Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 48 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[DETERMINATION OF THE HENRY'S CONSTANT OF VOLATILE AND SEMI-VOLATILE ORGANIC COMPONUDS OF ENVIRONMENTAL CONCERN BY THE BAS (BATCH AIR STRIPPING) TECHNIQUE: A NEW MATHEMATICAL APPROACH]]> Chemical transfer between environmental compartments plays a key role in an adequate command and control of pollutants. The gas-liquid partitioning equilibrium constant, better known as the Henry's constant (K H) represents a crucial parameter in order to determine the environmental fate of chemicals and therefore, an accurate determination at ambient conditions is extremely important to assess the mentioned process. Within the experimental dynamic methods, the batch air stripping technique (BAS) has as major drawback the equilibrium condition among phases, which is hardly achieved in open natural systems. The present work, based on previously published mathematical models (4, 22), centers in the development of a new mathematical approach to determine K H by means of the BAS in non-equilibrium conditions through experimental and theoretical determinations of volumetric mass transfer coefficients (K La) for volatile (1,1-DCE, ethylbenzene, p-xylene and toluene) and semivolatile (1,1,2-TCE, 1,2-DCP, penhylmethylether (anisole) and naphthalene) organic compounds of environmental concern. In order to validate the approach, values obtained were compared to the K H determined through the static EPICS (Equilibrium Partitioning in Closed Systems) method, confirming the calculated K H and ratifying the new approach <![CDATA[COCRYSTALLIZATION OF LOW AMMOUNTS OF M<SUP>2+</SUP> IONS DURING CoSO<SUB>4</SUB>7H<SUB>2</SUB>O CRYSTALLIZATION]]> The equilibrium cocrystallization coefficients D M/CoSO4.7H2O of low amounts (10-3- 10-1%w/w) of M2+ ions (M2+ = {Ni2+, Mg2+, Cu2+, Zn2+, Fe2+, Mn2+, Cd2+, Ca2+}) with CoSO(4)7H2O have been determined with the method of long-time stirring of crushed CoSO(4)7H2O crystals in their saturated solution at 20ºC and compared with coefficients determined by means of the method of isothermal decreasing of supersaturation during 3 ­ 360 hours of stirring. This enabled the time needed to reach equilibrium to be found. It is different for different microcomponents. The determined cocrystallization coefficients are diverse: from <0.008 for Ca2+ to 1.20 for Fe2+. Their dependence on some physicochemical and crystal-chemical properties of both sulfate hydrates (CoSO(4)7H2O and MSO4nH2O) and metal M2+ ions has been discussed. They depend mainly on solubility in water and structure of corresponding sulfate hydrates as well as on radii of M2+ ions. It is possible to calculate cocrystallization coefficients with empirical formula based on determined relationships between some of the considered properties of macrocomponent and microcomponents and D M/CoSO4.7H2O coefficients at the average relative error not exceeding 10% <![CDATA[ESTIMATING THE DENSITY AND PULPING YIELD OF <I>E. globulus</I> WOOD BY DRIFT-MIR SPECTROSCOPY AND PRINCIPAL COMPONENTS REGRESSION (PCR)]]> The ability of mid-infrared (MIR) spectroscopy as a quick technique for determining wood properties of Eucalyptus globulus plantations, specifically basic density and pulping yield, has been examined. Twenty-seven samples were used as a calibration set and other three, for prediction making based on calibration (validation set). Calibrations and predictions through principal components regression (PCR) were obtained through the Quant+ chemometrics. Spectral data for a PCR model based on diffuse reflectance infrared Fourier transform (DRIFT), gave standard prediction error values of 21.44 kg m-3 and 1.73 % for basic density and pulping yield, respectively. The method allows to predict density (R² = 0.84) and pulping yield (R²= 0.40) from a single spectral MIR measurement <![CDATA[CORROSION INHIBITION OF COPPER IN 0.5 M HYDROCHLORIC ACID BY 1,3,4-THIADIAZOLE-2,5-DITHIOL]]> The inhibition of copper corrosion by 1,3,4-thiadiazole-2,5-dithiol (bismuthiol), under 0.5 M HCl at 25 C, was studied by means of the potentiodynamic polarization technique. It was found that bismuthiol was chemically adsorbed on the copper surface, and follows a Langmuir isotherm. The inhibition mechanism was found to be mixed, and it was originated through the formation of bismutiol-copper complexes on the surface of the metal. Bismuthiol shows good inhibition efficiency under these conditions <![CDATA[APPLICATION OF THE HOT