Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 56 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>REACTIVITY STUDIES OF MALEIMIDE EPOXY RESIN WITH LONG CHAINED AMINES</b>]]> After phenylmaleimido group was successfully incorporated into bisphenol-A type epoxy resins (B-13 ) to result in compound possessing both oxirane ring and maleimide reactive groups. The cured maleimide epoxy samples are obtained by thermally curing of the maleimide epoxy (MIE) compounds with aliphatic long chained amines such as Tetraethylenepentamine (TEPA), Bishexamethylenetriamine (BHMT), 2-methyl pentamethylenediamine (2-MPMDA) and 2,2,4-trimethy diamines (2,2,4-TMDA) exhibited excellent thermal stability and good chemical (acid/alkali/solvent) and water absorption resistance. Morphological studies by the SEM technique further confirmed the phase homogeneity net work of the cured systems. <![CDATA[CHARACTERIZATION OF HYDRATED TITANIUM OXIDE WITH SHEET-LIKE AND TUBE-LIKE STRUCTURES PREPARED BY A HYDROTHERMAL PROCESSING]]> Hydrated titanium oxides structures have been synthesized successfully from rutile by a single-step hydrothermal process at 130 0C in NaOH at concentrations of 5 M and 10 M, monitoring up to two days. Field emission scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) images indicate that samples treated at 5M were composed of sheet-like structures, while nanotubes were mainly found at 10 M. XRD analysis for both concentrations indicated presence of two phases, hydrated titanium oxide not indexed yet and rutile. Besides, X-ray diffraction (XRD) patterns of the samples treated at 10 M exhibited high reflections from the nanostructures, i.e., they possess high crystallinity. Thermogravimetry Analysis (TGA) indicated that the nanostructures show crystallized water in their matrix, specifically it was found that this hydrated phase has half molecule of occluded water per unit cell. This result is consistent with Raman spectroscopy that corroborates the existence of crystallization water in the synthesized product, by a deep profile of hydrated titanium oxide. <![CDATA[<b>SIMULTANEOUS DETERMINATION OF ENALAPRIL AND STATIN'S IN PHARMACEUTICAL FORMULATIONS BY RP-HPLC</b>]]> Simple, specific, economical and precise high performance liquid chromatographic method for the simultaneous determination of enalapril in presence of statins (rosuvastatin, atorvastatin and simvastatin) in API (active pharmaceutical ingredient) and formulation has been developed and validated. Chromatography was carried out at 25"C on a prepacked Purospher Star, C18 (5 mm, 250 x 4.6 mm) column with the isocratic mobile phase of acetonitrile: water (60:40 v/v) adjusting pH to 2.8. The UV detection was carried at 230 nm. The results obtained showed good agreement with the declared contents. Enalapril and statins separated in less than 10 mins with good resolution and minimal tailing and without interference of excepients. The method was linear in the range of 2.5-100 μgmL-1 for enalapril concentration with a correlation co-efficient 0.9995 and in the range 0.625-25 μgmL-1 for statins concentrations having correlation coefficient 0.9990 (inter and intraday CV<2 .0%). The recovery was 99-102%. The method was validated according to ICH guidelines and the acceptance criteria for accuracy, precision, linearity, specificity and system suitability were met in all cases. The proposed method can be used for quantitative determination of enalapril and statins alone or in combination from API and formulations. <![CDATA[<b>DETERMINATION OF 10 - HYDROXY - 2 - DECENOIC ACID IN ROYAL JELLY BY</b> <b>CAPILLARY ELECTROPHORESIS</b>]]> Two commercial samples of Royal Jelly sold in Chile, consisting of two imported sample and another sample of known origin obtained freshly harvested from beekeepers were analyzed. The application of capillary electrophoresis (CE) for the separation and determination of the active compound, 10 hydroxy -2 -decenoic acid, in Royal Jelly (RJ) in a capillary column with UV detection at 214 nm is described. In addition, the physicochemical composition of commercial samples was analyzed by determining moisture, ash, lipid and other properties. The importance of determining the 10-HDA acid lies in the fact that it is the main difference between Royal Jelly and the other bee products, i.e., it is what confers this product its unique characteristics, generating a marked difference. Therefore, a low 10-HDA content implies a low Royal Jelly activity, ascribed to decomposition, poor quality, or something else to the commercialization of a product other than Royal Jelly. This determination was conducted by comparison with a pure 10-HDA standard. <![CDATA[<b>CHEMICAL STABILITY OF PREDNISONE ORAL SUSPENSION AND DRUG SUBSTANCE</b>]]> An accelerated chemical stability study of Prednisone oral suspension has been performed during 6 months. A stability indicating chromatographic method was developed and validated according to the ICH guidelines by reversed phase using a Chromolith® C-18e monolithic column 4.6 x 100 mm, water:tetrahydrofuran:methanol 73:23:4 v/v/v as mobile phase, UV detection at 243 nm and 1 mL/min flow rate. Prednisolone was used as internal standard. Prednisone drug substance was subjected to forced degradation by acid and basic hydrolysis and oxidation condition, UV-Vis radiation effect, temperature and relative humidity were studied to demonstrate the indicating capability of the chromatographic method. Two and five degradation products were detected at acid and basic forced degradation respectively. No degradation products were detected at the others studied conditions. One degradation product from Prednisone oral suspension was detected during the accelerated chemical stability study. The proposed method was adequate to determine Prednisone drug substance, Prednisone oral suspension and their degradation products. The kinetic parameters of Prednisone oral suspension under the studied conditions are also reported. <![CDATA[<b>SUPPORT VECTOR MACHINE REGRESSION FOR REACTIVITY PARAMETERS OF VINYL MONOMERS</b>]]> Recently, the support vector machine (SVM), as a novel type of learning machine, has been introduced to solve chemical problems. In this study, å- support vector regression (å-SVR) and v-support vector regression (v-SVR) were, respectively, used to construct quantitative structure-property relationship (QSPR) models of Q and e parameters in the Q-e scheme, which is remarkably useful in the interpretation of the reactivity of a monomer in free-radical copolymerizations. The quantum chemical descriptors used to developed the SVR models were calculated from styrene and radicals with structures CH3CH2C¹H2-C²HR³· (C¹H2=C²HR³ + CH3CH2· - CH3CH2C¹H2-C²HR³·). The optimum å-SVR model of lnQ (C= 9, å =0.05 and ã =0.2) and the optimum v-SVR model of e (C=100, v = 0.5 and ã =0.4) produced low root mean square (rms) errors for prediction sets: 0.318 and 0.266, respectively. Thus, applying SVR to predict parameters Q and e is successful. <![CDATA[<b>MICROW AVE-ASSISTED SYNTHESIS OF LOW-SILICA/ALUMINA-RATIO ZEOLITES FROM</b> <b>GEOTHERMAL SILICA</b>]]> Zeolites A, X, hydroxysodalite and Iiydroxycancrinite (ZA, ZX, ZS, and ZC, respectively) were obtained using geothermal silica (GS) as a raw material and microwaves (MW) as an energy source. GS is an industrial byproduct from the Cerro Prieto geothermal plant in Baja California, México. It is a potential raw material for zeolite manufacturing because of its chemical composition and its high reactivity given by its small particle size. First, GS was treated with NaOH to generate zeolite precursors; the resulting products were crystallized by MW using sodium alumínate to adjust the SiO2/Al2O3 ratio in the reaction mixture. An experimental design based on an orthogonal array was employed to study the effects of the main factors involved in the zeolitization process of GS. The obtained yields of zeolites ZC, ZA and ZS