Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 57 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>AN IMPROVED TOPOLOGICAL DESCRIPTOR<i> ED<sub>m</sub></i> AND ITS APPLICATION</b>]]> In this paper, on the basis of the topological index EDm derived from ionicity index matrix, improved distance matrix and branching degree matrix, we proposed the new topological descriptor EDm' by introducing the bond angle into hidden hydrogen graph of molecules and using the geometric distance instead of the sum of bond length between two vertexes. The EDm describes the molecular structure more accurately, and realizes unique characterization to cis-trans isomers. The quantitative structure-property relationship (QSPR) models, with correlation coefficients (R) in the range of 0.984-1.000 for the boiling point (b.p.), the standard enthalpy of formation ( DfHmθ), the molar refraction (Rm) and the molar volume (Vm) of some cis-trans isomers for alkenes, are subsequently developed by index EDm'. Moreover, the good stability and predictive ability of the models were demonstrated by LOO (leave-one-out) method and RSP (random sampling prediction) method, which further manifests the index EDm has high potential of wide applications in QSPR study. <![CDATA[<b>ADSORPTION OF Cr(VI) FROM AQUEOUS SOLUTION USING CARBON-MICROSILICA</b> <b>COMPOSITE ADSORBENT</b>]]> In this work, Microsilica, one kind of industry solid waste material, was utilized firstly to prepare a carbon-Microsilica composite adsorbent from a partial carbonization, mixture and sulfoxidation process and was proposed for the removal of Cr(VI) from solutions. The surface chemistry characteristics of the prepared adsorbent were analysis by XPS and FT-IR. The characterization results indicated that an abundant of oxygen functional groups, such as hydroxyl, carboxyl and sulfonic groups, were introduced into the surface of the prepared composite adsorbent. Meanwhile, the adsorption characteristics of Cr(VI) onto the adsorbent in aqueous solutions was studied as a function of solution pH, ionic strength, contact time, and temperature. The results showed that Cr(VI) adsorption onto the adsorbent is strongly dependent on pH and, to a lesser extent, ionic strength. Kinetics data were found to follow the pseudo-second-order kinetic model while the adsorption data corresponded to L-shape adsorption isotherm which corresponds to the classification of Giles. Activation thermodynamic parameters, such as activation enthalpy (ΔH*), activation entropy (ΔS*), activation Gibbs free energy (ΔG*) and activation energy (E), have been evaluated and the possible adsorption mechanism also was suggested. <![CDATA[<b>SYNTHESIS OF LA<sub>x</sub>SR<sub>1-x</sub>TIO<sub>3</sub> ANODE MATERIALS BY SOL-GEL AUTO-COMBUSTION METHOD</b>]]> A novel anode material for intermediate temperature solid oxide fuel cells with a composite of La xSR1-xTiO3 has been synthesized by a sol-gel auto-combustion method. X-ray diffraction (XRD) shows that La xSR1-xTiO3 has good chemical compatibility with Gd0.2 Ce0.8O1.9 electrolyte. The thermal expansion coefficient (TEC) of the as-prepared anode material is similar to that of Gd0.2 Ce0.8O1.9. The electric conductivity measurements show that the conductivity of La xSR1-xTiO3 increases with the increasing of lanthanum contents and reached a maximal value at x=0.3. At 800ºC, the electrical conductivity of La0.3Sr0.7TiO3 is 184Scm-1. <![CDATA[<b><sup>1</sup>H AND <sup>13</sup>C NMR SPECTRAL ASSIGNMENTS AND X-RAY CRYSTALLOGRAPHY OF 4,5,8,12b-TETRAHYDRO-ISOINDOLO[1,2 -</b><em><b>α</b></em><b> ]ISOQUINOLINE AND DERIVATIVES</b>]]> 12b-Hydroxy-5,6,8,12b-tetrahydroisoindolo[1,2-α] isoquinolin-8-one (4), 5,6,8,12b-tetrahydroisoindolo[1,2-α]isoquinoline (5) and 12b-hydroxy-5,6,8,12b-tetrahydroisoindolo[1,2-α]isoquinoline (6) were obtained by reduction of 4,5,8,12b-tetrahydroisoindolo[1,2-α]isoquinolin-8-one (3) with LiAlH4/THF/N2. The precursor and products were