[13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine

The room temperature [¹³C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [¹³C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol^–1, respectively, are in good agreement.     

N-demethylation of methylene blue by lignin peroxidase from Phanerochaete chrysosporium

Applied Biochemistry and Biotechnology - Phanerochaete chrysosporium lignin peroxidase (LiP) can degrade synthetic dyes such as heterocyclic, azo, and triphenylmethane on its activation by H2O2....     

Characterization of an all Sol-Gel Electrochromic Device WO3/Ormolyte/CeO2-TiO2

Electrochemical lithium intercalation in thin films of CeO₂-TiO₂ and WO₃, prepared by the sol-gel technique was investigated with cyclic voltammetry and spectroelectrochemical techniques in propylene carbonate solutions. A solid state system having the configuration WO₃/Ormolyte/CeO₂-TiO₂ has been assembled. The solid electrolyte, an organically modified electrolyte (ormolyte), was prepared with different [O]/[Li] ratios. The transmittance variation of this system during a potentiostatic step from –0.7 V to 0.8 V was about 35% at 550 nm.     

Application of Tungsten-Rhodium Permanent Chemical Modifier in Slurry Analysis: Determination of Cadmium

 A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in sediment slurries by electrothermal atomic absorption spectrometry. Slurries were ultrasonicated during 20 s before being delivered to the previously W-Rh treated platform. The permanent W-Rh modifier remains stable by approximately 250 measurements when 20 μl of slurries containing up to 1.0% m/v are delivered into the atomiser. In addition, the permanent modifier increases the tube lifetime up to 720 analytical firings. Also, when the W-Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput. The atomiser lifetime was limited to the THGA wall durability, because the W-Rh treated platform was intact after more than 720 analytical firings. Detection limits based on integrated absorbance for 1.0% m/v slurries were 1.5 ng g⁻¹ Cd for 250 μg W +200 μg Rh permanent modifier and 11.5 ng⁻¹ Cd for 5 μg Pd +3 μg Mg(NO₃)₂. Results for the determination of cadmium in sediment slurries using the W-Rh permanent modifier were in agreement with those obtained with dissolved sample solutions by using Pd + Mg(NO₃)₂, since no statistical differences were found by the paired t-test at the 99% level. Received September 6, 1999. Revision December 1, 1999.     

Evaluation of Mercury Levels in Sediment and Soil Samples from Vila Nova River Basin, in Amapá State, Brazil, Using Radiochemical Neutron Activation Analysis

In the present work, results from a survey on mercury concentration in sediments and soils from a gold mining area along the Vila Nova river, in Amapá State, Brazil, are presented. These values were compared with those from the Igarapé Pedra Preta basin, an area unaffected by mining activities. Total mercury contents were determined in the muddy (silt+clay) fraction of the sediments and in the <2 mm fraction of the soils using radiochemical neutron activation analysis (RNAA). The detection limit of the method was 54 µg·kg^–1 for soils and 14 µg·kg^–1 for sediments when 200 mg of sample were analysed. The Hg results obtained from a comparison between our current method (RNAA) and CV AAS are also presented. Mercury levels showed to be very high in the soils and sediments collected in the Vila Nova river (up to 2 mg·kg^–1) when compared to background values (0.3 mg·kg^–1) for this region. An enrichment factor was calculated, using Al as a normalizing factor. It showed values up to 8 in sediments of the Vila Nova river basin, indicating a relatively high degree of pollution as compared to the values of about 1 for the samples of the Igarapé Pedra Pretra basin.     

Evaluating Lipschitz Constants for Functions Given by Algorithms

This paper describes an efficient method (O(n)) to evaluate the Lipschitz constant for functions described in some algorithmic language. Considering arithmetical operations as the basis of the algorithmic language and supported by control structures, the rules to evaluate such Lipschitz constants are presented and their correctness is proved. An extension of the method to evaluate Lipschitz constants over interval domains is also presented. Examples are presented, but the effectiveness of the method is doubtful when compared to other approaches, and effective enhancements based on slope evaluations are also explored.     

