Thermochemical Features Research Articles

Investigation of thermochemical features of L-alanyl-glycine and β-alanyl-L-histidine (L-carnosine)

Thermal analysis of two dipeptides having alanine (Ala) as first term, using combustion calorimetry method and simultaneous TG-DSC measurements, have been carried out. The enthalpies of combustion and formation, the TG-DSC quantities related to the decomposition processes of these compounds, were compared with those of the free –α-amino acids contained in the dipeptides.Information about the stability and the influence of the components on the decomposition processes of the dipeptides was obtained.

DFT Meets Wave-Function Composite Methods for Characterizing Cytosine Tautomers in the Gas Phase.

A general strategy for the accurate computation of structural and spectroscopic properties of biomolecule building blocks in the gas phase has been further improved and validated with a special reference to tautomeric equilibria. The main improvements concern the use of the cc-pVTZ-F12 basis set in both DFT and CCSD(T)-F12 computations, the inclusion of core-valence correlation in geometry optimizations by double hybrid functionals, and the use of the cc-pVQZ-F12 basis set for complete basis set extrapolation at the MP2-F12 level. The resulting model chemistry is applied to the challenging problem of cytosine tautomers in the gas phase. The results are in remarkable agreement with experiment concerning both rotational and vibrational spectroscopic parameters and permit their unbiased interpretation in terms of structural and thermochemical features. Together with the intrinsic interest of the studied molecule, the accuracy of the results obtained at reasonable cost without any empirical parameter suggests that the proposed composite method can be profitably employed for accurate investigations of other molecular bricks of life.

Ameliorated optical, luminescent and thermo-chemical features of polymer derived PPy-SnO2 nanocomposite as efficient emissive layer material (EML)

PPy-SnO2 (PS) nanocomposite was synthesized with varying doses of SnO2 through in-situ oxidative polymerization technique. Morphological study was performed through FESEM analysis. Particle size of the 15% PS nanocomposite was estimated in the 13–35 nm range by XRD analysis. Elemental presence and its deconvoluted states in the 15% PS nanocomposite were confirmed by XPS analysis. Optical band gap for optimized 15% PS was calculated ∼1.83 eV. PL intensity increases with increase in the concentration of SnO2. Its value was found highest for 15% PS laid in the light blue region (close to white light). CIE color coordinate study of the nanocomposites elucidated that optimized 15% PS could be used as efficient emissive layer material for WLED application. A comparative TGA study of the PPy and 15% PS illustrated that optimized 15% PS nanocomposite proved to have better thermal stability.

Investigation of thermochemical Features of Gamma Irradiated Tryptophan Stereoisomers

Abstract. In this work, the use of differential scanning calorimetry (DSC) is demonstrated as a powerful technique that can provide accurate thermodynamic property values of nutritional supplements such as tryptophan. Nutritional supplements require a decontamination procedure and irradiation appears as a promising technique for this purpose. The valuable properties of tryptophan for food and pharmaceutical industry as dietary supplement have led to increasing interest in its technological behaviour. L-, D- isomers and DL-racemic mixture of tryptophan irradiated and non-irradiated were studied by DSC. Irradiation was performed at room temperature with gamma radiations using a 137Cs source, the irradiation dose range was between 0.6- 10 kGy. Two steps decomposition pattern for both irradiated and non-irradiated samples up to 350 oC was found. Fourier transform infrared spectroscopic studies were performed. The obtained results indicate that the irradiation process does not inhibit the thermal properties of tryptophan when irradiated up to 10 kGy. The HPLC method was employed to evidence the degradation of the irradiated material.
 
 Resumen. En este trabajo, se demuestra el uso de calorimetría diferencial de barrido (DSC) como una técnica poderosa que puede proporcionar valores precisos de propiedades termodinámicas de suplementos nutricionales como el triptófano. Los suplementos nutricionales requieren un procedimiento de descontaminación y la irradiación aparece como una técnica prometedora para este propósito. Las valiosas propiedades del triptófano para la industria alimentaria y farmacéutica como suplemento dietético han provocado un creciente interés por su comportamiento tecnológico. Los isómeros L-, D- y la mezcla racémica DL- de triptófano irradiado y no irradiado fueron estudiados por DSC. La irradiación se realizó a temperatura ambiente con radiaciones gamma utilizando una fuente de 137Cs, el rango de dosis de irradiación estuvo entre 0.6 - 10 kGy. Se encontró un patrón de descomposición de dos pasos para muestras irradiadas y no irradiadas hasta 350 ºC. Se realizaron estudios espectroscópicos de infrarrojos por la transformada de Fourier. Los resultados obtenidos indican que el proceso de irradiación no inhibe las propiedades térmicas del triptófano cuando se irradia hasta 10 kGy. Se empleó el método HPLC para evidenciar la degradación del material irradiado.