DISK METHOD TO THE THERMOPHYSICAL CHARACTERIZATION OF SOILS]]> The thermal properties of soils, as thermal conductivity, have been usually determined by different designs of the quasi-permanent hot wire method. In the present paper the hot disk method was used to determine the effective thermal diffusivity (ETD) and thermal conductivity (TC) of soils derived from volcanic materials (one Ultisol and two Andisols) as a function of temperature from 25C to 280C. The volumetric heat capacity was also calculated from ETD and TC estimations. The TC values at 25C ranges from 0.84-0.94 for Andisols to 1.27 Wm-1K-1 for the Ultisol, and are similar to those reported by the hot-wire method. Values decrease down to 0.28-0.32 for Andisols and 0.67 Wm-1K-1 for Ultisol when heating temperature increases from 25C to 280C. The TC increases when soil density or water content increases, and decreases when soil organic matter content increases. The values of the thermal properties depend on water and organic carbon content, and mineralogy of samples <![CDATA[IRON AND MANGANESE REDUCTION IN POREWATERS OF THE BAY OF CONCEPCION AND ADJACENT CONTINENTAL SHELF DURING THE "1997-98 EL NIÑO" EVENT]]> Porewater chemistry gives some indication as to specific diagenetic reactions occurring in sediments. Reduction of manganese and iron oxides can occur due to abiotic reactions with sulfide or microbially mediated as electron acceptors in the degradation of organic matter. Sedimentary porewaters obtained from the Bay of Concepcion (36°38'S; 73°02'W) and continental shelf (36°31'S; 73°08'W) were analised to determine the distribution of remobilised Fe2+ and Mn2+. Sampling of the area coincided with the presence of the strong "1997-98 El Niño event". Porewaters were extracted under a nitrogen atmosphere and analised by atomic absorption spectrometry. Subsurface maxima are observed for Fe2+ during "El Niño event" in the bay and adjacent continental shelf (86.8 ± 9.3 µM y 59.3 ± 35.5 µM, respectively). A year later when the oxygen minimum is present, the production of Fe2+ on bay surface sediments increases 3-fold. Maxima concentrations for Mn2+ appear on surface sediments during and after "El Niño event" within the bay. It is postulated that vertical displacement of maxima concentrations observed for Fe2+ and Mn2+ in these sediments are modulated by changes of the oxygen minimum depth in the water column and the amount and quality of organic matter deposited in surface sediments <![CDATA[MESOPOROUS ALUMINOSILICATE MOLECULAR SIEVE: CONTROL OF TEXTURAL PROPERTIES BY POST-SYNTHESIS HYDROTHERMAL REATMENT]]> By means of sol-gel synthesis with silicon and aluminium alkoxides, Triton X-114, and hydrothermal stabilization at various times and temperatures, were obtained aluminosilicates which have a porous structure (MSA) and are thermally stable and partially ordered. The as-synthesized MSA samples were subjected to hydrothermal treatment (HT) from 6 to 96 hours at 150 °C and at 110 to 175 °C for 6 hours to determine the effect of time and temperature on the structure of the final aluminosilicate. All the materials obtained are mesoporous, showing changes in their structural properties: surface area, pore diameter, and mesopore area and volume in direct relation to temperature and HT time <![CDATA[BEHAVIOR OF HERBICIDE BENSULFURON-METHYL IN MICROWAVE-ASSISTED SOLVENT EXTRACTION (MASE) FROM SOILS WITH DIFFERENT PHYSICOCHEMICAL CHARACTERISTICS]]> The feasibility of MASE application in the determination of Bensulfuron-methyl (BSM) in soils with different organic matter content, consequently with a different capability to adsorb this herbicide is studied. Hydrolysis experiments were performed to check the significance of degradation under various temperature and time conditions in aqueous-acetonitrile solutions at various pH. Results are shown of the application of the method developed in the determination of BSM in two characteristic Chilean soils (organic matter content 1.4 and 11.4 % and pH 7.2 and 5.1, respectively). The maximum temperature that can be used during the heating program is 60C, where the two main degradation products were undetected and recovery percentages reached 95%. <![CDATA[STUDY OF CHEMICAL SPECIATION IN SEDIMENTS: AN APPROACH TO VERTICAL METALS DISTRIBUTION IN RAPEL RESERVOIR (CHILE)]]> A sequential chemical extraction method, following a Tessier's protocol has been applied to sample sediment from lake Rapel (34S), an hydroelectric reservoir. This study is a first approach of