characterized by NMR spectroscopy and the X-ray crystal structure of 5 hydrochloride monohydrate (5a) was determined. ¹H and 13C NMR spectra were completely assigned for compounds 3, 4, and 5a, using two-dimensional experiments (H-H COSY, HMQC, HMBC and H-H NOESY). <![CDATA[<b>CORROSION RESISTANCE OF DECORATIVE CHROMIUM FILMS OBTAINED FROM TRIVALENT</b> <b>CHROMIUM SOLUTIONS</b>]]> In this work, the resistance to corrosion of chromium films obtained from trivalent chromium solutions of different compositions and the influence of solution compounds on the coatings electrochemical behavior and the microstructure were studied. The chromium coatings were obtained from trivalent solutions in a chloride-based bath with different complexing agents adding also sodium hypophosphite and aluminum chloride. UV-vis spectroscopy was carried out on all solutions before and after plating to observe changes in the chromium complexes chemical state due to the plating process. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) were performed to examine the coatings surface morphology and composition; respectively. The coulometric method was used for measuring coating thickness. Electrochemical impedance spectroscopy (EIS) was done using 3% NaCl as electrolyte and using a three-electrode cell with a standard calomel electrode (SCE) as reference. Bright chromium films were obtained from all baths however, differences were observed concerning morphology, thickness and corrosion resistance depending on the composition of the forming solution. <![CDATA[<b>TWO SELECTIVE SPECTROPHOTOMETRY METHODS FOR THE DETERMINATION OF THIORIDAZINE HYDROCHLORIDE IN TABLETS AND IN BIOLOGICAL FLUIDS</b>]]> Two simple, rapid and selective spectrophotometric methods have been developed for the analysis of the psychoactive drug thioridazine HCl (TRH) in tablets and in biological fluids. The first method is based on the oxidation of TRH by a known excess of N- bromosuccinimide (NBS), followed by the determination of unreacted oxidants by measuring the decrease in absorbance of two different dyes; amaranth (AM) and methylene blue (MB) at a suitable λmax 520 and 660 nm, respectively. Beer-Lambert plots showed good correlation in the concentration ranges of 0.8-4.8 and 0.8-5.6 µg/ml for AM and MB methods, respectively. The second method is based upon the formation of an ion-pair complexes (1: 1) with the acidic sulphonphthalein dyes bromophenol blue (BPB) and bromothymol blue (BTB). The formed complexes were extracted into methylene chloride and their absorbance was measured at 405 and 408 nm for BPB and BTB, respectively. Beer's law was obeyed with a good correlation coefficient (r = 0.9995-0.9989) in the concentration ranges of 4 - 24 µg/ml for both BPB and BTB methods, respectively. All measurements of the two procedures are carried out in an acidic medium at room temperature. Optimizations of the different experimental conditions are described for both methods. The two methods have been successfully applied to the determination of thioridazine HCl in pharmaceutical, serum and urine samples and average recoveries are in the range of 98.12 - 102.55%. Analytical results obtained with this novel method are satisfactory. <![CDATA[<b>FLAVONOIDS AND ANTIMICROBIAL ACTIVITY OF LEAVES OF <i>XYLOSMA LONGIFOLIUM</i></b>]]> The methanolic extract of the leaves of Xylosma longifolium afforded a new flavonodic compound named as Kaempferol-3-β-xylopyranoside-4'-α-rhamnoside along with Kaempferol, Quercetin, Kaempferol-3-rhamnoside, Quercetin-3-rhamnoside. Their structures were established on the basis of chemical and physical evidences (IR, ¹H NMR, and MS data). It was also screened for their antimicrobial activity. <![CDATA[<b>EFFECT OF COAL ASH ON THE MORPHOLOGICAL, THERMAL AND MECHANICAL PROPERTIES OF POLY(METHYL METHACRYLATE)</b>]]> Composite materials of Coal ash/ Poly(Methyl Methacrylate) (ash/PMMA) were prepared/synthesized and their properties were studied by