Thermochemical Study Research Articles

Unraveling the antioxidant potential of thiamine: Thermochemical and kinetics studies in aqueous phase using DFT

AbstractThe scavenging mechanism of thiamine (or vitamin B1) towards HO• and HOO• radicals has been revisited using density functional theory (DFT) at the M05‐2X/6‐311++G (d,p) level of theory. Enthalpies and Gibbs free energies of four common antioxidant reactions, i.e. formal hydrogen transfer (FHT), proton transfer (PT), single electron transfer (SET) and radical adduct formation (RAF), have been systematically calculated in the aqueous phase. Potential energy profiles accompanied with the optimized structures of all transition states (TS) and intermediate ones were also established. As a result, thiamine represents as a potent antioxidant notably via RAF mechanism with the lowest ΔH0 values at C12 position equal to ‐37.5 and ‐9.2 kcal/mol towards HO• and HOO• radicals, respectively. The reactions are also favorable with ΔG0 values of ‐28.8 and 2.8 kcal/mol, respectively. The order of the decrease in preponderance of the studied mechanism is as follows: RAF > FHT > SET > PT. The scavenging reactivity towards HO• radical is considerably higher than the one toward HOO• radical as expected. In comparing with trolox and ascorbic acid, their antioxidant potential could be classified in the decreasing order: ascorbic acid > thiamine > trolox.

Production of Mo2MB2-type (M = Ni, Fe, Co) ternary boride containing alloys by self-propagating high temperature synthesis

In this study, the production of Mo2MB2 (M: Ni, Fe, and Co) ternary boride containing alloys from their oxides by aluminothermic self-propagating high-temperature synthesis (SHS) method was investigated. The influence of different initial reactant ratios on the concurrent synthesis of reinforcement and matrix phases was studied. The thermochemical modeling studies were conducted to estimate the adiabatic temperature (Tad) change as well as high-temperature products. The phases, microstructure and chemical composition of the products were analyzed by X-ray diffraction, scanning electron microscopy (SEM) and atomic absorption spectroscopy (AAS) methods, respectively. It was found that, in the optimum conditions, the in-situ composite materials with Mo2MB2 as the reinforcement phases (i.e. Mo2NiB2, Mo2CoB2, or Mo2FeB2) and M3Al/M20Al3B6 intermetallic compounds as the matrix phases (i.e. Ni3Al/Ni20Al3B6, Co20Al3B6, or Fe3Al) can be synthesized by SHS method. Increasing both the B2O3/Al ratio (i.e. from 0.28 to 0.72) and MxOy/MoO3 ratio (i.e. from 0.58 to 1.5) significantly decreased the residual Al content and increased ternary boride phases in the products. It was also revealed that the microhardness values of these SHS produced alloys can reach up to 1301 ± 162 HV.

Thermodynamic properties of fluorapophyllite-(k) and hydroxylapophyllite-(k)

Thermochemical study of natural minerals of the apophyllite group: fluorapophyllite-(K) KCa4[Si8O20]F . 8H2O (Maharashtra, India) (I) and hydroxylapophyllite-(K) KCa4[Si8O20]OH . 8H2O (Norilsk, Russia) (II) were performed on a high-temperature heat-flux microcalorimeter Tian–Calvet “Setaram” (France) using the melt solution calorimetry method. The first data on the enthalpies of formation from the elements for the minerals studied are obtained: -13 205±13 kJ/mol (I) and -13 054±20 kJ/mol (II). The values of their standard entropies and Gibbs energies of formation are estimated.

Thermochemical analysis of smelting of ferruginous manganese ore for silicomanganese production

Ferruginous manganese ores contain high concentrations of iron and having low Mn/Fe ratio and are not suitable to produce standard grade of silicomanganese. Thermochemical calculations based on available thermodynamics databases were used to understand the smelting behavior of the ore mix consisting of ferruginous manganese ore and slag from high carbon ferromanganese. A basicity map was constructed in terms of input burden material basicity B (= (CaO wt%+MgO wt%)/SiO2 wt%) and input R (= (CaO wt%+ MgO wt%)/Al2O3 wt%) value for estimating the optimum operating basicity window for low manganese and silicon partition ratio or high alloy recovery. Various experiments were conducted to check the maximum grade and recovery of the alloy based on the thermochemical equilibrium simulation study. The present study reveals usefulness of preliminary thermochemical calculations to facilitate process design and development of silicomanganese smelting using ore mix consisting of ferruginous manganese ore and slag from high carbon ferromanganese.

