Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 56 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>COBALT ELECTRODEPOSITION ONTO STAINLESS STEEL 304 FROM AMMONIACAL SOLUTIONS</b>]]> In this work we studied the cobalt electrodeposition onto a stainless steel 304 electrode from an aqueous solution containing 10¹ M of CoSO4 + 1M (NH4)2SO4 at natural pH of 4.5. Black cobalt deposits were obtained under our experimental conditions. The average diffusion coefficient calculated was 9.8X10(6) cm²s-1 while the AG for the formation of stable nucleus was 1.013X10(20) J/nuclei. The critical cluster's size calculated was 0 which suggested that each active site is a critical nucleus on the SSE-304 surface. The Scanning Electron Microscopy images showed the formation of non-uniform cobalt particles. <![CDATA[SYNTHESIS AND CHARACTERIZATIONS OF POLY(ANILINE)/Sb<sub>2</sub>O<sub>3</sub> NANO COMPOSITE]]> This paper explains the synthesis and characterizations of Poly(aniline) (PANI)/Sb2O3 nano composite by in-situ polymerization method. It was indicated that Sb2O3 itself could catalyze the oxidative polymerization of aniline through its active surface effect. This could be due to the intercalation of PANI chains into the basal spacing of Sb2O3. TGA counseled the thermal stability of PANI. Through FTIR study, the structure of PANI was confirmed. Comparison of polymerized aniline composite with two different initiators was done. HRTEM confirmed the nano size of Sb2O3. The intercalating nature of PANI chains into the basal spacing of Sb2O3 was also tested. <![CDATA[<b>ENANTIOSELECTIVE EXTRACTION OF RACEMIC OFLOXACIN BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID AND TARTARIC ACID DERIVATIVES AS MIXED COMPLEX CHIRAL SELECTORS</b>]]> The distribution behavior of ofloaxcin (OFLX) enantiomers in a two-phase system was examined using a new mixed complex chiral selector consisting of di(2-ethylhexyl) phosphoric acid (D2EHPA) and two tartaric acid derivatives with n-octanol as diluents. The influence of composition of mixed complex chiral selector, initial concentration of OFLX, pH of aqueous phase and temperature was investigated. A maximum enantioselectivity of 2.43 was obtained when the molar concentration ratio of L-(-)-DBTA to L-(-)-DTTA is 2:3 L-(-)-DTTA concentration 0.18 mol/L, L-(-)-DBTA concentration 0.12mol/L) and the pH of aqueous phase is 6.86 at 25°C, with Dd and Dl up to a relative high value of 10.2 and 4.20, respectively. The results indicated a useful way of searching new efficient chiral selectors and it was proved also helpful to optimize the extraction systems and realize the large-scale production of the pure isomer of racemic mixtures with extraction methods. <![CDATA[<b>SPECTROPHOTOMETRYC DETERMINATION OF SERTRALINE IN PURE AND BLOOD SAMPLE</b>]]> A simple and sensitive spectrophotomteric method has been developed for the determination of Sertraline in pharmaceutical and blood sample. The current method is depend upon the reaction between the sertraline and chloranilic acid in slightly alkaline medium, giving a purple colour complex having maximum absorbance at 527.5 nm. The reaction is selective for sertraline with 0.01mg/mL.The colour reaction obeys Beer's law from 0.1mg to 5mg/mL of sertraline and relative standard deviation is 0.19%. The quantitative estimation of sertraline in blood sample is also studied. <![CDATA[<b>PRECONCENTRATION OF Cd<sup>2+</sup> IN DIFFERENT SAMPLES BY CHEMICALLY MODIFIED SIO<sub>2</sub>-DHAQ</b> <b>NANOPARTICLES</b>]]> A new analytical method using 1,8-dihydroxyanthraquinone modified SiO2 nanoparticles as solid-phase extractant has been developed for the preconcentration of trace amounts of Cd2+ in different samples. Conditions of the analysis such as preconcentration factor, effect of pH, sample volume, shaking time, elution conditions and effects of interfering ions for the recovery of analyte were investigated. The adsorption capacity of nanometer SiO2-DHAQ was found to be 85.83 μmol/g at optimum pH and the detection limit (3σ) was 0.60ng/mL. The extractant showed rapid kinetic sorption. The adsorption equilibrium of Cd²+ on nanometer SiO2-DHAQ was achieved within 20 min. Adsorbed Cd²+ was easily eluted with 6mL of 1M hydrochloric acid. The maximum preconcentration factor has been found to be 66.70. The method was applied for the determination of trace amounts of Cd²+ in different samples. <![CDATA[<b>CATALYTIC THERMAL DECOMPOSITION