Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> http://www.scielo.cl/rss.php?pid=0717-970720090001&lang=es vol. 54 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[<b>CHITOSAN METAL COMPLEXES AND CHITOSAN- Cu ESR STUDIES</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100001&lng=es&nrm=iso&tlng=es Properties of the polymer metal complexes can be explained up to certain extent by the molecular structure of the complexes, but this área has not been well studied in the case of the chitosan metal complexes. In this work, we are proposing that chitosan is bonded through the 4 nitrogen to copper by means of square planar geometry. The polymer requires some structural modifications in order to be arranged in that geometry. Two sites in the chitin were detected, one similar to chitosan and the other in a square planar tetrahedrically distorted arrangement, with three atoms of nitrogen and one of oxygen or two atoms of nitrogen and two of oxygen. ESR studies of the copper complexes by means of chlorine and nitrate as ion counter were carried out. Nitrate exhibits one type of retention site and, on the other hand, chlorine presents two types of retention sites. <![CDATA[<b>DYSPROSIUM COLLOIDS PREPARED IN POLAR ORGANIC SOLVENTS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100002&lng=es&nrm=iso&tlng=es Dysprosium colloids in organic solvents (2-methoxyethanol, 2-propanol and 1,2-dimethoxyethane) have been obtained by the CLD method al 77 K. These colloids were characterized by zeta potentials, UV-Vis, TEM, electron diffraction and EDX measurements. Colloid stability depends on both solvent and metal concentration. The highest stability was obtained in 2-methoxyethanol, which is in agreement with previous results for other lanthanide colloids already reported. Zeta Potential (ξ) of the colloids ranges between 0.1430 and 1.945 mV. UV-Vis spectra exhibit bands in the UV región. 2-methoxyethanol shows bands at 211 and 283 nm, which is very similar to 1, 2-dimethoxyethane colloids (222 and 273 nm). However, the 2-propanol exhibits a band at 207 nm for a 2.5E-4 M concentration. At the TEM particle size distribution, 2-methoxyethanol colloid exhibits ranges from 2.5 to 11.6 nm, but the 2-propanol shows ranges from 2.5 to 4.3 nm, depending on the polarity of the solvent. The electron diffraction gives the most common phases, corresponding to Dy (002) and Dy(2)0(3) (110). EDX confirms the metal presence in the colloids. Luminescence measurements for Dy-2-methoxyethanol at 280 nm exhibit a higher quantum yield at 2.0E-3 and 5.0E-4 which indicates a higher transfer from the metal ion to the solvent. <![CDATA[<b>RELEVANCE OF SECONDARY PROCESSES IN ORAC VALUES OBTAINED EMPLOYING PYROGALLOL RED AS TARGET MOLECULE</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100003&lng=es&nrm=iso&tlng=es Pyrogallol red (PGR) is readily bleached by peroxyl radicals . Addition of cinnamic acid derivatives (coumaric, caffeic, ferulic and sinapic acids), even at relatively high concentrations, barely protects PGR from bleaching, given very low ORAC (oxygen radical absorbance capacity) values. This lack of protection is contrary to that expected from the relative reactivity of cinnamic acid derivatives and PGR. It is concluded that the protection is not determined by competition of the antioxidant and the target molecule for peroxyl radicals , but for secondary processes involving phenoxyl and PGR derived radicals . In particular, the occurrence of processes such as <img border=0 width=247 height=22 src="http://fbpe/img/jcchems/v54n1/form03-01a.jpg"> can explain the lack of PGR protection even in conditions where most of the peroxyl radicals are trapped by the additive. <![CDATA[<b>STUDY OF KINETIC FORMATION AND THE ELECTROCHEMICAL BEHAVIOR OF POLYPYRROLE FILMS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100004&lng=es&nrm=iso&tlng=es Polypyrrole films have been electrochemically polymerized on platinum electrode under different conditions. The effect of the parameters used during the potentiostatic polymerization, such as monomer concentration, type of doping agent (i.e. counterion), deposition time (i.e. films thickness), concentration of doping agent and polymerization potential on the rate of growth and the electrochemical properties of the polymeric film has been studied. In addition, the effect of the sweep rate of polypyrrole films