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The aim of this work was the synthesis of starch macroinitiators for cationic polymer grafted starches that: (i) are free of cationic homopolymer, and (ii) display a high degree of conversion of the cationic monomer. We show that this can be achieved by a free-radical polymerization reaction using the cationic monomer N-methacryloyloxyethyl-N,N-dimethyl-N-benzylammonium chloride (MADAM-BQ) and a new starch-based macroazoinitiator. For this purpose, the acid chloride of 4-tert-butylazo-4-cyanovaleric acid was synthesized and bound covalently to starch (predominantly in the C6 position) to form a nonsymmetrically substituted macroinitiator that was used to polymerize MADAM-BQ in aqueous media. Essentially no MADAM-BQ homopolymer was formed. The initiator decomposes thermally to starch radicals of high reactivity and low-molar mass radicals that do not initiate polymerization. The reason for the different reactivities of the radicals is presumably due to the nonsymmetric constitution of the starch-bound azo groups. The graft polymerization of MADAM-BQ in aqueous solution performs according to an ideal overall kinetic. The structure of the synthesized starch-graft-poly(MADAM-BQ) products is similar to that of block copolymers because of the low radical efficiency of the starch initiators in aqueous solution. Especially, starch substrates with a higher content of azo groups did not lead to graft products with shorter graft distances because the state of solution of these macroinitiators becomes worse and aggregation occurs with an increasing degree of substitution.
Defensive behavior is linked to altered surface chemistry following infection in a termite society
(2023)
The care-kill response determines whether a sick individual will be treated or eliminated from an insect society, but little is known about the physiological underpinnings of this process. We exploited the stepwise infection dynamics of an entomopathogenic fungus in a termite to explore how care-kill transitions occur, and identify the chemical cues behind these shifts. We found collective responses towards pathogen-injected individuals to vary according to severity and timing of pathogen challenge, with elimination, via cannibalism, occurring sooner in response to a severe active infection. However, injection with inactivated fungal blastospores also resulted in increased albeit delayed cannibalism, even though it did not universally cause host death. This indicates that the decision to eliminate an individual is triggered before pathogen viability or terminal disease status has been established. We then compared the surface chemistry of differently challenged individuals, finding increased amounts of long-chained methyl-branched alkanes with similar branching patterns in individuals injected with both dead and viable fungal blastospores, with the latter showing the largest increase. This coincided with the highest amounts of observed cannibalism as well as signs of severe moribundity. Our study provides new mechanistic insight into the emergent collective behaviors involved in the disease defense of a termite society.