Photoelectrochemical sensing of tannic acid based on the use of TiO<Subscript>2</Subscript> sensitized with 5-methylphenazinium methosulfate and carboxy-functionalized CdTe quantum dots

The article describes a method for determination of tannic acid in extracts of medicinal plants. Tannic acid (TA) is an antioxidant and has anticancer and antimicrobial properties. Titanium dioxide nanoparticles (TiO₂) were co-sensitized with 5-methylphenazinium methosulfate (PMS) and carboxy-functionalized cadmium telluride quantum dots (CdTe QDs), and immobilized on a fluorine-doped tin oxide electrode. The surface morphology and electrochemical properties of the modified electrode were investigated by scanning electron microscopy and amperometry, respectively. A composite consisting of TiO₂, PMS and CdTe QDs in a nafion film has a response to TA under LED light higher than that observed for each separate component. Under optimized experimental conditions and at an applied voltage of +0.4 V vs Ag/AgCl, the photoelectrochemical sensor has a linear response in the 0.2 to 200 μmol L^?1 TA concentration range and a detection limit of 60 nmol L^?1. The sensor was successfully applied to the determination of TA in spiked extracts from three medicinal plants, with recovery values between 98.3 and 103.9 %.

Open image in new window

Graphical abstract Schematic diagram for photoelectrochemical detection of tannic acid based on a fluorine doped tin oxide electrode modified with titanium oxide, 5-methylphenazinium methosulfate and carboxy-functionalized cadmium telluride quantum dots

     

Electroanalytical methods for determination of the metal content and acetic-acid-available metal fractions in soils

The pseudo-total and available arsenic, cadmium, and lead content of soils have been determined by stripping voltammetry with a hanging-mercury-drop electrode and by atomic absorption spectrometry with electrothermal atomization. For determination of pseudo-total metals microwave digestion with a mixture of HNO3 and HClO4, with and without addition of HF, was investigated. The single-extraction procedure with 0.43 mol L-1 CH3COOH, proposed by BCR, was used to assess the availability of metals in soils. The results obtained were validated by analysis of a certified reference material.     

Rare earths and other trace elements in cretaceous clays from central Portugal

Eight rare-earth elements (REE), namely La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu, as well as other elements (Na, K, Sc, Cr, Fe, Co, Rb, Cs, Ba, Hf, Ta, and Th), have been determined in fifteen cretaceous clay samples of continental facies by instrumental neutron activation analysis. It was found that the REE contents are variable in absolute and relative values, but the means of these values are similar to those of European, shales. Analyses have also been made of the fractions <38 m and <2 m (clay-sized). The mineral contents of the clay-sized fraction were determined semi-quantitatively by X-ray diffraction. The results suggest the preferential presence of REE, Hf, and Th in fractions 2–38 m, which can be explained by the presence of apatite, monazite, and zircon. A correlation study of chemical and mineralogical data of the clay-sized fraction showed that kaolinite is correlated with REE, specially the lighter ones; illite with K, Rb, and Cs; and smectite with Na.     

A fast and easy computational method to calculate the (13)C NMR chemical shift of organic species adsorbed on the zeolite surface

Calculations of the 13C NMR chemical shifts for the methoxy and ethoxy groups adsorbed on Y and ZSM-5 zeolites were computed at GIAO/B3LYP/6-31+G*//MM+ level of theory, using a cluster representing a real part of the zeolites. The Y zeolite was represented by a cluster with 168 atoms, while ZSM-5 was represented by a cluster with 144 atoms. The calculated chemical shifts agreed well with reported experimental values, showing that the difference in chemical shifts is associated with differences in the geometry of the alkoxides on the two zeolites.     

Structure, bonding, and solvation of lithium vinylcarbenoids

[reaction: see text] Molecular modeling was used to determine the structure of lithium vinylcarbenoids in the gas phase and in THF solution. Solvent effects were modeled by microsolvation with explicit THF ligands on each of the lithium atoms. The carbenoid geometries are dependent on the heteroatom and on solvation. The calculations predict 1-chlorovinyllithium and 1-bromovinyllithium to be a mixture of monomer and dimer at 200 K and mostly monomer at higher temperatures, whereas the 1-fluoro-, 1-methoxy-, and 1-dimethylaminovinyllithium are predicted to be dimeric in solution.     

An overview of the ultraviolet index and the skin cancer cases in Brazil

This study relates regional and seasonal UV index (UVI) variations, number of skin cancer cases and population skin-color distribution in Brazil. UVI calculations were performed using the UV Global Atmospheric Model (UVGAME), whose characteristics and validations are provided in thiis article. Health and racial data sets are based on the health and census data collected by Brazilian governmental agencies in the past. The discussion covers cultural customs and details of health and educational campaigns in Brazil. Despite lower UV levels in the South and Southeast regions, the results show a number of nonmelanoma skin cancer (NMSC) cases regions, where the white population is predominant. In general, in the southern regions about 50 new NMSC cases per 100000 inhabitants have been diagnosed each year. These rates decrease almost 40% in the Central-North regions and more than 80% in Northeast region, where miscegenation is common. In addition, the UVI evaluation is extended to other South American sites with singular characteristics, e.g. populous cities located in high altitudes or those affected by the Antarctic ozone hole in the extreme south of the continent.