polymerized with several doping agents were investigated. The results show that the kinetic of formation, the shape, the peak intensity, the peak potential and the electrochemical stability of the electroactive polypyrrole film are reliant on the conditions used during the polymerization process. The empirical kinetics determined from the polymerization charge were found to depend on [Py]085 and [SO4²]05. The kinetic of the electrochemical response was alSO4 affected by the anion use as doping agent during the electrochemical synthesis. <![CDATA[<b>A NEW METHOD TO SYNTHESIZE 3,5-DIARYLPYRAZOL DERIVATIVES</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100005&lng=es&nrm=iso&tlng=es Twelve 3, 5-diarylpyrazoles have been synthesized by microwave-assisted condensation reaction in a short and concise manner using various aromatic aldehydes and aromatic ketones as starting materials. The corresponding products were obtained in good yields (87-96%). All products were identified by MS, ¹H NMR, 13C NMR and elemental analysis. The advantages of this novel protocol include the excellent yield, operational simplicity, short time and the avoidance of the use of expensive catalysts. <![CDATA[<b>PREPARATION AND PROPERTIES OF DIFFERENT FUNCTIONAL GROUP CONTAINING STYRENE BUTADIENE RUBBER</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100006&lng=es&nrm=iso&tlng=es Chemically modified styrene butadiene rubber (SBR) with nitro and chloro functionalities are prepared by the nitromercuration reaction of SBR through a phase transfer catalyst. Activation energy for this chemical reaction calculated from the time temperature data on the chemical reaction by the measurement of percentage of chlorine indicated that the reaction proceeded according to fist order kinetics. The chemical modification is characterized by FTIR, UV, NMR studies reveal the attachment functional group such as nitro and chloro group to the double bond of butadiene moiety. The glass transition temperature of the functionalized SBR is analyzed using differential scarming calorimetry. Thermogravimetric analysis (TGA) of the modified SBR is investigated in orderto study the basic decomposition pattern and thermal stability of the materials. Chemical modification of SBR is accompanied by a reduction of double bond which imparts excellent tensile strength. The fíame resistances of the modified samples are analyzed by the limiting oxygenindex value (LOI) and the result of the studies show that as the level modification increases the tendency of ealstomeric material to burn decreases. <![CDATA[<b>ALTERNATIVE APPROACHES TO THE SPECTRAL QUANTITATIVE RESOLUTION of TWO-COMPONENT MIXTURE BY WAVELET FAMILIES</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100007&lng=es&nrm=iso&tlng=es A new spectral continuous wavelet transform (CWT) methods are proposed for the quantitative analysis of the binary mixtures. The simultaneous spectral resolution of binary mixtures and tablets containing paracetamol (PAR) and chloroxozone (CHL) with overlapping absorption spectra is performed by six wavelet families with no chemical separation procedure. The calibration graphs for the six wavelet families are obtained by the help of the data collected from the CWT- signal amplitudes corresponding to the zero crossing points inthe spectral range of 210 nm-310nm. The validation of each wavelet family is carriedoutby analyzing various synthetic binary mixtures of the above mentioned drugs. The second derivative spectrophotometry (D2) is used to compare the experimental results provided by the analyzed continuous wavelet families and a good coincidence is reported for the proposed analytical approaches. <![CDATA[<b>STUDY OF THE COPPER, CHROMIUM AND LEAD CONTENT IN <i>MUGIL CEPHALUS </i>AND <i>ELEGINOPS MACLOVINUS </i>OBTAINED IN THE MOUTHS OF THE MAULE AND MATAQUITO RTVERS (MAULE REGION, CHILE)</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100008&lng=es&nrm=iso&tlng=es The Cu, Cr and Pb concentrations were determined in Mugil cephalus and Eleginops maclovinus, fish species inhabiting the mouths of the Maule and Mataquito Rivers (Maule Región, Chile) which are consumed by the coastal population in large quantities. Measurements were taken by fíame atomic absorption spectroscopy to analyse representative muscle tissue of the two species. The method was validated using certified reference material (DOLT-1). The concentration ranges of Cu, Cr and Pb (mg· kg-1, dry weight) mMugil cephalus from the Maule river were: Cu 0.5-36.2; Cr 0.3-6.3; Pb 0.4-11.2 and from the Mataquito river varied between: Cu 0.6-23.2; Cr 0.3-6.0 and Pb 0.4-11.1. Forthe species Eleginops maclovinus from the Maule river the concentration ranges were: Cu 0.8-13.2; Cr 0.2-5.6; Pb 0.2-9.6 and from the Mataquito river: Cu 0.5-18.4; Cr 0.2-3.2 and Pb 0.3-4.0. The concentration ranges of Cu and Cr recorded inthe two species of fish are within the levels permitted by FAO and EP A, however the concentrations of Pb in Mugil cephalus originating from both estuaries exceeds the levels permitted by current legislation. The statistical analysis done with one way ANOVA (p < 0.05) indicated that for each metal there are no significant differences between the species and the two sampling sites; however with two way ANOVA between the species and the two sampling sites a significant difference was found for Cu and Cr, but not for Pb. <![CDATA[<b>THE SYNTHESIS OF SALICYLATE PROMPTED BY BR0NSTED ACIDIC IONIC LIQUIDS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100009&lng=es&nrm=iso&tlng=es Brønsted acidic ionic liquids based on imidazolium cation were employed as a series of efficient and environmentally benign catalysts and solvents for the synthesis of salicylate, the yields could reach 76%-96%. The optimal reaction conditions were determined. The results showed that Brønsted acidic ionic liquids were efficient catalysts and solvents which could be recycled easily without obvious decline in catalytic activities. <![CDATA[<b>IMPROPER HYDROGEN BONDS - A THEORETICAL STUDY ABOUT THE MOLECULAR STRUCTURE OF INTERMOLECULAR SYSTEMS FORMED BY H<sub>3</sub>C-H<sup>+</sup></b><b><sup>Δ</sup></b><b><sup>...</sup></b><b>X AND H<sub>3</sub>C<sup>+</sup></b><b><sup>Δ</sup></b><b><sup>...</sup></b><b>H-Y WITH X = CL<sup>-</sup> OR F<sup>-</sup> AND Y = CL OR F</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100010&lng=es&nrm=iso&tlng=es In this work is presented a theoretical study of the molecular properties of the H3C-H...X and H3C+δ...H-Y intermolecular systems with X = CL- or F- and Y = Cl or F. In the H3C-H...X complex, it is formed a traditional hydrogen bond between the CL- or F- anions and the hydrogen atom of the methyl. About the H3C+δ...H-Y complex, it was observed an improper hydrogen bond because the carbon atom of the methyl cation function as a proton acceptor. In this insight, the capacity of methane to interact with halogen anions (CL- or F-) and molecular acids (HCl or HF) was examined at the B3LYP/6-311++G(3df,3dp) level of calculation. Moreover, the interaction strengths of the H3C-H...X and H3C+δ...H-Y complexes was evaluated by computing their intermolecular distances and binding energies. Finally, QTAIM calculations also were executed with the purpose to examine the intermolecular interactions through the quantification of their electronic densities (p) as well as by the interpretation of the Laplacian operators (<img border=0 width=25 height=17 src="http://fbpe/img/jcchems/v54n1/form10-01.jpg">). <![CDATA[<b>A VOLTAMMETRIC STUDY ON THE INTERACTION OF NOVOBIOCIN WITH CYSTEINE</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100011&lng=es&nrm=iso&tlng=es The interaction of novobiocin (NOV), an aminocoumarin antibiotic, with cysteine was studied by square-wave voltammetry technique on the hanging mercury drop electrode in different pH values. After the addition of NOV into the cysteine solution, the peak current of mercurous cysteine thiolate decreased and its voltammetric peak potential shifted to more positive values. Voltammetric results showed that NOV binds with cysteine forming 1:1 nonelectroactive molecular complex by means of electrostatic and hydrogen-bonding interactions. The binding constants of NOV with cysteine at pHs 5, 7 and 10 were calculated to be 3.06x10³, 1.54x10(4) and 1.06x10(5) M-1, respectively. Furthermore, apossible mechanism of such interaction was also discussed. <![CDATA[<b>SYNTHESIS AND CHARACTERIZATIONS OF Ag, Cu AND AgCu METALLIC NANOPARTICLES STABILIZED BY DIVALENT SULFUR LIGANDS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100012&lng=es&nrm=iso&tlng=es The synthesis of Ag, Cu and Ag-Cu nanoparticles with divalent disulfur ligand by the Brust method were obtained. The metals were reduced by sodium borohydride and