Fatty acids methyl esters (FAME) have been prepared under microwave irradiation, using homogeneous catalysis, either in batch or in a flow system. The quality of the biodiesel obtained has been confirmed by GC analysis of the isolated product. While the initial experiments have been performed in a small scale laboratory batch reactor, the best experiment has been straightforward converted into a stop-flow process, by the use of a microwave flow system. Compared with conventional heating methods, the process using microwaves irradiation proved to be a faster method for alcoholysis of triglycerides with methanol, leading to high yields of FAME.
The
5H-pyrido[4,3-b]indole,
11H-indolo[3,2-c]quinoline,
5H-benzo[f]pyrido[4,3-b]indole,
and 13H-benz[5,6]indolo[3,2-c]quinoline
heteroaromatic nuclei have been synthesized by the
Graebe−Ullmann method by classical heating or under microwave irradiation.
These tri-, tetra-, and
pentacyclic compounds were transformed into the corresponding cationic
derivatives by N-alkylation,
and the DNA-binding properties of the resulting cationic systems were
examined using UV−vis
spectroscopy, viscometric determinations, and molecular modeling
techniques. The tetracyclic
cations were transformed into bis-salts by means of a diethyl
bispiperidine rigid chain and a more
flexible polyamide linker, but the low solubility of these bis-salts
made the study of their
bisintercalating properties difficult.
The binding of echinomycin to DNA hexamers of the form GpApXpZpTpC, where the central XpZ step can be CpG, TpA, GpC, or ApT, has been studied by molecular modeling and molecular mechanics techniques. Interaction energies have also been calculated for the complexation of echinomycin with sequences containing the preferred central CpG step and different flanking base pairs. Besides, two more sets of sequences incorporating either 2,6-diaminopurine (DAP) or hypoxanthine in place of adenine or guanine, respectively, have been examined. The aim of this work was to evaluate the relative importance of hydrogen-bonding and stacking interactions in the association of echinomycin with DNA and further rationalize the experimental evidence. The results of these calculations are in consonance with available data from footprinting experiments and appear to support our previous hypothesis that, in addition to the crucial intermolecular hydrogen bonds in the central region, the stacking interactions involving the quinoxaline-2-carboxamide chromophores of the drug and the DNA base pairs play an important role in modulating the binding specificity of this bisintercalating antitumor antibiotic. This is most clearly seen when sequences with similar minor-groove environments are compared (e.g. CpI vs TpA or CpG vs TpDAP). The dipole moment of N-methylquinoxaline-2-carboxamide has been measured (mu = 4.15 +/- 0.03 D) and compares very well with the calculated value (mu = 4.14 D). The fact that G:C, I:C, A:T, and DAP:T base pairs are shown to be endowed with distinct van der Waals and electrostatic stacking properties with respect to this heteroaromatic ring system could have important implications for the design of novel DNA mono- and bis-intercalating agents.
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