Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 53 num. 2 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>EDITORIAL</b>]]> <![CDATA[<b>INTERFACE BETWEEN TWO IMMISCIBLE LIQUID ELECTROLYTES</b>: <b>A REVIEW</b>]]> An overview on electrochemistry on the interfaces between two immiscible electrolyte solutions is given. <![CDATA[<b>SYNTHESIS, CHARACTERIZATION AND CATALYTIC BEHAVIOR OF THE Ir/Nb<sub>2</sub>0<sub>5</sub>/Si0<sub>2</sub> SYSTEM IN THE CITRONELLAL HYDROGENATION</b>]]> The citronellal hydrogenation was studied on Ir/Nb(2)0(5)-Si0(2) catalysts. Aseries of catalysts was synthesized with different niobia contents (Ir/Nl 1.10%; Ir/N2 2.54%; Ir/N3 3.25%; Ir/N4 5.30%wt%) using the wet impregnation method. These catalysts were reduced in hydrogen atmosphere at low or high temperatures. 473K (LTR) or 773K respectively. Their structural and surface properties were investigated by XRD, TEM, XPS, DTP, FTIR, H2 chemisorption at 298 K and surface specific area by using the BET method. The X ray diffraction studies revealed only the peaks due to niobia, mainly in those with higher niobia loading. No diffraction lines due to Ir were observed due to its lower content and/or to its high dispersion. The catalytic tests in the hydrogenation of citronellal were carried out in a batch reactor operated at 6.2 bar of H2 and 343 K. All catalysts showed higher selectivity to isopulegol and to their products due to the cyclization of the citronellal molecule. <![CDATA[<b>CALCIUM CARBONATE GROWTH MODIFICATION BY CONSTITUENTS RELEASES FROM POROUS CELLULOSE FILTER MEMBRANES</b>]]> Filtration of a suspension of calcium carbonate (CaC0(3)) or other inorganic solutions are often part of the methodology for recovering crystals during biomimetic mineralization experiments performed by various procedures. However, the use of cellulose filter membranes (FM) may cause a problem in in vitro crystallization experiments, because constituents released from the filters into the filtrates can alter the morphology of CaC0(3) crystals. Therefore, it is possible to misinterpret data obtained when the effect of specific additives tested in the investigation of biomineralization mechanisms. Herein, we present essential information to avoid such misinterpretations of data obtained from mineralization experiments. CaC0(3) was precipitated at room temperature by the gas diffusion method in the presence of FM as support and particularly as filtrates of calcium chloride (CaCl2) obtained from various commercial FM. The occurrence or absence of morphological modifications of the calcite and vaterite crystals obtained with different FM correlates well with the different elemental compositions of the solutions where crystals are grown because of the constituents released from the filters into the filtrate. X-ray photoelectron spectroscopy (XPS) data indicate significant differences in the filter elemental composition. We assume that the observed chronological changes in CaC0(3) crystal modification could be due to incorporation into the calcite lattice of constituents released from the FM, most likely monomers, oligomers, or short-chain polymers. <![CDATA[<b>INCLUSION COMPOUNDS OF α-CYCLODEXTRIN WITH ALKYLTHIOLS</b>]]> We report the formation of á-cyclodextrin (áCD) inclusion compounds with octanethiol (OT), decanethiol (DT) and dodecanethiol (DDT). Elemental Microanalysis, ¹H-NMR solution, Scanning Electronic Microscopy (SEM) and Powder X-ray Diffraction analysis (PXRD) confirm the inclusion process of the alkylthiols in to the á-cyclodextrin molecules. The basic host structure of the products is similar to that of typical channel type structure cyclodextrin inclusion compounds. The guest presents extended linear (zig-zag) conformation. The presence of the -SH groups located in the (001) plane of the á-cyclodextrins-alkylthiol crystal, is evidenced by Energy dispersive X-ray (EDX) analysis. 