OF POLYETHYLENE BY PYROLYSIS GAS CHROMATOGRAPHY</b>]]> An experimental study of the thermal decomposition of polyethylene in an inert atmosphere has been carried out in the temperature range 300-800°C using Shimadzu PYR-2A pyrolyzer for heating the sample. The method allows the accurate control and measurement of the pyrolysis temperature. The production of hydrocarbons and the corresponding monomers of these polymeric systems were monitored. The effects of variation of temperature, sample size, pyrolysis atmosphere, residence time and catalyst on the distribution of these products were studied. As the carrier gas rapidly swept the primary products from the hot zone into the chromatographic column, so the secondary decomposition is largely eliminated and the pyrolysis products give accurate information about the nature, composition and structure of the pyrolysis material. <![CDATA[<b>THEORETICAL STUDY OF THE ISOMERIZATION OF MALEIC ACID INTO FUMARIC ACID</b>]]> The isomerization reaction of 2-butenedioic acid in gas phase has been studied using Hartree-Fock (HF), Meller-Plesset to 2nd order (MP2) and BLYP, B3LYP Density Functional Theory (DFT) levels of approximation. Potential energy surfaces (PES) of the singlet and triplet states of the molecule are constructed in order to corroborate the hypothesis that the reaction proceeds by a non-adiabatic path. A total of ten stationary points (eight singlet and two triplet) were characterized as energy minima or saddle points. Thermochemical analysis of the triplet conformers and singlet most stable structures yields a value of the AH0 of activation for isomerization that is in good agreement with the expected results. <![CDATA[<b>ONE-POT SYNTHESIS BENZILS FROM ALDEHYDES VIA NHC-CATALYZED BENZOIN DIMERIZATION</b> <b>UNDER METAL-FREE CONDITIONS IN WATER</b>]]> A simple and convenient one-pot procedure is reported for the synthesis of 1,2-diketones from corresponding benzoin-type condensation reaction of aromatic aldehydes in water with N,N-dialkylbenzimidazolium salt as condensation catalyst and air as oxidizing reagent. <![CDATA[<b>THERMAL AND OPTICAL PROPERTIES OF SILVER-POLYIMIDE NANOCOMPOSITE BASED ON DIPHENYL</b> <b>SULFONE MOIETIES IN THE MAIN CHAIN</b>]]> A new polyimide-silver nanocomposite containing diphenyl sulfone moiety in the main chain was synthesized using a convenient ultraviolet irradiation technique.AgNO3 was used as a source of the silver nanoparticles. Polyimide 3, as a polymer source , was synthesized by the polycondensation reaction of 4,4'-diamino diphenyl sulfone 1 with pyromellitic anhydride 2 in the presence of iso-quinoline as base and m-cresol as solvent. The resulting composite film 3a was characterized by FTIR spectroscopy, Uv-vis analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The X-ray diffraction analysis reveals that silver nanoparticles are present in polyimide matrix. This data is in good agreement with the result obtained from TEM and shows the silver nanoparticles homogeneously dispersed in the polyimide matrix. The UV-vis spectrum shows a single peak at 425 nm, arising from the surface plasmon absorption of the silver nanoparticles. <![CDATA[<b>SYNTHESIS AND CHARACTERIZATION OF POLY(METHYL METHACRYLATE)-SILICA, -ALUMINA AND</b> <b>-SILICA-ALUMINA SOL-GEL NANOCOMPOSITES</b>]]> The development of nanostructructured polymethilmethacrylate (PMMA) surfaces was studied by the incorporation of silica, alumina and silica-alumina, the former obtained by Sol-gel procedure. The materials were obtained in a polymer solution (acetone, isopropanol) and contains variable amounts of the inorganic component (10 and 20 % in the mass). The SEM studies show the modification of the polymer structure by the addition of the silicon oxide and aluminum oxide; though not all the samples show a high dispersion of the inorganic component. The FT-IR spectrum showed a reduction in the intensity of the carbonyl signal associated to the polymer, due to the incorporation of the filler and the presence of bands attributed to the inorganic components incorporated. Through TGA and DSC studies the modification of the thermal stability of the polymer was proved, depending on the inorganic component used and its composition. <![CDATA[<b>A MINIREVIEW OF CELLULOSE NANOCRYSTALS AND ITS POTENTIAL INTEGRATION AS CO-PRODUCT IN BIOETHANOL PRODUCTION</b>]]> Cellulose nanocrystals appeared as important bio-based products and the collected