chemical speciation in this sediment. The four elements determined in the extracts were Cu, Zn, Mn and Fe. Analysis of the extracts was carried out by flame atomic absorption spectrometry (FAAS) and X-Ray fluorescence. The sample sediment was extracted using a core from 1 cm to 40 cm and the level concentration range were: Fe (19850 mg/g - 43899 mg/g), Mn (752 mg/g - 1269 mg/g), Cu (149 mg/g - 478 mg/g) and Zn (224 mg/g - 596 mg/g). Cu was associated to organic matter and carbonate fraction, Zn was associated to oxides Fe-Mn and Fe and Mn were bonding to oxides. All the metals show significant concentration in residual fraction except Cu <![CDATA[THERMAL AND X-RAY CRYSTALLOGRAPHIC STRUCTURAL STUDIES ON (N,N-DIBENCYL)-4-NITROPHENYLSULFENAMIDE]]> Crystal and molecular structure and the thermal properties of (N,N-dibencyl)-4-nitrophenylsulfenamide, (C6H5CH2)2 NSC6H4-4-NO2, is herein presented. The structure is a divalent sulfur compound that crystallized in the monoclinic system, space group P2(1)/c with a=9.274(2), b=6.013(1), c=32.147(9) Å, b=95.55(2) and Dx=1.305 g cm-3 with Z=4. The plane C-S-N form a dihedral angle of 77.4(3) with the plane C19-N1-C20, and it represent a notable difference with other sulfenamides described in the literature. The thermogravimetric analysis reveal a decomposition of the product in two steps and another event, probably, associated to a endothermic phase transition <![CDATA[RED WINE ANTIOXIDANTS: EVALUATION OF THEIR HYDROPHOBICITY AND BINDING EXTENT TO SALIVARY PROTEINS]]> Absorption by the organism of the antioxidants present in beverages depends on their hydrophobicity and their capacity to avoid precipitation by the proline rich proteins present in saliva. In the present work, we show that the antioxidants present in red wine samples are compounds of high hydrophilicity that are only poorly adsorbed by the proteins present in saliva. The antioxidant capacity of red wine samples is decreased only in 13 % when extracted with n-octanol (1:1 , V:V) , irrespective of the pH of the wine sample. Similarly, only a small fraction of the antioxidants (12.2 ± 3.4 %) is precipitated when wine samples are shaken for a few minutes with non-stimulated human saliva (5:1, V:V). This last result implies that most of the polyphenols present in the red wine samples are able to surpass the barrier imposed by the saliva <![CDATA[ANTIOXIDANT PROPERTIES OF LIGNANS AND FERULIC ACID FROM THE RESINOUS EXUDATE OF LARREA NITIDA]]> From the resinous exudate of twigs end leaves of Larrea nitida, two lignans nor isoguaiacine 1 and meso-nor-dihydroguaiaretic acid 2 and ferulic acid 3 were isolated. The antioxidant activities of resin and pure compounds were assesed by bleaching of the ABTS derived radical-cation <![CDATA[A PEACH STONE ACTIVATED CARBON CHEMICALLY MODIFIED TO ADSORB AQUEOUS AMMONIA]]> The oxidation of an activated carbon prepared from peach stones as well as the adsorption of aqueous ammonia using untreated and modified carbons is described here in. Boehm method in conjunction with temperature-programmed desorption (TPD) were mainly used to assess the chemical changes. These methods were complemented by chemical analysis, pH measurements and FT-IR spectra. Textural characterization was obtained from CO2 and N2 adsorption. Chemical modifications performed under the same experimental conditions with aqueous solutions of HNO3 and H2O2 indicated evidences that carboxylic acids like group formation is enhanced by short periods of time of HNO3 treatment at temperatures about 353 K followed by a mild oven-dry process in atmospheric air. The activated carbon modified under such conditions resulted to be the best ammonia adsorbent <![CDATA[DEVELOPMENT AND VALIDATION OF A METHOD USING INSTRUMENTAL PLANAR CHROMATOGRAPHY FOR QUANTITATIVE ANALYSIS OF CARBAMAZEPINE IN SALIVA]]> An instrumental planar chromatography method for quantitative analysis of carbamazepine in saliva was developed. The linearity, precision, detection and quantification limits, accuracy and selectivity of the method were validated. The method was linear between 0.50 and 15.00 ng/spot, with a regression coefficient of 0.999. The intra-assay variation (repeatability) was between 5.1% and 7.4%, and the inter-assay (reproducibility) was between 5.6% and 7.4%. The detection limit was 0.18 ng, and the quantification limit was 0.54 ng. The method proved accurate, with a recovery percentage of 109.8%, and it was selective for the active principle tested. In conclusion, is a good method