scanning electron microscopy (SEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA) and universal testing machine (UTM). The morphological study presented that the ash particles were well dispersed and embedded within the PMMA matrix. The DSC thermograms showed that the melting temperature (Tm) of pure PMMA is about 166 ºC which was shifted towards lower temperature when ash were incorporated in the polymer matrix. The mechanical properties of the ash/PMMA composites were enhanced up to an optimum level (ash 3 wt %) and then decreased at higher incorporation of large quantity of filler. The TGA thermograms indicated that the thermal stability of the ash/PMMA composite was enhance significantly than pure PMMA. <![CDATA[<b>STUDIES ON COMPLEXATION IN SOLUTION WITH A PAPER ELECTROPHORETIC TECHNIQUE [THE SYSTEM MERCURY(II)/NICKEL(II)/ LEAD(II) - SARCOSINE]</b>]]> Complexation reactions of sarcosine with mercury(II), nickel(II) and lead(II) have been studied in the solution phase using a paper ionophoretic technique. This method is based on movement of a spot of metal ion in an electric field at various pHs of background electrolyte. A graph of pH versus mobility was used to obtain information on the metal complexes and to calculate stability constants. The stability constants of the ML+ and ML2 complexes of mercury(II), nickel(II) and lead(II) - sarcosine have been found to be (7.95 ± 0.02; 6.79 ± 0.06), (6.69 ± 0.01; 5.29 ± 0.04) and (4.34 ± 0.02; 2.69 ± 0.07) (logarithm stability constant values), respectively at a temperature of 35 ° C and ionic strength of 0.1 M. <![CDATA[<b>DEGRADATION OF ACID VIOLET 7 AND REACTIVE BLACK 5 IN WATER BY ELECTRO-FENTON AND</b> <b>PHOTO ELECTRO-FENTON BY</b>]]> The mineralization of solutions containing azo dyes Acid Violet 7 (AV7) and Reactive Black 5 (RB5) in aqueous solutions using electro-Fenton (EF) and Photo electro-Fenton (PEF) methods were determined. The electrochemical system includes a glassy carbon mesh electrode (cathode) with a concentric outer steel mesh as anode. The optimized parameters were: 0.01 mM of Fe²+ ions, and 250 mA of applied current at pH 3. All experiments were made at 35°C. The degradation was evaluated by color removal and total organic carbon (TOC) decay for solutions of 250 mg L-1 of both cases. The results indicate that the system achieves a degradation efficiency for both dyes proposed, being observed a quickly decolorization of the solutions and the complete transformation of organic compounds to carbon dioxide. The efficiency process and decoloration kinetic constant were evaluated. Generated carboxylic acids such oxalic, oxamic, citric and maleic were found by ion exclusion chromatography. A comparison of the electrochemical system with respect to Fenton's and Photo-Fenton reaction was also performed. <![CDATA[<b>SIMULTANEOUS COPRECIPITATION OF PD(II), RH(III) AND AU(III) WITH MN(OH)<sub>2</sub> WITHOUT CHELATING AGENT PRIOR TO FLAME ATOMIC ABSORPTION SPECTROMETRY DETERMINATION</b>]]> A separation-preconcentration procedure was developed for determination of trace amounts of palladium, rhodium and gold in dust and water samples by flame atomic absorption spectrometry after simultaneous coprecipitation by Mn(OH)2 without chelating agent. The precipitate could be easily dissolved with concentrated nitric acid. The influence of the various analytical parameters such as pH, sample volume, centrifuge time, standing time, centrifugation rate and time, amounts of manganese and matrix effects were studied for the quantitative recoveries of the analyte ions. Under the optimized experimental conditions, the calibration curves for Pd(II), Rh(III) and Au(III) were linear from 8.0 to 2000.0, 1.0 to 750.0 and 5.0 to 1000.0 ng mL-1, respectively. The relative standard deviations for seven replicate determinations of a mixture of 0.1 mg mL-1 palladium, rhodium and gold in the original solution were 2.1, 1.9 and 2.4%, respectively. The detection