Polarographic determination of sunscreen agents in cosmetic products in micellar media

This paper introduces a simple, fast and reliable electroanalytical method for differential-pulse polarography based on electrochemical reduction at a dropping mercury electrode. The method was validated for the determination of 2-ethylhexyl-4-methoxycinnamate (EHMC) alone and in association with 4-methylbenzylidene camphor (MBC) or 2-hydroxy-4-methoxybenzophenone (BENZ-3) in samples of commercial cosmetic preparations. The supporting electrolyte that provided the best-defined and most intense peak current for EHMC determination was Britton-Robinson buffer (pH 4.0) in the presence of a cationic surfactant. Under optimized conditions, EHMC exhibited one single peak of reduction at −1.49 V versus Ag/AgCl. A limit of detection of 3.76 × 10⁻⁸ mol L⁻¹ and a limit of quantitation of 1.25 × 10⁻⁷ mol L⁻¹ were found for the pure EHMC standard. A good average recovery rate was reached for all the samples analyzed.     

Incorporation of Ag nanoparticles into membrane mimetic systems composed by phospholipid layer‐by‐layer (LbL) films to achieve surface‐enhanced Raman scattering as a tool in drug interaction studies

The synergistic effect produced by nanoparticles when incorporated into different systems used as analytical tools represents a growing research field nowadays. On the other hand, the study of interactions involving pharmacological drugs and biological membranes using phospholipids as mimetic systems is a research field already well established. Here, we combine both the anionic phospholipid dipalmitoyl phosphatidyl glycerol (DPPG) and negative Ag nanoparticles (AgNP) to form layer‐by‐layer (LbL) multilayered films using the cationic polymer poly(allylamine hydrochloride) (PAH) as the supporting polyelectrolyte, which were further investigated in the presence of a phenothiazine compound (methylene blue—MB). The molecular architecture of the LbL films in terms of controlled growth, morphology with micro and nanometer spatial resolutions, and dispersion of both AgNP and MB within the DPPG matrix was determined combining spectroscopy [ultraviolet–visible (UV–Vis) absorption and micro‐Raman spectroscopy] and microscopy [scanning electron microscopy (SEM) and atomic force microscopy (AFM)]. The results showed that the LbL films can be grown in a controlled way at nanometer thickness scale with the surface morphology susceptible to the presence of both AgNP and MB. The surface‐enhanced phenomenon was applied to investigate the LbL films taking the advantage of the strong surface‐enhanced resonance Raman scattering (SERRS) signal presented by the MB molecules. Besides, as MB is a pharmacological drug of interest, its molecular arrangements when dispersed in LbL films containing DPPG, which is the biological membrane mimetic system here, were investigated. In this case, the AgNP played a key role in achieving the MB SERRS signal. Copyright © 2009 John Wiley & Sons, Ltd.     

A bundle-filter method for nonsmooth convex constrained optimization

For solving nonsmooth convex constrained optimization problems, we propose an algorithm which combines the ideas of the proximal bundle methods with the filter strategy for evaluating candidate points. The resulting algorithm inherits some attractive features from both approaches. On the one hand, it allows effective control of the size of quadratic programming subproblems via the compression and aggregation techniques of proximal bundle methods. On the other hand, the filter criterion for accepting a candidate point as the new iterate is sometimes easier to satisfy than the usual descent condition in bundle methods. Some encouraging preliminary computational results are also reported.     

Detection of trace levels of atrazine using surface-enhanced Raman scattering and information visualization

The detection of trace amounts of pesticides is essential for the quality control of waters, particularly with their inevitable increasing use with the growing demand for food. In this study, we report on the detection of atrazine, a highly toxic herbicide, down to 5?×?10^?12 M, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations. Such detection was performed with surface-enhanced Raman scattering (SERS) in atrazine incorporated into silver nanoparticles (AgNPs) colloids, with the SERS spectra being treated with Sammon’s mapping, an information visualization technique. In addition to providing a fingerprint of the atrazine molecules, SERS is advantageous in comparison with impedance spectroscopy and cyclic voltammetry applied to a sensor array of units made with layer-by-layer (LbL) films containing AgNPs and AuNPs. The combined use of SERS and information visualization methods is promising for monitoring water quality with regard to other pesticides, which may even approach single molecule detection.     

A Novel Asymmetric Total Synthesis of (+)-Artemisinin

A 12-step synthesis of the natural product (+)-Artemisinin, very active against malaria, is described. (-)-Isopulegol, which already contains two of the asymmetric centers of (+)-Artemisinin in the correct absolute configuration, was used as starting material.     

Bionanocomposites of Cassava Starch and Synthetic Clay

Starch-based biofilms containing synthetic Laponite clay and glycerol were prepared using a solvent casting technique. Electron microscopy images showed predominance of the exfoliated type of nanocomposite. Dynamic mechanical analysis revealed a larger influence of glycerol content on the polymer β relaxation and T _g than the clay content. Gas barrier properties were influenced by clay particles and plasticizer content. An increase of clay content led to lower gas permeability values. Although both glycerol and Laponite are hydrophilic, no significant changes were observed on the water sorption by starch films at different relative humidity values. Mechanical properties are kept similar after the inorganic filler incorporation.     

Poisson-Boltzmann description of the electrical double layer including ion size effects

The electrical double layer is examined using a generalized Poisson-Boltzmann equation that takes into account the finite ion size by modeling the aqueous electrolyte solution as a suspension of polarizable insulating spheres in water. We find that this model greatly amplifies the steric effects predicted by the usual modified Poisson-Boltzmann equation, which imposes only a restriction on the ability of ions to approach one another. This amplification should allow for an interpretation of the experimental results using reasonable effective ionic radii (close to their well-known hydrated values).     

High Quantum Efficiency of Nd3+ Ions in a Phosphate Glass System using the Judd–Ofelt Theory

The optical properties of trivalent neodymium embedded in a P₂O₅–Al₂O₃–Na₂O–K₂O phosphate glass system, synthesized by the fusion method, are studied. Absorption, luminescence, lifetime, and Raman spectroscopy measurements were performed and the Judd–Ofelt theory was applied to determine optical parameters such as the quantum efficiency and the stimulated emission cross section of the Nd³⁺-doped glass system. This structure has high quantum efficiency at low Nd³⁺ concentrations, comparable to the efficiency of a commercial YAG:Nd³⁺ crystal. We discuss the mechanisms responsible for the high quantum efficiency observed in the proposed phosphate glass system.     

New insights on integer-programming models for the kidney exchange problem

In recent years several countries have set up policies that allow exchange of kidneys between two or more incompatible patient–donor pairs. These policies lead to what is commonly known as kidney exchange programs.