Diffuse Ultraviolet Erythemal Irradiance on Inclined Planes: A Comparison of Experimental and Modeled Data

Values of measured and modeled diffuse UV erythemal irradiance (UVER) for all sky conditions are compared on planes inclined at 40° and oriented north, south, east and west. The models used for simulating diffuse UVER are of the geometric-type, mainly the Isotropic, Klucher, Hay, Muneer, Reindl and Schauberger models. To analyze the precision of the models, some statistical estimators were used such as root mean square deviation, mean absolute deviation and mean bias deviation. It was seen that all the analyzed models reproduce adequately the diffuse UVER on the south-facing plane, with greater discrepancies for the other inclined planes. When the models are applied to cloud-free conditions, the errors obtained are higher because the anisotropy of the sky dome acquires more importance and the models do not provide the estimation of diffuse UVER accurately.     

Application of NMR methods to the study of the interaction of natural products with biomolecular receptors

In this review, we present applications of NMR spectroscopy as a potent tool for the study of molecular interactions. It is clear that a variety of NMR methods may be employed to deduce key features of ligand–receptor molecular recognition processes, looking at the process from the perspective of the receptor or the ligand. We have not provided an exhaustive review, but we have tried to focus on describing the different aspects within this research topic. We have therefore selected examples accordingly, depending on the particular problem under study or the application/development of protocols to circumvent the technical problems that may be found when working in this field.     

On the variational procedure with orthogonalization pseudo-Hamiltonians

For the case of Hamiltonians with possibly non-Hermitian repulsive potential, the applicability is shown of the actual scheme used for construction of the variational expression in the eigen-value problem with Hermitian operator. The hydrogen atom up to the 4d-state is numerically solved with four such pseudo-Hamiltonians using the same trial function, which yields possibility of comparison.     

WKB analysis of guided and semileaky modes in graded-index anisotropic optical waveguides

WKB analysis of graded-index anisotropic optical waveguides is briefly presented. The angular dependencies of the propagation characteristics of both guided and semileaky modes are calculated numerically for the out-diffused and in-diffused LiNbO₃ waveguides with parabolic index profile. The results for the out-diffused waveguide are compared with those obtained from the rigorous theory and the applicability of the WKG method is discussed for semileaky mode loss calculations. The angular dependence of the propagation constants of a TiO₂-diffused LiNbO₃ waveguide is demonstrated experimentally, too.     

Quantization of a nonlinear oscillator as a model of the harmonic oscillator on spaces of constant curvature: One- and two-dimensional systems

The quantum version of a nonlinear oscillator, previously analyzed at the classical level, is studied first in one dimension and then in two dimensions. This is a problem of quantization of a system with position-dependent mass of the form m = (1 + λx ²)⁻¹ and with a λ-dependent nonpolynomial rational potential. The quantization procedure analyzes the existence of Killing vectors and makes use of an invariant measure. It is proved that this system can be considered as a model of the quantum harmonic oscillator on two-dimensional spaces of constant curvature. The text was submitted by the authors in English.     

Increase of Redox Potential during the Evolution of Enzymes Degrading Recalcitrant Lignin

To investigate how ligninolytic peroxidases acquired the uniquely high redox potential they show today, their ancestors were resurrected and characterized. Unfortunately, the transient Compounds I (CI) and II (CII) from peroxide activation of the enzyme resting state (RS) are unstable. Therefore, the reduction potentials (E°′) of the three redox couples (CI/RS, CI/CII and CII/RS) were estimated (for the first time in a ligninolytic peroxidase) from equilibrium concentrations analyzed by stopped-flow UV/Vis spectroscopy. Interestingly, the E°′ of rate-limiting CII reduction to RS increased 70 mV from the common peroxidase ancestor to extant lignin peroxidase (LiP), and the same boost was observed for CI/RS and CI/CII, albeit with higher E°′ values. A straightforward correlation was found between the E°′ value and the progressive displacement of the proximal histidine Hϵ1 chemical shift in the NMR spectra, due to the higher paramagnetic effect of the heme Fe³⁺. More interestingly, the E°′ and NMR data also correlated with the evolutionary time, revealing that ancestral peroxidases increased their reduction potential in the evolution to LiP thanks to molecular rearrangements in their heme pocket during the last 400 million years.     

Mercury speciation in sea food by flow injection cold vapor atomic absorption spectrometry using selective solid phase extraction

An on-line inorganic and organomercury species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS or CV-ETAAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (i.d., 3 mm; length 3 cm) packed to a height of 0.7 cm with a chelating resin aminopropyl-controlled pore glass (550 A) functionalized with [1,5-bis (2 pyridyl)-3-sulphophenyl methylene thiocarbonohydrazyde] placed in the injection valve of a simple flow manifold. Methylmercury is not directly determined. Previous oxidation of the organomercurial species permitted the determination of total mercury. The separation of mercury species was obtained by the selective retention of inorganic mercury on the chelating resin. The difference between total and inorganic mercury determined the organomercury content in the sample. The inorganic mercury was removed on-line from the microcolumn with 6% (m/v) thiourea. The mercury cold vapor generation was performed on-line with 0.2% (m/v) sodium tethrahydroborate and 0.05% (m/v) sodium hydroxide as reducing solution. The determination was performed using CV-AAS and CV-ETAAS, both approaches have been used and compared for the speciation of mercury in sea food. A detection limit of 10 and 6 ng l(-1) was achieved for CV-AAS and CV-ETAAS, respectively. The precision for 10 replicate determinations at the 1 microg l(-1) Hg level was 3.5% relative standard deviation (R.S.D.), calculated from the peak heights obtained. Both approaches were validated with the use of two certified reference materials and by spiking experiments. By analyzing the two biological certified materials, it was evident that the difference between the total mercury and inorganic mercury corresponds to methylmercury. The concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total Hg(2+) and CH(3)Hg(+), according to the t-test for a 95% confidence level. It is amazing how this very simple method is able to provide very important information on mercury speciation.     

Ion mobility spectrometry of volatile compounds from Iberian pig fat for fast feeding regime authentication

Characteristic ion mobility spectra for volatile compounds present in fat were used to authenticate the feeding regime of Iberian pigs. Volatile compounds were obtained by heating the solid samples at 150 degrees C for 40 min. This produced a headspace that was introduced in the spectrometer ionization chamber by means of a highly purified nitrogen stream. The spectra thus, obtained for the fat samples were processed chemometrically in order to assess their usefulness for discriminating meat from free-range pigs fed on pasture and acorns and confined pigs fed with commercial feed including high-oleic acid products. Principal component analysis was used as both an exploratory tool and a variable reduction method, and linear discriminant analysis was employed to classify 65 subcutaneous fat samples according to pig feeding regime. Only 2.3% of the samples from pigs reared in confinement were misclassified. 95.5% of the free-range samples were correctly predicted.