information in term of production, characterization and application suggest that this nanomaterial could be easily extrapolated to bioethanol production. This review describes recent published syntheses using chemical and enzymatic hydrolyses and different preparations such as high pressure homogenization. Their industrial and medical applications, such as controled of delivery carriers, suggest a large projection of this nanomaterial. The most important aspect in this collected data is the potential to decrease significantly the final cost of the enzymes or the hydrolysis pre-treatment of lignocellulosic materials of all bioethanol processes in such a way that it could be economically feasible from materials such as bagasse, straw or wood resources. <![CDATA[<b><i>CARYOPTERIS ODORATA</i></b>: <b>A RICH SOURCE OF ANTIOXIDANTS FOR PROTECTION AGAINST CHRONIC</b> <b>DISEASES AND FOOD PRODUCTS</b>]]> This study was designed to examine the in vitro antioxidant potential of the different fractions of Caryopteris odorata (Ham. ex Roxb.). The methanolic extract of this plant was dissolved in distilled water and partitioned with n-hexane, chloroform, ethyl acetate and n-butanol, successively. These organic fractions and the remaining aqueous fraction were screened for their possible antioxidant activities by different methods: 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity, total antioxidant activity, ferric reducing antioxidant power (FRAP) assay and ferric thiocyanate assay. The total phenolics were also determined. The results revealed that among these fractions ethyl acetate soluble fraction showed very good antioxidant potential, having an IC50 value of 8.01 ± 0.254 µg/mL. It also exhibited the highest total antioxidant activity (2.358 ± 0.035), FRAP value (2505.8 ± 0.58 µg/mL), inhibition of lipid peroxidation (77.53 ± 0.784 %) value and total phenolic contents (87.08 ± 1.5µg/g) as compared to other fractions. <![CDATA[<b>FERROSPECTRAL SORBED ON DEAE SEPHADEX A-25 FOR THE SOLID PHASE SPECTROPHOTOMETRIC DETERMINATION OF IRON AND COBALT BY BATCH AND CONTINUOUS FLOW MODES</b>]]> In this work, Ferrospectral;3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine (FST) sorbed on DEAE Sephadex A-25 is used as solid phase for spectrophotometric determination of iron and cobalt by batch and continuos flow modes. In batch simultaneous determination, the second derivative at 536.0 and 601.4 nm were used for iron and cobalt determination, respectively. In this modality, the detection limits (3 o criterion), for iron and cobalt were 1.3, 9.1, ug L¹ and the determination ranges were: 4.3 to 220 and 30.3 to 800 ug L¹. The method by FIA mode was carried out by stopped flow and then the analytical signal was evaluated by second derivative at 560.9 and 482.3 nm for iron and cobalt determination; respectively. In FIA modality, the detection limits for iron and cobalt were 6.4, 31 ug L¹, and the determination ranges 21 to 200 and 106 to 1000 ug L¹ iron and cobalt, respectively. In both modalities the repeatability for iron and cobalt were < 4 % and the recovery was near to 100%. These methods were applied successfully in drinking water and soil samples. <![CDATA[<b>CHARACTERIZATION OF PHENOLIC ACIDS PROFILE FROM CHILEAN RED WINES BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY</b>]]> The success of Chilean wine in the international market has led to an important attention on the development of science and technology for wine differentiation, productivity, and quality. In order to report the profile of phenolic acid compounds in Chilean red wines, an SPE technique over ODS column was used followed by a reverse phase HPLC program that was developed to separate, characterize and quantify six phenolic acids (caffeic, gallic, p-coumaric, protocatechuic, syringic and vanillic acids) in four red Chilean wines varieties (Cabernet Sauvignon, Carménère, Merlot and Syrah) from grapes cultivated in the central zone of Chile. The separation was carried out on an RP C-18 column using a binary gradient elution and diode array detection. <![CDATA[<b>ADSORPTION ESSAYS OF PALLADIUM IN MODIFIED SILICA GEL WITH THIOURONIUM GROUPS</b>: <b>EXPERIMENTAL AND THEORICAL STUDIES</b>]]> The silylant 3-cloropropyltriethoxysilyl was anchored over silica gel in anhydrous conditions in order to react with thiourea to obtain modified silica gel with thiouronium. The aim to obtain an inorganic support that is