Synthesis of [60]fullerene derivatives bearing five-membered heterocyclic wings and an investigation of their photophysical kinetic properties

The preparation, characterization and photophysical properties of six new stable [6,6]-closed fullerene cycloadducts bearing five-membered heterocycles are described. The modified [60]fullerenes are obtained by a simple and rapid synthesis via a Bingel-type reaction with tetrazole and oxadiazole malonate derivatives. The photophysical kinetics of these new fullerene derivatives in toluene solution under ultraviolet illumination (375 nm, UVA) are studied by electron paramagnetic resonance and free-radical spin-trapping using α-phenyl-N-tert-butyl nitrone as a spin-trap. The results are compared with pure [60]fullerene and [6,6]-phenyl C₆₁ butyric acid methyl ester (C₆₀-PCBM). It is concluded that for all six new compounds as well as pure [60]fullerene and PCBM both superoxide and singlet oxygen are produced in the first stages of UVA illumination following the type I and II mechanisms, respectively. In all cases singlet oxygen is produced as the primary dominant species; however, the type I mechanism always occurs in parallel with type II. In the end, the superoxide is self-dismuted into hydroxyl radicals, thus yielding PBN-OH spin adducts (g = 2.007 and a_hf (¹⁴N) = 1.54 mT). The kinetic reaction constants and their efficiencies in the production of reactive oxygen species at 375 nm and per mW of absorbed power are determined. The experimental results are consistent with an autocatalytic reaction model in which the system evolutes under UVA illumination, with superoxide catalyzing the conversion of singlet oxygen into more superoxide.     

Gevrey global solvability of non-singular real first-order differential operators

In this article we deal with Gevrey global solvability of non-singular first-order operators defined on an n-dimensional s-Gevrey manifold, s > 1. As done by Duistermaat and Hörmander in the C ^∞ framework, we show that Gevrey global solvability is equivalent the existence of a global cross section.     

Increase of Fluorescence of Humic-Like Substances in Interaction with Cd(II): a Photoinduced Charge Transfer Approach

Journal of Fluorescence - Described is the enhancement of fluorescence intensity due to the interaction of a humic-like substance (HLS 1%) extracted from process water (PW) and Cd(II) ions in...     

A validated HPLC method for the assay of xanthone and 3-methoxyxanthone in PLGA nanocapsules

This work relates the development and validation of a simple reversed-phase high-performance liquid chromatographic (HPLC) method for the analysis of xanthone (XAN) and 3-methoxyxanthone (3-MeOXAN) in poly(D,L-lactide-co-glycolide) (PLGA) nanocapsule formulations. This method does not require any complex sample extraction procedure. Chromatographic separation is made with a reversed-phase C(18) column, using methanol-water (90:10, v/v) as a mobile phase at a flow rate of 1 mL/min. Identification is made by UV detection at 237 nm. The isocratic system operates at ambient temperature and requires 7 min of chromatographic time. The developed method is statistically validated according to United States Pharmacopoeia 25 and International Conference on Harmonization guidelines for its specificity, linearity, accuracy, and precision. The assay method proposed in this study is specific for XAN and 3-MeOXAN in the presence of nanocapsule excipients. Diode-array analyses confirm the homogeneity of XAN and 3-MeOXAN peaks in stressed conditions. Standard curves are linear (r > 0.999) over the concentration range of 0.4-2.5 and 1.0-5.8 micro g/mL for XAN and 3-MeOXAN, respectively. Recovery from nanocapsules ranges from 99.6% to 102.8% for XAN and 98.8% to 102.4% for 3-MeOXAN. Repeatability (intra-assay precision) is acceptable with relative standard deviation values of 1.2% for XAN and 0.3% for 3-MeOXAN.     

Antioxidant,antibacterial and cytotoxic potential of the ripe fruits of Solanum lycocarpum A. St. Hil. (Solanaceae)

Ethanol extract (EE) and fractions obtained from the ripe fruits of Solanum lycocarpum were examined in order to determine their phenolic composition, antioxidant capacity, antibacterial activities and cytotoxic potential. High-performance liquid chromatography coupled with DAD analysis indicated that caffeic and chlorogenic acids were the main phenolic compounds present in the EE, dichloromethane (DCM) and ethyl acetate (Ac) fractions. The antioxidant activity assessed by the scavenging ability on 1,1-diphenyl-2-picrylhydrazyl radical was significantly more pronounced for DCM and Ac fractions than that of the commercial antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT). EE and fractions exhibited selective antibacterial activity against Gram-positive bacteria, especially the hexane (Hex) and DCM fractions. EE and fractions exhibited low toxicity towards the LLC-MK2 cell line, especially the Hex, DCM and Ac fractions. This work provides the knowledge of phenolic composition in the extract and fractions from the ripe fruits of S. lycocarpum and their antioxidant, antibacterial and cytotoxic activities.     

Evaluation of seasonal chemical composition,antibacterial, antioxidant and anticholinesterase activity of essential oil from Eugenia brasiliensis Lam.