A Disequilibrium Reactive Transport Model for Mantle Magmatism

AbstractBesides standard thermo-mechanical conservation laws, a general description of mantle magmatism requires the simultaneous consideration of phase changes (e.g. from solid to liquid), chemical reactions (i.e. exchange of chemical components) and multiple dynamic phases (e.g. liquid percolating through a deforming matrix). Typically, these processes evolve at different rates, over multiple spatial scales and exhibit complex feedback loops and disequilibrium features. Partially as a result of these complexities, integrated descriptions of the thermal, mechanical and chemical evolution of mantle magmatism have been challenging for numerical models. Here we present a conceptual and numerical model that provides a versatile platform to study the dynamics and nonlinear feedbacks inherent in mantle magmatism and to make quantitative comparisons between petrological and geochemical datasets. Our model is based on the combination of three main modules: (1) a Two-Phase, Multi-Component, Reactive Transport module that describes how liquids and solids evolve in space and time; (2) a melting formalism, called Dynamic Disequilibirum Melting, based on thermodynamic grounds and capable of describing the chemical exchange of major elements between phases in disequilibrium; (3) a grain-scale model for diffusion-controlled trace-element mass transfer. We illustrate some of the benefits of the model by analyzing both major and trace elements during mantle magmatism in a mid-ocean ridge-like context. We systematically explore the effects of mantle potential temperature, upwelling velocity, degree of equilibrium and hetererogeneous sources on the compositional variability of melts and residual peridotites. Our model not only reproduces the main thermo-chemical features of decompression melting but also predicts counter-intuitive differentiation trends as a consequence of phase changes and transport occurring in disequilibrium. These include a negative correlation between Na2O and FeO in melts generated at the same Tp and the continued increase of the melt’s CaO/Al2O3 after Cpx exhaustion. Our model results also emphasize the role of disequilibrium arising from diffusion for the interpretation of trace-element signatures. The latter is shown to be able to reconcile the major- and trace-element compositions of abyssal peridotites with field evidence indicating extensive reaction between peridotites and melts. The combination of chemical disequilibrium of major elements and sluggish diffusion of trace elements may also result in weakened middle rare earth to heavy rare earth depletion comparable with the effect of residual garnet in mid-ocean ridge basalt, despite its absence in the modelled melts source. We also find that the crystallization of basalts ascending in disequilibrium through the asthenospheric mantle could be responsible for the formation of olivine gabbros and wehrlites that are observed in the deep sections of ophiolites. The presented framework is general and readily extendable to accommodate additional processes of geological relevance (e.g. melting in the presence of volatiles and/or of complex heterogeneous sources, refertilization of the lithospheric mantle, magma channelization and shallow processes) and the implementation of other geochemical and isotopic proxies. Here we illustrate the effect of heterogeneous sources on the thermo-mechanical-chemical evolution of melts and residues using a mixed peridotite–pyroxenite source.

On the chemical composition and pyrolytic behavior of hybrid poplar energy crops from northern Spain

Short Rotation Woody Coppices (SRWCs) where several tree species and clones grown on marginal land typically over 3–10 year cycles have been recognized as providers of sustainable energy and as feedstocks for producing other fuels and chemicals. A thorough physical and chemical characterization is crucial for understanding and optimizing harvesting and production strategies. Accordingly, this study focuses on the evaluation of chemical and thermochemical features of three parts of harvested shoots (base and middle of the shoot, and branches) of selected hybrid poplars of short rotation -AF2, Beaupré and I214 of 5, 9 and 8 years-old, respectively-. Results show a decrease in the ash content from the top to the base of each species with ash levels always around or below 1 wt%, and at the same time a decrease in high heating value -HHV-. The differences in HHV between the different parts of the hybrid poplars are in good agreement with results obtained from FTIR and thermogravimetric patterns.