13C CP-MAS NMR spectra of new á-cyclodextrin host-guest inclusion compounds are described. <![CDATA[<b>INTERCALATION OF POLYETHYLENE OXIDE IN LAYERED THIOPHOSPHATE OF BI AND SB</b>]]> The intercalation compounds Li0,43(PEO)2.4(H2O)1.4K0.57BiP2S6 and Li0.38(PEO)2.1(H2O)1.6K0.62SbP2S6 have been synthesized by the insertion of polyethylene oxide PEO in LiKMP2S6 (M=Bi, Sb), that contained Li+ and K+ exchangeable cations in their interlayer space. The polymer PEO is able to associate interlayer Li+ cation modifying the ionic conductivity of pristine phases. These intercalation compounds constitute a new family of intercalates in the thiophosphate of Bi and Sb with Polyethylene oxide as guest species. They have been characterized by powder X-ray diffraction, FTIR-Raman, DTA/TGA analysis and electrical conductivity measurements. The studied nanocomposite shows values of electrical conductivity (σi) of about 10-6 Ω-1 cm-1 at room temperature. <![CDATA[<b>SYNTHESIS AND STRUCTURE OF DICARBONYLDICHLORO{2-(DIPHENYLPHOSPHINEOXIDE)PYRIDINE}RUTHENIUM(II)</b>]]> Reaction of the dinuclear complex [{Ru(CO)3Cl2}J with the Hgand 2-(diphenylphosphineoxide)pyridine (PyPOPh2) in ethanol solution gave the neutral mononuclear complex [Ru(k²-PyPOPh2-N,0)(CO)2Cl2]. The complex was characterized by elemental analysis, IR and RMN spectroscopy, and its molecular structure was determined by single-crystal X-ray diffraction. <![CDATA[<b>HYDROGELS FROM N,N'-DIMETHYLACRYLAMIDE-co-2-ACRYLAMIDO-2-METHYL-1-PROPANESULFONIC ACID WITH SALT-, TEMPERATURE- AND pH-RESPONSIVENESS PROPERTIES</b>]]> The synthesis of copolymer hydrogels of JV, W-dimethylacrylamide (NNDMAAm) with 2-acrylamido-2-methyl- 1-propanesulfonic acid (AMPS) were prepared by solution free radical polymerization at different feed mole ratios (mole ratios of nNNDMAAm/nAMps = 0.5/0.5; 0.33/0.66; 0.66/0.33; 0.25/0.75; 0.75/0.25). In this reaction ammonium persulfate (APS) and N,N'-methylene-bis-acrylamide (MBA) were used as initiator and cross-linking reagents respectively. These copolymers were insoluble in water and it were characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Aqueous solutions of the copolymers showed lower critical solution temperature behavior (LCST). The phase transition temperatures of aqueous solutions of these copolymers increased with increasing of hydrophilic AMPS comonomer content in the copolymers. The effects of reaction parameters, including the concentration of cross-linking reagent, the monomer concentration, pH, temperature, salt solutions, and solvent polarity on the water absorption have been also studied. Under the experimental conditions, the copolymer poly(NNDMAAm-co-AMPS) with a feed mol ratio 1:2 presents the best swelling properties. The monomer reactivity ratios for poly(NNDMAAm-co-AMPS) are the following: r1 = 0.217 and r2 = 2.20, (r1 x r2 = 0.48). <![CDATA[<b>STUDY OF THE EFFECT OF BRANCHING IN DEGRADATION OF POLYETHYLENES OBTAINED VIA METALLOCENE CATALYST</b>]]> Polyethylenes, homo and copolymers obtained via metallocene catalyst, were synthesized and used to study the effect of comonomer size and content in the main linear backbone polymer on its degradation. Homoethylene metallocene polymer, ethylene-1-hexene and ethylene-1-octadecene metallocene copolymer films were characterized and analyzed during their aging in a forced draft oven at 60 °C for one year. The polymers were characterized before and after ageing using GPC, DSC, FTIR, and tensile tests in order to detect changes in chemical structure, size, and molecular weight distribution as well as to quantify the effect of time over their useful life. As a qualitative reference parameter, the carbonyl index, the ratio of the infrared absorbance of the CO stretching band at 1715 cm-1 and the absorbance of a reference band at 718 cm-1 , was determined. Results showed that kinetic thermooxidation is related to comonomer size and content in the main backbone polymer. As comonomer size decreases or comonomer content increases, degradation rate increases. This can be observed through the scission factor (S) and carbonyl index (CI) graphs of each material which show a slope increasing