Irena Valterová

Rubber substrates and their influence on isomerization of conjugated dienes in pheromone dispensers

Release rate and degree of isomerization of pheromones with conjugated double bonds were studied in dispensers prepared from several rubber substrates. The substrates compared were made of rubber, cured with elemental sulfur or accelerators based on organic sulfur compounds or organic peroxides. Isomerization of the double bonds occurs immediately after impregnation of the substrate, and the degree of isomerization increases during field use and/or storage. The propensity of the isomers to isomerize corresponds to their proportion in the equilibrium mixture. AnE,Z isomer is isomerized faster than theE,E isomer, and finally a near-equilibrium mixture of the four isomers is present. Minimal isomerization was found in non-sulfur-cured substrates which are the material of choice.

Chirality of the monoterpene alarm pheromones of termites

ity. Our results imply that the chromatographic determination of enantiomeric compositions is to be preferred to the traditional determination of optical purities by resorting to chiroptical methods (e.g., polarimetry [5]). For very complex matrices the enantiomer analysis may preferentially be performed by gas chromatography-mass spectrometry in the selected ion monitoring (SIM) mode [3]. Generous support of this work by the Deutsche Forschungsgemeinschaft and the Fonds der chemischen Industrie is gratefully acknowledged.

Enantiomeric composition of monoterpene hydrocarbons from the liverwort Conocephalum conicum

Volatiles from the essential oil of the liverwort Conocephalum conicum were analysed. The chirality of the monoterpene hydrocarbons was studied by two-dimensional ps chromatography. All compounds e ...

On the natural occurrence of (−)-3-carene, a component of termite defense secretions

The soldiers caste of termites of the subfamily Nasutitermitinae has a highly developed defense system. In their frontal gland, they produce and store a defense secretion, usually consisting of a mixture of monoterpene hydrocarbons and oxygenated polycyclic diterpenes [1]. The enantiopurity of otpinene and limonene in the secretions of several termite species has already been studied and found to be rather high [2, 3]. It was of interest to focus attention now on the chirality of 3carene in termite defense secretions because of its common occurrence in pure (+)-form in plants [4]. Two termite species, Nasutitermes ephratae and N. costalis, had earlier been reported to have a defense secretion containing 3-carene as the main component [5, 6] and hence these species were chosen for our study. N. ephratae was collected in Peru (three colonies from Iquitos) and N. costalis in Cuba (16 colonies from three different localities in the provinces Habana, Escambray, and Oriente). The defense secretions were extracted with ethanol. The volatile fraction was evaporated under reduced pressure and collected in a cold trap. The condensate was extracted with hexane and the hexane solution was used for the analysis. The monoterpene hydrocarbons were identified by means of gas chromatography-mass spectrometry [Finnigan 4 500 equipped with a Varian 3 400 gas chromatograph, DB-WAX capillary column (30 m z 0.25 mm)]. The constituent giving the main peak, 3-carene, was isolated by the preparative GC on