Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> http://www.scielo.cl/rss.php?pid=0717-970720040002&lang=pt vol. 49 num. 2 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[<B>BACK TO BASICS</B>: <B>MODERN REACTIVITY CONCEPTS WITHIN THE HMO THEORY FRAMEWORK è..</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200001&lng=pt&nrm=iso&tlng=pt We describe how modern concepts of chemical reactivity and selectivity, defined as response functions in the conceptual density functional theory (DFT), may be implemented within a simple Huckel Molecular Orbital (HMO) formalism. Concepts like electrophilicity may be easily explained using the electronic chemical potential. Intramolecular and intermolecular selectivity may in turn be conveniently described by the Fukui function, which is formulated in terms of single coefficients of the frontier molecular orbitals within the HMO frame. The conceptual value obtained by merging a powerful formalism based on response functions with a simple model of electronic structure is the transparent interpretation of modern concepts of reactivity in terms of classical chemical quantities. The model is illustrated for the reactivity and intermolecular selectivity of Diels-Alder reactions <![CDATA[<B>TOWARDS A QUANTUM MOLECULAR MEASUREMENT THEORY: STERN-GERLACH THOUGHT EXPERIMENTS AT THE INTERFACE OF HILBERT AND REAL SPACES</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200002&lng=pt&nrm=iso&tlng=pt We describe how modern concepts of chemical reactivity and selectivity, defined as response functions in the conceptual density functional theory (DFT), may be implemented within a simple Huckel Molecular Orbital (HMO) formalism. Concepts like electrophilicity may be easily explained using the electronic chemical potential. Intramolecular and intermolecular selectivity may in turn be conveniently described by the Fukui function, which is formulated in terms of single coefficients of the frontier molecular orbitals within the HMO frame. The conceptual value obtained by merging a powerful formalism based on response functions with a simple model of electronic structure is the transparent interpretation of modern concepts of reactivity in terms of classical chemical quantities. The model is illustrated for the reactivity and intermolecular selectivity of Diels-Alder reactions <![CDATA[<B>USE OF ULTRAFILTRATION ON THE EVALUATION AND QUANTIFICATION OF THE INTERACTIONS BETWEEN POLYMERS AND LOW MOLECULAR-WEIGHT MOLECULES IN AQUEOUS SOLUTIONS</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200003&lng=pt&nrm=iso&tlng=pt The theory and mathematical treatment of the evaluation of the interactions of water-soluble polymers with low molecular-weight molecules is presented. The interaction of the water-soluble polymer poly(sodium 4-styrenesulfonate) with L-tryptophan (Try), L-phenylalanine (Phe), chlorpheniramine maleate (CPM), and 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) is studied by this technique. Ultrafiltration experiments at pH 7.5, and different ionic strength values show weak interactions of the low molecular weight molecules TTC and CPM with the polymer with apparent dissociation constants of 0.26 and 0.32 respectively in the absence of NaNO3, and 2.02 and 1.2 in the presence of 0.10 of NaNO3 and 0.13 M of NaCl respectively. Negligible interactions are found for Try or Phe at pHs ranging between 4 and 10 and NaNO3 concentrations ranging between 0.0 and 0.15 M. This suggests that the interactions are mainly due to both long-range electrostatic forces and short-range interactions that may include hydrophobic forces or charge transfer complexation. The interaction of TTC with PSS in the absence of NaNO3 is reflected in UV-Vis spectroscopic studies by a decrease on the intensity of the maximum at 248 nm <![CDATA[<B>SENSING PROPERTIES OF HYBRID POLYMERIC FILMS OBTAINED BY SOL-GEL</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200004&lng=pt&nrm=iso&tlng=pt Hybrid nanocomposites based on siloxane sols, chitosan and poly(monomethyl itaconate) (PMMI) as organic