Prediction of solvent accessibility of amino acid residues: critical aspects

For predicting solvent accessibility from the sequence of amino acids in proteins, we use a logistic function trained on a non-redundant protein database. Using a principal component analysis, we find that the prediction can be considered, in a good approximation, as a monofactorial problem: a crossed effect of the burial propensity of amino acids and of their locations at positions flanking the amino acid of interest. Complementary effects depend on the presence of certain amino acids (mostly P, G and C) at given positions. We have refined the predictive model (1) by adding supplementary input data, (2) by using a strategy of prediction correction and (3) by adapting the decision rules according to the amino acid type. We obtain a best score of 77.6% correct prediction for a relative accessibility of 9%. However, compared to trivial strategy only based upon the frequencies of buried or exposed residues, the gain is less than 4%. Received: 4 June 1998 / Accepted: 17 September 1998 / Published online: 10 December 1998     

Some new aspects related to the synthesis of meso-substituted porphyrins

A general analysis of the steps of the Rothemund reaction, allowed for a better understanding and a significant improvement of this reaction as a synthetic method in some of the previously known difficult syntheses.     

Medical and organizational aspects related to the Goiânia accident

On 13 September 1987, a severe radiation accident occurred in the city of Goiânia in central Brazil. Approximately 250 people were directly affected by the radiation, receiving slight to very severe external, partial or whole body, irradiation, and presenting internal and external contamination. Fourteen patients developed some degree of marrow failure, eight developed the clinical signs and symptoms of acute radiation syndrome (ARS), and four eventually died of ARS complications. Twenty-eight people showed acute localized radiation injuries ranging from first to third degree. The author describes the circumstances of the event, the first-aid measures taken on the site, and the medical structure organized to triage and treat the casualties. Aspects relating to hospital contamination control, radiation protection and decontamination procedures are also discussed.     

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

The application of thermodynamics of eutectoid copolymers and a generalized Tabor-relation to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by results on melt-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despite being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries (meso-crystals) which yield cooperatively.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.     

Critical aspects related to processing of carbon nanotube/unsaturated thermoset polyester nanocomposites

Carbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH₂) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix.     

Phenomenological aspects related to the electrochemical behaviour of smooth palladium electrodes in alkaline solutions

The voltammetric behaviour of smooth palladium electrodes in 1 M NaOH is studied in the potential range related to the thermodynamic stability of water. The electrosorption of H atoms on bulk Pd appears as a reversible reaction coupled to a diffusion process which occurs within bulk Pd. The voltammetric electrodesorption of H from bulk Pd is a process under mixed control, i.e. the diffusion from the bulk and the surface oxidation of H atoms. Fast pseudocapacitive reactions are detected in the range 0.2–0.4 V associated with the adsorption of H atoms at the submonolayer level. The initial stages of Pd oxide layer formation, at ca. 0.68 V, involves two reversible stages. The Pd oxide monolayer formation is achieved at 1.25 V/RHE and is followed by the formation of a third reversible system. This system is enhanced by an excursion in the potential range of the oxygen evolution reaction. This reversible system is probably a redox system involving Pd(II)/Pd(IV) species. The voltammetric electroreduction of the Pd oxide film shows rather irreversible behaviour. Inhibition effects on the reversible adsorption of H atoms due to residual oxide species were observed as well as inhibition on loading the Pd electrode with hydrogen to form the (α + β)-PdH phase. Rotating ring-disc experiments demonstrate that Pd electrodissolution in basic solutions is much smaller than in acid solutions. However, soluble palladium species are detected, especially during the formation of the fast redox systems, in the potential range related to Pd oxide layer growth.     

Applicability of direct total reflection X-ray fluorescence analysis for selenium determination in solutions related to environmental and geochemical studies

A significant amount of environmental studies related to selenium determination in different environmental compartments have been published in the last years due to the narrow range between the Se nutritious requirement as essential element and toxic effects upon exposure. However, the direct analysis of complex liquid samples like natural waters and extraction solutions presents significant problems related to the low Se concentrations and the complicated matrix of this type of samples.     