limits based on 3Sb for Pd(II), Rh(III) and Au(III) in the original solution were 2.2, 0.3 and 1.3 ng mL-1, respectively. The proposed method has been applied for determination of trace amounts of palladium, rhodium and gold ions in the standard, road dust and water samples and satisfactory results were obtained. <![CDATA[<b>THE INFLUENCE OF PLATINUM ON THE STRUCTURE AND PHOTOCATALYTIC PERFORMANCE</b> <b>OF HYDROGEN TITANATE NANOTUBES</b>]]> Via photoreductive deposition process, platinum-modified TiO2 photocatalysts (Pt/TiO2) with various Pt contents are prepared by using H2PtCl6 and hydrogen titanate nanotubes as precursors. The structures and photocatalytic performances of Pt/TiO2 obtained are characterized. The experimental results indicate that platinum has obvious influence on the structure and photocatalytic performances of the hydrogen titanate nanotubes. The tubular structures of some nanotubes are destroyed during the photoreductive deposition process. It is possible that the hydrogen coming from splitting water over formed Pt/TiO2 results in the breach of nanotubes. The existence of platinum can enhance the photocatalytic performance of titanate nanotubes, and the photocatalytic activity arrives at the highest when the Pt content is 1.5 wt.%. <![CDATA[<b>COMPARATIVE STUDIES OF LEWIS ACIDITY OF ALKYL-TIN CHLORIDES IN MULTICOMPONENT BIGINELLI CONDENSATION USING GRINDSTONE CHEMISTRY TECHNIQUE</b>]]> A simple and efficient procedure for the one pot Biginelli Condensation Reaction of aldehydes, â-ketoester and urea employing SnCl4.5H2O /mono/di/tri-butyl- tin chloride as a novel catalyst is described. Compared to classical Biginelli reaction conditions, the present method has the advantages of good yields, short reaction times and experimental simplicity. Further, comparative efficiency of alkyl- tin chlorides in multicomponent Biginelli Condensation Reaction is also studied under solvent free conditions. <![CDATA[<b>STABILITY - INDICATING LC METHOD FOR THE SIMULTANEOUS DETERMINATION OF TELMISARTAN AND HYDROCHLOROTHIAZIDE IN DOSAGE FORM</b>]]> A simple, rapid, and precise method is developed for the quantitative simultaneous estimation of telmisartan and hydrochlorothiazide in combined pharmaceutical dosage form. A chromatographic separation of the two drugs was achieved with an ACE 5 C18 (250 x 4.6 mm) analytical column using buffer-acetonitrile (55:45 v/v). The buffer used in mobile phase contains 0.1M sodium perchlorate monohydrate in double distilled water pH adjusted 3.0 with trifluoroacetic acid. The instrumental settings are flow rate of 1.5 ml min-1, column temperature at 30ºC, and detector wavelength of 215 nm using a photodiode array detector. The resolution between hydrochlorothiazide and telmisartan founds to be more than 5. Theoretical plates for hydrochlorothiazide and telmisartan were 13022 and 6629 respectively. Tailing factor for hydrochlorothiazide and telmisartan was 0.94 and 0.98 respectively. Telmisartan, hydrochlorothiazide and their combination drug products stressed samples were analysed by the proposed method. The described method shows excellent linearity over a range of 70 to 130% of target analyte concentration. The correlation coefficient for telmisartan and hydrochlorothiazide are 0.9999. The relative standard deviation for six measurements in two sets of each drug in tablets is always less than 2%. The proposed method was found to be suitable and accurate for quantitative determination and stability study of telmisartan and hydrochlorothiazide in pharmaceutical preparations. <![CDATA[<b>THEORETICAL STUDY OF THE ADSORPTION OF OXYGEN ON SMALL BIMETALLIC K Cu (m, n ≤ 4 ANDm, n=1, 12) CLUSTERS</b>]]> A theoretical study of the adsorption of molecular oxygen on small bimetallic KmCu n (m, n ≤ 4 and m, n=1,12) clusters was carried out using density functional methods, and compared with the adsorption of O2 on bimetallic Li mCu n (m, n ≤ 4) clusters. The study of the O2-KmCu n