Investigation and characterization by TG/DTG–DTA and DSC of the fusion of Riboflavin,and its interaction with the antibiotic norfloxacin in the screening of cocrystal

This work synthesized and characterized the NOR-RIB 1:1 (mol–mol) cocrystal. During a study of the reagents, Riboflavin (RIB) melted at 304 °C, which is different from the temperature previously reported in the literature (280–290 °C); therefore, this compound was characterized individually. Subsequently, the cocrystal was synthesized with the active pharmaceutical ingredient (API) norfloxacin (NOR) with the RIB coformer, and the mechanochemical synthesis route was adopted. NOR, RIB, and the cocrystal were characterized by thermogravimetry–differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC), DSC coupled to a microscope (photo-DSC), mid-infrared spectroscopy (MIR), and powder X-ray diffraction. The results of thermal analysis showed that the RIB starts decomposition process (260 °C) and then melts (304 °C). The MIR found that beginning at 295 °C, the RIB passes into the form of a decomposition intermediate; therefore, the melting point observed in the DSC curve is related to this decomposition material. The cocrystal presented thermal stability (200 °C) lower than the API (235 °C) and the coformer (260 °C). The DSC curve did not contain a melting peak. The bands at 1726 cm^?1 (C=O of the carboxylic acid) for the NOR, and the band at 3326 cm^?1 (stretch O–H), among others, were not visible for the cocrystal in the MIR spectrum, indicating interactions in these regions. The X-ray diffractograms showed a new diffraction pattern, which proved the obtainment of a new phase and cocrystal formation.

     

Characterization of commercial artists’ acrylic paints and the influence of UV light on aging

A large part of Mexican artistic heritage was created with artists’ acrylic emulsion paints, so it is crucial to investigate their composition, behavior, and decay. Acrylic films are complex chemical systems combining organic and inorganic compounds; therefore, the degradation studies require a variety of techniques. We characterize three acrylic films before and after ultraviolet aging. The relative composition of the polymer matrix was studied by nuclear magnetic resonance, pyrolysis—gas chromatography—mass spectrometry and direct analysis in real time mass spectrometry with direct analysis in real time. The inorganic compounds and surfaces were characterized by microscopic techniques, such as digital microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and micro X-ray diffraction. The combined use of these techniques proved to be effective for an in-depth study of the acrylic painting degradation process. The main results were the gradual degradation for the organic surfactant and the loss of inorganic aggregates (talc and carbonates), that led to the disruption of the paint film, which points out the importance of studying the role and interaction of all compounds.     

Characterization of moisture mobility and diffusion in fresh tobacco leaves during drying by the TG–NMR analysis

This paper presents the stabilization effects of inorganic filler, cerium-doped lead zirconate titanate on high-density polyethylene. The filler was loaded in two concentrations (1 and 3 wt%). The dopant contents in PbZrO₃ were 0, 0.05, 0.075, 0.1 and 0.125 mol%. The degradation of hybrid samples was accomplished by γ-irradiation at various doses up to 200 kGy. The isothermal and nonisothermal chemiluminescence (CL) and thermal analysis (TG-DSC) were applied for the thermal stability characterization of modified HDPE samples. The mechanistic considerations and radiochemical consequences caused by the variation of filler concentration and doping level are discussed. The results demonstrate that the filler acts efficiently as stabilizer at low concentration of additive when the lower filler amount is present. The start of degradation precedes melting by four processes through which the chain scission and radical oxidation represent the essential degradation stage. The filler concentration influences the degradation due to the intimate interaction between solid-state defects and free radicals. The polymer protection against oxidation is based on the scavenging of radicals by the doping elements, that is, they trap and block radicals delaying material aging. The present results open a new perspective in the quality amelioration of organic products toward high durability.

     

The use of TG/DSC–FT-IR to assess the effect of Cr sorption on struvite stability and composition

Struvite (MgNH₄PO₄·6H₂O; MAP) can be recovered from animal and human wastes for use as fertilizer. This encourages the sustainable use of phosphorus (P), closing the human P cycle. The toxic metalloid chromium (Cr) is a common component of wastes, and can substitute for P in geochemical and biological systems. Thus, its sorption to, and effect on the stability and composition of recovered MAP requires assessment. MAP precipitated from solutions with 1?C100???M Cr(III) had higher Cr loadings compared to those reacted in the presence of Cr(VI), indicative of higher sorption affinity of the lower oxidation state. Simultaneous thermal analysis of unreacted MAP revealed an endothermic peak at 126?±?0.5?°C by DSC with a mass loss of 52.9% by TG. Sorption of Cr produced minimal effects on the transition temperature and overall mass loss. The inflection in the TG curve indicated that Cr increased the temperature of maximum decomposition, but also the mass loss at this point. Combining TG results with FT-IR spectra revealed that for initial concentrations of 10?C50???M Cr(III) and 1?C5???M Cr(VI), NH₄ ⁺ was added, and H₂O(s) lost from the MAP structure. The change in composition was consistent with substitution of Cr(III) or Cr(VI) into the MAP structure. The TG/DSC?CFT-IR technique confirmed that Cr contamination affects the MAP composition and may accelerate the release of nutrients upon mineral decomposition. This has implications for the use of MAP fertilizers and subsequent cycling of P and contaminants in agricultural systems.     