Synthesis, structure, and biological aspects of cyclopeptides related to marine phakellistatins 7-9

Phakellistatins 7, 8 and 9, three cyclic decapeptides naturally occurring in marine sponges of the genus Phakellia and characterized by the distinctive presence of Pro-Pro tracts, pose a non-trivial synthetic challenge, despite only containing coded amino acid residues. Their chemical synthesis was approached using a combination of solid and solution-phase techniques. As expected, our synthetic efforts yielded, for each cyclopeptide, a mixture of geometric isomers, owing to their cis-trans isomerism at Pro peptide linkages. A further complication arose because their synthesis yielded, together with the desired monomeric cyclopeptides, cyclodimeric species. In the case of phakellistatin 7 (originally determined as cis-Pro², cis-Pro⁸) our synthetic product was chemically and spectrally identical to the natural one, whereas none of the different isomeric products obtained for both phakellistatins 8 and 9 resulted to be fully equivalent (with respect to Pro geometries) to their natural counterparts. Finally, all synthetic cyclopeptides were submitted to biological assays and, as noted before for other members of the ‘proline rich’ family, synthetic compounds did not fully reproduce the biological properties (in terms of in vitro cytotoxicity against a panel of cancer cell lines) originally found for the natural products.     

Conversion of spent coffee grounds to biochar as promising TiO2 support for effective degradation of diclofenac in water

A novel composite, biochar derived from spent coffee grounds with immobilized TiO₂ (biochar–TiO₂) was prepared, characterized, and applied as an alternative, effective, and sustainable photocatalyst for degrading diclofenac from aqueous solution. Composites with different mass ratios between TiO₂ and biochar were prepared by mechanical mixing and subsequent pyrolysis in an inert atmosphere of N₂ at 650°C. The sample with biochar–TiO₂ ratio of 1:1 presented a degradation efficiency of 90% at just 120 min versus 40% for TiO₂ used as reference. This fact is associated with a set of intrinsic characteristics obtained during the formation of the composite, such as superior pore size, avoiding the recombination of the ē/h⁺ pair, bandgap reduction, and promotion of reactive oxygen species due to phenolic groups present on the biochar surface. The dominant reactive species involved during the photocatalytic degradation of diclofenac were h⁺ and ^•OH. The diclofenac degradation pathways were determined based on the identification of intermediates and nonpurgeable organic carbon (NPOC) analysis. The novel biochar–TiO₂ composite prepared in this work showed high physical–chemical stability and efficiency over five consecutive cycles of reuse, proving to be a highly promising photocatalyst for degrading diclofenac in water.     

Three-way catalytic converter reactions aspects at near-ambient temperatures on modified Pd-surfaces

The dissolution of oxygen in palladium plays an important role in palladium catalysis. The present study shows that the surface modification (SM) due to the dissolution of atomic oxygen into the subsurfaces of palladium can be used as a control to tune its catalytic activity. CO oxidation and NO + H₂ + O₂ reaction was separately carried out on metallic Pd and on surface modified Pd using a molecular beam instrument and the results were compared. The metallic Pd does not show activity below 400 K for both reactions, whereas the SM-Pd shows activity at near-ambient temperatures. The electronic change due to SM was investigated using ambient pressure photoelectron spectroscopy, and the investigation clearly shows the effect of subsurface oxygen in the ambient temperature activity of palladium.     

Toxicological problems relating to changes in the environment

Assessment of the toxicological risk from foreign substances in the environment is based on the determination of action thresholds below which effects injurious to health no longer occur, even with life-long intake. According to the latest theories it is likely that such thresholds exist even for “irreversible” (carcinogenic, mutagenic) effects. However, the difficulties besetting the determination of threshold values by experimental or epidemiological methods still appear to be virtually insuperable. The problems are both quantitative (excessive numbers of animals and observations required) and qualitative (poor predictability of effects owing to substantial differences in biological reactivity between species). Neither animal experiments nor experience with human subjects can guarantee total security from toxic effects. Legislative measures designed to restrict the introduction of chemical substances into the environment must therefore be based on compromise. Scientists must be consulted, but ultimately the decisions must be political, and politicians have to assume the responsibility for them.     