stabilized with 2,2'-dithioethanol (Ll), N,N'-dithiophtalimide (L2) and triphenylmethanesulfenamide (L3). The nanoparticles were characterized by TEM, EDX, electron diffraction and FTIR. The stability of the colloids at room temperature was also measured. We can observe a high stability for the colloids dispersion with L3 ligand (>1 week by AgCu-L3, Ag-L3 and Cu-L3). We found TEM studies show a size distribution between 9.7 and 15.8 nm, depending on the ligand. Electron diffraction analysis for the metallic nanoparticles shows the presence of Ag2S, Ag, CuO and bimetallic compounds such as CuAgS. The active solids were obtained by solvent evaporation from the nanoparticles dispersed to 50 °C. The FT-IR exhibit the presence of the ligand incorporated in the solid. <![CDATA[<b>MONOTERPENES, SESQUITERPENES AND FATTY ACIDS FROM <i>JULOCROTON TRIQUETER </i>(EUPHORBIACEAE) FROM CEARA - BRAZIL</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100013&lng=es&nrm=iso&tlng=es In this study the volatile constituents from leaves and fruits of Julocroton triqueter (Lam.) Didr. (Euphorbiaceae), a medicinal plant from northwest Brazil, were investigated by GC/MS. Twenty one compounds, which represent about 96% of the total constituents of the essential oil, were identified. Caryophyllene oxide, humulene epoxide II, trans-caryophyllene, occidentalol, á-humulene in the fruit and CM-carvyl acetate, spathulenol, CM-carveol, trans-caryophyllene, trans-carvyl acetate and á-humulene in the leaves were the principal components. From one fraction of the hexane extract of the fruits a mixture of fatty acids were identified as: dodecanoic, tetradecanoic, hexadecanoic, 9-octadecenoic, eicosanoic, trieicosanoic and tetracosanoic acids. The partial analysis of the non-volatile constituents (hexanic fraction) from fruit allowed the isolation and characterization of tetracosan-1-ol (identify by ¹H and 13C NMR, FTIR). <![CDATA[<b>SCAVENGING ACTIVITY OF DICLOFENAC</b>: <b>INTERACTION WITH ABTS RADICAL CATION AND PEROXYL RADICALS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100014&lng=es&nrm=iso&tlng=es The scavenging activity of diclofenac was estimated by its capability to bleach ABTS radical cation, and ORAC (oxygen radical absorbance capacity) methodology. In addition, GC-MS technique was used to establish if the lactamic derivative of diclofenac was formed as final product in the interaction with peroxyl radicals. Diclofenac bleached ABTS radical cation in a concentration-dependent way. In ORAC assays, diclofenac inhibited the consumption of fluorescein and c-phycocyanin mediated by peroxyl radicals. An ORAC-fluorescein, and ORAC-c-phycocyanin value of 0.3, and 0.004 was estimated, respectively. From the downcurvature observed in Stern-Volmer-like plots, we postulated that the low protection of c-phycocyanin is related to secondary damage of c-phycocyanin by the secondary radical of diclofenac. By GC-MS studies only a 2,6-dichloroaniline derivative was detected as product afterthe reaction with peroxyl radicals. <![CDATA[<b>A SILVER(I) PVC-MEMBRANE SENSOR BASED ON SYNTHESIZED DILAKTAM CROWN ETHER</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100015&lng=es&nrm=iso&tlng=es In this work, we introduce a highly selective and sensitive silver(I) PVC-membrane sensor. Dilaktam Crown ether (DLCE) was used as a membrane-active component to prepare a highly sensitive Ag(I)-selective polymeric membrane electrode. This sensor illustrated very good selectivity and sensitivity towards silver ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The sensor exhibited a Nernstian behavior (with a slope of 59.8 ± 0.2 mV per decade) for a concentration range (1.0 x 10-5-1.0 x 10¹ M) with a detection limit of 6.8xl0-6 M. It displayed a response time in the whole concentration range (~20 s) and its usage exceeded a 75 days period in the pH range of 5.1-7.2. The proposed electrode application was found to be successful as an indicator electrode in the titration with NaCl. <![CDATA[<b>ANTIMICROBIAL ACTIVITY OF EXTRACTS, ESSENTIAL OIL AND METABOLITES OBTAINED FROM <i>TAGETES MENDOCINA</i></b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100016&lng=es&nrm=iso&tlng=es Extracts from the Argentinean herb Tagetes mendocina Phil. (Asteraceae) were tested for antimicrobial activity against fungi, bacteria and protozoa. The different extracts (PE, DCM, MeOH and EtOAc) and the