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281.
282.
Svetlana Marković Jelena Đurđević Svetlana Jeremić Ivan Gutman 《Journal of molecular modeling》2011,17(4):805-810
Three fluoranthenes and one substituted fluoranthene, 2,2-dimethyl-2H-dibenzo[cd,k]fluoranthene, were investigated using the unrestricted symmetry-broken and complete active space methods. It was shown that
four Kekuléan hydrocarbons are diradicals, implying that their ground state is a triplet. In the energetically less favorable
singlet state these hydrocarbons exhibit pronounced diradical character. This occurance is explained with the tendency of
the investigated molecules to delocalize their π-electrons. This leads to aromatic stabilization which is stronger than destabilization
due to unpaired electrons. Our results for 2,2-dimethyl-2H-dibenzo[cd,k]fluoranthene are in excellent accord with experimental findings of McMaster et al. concerning this compound. 相似文献
283.
Iwona Żur Ewa Dubas Elżbieta Golemiec Magdalena Szechyńska-Hebda Franciszek Janowiak Maria Wędzony 《Plant Cell, Tissue and Organ Culture》2008,94(3):319-328
The accumulation of abscisic acid (ABA) and the activities of antioxidative enzymes along with cell metabolic activity were
monitored during androgenesis induction in triticale (×Triticosecale Wittm.). Tested cultivars ‘Mieszko’ and ‘Wanad’ were selected due to their significantly different responses to androgenic
induction. Significant variation was observed in respect of superoxide dismutase activity and endogenous ABA content in anthers
isolated from freshly cut tillers. For both cultivars, tillers pretreatment with low temperature decreased peroxidase activity
by 36%, highly accelerated respiration rate and reduced heat production. At the same time, the level of ABA in ‘Mieszko’ was
increased to the level measured in ‘Wanad’. This effect was associated with higher microspore culture viability and increased
stress tolerance in ‘Mieszko’. Low temperature and metabolic starvation during 4-day anther preculture did not influence activities
of antioxidative enzymes, while it resulted in slight decrease in respiration rate and heat emission. The importance of these
changes for effective androgenesis induction is discussed. 相似文献