The thermodynamic characteristics of point defects and the mechanism of charge transfer in lanthanum cobaltite doped with strontium and nickel

The specific conductivity and thermal electromotive force (EMF) coefficient of lanthanum cobaltite doped with strontium and nickel La_0.9Sr_0.1Co_0.9Ni_0.1O_3−δ were measured over the temperature and pressure ranges 1023–1223 K and 10⁻⁶−1 atm. The oxide was found to exhibit metallic-type conductivity (800 Ω⁻¹ cm⁻¹ ≤ σ ≤ 1150 Ω⁻¹ cm⁻¹) and small positive thermal EMF coefficient values. A joint analysis of the thermodynamic characteristics of formation of point defects and external T and p _{O 2} parameter dependences of conductivity and thermal EMF showed that charge was transferred in the oxide by small-radius polarons according to the hopping mechanism. The role of polarons was played by electrons Me ^′_Co and holes Me ^•_Co localized on 3d transition metals. The isothermal dependences of the concentrations and mobilities of charge carriers on the degree of oxygen nonstoichiometry of the oxide studied were calculated.

     

The thermodynamic parameters of oxygen nonstoichiometry defects in lanthanum cobaltite doped with acceptor impurities (Sr and Ni)

The oxygen nonstoichiometry δ of lanthanum cobaltite doped with acceptor impurities (Sr and Ni), La_{1 ? x} Sr_xCo_0.9Ni_0.1O_{3 ? δ} (x = 0.1, 0.3), was studied by high-temperature thermogravimetry over the temperature and pressure ranges 723 K ≤ T ≤ 1373 K and 10^?3 atm ≤ $p_{O_2 } $ ≤ 1 atm. The partial replacement of cobalt with nickel and lanthanum with strontium increased the oxygen nonstoichiometry δ. The partial molar enthalpies $\Delta \bar H^\circ _O $ and entropies $\Delta \bar S^\circ _O $ of solution of oxygen in the solid phase were calculated. Models of point defect formation were suggested and analyzed. The equilibrium constants of formation and concentrations of predominant point defects, ionized oxygen vacancies V _o ^.. , holes Me _Co ^. (Co _Co ^. and Ni _Co ^. ), and electrons Me _Co ^′ (Co _Co ^′ and Ni _Co ^′ ) localized on 3d transition metals, were determined by nonlinear regression from the experimental and theoretical logp $p_{O_2 } $ ?δ dependences.     

The diffusion of oxygen and ion transport in lanthanum cobaltite LaCoO<Subscript>3-δ</Subscript>

The chemical diffusion coefficient of oxygen vacancies and oxygen ion conductivity in lanthanum cobaltite LaCoO₃ were determined by the polarization method as functions of oxygen partial pressure \(p_{O_2 } \) (atm) and temperature T(K) over the ranges ?4 ≤ log \(p_{O_2 } \) ≤ 0 and 1173 K ≤ T ≤ 1323 K. The mobilities (cm²/(V s)) of oxygen vacancies calculated over the temperature range studied satisfy the inequalities 1.8 × 10^?5 ≤ \(v_{v_0 } \) ≤ 3.4 × 10^?5. The transfer numbers of oxygen vacancies were calculated. These numbers change depending on oxygen partial pressure over the range 5 × 10^?7 ≤ t ₀ ≤ 1 × 10^?5. The activation energy of self-diffusion of oxygen vacancies was found to be E _a= 104 ± 10 kJ/mol (1.1 ± 0.1 eV).     

The oxygen nonstoichiometry,defect structure,and thermodynamic characteristics of disordering of nickel-and iron-substituted lanthanum cobaltites

The oxygen nonstoichiometry of nickel-and iron-substituted lanthanum cobaltites of the compositions LaCo_1?x Ni _x O_3?δ (x = 0.1, 0.3) and LaCo_0.9Fe_0.1O_3?δ was studied by high-temperature thermogravimetric analysis over the temperature and oxygen partial pressure ranges 1223–1473 K and 10^?3–0.21 atm. The partial replacement of cobalt with nickel (an acceptor impurity) in lanthanum cobaltite was found to increase the number of defects in the oxygen sublattice, whereas the replacement with iron (a donor impurity) decreased this number. Correlations between the experimental \(\log p_{O_2 } = f(\delta )\) dependences and the suggested models of formation of point defects were analyzed taking into account the formation of Schottky defects. Interrelation between the defect structure, partial molar thermodynamic characteristics of oxygen release from the crystal lattices of the oxides studied, and the nature of substituting impurities (Ni and Fe) in lanthanum cobaltite was demonstrated.     