Calorimetric and thermogravimetric study on the influence of calcium sulfate on the hydration of ye’elimite

Calcium sulfoaluminate (CSA) cements, which represent a CO₂-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.     

Experimental study of the influence of solvent and asphaltenes on liquid–solid phase behavior of paraffinic model systems by using DSC and FT-IR techniques

This experimental work presents the results of a study about the liquid–solid phase behavior of high molecular weight n-paraffins (C₂₄–C₂₈ mixture and C₃₆ pure) in aliphatic (n-decane and squalane) and aromatic (xylene and 1-phenyl dodecane) solvents. The effect of asphaltenes of different chemical nature over the liquid–solid behavior of heavy n-paraffins is also studied. Differential Scanning Calorimetry (DSC) was used to obtain the phase transitions onsets and enthalpies as well as the wax solubility curves. Crystallinity was studied by using both DSC and Infrared Spectroscopy (FT-IR) techniques. The results obtained and presented in this study showed that both, solvent and asphaltenes as well as their chemical nature have a significant effect on paraffin crystallization process.     

Thermal characterization and kinetic analysis of nesquehonite,hydromagnesite, and brucite,using TG–DTG and DSC techniques

Nesquehonite, hydromagnesite, and brucite are important precursors for the preparation of high-purity magnesia (MgO) using magnesium resources from salt lake as raw materials. In this paper, TG–DTG and DSC were used to investigate the thermal decomposition behaviors of the three precursors. Decomposition kinetic parameters at each stage were evaluated based on the TG data using the iso-conversional method. Decomposition mechanisms were determined using the master-plots method. The decomposition temperature range, heat absorption, and kinetic parameters of the three phases were then compared. The most probable mechanism of each stage from the perspective of crystal structure was found to be consistent with the calculation results from the master-plots method. Results led to the conclusion that nesquehonite is the most appropriate precursor for the preparation of high-purity MgO. Further studies on precursor selection and calcining condition selection for the preparation of MgO using bischofite will benefit from this research.     

Influence of β-cyclodextrin on the protolytic and complexing ability of p-aminobenzoic acid

UV spectroscopy was used to study the protolytic properties and determine the ionization constants of p-aminobenzoic acid in the presence of β-cyclodextrin. Formation of supramolecular structures of 1: 1 composition was established. Stability constants of the β-cyclodextrin-p-aminobenzoic acid inclusion complex were calculated, as were the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) of its formation. The complexing process between β-cyclodextrin and p-aminobenzoic acid was found to occur spontaneously in the temperature range under investigation while being accompanied by energy liberation and leading to a reduction in the system’s entropy.     

The influence of the dialkylphenyltolane’s difluorosubstitution on mesomorphic and dielectric properties

The synthesis of variously difluoro-substituted 4-butyl-4?-[2-(4-butylphenyl)ethynyl]-1,1?-biphenyls is presented and discussed. Molecular correlations between positions of fluorine atoms at phenyltolane core and mesomorphic, dielectric properties of newly synthesised liquid crystals (LC) have been drawn and discussed. New LC molecules exhibit a wide range of nematic phase and are promising components of liquid crystalline mixtures. They were characterised by ¹H NMR spectroscopy and mass spectrometry analysis. Phase transition temperatures, enthalpies, mesomorphic and dielectric properties were confirmed by a polarising optical microscopy, differential scanning calorimetry and dielectric spectroscopy.     

Study on the effects of flame retardants on the thermal decomposition of wood by TG–MS

The effect of three flame retardants, K₂CO₃, Na₂SiO₃·9H₂O, and Na₂B₄O₇·10H₂O on the process and composition of volatile products of the thermal degradation of wood has been investigated by the thermogravimetric (TG), differential thermogravimetry (DTG), differential thermal analysis (DTA), and the synchronous thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the ion current intensity and ion peak area of m/z = 18 and 44 MS signals were increased by the flame retardants but the ion peak area of m/z = 28 MS signal was decreased (except K₂CO₃) at the meantime. What’s more, the ion current intensity and ion peak area of m/z = 60 and 68 MS signals were also decreased (except K₂CO₃), which mean that Na₂B₄O₇ can significantly enhances the dehydration and inhibits the depolymerization of wood. Although K₂CO₃ accelerates the dehydration reaction, it cannot inhibit the depolymerization reaction effectively, so the flame retardant efficiency of K₂CO₃ is decreased with the higher concentration. The catalysis of dehydration reaction of Na₂SiO₃ is the worst one.     

