Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 49 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[ANTIBACTERIAL ACTIVITY OF COMPOUNDS ISOLATED OF THE RESINOUS EXUDATE FROM HELIOTROPIUM SINUATUM ON PHYTOPATHOGENIC BACTERIA]]> From the resinous exudates of Heliotropium sinuatum have been isolated and characterized two compounds, pentaeicosanol 1 and 1-hydroxy-3-doeicosanone 2. Those structures and previously isolated pure compounds have been tested in their antibacterial activity on phytopathogenic bacteria. Ketone 2 and the flavonoid hesperetine 10 showed antibacterial activity on Erwinia carotovora subsp. carotovora, while the flavonoid 3-O-methylgalangine 4 showed activity on Clavibacter michiganensis subsp. michiganensis <![CDATA[INFLUENCE OF PARTICLE SIZE ON <SUP>31</SUP>P-NMR ANALYSIS OF EXTRACTS FROM VOLCANIC ASH-DERIVED SOILS IN CHILE]]> The phosphorus distribution in soil (<2 mm) and in clay size separates (<2 mu m) of two uncultivated volcanic soils from southern Chile (one Ultisol and one Andisol) was studied by phosphorus-31 nuclear magnetic resonance spectroscopy (31P-NMR). The total P content ranges of the Ultisol samples were 733-1108 mg kg-1 (soil) and 746-896 mg kg-1 (clay), lower than 2163-2216 mg kg-1 (soil) and 2683-3362 mg kg-1 (clay) obtained for Andisol samples. In both fractions the 31P-NMR spectra of a single alkaline extraction, using 0.25 M NaOH and Chelex 100, showed the presence of inorganic orthophosphate, monoester-P, diester-P and pyrophosphate. Phospholipids-teichoic acids P were observed, but only in the clay size separates of the Andisol. Important differences in spectra of soils and clay size separates were observed only in samples with high organic matter content. The clay size separates enriched with organic matter have more and better defined signals of organic P forms. This allows the identification of P forms that might not be detected by 31P-NMR in the whole soil extracts <![CDATA[DRIFTS STUDIES OF ACRYLONITRILE ADSORPTION ON Pd/SdO<SUB>2</SUB> AND PdSd/SdO<SUB>2</SUB>]]> The acrylonitrile adsorption over Pd/SiO2 and PdSn/SiO2 catalysts wasprepared by "Solvated Metal Atom Dispersion" (SMAD) and analyzed by DRIFTS FTIR are studied. The catalysts were used in pellets and treated with dry N2(g) flow inside a flask in contact with the acrylonitrile vapours for 6 h. A change in the adsorption capacity of acrylonitrile with the increase in Sn content in the catalysts by following the C<FONT FACE=Symbol>º</FONT> N IR band was studied. The decrease in the acrylonitrile adsorption produced a decrease in the hydrogenation rates of acrylonitrile and an increase in the hydrogenation selectivity to obtain allylamine, mainly due to a greater interaction of C<FONT FACE=Symbol>º</FONT> N with Sn <![CDATA[1-BENZYL-1,2,3,4-TETRAHYDROISOQUINOLINES: <SUP>1</SUP>H NMR CONFORMATIONAL STUDIES AND ROTATIONAL BARRIERS]]> The conformational preferences of a series of 1-benzyl-1,2,3,4-tetrahydroisoquinolines (norlaudanosine and coclaurine analogues) were investigated with the aid of their 1H NMR spectra and NOESY experiments, coupled with ab initio theoretical studies to estimate energy barriers among the various stable conformers of these systems. The secondary amines prefer an extended conformation, while the N-alkylated derivatives prefer a semi-folded one, with considerable freedom to exchange between both forms. A third, folded conformation, although not much higher in energy, is relatively inaccessible <![CDATA[TEMPLATE SYNTHESIS OF 2,11-DIMETHYL-3,12-DIETHYL / PROPYL / PHENYL-1,4,10,13-TETRAAZACYCLOOCTADECA-1,3,10,12-TETRAENE COMPLEXES OF Mg(II), Ca(II), Sr(II) AND Ba(II)]]> 2+2 Cyclocondensation of 1,5-diaminopentane with beta-diketones viz. 2,3-pentanedione, 2,3- hexanedione or 1-phenyl -1,2- propanedione in the presence of alkaline earth metal ions as templates yield a series of hexacoordinated complexes of the type [ML(X2)] ( where L=N4 macrocyle having 18-membered ring and X = Cl or NCS) The resulting complexes have been characterized by elemental analyses, conductance measurements, IR and ¹H NMR spectra <![CDATA[CONSTRUCTION OF A POLYMERIC LIQUID-MEMBRANE ION-SELECTIVE ELECTRODE (ISE)AND ITS APPLICATION FOR DETERMINATION OF NITRATE IN TOMATOES]]> A potentiometric all-solid-state type ion-selective electrode (ISE) for NO3- was constructed and characterized. It is based on a mixture of tetra-decyl-ammonium nitrate (TDAN) as ionophore, di-butyl phthalate (DBP) as plasticizer and poly (vinyl chloride) (PVC) as matrix. Nitrate