were 95, 97, and 76.6% respectively. These zeolites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF), and their calcium binding capacity (CBC) was determined. The obtained results were similar to those of commercial zeolites. <![CDATA[<b>CHEMICAL CONSTITUENTS FROM ALGERIAN FOENICULUM VULGARE AERIAL PARTS AND</b> <b>EVALUATION OF ANTIMICROBIAL ACTIVITY</b>]]> Phytochemical study of the aerial parts of Foeniculum vulgare led to the isolation of seven compounds isolated for the first time from this species. After isolation and purification, these metabolites were characterized on the basis of spectroscopic analyses using 1D and 2D NMR as well as mass spectrometry. Furthermore, antimicrobial activity of the crude extract was evaluated using agar diffusion method. The antimicrobial test results showed that the crude extract had a great potential as antimicrobial activity against all 9 microorganisms especially fungal strains. <![CDATA[USE OF THE ORAC-PYROGALLOL RED/ORAC-FLUORESCEIN RATIO TO ASSESS THE QUALITY OF <b>ANTIOXIDANTS IN CHILEAN WINES</b>]]> We have recently proposed that ORAC (Oxygen Radical Absorbance Capacity) methods employing fluorescein (ORAC-FL) and pyrogallol red (ORAC-PGR) as target molecules could be considered as complementary indexes. In particular, the ratio ORAC-PGR/ORAC-FL would reflect the average quality of the antioxidants present in a particular sample. In the present work, we evaluated the antioxidant capacity and the total phenol content of twelve Chilean wines (red, rose, and white) employing ORAC and Folin-Ciocalteau methods, respectively. Red wines showed higher Folin and ORAC values than rose and white wines. However, the ORAC-PGR/ORAC-FL ratio of all tested wines was close to 0.5. The results show that it is important to consider both, the phenol content of the sample (measured by ORAC-FL or Folin indexes) and their average reactivity (measured by the ORAC-PGR/ORAC-FL ratio). Both factors are considered relevant in the evaluation of the antioxidant capacity of wines. <![CDATA[<b>CHEMICAL DEFENSE RESPONSES IN <i>Eucalyptus globulus</i> (Labill) PLANTS</b>]]> This study evaluated the expression of defense compounds by the secondary metabolism of Eucalyptus globulus plants subjected to attacks by the insect Ctenarytaina eucalypti (blue gum psyllid) and abiotic mechanical damage using gas chromatography with flame ionization detection (GC-FID) and mass detection (MS). The results show that both biological and mechanical attacks activated defense responses in the plants. We identified 34 compounds in the leaves of the treated plants. In the case of the plants damaged by C. eucalypti, four of the compounds differed from those of the control: three oxygenated monoterpenes (borneol, exo-2-hydroxy cineole and thymol) and one quinone (6-acethyl-flaviolin). In the case of the mechanical damage, five compounds differed from the control: three sesquiterpenes (alloaromadendrene, eremophilene, and caryophyllene-oxide), borneol, and 6-acethyl-flaviolin. According to the results, different compounds are biosynthesized when faced with biotic and abiotic inductions, indicating a certain level of specificity in the response of the plants to different types of damage. <![CDATA[<b>SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL EVALUATION OF TRIAZOLE AND FUSED TRIAZOLE DERIVATIVES</b>]]> Triazole and fused heterocyclic triazole derivatives like Schiff bases, thiadiazoles, thiadiazepine, thiadiazine etc. were synthesized and characterized by IR, MS and ¹H NMR. The triazole derivatives were evaluated for their antibacterial activity against the gram-positive bacteria B. megaterium and S. aureus, the gram-negative bacteria E. aerogenes and P. Aeruginosa using DMSO as a solvent. <![CDATA[<b>PARTIAL LEAST SQUARES FOR SIMULTANEOUS DETERMINATION OF FE (III) AND HG(II) IN WATER AND PHARMACEUTICAL PREPARATIONS BY RP-HPLC USING 1,4-BIS-(4-PYRIDIL)-2,3-DIAZO-1,3-BUTADIENE CHELATING AGENT</b>]]> A method has