Peptide Synthesis with Macroinitiators

1 Amine-Initiated NCA Polymerization for Synthesis of the Polypeptide Block 

Vesicles of poly(Llysine)-b-poly(L glutamic acid) (PLL-b-PGA) have been reported to show pH-responsive inside-out aggregation. At acid pH, the PEL block forms the corona and the a-helical PGA block forms the core (see Fig. 2). However, at alkaline pH the PEL forms the core of the vesicle wall with the PGA as cormia [48]. This principle was further expanded towards pH- and temperature-sensitive block copolymers. At acidic pH and room temperature, PNIPAM-b-PGA forms micelles with a PGA core and a PNIPAM corona, whereas at alkaline pH and elevated temperatures PNIPAM forms the core and the PGA the corona. At alkaline pH and room temperature, the block copolymer is moleculary dissolved [42]. PNIPAM-b-PEE behaves similarly but forms PEE core micelles at alkaline pH and room temperature [43]. 

2 Self-assembly of the dibloek copolymer POA15-b-PLL15 into vesicles. Reprinted with permission liom [48]. Copyright (2005) American Chemical Society 

Other peptide-polymer conjugates with interesting optical properties are rod-rod systems with 7i-conjugated aromatic polymers. The latter are appealing systems because of their optoelectronic and photoconductive properties, which strongly depend on the solid state morphology. Jenekhe and coworkers reported on triblock copolymers with a polyfluorene middle block and PBLG outer blocks 

PEG and poly(2-methyl-2-oxazoline) (PMeOx) with amine end groups were used to polymerize BLG-NCA and 5-benzyloxy carbonyl-L cysteine NCA. The resulting copolymers were compared with regard to their aggregation behavior. There is not very much influence on the aggregation behavior caused by the hydrophilic polymer (PEG or PMeOx), whereas the peptide block has a substantial influence on the size of the micelles and the critical micelle concentration. The authors ascribe this to the different secondary structure and hydrophobicity of the polypeptide blocks [52]. 

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Figure 8 Synthesis of polymer-coated peptide nanotubes using an ATRP bio-macroinitiator approach. Reprinted with permission from Couet, J. Jeyaprakash, J. D. Samuel, S. etal. Angew. Chem., Int. Ed. 2005, 44, 3297. Copyright 2005, Wiley VCH. ...

Tsutsumiuchi K, Aoi K, Okada M (1997) Synthesis of polyoxazoline-(glyco)peptide block copolymers by ring-opening polymerization of (sugar-substituted) alpha-amino acid N-carboxyanhydrides with polyoxazoline macroinitiators. Macromolecules 30(14) 4013-4017... 

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