concentrations in tomatoes samples, randomly collected from central market at Santiago de Cuba, were determined using the described ISE by standard addition potentiometry. Spectrophotometric determinations using Brucine were performed as comparative method. Accurate and precise results were obtained. Accordingly, an analytical procedure for NO3- determination in tomatoes using the constructed ISE could be formulated <![CDATA[ON THE REDUCTION OF 4-OXO-4H-BENZOPYRAN-3-CARBALDEHYDES: GLOBAL AND LOCAL ELECTROPHILICITY PATTERNS‡]]> The theoretical global and local electrophilicity patterns of substituted and chelated 4-oxo-4H-benzopyran-3-carbaldehydes (formylchromones) have been evaluated using the electrophilicity index proposed by Parr et al [J. Am. Chem. Soc. 1999, 121, 1922]. The complexation of formylchromones with aluminum predicts a strong electrophilic character of these compounds against nucleophiles. Local response at the active sites may also be assessed in terms of a global contribution described by the global electrophilicity, and a local contribution described by the variations in electrophilic Fukui function at those sites. The highest local electrophilicity is found at the formyl group of the chelated formylchromones, in spite of that, the highest positive charge is located on the pyrone carbonyl group. This result is consistent with the experimental observed reactivity displayed by 4-oxo-4H-benzopyran-3-carbaldehydes in the presence of 2-propanol and alumina <![CDATA[IR AND <SUP>13</SUP>C-NMR SPECTRAL PROPERTIES OF THE LAYERED INCLUSION COMPOUND BIS(THIOUREA)HEXAMETHYLENETETRAMINE]]> The structure of the 1: 2 adduct of hexamethylenetetramine and thiourea was reanalyzed reinterpreting X-ray diffraction data and providing additional IR and NMR spectroscopic features. The product is thus described as supramolecular commensurate host-guest complex corresponding to the intercalation of hexamethylenetetramine in a layered thiourea matrix. FT-IR spectra evidence a simultaneous strengthening of both C-N and C-S bonds, that appearing as a pattern characteristic for described layered thiourea matrix. 13CP MAS-NMR spectra of the intercalated hexamethylenetetramine is essentially determined by nuclear dipolar magnetic interactions and host-guest chemical interactions arising from 13C-14N residual dipolar interaction not averaged to zero by MAS-NMR and from the magnetic non-equivalence of the guest carbon atoms caused by the hydrogen bonding interaction with the thiourea matrix <![CDATA[Antibacterial and antifungal activity of some thiosemicarbazones and 1,3,4-thiadiazolines]]> A series of thiosemicarbazones and thiadiazolines was evaluated for biological activity against various microorganisms such as Bacillus subtilis, Micrococcus luteus, Listeria monocytogenes, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, Trichophyton mentagrophites and Aspergillus niger. Some of the assayed compounds showed interesting activity against Bacillus subtilis, Candida albicans, Micrococcus luteus, Trichophyton mentagrophites and Aspergillus niger <![CDATA[QUANTITATIVE REPRESENTATION OF REACTIVITY, SELECTIVITY AND SITE ACTIVATION CONCEPTS IN ORGANIC CHEMISTRY@]]> Reactivity, selectivity and site activation are classical concepts in chemistry which are amenable to quantitative representation, in terms of static global, local and non local density response functions. The use of these electronic indexes describing chemical interconversion is developed in this work along the perspective of the pioneering work conducted in Chile by the late Professor Fernando Zuloaga, to whom this article is dedicated in memoriam. While global responses, represented as derivatives of the electronic energy with respect to the total number of electrons quantitatively describe the propensity of a system to interconvert into another chemical species (chemical reactivity), the local counterparts assesses well those regions in the molecule where the reactivity pattern dictated by the global quantities is developed (selectivity). Site activation /deactivation may in turn be described by the variations in the local or regional patterns of reactivity, that may be induced by solvent effects or chemical substitution. These concepts are illustrated for a series of chemical reactions in Organic Chemistry, including electrocyclic processes, cycloadditions and electrophilic addition reactions. Some relationships between quantitative scales of reactivity and reaction mechanisms are discussed <![CDATA[KINETICS