Natural kaersutite: ftir, raman, thermal and thermochemical investigations

A thermochemical study of the natural oxo-amphibole ─ kaersutite Na0.4K0.3(Ca1.6Na0.4)(Mg2.9Fe0.82+Al0.7Ti0.6Fe0.53+)[Si6.1Al1.9O22](OH)0.2O1.8.(alkaline basalts of Mongolia) was performed on a Tian-Calvet microcalorimeter. The enthalpy of formation from the elements ∆fH el0(298.15 K) = – 12102 ± 16 kJ/mol) was obtained by the method of high-temperature melt solution calorimetry. The entropy, enthalpy and Gibbs energy of the formation of the end-members of the isomorphic series kaersutite NaCa2Mg3TiAl[Si6Al2O22]O2 – ferri-kaersutite NaCa2Mg3TiFe3+[Si6Al2O22]O2 were estimated.

Synthesis, thermochemical and quantum chemical studies on antimony(III) and bismuth(III) complexes with 2,2′-bipyridine and 1,10-phenanthroline

A thermochemical study of [SbCl3(L)] and [BiBr3(L)] complexes, wherein L is 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen), was performed by calorimetric measurements in solution. The complexes were synthesized and characterized by elemental analysis, FTIR spectroscopy and thermal analysis. From the enthalpies of dissolution of the complexes, salts and ligands in combination with auxiliary thermodynamic data, some thermochemical parameters of the complexes were determined by use of thermochemical cycles. Theoretical study on the complexes was performed using M06-2X/def2-TZVPP method. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Our findings suggest that both the reorganization energy of the acceptor metal trihalide MX3 (113–136 kJ · mol−1) and the rigidity of the phen govern the dissociation energy of the complexes. The theoretical results indicated that the chemical stabilities of the complexes decreases in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], agreeing with the experimental enthalpies of coordination in solid state.

Development of the Integrated Approach to Stratigraphic Subdivision and Correlation of Middle–Upper Jurassic Deposits in Southeastern West Siberia

On the basis of integrated paleobotanic, lithogeochemical, IR-spectrometric, and thermochemical studies, stratigraphic subdivision and correlation of productive Middle–Upper Jurassic sediments represented by the Tyumen and Naunak formations in the Dvoinaya and Snezhnaya areas (southeastern part of West Siberia, central Tomsk oblast) are carried out. A reliable basis is created for an optimal correction of reserves calculation and effective development of hydrocarbon deposits. It is found that the index species among paleobotanic remains of the Tyumen Formation are the ferns Coniopteris vialovae and Raphaelia diamensis and Czekanowskiales Czekanowskia irkutensis, Cz. rigida, and Phoenicopsis mogutchevae; for the Naunak Formation, it is Czekanowskia tomskiensis. This is due to the paleoclimatic environment which predetermined the compositions of plant communities and the species of coal-forming plants. For reliable correlation, a lithogeochemical study of sediments is carried out taking into account the analysis of coal origin. The difference in composition of plant complexes in the studied formations is confirmed by the difference in genetic properties of the marking coal-bearing deposits: degree of biochemical stability of the organic mass of the peat, gelification, and floristic restorability of the organic mass in coals, as well as yields of light and heavy hydrocarbons.

Mechanism of Catalytic O2 Reduction by Iron Tetraphenylporphyrin.