system is important to understand the promotion effects of the alkali atoms on the copper surface participating in the catalytic processes. Adsorption energies ranging from 5.7 to 48.6 kcal/mol were found, which represented values slightly smaller than those calculated for the adsorption of O2 on Li mCu n clusters in a previous study. However, the global reactivity towards O2 was higher in KmCu n than in Li mCu n clusters. <![CDATA[<b>4,4'-(DIPHENYLMETHANE-4,4'-DIYLDINITRILO)DIPENTAN-2-ONE AND 4,4'-(DIPHENYLETHER-4,4'-DIYLDINITRILO)DIPENTAN-2-ONE LIGANDS AND THEIR Ni(II), Cu(II) COMPLEXES</b>: <b>SYNTHESIS,</b> <b>CHARACTERIZATION, DNA CLEAVAGE STUDIES</b>]]> The synthesis of two new ligands 4,4'-(diphenylmethane-4,4'-diyldinitrilo)dipentan-2-one (H2L¹) and 4,4'-(diphenylether-4,4'-diyldinitrilo)dipentan-2-one (H2L²) is reported. The ligands have two acetylacetone subunits separated by diphenylmethane or diphenylether group. The ligands form stable dinuclear complexes with Ni(II) and Cu(II) ions. Ligands and their complexes were characterized by elemental analysis, m.p., IR, molar conductivity and magnetic moment measurements. The interaction between these compounds with DNA has also been investigated by agarose gel electrophoresis, we found that the nickel(II) and copper(II) complexes can cleave supercoiled pBR322 DNA to nicked and linear forms. The copper(II) complexes with H2O2 as a cooxidant exhibited the strongest cleaving activity. The free ligands were also characterized by ¹H NMR spectra. The IR of the free ligands and their complexes are compared and discussed. The extraction ability of the ligands have been examined by the liquid-liquid extraction of selected transition metal [Mn²+, Co²+, Ni²+, Cu²+, Zn²+, Cd²+, Hg²+ and Pb²+] cations. The ligands show strong binding ability toward mercury(II) ion. <![CDATA[<b>SIMULTANEOUS DETERMINATION OF PROPRANOLOL HYDROCHLORIDE AND FLUNARIZINE DIHYDROCHLORIDE IN BULK AND CAPSULE USING REVERSED - PHASE HIGH -PERFORMANCE THIN</b> <b>LAYER CHROMATOGRAPHY / DENSITOMETRY</b>]]> A simple, rapid and sensitive RP- HPTLC method has been established for the determination of Propranolol hydrochloride (PRH) and Flunarizine Dihydrochloride (FNZ) in bulk and capsule formulation. Separation of both these drugs were achieved on aluminum backed silica gel 60 RP-18 F254S HPTLC plates, prewashed with methanol using methanol: toluene: ammonia (7:3:0.5 v/v) as mobile phase. Densitometric scanning was performed at 267 nm. The Rf values for PRH and FNZ were found to be 0.63 and 0.48, respectively. The amount of PRH and FNZ estimated in capsule formulation were found to be 99.20 ± 1.04 and 98.89 ± 1.23, respectively. The accuracy of the method was found to be in the range of 99.30 - 100.41% for PRH and 99.56 -100.87 for FNZ. The method was validated as per ICH guidelines and can regularly used for analysis of PRH and FNZ in capsule dosage form. <![CDATA[<b>SYNTHESIS OF 4-THIAZOLIDINE DERIVATIVES OF 6-NITROINDAZOLE</b>: <b>PHARMACEUTICAL IMPORTANCE</b>]]> New series of N-[3-(1H-6-nitroindazol-1-yl)-propyl]-2-(substituted phenyl)-4-oxo-5-(substituted benzylidene)-1,3-thiazolidine-carboxamide, compounds 5(a-j) have been synthesized from 6-nitroindazole. Structures of all the synthesized compounds were confirmed by chemical and spectral analyses such as IR, ¹H NMR, 13C NMR and FAB-Mass. All the synthesized compounds were screened for their antibacterial, antifungal, antitubercular and antiinflammatory activities. <![CDATA[<b>SYNTHESIS AND ANTIMICROBIAL ACTIVITIES OF BENZOTHIOPHENE DERIVATIVES</b>]]> 3-Chlorobenzothiophene-2-carbonyl chloride 1 was reacted with 4-aminoacetophenone in acetone to give compound 2. In order to prepare chalcones 3a-d, compound 2 was condensed with various aldehydes in the presence of KOH in DMF. These chalcones 3a-d on cyclization with urea, thiourea, hydroxylamine hydrochloride, phenyl hydrazines and hydrazine hydrate gave the corresponding oxapyrimidines 