Calorimetric and thermal analysis studies on the influence of waste aluminosilicate catalyst on the hydration of fly ash–cement paste

Binders containing large amounts of cement substitutes have been a subject of interest for many years because of the possibility to reduce the amount of cement in concrete, and in consequence decrease negative influence of cement production on natural environment. In this work, studies related to hydration of binders where 80 % of cement was substituted by blended pozzolana were carried out. The aim of this work was to investigate activation of fly ash–cement system by addition of spent aluminosilicate catalyst, using calorimetry and thermal analysis as main methods of investigations. It was demonstrated that spent fine-grained fluidised catalytic cracking catalyst acts acceleratingly on early hydration of binder. It seems to be beneficial to use up to 10 mass% of this spent catalyst. Higher amounts may cause changes in the mechanism of early hydration. Because Ca(OH)₂ in such systems is quickly consumed due to pozzolanic reaction it seems beneficial to modify composition of binders by introducing additional amounts of Ca(OH)₂ or cement.     

XAS combined with TG–DTG study on synergic effect on sulfur transformation during co-pyrolysis of sawdust and lignite

The synergic effect of sawdust (SD) and a lignite can be observed by analyzing their co-pyrolysis behavior. The co-pyrolysis behavior of SD and lignite mixtures was investigated by thermo-gravimetric analysis, and their sulfur transformation was measured by X-ray absorption spectroscopy (XAS). The pyrolysis process can be divided into three stages for SD and lignite, while four their mixtures. The experimental mass loss of SD and lignite mixture during co-pyrolysis is higher than its theoretically calculated mass loss, especially at the mixing ratio of 1:1. This indicates that synergy occurs during SD and lignite co-pyrolysis process. XAS spectra of sulfur show that SD can promote FeS to decompose before 900 °C during co-pyrolysis, as the peak of FeS decreases in the mixture’s char. However, the experimental sulfur removal of mixtures is lower than the theoretically calculated one. This indicates that synergic effect has no effect on sulfur removal, which is very corresponding to more thiophenes gathering in the mixture’s char, because the peak of thiophenes is very steep for the mixture after pyrolysis. And other sulfurs transformation in the mixture is very similar to that of CF coal. For CF coal and its mixture, sulfate peak increases obviously after pyrolysis, which is mostly caused by absorbing SO₂ of alkaline minerals during pyrolysis. This also suggests SD cannot prevent sulfate from forming during co-pyrolysis. Therefore, SD can be added to promote high-pyrite coal to increase sulfur removal, since the decomposition of FeS needs higher temperatures.

     

Sol–gel treatments for enhancing flame retardancy and thermal stability of cotton fabrics: optimisation of the process and evaluation of the durability

Cotton fabrics have been treated by sol–gel processes in order to create a silica compact coating on the fibres to enhance their thermal stability and flame retardancy. The effect of process parameters such as silica precursor:water molar ratio and drying conditions (temperature and time) has been thoroughly investigated, aiming at optimization of target properties. Thermogravimetry and cone calorimetry have been respectively used to assess thermal stability and combustion behaviour of treated fabrics. Coating durability to different washing programmes has been evaluated as well.     

Study on thermal decomposition of polymers by simultaneous measurement of TG–DTA and miniature ion trap mass spectrometry equipped with skimmer-type interface

Simultaneous thermogravimetry–differential thermal analysis and miniature ion trap mass spectrometry (TG–DTA–ITMS) instrument equipped with a skimmer-type interface has been successfully developed. The system allows precise real-time monitoring analysis of activated organic compounds such as pyrolysates because gaseous transformation of the evolved gases from the TG–DTA is suppressed by the skimmer-type interface. Also, excessive fragmentation during ionization of molecules can be avoided with the soft ionization method by photoionization. In addition, the miniaturized ITMS is equipped with unique tandem MS capability. These features permit a better understanding of the complicated thermal behavior and the precise pyrolysates of materials. The pyrolysis of various standard reagent polymers such as polymethyl methacrylate, polystyrene, and polyphenylene sulfide has been examined by the TG–DTA–ITMS in inert atmosphere. The synergy effect of the skimmer-type interface and the ITMS was evaluated comparatively with conventional quadrupole mass spectrometry results. It was confirmed that the real-time monitoring ITMS/MS worked satisfactorily. Here, we demonstrate a valuable application of the TG–DTA–ITMS in the detailed analysis of commercial polymers.     