related to the autocatalytic rate of oxidation. <![CDATA[<b>LITHIUM COBALT SPINEL OXIDE</b>: <b>A STRUCTURAL AND ELECTROCHEMICAL STUDY</b>]]> Lithium cobaltite, LiCo(2)0(4), prepared by thermal decomposition of nitrates salts was synthesized at 400 °C. X-ray Rietveld refinement showed the presence of two phases: a cubic spinel (Co(3)0(4)) and other corresponding to spinel-like, which could not be classified as LiCo(2)0(4) or LiCo0(2) since both crystallized in Fd3m S.G. Electrochemical determinations (charge-discharge curves and impedance spectroscopy measurements) showed that Li+ ion is inserted into the spinel lattice, with D = 8 10-16 cm s-1 at 2.00-2.25 V potential range whereas lithium extraction occurred at 3.2-3.8 V potential range. <![CDATA[<b>CONDUCTIVITY PROPERTIES OF THIOUREA- AND UREA-HALOGEN INCLUSION COMPOUNDS WITH DIQUINUCLIDINIUM CATION AS GUEST</b>]]> Thiourea and urea can modify their typical host properties to form new ternary polymolecular anionic halogen hosts in which the diquinuclidinium cation is included. A comparative study of the proton conductivity properties of this kind of inclusion compounds is presented. The hexagonal binary inclusion compound [quinuclidine]3thiourea 1 was taken as reference. The study shows the conductivity properties of [quinuclidine2H]+[thiourea2Cl]-2, [quinuclidine2H]+[thiourea2Br]- 3, [quinuclidine2H]2(2+)[thiourea2I2]2- 4, [quinuclidine2H]+[urea5Cl]- 5, [quinuclidine2H]+[urea2Br]- 6, and [quinuclidine2H]+[urea2I]- 7. Ionic conductivities of all the compounds in pellets, and of 2 and 3 in large single crystals were measured by electrochemical impedance spectroscopy (EIS). Anisotropic conductivity behaviour in crystals of adequate dimensions of 2 and 3 was detected. The conductivity values of 2 and 3 in the crystals were 2.19x10-4 and 6.03x10-6(S/cm), respectively, in the assµmed channel direction, and 2.42x10-6 and 8.27x10-9 (S/cm), respectively, in the perpendicular direction to the former, at 298 K. Conductivities at room temperature of the thiourea-halide derivatives in pellets show a changing behaviour from insulator (10-11 S/cm) for 2,3 and 4 measured in vacuµm, to semiconductor (10-7-10-8S/cm) for the thiourea-halide derivative measured at atmospheric pressure. For the urea-halide system the highest conductivity value corresponds to derivative 7 (8.66x10-5 S/cm) at atmospheric pressure, and the lowest to derivative 5 (5.48x10-7 S/cm) measured in vacuµm. Comparisons considering structural aspects are also discussed. <![CDATA[<b>SYNTHESIS AND CHARACTERIZATION OF THE LAMELLAR OXYCHLORIDE C0<sub>2</sub>CU<sub>4</sub>TE<sub>4</sub>O<sub>11</sub>CL<sub>4</sub></b>]]> In this work we describe the synthesis and characterization of the Co2Cu4Te4O11Cl4 phase prepared by the hydrothermal technique. From the polycrystalline X-ray diffraction pattern the obtained new phase was indexed in the P-l space group with cell parameters a= 9.274(7), b= 12.132(2), c= 9.252(2) Å, á = 98.18(14), ß = 108.22(13) and γ = 111.07(8) °. The nominal composition and morphology were obtained using SEM-EDX measurements. The optical band gap of the material corresponds to an insulating system with 2.7 eV, and the thermogravimetric data shows that the phase is stable up to 700 °C. <![CDATA[<b>SELF-ASSEMBLY OF TRIBLOCK COPOLYMERS IN AQUEOUS SOLUTION</b>]]> The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy. <![CDATA[<b>PREPARATION AND PROPERTIES OF CHITOSAN HYBRID FILMS FROM MICROWAVE IRRADIATED SOLUTIONS</b>]]> The effect of microwave irradiation (MW, 1.55 kW at 2450 MHz on the dissolution chitosan(CHI) and on the properties of the solutions was studied and the results compared with those obtained by using mechanical stirring. MW effects were tested by analysing the viscosity of the solutions as well as the properties of the films of the nanocomposite the chitosan with poly(3-(aminopropyl)triethoxysilane)(pAPS) they produce. Microwave irradiation induces rapid dissolution, leading to solutions with relatively low viscosity, which asymptotically