polymer counterparts were prepared. Tetraethyl ortosilicate was used as inorganic network forming reagent that was first transformed into soluble polymeric species by acid catalyzed hydrolysis and condensation reactions. The siloxane sol was then mixed with different amounts of PMMI and chitosan at room temperature to form the hybrid material. These hybrid materials could be easily cast as transparent and flexible films. Atomic force microscopy study showed that the organic components are more or less homogeneously distributed at nanometer scale. The hybrid films were used as membranes for the construction of all-solid-state type potentiometric electrodes. The ion-sensing capacity of the nanocomposite was tested for different anions and the best results were obtained for NO3-. It was concluded that the ­NH3+HCOO- groups of chitosan act as anion exchanger creating a potential difference that vary with ion concentration in solution in the concentration range of 1.5 ·10-4 ­ 10-2 mol/dm³ <![CDATA[<B>SYNTHESIS AND CHARACTERIZATION OF MACROMONOMERS FROM 2-ALKYL-2-OXAZOLINES</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200005&lng=pt&nrm=iso&tlng=pt Macromonomers from 2-oxazoline derivates were synthesized by using 2,2'-iminediethanol and 1-(2-hydroxyethyl) piperazine as terminating agents. The macromonomers are soluble in water and in common organic solvents like chloroform, methanol, and tetrahydrofuran. They were characterized by FT-IR, ¹H-NMR , and 13C-NMR spectroscopies. The molecular weight and molecular weight distribution by gel permeation chromatography were determined <![CDATA[<B>SECONDARY METABOLITES IN THE EPICUTICLE OF <I>HAPLOPAPPUS FOLIOSUS</I> DC. (ASTERACEAE)</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200006&lng=pt&nrm=iso&tlng=pt From the CH2Cl2 extract of the surface of Haplopappus foliosus, monoterpenes, sesquiterpenes, flavonoids, coumarins, phenyl propanoids, n-alkanes and different miscellaneous compounds were identified. The complexity of the chemistry in terms of number of families and compounds makes attractive the use of this specie as a model to study variations in the cuticle chemistry, triggered by different ecological pressures. Keywords: Haplopappus foliosus; Monoterpenes; Sesquiterpenes; Flavonoids; Coumarins; phenyl propanoids, n-Alkanes; miscellaneous compounds <![CDATA[<B>ANTIVIRAL ACTIVITY ON HANTAVIRUS AND APOPTOSIS OF VERO CELLS OF NATURAL AND SEMI-SYNTHETIC COMPOUNDS FROM HELIOTROPIUM FILIFOLIUM RESIN</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200007&lng=pt&nrm=iso&tlng=pt The antiviral activity on Hantavirus Andes variety of resinous exudate from Heliotropim filifolium and its pure compounds was studied. From filifolinol 2, the main compound of the resins, filifolinoic acid 1 was obtained. The resin was the most active. Furthermore, we observed cytostatic effect and apoptosis on Vero E6 cells with 3-O-methylgalangine 5 <![CDATA[<B>Isolation and characterization of cobalt(III)tris-D-glucosamine</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200008&lng=pt&nrm=iso&tlng=pt Mixed bis-phenanthroline Co(III) complexes with amino sugars disproportionate over a period of months, giving non-ionic tris-(aminosugar)complexes. The complex with a-D-glucosamine has the L-configuration with facial isomerism on the base of molecular composition and absorption and circular dichroism spectra <![CDATA[<B>TUNING THE EXCITED STATES IN <I>fac</I>-[Re(X<SUB>2</SUB>dppz)(CO)<SUB>3</SUB>(L)]</B>: <B>INTRALIGAND, CHARGE TRANSFER OR BOTH?