Allelochemical effects were observed when Tribolium castaneum (Herbst) adults were treated with Baccharis salicifolia (Ruiz & Pavon) Pers essential oil. The main biological activities were toxicity and repellence. Terpenes present in the essential oil were identified by GC-MS, and some authentic samples were tested to assess their activity individually. The most acutely toxic compounds after 3 days were beta-pinene and pulegone. Most of the monoterpenes elicited symptoms indicative of neurotoxicity. The most repellent compound was alpha-terpineol. Toxic and repellent effects of chemical derivatives of the major sesquiterpene present in B salicifolia essential oil, as well as a series of monoterpenes, were evaluated in order to investigate structure-activity relationships. The reduced derivatives of the monoterpenes and sesquiterpenes were more repellent that their carbonyl analogues. In addition, unsaturation in the germacrane skeleton enhanced repellent activity.

No abstract

The study of electron ionization (EI) induced decomposition patterns is usually undertaken by extensive metastable-ion investigations, mainly depending on spectra of the unimolecular decomposition of parent ions carried out in double-focusing instruments.By such an approach, in the last decades most of the definitive data on ion structures and on the mass spectrometric behaviour of many classes of compounds have been achieved. Unfortunately, single-quadrupole analysers do not give any definitive information on the unimolecular decomposition pathways of selected species; only by collision experiments in triple-stage quadrupolar systems can such data be obtained.','The ion-trap mass spectrometer3 (ITMS) offers a particularly interesting mass spectrometric approach due to its ability to store ions for further experiments, first of all being mass analysis. In particular, the use of a supplementary AC voltage (the so-called 'tickle' voltage) leads to effective collision-induced decompositions of preselected ionic species, even in cases where the energy deposition into the stored ionic species is lower than that usually observed in high-energy collision experiments.For these reasons ITMS seems to be highly promising for ion structure investigations as an alternative to the more complex (and more expensive) systems such as double-focusing sector instruments and triple-stage quadrupoles. In other words, what is usually obtained by the study of natural or collision-induced decomposition in multiple-stage analysers, is achieved in the ITMS by a simple, single-stage device by means of time separation of the different steps, namely electron ionization, ionic species isolation, collision of the preselected ions, mass analysis and detection of the collisioninduced decomposition products.Following our previous mass s ectrometric investigations of flavonoid cornpounds?'in this paper we will discuss the data obtained by ITMS on structure investigation of [M -HI+ ions of chalcone (2-propen-1-ona-1,3-diaphenyl) (l), whose EI mass spectrum has + Partially and preliminarily communicated at the European Meeting on Tandem Mass Spectrometry, Manchester UK, 9-11 July 1990.* Author to whom correspondence should be addressed.already been reported together with those of some of its derivatives.6-8 In such early papers the major fragmentation pathways and rearrangement processes were used to determine the type of chalcone and, in some cases, the position of substituents on the molecular skeleton. Some disagreement was expressed concerning the structure assignment of their [M -H]+ species.Ronayne and co-workers' postulated that the commonly observed intense [M -H]+ ion of chalcone was due to the loss of hydrogen from ring A in the resonance-stabilized flavylium ion structure a. The same mechanism was also proposed by Van

No abstract