4a-d, isoxazolines 5a-d, pyrazoles 6a-h, pyrazolines 7a-d and thiopyrimidines 8a-d, respectively. The structures of all the synthesized compounds were confirmed by spectral data and had been screened for antibacterial activity. <![CDATA[<b>EFFECT OF PREPARATION METHODS OF CeO<sub>2</sub>-MnO<sub>x</sub> MIXED OXIDES ON PREFERENTIAL OXIDATION OF</b> <b>CO IN H<sub>2</sub>-RICH GASES OVER CuO-BASED CATALYSTS</b>]]> The CeO2-MnOx mixed oxides were prepared by deposition-precipitation (DP) and surfactant-templated (CB) methods, and then used as the support of CuO/ CeO2-MnOx catalysts. The samples were characterized by means of XRD, BET, H2-TPR, CO-TPD and XPS. Results show that preparation methods of CeO2-MnOx support have a direct effect on the physicochemical properties and catalytic activities of CuO/CeO2-MnOx catalysts for the CO preferential oxidation in H2-rich gases(CO PROX). CuO/CeO2-MnOx (CB) catalyst exhibits higher CO conversion and stability in H2-rich gases than CuO/CeO2-MnOx (DP), with 100% conversion of CO at 140 °C after a temperature cycle, which indicates that CeO2-MnOx (CB) as support of CuO based catalyst is more useful for CO PROX reaction than CeO2-MnOx (DP). Compared with CuO/CeO2-MnOx (DP), there are richer oxygen vacancies and more Mn4+ species on the surface of CuO/CeO2-MnOx (CB), and stronger interaction between CeO2 and MnOx in it. More amounts of active copper species and complicated transfer of electrons density on CuO/CeO2-MnOx (CB) also favour the activity of the catalyst. <![CDATA[<b>EVALUATION OF PROTONATION CONSTANTS OF MERCAPTOSUCCINIC ACID IN AQUEOUS SOLUTIONS</b> <b>OF PROPYLENE GLYCOL AND DIOXAN</b>]]> The protonation constants values of mercaptosuccinic acid were determined in propylene glycol- and dioxan-water mixtures (0-60% v/v) at 303.0 K at an ionic strength of 0.16 M using pH-metric technique. The protonation constants were calculated with the computer program MINIQUAD75 and selection of the best fit chemical models was based on the statistical parameters. The log K values were found to increase with increase of the organic solvent content. The linear variations of the protonation constants with the reciprocal of the dielectric constant of the medium have been attributed to the dominance of electrostatic forces. Distribution of species, protonation equilibria and effect of influential parameters on the protonation constants have also been presented. <![CDATA[<b>ISOTHERMAL AND THERMODYNAMICAL MODELING OF CHROMIUM (III) ADSORPTION BY COMPOSITES OF POLYANILINE WITH RICE HUSK AND SAW DUST</b>]]> The adsorption of Cr (III) from water by polyaniline composites with rice husk and saw dust of Eucalyptus camaldulensis has been investigated in this study. The surface of adsorbents was characterized by FT-IR. Effect of various operational conditions like agitation time, initial pH, adsorbent dose, particle size of composites and temperature were studied in batch mode. The suitability of the data was confirmed by Langmuir and Freundlich isotherms. Thermodynamic studies showed that adsorption of Cr (III) on these composites occur spontaneously. Rice husk and saw dust modified the morphology of polyaniline by preventing its aggregation and improving its adsorption capacity. <![CDATA[<b>FE DE ERRATAS</b>]]> The adsorption of Cr (III) from water by polyaniline composites with rice husk and saw dust of Eucalyptus camaldulensis has been investigated in this study. The surface of adsorbents was characterized by FT-IR. Effect of various operational conditions like agitation time, initial pH, adsorbent dose, particle size of composites and temperature were studied in batch mode. The suitability of the data was confirmed by Langmuir and Freundlich isotherms. Thermodynamic studies showed that adsorption of Cr (III) on these composites occur spontaneously. Rice husk and saw dust modified the morphology of polyaniline by preventing its aggregation and improving its adsorption capacity.