PROFILES IN THE REACTION OF ABTS DERIVED RADICALS WITH SIMPLE PHENOLS AND POLYPHENOLS]]> The kinetic profile associated to the reaction of phenols with 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) derived radicals is extremely dependent of the characteristics of the substrate. In particular, polyphenols present complex profiles that can be associated to successive reactions of different reactive centers present in the target molecule. Also, changes in the secondary reactions of the produced radicals can lead to a partial recovery of the ABTS radical concentration at intermediate reaction times, as observed employing 1,4-dihydroxybenzene. Although the kinetic profiles of monophenols are considerably simpler, the stoichiometry of the process is unexpected. For example, the data obtained imply that four radicals are consumed by each p-tertbutylphenol molecule introduced into the system. This large stoichiometric coefficient is not compatible with a simple, phenol promoted, back reduction of the ABTS radical. These results, as well as the overshoot observed employing 1,4-dihydroxybencene, cast doubts on the use of ABTS based methodologies to quantitatively measure the capacity of a given compound to trap free radicals or the amount of free radical scavengers present in complex mixtures <![CDATA[GROWTH AND ACCUMULATION OF TOTAL CAROTENOIDS IN TWO STRAINS OF <I>Dunaliella salina </I>Teod. (CHLOROPHYCEAE) FROM THE NORTHERN AND CENTRAL COAST OF PERÚ]]> In order to know the dynamics of growth and accumulation of total carotenoids in two strains of Dunaliella salina from the northern (Colán) and central (Chilca) coast of Perú, both strains were cultured during 40 days in controlled laboratory conditions, at 25±2°C, with 150 mol m-2 s-1, without aereation. The strains were grown in two culture media with two different salinities: a modified Johnson medium with addition of 15 and 23% NaCl and a Provasoli enriched seawater medium with 12.5 and 20% NaCl. A period of exponential growth during the first 5 days was observed in both strains, followed by a slow linear growth phase and a stationary phase which lasted until the end of the experiment (day 40). The maxima cellular densities were obtained in the modified Johnson medium at 15% NaCl in both strains, being higher in Chilca (2.2x10(6) cell mL-1) than in Colán (1.6x10(6) cell mL-1). The accumulation of total carotenoids per volume was similar in both strains but different in both media; the highest values were obtained in the Provasoli medium with 20% NaCl (13.3± 2.9 mg L-1, Colán and 10.6± 2.5 mg L-1, Chilca). On the contrary, the total content of carotenoids per cell was different in both strains and media; the highest values were obtained in the Provasoli medium with 20% NaCl (110.9± 0.7 and 58.7± 1.3 pg cell-1 in the strains Colán and Chilca, respectively) <![CDATA[Molecular Orbital Calculations of Hydrogen Bonding in Ammonia - Formic Acid System in the Presence of Electric Fields]]> The effects of electric fields on hydrogen bonding in ammonia - formic acid system, are examined with STO-3G and 6-31 G(d) wavefunctions. This system was used in a previous work to model hydrogen bonding in crystalline amino acids and the calculations were performed at HF / STO-3G level. The results on the relative position of the tautomeric equilibrium between the neutral and zwitterionic forms were explained in terms of the relative stabilization of the ionic partners as a function of their placement in positive and negative wells created by the external electric field. In order to rationalize those results at electronic structure level, in this paper we analyze the response of the molecular orbitals implicated in the hydrogen bridge, N··H··O, to various imposed external fields. It is found that the stabilization of the zwitterionic structure occurs due to the destabilization of the MO localized essentially at the nitrogen electron lone pair, n-orbital, and concomitant with the stabilization of the MO essentially localized at the functional oxygen electron lone pair, o-orbital. The stabilization of the neutral structure occurs in the opposite situation. In addition, these eigenvalues are shown to be adequate regional molecular descriptors of the base reactivity of amines and conjugated bases of carboxylic acids, in gas phase and in the presence of electric fields<hr/>Se estudian los efectos producidos por campos eléctricos sobre el enlace por hidrógeno en el sistema amoníaco - ácido fórmico, utilizando funciones de onda STO-3G