essential oil displayed activity mainly against dermatophytes, a group of fungi that produces skin infections. The bioassay-guided fractionation of PE, DCM and EtOAc extracts led to the isolation of eight compounds including two thiophenes, two acetophenone derivatives, dihydrorosefuran and three flavonoids. ITie thiophenes 5-(4-hydroxy- l-butynyl)-2,2'-bithienyl (BBTOH) (1) and its acetate (BBTOAc) (2) proved to be highly active against the dermatophytes Microsporum gypseum, Trichophyton rubrum and T. mentagrophytes with MIC values of 3.12, 3.12 and 6.25 µg/mL for compound 1 and 25, 3.12 and 6.25 µg/mLfor compound 2, respectively. In turn, the essential oil displayed a weak to modérate antifungal effect against M. gypseum with MIC = 250 µg/mL. ITie essential oil was examined by GC and GC-MS and 21 constituents (97.3%) were identified. (E) p-ocimene, (Z)-tagetone, (ii)-tagetone, (Z)-ocimenone, á-pinene and (E)-ocimenone were the major components. In addition, thiophenes 1 and 2 and 2-hydroxyacetophenone 3 showed antiprotozoal activity against Leishmania amazonensis, L. brasiliensis andi. infantum promastigotes with 100% lysis at 100 µg/mL. <![CDATA[<b>EQUILIBRIUM AND KINETIC STUDIES OF PHENOL SORPTION BY CHITOSAN COATED MONTMORILLONITE</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100017&lng=es&nrm=iso&tlng=es In order to provide physical support for chitosan and increase the accessibility of the binding sites for sorption process applications, chitosan was coated on the surface of montmorillonite. For the optimization of the sorption of phenol on chitosan coated montmorillonite (CCM), effects of pH, initial concentration and temperature on the sorption of phenol by CCM were investigated. In order to find the sorption characteristics, the isothermal data were applied to Langmuir and Freundlich linear isotherm equation, and the thermodynamic parameters (ΔH, ΔG and ΔS) were also calculated according to the values of binding Langmuir constant K L . The L type sorption isotherm between phenol and CCM suggests a relatively high affinity between the adsórbate and adsorbent, and the mechanism involved in the association of phenol with CCM were protón transfer, hydrogen bonding, London-Van der Waals forces because of lots of the OH and NH2 groups in the chitosan chain. The negative ΔH constant confirmed that the more phenol was adsorbed by CCM at lower temperature and the driving force for sorption process is an enthalpy effect. The kinetics of the sorption process of phenol on CCM were also investigated using the pseudo-first order and pseudo-second order kinetics, results showed that the second order equation model provided the best correlation with the experimental results. It was reached that modification of chitosan with montmorillonite increased the possibility of utilization of chitosan for phenol remo ve from aqueous solution. <![CDATA[<b>MICROWAVE-ASSISTED SYNTHESIS OF BENZOFURAN ANALOGS OF FENAMATES AS NON STEROIDAL ANTI-INFLAMMATORY AGENTS</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100018&lng=es&nrm=iso&tlng=es A series of benzofuran analogs of anthranilic acid derivatives were easily synthesized by microwave irradiation and conventional heating method. The microwave irradiation method gives the comparable yield as that of conventional heating with a shorter reaction time. All the new compounds have been characterized by spectral data and screened for anti-inflammatory activity. <![CDATA[<b>IDENTIFICATION OF KURARINONE BY LC/MS AND INVESTIGATION OF ITS THERMAL STABILITY</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100019&lng=es&nrm=iso&tlng=es A herbal ingredient kurannone (7, 2', 4,-trihydroxy-8-lavandulyl-5-methoxy flavanone) was isolated from the roots of sophoraflavescens Ait by ultrasonic extraction, which is one of tradicional Chinese medicine (TCM) materials. A reliable high performance liquid chromatography with mass spectrometry (HPLC-MS) method was used for determination of kurarinone. C18 column (150x4.6 mm, 5 µm) and methanol-water mobile phase (70:30, by volume) were used in the chromatographic separation of active components from the herb. HPLC-ESI-MS (UV, 288 nm; m/z, 437.5 [M-H]-) was adopted for kurarinone identification. Kurarinone with purity of 95.5% was obtained by silica gel column foUowed by reverse-phase column chromatography. The thermal stability of kurarinone was investigated, which