Antibacterial properties of 3 H-spiro[1-benzofuran-2,1'-cyclohexane] derivatives from Heliotropium filifolium

A re-examination of cuticular components of Heliotropium filifolium allowed the isolation of four new compounds: 3'-hydroxy-2',2',6'-trimethyl-3H-spiro[1-benzo-furan-2,1'-cyclohexane]-5-carboxylic acid(2), methyl 3'-acetyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (3), methyl 3'-isopentanoyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (4) and methyl 3'-benzoyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (5).Compounds 2-5 were identified by their spectroscopic analogies with filifolinol (1), and their structures confirmed by chemical correlation with 1. The antimicrobial properties of the compounds were tested against Gram positive and Gram negative bacteria. Some of them proved to be active against Gram positive, but inactive against Gram negative bacteria. In searching for structure-activity relationships from the obtained MIC values, lipophilicity was shown to be an important variable.     

Synthesis and characterization of CeO<Subscript>2</Subscript>–graphene composite

The synthesis and characterization of graphite oxide (GO), graphene (GS), and the composites: GS–CeO₂ and GO–CeO₂ are reported. This synthesis was carried out by mixing aqueous solutions of CeCl₃·7H₂O and GO, which yields the oxidized composite GO–CeO₂. GO–CeO₂ was hydrothermally reduced with ethylene glycol, at 120 °C, yielding the reduced composite GS–CeO₂. GO, GS ,and the composites with CeO₂ were characterized by CHN, TG/DTG, BET, XRD, SEM microscopy, FTIR, and Raman spectroscopy. The estimation of crystallite size of CeO₂ anchored on GO and on GS by Raman, XRD, and SEM agreed very well showing diameters about 5 nm. The role of particles of CeO₂ coating carbon sheets of GO and GS was discussed.     

Direct determination of vanadium in high saline produced waters from offshore petroleum exploration by electrothermal atomic absorption spectrometry

The present work reports the development of a methodology for the direct determination of vanadium in high saline waters derived from offshore petroleum exploration employing electrothermal atomic absorption spectrometry. Such waters, usually called produced waters, present complex composition containing various organic and inorganic substances. In order to attain best conditions (highest sensitivity besides lowest background) for the methodology, studies about the effects of several variables (evaluation of pyrolysis and atomization temperatures, type of chemical modifier, concentration of modifier and pyrolysis time) and the convenient calibration strategy were performed. Best conditions were reached with the addition of 10 μg of NH₄H₂PO₄ as chemical modifier employing pyrolysis (during 10 s) and atomization temperatures of 1500 and 2700 °C, respectively. Obtained results indicated that, in this kind of sample, vanadium can be determined by standard addition method or employing an external calibration approach with standard solutions prepared in 0.8 mol l⁻¹ NaCl medium. In order to evaluate possible matrix interferences, a recovery test was performed with five spiked samples of produced waters. The limit of detection, limit of quantification and relative standard deviation in 0.8 mol l⁻¹ NaCl medium were also calculated and the derived values were 1.9 μg l⁻¹, 6.3 μg l⁻¹ and 5.6% (at 10 μg l⁻¹ level), respectively.     

4,6-bis(supermesitylphosphanylidenemethyl)dibenzofuran. Synthesis, X-ray structure and reactivity towards group 11 metals

New kinetically stabilized mono- and bis-phosphaalkene ligands (2 and 3, respectively) were synthesized via the phospha-Wittig approach. Ligand 3 was characterized by X-ray diffraction. The coordinating behaviour of the bidentate ligand was investigated towards group 11 metal centers in order to test its capacity to bind two coordination sites located in a trans-fashion. The [Au(3)][BF4], [Ag(3)(H2O)][BF4] and [Cu(3)(CH3CN)][BF4] complexes 4 , 5 and 6, respectively, were characterized by X-ray diffraction. The peculiar geometries of 4 and 6 were rationalized by means of DFT calculations.     

Two new isoflavonoids from Bowdichia virgilioides

Two new isoflavonoids 7,8,4'-trimethoxyisoflavone and 7,8,4'-trimethoxyisoflavanone and calycosin (7,3'-hydroxy-4'-methoxyisoflavone) were isolated from the wood of the leguminous tree Bowdichia virgilioides by usual chromatographic procedures. Besides these compounds the pterocarpane (-)-maackianin, isoliquiritigenin (4,2',4'-trihydroxychalcone), and the hydrobenzylfurane derivative bowdenol were also obtained. The structures of these new compounds were determinated by MS and 1D and 2D NMR spectral analysis.     

pH at the micellar interface: synthesis of pH probes derived from salicylic acid, acid-base dissociation in sodium dodecyl sulfate micelles, and Poisson-Boltzmann simulation