able to hijack metals from the VIII group such as palladium. The product was characterized by Sbet and FTIR infrared spectroscopy. For the determination of the structure in the modified silica gel NMR spectra of silicon and carbon were preformed in solid state. The coordination form of the modified silica gel to the metal was studied computationally in the context of the DFT theory, using the ADF code. This was a collaborative work with "Fundación Chile" for the recuperation of precious metals from the mining industry. <![CDATA[<b>SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF A SERIES OF SUBSTITUTED POLYPYRIDINE Co(II)/Co(III) COUPLES AND THEIR POTENTIALITY AS MEDIATORS FOR SOLAR CELLS</b>]]> This paper reports the synthesis, characterization and spectroscopic and electrochemical study of a series of polypyridine Co(II) and Co(III) complexes. The effect on the redox potential of the presence of donor or acceptor substituents on the ligand, as well as the effect of an increased ligand aromaticity, was analyzed. Specifically, complexes of [Co(L-L)3]11+ type were prepared, with n = 2,3, and L-L = 1,10-phenanthroline (phen), 5-amino-1,10'-phenanthroline (phen-NH2), 3,4,7,8-tatramethyl phenantroline (phen-4Me), pyrazino[2,3-ƒ][1,10]phenanthroline (ppl), 2-methylpyrazino[2,3-ƒ][1,10]phenanthroline (ppl-Me), dipyrido[3,2-a:2',3'-c]phenazine (dppz), 7-methyldipyrido[3,2-a:2',3'-c]phenazine (dppz-Me) and 7-aminodipyrido[3,2-a:2',3'-c]phenazine (dppz-NH2). The results of this study open the possibility to have a battery of potential mediators for photoelectrochemical solar cells. Ultimately, the election of a determined couple as mediator will depend mainly on the electronic properties of the specific dye in a given cell. <![CDATA[<b>APPLICATION OF HIGH-PERFORMANCE THIN-LAYER CHROMATOGRAPHIC METHOD FOR THE SIMULTANEOUS DETERMINATION OF LAMIVUDINE AND TENOFOVIR DISOPROXIL FUMARATE IN</b> <b>PHARMACEUTICAL DOSAGE FORM</b>]]> A simple, precise and accurate high performance thin layer chromatographic method has been developed for the simultaneous determination of lamivudine (LAM) and tenofovir disoproxil fumarate (TDF) in pharmaceutical dosage form. The separation was carried out on Merck HPTLC aluminum plates of silica gel 60 F254,(20 x 10 cm) with 250 µm thickness using chloroform: methanol: toluene (8: 2: 2, v/v/v) as mobile phase. HPTLC separation of the two drugs followed by densitometric measurement was carried out in the absorbance mode at 265 nm. The drugs were satisfactorily resolved with Rf values of 0.27± 0.01 and 0.51± 0.01 for LAM and TDF, respectively. The linear regression analysis data for the calibration plots showed good linear relationship with r²=0.9999 and 0.9996 for LAM and TDF, respectively in the concentration range of 60-210 ng spot¹ for each drug. The method was validated for precision, robustness, specificity and accuracy The limit of detection and quantitation were 20 and 40 ng spot¹, respectively for LAM and 30 and 60 ng spot¹, respectively for TDF. The proposed developed HPTLC method can be applied for identification and quantitative determination of LAM and TDF in bulk drug and pharmaceutical dosage form. <![CDATA[<b>VALIDATED CHIRAL LC METHOD FOR DEXRABEPRAZOLE ON REVERSE PHASE AMYLOSE BASED</b> <b>STATIONARY PHASE</b>]]> A simple, rapid and robust LC method was developed and validated for the enantiomeric separation of dexrabeprazole in bulk drug and formulation. The enantiomers of dexrabeprazole were resolved on a Chiralpak AD-RH (amylose based stationary phase) column using a mobile phase consisting of water: acetonitrile (50:50, v/v) at a flow rate of 0.5 ml min¹. The resolution between the enantiomers was found to be more than 1.5 in optimized method. The developed method was extensively validated and proved to be robust. The calibration curve for (S)-enantiomer showed excellent linearity over the concentration range of 0.05 µg ml¹ (LOQ) to 1 µg ml¹. The limit of detection and limit of quantification for (S)-enantiomer were 0.015 µg ml¹ and 0.05 µg ml¹, respectively. The percentage recovery of the (S)-enantiomer ranged between 97 to 101 % in bulk drug samples of dexrabeprazole. The proposed method was found to be suitable and accurate for quantitative determination of (S)-enantiomer in bulk drug substance. <![CDATA[<b>OZONE LEVELS ASSOCIATED TO THE PHOTOCHEMICAL SMOG IN SANTIAGO OF CHILE</b>: <b>THE ELUSIVE</b> <b>ROL OF HYDROCARBONS</b>]]> Santiago