y 6-31G(d). Este sistema fue utilizado en un trabajo previo, como modelo de aminoácidos en estado cristalino. Los resultados obtenidos acerca de la posición del equilibrio tautomérico entre las formas neutra y zwiteriónica, fueron explicados a través de la estabilización relativa de las formas iónicas en pozos positivos y negativos de potencial electrostático, creados por el campo externo. Con el propósito de racionalizar estos resultados, a nivel de estructura electrónica, en este artículo se analiza la respuesta de los orbitales moleculares implicados en el puente hidrógeno, N··H··O, frente a una serie de campos eléctricos aplicados al complejo molecular. Se encuentra que la estabilización del zwitterión se produce debido a la desestabilización del orbital molecular localizado esencialmente en el par electrónico libre del N, n-orbital, concomitante con la estabilización del orbital molecular localizado esencialmente en el par electrónico libre del oxígeno funcional, o-orbital. La estabilización de la forma neutra ocurre en la situación opuesta. Se muestra, además, que la energía de los orbitales moleculares mencionados, constituye un descriptor molecular adecuado para la reactividad ácido base de aminas y ácidos carboxílicos, en fase gaseosa y en la presencia de campos eléctricos <![CDATA[Tuning the Excited States in -fac--[Re(X2dppz)(CO)3(L)]: Intraligand, Charge Transfer or both?]]> Excited state lifetime measurements - emission, emission lifetime and Resonance Raman - have been conducted on the series -fac--[Re(X2dppz)(CO)3(L)]0,+ (L = Cl-, 4-ethylpyridine (4-Etpy), 4,4´-bipyridine (4,4´-bpy)), with the X2dppz substituted dipyrido[3,2-a:2',3'-c]phenazine ligands (X = CH3 and Cl). The results are consistent with closely lying excited states, with <FONT FACE=Symbol>pp</FONT>* lowest, but MLCT contributing significantly to excited state lifetimes for the neutral complexes. -fac--[Re(Cl2dppz)(CO)3Cl] appears to undergo a crossover from lowest <FONT FACE=Symbol>pp</FONT>* to lowest MLCT through the glass to fluid transition <![CDATA[CRYSTAL AND MOLECULAR STRUCTURE OF THE COMPLEX SALTS DIETHYLAMMONIUM AND MORPHOLINIUM OF 5-NITROPYRIDINE SULFONATE]]> The two title salts, (CH2-CH3)2NH2+ C5NH3NO2SO3- and C4H8ONH2+ C5NH3NO2SO3-, crystallize in space group P2(1)/n and P2(1)/a respectively, with one ion pair in the asymmetric unit. In both structures, conventional hydrogen bonds link anions and cations in chains running along directions [1 0 1] and [0 1 0] for the first and second salts respectively <![CDATA[DESIGN OF A QSRR: E INDEX WITH HIGH MOLECULAR INFORMATION CONTENT TO DIFFERENCIATE CIS AND TRANS ALQUENES]]> Using QSRR modelling, an E index was designed based on the H. P. Schultz MTI index. The E index is a molecular descriptor consisting of a vector and adjacent and distant matrices. Linear regressions were obtained by means of a QSRR - GLC study of a set of 11 cis and 11 trans alquenes characterized by the Ecis, Etrans indices. The correlation indices (r) were 0.97495 and 0.95767 respectively. It was demonstrated that in the linear regressions above, a smaller r was obtained, when the E index was replaced by the refractive molar index taken as reference (IRM). The discrimination E values for cis and trans alquenes were obtained by multiplying by (-1) the distance matrix diagonal elements, corresponding to the carbon atoms that support the π bonds in cis alquenes <![CDATA[AZA NITROGENS EFFECT ON THE ELECTRONIC PROPERTIES OF COBALT PORPHYRINE AND DERIVATIVES]]> A set of electronic properties calculated at the B3LYP/LACVP(d) level of theory for four cobalt macrocycles containing a ligand like porphyrin (CoP) and a benzoporphyrin (CoTBP) has been analyzed. The effect of aza nitrogen atoms (aza-N) present in the ligand (CoTAP, CoPc) on the electronic properties chosen has been studied. For the pair CoP/CoTAP we found a notorious effect of the presence of aza-N atoms in each electronic property studied. However, for the pair CoTBP/CoPc a different result was obtained. The dipole moment and the atomic charges, the latter evaluated on the cobalt atom and on the aza-N atoms, do not show the isolated effect of the aza nitrogen atoms and rather it appears to be mixed with the effect produced by the ligand size. On the contrary, electronic properties such as spin density and electrostatic potential evaluated on the cobalt atom clearly show the effect of the aza nitrogen atoms predicting that the latter present an electron withdrawing behavior in this kind of molecules