈⁻, H₆P₂O₈, CdHPO₄ and CdH₂PO₄⁺ has been considered. The increase observed for the extraction constant value when increasing the phosphoric acid concentration is probably due to the significant increase of the cadmium activity coefficient. A reaction extraction including water as a component has been proposed, and the value of the thermodynamic extraction constant of log K⁰=7.02 for the formation of CdR₂(HR) species, HR being the major component of Cyanex 302, has been obtained.     

Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (V_a) of 1-alkanols (carbon number, m=5, 6, 7) in - and -cyclodextrin (CD) solutions at 5.00 mmol kg^–1 have been determined as a function of alkanol concentration (C_a) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in C_a, V_a increased in -CD solution but decreased in -CD solution, asymptotically to a value of V_a in CD-free water. The dependence of V_a on C_a provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.     

The kinetics of reduction of palladium (II) complexes with β-alanine at dropping mercury electrode and the complexes’ stability constants

By using dc and ac polarography, the kinetics of electroreduction of the palladium (II) complexes with β-alanine at a dropping mercury electrode was studied in solutions with the palladium (II) concentration from 2 × 10^?5 to 2 × 10^?4 M and variable β-alanine and sodium perchlorate concentrations (pH 6–12). One polarographic wave was observed in solutions with pH 9 and 10 at the β-alanine overall concentration of c _βala = 1 × 10^?3 to 5 × 10^?2 M; two waves, at lower pH or higher c _βala. It was concluded on the formation of different forms of palladium (II) complexes in the studied solutions; the complexes contained two to four β-alanine coordinated anions. Using the limiting diffusion currents for the two waves at pH 9–11 and c _βala = 0.1 and 0.5 M, the stepwise stability constant for the Pd(βala) ₄ ^2? complex was calculated. Using two ac peaks observed at pH 7–8 and c _βala = 1 × 10^?2 to 0.1 M, the stepwise stability constant for the Pd(βala) ₃ ^? . was calculated. The perchlorate ions adsorbed at the dropping mercury electrode, as well as βala^? anions at their higher concentrations, hamper the electroreduction of the palladium (II) complexes with β-alanine.     

Determination of the stability constants of Pb–(DIPSO)x–(OH)y and Pb–(AMPSO)x–(OH)y systems

In this work, complexation between lead ion and the ligands 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) and N-(1,1-dimethyl-2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid (AMPSO), which are commercial pH buffers, is presented. Both ligands form complexes with lead in their pH buffer range (between pH 6.5 and 8.5 for DIPSO and between pH 8.0 and 9.0 for AMPSO). The final models and the overall stability constants, which are reported here, were determined by direct current polarography and glass electrode potentiometry [only for the Pb–(DIPSO)_x–(OH)_y system] at 25.0 °C and 0.1 M KNO₃ ionic strength. For the Pb–(DIPSO)_x–(OH)_y system, the proposed final model contains PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂ with stability constants, as log β, of 3.4 ± 0.1, 6.35 ± 0.15, 12.8 ± 0.2, and 18.0 ± 0.3, respectively. For the Pb–(AMPSO)_x–(OH)_y system, the species observed are PbL, PbL(OH), and PbL(OH)₂ with stability constants, as log β, of 2.9 ± 0.5, 9.4 ± 0.1, and 14.5 ± 0.2, respectively. For AMPSO, the possible adsorption of the ligand at the mercury electrode surface was evaluated by alternating current polarography through calculation of the capacitance of the double layer.     

X-ray study of volatile Ni(II), Cu(II), and Pd(II) complexes of β-ketoimine pivalyltrifluoroacetone

Synthesis of volatile complexes based on -ketoimine pivalyltrifluoroacetone, C(CH₃)₃C(NH)CH₂COCF₃, is described. The general formula of the complexes is M(L)₂, where M = Cu, Ni, Pd. Complexes of this kind with Ni and Pd were obtained for the first time. The Cu and Pd complexes were found to be isostructural. A comprehensive crystal-chemical study showed that all structures are molecular and built of trans-complexes. The central atom has a square plane environment. The average M-O and M-N distances are nearly equal in all compounds: 1.84 , 1.92 , and 1.98 for Ni, Cu, and Pd complexes, respectively; the mean values of the O-M-N chelate angles are 93.4°, 91.9°, and 92.7°, respectively.Original Russian Text Copyright © 2004 by I. A. Baidina, G. I. Zharkova, N. V. Pervukhina, S. A. Gromilov, and I. K. IgumenovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 713–722, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