On aspects of the dynamic behavior of persistent chemicals in a multimedia environment related to exposure-based hazard assessment

The present research study focuses on the analysis and characterization of certain aspects of the dynamic behavior displayed by persistent chemicals in a multimedia environment (chemodynamics), which is jointly determined by the inherent physicochemical properties of the chemical substance under consideration, as well as underlying environmental processes such as degradation in different phases/media (soil, water and air) coupled with intermedia transport (interphase mass transfer). In particular, dynamic multimedia environmental models are considered with constant source terms describing steady chemical release/discharge rates into various environmental media of interest, and key risk-related aspects of the dynamic behavior of persistent chemicals are analyzed using perturbation theory techniques under conditions where degradation rates in different media are considerably slower than intermedia transport rates. Under the above conditions, the problem of defining physically meaningful and practical quantitative measures of overall persistence of chemicals in a multimedia environment is revisited, given its role as a key exposure-based indicator within all major chemical risk assessment frameworks, and a proof is provided that rigorously establishes equivalence between two important and popular persistence measures, namely the characteristic time at steady state and the inverse of the associated chemodynamics overall decay rate (slowest chemodynamic mode).     

Analytical and environmental aspects of the flame retardant tetrabromobisphenol-A and its derivatives

The present article reviews the available literature on the analytical and environmental aspects of tetrabromobisphenol-A (TBBP-A), a currently intensively used brominated flame retardant (BFR). Analytical methods, including sample preparation, chromatographic separation, detection techniques, and quality control are discussed. An important recent development in the analysis of TBBP-A is the growing tendency for liquid chromatographic techniques. At the detection stage, mass-spectrometry is a well-established and reliable technology in the identification and quantification of TBBP-A. Although interlaboratory exercises for BFRs have grown in popularity in the last 10 years, only a few participating laboratories report concentrations for TBBP-A. Environmental levels of TBBP-A in abiotic and biotic matrices are low, probably due to the major use of TBBP-A as reactive FR. As a consequence, the expected human exposure is low. This is in agreement with the EU risk assessment that concluded that there is no risk for humans concerning TBBP-A exposure. Much less analytical and environmental information exists for the various groups of TBBP-A derivatives which are largely used as additive flame retardants.     

砷污染对植物和人体健康的影响及防治对策

讨论了土壤环境背景值及来源，地植物和人体健康的影响，砷的环境质量标准，国内外砷对环境的情况，以及砷污染防治对策。。     

Fluorescence polarization immunoassays and related methods for simple, high-throughput screening of small molecules

Fluorescence polarization immunoassay (FPIA) is a homogeneous (without separation) competitive immunoassay method based on the increase in fluorescence polarization (FP) of fluorescent-labeled small antigens when bound by specific antibody. The minimum detectable quantity of FPIAs with fluorescein label (about 0.1 ng analyte) is comparable with chromatography and ELISA methods, although this may be limited by sample matrix interference. Because of its simplicity and speed, FPIA is readily automated and therefore suitable for high-throughput screening (HTS) in a variety of application areas. Systems that involve binding of ligands to receptor proteins are also susceptible to analysis by analogous FP methods employing fluorescent-labeled ligand and HTS applications have been developed, notably for use in candidate drug screening.     

生物传感器在环境监测中的应用

对1994~2009年间生物传感器在环境监测中的应用进展作了评述,涉及的主题有生物传感器在水样、大气和土壤分析中的应用(引用文献42篇)。     

电感耦合等离子体原子发射光谱法在环境分析中的应用

对1996—2010年间电感耦合等离子体原子发射光谱法在环境分析中的应用进展作了评述,主要涉及在大气和飞灰、水、土壤、污泥和植物等方面中的应用(引用文献23篇)。     

Proficiency testing in occupational and environmental health – Current practice and international initiatives for harmonisation

An increasing number of proficiency testing schemes (PT schemes) related to occupational and environmental health have been organised. Most schemes emphasise the importance of the validation of analytical results. With regards to harmonisation of the schemes, there are many differences between the schemes at many levels. These include factors concerning their relationship with legislation, national status, type and quality of proficiency testing material, analytical range and priorities for future development. Since differences between PT schemes have been recognised at the European level by organisers of PT schemes and external quality assessment schemes (EQASs) it seems appropriate to reinforce collaboration between scheme organisers in order to improve the quality of analytical performance in occupational and environmental health.