Defects in doped perovskite-like lanthanum cobaltite crystals La1−x SrxCo1−y MeyO3−δ (Me = Cu and Mn)

The paper presents a thermodynamic analysis of the formation of equilibrium defects in perovskitelike La_1?x Sr_xCo_1?y Me_yO_3?δ oxides, where Me = Cu or Mn, x = 0.0 or 0.3, and y = 0.0, 0.25, or 0.3, at high temperatures (873 K ≤ T ≤ 1373 K) depending on the composition and oxygen pressure (10^?8 atm ≤ $p_{O_2 } $ ≤ 1 atm). The results were used to study the nature of charge transfer. Small-radius polarons were shown to be responsible for the electric properties of the cobaltites under consideration; their concentrations and mobilities were calculated.     

Synthesis and Structure of 2-(1Н-Indol-1-yl)-6-ferrocenyl-4-(2-chloroimidazo[1,2-a]pyridin-3-yl)pyrimidine

A 2,4,6-trisubstituted pyrimidine including a 2-(1H-indol-1-yl) substituent was synthesized by the reaction of 1-ferrocenyl-3-(2-chloroimidazo[1,2-a]pyridin-3-yl)propanone with 2,5-dimethoxytetrahydrofuran. The structure of the synthesized compound was confirmed by IR and ¹Н NMR spectroscopy, and X-ray diffraction analysis. It has been shown that the ferrocene-containing compounds synthesized in the present work all demonstrate intramolecular charge transfer which is evidenced by the observation of the corresponding absorption bands with λ ^abs_max > 480 nm. The oxidation potential of ferrocene (E ^Fc_ox ) in all the compounds is higher than 700 mV.

     

A Bifunctional Perovskite Catalyst for Oxygen Reduction and Evolution

La_0.3(Ba_0.5Sr_0.5)_0.7Co_0.8Fe_0.2O_3?δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm‐scale rhombohedral LaCoO₃ cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A‐site cations with La³⁺ and local stress on Co‐site sub‐lattice with the cubic perovskite structure.     

A new method for electrocrystallization of AgTCNQF4 and Ag2TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile

Semiconducting AgTCNQF₄ (TCNQF₄ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been electrocrystallized from an acetonitrile (0.1 M Bu₄NPF₆) solution containing TCNQF₄ and Ag(MeCN) ⁺₄ . Reduction of TCNQF₄ to the TCNQF ¹⁻₄ anion, followed by reaction with Ag(MeCN) ⁺₄ forms crystalline AgTCNQF₄ on the electrode surface. Electrochemical synthesis is simplified by the reduction of TCNQF₄ prior to Ag(MeCN) ⁺₄ compared with the analogous reaction of the parent TCNQ to form AgTCNQ, where these two processes are coincident. Cyclic voltammetry and surface plasmon resonance studies reveal that the electrocrystallization process is slow on the voltammetric time scale (scan rate = 20 mV s⁻¹) for AgTCNQF₄, as it requires its solubility product to be exceeded. The solubility of AgTCNQF₄ is higher in the presence of 0.1 M Bu₄NPF₆ supporting electrolyte than in pure solvent. Cyclic voltammetry illustrates a dependence of the reduction peak potential of Ag(MeCN) ⁺₄ to metallic Ag on the electrode material with the ease of reduction following the order Au < Pt < GC < ITO. Ultraviolet-visible, Fourier transform infrared, and Raman spectra confirmed the formation of reduced TCNQF ¹⁻₄ and optical microscopy showed needle-shaped morphology for the electrocrystallized AgTCNQF₄. AgTCNQF₄ also can be formed by solid–solid transformation at a TCNQF₄-modified electrode in contact with aqueous media containing Ag⁺ ions. Chemically and electrochemically synthesized AgTCNQF₄ are spectroscopically identical. Electrocrystallization of Ag₂TCNQF₄ was also investigated; however, this was found to be thermodynamically unstable and readily decomposed to form AgTCNQF₄ and metallic Ag, as does chemically synthesized Ag₂TCNQF₄.

