Piezoelectric coefficients d(14), d(16), d(34) and d(36) of an L-arginine hydrochloride monohydrate crystal by X-ray three-beam diffraction

Previous work employed X-ray three-beam diffraction techniques to obtain part of the L-arginine hydrochloride monohydrate (L-AHCL. H2O) piezoelectric coefficients, namely d(21), d(22), d(23) and d(25). Those coefficients were obtained by measuring the shift in the angular position of a number of secondary reflections as a function of the electric field applied in the [ 010] piezoelectric direction. In this paper a similar procedure has been used to measure the remaining four piezoelectric coefficients in L-AHCL. H2O: with the electric field applied in the [100] direction, d(14) and d(16) were measured; with the electric field applied in the [001] direction, d(34) and d(36) were obtained. Therefore the entire piezoelectric matrix of the L-AHCL. H2O crystal has been successfully measured.13643543

EVALUATION OF THE CHEMICAL COMPOSITION AND ALLELOPATHIC POTENTIAL OF ESSENTIAL OILS FROM THREE SPECIES OF ASTERECEAE AGAINST SEED GERMINATION AND SEEDLING VIGOR OF LETTUCE

The allelopathic properties of the essential oils have been exploited because they are biodegradable natural compounds that can be used in combination or as prototypes for new bioherbicides. The objectives of this study were to chemically characterize the essential oils from B. dracunculifolia, C. bonariesis and T. diversifolia and to evaluate their allelopathic potential. The essential oils were extracted by hydrodistillation and their chemical compositions were determined by GC-MS. Allelopathic activities were determined by methods that evaluate the effects of volatile compounds and direct contact of those compounds on the seed germination and seedling vigor of lettuce. The principal constituents of the essential oil from B. dracunculifolia were limonene, trans-nerolidol and β-pinene; those in the oil from C. bonariesis were limonene, trans-β-ocimene and cis-verbenol (4.4%); and those in the oil from T. diversifolia were β-pinene, α-pinene and limonene. Minor differences in the germination and vigor of lettuce seedlings were observed when they were exposed to the volatile essential oils from the leaves of the three species of the Asteraceae family. However, upon direct contact with these oils, those of C. bonariesis presented the greatest allelopathic potential, which was attributed to its higher content of oxygenated monoterpenes