The stability constants of ML and ML2 complexes of Be(II) and Co(II)—isoleucine according to paper ionophoretic data

Complexation reactions of isoleucine with beryllium(II) and cobalt(II) have been studied in solution phase using paper ionophoretic technique. The stability constants of ML and ML₂ complexes of Be(II)—isoleucine and Co(II)—isoleucine systems have been found to be (7.49 ± 0.07, 5.89 ± 0.03) and (4.57 ± 0.11, 2.99 ± 0.09) (logarithm stability constant values), respectively at ionic strength of 0.1 mol L^?1 and a temperature of 35°C.     

Formation kinetics of heteroligand Ni(II) complex with alkyl-substituted 2,2′-dipyrrolylmethenes

The formation kinetics of heteroligand Ni(II) complexes with alkylated dipyrrolylmethenes of symmetric and asymmetric structure was studied. The kinetic and activation parameters of the reactions were determined. The spectral and kinetic data obtained, as well as available data on the solvation of Ni(II) acetate in electron-donor solvents, allowed us to propose an associatively activated concerted mechanism. The Ni(II) complex formation is mainly determined by the rate of substitution of the entering ligand for solvent molecules in the initial Ni(II) complex, that is, by creation of conditions for efficient donor-acceptor interaction.     

Synthesis,structure and magnetism of a hydrogen-bond-linked three-dimensional network of a novel nickel(II)–cobalt(II)–nickel(II) complex containing a new macrocyclic mononuclear complex ligand

A novel trinuclear complex, [Co(NiL)₂(H₂O)₂](ClO₄)₂ · 2C₂H₅OH, was prepared by self-assembly using [NiL] as a new complex ligand; L is the dianion of dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate. The structure of the trinuclear complex was determined by X-ray crystallography. The Co^II ion is at the center of the trinuclear complex cation and occupies a distorted octahedral O₆ environment, approximating to O _h with a ⁴ T _1g ground state for Co^II that has an unquenched spin–orbit coupling reflected in the magnetic properties. Two Ni^II ions reside in completely same and slightly distorted square-planar N₄ coordination geometries. Co^II and each Ni^II are bridged by an oxamido group from one of the two macrocyclic ligands (L). O—H...O and ... interactions link the trinuclear fragments, perchlorate ions and C₂H₅OH molecules to form a three-dimensional supramolecular architecture.     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols at Ni(II)–quercetin complex modified multi-wall carbon nanotube paste electrode

A modified electrode Ni(II)–Qu–MWCNT-PE has been fabricated by electrodepositing nickel(II)–quercetin [Ni(II)–Qu] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. Ni(II)–Qu–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–MWCNT-PE and Ni(II)–Qu-carbon paste electrode. It also shows electrocatalytic activity toward the oxidation of methanol and other short chain aliphatic alcohols, such as ethanol, 1-propanol, and 1-butanol. The catalytic peak current and peak potential decrease in exponential form with the increase of carbon number of the chains. Kinetic parameters such as the electron transfer coefficient, α, rate constant, k _s, of the electrode reaction, and the catalytic rate constant, k _cat, for oxidation of methanol are determined. The stability and reproducibility of the Ni(II)–Qu–MWCNT-PE are good for practical applications.     

Synthesis of nickel(II) azacorroles by Pd-catalyzed amination of α,α'-dichlorodipyrrin Ni(II) complex and their properties

Synthesis of nickel(II) complexes of meso-aryl-substituted azacorroles was performed by Buchwald-Hartwig amination of a dipyrrin Ni(II) complex with benzylamine through C-N and C-C coupling. The highly planar structure of Ni(II) azacorroles was elucidated by X-ray diffraction analysis. (1)H?NMR analysis and nucleus independent chemical shift (NICS) calculation on Ni(II) azacorrole revealed its distinct aromaticity with [17]triaza-annulene 18π conjugation. In addition, acylation of azacorrole selectively afforded N- and C-acylated azacorroles depending on the reaction conditions, showing the dual reactivity of azacorroles.     

