Thermal Analysis Applied to Solid Catalysts Acidity,Activity and Regeneration

The use of catalysts in numerous important processes is widespread throughout the chemical and petroleum-processing industries. Thermal analytical techniques can be used to evaluate important properties and processes associated with solid catalysts. This paper presents examples carried out in our laboratory of the general application of TG and DSC to the acidity, activity and regeneration of solid catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acid Properties of SiMCM-41 Mesoporous Molecular Sieve

The SiMCM-41 mesoporous molecular sieve was synthesised by the hydrothermal method. The physicochemical characterisation by infrared spectroscopy, X-ray diffraction and thermogravimetry, showed that the material presents a well-defined structure. In this study, the determination of the total acidity and relative strength of the acid sites of the SiMCM-41,was performed by desorption of adsorbed n-butylamine combined with thermogravimetric measurements. The total acidity, determined by means of the amount of amine desorbed normalised by mass of solid, was equivalent to 0.927 mmol g^–1, in the temperature range from 96 to 235°C. By using the Flynn and Wall integral kinetic model, at 5, 10 and 20°C min^–1 heating rates, it was determined that the activation energy to desorb n-butylamine was 90.7 kJ mol^–1, in the same temperature range, evidencing that SiMCM-41 presents only weak acid sites on its surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of histamine in port wines and grape juices by ion-pair extraction and stable isotope dilution GC-MS

Summary An isotope dilution, GC-MS method for the quantitation of histamine in wines and grape juices was assayed. This method includes isolation of histamine and its, deuterated analogue [α,α,β,β-²H₄]histamine, used as the labelled internal standard, by ion-pair extraction with bis-2-ethylhexylphosphate, conversion to the volatile derivative: tris-pentafluorobenzyl-histamine, capillary GC separation and measurement of the abundance ratio of the (M-181)⁺ ions from labelled and unlabelled derivatives. The method was successfully applied to the determination of histamine in several samples of Port wine, red and white table wine and grape juice. Data are given on detectability, linearity, repeatability and recovery.     

Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved. Received: 18 May 1999 / Revised: 5 July 1999 / Accepted: 7 July 1999     

Analysis of Rotenoids by High Temperature High Resolution Gas Chromatography-Mass Spectrometry

A short glass capillary column coated with PS-090 (20% phenyl–80% methylpolysiloxane, of 10 m × 0.30 mm i.d.; with 0.1 μm film thickness) was used to analyze samples from Tephrosia candida; eighteen rotenoids were separated and identified without derivatization by HT-HRGC and HT-HRGC-MS. The mass spectra show the typical fragmentation pattern for rotenoids, with the base peaks either at M⁺, or originating from RDA (Retro Diels-Alder) rearrangements. HT-HRGC and HT-HRGC-MS were shown to be extremely valuable and neglected techniques for structural studies as well as the routine analysis of rotenoids in crude extracts. Possible applications to other classes of aromatic natural products, e.g. flavonoids, are envisaged.     

Synthesis of 6-Membered-Ring Fused Thiazine-Dicarboxylates and Thiazole-Pyrimidines via One-Pot Three-Component Reactions

A facile and efficient one-pot three-component reaction method for the synthesis of thiazine-dicarboxylates is reported. Reaction of an isocyanide and dialkyl acetylenedicarboxylate with 2-amino-4H-1,3-thiazin-4-one derivatives containing both an acidic proton and an internal nucleophile gave the products in good yields of 76–85%. The reactivity of dialkyl acetylenedicarboxylates was further tested in the synthesis of thiazole-pyrimidines where a two-component reaction of 2-aminothiazole with dialkyl acetylenedicarboxylates was successfully converted to a more efficient three-component reaction of a thiourea, α-haloketone and dialkyl acetylenedicarboxylate (DMAD/DEtAD) to give thiazole-pyrimidines in good yields of 70–91%.     

Vector potential formulation for magnetostatics and modelling of permanent magnets

A very general magnetostatic problem involving inhomogeneousanisotropic materials filling irregular regions and with mixedboundary conditions is formulated in terms of magnetic vectorpotential. Some restrictions inherent to the introduction ofa vector potential become apparent and additional conditionsfor the uniqueness of the vector potential naturally arise.The modelling of permanent magnets is introduced in both thevector potential and the field formulations by weakening theregularity requirements on the source term. The vector potentialformulation is also shown to be equivalent to a penalized formulationwidely used in numerical applications.     

On the origin of the multiple melting behavior in poly(ethylene naphthalene‐2,6‐dicarboxylate): Microstructural study as revealed by differential scanning calorimetry and X‐ray scattering

In this article a study on the melting behavior and microstructure of semicrystalline poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) prepared by crystallization from the glass under different annealing conditions is presented. The influence of the annealing temperature (T_a), annealing time (t_a), and the heating rate (R_h) at which T_a is reached on the endothermic behavior of the samples was investigated by means of differential scanning calorimetry (DSC). A dual melting behavior appeared for low R_h values (2 deg · min⁻¹) within the range of 145 °C < T_a < 250 °C and 1 min ≤ t_a. ≤ 16 h. Samples subjected to fast heating rates (R_h = 200 deg · min⁻¹) to reach a T_a ≥ 230 °C showed DSC traces in which a transition is observed from three peaks to a single melting peak when t_a increases in the 30–240 min range. On the basis of the DSC results, PEN samples were prepared displaying single or dual endothermic behavior. The microstructure of these samples was studied by wide (WAXS) and small‐angle X‐Ray scattering (SAXS) techniques. The SAXS data were analyzed using the correlation function and interface distribution function formalisms, respectively. In samples with a single melting behavior, microstructural parameters such as the long spacing, the amorphous and the crystalline phase thicknesses are consistent with a lamellar stacking model in which the thickness distributions of both phases are almost the same. For samples exhibiting two melting endotherms, a dual lamellar model, which is in agreement with the experimental results is proposed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1167–1182, 2000     

N-Heterocyclic Carbene Iron Complexes as Anticancer Agents: In Vitro and In Vivo Biological Studies

Cisplatin and its derivatives are commonly used in chemotherapeutic treatments of cancer, even though they suffer from many toxic side effects. The problems that emerge from the use of these metal compounds led to the search for new complexes capable to overcome the toxic side effects. Here, we report the evaluation of the antiproliferative activity of Fe(II) cyclopentadienyl complexes bearing n-heterocyclic carbene ligands in tumour cells and their in vivo toxicological profile. The in vitro antiproliferative assays demonstrated that complex Fe1 displays the highest cytotoxic activity both in human colorectal carcinoma cells (HCT116) and ovarian carcinoma cells (A2780) with IC₅₀ values in the low micromolar range. The antiproliferative effect of Fe1 was even higher than cisplatin. Interestingly, Fe1 showed low in vivo toxicity, and in vivo analyses of Fe1 and Fe2 compounds using colorectal HCT116 zebrafish xenograft showed that both reduce the proliferation of human HCT116 colorectal cancer cells in vivo.     

Biodegradable thermoactive packaging using phase change material particles on cellulosic materials

Cellulose - Environmental concerns about the use of non-renewable raw materials and non-biodegradable waste production have increased exponentially in recent decades. Phase change materials respond...