increases with further irradiation. Dissolution-precipitation-redissolution experiments with samples prepared using both methods indicate that MW effects are more related with the aggregation state of the macromolecule in the solution than with the chitosan degradation. CHI/pAPS hybrid materials appear to be different when the solutions of chitosan used as precursor are obtained by MW irradiation. Thus, MW appears to affect the chitosan self-association so changing the equilibria between the micro domains involved in the macromolecular complex formation. <![CDATA[<b>TRITERPENOIDS AND FATTY ACIDS IDENTIFIED IN THE EDIBLE MUSHROOM <i>Pleurotus sajor-cajú</i></b>]]> From the ethyl acetate extract obtained from the methanol extract of the mushroom Pleurotus sajor-cajú, ten compounds conforming the triterpenic fraction were isolated by means of chromatographic techniques like CC and PTLC, and were identified by their MS as: Ergosta-2,5,7,9(1 l),22-pentaene, Ergosta-5,7,9(1 1),22-tetraen-ß-ol, Ergosta-5á,8á-epidioxy-6,22-dien-3R-ol (ergosteryl peroxide), Ergosta-5,7,22-trien-3R-ol (Ergosterol), Ergosta-7,22-dien-3R-ol, 19-Norergosta-5,7,9,22,tetraen-ß-ol (Neoergosterol), Ergosta-7-en-3R-ol, Ergosta-3ß-5á,6ß-trihydroxy-7,22-diene (Cerevisterol), Ergosta-4,6,8(14),22-tetraen-3-one and Ergosta-4,6,15(16),22-tetraen-3-one. Likewise, three fatty acids were found and identified as palmitic acid, linoleic acid and stearic acid. <![CDATA[<b>COMPARISON OF VOLATILE COMPONENTS FROM <i>MARCHANTIA CONVOLUTA </i>OBTAINED BY MICROWAVE EXTRACTION AND PHYTOSOL EXTRACTION</b>]]> The volatile oils from Marchantía convoluta were obtained by microwave extraction (ME) and phytosol extraction (PE) methods. The attained extracts were analyzed by gas chromatography with mass spectrometric detector (GC-MS). The compounds were identified according to their retention indices and mass spectra (El, 70 eV). A total of fourteen compounds were identified in ME extract accounting for 80.72% of total peak area. Isolongifolene (24.588%), 1, 2-benzenedicarboxylic acid, butyl cyclohexyl ester (10.768%), pyrene (9.328%) and hexadecanoic acid, ethyl ester (8.570%) were the major compounds identified from ME extract. The analytical results of ME extract were compared with PE method. The ME extract was found to be markedly different from that of PE extract. A total of seven compounds in PE extract were identified accounting for 74.275% total peak area. 1-Phenanthrenecarboxylic acid, 1,2,3,4,4a,9,10, 10a-octahydro-1, 4a-dimethyl-7-(1-methylethyl) methyl ester were the major compounds <![CDATA[<b>CYTOTOXIC CONSTITUENTS FROM THE ROOT WOOD OF FORMOSAN <i>MICHELIA COMPRESSA</i></b>]]> The methanolic extract of the root wood of Michelia compressa (Maxim.) Sargent showed cytotoxicity against MCF-7, NCI-H460 and SF-268 cancer cell lines. Bioassay-guided fractionation of the chloroform-soluble layer led to the isolation of costunohde and liriodenine with cytotoxic activities, along with the isolation of twenty-seven known compounds. The active costunohde existed as major constituent in this study. <![CDATA[<b>FORMATION OF METASTABLE VATERITE CRYSTALS IN A POLYMER MATRIX BY GASEOUS DIFFUSION</b>]]> A composite consisting of a polymer and calcium carbonate has been synthesized by allowing carbon dioxide to diffuse into a poly(ethylene oxide) film containing a source of calcium ions. The X-ray pattern of the synthetic composite material shows that the least thermodynamically stable polymorph of calcium carbonate, vaterite is the mineral phase which is formed, rather than the most thermodynamically stable calcite phase. This effect has been seen in other reports of crystallization of inorganic phases which have been mediated by a polymer matrix and/or other organic moieties. In this paper, some possible explanations are presented which may help explain this phenomenon. <![CDATA[<b>MAGNETIC BEHAVIOR AND ANTIBACTERIAL ACTIVITY OF IRON (III) COMPLEXES</b>]]> The preparation, magnetic characterization and antimicrobial properties of the