Crystal structure, Hirshfeld surface, spectroscopic analyses, electronic properties, NLO profile and thermochemical study of an antispasmodic agent trimebutine

Absolute molecular geometry of trimebutine was determined with single crystal X-Ray diffraction (SCXRD). The C–H⋯O and C–H···π interactions within crystal packing were supported by Hirshfeld surface analysis. Spectral properties of trimebutine were investigated by using analysis techniques such as FT-IR, micro-Raman, NMR chemical shift and UV–Vis. spectroscopies. In order to investigate vibrational profile of the important functional groups within the compound, the detailed assignments of vibrational wavenumbers were performed by using potential energy distribution. Theoretical investigations on structural, spectroscopic, electronic, non-linear optical and thermochemical features were carried out with the DFT/B3LYP method at the 6–311++G(d,p) basis set. The 13C and 1H NMR chemical shifts of each atom within the compound were studied both experimentally and theoretically. The UV–Vis. spectroscopic analysis of trimebutine was used to evaluate intra-molecular electronic transitions. The HOMOs and LUMOs analyses were done to determine the nature and origin of the π→π* and n→π* electronic transitions. Additionally, the global reactivity descriptors were defined depending upon energy values of HOMO and LUMO. The π→π* and n→π* hyperconjugative interactions between donor and acceptor groups were investigated by NBO analysis. According to the computed αtotal, Δα and β0 values in the static state of trimebutine single crystal, it exhibits an excellent non-linear optical material property. Thermochemical features were calculated and studied in the gas phase of the compound.

Structural, Spectroscopic, Electronic and Molecular Docking Studies on (11R,12 S)‐16‐Aminotetracyclo[6.6.2.02,7.09,14]hexadeca‐2(7),3,5,9(14),10,12‐hexaen‐15‐ol

AbstractMolecular structure analysis, vibrational and electronic spectroscopic studies and thermochemical features of (11R,12 S)‐16‐aminotetracyclo[6.6.2.02,7.09,14]hexadeca‐2(7),3,5,9(14),10,12‐hexaen‐15‐ol were investigated via both theoretical and experimental techniques. Experimental investigations were made by using FT‐IR, Raman, 1H and 13C NMR and UV‐Vis. spectroscopies. To support experimental evidences, molecular electronic structure computations were obtained with the DFT/B3LYP method at the 6–311G++(3d,3p) basis set. 2D and 3D Hirshfeld surfaces studies were performed to understand non‐bonding intermolecular interactions in solid phase crystal packing of the compound. MEP surface analysis was performed to investigate nucleophilic and electrophilic reactive sites of the compound. The highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMO) analyses were theoretically used for determination of electronic transitions corresponding to UV‐Vis. electronic absorption wavelengths. Enzyme‐ligand interactions between the compound with BACE1 (Beta‐Secretase1) inhibitor were determined via molecular docking study.

Thermo-optical properties of residential coals and combustion aerosols

In this study, we present the inherent optical properties of carbonaceous aerosols generated from various coals (hard through bituminous to lignite) and their correlation with the thermochemical and energetic properties of the bulk coal samples. The nanoablation method provided a unique opportunity for the comprehensive investigation of the generated particles under well controlled laboratory circumstances. First, the wavelength dependent radiative features (optical absorption and scattering) and the size distribution (SD) of the generated particulate matter were measured in-situ in aerosol phase using in-house developed and customised state-of-the-art instrumentation. We also investigated the morphology and microstructure of the generated particles using Transmission Electron Microscopy (TEM) and Electron Diffraction (ED). The absorption spectra of the measured samples (quantified by Absorption Angström Exponent (AAE)) were observed to be distinctive. The correlation between the thermochemical features of bulk coal samples (fixed carbon (FC) to volatile matter (VM) ratio and calorific value (CV)) and the AAE of aerosol assembly were found to be (r2 = 0.97 and r2 = 0.97) respectively. Lignite was off the fitted curves in both cases most probably due to its high optically inactive volatile material content. Although more samples are necessary to be investigated to draw statistically relevant conclusion, the revealed correlation between CV and Single Scattering Albedo (SSA) implies that climatic impact of coal combusted aerosol could depend on the thermal and energetic properties of the bulk material.

Features of the thermodynamics of trivalent lanthanide/actinide distribution reactions by tri-n-octylphosphine oxide and bis(2-ethylhexyl) phosphoric acid.

A new methodology has been developed to study the thermochemical features of the biphasic transfer reactions of trisnitrato complexes of lanthanides and americium by a monofunctional solvating ligand (tri-n-octylphosphine oxide, TOPO). Stability constants for successive nitrato complexes (M(NO3)x(3-x)(aq) where M is Eu(3+), Am(3+), or Cm(3+)) were determined to assist in the calculation of the extraction constant, K(ex), for the metal ions under study. Enthalpies of extraction (ΔH(extr)) for the lanthanide series (excluding Pm(3+)) and Am(3+) by TOPO have been measured using isothermal titration calorimetry. The observed ΔH(extr) were found to be constant at ~29 kJ mol(-1) across the series from La(3+) to Er(3+), with a slight decrease observed from Tm(3+) to Lu(3+). These heats were found to be consistent with enthalpies determined using van't Hoff analysis of temperature dependent extraction studies. A complete set of thermodynamic parameters (ΔG, ΔH, ΔS) was calculated for Eu(NO3)3, Am(NO3)3, and Cm(NO3)3 extraction by TOPO and Am(3+) and Cm(3+) extraction by bis(2-ethylhexyl) phosphoric acid (HDEHP). A discussion comparing the energetics of these systems is offered. The measured biphasic extraction heats for the transplutonium elements, ΔH(extr), presented in these studies are the first ever direct measurements offered using two-phase calorimetric techniques.