been developed for simultaneous determination of Fe(III) and Hg(II) by RP-HPLC, utilizing partial least squares technique. Vertex C18, with UV-visible detector was applied in reversed phase high performance liquid chromatography, while 1,4-bis-(4-Pyridil)-2,3-diazo-1,3-butadiene (4-bpdb) was added to the mobile phase as the chelating agent. Several effective parameters e.g. mobile phase make up, buffers, concentration of 4-bpdp and pH salts were investigated in order to optimize the quantification conditions. The optimum condition was achieved at 25°C, 10% methanol containing mobile phase, 30 mmol L¹ acetate buffer, 0.05 mmol L¹ 4-bpdb and pH=4.5. Partial least squares chemometric technique was applied. The root mean square error (RMSE) of independent test set in the optimized model was 0.024 and 0.393 for Fe(III) and Hg(II) respectively. <![CDATA[<b>SYNTHESIS AND ANTITUBERCULAR ACTIVITY OF PYRIDAZINONE DERIVATIVES</b>]]> Two series of pyridazinone derivatives (19-34) were synthesized and evaluated for antitubercular activities against Mycobacterium tuberculosis H37Rv strain. The results illustrated that among the synthesized compounds, compound 25, 5-(4-hydroxy-3-methoxybenzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone emerged as a lead compound with good antitubercular activity. Four more compounds, (21, 22, 29 & 33) were significant in their antitubercular action. <![CDATA[<b>PHOTOELECTROCHEMICAL REDUCTION OF NITRATE IONS ON POROUS SILICON AND DIFFERENT SILICON MODIFIED ELECTRODES</b>]]> We examined the reduction reaction of nitrate ions on different electrode systems: silicon monocrystalline («-type and p-type), porous silicon, and silicon modified by electrodeposited metallic rhenium. In a first stage, voltammetric analysis in different HF media was performed. With this technique it was possible to establish the different processes associated to porous silicon formation. The morphology of the porous silicon was studied using AFM. Voltammetric analysis was then performed using different silicon substrates. This was then used to study the electrochemical reduction reaction of nitrate ions. A decrease in the overpotential of the reaction was observed, with a consequent increase in current density when the silicon electrodes were modified by electrodeposited rhenium. Finally, an analysis of the reaction products from the nitrate electroreduction was carried out using photoelectrolysis at controlled potential. <![CDATA[X-RAY STUDIES AND ANTIBACTERIAL ACTIVITY IN COPPER AND COBALT COMPLEXES WITH IMIDAZOLE DERIVATIVE LIGANDS]]> The complexes Diaqua-bis(5-nitroimidazole)-copper(II)-dinitrate (1); Tetrakis(4- phenylimidazole)-copper(II)-dinitrate, ethanol solvate (2); Bis(4-phenylimidazole)-bis(acetate)-copper(II) (3); Hexakis(4-phenylimidazole)-cobalt(II)-acetate (4) and Bis(2- phenylimidazole)-bis(acetate)-cobalt(II) (5), have been synthesized. Their structures were determined by X-ray analysis. The antimicrobial activities of these complexes have been screened in vitro against the microorganisms Escherichia coli, Klebsiella pneumoniae, Shigella flexneri, Salmonella typhi, Salmonella enteritidis, Salmonella entérica, Staphylococcus aureus, Listeria monocytogenes. Complexes (1) and (3) showed antimicrobial activity over Gram positive and negative bacteria by a bacteriostatic effect. On the other hand, complexes (4) and (5) showed antibacterial activity with a bacteriolytic effect over Gram positive and negative bacteria. The cytotoxicity of complexes (3) and (4) was tested in vitro. These complexes presented cytotoxic effect to values near the MIC. <![CDATA[LIQUID-PHASE HYDROGENATION OF m-DINITROBENZENE OVER PLATINUM CATALYSTS]]> The m-dinitrobenzene hydrogenation to m-phenylenediamine in liquid phase was studied with platinum supported on SiO2, TiO2, Al2O3 and Nb2O5 catalysts. Incipient impregnation method was used to prepare the catalysts with 1wt% of Pt. The effect of the support and the reduction temperature (473 K or 773 K) were analyzed. The materials were characterized by X-ray diffraction (XRD), nitrogen physisorption (77 K), hydrogen chemisorption (298 K), transmission electron microscopy (TEM), temperature programmed reduction (H2-TPR) and temperature programmed desorption of ammonia (NH3-TPD). The results showed that Pt/ TiO2 (HT) catalyst had a higher yield (60%) toward m- phenylenediamine and conversion level (98.2%) of m-dinitrobenzene. This behavior can be attributed to the reduction of PtO crystallites to metallic Pt, small particle size and the strong metal-support interaction due to the migration of TiO species on the Pt crystallites. <![CDATA[<b>DEVELOPMENT AND VALIDATION OF A SOLID-PHASE EXTRACTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY METHOD FOR THE SIMULTANEOUS QUANTIFICATION OF OPIOID DRUGS IN HUMAN WHOLE BLOOD AND PLASMA</b>]]> A rapid, selective, sensitive, and specific method is presented to simultaneously quantify morphine, 6-monoacetylmorphine (6-MAM), codeine, heroin, fentanyl, and methadone in human whole blood and plasma. The drugs were extracted with phosphate buffer at pH 6, followed by solid-phase extraction (SPE) and quantification by GC/MS with electron impact ionization using helium as carrier gas. Quantification was performed based on nalorphine as internal standard (IS). The specificity, linearity, intra- and inter-assay precision and accuracy, and extraction recovery were fully evaluated. The limits of detection (LODs) were 0.40 - 7.63 ng/mL for whole blood and 0.80 - 32.00 ng/mL for plasma. The method is fast, simple, and accurate, with the sensitivity and specificity required in forensic and clinical toxicology. <![CDATA[SCREEN-PRINTED ELECTRODE MODIFIED WITH SILVER HEXACY ANOFERRATE-NAFION® FOR ASCORBIC ACID DETERMINATION]]> A flow injection system using a new and/or re-used graphite screen-printed electrode modified with silver hexacyanoferrate and a Nafion® polymer layer (AgHCF/GSPE) was employed for the determination of ascorbic acid in orange juice and drugs samples. Both modified electrodes showed an initial sensitivity of 0.015 A.cm²־.M¹־, with a linear response over the range from 50 to 300 mg L¹ , relative standard deviations smaller than 2%, detection and quantification limits of c.a. 5.0 and 25.0 mg.L¹. The response of the electrodes was stable, with no variation of base line after 6-8 hours of continuous operation. With this system it is possible to measure 65-70 samples (20μΚ) per hour. By using 1.06 mg of AgNO3, 4.12 mg of K3Fe(CN)6, 50.5 mg of KNO3 and 800μL of HNO3, it is possible to obtain between 25 and 30 modified electrodes. The proposed system showed to be inexpensive, versatile, robust and suitable for industrial application. The surface morphology of the bare and/or modified graphite screen-printed electrode was characterized by scanning electron microscopy. <![CDATA[PRENYLLIPIDS AND PIGMENTS CONTENT IN SELECTED ANTARCTIC LICHENS AND MOSSES]]> The content and relative composition of tocopherols, plastochromanol, plastoquinone and pigments in fifteen Antarctic species (five mosses and ten lichens) were analyzed by HPLC. Total tocopherols in mosses ranged from 90 mg/g (Warnstrofia sarmentosa) to 220 mg/g (Syntrichia magellanica), while in lichens it ranged from 0.89 mg/g in Caloplaca sp. to 45 mg/g in Placopsis contortuplicata. With the exception of Ochrolechia frigida, in all other mosses and lichens species, a-tocopherol accounted for more than 90% of total tocopherols. Plastochromanol was detected in four mosses and two lichen species; the highest level was found in Polytrichastrum alpinum (19.1 mg/g). The highest content of plastoquinone-9 (PQ-9) in mosses was found in Bryum pseudotriquetrum (42.6 mg/g), whereas in lichens it was 24.5 mg/g in Stereocaulon alpinum, and 23.17 mg/g in Umbilicaria antarctica. Pigment composition in mosses was typical for higher plants. Some lichen species lacked chlorophyll b, violaxanthin and β-carotene. Based on these