illustrates that kurarinone was stable below 25 °C in 48 h, but a degradation of 25.54% was observed at 80 °C for 2 h. <![CDATA[<b>SYNERGISTIC EFFECT OF CALOTROPIS PLANT IN CONTROLLING CORROSION OF MILD STEEL IN BASIC SOLUTION</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100020&lng=es&nrm=iso&tlng=es The alcoholic extracts of leaves, latex and fruit from the Calotropis procera and Calotropis gigantea are tested for corrosion inhibition in basic solution by mass loss method and thermometric method. In the present investigation the extract reduces the corrosion rate of mild steel in basic solution. The inhibition efficiency increases as the extract concentration is increased. The alcoholic extract of Calotropis is found effective corrosion inhibitor in basic media and give up to 80.89% efficiency. <![CDATA[<b>A FACILE AND EFFICIENT SYNTHESIS OF HIGHLY FUNCTIONALIZED TERMINAL OLEFINES FROM </b><b>á</b><b>-ALKOXY-ß-HALIDES USING ZINC DUST</b><b><sup><a href="#z">Ψ</a></sup></b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100021&lng=es&nrm=iso&tlng=es A simple and efficient method of zinc dust/ammonium chloride system for the terminal olefination of á-alkoxy- ß-halides has been described. The reaction is carried out under mild conditions and yields of the corresponding terminal olefinic products are good. The significant feature of this method is the isolation of the pure product by simple work up in a short time. <![CDATA[<b>NITRATE DETERMINATION IN CHILEAN CALICHE SAMPLES BY UV-VISIBLE ABSORBANCE MEASUREMENTS AND MULTIVARIATE CALIBRARON</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100022&lng=es&nrm=iso&tlng=es Multivariate calibration of UV-visible spectral data using partial least-squares (PLS) has been applied to the determination of the nitrate content in Chilean Caliche samples, in the concentration range from 1 to 20% NaNO3 The multivariate approach is required since the samples do also contain unknown interferences which are spectrally active in the useful wavelength region for nitrate quantitation (near 301 nm). A set of fifteen calibration samples was employed to build the multivariate model, selected using the Kennard-Stone methodology, starting from real Caliche samples whose nitrate content was previously determined using the reference Devarda method. The figures of merit of the multivariate model were satisfactory (the limit of detection and quantitation reached 0.04% and 0.12 % of NaNO3, respectively, with an average error of prediction of 0.3 % of NaNO3). Then, the PLS model was then applied to a set of independent Caliche samples. The results were compared with a univariate UV approach, and with the nitrate content determined by the reference method, using the linear regression of predicted vs. reference concentration values, together with the elliptical joint confidence region test for the slope and intercept of the latter regression. The results indícate that the univariate method is unsuitable for analyzing the presently studied samples, unlike the multivariate model. Finally, the analytical methodology proposed appears as reliable and cheap alternative for routine analysis of a large number of caliche samples. <![CDATA[<b>THE EFFECT OF C2 AND C5 SUBSTITUTIONS ON THE NITROGEN LONE PAIR INVERSION IN 1,3-OXAZINES"</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000100023&lng=es&nrm=iso&tlng=es A series of N-methyl-2-R1,R2-5-R3,R4- 1,3-oxazines (where R are either H or p-nitro phenyl group and R3,4 = H or CH3- group) have been theoretically studied by ab initio methods in the frame of MO theory. Optimized geometries were obtained at HF and B3LYP/6-31G" levels, whereas energies were derived at MP2 and B3LYP levels employing the same basis set. Geometries obtained at DFT level are needed to obtain consistent values and good correlations between the experimental and theoretical ¹H-NMR data. The nitrogen lone pair would be axial orientated in I and II, since the N-methyl group lies in the equatorial position in the gas phase, whereas in compounds III and IV the methyl axial conformers increase their concentration, implying that inversion of the nitrogen lone pair takes place in an appreciable extent. PCM method predicts that solvents (CCl4, CHCl3, CH2Cl2) produce a significant effect on conformers preference, but just a modest influence on the equilibrium geometries and ¹H-NMR properties.