This study describes the seasonal composition and the antibacterial, antioxidant and anticholinesterase activity of the essential oil from Eugenia brasiliensis leaves. Analysis by using GC allowed the identification of 40 compounds. It was observed that the monoterpenes varied more (42%) than the sesquiterpenes (14%), and that the monoterpene hydrocarbons suffered the greatest variation throughout the year (64%). Major compounds were spathulenol in the spring (16.02 ± 0.44%) and summer (18.17 ± 0.41%), τ-cadinol in the autumn (12.83 ± 0.03%) and α-pinene (15.94 ± 0.58%) in the winter. Essential oils were tested for their antibacterial activity, and the best result was obtained from the autumn oil, with MIC = 500 μg mL^? 1 against Staphylococcus saprophyticus and Pseudomonas aeruginosa. Antioxidant activity was evaluated using DPPH, lipid peroxidation and iron-reducing power assays, as well as the anticholinesterase activity. Both tests showed a weak performance of the essential oils.     

Quenching of singlet molecular oxygen, O2(1Deltag), by dipyridamole and derivatives

Dipyridamole (DIP) is known for its vasodilating and antiplatelet activity, exhibiting also a potent antioxidant effect, strongly inhibiting lipid peroxidation. This effect has been studied in mitochondria and a correlation between the DIP derivatives' structure, the ability to bind to micelles and biological activity has been suggested. In the present work, the quenching of singlet molecular oxygen, O(2)((1)Delta(g)), by DIP and RA47 and RA25 derivatives was analyzed in acetonitrile (ACN) and aqueous acid solutions. Laser flash photolysis excitation of methylene blue (MB) was made at 532 nm and monomol light emission of O(2)((1)Delta(g)) was monitored at 1270 nm. Bimolecular quenching constants in ACN are consistent with an efficient physical quenching, presenting values a bit lower than the diffusion limit (k(t) = 3.4-6.8 x 10(8) M(-1 )s(-1)). The quenching process probably occurs via reversible charge transfer with the formation of an exciplex. Calculation of DeltaG(et) associated with O(2)((1)Delta(g)) quenching corroborates with uncompleted electron transfer. In aqueous acid solutions (pH = 3.0), the k(t) values for DIP and derivatives are 20-fold smaller when compared with ACN. The electrochemical properties of DIP in ACN are characterized by two consecutive one-electron processes with half-wave oxidation potentials of 0.30 and 0.67 V vs saturated calomel electrode (SCE). However, in an aqueous acid medium, a single oxidation wave is observed involving a two-electron process (0.80 V vs SCE). Therefore, O(2)((1)Delta(g)) quenching is consistent with electrochemical data.     

Application of pressurized fluid extraction to determine cadmium and zinc in plants

A procedure for the determination of Cd and Zn in plants is proposed. The metals are extracted by pressurized fluid extraction (PFE). Operational conditions are: pressure 1500 psi, temperature 75 °C, static time 5 min, flush volume 35%, purge time 60 s, cycles 1 and 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA) 0.01 M at pH 4.5 as extracting solution. Determination of Zn is carried out by flame atomic absorption spectroscopy and depending on the concentration level, Cd content is determined by flame or electrothermal atomic absorption spectroscopy. Certified samples of Virginia tobacco leaves, tea leaves, spinach leaves, poplar leaves, a commercial spinach sample (Spinacea oleracea) and genetically modified Arabidopsis thaliana were analysed by the proposed procedure and also by microwave acid digestion and extraction with HCl-Triton X-100. Confidence intervals for Cd and Zn content obtained by the proposed procedure overlap with the certified values. The other procedures, however, provide inaccurate results for Cd. Recoveries obtained for a confidence level of 95% are 96 ± 6% and 95 ± 5% for Zn and Cd, respectively. Reproducibility of Zn by the proposed procedure is 7% (n = 8), similar to the other tests and the detection limit is 2.6 μg. For Cd reproducibility is 8.5% (n = 8), better than with HCl-Triton X-100 and similar to acid digestion, the detection limit is 3.5 ng of Cd.     

Design of molecular scaffolds based on unusual geometries for magnetic modulation of spin-diverse complexes with selective redox response

A weakly coupled heterometallic [CuFe] complex has been prepared in which the metal centers are coordinated to a new electroactive ligand. The spin-diverse system delivers distinct ground states upon application of selective redox potentials. Ligand oxidation fosters radical generation, and the initial ground state associated with a weakly coupled [CuFe] core switches to a ground state associated with the [Fe-radical] coupling; the Cu(II) ion remains uncoupled. A third state is obtained upon reduction of the cupric center and in absence of the radical. The possibilities and limitations of these systems are discussed.     

Sucrose-Branched Polymer Synthesized by Protease from Bacillus Subtilis

Summary: Vinyl sugar ester, 1′-O-vinyladipoyl-sucrose, was synthesized using sucrose and DVA (divinyl adipate) in organic medium (dimethylformamide), catalyzed by protease from Bacillus subtilis. Several reaction conditions were examined by means of qualitative analysis (TLC). The monomer obtained has undergone chemical polymerization with potassium persulfate and hydrogen peroxide to produce an amphiphilic polymer having sugar branches. The monomer was characterized by ¹³C-NMR and FTIR spectra. The IR analysis confirmed the synthesis of the poly (1′-O-vinyladipoyl-sucrose).