</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200009&lng=pt&nrm=iso&tlng=pt Excited state lifetime measurements ­ emission, emission lifetime and Resonance Raman ­ have been conducted on the series fac-[Re(X2dppz)(CO)3(L)]0,+ (L = Cl-, 4-ethylpyridine (4-Etpy), 4,4´-bipyridine (4,4´-bpy)), with the X2dppz substituted dipyrido[3,2-a:2',3'-c] phenazine ligands (X = CH3 and Cl). The results are consistent with closely lying excited states, with <FONT FACE=Symbol>pp</FONT>* lowest, but MLCT contributing significantly to excited state lifetimes for the neutral complexes. fac-[Re(Cl2dppz)(CO)3Cl] appears to undergo a crossover from lowest pp* to lowest MLCT through the glass to fluid transition <![CDATA[<B>ANTIBACTERIAL AND ANTIFUNGAL TERPENES FROM Pilgerodendron uviferum (D. DON) FLORIN</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200010&lng=pt&nrm=iso&tlng=pt Ten sesquiterpenes (a-cubebene, copaene, alpha-caryophyllene, caryophyllene-4,5-epoxide, delta-cadinene, cubenol, epicubenol, torreyol, humulene-1,2-epoxide, 15-copaenol) and six diterpenes (hinokione, hinokiol, ferruginol, 6,7-dehydroferruginol, totarol, sugiol) were isolated and identified from Pilgerodendron uviferum (D. Don) Florin wood and bark. The molecular structures were elucidated by spectroscopic methods. Twelve pure compounds were tested for antimicrobial activity against standard bacterial (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aureginosa, Streptococcus pyogenes) and fungal strains (Ophiostoma piliferum, Rhizoctonia solani, Phragmidium violaceum, Fusarium graminearum, Pythium irregulare, Botrytis cinerea, Schizophyllum commune), as were crude total extracts, n-hexane, dichloromethane, and ethyl acetate partial extracts. All the compounds tested exhibited biological activity, with the most active being ferruginol, hinokiol, 15-copaenol, cubenol, torreyol, and n-hexane wood extracts and ethyl acetate bark extract <![CDATA[<B>SCREENING OF SOME TRANSITION METAL IONS AND QUANTITATIVE DETERMINATION OF COPPER, CADMIUM AND ZINC BY SOLID PHASE DERIVATIVE SPECTROPHOTOMETRY</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200011&lng=pt&nrm=iso&tlng=pt A simple solid phase spectrophotometric method for both screening of eight transition metal ions plus lead and quantitative determination of copper, cadmium and zinc is described. The method is based on the preparation of a sensitive analytical zone by immobilization of the organic reagent 1-(2-pyridylazo)-2-naphthol (PAN) in a Dowex 50WX2-100 resin, in which Cd, Cu, Zn, Co, Fe, Ni, Ag, Pb and Hg react at pH 10, to form colored complexes on the surface of the resin. Absorbance can be measured directly on the solid phase at 550 nm, to detect the presence or absence of these cations in a solution sample. Physical-chemical variables of the method were optimized in order to find suitable analytical conditions for the simultaneous determination of Cu, Cd and Zn by solid phase derivative spectrophotometry. Under the selected conditions the three analytes can be accurately determined between 1 and 100 ng·mL-1, with a detection limit (3s criterion) of 0.9, 0.5, and 0.4 ng·mL-1, for Cu, Cd and Zn, respectively. The repeatability, expressed as the relative standard deviation (RSD), was lower than 2 %. The percentage recoveries in the determination of Cu, Cd, and Zn in a quality control standard were between 98 and 103 % <![CDATA[<B>STUDY OF STABILITY PHYSICAL CHEMICAL OF 3-[2´-THIAZOLYLAZO]-2,6-DIAMINOPYRIDINE AND THE FORMATION OF 3-[N,N-ETHYL-MET-AZO]-2,6-DIAMINOPYRIDINE AS NEW LIGAND CHROMOPHORE</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200012&lng=pt&nrm=iso&tlng=pt The 3-[2´-thiazolylazo]-2,6-diaminopyridine or 2,6-TADAP have been used as chromophore reagent for the determination of metals of the platinum group. In this work a study of the stability of the 2,6-TADAP is included, a synergetic action of the temperature, the reaction time and the acidity of the medium was found. According to spectral behavior it can be postulated that 2,6-TADAP ligand suffers structural changes, having as consequence the formation of another azocompound. Besides, the mechanism of decomposition and characterization of the formed compound was also included. The characteristic chemical of new azocompound is appropriate for the development of analytic methods for the determination of metals belonging to the platinum group, using the new ligand called 3-[N,N-ethyl-met-azo]-2,6-diaminopyridine or 2,6-DAPEMA <![CDATA[<B>WATER VAPOR PERMEABILITY AND MECHANICAL PROPERTIES OF CHITOSAN COMPOSITE