Simultaneous TG/DTG–DSC–FTIR characterization of collagen in inert and oxidative atmospheres

In this paper, a TG/DTG–DSC–FTIR study of type I collagen extracted from bovine Achilles tendon both in inert (nitrogen) and oxidative atmosphere (synthetic air and oxygen) from room temperature to 700 °C was performed. The thermal analysis results have shown that after initial dehydration, collagen exhibits a single decomposition step in nitrogen (due to pyrolysis), while in air and oxygen two steps are observed due to thermo-oxidative decomposition, the latter being highly exothermic. The CO₂ bands dominate the FTIR spectra of evolved gases in all atmospheres (especially in air and oxygen), along with the characteristic bands of ammonia, water, HNCO, methane. In nitrogen, the bands of pyrrole, HCN, and ethane were also identified, while in oxidative atmospheres, nitrogen oxides and CO are released. A study was also performed by comparing the DTG and gas evolution curves observed for the three atmospheres.     

The effect of complexing agents on the DMF–chromium(VI) reaction. A kinetic study

The kinetics of the reduction of chromium(VI) by dimethylformamide (DMF) in the presence of ethylenediaminetetraacetic acid (EDTA) and 2,2-bipyridyl (bpy) was investigated in aqueous HClO₄ acid solutions spectrophotometrically. The experimental findings, that the reaction has an induction period followed by autoacceleration, is explained. After the reduction, chromium(III) is present as the EDTA- and bpy-complexes, although such complexes form very slowly under the same experimental conditions from chromium(III) and the EDTA and bpy, respectively. Increases in the reaction rate with increasing [EDTA] were observed, while added bpy had negligible effect on the reaction rate. The reaction is first-order each in [Cr^VI] and [H⁺]. The first-order kinetics with respect to EDTA at low concentrations shift to zero-order at higher concentrations. The reaction is considered to proceed through the formation of a very stable chromium(VI)–DMF–EDTA complex. The suggested mechanism refers only to the induction period of the reaction. The net rate of oxidation of DMF, as measured by the consumption of chromium (VI), is given by: –d[Cr^VI]/dt = kK ₁ K _b[H⁺][DMF]_T[EDTA][Cr^VI]_T/(1 + K ₁[EDTA])(1 + K _b[H⁺])     

Van Helmont’s hybrid ontology and its influence on the chemical interpretation of spirit and ferment

This essay proposes to discuss the manner in which Jan Baptista van Helmont helped to transform the Neoplatonic notions of vital spirit and of ferment by giving these notions an unambiguously chemical interpretation, thereby influencing the eventual naturalization of these ideas in the work of late seventeenth century chymists. This chemical interpretation of vital spirit and ferment forms part of Helmont’s hybrid ontology, which fuses a corpuscular conception of minima naturalia with a non-corporeal conception of semina rerum. For Helmont, chemical alterations involve the minima as physical units but also depend upon ferments that are contained in the semina, which function as formative spiritual agents. Helmont’s nuanced ontology ultimately contributes to the development of modern corpuscularian theory by explaining many chemical reactions in fundamentally corpuscular terms, as the addition and subtraction of particles.     

Characterization of chemopreventive agents from the dichloromethane extract of Eurycorymbus cavaleriei by liquid chromatography–ion trap mass spectrometry

In the present study, we examined the potential chemopreventive activity of dichloromethane extract of Eurycorymbus cavaleriei by investigating the change of constitutions after incubation with glutathione (GSH). The major constitutions in the dichloromethane extract of E. cavaleriei were cumarin compounds and their cleavage pattern was examined by LC–MS-MS and the characteristic product ions at m/z 206 and 207 were helpful to determine the substitutions of coumarinolignoid compounds. The mechanism of conjugations of 5′-demethylaquillochin and its isomer with GSH was discussed and validated through analysis of the conjugations of reference compound 6-hydroxy-7-methoxycoumarin with GSH by LC–MS-MS and NMR spectrum. The relative ability to induce the detoxification enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1) of nine coumarin compounds was tested which also showed 5′-demethylaquillochin exhibited the most potential chemopreventive ability. These observations suggest that 5′-demethylaquillochin and its isomer from the dichloromethane extract of E. cavaleriei have potential as chemopreventive agents through induction of detoxification enzymes.     

Characterization of polypropylene�Cpolyethylene blends by temperature rising elution and crystallization analysis fractionation

The introduction of single-site catalysts in the polyolefins industry opens new routes to design resins with improved performance through multicatalyst-multireactor processes. Physical combination of various polyolefin types in a secondary extrusion process is also a common practice to achieve new products with improved properties. The new resins have complex structures, especially in terms of composition distribution, and their characterization is not always an easy task. Techniques like temperature rising elution fractionation (TREF) or crystallization analysis fractionation (CRYSTAF) are currently used to characterize the composition distribution of these resins. It has been shown that certain combinations of polyolefins may result in equivocal results if only TREF or CRYSTAF is used separately for their characterization.