An improved photothermal gas analyser: Monitoring of simultaneous thermal diffusivity and thermal effusivity

In this paper we describe a new, simple and fast photothermal method for characterizing simultaneously the thermal diffusivity and thermal effusivity. The improved PTGA essentially combines a photoacoustic cell and a thermal wave pyroelectric cell enclosed in a single compact gas analyzer. The photo- acoustic cell is kept filled with nitrogen and sealed. The pyroelectric cell is also filled with nitrogen and after some warm up time, the nitrogen is exchanged to the gas of interest. It is shown that the analysis of the transient and saturation signals of both photoacoustic and pyroelectric cells are capable of measuring the thermal properties with an accuracy of 5%. The measurements were performed for hydrocarbons as ethane and propane, which are combustible gases. Knowing thermal diffusivity and effusivity, others important properties can be determinate: the thermal conductivity and the volumetric thermal capacity.     

Phytochemical characterisation and bioprospection for antibacterial and antioxidant activities of Lippia alba Brown ex Britton & Wilson (Verbenaceae)

Ethanol extract and fractions obtained from fresh and dry aerial parts of Lippia alba were examined in order to determine their phytochemical composition, antioxidant capacity and antibacterial activities. The ethanol extracts and fractions exhibited an antioxidant effect by the DPPH assay, especially samples of fresh plant. HPLC analysis of the ethyl acetate fractions identified the presence of phenolic acids and flavonoids. The ethanol extract and fractions showed activity against reference and multidrug-resistant strains of Staphylococcus aureus and Enterococcus faecalis (MIC range 2000–250 μg/mL). The hexane and dichloromethane fractions of fresh plant showed better activity against reference strains of Escherichia coli (MIC of 250 and 125 μg/mL, respectively), but all extracts and fractions were less active against multidrug-resistant strains of all the Gram-negative species evaluated. The results showed that the extract and fractions of L alba aerial parts showed antibacterial activity, even against multidrug-resistant Gram-positive bacteria, and antioxidant effect (DPPH assay).     

Study of thermoanalytical behavior of heavier lanthanides terephthalates in air atmosphere

Journal of Thermal Analysis and Calorimetry - Coordination compounds of heavier lanthanides with terephthalate ligand have been synthesized and characterized employing simultaneous thermogravimetry...     

Solid-state 2-methoxybenzoates of light trivalent lanthanides

Solid-state LnL₃ compounds, where L is 2-methoxybenzoate and Ln is light trivalent lanthanides, have been synthesized. Thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy and elementary analysis were used to characterize and to study the thermal behaviour of these compounds. The results led to information on the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds. On heating these complexes decompose in three (Ce, Pr) or five (La, Nd, Sm) steps with the formation of the respective oxide: CeO₂, Pr₆O₁₁ and Ln₂O₃ (Ln=La, Nd, Sm) as final residues. The theoretical and experimental spectroscopic study suggests predominantly the ionic bond between the ligand and metallic center.     

Regioselective electrophilic substitution of 2,3-aziridino-γ-lactones: preliminary studies aimed at the synthesis of α,α-disubstituted α- or β-amino acids

2,3-Aziridino-γ-lactones are versatile synthons for the preparation of polysubstituted α- or β-amino acids. With the intention of preparing α,α-disubstituted α- or β-amino acids, regioselective electrophilic substitution of aziridino-γ-lactones at C2 was realized using two different methods. In the first, the anion was generated at C2 with LDA in the presence of the electrophilic agent. In the second method, the anion was trapped with TMS. Subsequent treatment of the C2 silylated product with a fluoride ion source regenerated the anion, which then reacted in situ with various electrophiles. Intramolecular aziridine opening of the C2 benzyl derivative prepared by the first method allowed access to a novel furan derivative, a direct precursor of an α,α-disubstituted β-amino acid.     

ESR and endor studies of the VK center in SrF2

The results of electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) studies of a self-trapped hole (V_K center) in SrF₂ are reported. The g-factor and hyperfine interaction constants were determined for the flourine nuclei forming the center and for those in the nearest three different sites. The values of hyperfine interaction constants are intermediate to the known values for CaF₂ and BaF₂.     

The calculated performance of forest structure and biomass estimates from interferometric radar

Vertical structure and biomass are key characteristics of the forest random medium. This paper calculates the power and interferometric synthetic aperture radar (InSAR) sensitivity to tree height and vegetation density as it manifests in extinction, using a homogeneous, random-volume model of the forest medium, and accounting for speckle and thermal noise. Tree height and extinction are both related to biomass within the context of this simple model. Signal and noise calculations show that InSAR coherence and phase are more sensitive than radar power to structure and biomass to 10% variations in structure parameters over a wide range of medium to high density forests. For example, for extinctions of 0.2 db m^-1 and other parameters as noted in the text, the sensitivity of InSAR coherence to 10% changes in tree height exceeds observation errors for trees shorter than about 37 m, as opposed to 14 m for radar power. InSAR phase sensitivity to 10% structural and associated biomass changes exceeds observation errors for all tree heights. Only for the very lowest densities, for extinctions less than 0.15 db m^-1, does radar power sensitivity to density exceed that of InSAR; even at low densities, InSAR sensitivity to tree height outperforms that of radar power in these calculations.     

Myeloperoxidase inhibitory and radical scavenging activities of flavones from Pterogyne nitens

Two new flavone glucosides, nitensosides A and B (1, 2), together with four known compounds, sorbifolin (3), sorbifolin 6-O-beta-glucopyranoside (4), pedalitin (5), and pedalitin 6-O-beta-glucopyranoside (6) were isolated from Pterogyne nitens. Their structures were elucidated from 1D and 2D NMR analysis, as well as by high resolution mass spectrometry. All the isolated flavones were evaluated for their myeloperoxidase (MPO) inhibitory activity. The most active compound, pedalitin, exhibited IC50 value of 3.75 nM on MPO. Additionally, the radical-scavenging capacity of flavones 1-6 was evaluated towards ABTS and DPPH radicals and compared to standard compounds quercetin and Trolox.