FILMS</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200013&lng=pt&nrm=iso&tlng=pt Chitosan films or membranes can be obtained by casting chitosan solutions in acetic acid at 1 % w/v concentration at room temperature. The films set were elaborated from 2% chitosan solutions mixed with three plasticizers (polyethylene glycol 200 (PEG), sorbitol and glycerol) and two surfactants (Tween 60 and Tween 80) at two concentrations. The goal was to decrease the water vapor permeability and to improve the mechanical properties of chitosan films. The effects of plasticizers (PEG, sorbitol and glycerol) and emulsifiers (Tween 60 and Tween 80) at two concentrations from chitosan solution on water vapor permeability and mechanical properties of cast films were evaluated. Water vapor permeability ranged from 3.64 to 6.56 g mm / h m² KPa., tension force from 7.23 to 48.3 MPa and elongation percentage from 22.9 to 167.02 were obtained. Chitosan two percent with 0.3 % Tween 80 produces films that showed the lowest permeability value. Chitosan with 0.6 % glycerol has the highest percentaje of elongation, being 4.5 times higher than chitosan films. Chitosan with 0.6% Tween 80 improved the hydrophobicity of the chitosan film in 1.14 times. The highest value for tension force was found for chitosan with 0.6 % of Tween 60. These values are similar to some polymers based on mineral oil <![CDATA[<B>Catalytic epoxidation of cyclohexene using Molybdenum complexes</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200014&lng=pt&nrm=iso&tlng=pt Three oxomolybdenum complexes, MoO2(acac)2, MoO2(oxine)2 and MoO2(PDTC)2, were prepared, characterised and essayed as catalysts for the epoxidation of cyclohexene in a batch reactor. The reaction was performed at 60 and 70°C using tert-butylhydroperoxide as oxidant agent and toluene and dichloroethane as solvents. All the complexes exhibit high selectivity to the corresponding epoxide under the studied conditions, being the MoO2(acac)2 the one that exhibits the highest specific rate constant. An enhancement in the specific rate constant is observed at higher reaction temperatures and by using dichloroethane as solvent. A detailed kinetic study showed that the cyclohexene epoxidation is a global second order reaction: order one with respect to cyclohexene and also order one dependence in tert-butylhydroperoxide. A reaction mechanism that explains the experimental results is proposed <![CDATA[<B>INTAKE OF COPPER PARTICLES IN POLY(o-PHENYLENEDIAMINE-co-p-BENZOQUINONE) DEPOSITED ONTO PLATINUM ELECTRODE</B>: <B>RESPONSE TO <FONT FACE=Symbol>g</FONT>-AMINOBUTIRIC ACID</B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200015&lng=pt&nrm=iso&tlng=pt Modified electrodes with o-phenylenediamine and p-benzoquinone copolymer were prepared optimizing the conditions to obtain a polymeric film with an adequate intake of copper. Various electrode materials were assayed, and the copolymer deposit was potentiodynamically prepared on a platinum electrode. The film thickness was varied with the number of potentiodynamic cycles. The wide potential window shown by this modified electrode allowed attempting the insertion of copper in the polymeric matrix using several strategies. The response of the electrode was checked in the presence of g-aminobutyric acid (GABA). This way it was possible to obtain an electrode with an adequate and reproducible response for the detection of GABA in the concentration range between 10-4-10-5 mole·L-1 being the reading stable after several measurements <![CDATA[<B>PULSED FIELD GRADIENTS IN NMR HIGH RESOLUTION EXPERIMENTS </B>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000200016&lng=pt&nrm=iso&tlng=pt High-resolution NMR spectra of selective 1D, 2D homonuclear and 2D heteronuclear experiments were registered of the mixtures of the natural products 3-4 and the methyl esters (5-6) and acetyl derivates (7-8) of the natural product 1-2, using Pulsed Field Gradients (PFGs) technique. Thus, it was possible to obtain high-resolution spectra, smaller time of acquisition and larger structural information