complexes [Fe(3)0(CH3COO)6(CH3COOH)(H(2)0)]Cl(MeImid)-(H(2)0) (1) and [Fe(4)0(2)(CH3COO)(7)0(2)(BPA)2(H(2)0)]- CH.25(CH3CH2OH)(H(2)0) (2), where Melmid is 2-methyl-imidazolium and BPA is 2,2'-bipyridine, are described. The variable temperature susceptibilities of these complexes were investigated in the temperature range 2-300K. The data have been modeled on the assumption of "butterfly" arranged for (2) and equilateral triangle of ferric ions for (1). The antimicrobial activities of these complexes have been screened in vitro against different bacterial strains. The complexes (1) and (2) display activity over Gram negative bacteria and these compounds not present activity over Gram positive strains. These complexes have bacteriostatic effect over bacterial target. The toxicity analyses of iron complexes showed these have cytotoxicity effect to values around the MIC on human cell. <![CDATA[<b>POLYCYCLIC AROMATIC HYDROCARBONS AND POLYCHLORINATED BIPHENYLS IN COASTAL ENVIRONMENTS OF VALDIVIA AND VALPARAÍSO, CHILE</b>]]> PAHs and PCBs were measured in the mussel Perumytilus purpuratus (Lamarck) collected from three different sites along the coast of Valdivia and Valparaiso, South-Central and Central Chile, respectively. Pollution at these sites is considered low with PAHs originating mainly from pyrolytic sources according to the Phenanthrene/Anthracene and Fluoranthene/Pyrene ratios. Temporal variation of PAHs was observed in Valdivia, while site variation was observed along the Valparaiso area. Total PAH concentrations in Valdivia ranged from 29.2 ng/gto 89.5 ng/g in 2001 and from 31.0 ng/g to 48.6 ng/g in 2002 while in Valparaiso samples the total PAHs ranged from 27.3 ng/gto 253.1 ng/g and from 12.1 ng/gto 26.3 ng/g in 2001 and 2002, respectively. Polychlorinated biphenyls were not found in mussels from Valdivia; however five non-planar congeners were detected in samples from Valparaiso with total concentrations between 1.0 ng/g and 16.6 ng/g in 2001 and between 3.4 ng/g and 29.0 ng/g in 2002. The pesticide heptachlor epoxide was detected in all sampling sites of Valdivia during the years 2001-2002 at concentrations ranging between 1 and 3.5 ng/g. <![CDATA[<b>SECONDARY METABOLITES FROM <i>PEPEROMIA </i></b><b><i>SUI</i></b>]]> One chromone, peperosuione (1), together with eighteen known compounds were identified from the whole plant of Peperomia sui (Piperaceae). Peperovulcanone A (2) isolated firstly from the P. vulcanica also obtained from this study, its structure was revised on the basis of spectroscopic evidences. All of the isolates constituents were determined by means of spectral analyses. <![CDATA[<b>SIMULTANEOUS DETERMINATION OF ACETAMINOPHEN AND TRAMADOL BY SECOND DERIVATIVE SPECTROPHOTOMETRY</b>]]> A rapid method for the simultaneous determination of acetaminophen (A) and tramadol (T) by second derivative spectrophotometric has been developed. From a solvent effect studies and the spectral behaviours of A and T, ethanol was selected as solvent. For a Δλ value of 210 nm a smoothing factor of 8,000 and scale factor of 1,000,000 were selected, because in these conditions the signal/noise ratio was favoured in order to avoid error. In these conditions also it is possible the simultaneous determination of A/T in a molar relation of 17/1 contained in pharmaceutical formulations. At 285.7 nm the second derivative value is T concentration dependent, corresponding to zero-crossing point of A. On the other hand, T does not absorb between 296.0 to 400.0 nm, thus 308.0 nm was selected for A determination by graphic method. The determination ranges for A and T were 8.1x10-7 - 5 1x10-5 mol/L and 3.4 x10-7 - 5.0 x10-5 mol/L, respectively and can be determined with good precision and accuracy, without previous separation. A study of interferents, was carried out by using the excipients Zafin® tablet. The recoveries were 97.4 ± 2.0% and 100.6 ± 1.7% for A and T, respectively. This tablet containing both drugs was assayed using the methods developed, showing a good accuracy and precision.