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Ru(edta)H20]-adsorbed on zirconium(1v) oxide coated on the surface of silica gel was used for the construction of an amperometric sensor for O2 in water, using a carbon paste electrode. The adsorbed complex electrocatalyses the oxygen reduction reaction at -250 mV versus SCE. The cathodic current was linear for an oxygen concentration between 0.55 and 8.0 ppm, with a correlation coefficient of 0.998 and a relative standard deviation of 2.7 % . The sensor response is constant within the solution pH values 2.0 and 6.5. The concentration of 0 2 in a natural sample was also determined.A precise and specific method for the determination of oxygen is a matter of great interest. The most used device for such purpose has been the membrane covered Clark-type electrode' , in which oxygen diffuses through a gas-permeable membrane and is reduced on a platinum cathode polarized between -0.6 and -0.8 V versus Ag/AgCl as reference. The resultant current flow is linearly related to the partial pressure of the oxygen in the sample. However, changes in the membrane permeability or cathode surface area can cause a considerable decrease in the sensor response. These can be avoided by use of chemically modified electrodes which allow direct contact of the sensor with the species in solution. However, such kind of electrodes are relatively rare.24The study of the immobilization and electrochemical properties of electroactive species on metal oxide coated on silica gel surfaces has been a subject of interest in our laboratory in recent year~.~.8 Carbon paste electrodes prepared with these materials have been used as chemical sensors.'-IThe electroactive species strongly adhere to the modified surfaces with an additional advantage that silica gel has high chemical stability and mechanical resistance. Of particular interest is the [Ru-(edta)H20] -complex immobilized on zirconium(1v) oxide coated on a silica gel surface which electrocatalyses oxygen reduction in aqueous solution. l2 Taking into account the potential use of this material for the development of a new sensor for oxygen determination, a study of its preparation and uilization as an amperometric sensor is described here. Experimental Zirconium(iv) Oxide Coating on the Silica Gel SurfaceSilica gel (Merck, Elmsford, NY, USA) with a specific surface area, SBET, of 500 m2 g-1, an average pore diameter of 6 nm and a particle size between 0.025 and 0.2 mm, was dried at 423 K under vacuum (0.13 Pa) for 4 h. About 50 g of the activated * To whom correspondence should be addressed. silica was added to a solution containing 11.6 g (0.05 mol) of pure ZrC14 dissolved in 300 cm3 of dry ethanol. The mixture was refluxed for 8 h, under a nitrogen atmosphere, and the resulting solid was washed by decantation and then heated at 400 K under vacuum (0.13 Pa). The material was carefully hydrolysed by immersion in demineralized water. The solid was washed with water to remove all chloride ions and then dried in an oven at 393 K for 5 h.The following equations can be written to represent the reacti...

Zirconium(iv) oxide coated on a silica gel surface was found t o be very effective for extracting Crvl from aqueous solutions at a pH of about 3. A microcolumn packed with this material was inserted into a flow injection system for the separation and preconcentration of Crv'. By this process, a concentration level of 2 ppb was detected with a relative standard deviation of 2.4%. Because of the high selectivity of the immobilized substrate, it was possible t o determine CrV' in the presence of larger amounts of other ions. The analysis was also carried out on natural water spiked with Crvl, and compared with a standard method.

This manuscript relates, for the first time, palladium nanoparticle production by bio-reduction using an Ilex paraguariensis aqueous extract. The solid obtained, PdISM, was used as a catalyst in Suzuki–Miyaura cross-coupling, composing a new eco-friendly, ligand-free, and low cost catalytic system. Excellent yields were obtained in the coupling of aryl iodides and bromides with phenylboronic acid. The same catalyst load was able to be recycled 3x. Graphical Abstract

Annona crassiflora is a species native to the cerrado region but also found in other regions of Brazil. The species belongs to the family of Annonaceae and their fruit is popularly known as araticum, ariticum, and marolo [1]. The species is used in folk medicine in the treatment of wounds and snakebites, and as an antimicrobial and antidiarrheal [2]. Some studies have shown that this species has antioxidant and cytotoxic activity [3,4].The objective of this study was to determine the chemical composition of the essential oil from different parts at different times of A. crassiflora collected in southern Brazil.The leaves, fruits, and flowers of A. crassiflora were collected in the town of Tres Rios, Brazil in 2010. A voucher specimen (SMDB 12.938) has been deposited in the Herbarium of the UFSM. The fresh leaves were submitted to hydrodistillation (4 h) to yield ca. 0.3% of oil. The oil was submitted to GC analysis in a Shimadzu (GCMS-QP2010 Plus) instrument equipped with a capillary fused silica column (30 m u 0.25 Pm) coated with RTx-5MS. The injector and detector temperatures were 240 and 260qC, respectively. He was used as carrier gas at a flow rate of 1 mL min -1 , injection was in the split mode (1:10), and the injection volume was 1 mg mL -1 of a solution containing withdraw oil in hexane. MS spectra were obtained using electron impact at 70 eV with a scan interval of 2.94 scan s -1 . Compound identification was based on the comparison of retention indexes with the same columns and mass spectra described [5,6]. Retention indices (RI) were obtained according to the method of Van den Dool relative to C7-C30 saturated n-alkanes standard. Quantitative analyses of the chemical constituents was performed using a flame ionization detector (FID) using a Shimadzu (GC-2010) instrument under the same conditions and with the same column as reported for the GC-MS. Table 1 lists the essential oils of the compounds obtained from A. crassiflora. Twenty-five compounds were identified, representing 94.0% of the oils.The essential oil of A. crassiflora consists mainly of oxygenated sesquiterpenes. Nerolidol was found in the highest concentration in all the oils analyzed. The oil from the leaves collected in summer showed a higher concentration of nerolidol (57.1%), and the oil of the fruit collected in summer showed the lowest concentration (18.7%).The essential oil obtained from the fruit showed no sesquiterpene hydrocarbons. Octanol acetate, epi-longipinalol, spathulenol, and dihydromyrcene comprises the majority of the fruit essential oil.The leaves collected in the spring contained spathulenol and caryophyllene oxide as major compounds. The oils collected from leaves (summer and autumn) show '-elemene and E-caryophyllene in higher concentrations than other oils, and E-caryophyllene was found in the leaves in these two seasons.

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IntroductionCompounds containing a chain with three nitrogen atoms, the triazenes, are largely described on the literature [1,2]. Among other uses, they were studied as chemotherapeutic agents. Triazenes and anionic triazenide ligands can show different types of coordination in metal complexes [1][2][3][4][5]. They can be monodentate, (N1,N3)-chelating towards one metal atom or (N1,N3)-bridging over two metal atoms.Compounds containing two chains of three nitrogen atoms, the bistriazenes, are also known [6][7][8][9][10][11][12][13][14]. The possibilities of coordination are enhanced when two nitrogen chains are present on the ligand. Complexes of ortho-, meta-and para-bis(phenyltriazene)benzenes ligands were synthesized and characterized. As expected, several different coordination types were observed. Bistriazenes show the coordination properties of triazenes and also the capacity to force close contacts between metal atoms.Although the structure of complexes with bistriazene ligands have been described, no reports were found in the literature related to electrochemical properties of these compounds. These studies are important for characterization and to a better understanding of their reactivity, stability and possible applications.The 1,2-bis(phenyltriazene)benzene ligand, C 6 H 5 NNN(H)C 6 H 4 NNN(H)C 6 H 5 , was used to synthesize the complex bis-(µ 2 -oxo)-tetrakis{[1-