     

Thermodynamic protonation constants of vardenafil by the nonlinear regression of multiwavelength pH-spectrophotometric titration data

pH-spectrophotometric titration data were used to determine protonation constants of vardenafil at different ionic strengths I and temperatures of 25°C and 37°C. The use of two different multiwavelength and the multivariate treatment of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis is presented. The reliability of the protonation constants of the drug was proven with goodness-of-fit tests of the pH-spectra. The thermodynamic protonation constants log K _T ⁱ were estimated by a nonlinear regression of (log K, I) data using the Debye-Hückel equation, yielding log K ₄ ^T = 3.59(1) and 3.26(1), log K ₃ ^T = 5.64(1) and 5.81(1), log K ₂ ^T = 9.41(1) and 8.59(2), log K ₁ ^T = 10.92(2) and 10.05(1) at 25°C and 37°C, where the figure in brackets is the standard deviation in last significant digit. Concurrently, the experimental determination of four thermodynamic protonation constants was combined with the computational prediction of the MARVIN program based on knowledge of the chemical structures of the drug and was in good agreement with its experimental value. The factor analysis of spectra in the INDICES program predicts the correct number of light-absorbing components when the instrument error is known and when the signal-to-error ratio SER is higher than 10.      

Activation parameters of supercritical and gas-phase β-pinene thermal isomerization

New data on enthalpy and entropy contributions to the energy barrier of β-pinene thermal isomerization were obtained. The rate of β-pinene conversion is higher in supercritical EtOH (P = 120 atm) than in the gas phase (P ≤ 1 atm, without solvent, or for inert carrier gas N₂) at equal temperatures. The highest activation energy E _Σ of total β-pinene conversion is also observed in reactions in the supercritical (sc) condition. Activation parameters ΔH _Σ ^# , ΔS _Σ ^# , and ΔG _Σ ^# depend strongly on the reaction pressure. Thus, at P ≤ 1 atm (gas-phase reaction) the values of ΔS _Σ ^# are negative, while at sc conditions at P = 120 atm is positive. The linear dependences lnk _Σ0 ? E _Σ and ΔS _Σ ^# ? ΔS _Σ ^# indicate an isokinetic relation (IKR) and enthalpy-entropy compensation effect (EEC). The isokinetic temperature was calculated (T _iso = 605.5 ± 22.7 K). It was shown that elevation of temperature reduces the value of ΔG _Σ ^# (T) upon sc thermolysis only, whereas in all gas-phase reactions ΔG _Σ ^# (T) increases. At equal reaction temperatures, the greatest values of K _eq ^# (T) proved to be typical for thermolysis in sc-EtOH. We hypothesize that the rate of total β-pinene conversion increases dramatically due to a considerable shift in equilibrium toward higher concentrations of activated complex y _TS ^# . A detailed analysis of activation parameters shows that the IKR and EEC coincide, evidence of a common mechanism of β-pinene conversion observed under different reaction conditions, including thermolysis in sc-EtOH.     

The influence of pH on the stability constants of lanthanum and europium complexes with humic acids

Complex formation of humic acids (HA)_n with La³⁺ and Eu³⁺ was studied. Commercial (HA)_n was purified and characterized. The stability constants were determined at several pH values and 0.2?M NaClO₄ ionic strength by the Shubert??s method of radiochemical ionic exchange. The slopes of the lines $ \log ((\lambda_{0} /\lambda ) - 1) = \log \beta_{\text{M,j(HA)n}}^{\exp } + {\text{j}} * \log \left[ { ( {\text{HA)}}_{\text{n}} } \right] $ were dependent on the [(HA)_n]. The values of log $ \beta_{\text{M,j(HA)n}}^{\exp } $ for j?=?1 were the following: 6.29?±?0.04 (pH 4.9?±?0.4) and 7.61?±?0.03 (pH 5.9?±?0.1) for lanthanum and 7.31?±?0.01 (pH 5.9?±?0.2) for europium. Log $ \beta_{\text{M,j(HA)n}}^{\exp } $ was determined as well for higher values of the j parameter and these values were: 12.2?±?0.1 (j?=?2, pH 7.7?±?0.2), 15.6?±?0.2 (j?=?3, pH 4.9?±?0.4) and 16.05?±?0.07 (j?=?3, pH 5.9?±?0.1), for lanthanum and 13.18?±?0.03 (j?=?2, pH 5.9?±?0.1) for europium. A discussion is presented about the complex formation regarding pH and [(HA)_n].     