The study of the H+ concentration at the micellar interface is a convenient system for modeling the distribution of H+ at interfaces. We have synthesized salicylic acid derivatives to analyze the proton dissociation of both the carboxylic and phenol groups of the probes, determining spectrophotometrically the apparent pK(a)'s (pK(ap)) in sodium dodecyl sulfate, SDS, micelles with and without added salt. The synthesized probes were 2-hydroxy-5-(2-trimethylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumhexanoyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumundecanoyl)benzoate; 2-hydroxy-5-acetylbenzoic acid; and 2-hydroxy-5-dodecanoylbenzoic acid. Upon incorporation into SDS micelles the pK(ap)'s of both carboxylic and phenol groups increased by ca. 3 pH units and NaCl addition caused a decrease in the probe-incorporated pK(ap). The experimental results were fitted with a cell model Poisson-Boltzmann (P-B) equation taking in consideration the effect of salt on the aggregation number of SDS and using the distance of the dissociating group as a parameter. The conformations of the probes were analyzed theoretically using two dielectric constants, e.g., 2 and 78. Both the P-B analysis and conformation calculations can be interpreted by assuming that the acid groups dissociate very close to, or at, the interface. Our results are consistent with the assumption that the intrinsic pK(a)'s of both carboxylic and phenol groups of the salicylic acid probes used here can be taken as those in water. Using this assumption the micellar and salt effects on the pK(ap)'s of the (trialkylammonium)benzoate probes were described accurately using a cell model P-B analysis.     

Water-in-Oil-in-Water Double Emulsions as Protective Carriers for Sambucus nigra L. Coloring Systems

The use of natural colorants is needed to overcome consumer concerns regarding synthetic food colorants′ safety. However, natural pigments have, in general, poor stability against environmental stresses such as temperature, ionic strength, moisture, light, and pH, among others. In this work, water-in-oil-in-water (W₁/O/W₂) emulsions were used as protective carriers to improve color stability of a hydrophilic Sambucus nigra L. extract against pH changes. The chemical system comprised water and corn oil as the aqueous and oil phases, respectively, and polyglycerol polyricinoleate (PGPR), Tween 80, and gum Arabic as stabilizers. The primary emulsion was prepared using a W₁/O ratio of 40/60 (v/v). For the secondary emulsion, W₁/O/W₂, different (W₁/O)/W₂ ratios were tested with the 50/50 (v/v) formulation presenting the best stability, being selected as the coloring system to test in food matrices of different pH: natural yogurt (pH 4.65), rice drink (pH 6.01), cow milk (pH 6.47), and soy drink (pH 7.92). Compared to the direct use of the extract, the double emulsion solution gave rise to higher color stability with pH change and storage time, as corroborated by visual and statistical analysis.     

Degradation of the insecticide parathion in methanol by gamma-irradiation

The gamma-radiation from⁶⁰Co was used to induce parathion degradation in methanol solution, and the resulting products were quantified by GC-NPD and identified by GC-MS. The insecticide was completely degraded (99%) in methanol after treatment with 30 kGy doses at a dose rate of 3.12 kGy h⁻¹. The metabolites detected after radiolysis were p-aminophenol, paraoxon and aminoparathion, but no p-nitrophenol. The parathion radiation yield (G-parathion) in methanol solution was also calculated.     

Kinetics of methylation of a solvatochromic vinylogous α‐pyridone in different solvents

The kinetics of the reaction with iodomethane of the solvatochromic dye 4‐[2‐(N‐methyl‐4,6‐diphenylpyridiniumyl)]phenoxide 2, generated in situ from the corresponding N‐methyl‐2,4‐diphenyl‐6‐(4‐hydroxyphenyl)pyridinium salt 4, was studied in various solvents and solvent mixtures, in search of a possible correlation between its reactivity and solvatochromism in solution. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 819–825, 1999     

Stereochemistry and some synthetic uses of the heteroarylation of phospholes

Further studies have been conducted on the condensation of electron-rich arenes or heteroarenes with the dienic system of phosphole P-complexes. According to the X-ray crystal structure analysis of one of the resulting 2-aryl-3-phospholene P-complexes, the condensation takes place on the side of the diene opposite to the complexing group. The decomplexation of the phospholene P–Mo(CO)₅ and P–W(CO)₅ complexes, respectively, by reaction with sulfur or halogens and tertiary amines yields the corresponding P-sulfides and oxides with full retention of the stereochemistry at phosphorus. Double condensation of the phosphole P-complexes onto the 2 and 5 positions of thiophene and furan ultimately leads to phosphole–thiophene–phosphole and phosphole–furan–phosphole chains. The first type has been characterized by X-ray crystal structure analysis of its P,P-disulfide. No electronic delocalization appears to take place along the chain.