Spectrophotometric study of the complexation equilibria of cobalt(II) with 4-(5′-methyl-3′-isoxazolylazo)-resorcinol and determination of cobalt(II)

The reaction of cobalt(II) with 4-(5′-methyl-3′-isoxazolylazo)-resorcinol (MIAR) in 4% v/v ethanol-water medium at I = 0.1 M (NaClO₄) was investigated spectrophotometrically. Graphical and numerical calculation methods were used to establish the equilibria in solution and to evaluate the stability constant of the complexes formed (log β₁₀₁ = 7.48±0.06, log β₁₁₁ = 12.77 max 12.99, log β₁₀₂ = 16.41±0.07). The optimum conditions for the spectrophotometric determination of Co(II) with MIAR were established and the method applied to its determination in some low alloy steels and hydrofining catalysts.     

Ruthenium(II)–NNN complex catalyzed Oppenauer-type oxidation of secondary alcohols

Highly efficient Oppenauer-type oxidation of secondary alcohols to the corresponding ketones has been realized by means of the ruthenium(II) complex catalysts bearing a 2-(benzoimidazol-2-yl)-6-(3,5-dimethylpyrazol-1-yl)pyridine ligand. The oxidation reaction underwent in the presence of acetone as oxidant under mild conditions, reaching final TOF values up to 3960 h⁻¹. The hemilability of the ligand is attributed to the high catalytic activity of these Ru(II) complexes.     

An ESR study of the copper(II)–glycyl-l-serine and copper(II)–l-seryl-glycine systems by the simultaneous analysis of multi-component isotropic spectra. Formation constants and coordination modes

The formation constants and the isotropic ESR parameters (g-factors, ⁶³Cu, ⁶⁵Cu, ¹⁴N hyperfine coupling constants and relaxation parameters) of the various species were determined by the simultaneous analysis of a series of spectra, taken in a circulating system at various pH and ligand-to-metal concentration ratio. For both systems the new [CuLH]²⁺ complex was identified in acidic solutions. With the glycyl-l-serine ligand below pH 11.5 the same complexes and coordination modes are formed than with simple dipeptides. The side-chain donor group is bound only over pH 11.5 in the complex [CuLH₋₂(OH)]²⁻, where it is deprotonated and substitutes the carboxylate O in the third equatorial site. For the bis complex [CuLH₋₁(L)]⁻ an isomeric equilibrium was shown, where the difference between the isomers was based on which of the donor atoms of the ‘L’ ligand, the peptide O or the amino N, occupies the fourth equatorial position, and which one is coordinated axially. The l-seryl-glycine ligand forms the same species as simple dipeptides and glycyl-l-serine up to pH 8. The only difference is that the axial binding of the alcoholic OH group fairly stabilizes the bidentate equatorial coordination of the ‘L’ ligand through the amino N and peptide O atoms in the [CuL]⁺ complex as well as in the major isomer of the [CuLH₋₁(L)]⁻ complex. For this system we showed that (1) proton loss and the equatorial coordination of the alcoholic OH group occurs at relatively low pH (over pH 8–9), which results in the [CuL₂H₋₂]²⁻ complex with excess ligand, and also the newly identified species [Cu₂L₂H₋₄]²⁻: (2) this process is in competition with the proton loss of a coordinated water molecule. For both systems, the ESR-inactive species [Cu₂L₂H₋₃]⁻ was also shown.     

Phase transformations in Cd–Ni nanostructured system at elevated temperatures

Russian Chemical Bulletin - Using X-ray diffraction (both in vacuum and in air), derivatomass-spectrometry and thermo-programmed oxidation, phase transformations in nanostructured Cd–Ni...     

Preparation of α-alkyl-β-amino acids via β-alanine Ni(II) complex

A new β-amino acrylic acid Ni(II) complex has been developed and used for the synthesis of α-alkyl-β-amino acids via alkylation with alkyl halides under operationally convenient conditions. The pivotal α-alkylated intermediate can be converted into the corresponding α-alkyl-β-amino acids via two steps with a wide range of substituents.