Application to QSAR studies of 2-furylethylene derivatives

A quantitative structure–activity relationship (QSAR) is a mathematical model that relates a molecular structure to a physicochemical property or a biological activity. The log P of a set of 38 of 2-furylethylenes, biologically active substances exhibiting a broad spectrum of antimicrobial, antiparasitic, cytotoxic, carcinogenic and mutagenic activities, was modeled by using topological indices provided by TOPOCLUJ and DRAGON software packages. The models derived showed good stability and predictability (as given by the leave-one-out LOO cross-validation data). The results are compared with those reported in literature, obtained by different methodology.     

Extended diffusion in a double well potential: Transition from classical to quantum regime

The transition between the classical and quantum regimes in the diffusion of a particle in a 2-4 double-well potential is treated via the strong collision model in the high-temperature limit. Both the classical and semiclassical position correlation functions, their spectra, and correlation times are evaluated using the memory function formalism. It is shown that even in the high temperature limit, marked classical-quantum transition effects appear in the observables when collisions are rare.     

Siloxane‐Crown Ether Polyamide Based Electrode for Electrochemical Determination of Lead(II) in Aqueous Solution

A siloxane‐crown ether polyamide copolymer (PDMS‐PA‐DB18C6) was electrochemically investigated for fabrication of lead‐sensitive electrodes for trace analysis in aqueous solutions. The PDMS‐PA‐DB18C6 electrodes were successfully evaluated for anodic stripping voltammetric determination of lead(II) as a promising alternative for the detection of lead at ppb levels. By a judicious choice of the deposition time, electrolyte concentration and pulse amplitude, good analytical performance of the developed sensor could be achieved, with a linear response in the range of 20–700 ppb, when LOD of 3.5 ppb could be attained. This method showed a good degree of selectivity and sensitivity for lead, suitable for the determination of Pb²⁺ in wastewater sample.     

Synergistic effect of mediator–carbon nanotube composites for dehydrogenases and peroxidases based biosensors

Very sensitive, low cost and reliable NADH and H₂O₂ sensors were realised and used for development of enzyme based biosensors. The active surface of the electrodes was modified with a nanocomposite obtained by modification of SWNT with a proper mediator: Meldola Blue (for NADH) and Prussian Blue (for H₂O₂). Low applied potential of − 50 mV vs. Ag/AgCl reference electrode proved the synergistic effect of nanocomposite materials towards NADH and H₂O₂ detection. Biosensors for malic acid and alkylphenols have been developed, using mediator-functionalised-SWNT-based electrodes and two different classes of enzymes: NAD⁺-dependent dehydrogenases and peroxidases. Immobilization of the enzymes was realised using a series of different procedures — adsorption, Nafion membrane, sol–gel and glutaraldehyde, in order to find the best configuration for a good operational stability. A higher sensitivity comparing with other reported biosensors of about 12.41 mA/M·cm² was obtained for l-malic acid biosensor with enzyme immobilised in Nafion membrane. Phenol, 4-t-octylphenol and 4-n-nonylphenol were used as standard compounds for HRP based biosensor. Fast biosensor response and comparable detection limit with HPLC methods were achieved.     

Characterisation of five coins from the archaeological heritage of Portugal

This paper reports a study carried out on three Roman and two Portuguese coins found in the archaeological site of São Pedro, in Fronteira (Alentejo, Portugal). The three Roman coins have been identified as a Follis, an AE 2 and an AE 3 (bronze alloys), while the Portuguese coins have been identified as a Ceitil (copper) and the “6 vinténs” (Ag–Cu alloy). Scanning electron microscopy (SEM) coupled to energy dispersive spectroscopy (EDS) has allowed the semi-quantitative determination of the elemental composition of both the corrosion products and the alloy used in the manufacture of the coins. The crystalline corrosion products constituents of the patinas were identified by X-ray powder diffraction spectroscopy (XRD). The more deteriorated coin, the AE 3, was submitted to electrochemical studies in Na₂SO₄ aqueous solution and the corresponding data analysed. After 3 weeks, the E _OCP was still quite stable, ranging between ?0.050 and ?0.070 V vs. SCE; the corrosion resistance, R _p, was of the order of 5 to 3?×?10³ Ω. Chemical treatment of the sample by 1-h immersion in 0.1 M NaOH produced a more active surface, with R _p showing a decrease of a factor of about ten. On the other hand, it was concluded from voltammetric data that polarisations of E _a?≥?0.050 V vs. SCE led to copper oxidation, with no reduction of the other corrosion products.     

Relationship between polypyrrole morphology and electrochemical activity towards oxygen reduction reaction

The relationship between the morphology of polypyrrole and their electrocatalytic performances towards the oxygen reduction reaction (ORR) in alkaline media is described; annealed polypyrrole with granular- and tubules-like morphology exhibited different catalytic efficiencies.     

Application of sulphur isotopes for stratigraphic correlation

The sulphur isotopic composition of dissolved sulphate in seawater has varied considerably through time. Certain time intervals are characterised by distinct variations and a relatively high rate of change. These relatively rapid fluctuations allow for correlation of sediment sections using sulphur isotopes. Sulphur isotope reconstructions based on the analysis of carbonate associated sulphate or marine barite result in sulphur isotope records with an age resolution of 1-5 million years (Ma), and for some age intervals the resolution is<0.25?Ma. At these specific time intervals, where higher resolution records exist and excursions in the record are identified, the trends could be used for stratigraphic correlations. Such records are particularly useful in sections from deep marine sites that lack biostratigraphic controls or where biozones do not provide sufficient resolution.     

Thermal stabilities of some benzaldehyde 2,4-dinitrophenylhydrazones

The thermal stability of some benzaldehyde 2,4-dinitrophenylhydrazones has been studied using DSC technique. The crystalline solids are thermally stable and start to decompose after melting. Non-isothermal DSC curves, recorded at several heating rates, were used to evaluate the melting properties and the kinetics of thermal decomposition. Both isoconversional and model fitting methods were used for the evaluation of the kinetic parameters. Based on the results of the model free method, a kinetic model was derived and the kinetic parameters were obtained by means of a multivariate non-linear regression. A good agreement between the experimental and fitted data was found.     

Assembly of a novel supramolecular synthon of calix[4]arene presenting four carboxylic acids

An extremely complex solid state structure described by two virtual channels and a 2-D square grid of hydrogen bonds is generated by four carboxylic acids groups of calix[4]arene tetrabutyroxycarboxylic acid.     

Exponential Dichotomy on the Real Line and Admissibility of Function Spaces

The purpose of this paper is to give characterizations for uniform exponential dichotomy of evolution families on the real line. We consider a general class of Banach function spaces denoted and we prove that if with and the pair is admissible for an evolution family then is uniformly exponentially dichotomic. By an example we show that the admissibility of the pair for an evolution family is not a sufficient condition for uniform exponential dichotomy. As applications, we deduce necessary and sufficient conditions for uniform exponential dichotomy of evolution families in terms of the admissibility of the pairs and with