The catalytic reduction of O2 to H2O is important for energy transduction in both synthetic and natural systems. Herein, we report a kinetic and thermochemical study of the oxygen reduction reaction (ORR) catalyzed by iron tetraphenylporphyrin (Fe(TPP)) in N, N'-dimethylformamide using decamethylferrocene as a soluble reductant and para-toluenesulfonic acid ( pTsOH) as the proton source. This work identifies and characterizes catalytic intermediates and their thermochemistry, providing a detailed mechanistic understanding of the system. Specifically, reduction of the ferric porphyrin, [FeIII(TPP)]+, forms the ferrous porphyrin, FeII(TPP), which binds O2 reversibly to form the ferric-superoxide porphyrin complex, FeIII(TPP)(O2•-). The temperature dependence of both the electron transfer and O2 binding equilibrium constants has been determined. Kinetic studies over a range of concentrations and temperatures show that the catalyst resting state changes during the course of each catalytic run, necessitating the use of global kinetic modeling to extract rate constants and kinetic barriers. The rate-determining step in oxygen reduction is the protonation of FeIII(TPP)(O2•-) by pTsOH, which proceeds with a substantial kinetic barrier. Computational studies indicate that this barrier for proton transfer arises from an unfavorable preassociation of the proton donor with the superoxide adduct and a transition state that requires significant desolvation of the proton donor. Together, these results are the first example of oxygen reduction by iron tetraphenylporphyrin where the pre-equilibria among ferric, ferrous, and ferric-superoxide intermediates have been quantified under catalytic conditions. This work gives a generalizable model for the mechanism of iron porphyrin-catalyzed ORR and provides an unusually complete mechanistic study of an ORR reaction. More broadly, this study also highlights the kinetic challenges for proton transfer to catalytic intermediates in organic media.

Thermochemical Study of Sodium and Sodium–Calcium Amphibols

Thermochemical Study of Sodium and Sodium–Calcium Amphibols

Development of the integrated approach for stratigraphic dissolution and correlation of Middle–Upper Jurassic disturbances of south-east of western Siberia

Based on complex paleobotanical, lithogeochemical, IR spectrometry and thermochemical studies, stratigraphic dismemberment and correlation of productive Middle–Upper Jurassic sediments, represented by Tyumen and Naunak formations in the Dvojnaya and Snezhnaya areas, in the southeast of Western Siberia (the central part of the Tomsk Region) were carried out. A reliable basis has been created for an optimal correction of the calculation of reserves and effective development of hydrocarbon deposits. It is established that for the Tyumen formation the leading paleobotanical remains are the ferns of Coniopteris vialovae, Raphaelia diamensis and Czekanowski czekanowskia irkutensis, Cz. rigida, Phoenicopsis mogutchevae, and for the Naunak formation – Czekanowski czekanowskia tomskiensis. This is due to the paleoclimatic situation, which predetermined the composition of the plant community and the types of plant-coal-forming plants. For reliable correlation, a lithogeochemical study of sediments was carried out, taking into account the analysis of the origin of the coal. The difference in the composition of plant complexes in the suites was confirmed by the difference in the genetic properties of the marking coal-bearing deposits: the degree of biochemical stability of the organic mass of the peat, the level of gelification and the floral regeneration of the organic mass of the coals, and also the yields of light and heavy hydrocarbons.

Production of hydrocarbons from a green algae (Oscillatoria) with exploration of its fuel characteristics over different reaction atmospheres

Authors conducted non-catalytic, catalytic, and hydropyrolysis at 550 °C temperature and 1 bar pressure to produce biofuels from an ignored algal biomass of Oscillatoria by thermo-chemical degradation study in a tubular reactor having an internal diameter of 25 mm and 300 mm of active length covered by a furnace of a single heating zone. The catalysts used for the catalytic pyrolysis and hydropyrolysis study are TiO2: ZnO on 1:1 basis. Characterization of bio-oils by Fourier Transform Infrared Spectroscopy (FTIR) shows substantial variation in functional groups of all three types of bio-oils. Gas Chromatography-Mass Spectroscopy (GCMS) gives a detailed list of available hydrocarbons in bio-oil samples and proton NMR confirms the functionality of bio-oil by available proton assignments. Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) shows morphology and the structural analogy of biochars with respect to biomass. Calorific values of three types of bio-oils ranges from 16.597 to 16.664 MJ/kg; and revealed that this particular biomass has potential as a resource of feedstock with an approximate yield of one-third of biomass on the dry weight basis. The pH of these bio-oils obtained from green algae varies in the range of 8.25 to 6.07 that indicates the less number of oxygenated compounds unlike very low pH bio-oils obtained from other types of biomass feedstock. Additionally, present results revealed that these bio-oils include formative compounds of most popular hydrocarbons, i.e., benzene, toluene and xylene (BTX). Further, they also include furans, phenols, benzaldehyde, guaiacol, caprolactam, styrene, oximes, etc. which can be used as green chemicals.