for the quantitative determination of carbamazepine in saliva <![CDATA[X-RAY CRYSTAL AND MOLECULAR STRUCTURE OF AN ORGANOMETALLIC HYDRAZONE CONTAINING A ZIGZAG p-CONJUGATED SPACER: [CpFe(h<SUP>6</SUP>-C<SUB>6</SUB>H<SUB>5</SUB>)-N(Me)N=CH-C<SUB> 6</SUB>H<SUB>4</SUB>-4-NMe<SUB>2</SUB>]<SUP>+</SUP> PF<SUB>6</SUB><SUP>-</SUP>]]> The crystal and molecular structure of the complex [CpFe(h6-C6H5)-N(Me) N=CH-C6H4-4-NMe2]+PF6-, [1]+PF6-, was solved by single crystal X-ray diffraction analysis. One of the most salient features observed in this structure is the depyramidalization of both the benzylic nitrogen and the dimethylamino nitrogen atoms which reveals the delocalization of the p-electron system along the entire hydrazone skeleton from the donor to the acceptor termini, through a quinonoidal deformation and a pseudo-cyclohexadienyl conformation (folding dihedral angle of ca. 7.4°) of the free and coordinated phenyl rings, respectively. Both Cipso-N bond lengths are virtually identical (1.37 Å), lying between pure single and double bonds. These and other peculiarities are described and compared with the structures of other organometallic hydrazones <![CDATA[A FAMILY OF RYTHENIUM COMPLEXES CONTAINING THE NON-INNOCENT LIGAND O-BENZOQUINONEDIIMINE: AN INFRARED STRUCTURAL INTERPRETATION]]> It has been shown that innocent ligands always contribute with a similar electron density to a metal centre in a complex regardless of which other innocent ligands are bonded to the same centre, while non-innocent ligands are capable of tuning electron density on the metal centre depending on the nature of the other ligands. The present work reports the IR spectral characterisation of four ruthenium complexes containing the non-innocent ligand o-benzoquinonediimine and different innocent ligands (Ru(C6H4{NH}2)(Cl) 2(PPh3)2; [Ru(CH3CN)(C6H4{NH} 2)(Cl)(PPh3)2][BF4 ]; [Ru(CH3CN)2(C6H 4{NH}2)(PPh3)2 ][BF4]2, and [Ru(C6H4{NH}2)({C 2H5}2NCS2) (PPh3)2][Cl]. The C=N vibration correlates with the E L values of the ligands. We found that the o-benzoquinonediimine ligand modulates the vibrational energies depending on the nature of the innocent ligands bonded to the ruthenium atom <![CDATA[A COMPARISON OF SEMIEMPIRICAL AND <I>AB</I> <I>INITIO</I> METHODS FOR CALCULATING THE ELECTRONIC STRUCTURE OF C<SUB>60</SUB> AND C<SUB>70</SUB> FULLERENES]]> The aim of this work is to find a method suitable at least for obtaining the isolated molecule band structure approximated by a Gaussian broadening of the discrete eigenvalues, to apply it for a first scan of bigger and more complex structures. We compared the results of several semiempirical and ab initio quantum-chemical methods to calculate the band structure of isolated C60 and C70 fullerenes. Theoretical results were compared with experimental photoemission and inverse photoemission spectra. The results show that Extended Hückel Theory is the best method of all analyzed here. It compares well with experimental results related to valence and conduction bands for fullerene but underestimates the valence-conduction band gap by about 50%. Therefore, it is suitable for a first screening of fullerene-like molecules. Finally, EHT is employed to predict the electronic structure of several hypothetical molecules (P60O60, N70, C30N30 and N60 ) <![CDATA[CHARGE DEVELOPMENT AND ACID-BASE CHARACTERISTICS OF SOIL AND COMPOST HUMIC ACIDS]]> In previous works, the acid-base properties, charging behavior and chemical heterogeneity of humic substances have been studied using different mathematical equations to fit the experimental data. The objective of this research is to study the charge behavior, acid-base properties and analyze the chemical heterogeneity of humic acids (HA) extracted from soil and composted municipal solid waste by potentiometric titrations. The humic acids extracted from compost have some characteristics and behavior similar to those obtained from soil. The negative charge development of HA extracted from composted material are lower than those extracted from soil and increase as ionic strength increase. The amount of carboxylic groups is lower in compost HA than in soil HA The heterogeneity of HA extracted from compost is higher than those extracted from soil. As the time of composting period increase the humification processes that take place trends to produce compost HA that has similar characteristics to soil HA. We suggest that HA extracted from composted material are macromolecules "like soil humic acids", i.e. "humiclike fraction"