Alternatives to a Semi-Parametric Estimator of Parameters of Rare Events—The Jackknife Methodology*

In this paper, and in a context of regularly varying tails, we propose different alternatives to a well-known estimator of the tail index—the Hill estimator (Hill, 1975). These alternatives have essentially in mind a reduction in bias, preferably without increasing Mean Square Error, by the use of suitable Generalized Jackknife methodologies (Gray and Schucany, 1972). The first estimate obtained through this methodolgy is the one introduced by Peng (1998), under a different context. Other Generalized Jackknife estimators are linear combinations of Hill estimators at different levels. This methodology of affine combinations of Hill estimators at different levels may be easily generalized to other semi-parametric estimators of the tail index, like Pickands' estimator (Pickands, 1975) or the Moment's estimator (Dekkers et al., 1989), and consequently to a general real tail index, seeming to be a promising field of research.     

A Single-Gallery Model for the In Situ Production of Polyethylene-Clay Nanocomposites

Polyolefin-clay nanocomposites are finding many new applications because of their improved properties, such as high modulus, elevated scratch resistance and low gas permeability. Currently, these composites are produced by melt blending organically modified clay with polyolefins. The most challenging step in this process is the intercalation and exfoliation of the clay to produce a homogenously dispersed phase at the nanoscale. A promising alternative to melt blending is in-situ polymerization, where the polymer is produced between the clay layers in the polymerization reactor. In-situ polymerization of olefins with metallocene catalysts supported on clay can produce nanocomposites using conventional polymerization reactors, provided that the clay can be used as a support for the olefin polymerization catalyst. In this approach, the clay fulfills the functions of catalyst support and dispersed phase in the final nanocomposite. In this work, a mathematical model describing particle growth during in-situ polymerization of ethylene with a metallocene catalyst supported on clay will be discussed. The model expands the approach of the multi-grain model used in heterogeneous olefin polymerization to account for the layered structure of clays.     

Effect of Wood Content on The Thermal Behavior and on The Molecular Dynamics of Wood/Plastic Composites

Summary: In the last decades, the growing environmental awareness has resulted in a renewed interest in the use of natural materials for different applications. In this context, the use of wood in plastic to obtain composites has grown significantly. In the present work, heartwood and sapwood from Angelim Pedra (Hymenolobiun petraeum) were used to prepare PVC/wood composites. To study the composites with different wood types and filler contents the molecular dynamic was investigated through low field NMR by poton spin- lattice relaxation time measurements (T₁H) and the thermal behavior was characterized by means of differential scanning calorimetry (DSC) focusing the glass transition temperature and thermogravimetric analyses (TGA) observing the changes in the thermal stability. It was found that increasing addition of wood flour (sapwood and heartwood) caused a small but progressive improvement of the decomposition temperature of the composites, whereas the glass transition temperature remains practically unchanged. In the molecular dynamic behavior, a gradual decrease in T₁H values was observed with increasing sapwood and heartwood content, indicating that the composites became less rigid. The distribution curves of the domains showed a better interaction and phase dispersion between the composite components with higher filler content.     

Thermal Characterization of Warifteine by Means of TG and a DSC Photovisual System

This work proposes thermal characterization as analytical methodology for the identification and purity assay of warifteine, an alkaloid in Cissampelos sympodialis Eichl. Thermal and kinetic parameters were determined by means of TG and DSC photovisual studies. The TG results showed that the decomposition of warifteine in air and nitrogen atmospheres proceeds in three and four steps, respectively. The TG data allowed calculation of the kinetic parameters of warifteine. The activation energy values obtained by different methods displayed a good correlation. With the DSC photovisual system applied it is possible to detect the impurity level in warifteine after its purification. This revised version was published online in July 2006 with corrections to the Cover Date.