results it is suggested that tocochromanols and carotenoid pigments are involved in the protection of mosses and lichens against the oxidative stress caused by the extreme Antarctic conditions. <![CDATA[<b>SYNTHESIS OF SOME NOVEL AND BIOLOGICALLY ACTIVE SCHIFF BASES BEARING A 1,3,4-THIADIAZOLE MOIETY UNDER ACIDIC AND PTC CONDITIONS</b>]]> The synthesis of some new Schiff bases bearing a 1,3,4-thiadiazole moiety, 3a-l, by reaction of 2-amino-5-mercapto-1,3,4-thiadiazole with aromatic aldehydes under acidic and phase transfer catalyst (PTC) conditions was studied. The structure of all the Schiff bases was characterized using FT-IR and NMR spectroscopy, and elemental analyses. The antibacterial activity of these compounds was investigated against Staphylococcus aureus (RTCC, 1885), and Escherichia coli (ATCC, 35922). <![CDATA[<b>SIMULTANEOUS ESTIMATION OF PIOGLITAZONE, GLIMEPIRIDE AND GLIMEPIRIDE IMPURITIES IN COMBINATION DRUG PRODUCT BY A VALIDATED STABILITY- INDICATING RP-HPLC METHOD</b>]]> A new, single, stability indicating RP-HPLC method has been developed and validated for the simultaneous estimation of pioglitazone, glimepiride and glimepiride impurities i.e., related compound B and related compound C from combination drug product containing pioglitazone, glimepiride and metformin HCl. The chromatographic separation was achieved on a cyano stationary phase (250 x 4.6mm, 5.0 microns particles) with simple mobile phase combination delivered in gradient mode at a flow rate of 0.8mL min¹ at 230nm. In the developed method, the critical close eluting compound of glimepiride related compound B and related compound C was found more than 6.5 resolutions. This method is capable to detect glimepiride related compound B and related compound C at a level below 0.005% with respect to glimepiride sample concentration of 0.1mg mL-1 for a 25 µL injection volume. The proposed method was validated according to the ICH guidelines and proved suitable for routine and stability analysis of these drugs in pharmaceutical preparations. <![CDATA[<b>η</b><b><sup>2</sup></b><b>-COORDINATION OF CHLOROBENZENES TO RHENIUM FRAGMENT Cp*Re(CO)<sub>2</sub></b>: <b>CHEMICAL AND PHOTOCHEMICAL SYNTHESES OF Cp*Re(CO)<sub>2</sub>(</b><b>η</b><b><sup>2</sup></b><b>-C<sub>6</sub>H<sub>6-n</sub>Cl<sub>n</sub>)</b>]]> The complexes Cp*Re(CO)2(η²-C6H6-nCl n), n = 4, (5,6-η²-1,2,3,4-C6H2Cl4) 2a; n = 3, (5,6-η²-1,2,4-C6H3Cl3) 2b; n = 2, (2,3-η²-1,4-C6H4Cl2) 2c and (4,5-ç²-1,3-C6H4Cl2) 2d, have been conveniently prepared by two alternative procedures: Directly, by the photochemical reaction of Cp*Re(CO)2(N2) in neat or saturated hexane solution of the corresponding partially chlorinated benzene or stepwise, by the reaction of the appropriate trans-Cp*Re(CO)2(ArCl)X, X = Cl, Br (1a-d) with LiBHEt3 followed by protonation with HCl to form the hydrido complexes trans-Cp*Re(CO)2(ArCl)H which resulted thermally unstable in solution and convert to η ²-coordination complexes 2a-d. Due to their low stability as solids and in solution, the new complexes were only characterized by IR and ¹H and 13C NMR spectroscopy. The ¹H NMR spectra of the two derivatives containing dichlorobenzene (2c and 2d) indicate that a rapid exchange occurs between the hydrogen atoms on the coordinated carbons and those on the non-coordinated carbons. <![CDATA[STRUCTURAL AND PHOTOPHYSICAL PROPERTIES OF A MONONUCLEAR Re(I) COMPLEX:[P,N-{(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>(C<sub>5</sub>H<sub>5</sub>N)P}Re(CO)3Br]]]> We have prepared a new monometallic rhenium(I) carbonyl, the complex [P,N-{(C6H5)2(C5H5N)P}Re(CO)3Br] by direct reaction of (Re(CO)3Br(THF))2 and the ligand (C6H5)2(C5H5N)P The structure in the complex shows the pyridinic-phosphine ligand in a chelating mode, occupying cis positions around the rhenium octahedral environment. The molecule displays an absorption band centered at 315 nm which has been assigned to a MLCT transition, and a luminescence quantum yield of 0.001.