Chemical Aspects of the Candidate Antiferromagnetic Topological Insulator MnBi2Te4

Crystal growth of MnBi$_{2}$Te$_{4}$ has delivered the first experimental corroboration of the 3D antiferromagnetic topological insulator state. Our present results confirm that the synthesis of MnBi$_{2}$Te$_{4}$ can be scaled-up and strengthen it as a promising experimental platform for studies of a crossover between magnetic ordering and non-trivial topology. High-quality single crystals of MnBi$_{2}$Te$_{4}$ are grown by slow cooling within a narrow range between the melting points of Bi$_{2}$Te$_{3}$ (586 {\deg}C) and MnBi$_{2}$Te$_{4}$ (600 {\deg}C). Single crystal X-ray diffraction and electron microscopy reveal ubiquitous antisite defects in both cation sites and, possibly, Mn vacancies. Powders of MnBi$_{2}$Te$_{4}$ can be obtained at subsolidus temperatures, and a complementary thermochemical study establishes a limited high-temperature range of phase stability. Nevertheless, quenched powders are stable at room temperature and exhibit long-range antiferromagnetic ordering below 24 K. The expected Mn(II) out-of-plane magnetic state is confirmed by the magnetization, X-ray photoemission, X-ray absorption and linear dichroism data. MnBi$_{2}$Te$_{4}$ exhibits a metallic type of resistivity in the range 4.5-300 K. The compound is an n-type conductor that reaches a thermoelectric figure of merit up to ZT = 0.17. Angle-resolved photoemission experiments provide evidence for a surface state forming a gapped Dirac cone.

Influence of the La6W2O15 Phase on the Properties and Integrity of La6-xWO12-?–Based Membranes

The aim of the present work is to evaluate the influence of La 6 W 2 O 15 secondary phase on the properties and integrity of La 6-x WO 12-? –based membranes. Structural, microstructural and thermo–chemical study was carried out evidencing significant crystallographic and thermal expansion anisotropy: the reason for poor thermo–mechanical stability of La 6 W 2 O 15 . Conductivity of La 6 W 2 O 15 was one to two orders of magnitude lower compared to the phase pure La 6-x WO 12-? in the range of 300 to 900 °C. The relaxation study showed that the hydration process was faster for the La 6 W 2 O 15 compared to the LWO phase, due to the higher electronic contribution to the total conductivity. Short–term stability tests in H 2 at 900 °C and in a mixture of CO 2 and CH 4 at 750 °C were conducted and material remained stable. Remarkable reactivity with NiO and YSZ at elevated temperatures was further evidenced compared to the relative inert behavior towards MgO and CGO. Keywords: La 6 W 2 O 15 , La 6-x WO 12-? , mixed protonic–electronic conductor, dense ceramic membrane, hydrogen separation.

Spectral and thermochemical research of the DNA polyplex with chitosan formation process and the influence of anionic and cationic compounds.

In this paper, the results of a spectral and thermochemical study of the DNA polyplex formation with chitosan and the effect of ethidium bromide polyplexes, sodium dodecyl sulfate, n-octyltrimethyl ammonium bromide, poly(4-styrenesulfonic acid), and heparin on the stability of the complexes are considered. It has been established that chitosan forms thermodynamically stable complexes with ethidium bromide (EtBr), in which there exists one monomer unit of chitosan for two ethidium bromide ones. The interaction of ethidium bromide with chitosan leads to a charge exchange of the polymer surface. The impact of chitosan on the intercalated DNA-EtBr complex conditions a release of EtBr with a polyplex formation. The process of polyplex formation in the presence of ethidium bromide proceeds endothermically, and in its absence the reaction is exothermic. The polyplex particles formed from DNA after release of EtBr are larger and have a smaller charge, as compared to the polyplex particles obtained without ethidium bromide. It has been found that anionic compounds cause the degradation of polyplexes, and it can prove to be a significant obstacle for using chitosan polyplexes in transfection, since in the presence of heparin in the bloodstream, the complexes will break down before reaching the target.

Recovery of 3-hydroxypropionic acid from organic phases after reactive extraction with amines in an alcohol-type solvent

Reactive extraction is a well-known method for the recovery of organic acids from dilute streams. The extraction through complex formation with amines is followed by its back-extraction. Their affinity for amine extractants makes their back-extraction a limiting step. The case of 3-hydroxypropionic acid is addressed here. Three methods were compared: salts additions, diluent swing and temperature swing. Mineral bases led to complete 3-HP recovery but as a salt. Diluent swing was tested using n-hexane as the anti–solvent. Results showed that increasing the n-hexane content led to a great increase of 3-HP recovery. However, high recovery yields are associated with high dilutions. The temperature was varied from 4 to 140 °C and it led to a high decrease of the acid-amine complex formation. Our thermochemical study showed an apparent heat of reaction of −25.3 kJ/mol and, at 140 °C, 78% of 3-HP can be recovered in a single step.

