Chiral Amplification in the Transcription of Supramolecular Helicity into a Polymer Backbone

✍ Scribed by Andrew J. Wilson; Mitsutoshi Masuda; Rint P. Sijbesma; E. W. Meijer

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 346 KB
• Volume: 117
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/ange.200462347

✦ Synopsis

on the occasion of his 60th birthday Herein, we describe the expression of chirality into a polymer backbone during the photopolymerization of achiral monomers. The monomers are brought into a chiral self-organized supramolecular structure by using an enantiomerically pure structure-directing agent. The polymer obtained, despite incomplete tacticity, holds enough chiral information to fold itself into an almost homochiral, helical structure. In reporting this system we outline the first example of a chiral supramolecular "sergeant" [1] that affects backbone stereochemistry during a polymerization process by controlling the intrinsic helicity of self-assembled achiral monomers. It implies that self-organization [2][3][4][5] can play a critical role in amplifying the enantiomeric purity of the monomeric constituents of polymers. [6] Cooperative expression and amplification of chirality present in the monomeric components of biopolymers is central to biological function, particularly with respect to folding and hierarchical self-assembly of large functional nanoscale ensembles. For synthetic chiral polymers, asymmetric synthesis of the polymer backbone with chiral monomers, catalysts, initiators, and solvents is well established. [7,8] However, in investigating why biopolymers are composed of enantiomerically pure monomers, it is useful to consider mechanisms [9,10] through which small unbalances in enantiomeric excess [11] are amplified. [12] In synthetic polymers without stereocenters, the latent helical conformation of polyisocyanates, [13] polyisocyanides, [14,15] and polysilanes [16] can be expressed by using small quantities of chiral monomer, chiral