Mathematical Modelling of Biomass Gasification in a Circulating Fluidized Bed CFB Reactor

The scope of the present paper is to investigate the suitability of a mathematical model for Circulating Fluidized Bed (CFB) coal combustion (developed by the International Energy Agency), to predict and simulate the performance of the 100 kWth CFB for air-blown biomass gasification. The development of a mathematical model allows to simulate the operative conditions during biomass gasification, control the quality of the synthesis gas and improve the gasifier design. The geometrical, mechanical, hydro dynamical and thermo chemical features were introduced in the model by properly setting the input file and, some changes have been made in the code to assure the final convergence. A sensitivity analysis has been performed to study the variation in the input parameters of the program, and it has been finally verified by comparing the results with the empirical data collected during coal and wood combustion tests. The program, in the same case, could not successfully run; probably depending on wood char density value. For these reason the influence of char density will be investigated. The model predicts the development of tar and other hydrocarbons, valuating the agreement between the measured and calculated efficiency. A further development, to consider solid biomass, with a certain volatile percentages (20% - 40%), as a fuel has been previewed and analyzed. Finally some investigations have been carried out to provide some useful indications for future developments of the code, in the biomass gasification modelling

Thermal and Tribological Properties of Fullerene‐Containing Composite Systems. Part 3. Features of the Mechanism of Thermal Degradation of Poly‐(N‐Vinyl‐Pyrrolidone) and Its Compositions with Fullerene C60

By mass‐spectrometric thermal analysis (MTA) the thermochemical features of poly(N‐vinyl pyrrolidone) (PVP) and its compositions with fullerene C60 were studied. The mechanism of PVP thermal degradation was investigated; in particular the nature of the low‐temperature degradation (between 75 and 300°C) accompanied by output of pyrrolidone was explained as well as the influence of fullerene C60 on this mechanism. It was shown that during thermal degradation of copolymer PVP‐C60, there is a disappearance of the low‐temperature peaks of the output of pyrrolidone that is interpreted as an increase of the thermal stability of N‐vinyl‐pyrrolidone fragments in this product in comparison with their thermal stability in pure PVP.

Comparing Electrochemical and Biological Water Splitting

On the basis of density functional theory calculations, we compare the free energies of key intermediates in the water splitting reaction over transition metal oxide surfaces to those of the Mn cluster in photo system II. In spite of the very different environments in the enzyme system and on the inorganic catalyst surface of an acidic electrolysis cell, the thermochemical features of the catalysts can be directly compared. We suggest a simple test for a thermochemically optimal catalyst. We show that, although both the RuO2 surface and the Mn cluster in photo system II are quite close to optimal, the biological catalyst appears to be best.

Calculated Phase Diagrams for the Electrochemical Oxidation and Reduction of Water over Pt(111)

Ab initio density functional theory is used to calculate the electrochemical phase diagram for the oxidation and reduction of water over the Pt(111) surface. Three different schemes proposed in the literature are used to calculate the potential-dependent free energy of hydrogen, water, hydroxyl, and oxygen species adsorbed to the surface. Despite the different foundations for the models and their different complexity, they can be directly related to one another through a systematic Taylor series expansion of the Nernst equation. The simplest model, which includes the potential only as a shift in the chemical potential of the electrons, accounts very well for the thermochemical features determining the phase-diagram.

Crystal structure of p-nitroanilinium hexafluorosilicate

Complex (p-O2NC6H4NH3)2SiF6 (I) is prepared by reacting fluorostlicic acid with p-nitroaniline in methanol and structurally studied using single-crystal X-ray diffraction. In the ionic structure of this complex, SiF 6 2− centrosymmetrical anions (avg. Si-F, 1.671(3) A) and O2NC6H4NH 3 + cations are linked through NH…F interionic H-bonds (N…F 2.823(5)-3.205(7) A). The thermochemical features of complex I are discussed in light of the structure data.

