Biomedical subjects
Publications and source records attributed to Andreas Heise.
This report presents the first simultaneous, metal-free synthesis of block copolymers through combination of enzymatic ring-opening polymerisation of epsilon-caprolactone with RAFT-mediated controlled radical polymerisation of styrene.
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Co- and terpolyesters based on succinic acid and isosorbide in combination with other renewable monomers such as 2,3-butanediol, 1,3-propanediol, and citric acid were synthesized and characterized. Linear polyesters were obtained via melt polycondensation of nonactivated dicarboxylic acids with OH functional monomers. Polymer end functionality (i.e., hydroxyl or carboxylic acid) was controlled by adjusting the monomer stoichiometry. The glass transition temperatures of the resulting polyesters could be effectively adjusted by varying the polymer composition and molar mass. By adding polyfunctional monomers such as trimethylolpropane or citric acid, polyesters with enhanced functionality were obtained. These biobased polyesters displayed functionalities and Tg values in the appropriate range for (powder) coating applications. The polyesters were cross-linked using conventional curing agents. Coatings from branched polyesters--hydroxyl as well as acid functional--showed significantly improved mechanical and chemical resistance compared to those formulated from linear polymers. These renewable polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance, and hardness.
A bifunctional initiator was synthesized and used for a sequence of a nickel initiated polymerization of gamma-benzyl-L-glutamate-N-carboxy anhydride and atom transfer radical polymerization of methyl methacrylate yielding a rod-coil block copolymer.
Iterative tandem catalysis is presented as a flexible tool for obtaining chiral macromolecules from racemic or prochiral monomers. Here, we combine lipase-catalyzed ring-opening of omega-substituted lactones with ruthenium-catalyzed racemization. In a two-pot system, enantioenriched oligomers of 6-methyl-epsilon-caprolactone were synthesized, which could not have been obtained by enzymatic ring-opening alone. A one-pot experiment proved highly promising in developing a novel route toward enantiopure polyesters.
We demonstrate the single-step one-pot synthesis of block copolymers by simultaneous enzymatic ring-opening polymerization and chemically catalyzed atom transfer radical polymerization in supercritical carbon dioxide. Both catalyst systems function simultaneously under these conditions, providing a simple route to the formation of block copolymers of dissimilar monomers.
Disease resistance of plants involves two distinct forms of chemical communication with the pathogen: recognition and defense. Both are essential components of a highly complex, multifaceted defense response, which begins with non-self recognition through the perception of pathogen-derived signal molecules and results in the production, inter alia, of antibiotically active compounds (phytoalexins) and cell wall-reinforcing material around the infection site. To elucidate the molecular details and the genomic basis of the underlying chains of events, we used two different experimental systems: suspension-cultured cells of Petroselinum crispum (parsley) and wild-type as well as mutant plants of Arabidopsis thaliana. Particular emphasis was placed on the structural and functional identification of signal and defense molecules, and on the mechanisms of signal perception, intracellular signal transduction and transcriptional reprogramming, including the structural and functional characterization of the responsible cis-acting gene promoter elements and transacting regulatory proteins. Comparing P. crispum and A. thaliana allows us to distinguish species-specific defense mechanisms from more universal responses, and furthermore provides general insights into the nature of the interactions. Despite the complexity of the pathogen defense response, it is experimentally tractable, and knowledge gained so far has opened up a new realm of gene technology-assisted strategies for resistance breeding of crop plants.
The Arabidopsis thaliana genome contains at least 50 predicted AtCMPG genes. The encoded protein family is defined by a common domain possessing four strictly conserved amino acid residues [Cys, Met, Pro, and Gly (CMPG)] that designate the family. Two members, AtCMPG1 and AtCMPG2, with high sequence similarity to the previously described, immediate-early pathogen-responsive PcCMPG1 gene from Petroselinum crispum were selected for analysis of their expression modes and defense-related promoter elements. Among the most striking similarities with PcCMPG1 were immediate-early transcriptional activation on infection or treatment with a pathogen-derived elicitor and the functional importance of a W-box-containing AtCMPG1 promoter element. Remarkably, this strongly pathogen/elicitor-responsive element, F, did not respond to wounding, in contrast to the AtCMPG1 promoter itself. Comparative analysis, both within the A. thaliana genome and across species, provided further insight into the large structural diversity of W-box-containing elements. Possible roles of AtCMPG proteins in regulatory processes are discussed with reference to a large variety of family members, partly with assigned functions, from plants as well as animals.
The enantioselective polymerization of methyl-substituted epsilon-caprolactones using Novozym 435 as the catalyst was investigated. All substituted monomers could be polymerized except 6-methyl-epsilon-caprolactone (6-MeCL), which failed to propagate after ring opening. Interestingly, an odd-even effect in the enantiopreference of differently substituted monomers was observed. The combination of 4-methyl-epsilon-caprolactone with Novozym 435 showed good enantioselectivity also in bulk polymerization and resulted in enantiomerically enriched P((S)-4-MeCL) (eep up to 0.88). Subsequently, a novel initiator combining a primary alcohol to initiate the ring opening polymerization and a tertiary bromide to initiate atom transfer controlled radical polymerization (ATRP) was synthesized, and showed high initiator efficiencies (> 90%) in the ring opening polymerization of 4-methyl-epsilon-caprolactone in bulk. In addition, the enantioselectivity was retained (E = 11). By using Ni(PPh3)2Br2 as the ATRP catalyst, Novozym 435 could be effectively inhibited at the desired conversion of 4-methyl-epsilon-caprolactone, thus ensuring a high enantiomeric excess in the polymer backbone. At the same time, Ni(PPh3)2Br2 catalyzed the ATRP of methyl methacrylate resulting in the formation of P((S)-4-MeCL-b-MMA) block copolymers. By this combination of two inherently different polymerization reactions, chiral P((S)-4-MeCL-b-MMA) block copolymers can be conveniently obtained in one pot without intermediate workup.