Oxidation of caffeine with hydrogen peroxide catalyzed by metalloporphyrins

The biomimetic oxidation of caffeine with hydrogen peroxide using metalloporphyrins as catalysts, which are known to be good biomimetic models of cytochrome P450 enzymes, is investigated. The two manganese porphyrins tested, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III), [Mn(TDCPP)Cl], and chloro [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III), [Mn(TPFPP)Cl], afford high conversions of caffeine for all substrate/catalyst molar ratios. Selectivity was found to be dependent on the catalyst employed, and a new spiro racemic compound is described and fully characterized in the solid state from X-ray diffraction studies.     

Autostratification in drying colloidal dispersions: experimental investigations

In films cast from a colloidal dispersion comprising two particle sizes, we experimentally examine the distribution of particles normal to the substrate. The particle concentrations at various positions in the film are determined through atomic force microscopy and NMR profiling. The results are compared to a previously derived diffusional model. Evidence for diffusional driven stratification is found, but the importance of other flows is also highlighted. The conditions that enhance particle stratification are found to be a colloidally stable dispersion, low initial volume fractions, a low concentration of the stratifying particle, and for the Peclet numbers of the two components to straddle unity.     

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (ESI‐MS²), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe²⁺/H₂O₂) and Fe²⁺/O₂ systems. The reactions were followed by ferrous oxidation‐xylenol orange method together with GC‐MS and GC‐FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH^· radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI‐MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra. Copyright © 2012 John Wiley & Sons, Ltd.     

Rapid method for simultaneous determination of ascorbic acid and zinc in effervescent tablets by capillary zone electrophoresis with contactless conductivity detection

Ascorbic acid and zinc are essential nutrients that play important roles in nutrition, immune support, and maintenance of health. For this reason, both compounds are widely used as ingredients in dietary supplements. We report, for the first time, an analytical method for fast simultaneous determination of ascorbic acid and zinc. A single analysis run is possible every 80 s (45 injections/h). The method is based on capillary electrophoresis with capacitively coupled contactless conductivity detection using a fused silica capillary with 50 cm length (effective length of 10 cm). The separation was achieved by using a background electrolyte composed by 30 mmol/L of 2‐(morpholin‐4‐yl)ethane‐1‐sulfonic acid and 30 mmol/L of histidine, pH 6.1. The detection limits were 10 and 20 μmol/L and recovery values for spiked samples were 101 and 100% for zinc and ascorbic acid, respectively. The results obtained with the developed procedure were compared to those obtained by titration (ascorbic acid) and flame atomic absorption spectroscopy (zinc), and no statistically significant differences were observed (95% confidence level).     

Tetracycline and/or hydrocortisone incorporation and release by bioactive glasses compounds

The delivery of the tetracycline and hydrocortisone drugs that have been incorporated into bioactive glasses was studied in this work. The potentiality of these systems in direct pulp capping is also discussed. A bioactive glass with a composition of (SiO₂)_0.80(P₂O₅)_0.04(CaO)_0.16, was prepared by sol-gel. Sols were prepared with the addition of approximately 2 wt% of tetracycline or hydrocortisone separately for the delivery studies. A third set of samples of bioglass sols containing 2 wt% of each drug were prepared with the same purpose. The amounts of drugs delivered were monitored by ultraviolet spectrophotometry in the tetracycline and hydrocortisone wavelengths. The drug release behavior was strongly dependent on the system. The glass-tetracycline samples showed a rapid drug release kinetics, while glass-hydrocortisone samples show much slow release profiles. The different drug release behaviors have been explained by faster gel formation reaction between hydrocortisone and TEOS due to a stronger interaction between these reagents. On the samples with both drugs, the release was simultaneous and for each drug, the amounts delivered followed a profile similar to the samples with only this specific drug.     

Detection and characterization of hydroxyl radical adducts by mass spectrometry

The study of the influence of free radicals in the biological process depends primarily on the capacity to detect these reactive species. In this work we have studied the application of mass spectrometry to the identification of hydroxyl radical species. The detection and identification by collisional activation mass-analyzed ion kinetic energy spectrometry (CA-MIKES) of a spin adduct of DMPO with the hydroxyl radical [(DMPO + O) + H]+ (m/z 130) has demonstrated that mass spectrometry can be a powerful tool in the detection and identification of spin adducts of DMPO with hydroxyl radical species. We were also able to detect the capture of secondary free radicals using ethanol by detecting and identifying the corresponding adduct [(DMPO + ethanol) + H]+. Other spin adducts have also been detected and identified. We consider that the use of mass spectrometry is a relevant technique for the detection of free hydroxyl radicals, especially in complex mixtures, since mass spectrometry is able to discriminate these adducts in such situations. Moreover, using this approach, it was possible to identify new spin adducts.     

The study of biocatalyzed thio-Michael reaction: a greener and multi-gram protocol

This Letter introduces a new, cheap and green protocol for the thio-Michael reaction. Here we applied three free enzymes such as lipase from pancreas porcine, chymosin and papain and an immobilized one: the Liposyme®. The reactions were executed at room temperature and resulted in the thio-Michael adduct in good or excellent yields. The protocol describes the use of EtOH as solvent and a less percentage of enzymes, which is in concordance with the green chemistry topics, so we can mention that chymosin and papain were used as biocatalyst in an organic reaction for the first time in this Letter.     

A heuristic for large-sizep-median location problems with application to school location

This paper initially proposes a heuristic algorithm for thep-median problem designed for large weighted graphs. The problem is approached through the construction ofp trees whose shapes are progressively modified according to successive tests over the stability of their roots and vertices. The algorithm seems promising because: (i) on a regular PC it can handle problems of the order of 500 vertices, while the mainframe version goes indefinitely further, (ii) contrary to what normally would be expected, execution times seem to be inversely proportional top, and even for large problems, they may be reasonable, especially ifp is large relative to the number of vertices, and (iii) it produces solutions of good quality and in most of the cases studied, it outperforms the traditional heuristic of Teitz and Bart. A real application of the algorithm embedded in a methodology to evaluate the location of 85 public schools, among 389 possible vertices, in the metropolitan area of Rio de Janeiro is reported. Results confirmed the conjecture of poor location and the procedure was able to identify several micro-regions simply void of schools. The methodology is being well received by the education authorities and its extension to the whole metropolitan area is being considered.     

Magnetic studies on synthetic phosphoferrite Fe 3 2+ (H2O)3(PO4)2

Synthetic crystals of phosphoferrite were studied by Mössbauer spectroscopy for temperatures ranging from 4.2 to 17.5 K. The analysis of the behaviour of the hyperfine fields for the two unequivalent sites near the Néel temperature (17.4 K) allowed the determination of the critical exponent for each site as ₁=0.171 and ₂=0.314.