of Chile presents, in autumn and summer, high levels of oxidants and, in particular of ozone. Peculiar features of this phenomenon are a strong dependence of the contamination with the daily maxima temperature and a weekend effect, comprising relatively high ozone levels in spite of reduced emissions of its precursors. A common explanation of these effects could be an increase in the VOCs/NOx ratio. In order to test this possibility we perform la multiparametric analysis of Santiago's historical data. This data treatment corroborates a robust dependence of maxima ozone levels with temperature and a moderate weekend effect. In fact, ozone levels in weekend days are similar to those of working days, in spite of significantly reduced primary emissions (29 % of NOx and 20 % of CO). However, no increase in VOCs/NOx ratios, measured at the early morning rush out hours, is observed in high temperature days. On the other hand, the data suggest a moderate increase of the VOCs/NOx ratio in week ends. This would indicate that other factors beyond a simple increase in VOCs levels contribute to the above mentioned peculiarities of oxidant levels in the urban atmosphere of Santiago. <![CDATA[<b>COMPOSITION AND ANTIMICROBIAL SCREENING OF THE ESSENTIAL OIL FROM THE LEAVES AND</b> <b>STEMS OF <i>Senecio atacamensis </i>Phil. FROM CHILE</b>]]> An essential oil from Senecio atacamensis Phil. (Asteraceae) was obtained by hydrodistillation of its aerial parts (leaves and stems) and its composition was determined by GC and GC/MS analysis. The identification by GC of the essential oil components, in both leaves and stems respectively, showed α-terpinene (36.05% and 20.57%); α-phellandrene (27.79% and 25.37%), and p-cymene (11.85% and 22.55%) as the most abundant monoterpenes. Furthermore, the oil was tested for its antimicrobial activity using paper disc diffusion and the dilution broth method, exhibiting moderate inhibition of human pathogenic bacteria. <![CDATA[SENSITIVE AND SELECTIVE EXTRACTION FREE ION-PAIR COMPLEXOMETRIC DETERMINATION OF DOMPERIDONE IN PHARMACEUTICALS AND IN SPIKED HUMAN URINE]]> Domperidone (DOM) is a drug used as an antiemetic and to control gastrointestinal effects of dopaminergic drugs in the management of perkinsonism. Two simple, rapid, sensitive and selective extraction free spectrophotometric methods have been developed for the assay of DOM in pure drug, in pharmaceuticals and in spiked human urine sample. The methods are based on the formation of yellow ion-pair complexes between DOM and two sulphonphthalein dyes viz., thymol blue (method A) and bromothymol blue (method B) in acetone and dichloromethane medium. The complexes showed absorption maxima at 390 nm and 410 nm in method A and method B, respectively. Reaction conditions were optimized to obtain the maximum color intensity. The absorbance was found to increase linearly with increase in concentration of DOM, which was corroborated by the calculated correlation values of 0.9991 in method A and 0.9986 in method B. The systems obeyed Beer's law over the concentration range of 1.25 - 20 µg mL-1 in both the methods. The molar absorptivity values are calculated to be 1.53 x 10(4) and 2.06 X 10(4) L mol¹ cm¹ for method A and method B, respectively and the corresponding Sandell sensitivity values are 0.028 and 0.021 µg cm². The composition of the ion-pairs was found to be 1 : 1 by Job's method and the conditional stability constant (Kf) of the complexes have been calculated. The proposed methods were applied successfully to the determination of DOM in tablets as well as in spiked urine sample with good accuracy and precision. <![CDATA[<b>SYNTHESIS OF AMIDOXIMES USING AN EFFICIENT AND RAPID ULTRASOUND METHOD</b>]]> This is a report on an efficient and rapid synthesis of amidoximes using ultrasound irradiation with appropriate nitrile and hydroxylamine hydrochloride in water/ethanol. This new synthetic methodology is compared with previously known methods. The main advantages of the process reported are shorter reaction times, easier work-up, and good yield. <![CDATA[<b>ERRATUM</b>]]> This is a report on an efficient and rapid synthesis of amidoximes using ultrasound irradiation with appropriate nitrile and hydroxylamine hydrochloride in water/ethanol. This new synthetic methodology is compared with previously known methods. The main advantages of the process reported are shorter reaction times, easier work-up, and good yield.