NMR Studies on Solution Structures of Methanol and Ethanol Saturated with CO2

²H and ¹⁷O NMR relaxation times, T ₁(²H) and T ₁(¹⁷O), and ²H NMR chemical shifts, δ(²H), in CO₂-saturated CD₃OD and C₂D₅OD solutions were measured at 313.2 K over the pressure range up to ~6 MPa. The rotational correlation times, τ _r, of the CD and OD axes within CD₃OD and C₂D₅OD molecules and the CO axis within the CO₂ molecule were determined from T ₁(²H) and T ₁(¹⁷O), and the magnetic susceptibility-corrected chemical shifts, δ _corr, were derived from δ(²H). The differences in τ _r and δ _corr observed between the two alcohol systems: τ _r and δ _corr of OD in C₂D₅OD, decreased rapidly with increasing CO₂ concentration, while those of OD in CD₃OD remained almost unchanged at mole fractions of CO₂, \( x_{\text CO_{2}} \) , lower than ~0.25 and then slightly decreased at higher \( x_{\text CO_{2}} \) . The hydrogen bonding structure in C₂D₅OD was found to be gradually broken down by CO₂ dissolution. On the other hand, in CD₃OD, it has been revealed that the hydrogen bonding structure can persist at \( x_{\text CO_{2}} \)  < ~0.25 but then collapses at higher \( x_{\text CO_{2}} \) .     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

New method for calculating the moments of thermally averaged densities of distribution of internuclear distances in polyatomic molecules using the Bloch integral equation

A convenient method is suggested for calculating thermally averaged powers of the normal vibrational coordinates Q _i by iteratively solving the Bloch integral equation with an anharmonic function of potential energy using multidimensional Hermite polynomials. Analytical formulas of the first approximation regarding anharmonicity constant have been obtained for the following moments of thermally averaged density: 〈Q ₁〉, 〈 Q ₁ ² 〉, 〈Q ₁ Q ₂〉, 〈Q ₁ ³ 〉 〈Q ₁ ³ 〉, 〈Q ₁ Q ₂ Q ₃〉, 〈Q ₁ ⁴ 〉, 〈Q ₁ ² Q ₂ ² 〉, 〈Q ₁ Q _2/3〉, 〈Q ₁ Q ₂ Q ₃ ² 〉, 〈 Q 1 Q ₂ Q ₃ Q ₄〉.     

Thermal properties of dimethylgold(III) 8-hydroxyquinolinate and 8-mercaptoquinolinate

Dimethylgold(III) complexes with 8-hydroxyquinoline Me₂Au(Ox) (I) and 8-mercaptoquinoline Me₂Au(Tox) (II) were synthesized and studied. Complex II obtained for the first time was identified from the elemental analysis, IR, ¹H NMR, and mass spectrometry data. The thermal properties of complexes I, II in condensed state were investigated by thermography. The temperature dependences of the saturated vapor pressure over crystals were measured by the Knudsen effusion method with mass spectrometric recording of the gas phase composition and the thermodynamic characteristics of the sublimation process were determined: for I, log P[Torr] = (14.6 ± 0.3) ? (6.34 ± 0.10) × 10³/(T, K), Δ H _subl ^o = 121.2 ± 1.9 kJ^?1, Δ S _subl ^o = 224.1 ± 4.6 J mol^?1 K^?1 (the temperature interval under study 80–115°C); for II, log P [Torr] = (13.3 ± 0.2) ? (6.30 ± 0.09) × 10³/(T, K), Δ H _subl ^o = 120.5 ± 1.7 kJmol^?1, ΔS _subl ^o = 199.3 ± 3.0 J mol^?1 K^?1 (86–145°C).     