Ab initio calculation of entropy and heat capacity of gas-phase n-alkanes with hetero-elements O and S: Ethers/alcohols and sulfides/thiols

In this paper, the performance of the one-dimensional hindered rotor approach (1D-HR) is evaluated for n-alkanes with hetero-elements O or S. The internal rotations in these molecules show a behavior distinct from those in n-alkanes, for which 1D-HR is a cost-efficient method to describe the thermochemical features (entropy and heat capacity). It turns out that also for ethers, alcohols, sulfides and thiols this approach gives a satisfactory experimental agreement. This work confirms earlier results, and consolidates the assumption that the 1D-HR model is highly suitable for reproducing thermodynamic properties of single chain molecules, and that multi-dimensional coupled hindered rotor approaches (nD-HR) are not necessarily required for attaining high accuracy. Moreover, it seems that the 1D-HR results are almost independent of the details of the level of theory.

Thermochemical Study of the Ternary System Water-Formamide-Dimethylacetamide

The enthalpy of mixing of dimethylacetamide with 1 : 3, 1 : 1, 3 : 1 water-formamide binarymixtures was determined calorimetrically, and the enthalpy of mixing at 298.15 K in the ternary system di-methylacetamide-water-formamide was estimated. The thermochemical features of the ternary system and its binary subsystems are discussed. The observed exothermic effects of mixing in the ternary system are caused by intermolecular hydrogen bonding of dimethylacetamide with water and formamide.

Thermochemical features of lamellar silica, copper, nickel and cobalt-doped forms synthesized from neutral amine route

Lamellar silica prepared from sol–gel process through neutral amine route, was doped with cobalt, nickel or copper. X-ray diffraction pattern, thermogravimetry, and differential scanning calorimetry and reaction–solution calorimetry characterized these synthesized hybrids. The wetting enthalpy, Δ wet H m θ, for lamellar matrix doped with 10.0 and 15.0 mmol of CuCl 2 gave 41.81±0.02 and 40.54±0.02 J g −1, respectively. The enthalpy of cation adsorption was carried out by using 100.0 cm 3 of 8.0×10 −3 or 0.127 mol dm −3 solutions of Co 2+, Ni 2+ or Cu 2+. The measurements were also performed using 50.0/50.0 cm 3 mixture of Co 2+ and Cu 2+ solutions. The results gave 20.73±0.07;−69.22±0.03; 10.91±0.06 and−34.44±0.06 J g −1 for nickel, copper, cobalt and copper–cobalt solutions, for a concentration of 8.0×10 −3 mol dm −3. The same sequence of cations gave the enthalpic values −97.12±0.06, −106.90±0.01, 42.56±0.06, 34.97±0.12 J g −1 for 0.127 mol dm −3 solution. The results showed that the lamellar silica matrix can be used as a sequestrating agent for these cations with a capacity of adsorption established as Ni 2+>Cu 2+>Co 2+. The wetting enthalpic values as well as the thermal stability of these matrices are associated to the crystallinity of the samples.

The Impact of Scaling Criteria on the Characteristics of Pulverised Coal Flames

AbstractResults are presented of a series of experiments where a 12 MW, large‐scale swirl stabilised burner is compared with two 2.5 MW, geometrically similar burners designed around a constant‐velocity and constant‐residence‐time scaling criterion. High and low NOx flames were produced from all burners and selected flames were extensively probed to determine in‐flame thermo‐chemical structures. Results show that complex differences exist between flames. Results are also presented on the effect of scale on the ignition properties of axial turbulent jet flames. Experimental findings show an important effect of ignition distance on NOx that has important implications with respect to scaling effects on these flame types. The results detailed in the text are interpreted with reference to the effect of scale on turbulent mixing, two‐phase interactions and ignition properties. Results confirm that, regardless of the scaling criterion selected, similarity of the in‐flame thermochemical features is almost impossible to maintain as burner scale is changed irrespective of the scaling approach employed.

Thermochemical features of complexes of thioacetamide and thiourea with antimony and bismuth triiodides

Complexes of the type MI 3· nL [where M is Sb and Bi; L is thiourea (TU) or thioacetamide (TA)] were prepared and characterized by their melting interval, elemental analyses, thermogravimetry, IR spectroscopy and mass spectra. The solution-reaction was used to determine the enthalpy of formation at 298.15 K of crystalline SbI 3·2TU −291.3, SbI 3·2TA −258.8, BiI 3·2TU −340.8, and BiI 3·TA −233.1 kJ mol −1. The standard enthalpies of decomposition of the complexes, as well as the lattice standard enthalpies and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase were calculated through adequate thermochemical cycles. The standard mean element-sulphur bond enthalpies were estimated as 101.1 and 113.2 kJ mol −1 for SbI 3·2TA and SbI 3·2TU and 146.5 and 129.3 kJ mol −1 for BiI 3·TA and BiI 3·2TU, respectively.