Title : Biomimic and Stimuli-Responsive Macromolecules
Speaker: Prof.A'fang Zhang, Shanghai University
Host: Yiyun Cheng
When: 2012-11-21 14:00
Where: Conference Room 469, School of Life Sciences
Abstract：This talk will include the following three parts: (1) Ordered secondary structures of peptides in nature, such as a-helices and b-sheets, play crucial role in forming organized tertiary structures of proteins, which dominate their functions and properties as well as their biological activities. The stabilization of these secondary conformations will not only guarantee the proper activities of the proteins but also prevent them from forming abnormal amyloid fiber aggregates. Peptide-based polymers combine the structural characteristics and properties from both peptides and polymers, thus, are promising for applications at various areas. At the same time, the polymer architecture may also show influence on the ordered structures of the peptide units. Therefore, we here report on several examples developed recently from our group to show how architecture exhibit effects on stabilizing the secondary structures of peptides, and how the ordered structures of peptides are mediated by local environmental variation within the polymer matrix. (2) Chiral helical polymers have received considerable attention in recent years not only by mimicking the structures and functions of biological helices, but also due to their unique optical properties as well as molecular recognition ability. We here report our recent progress on developing novel chiral and helical polymers based different methodology. (3) Responsive behavior is rather typical for biomacromolecules and has been mimicked in fields ranging from advanced artificial devices, smart surfaces and sensors to medicine and biomineralization. It presents a substantial scientific and engineering challenge with a considerable application potential. An interesting class of stimuli-responsive materials is thermoresponsive synthetic polymers. They are water-soluble at room temperature but start to collapse close to their lower critical solution temperatures (LCSTs) due to dehydration of the chains, and subsequently form aggregates. The LCST of a polymer is not only dependent on the balance of the hydrophilic and hydrophobic units, with the more hydrophilic polymers commonly showing higher LCSTs than the more hydrophobic ones, but also on how these units are incorporated into the molecular structure. Here we describe the efficient synthesis of a series of first (G1) and second (G2) generation thermoresponsive dendronized polymers and dendrimers based on oligoethylene oxide (OEO) as linking and gallic acid as branching unit (see figure). The LCSTs of these macromolecules can be tuned from 27 oC to 64 oC by modification of the peripheral units, OEO length or the dendron generation. Their thermally induced phase transitions as well as aggregations will be addressed. This includes their fast and sharp transition with virtually no hysteresis between heating and cooling process. Interestingly, the unprecedented thermoresponsiveness based on OEG-dendritic scaffolds have been also realized via supramolecular interactions. Besides, all of the macromolecules show negligible in vitro cytotoxicity, except G1 dendrimers. We believe to have a versatile and powerful “smart” system at hand which eventually will span considerable applications in the material or biomedicine areas.