Liquid secondary ion mass spectrometry of several β-diketonates of cobalt(III) and chromium(III)

The positive, liquid secondary ion (LSI) mass spectra of six cobalt(III) and three chromium(III) (β-diketonates ligand = L^?) were examined in a 3-nitrobenzyl alcohol matrix. The complexes of both metals yield clean, matrix-free mass spectra, but there are important differences between them. The cobalt compounds show prominent peaks assignable to the molecular ion, CoL ₃ ⁺ , of the monomeric chelates, together with abundant dimeric ions, such as Co₂L ₄ ⁺ and Co₂L ₃ ⁺ ; in contrast, chromium complexes show protonated monomers, CrL₃H⁺, in addition to ionized monomers, CrL ₃ ⁺ , and only minor formation of dimeric ions. The collisionally-activated dissociation (CAD) mass spectrum of Co₂L ₄ ⁺ shows fragmentation to CoL ₂ ⁺ and Co₂L ₃ ⁺ . That of Co₂L ₃ ⁺ shows fragmentation only to dimeric ions, including Co₂L ₂ ⁺ and, for thienyl or phenyl substituted ligands, to Co₂L₂Ar⁺ or Co₂LAr⁺ (Ar = thienyl or phenyl). Neither Co₂L ₄ ⁺ nor Co₂L ₃ ⁺ dissociates to the CoL ₃ ⁺ ion. The LSI mass spectrum of a mixture of two different cobalt chelates shows dimeric ions containing both types of ligand, which can be explained by ion-molecule reactions in the selvedge region. The differing behaviors of the cobalt and chromium complexes is attributed to the relatively greater stability of the +2 oxidation state for cobalt than for chromium.     

Structural basis of pyrazolopyrimidine derivatives as CAMKIIδ kinase inhibitors: insights from 3D QSAR,docking studies and in silico ADMET evaluation

Ca²⁺/calmodulin-dependent protein kinase II (CAMKIIδ) belongs to the serine/threonine kinase family, which is involved in a broad range of cellular events in cell survival and proliferation as well as a number of other signal transduction pathways. Thus, it is regarded a promising target for treatment of cancers. In the present paper, a three-dimensional quantitative structure–activity relationship and molecular docking were applied to investigate a series of new CAMKIIδ inhibitors of pyrazolopyrimidine derivatives. The determination coefficient (R²) and leave-one-out cross-validation coefficient (Q²) of CoMSIA model are 0.676 and 0.956, respectively. The predictive ability of this model was evaluated by the external validation using a test set of eight compounds with a predicted determination coefficient \(R^{ 2}_{\text{test}}\) of 0.80, besides the mean absolute error of the test set was 0.328 log units. Docking results are in concordance with CoMSIA contour maps, gave the information for interactive mode exploration. Based on those satisfactory results, newly designed molecules were predicted with highly potent CAMKIIδ inhibitory activity, additionally, they have showed promising results in the preliminary in silico ADMET evaluations. This study could expand our understanding of pyrazolopyrimidine derivatives as inhibitors of CAMKIIδ and would be of great help in lead optimization for early drug discovery of highly potent CAMKIIδ inhibitors.     

Synthesis,structure, physicochemical properties,and solid-phase thermolysis of Co<Subscript>2</Subscript>Sm(Piv)<Subscript>7</Subscript>(2,4-Lut)<Subscript>2</Subscript>

Heterometallic pivalate Co₂Sm(Piv)₇(2,4-Lut)₂ (1) was prepared for the first time and structurally characterized at 293 and 160 K. Antiferromagnetic exchange interactions are dominant in complex 1. This compound experiences a first-order phase transition within 210–260 K. A set of thermodynamic functions was obtained for this complex (C _p , H _T ⁰ - H ₁₈₀ ⁰ , and S _T ⁰ ), and parameters were determined for solid-phase thermolysis where samarium cobaltate SmCoO₃ is the only product.     

Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV-Xα method

Optical absorption spectra of cobalt cluster ions, Co _n ⁺ , and vanadium cluster ions, V _n ⁺ , were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co ₄ ⁺ , Co ₃ ⁺ , and V ₄ ⁺ have, respectively, a tetrahedral structure with a bond distance of 2.00Å, an equilateral triangle with a bond distance of 2.30Å, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Å and one of 2.89Å. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co ₃ ⁺ , Co ₄ ⁺ , and V ₄ ⁺ , respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.