Soybean biodiesel methyl esters, free glycerin and acid number quantification by 1H nuclear magnetic resonance spectroscopy.

Production of alternative fuels, such as biodiesel, from transesterification of vegetable oil driven by heterogeneous catalysts is a promising alternative to fossil diesel. However, achieving a successful substitution for a new renewable fuel depends on several quality parameters. (1)H NMR spectroscopy was used to determine the amount of methyl esters, free glycerin and acid number in the transesterification of soybean oil with methanol in the presence of hydrotalcite-type catalyst to produce biodiesel. Reaction parameters, such as temperature and time, were used to evaluate soybean oil methyl esters rate conversion. Temperatures of 100 to 180 °C and times of 20 to 240 min were tested on a 1 : 12 molar ratio soybean oil/methanol reaction. At 180 °C/240 min conditions, a rate of 94.5 wt% of methyl esters was obtained, where free glycerin and free fatty acids were not detected.

Characterization of amide bond conformers for a novel heterocyclic template of N-acylhydrazone derivatives.

Herein we describe NMR experiments and structural modifications of 4-methyl-2-phenylpyrimidine-N-acylhydrazone compounds (aryl-NAH) in order to discover if duplication of some signals in their ¹H- and ¹³C-NMR spectra was related to a mixture of imine double bond stereoisomers (E/Z) or CO-NH bond conformers (syn and anti-periplanar). NMR data from NOEdiff, 2D-NOESY and ¹H-NMR spectra at different temperatures, and also the synthesis of isopropylidene hydrazone revealed the nature of duplicated signals of a 4-methyl-2-phenylpyrimidine-N-acylhydrazone derivative as a mixture of two conformers in solution. Further we investigated the stereoelectronic influence of substituents at the ortho position on the pyrimidine ring with respect to the carbonyl group, as well as the electronic effects of pyrimidine by changing it to phenyl. The conformer equilibrium was attributed to the decoplanarization of the aromatic ring and carbonyl group (generated by an ortho-alkyl group) and/or the electron withdrawing character of the pyrimidine ring. Both effects increased the rotational barrier of the C-N amide bond, as verified by the DG(≠) values calculated from dynamic NMR. As far as we know, it is the first description of aryl-NAH compounds presenting two CO-NH bond- related conformations.

Post translational modifications of Trifolitoxin: a blue fluorescent peptide antibiotic.

Trifolitoxin (TFX, C41H63N15O15S) is a selective, ribosomally-synthesized, post-translationally modified, peptide antibiotic, produced by Rhizobium leguminosarum bv. trifolii T24. TFX specifically inhibits α-proteobacteria, including the plant symbiont Rhizobium spp., the plant pathogen Agrobacterium spp. and the animal pathogen Brucella abortus. TFX-producing strains prevent legume root nodulation by TFX-sensitive rhizobia. TFX has been isolated as a pair of geometric isomers, TFX1 and TFX2, which are derived from the biologically inactive primary amino acid sequence: Asp-Ile-Gly-Gly-Ser-Arg-Gln-Gly-Cys-Val-Ala. Gly-Cys is present as a thiazoline ring and the Arg-Gln-Gly sequence is extensively modified to a UV absorbing, blue fluorescent chromophore. The chromophore consists of a conjugated, 5-membered heterocyclic ring and side chain of modified glutamine.

Chromones from Licania arianeae (Chrysobalanaceae).

The phytochemical studies of the leaves of Licania arianeae Prance (Crysobalanaceae) have led to the identification of ten new chromones, four 5,7-dihydroxy-2-alkylchromones, four 5,7-dihydroxy-6-chloro-2-alkylchromones and two 5,7-dihydroxy-6,8-dichloro-2-alkylchromones. The structures were established from IR, NMR and FAB-MS spectra data including 2D NMR experiments of natural substances and of the methyl derivatives.

Structural insights into cholinesterases inhibition by harmane ß-carbolinium derivatives: a kinetics-molecular modeling approach.

The natural indole alkaloids, the ß-carbolines, are often associated with cholinesterase inhibition, especially their quaternary salts, which frequently have higher activity than the free bases. Due to lack of information explaining this fact in the literature, the cholinesterase inhibition by the natural product harmane and its two ß-carbolinium synthetic derivative salts (N-methyl and N-ethyl) was explored, together with a combination of kinetics and a molecular modeling approach. The results, mainly for the ß-carbolinium salts, demonstrated a noncompetitive inhibition profile, ruling out previous findings which associated cholinesterase inhibition by ß-carbolinium salts to a possible mimicking of the choline moiety of the natural substrate, acetylcholine. Molecular modeling studies corroborate this kind of inhibition through analyses of inhibitor/enzyme and inhibitor/substrate/enzyme complexes of both enzymes.