Thermodynamic properties of ε-caprolactam and ε-caprothiolactam

This paper is concerned with experimental and computational thermochemical studies of ε-caprolactam and ε-caprothiolactam, molecules whose flexible ring structure provides several conformational forms.The gas-phase standard enthalpy of formation at the reference temperature of 298.15 K of the two title compounds have been determined from the enthalpy of formation in the crystalline phase, derived from bomb combustion calorimetry, and from the enthalpy of sublimation, derived from Calvet microcalorimetry and Knudsen effusion techniques.The equilibrium geometries and the thermodynamic properties of three minimum energy conformers obtained with the composite G3(MP2)//B3LYP approach were used to determine the conformational composition of the two lactam derivatives, by means of Boltzmann’s distribution. The computed gas-phase standard molar enthalpies of formation of ε-caprolactam and ε-caprothiolactam have been determined using hypothetical gas-phase reactions, taking into account the conformational compositions of each one of the species. This parameter together with the corresponding experimental one are compared.

A thermochemical computational study on hydroxyquinolines and their azulene analogues

Ab initio CBS-QB3 method has been used to determine gas-phase enthalpies of formation for 34 compounds including a number of hydroxyquinoline isomers, the corresponding azulene analogues and their parent systems. The mean absolute deviation of 4.43 kJ/mol reveals good agreement between our results and the available experimental data. Relative thermodynamic stabilities of hydroxyquinoline isomers and related analogues were discussed and several isomerization reactions enthalpies were derived. The same level of theory has also been utilized to calculate adiabatic ionization energies and electron affinities for the molecules with known experimental values and the agreement between theory and experiment was found to be within 8 kJ/mol.

Homolytic S Cl bond dissociation enthalpies of sulfenyl chlorides – a high-level G4 thermochemical study

Numerous reactions between sulfenyl chlorides and organic molecules proceed by way of radical reactions, in which homolytic cleavage of the SCl bond is a key step. Owing to the lack of data concerning the quantitative effect of substituents in governing the strength of SCl bonds toward homolytic cleavage, the present article reports an extensive dataset of gas-phase SCl bond dissociation enthalpies (BDEs) obtained using the high-level G4 thermochemical protocol. The BDEs of the species in this set range from 207.2 (ONSCl) to 279.7 kJ mol−1 (tBuSCl), with HSCl having a BDE of 267.6 kJ mol−1. In addition, the gas-phase SCl BDEs of six sulfonyl chlorides have also been reported, and these range from 267.2 kJ mol–1 (CF3SO2Cl) to 283.0 kJ mol−1 (FSO2Cl).

A Thermochemical Parameters and Theoretical Study of the Chlorinated Compounds of Thiophene

This contribution sets out to compute thermochemical and geometrical parameters of the complete series of chlorinated isomers of thiophene based on the accurate chemistry model of CBS-QB3. Herein, we compute standard entropies, standard enthalpies of formation, standard Gibbs free energies of formation, and heat capacities. Our calculated enthalpy values agree with available limited experimental values. The DFT-based reactivity descriptors were used to elucidate the site selectivity for the chlorination sequence of thiophene. The relative preference for chlorination was found to be in accord with the thermodynamic stability trends inferred based on the H scale. Calculated Fukui indices predict a chlorination sequence to ensue as follows: 2-chloro → 2,5-dichloro → 2,3,5-trichloro → 2,3,4,5-tetrachlorothiophene.

Calorimetric Computation of Enthalpy of Formation of Trisacetylacetonato Chromium(III) [Cr(C5H7O2)3(c)

From thermochemical studies of organometallic compounds, a host of thermodynamic parameters viz., heat capacity, entropy, Gibbs energy etc., can be evaluated. The present communication deals with the evaluation of enthalpy of combustion and thereby estimation of enthalpy of formation of crystalline trisacetylacetonato chromium(III) [Cr (C5H7O2)3 (c)] or [Cr (acac)3 cH) and enthalpy of formation fH° –1 –1 respectively. Experimental data obtained are in good agreement with one another.