Abstract
Ring opening polymerization (ROP) of N-carboxy anhydride (NCA) amino acids presents a rapid way to synthesize high molecular weight polypeptides with different amino acid compositions. The compositional and functional versatility of polypeptides make these materials an attractive choice for biomaterials. The functional performance of polypeptide materials is equally linked to their conformation which is determined by the amino acid sequence in the polymer chains. Here, the interplay between composition and conformation of synthetic polypeptides obtained by NCA polymerization was explored. Various copolypeptides from Glu(Bzl) and Ser(Bzl) were prepared to investigate how polypeptide composition affected the conformation of the resulting copolymer. Polymerization kinetics indicated that the copolymerization of Glu(Bzl) and Ser(Bzl) preferentially yielded alternating copolymers. Both the polydispersity and the conformation of the polypeptides were dependent on the Ser(Bzl) content in the polymer, demonstrating that polypeptide functionalities could be tuned directly by altering the relative amounts of amino acids in the chain. This work presents the first step toward an improved understanding and control over polypeptide conformation through modulating the amino acid composition of the material. Understanding this sequence–functionality relationship is essential to advancing the use of ROP as a technique to design smart polypeptide based materials with specific functions. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2331–2336
Highlights
Synthetic polypeptides have great compositional and conformational diversity which directly contributes to their functional versatility
Synthesis and Characterization of Copolypeptides with Systematically Changing Composition To prepare a series of serine and glutamic acid copolymers with a systematic change in amino acid composition via N-carboxy anhydride (NCA) polymerization (Scheme 1), polymerizations were carried out with varying monomer feed ratios (Table 1) but constant total monomer (0.5 M) and initiator concentrations (2 mol %)
To fabricate well-defined polypeptides using Ring opening polymerization (ROP) it is essential to understand and to be able to modulate the properties of these polypeptides in a controlled manner
Summary
Synthetic polypeptides have great compositional and conformational diversity which directly contributes to their functional versatility. They have found applications as responsive materials, for example, for pH-dependent sustained drug release,[1] photoresponsive antibacterial devices,[2,3] and enzyme responsive scaffolds in tissue engineering.[4]. The properties of natural and synthetic peptides are related to the peptides’ conformation which in turn depends on the type, amount, and distribution of amino acids in the peptide sequence Understanding and manipulating these variables provides an attractive route to access peptide materials with a range of different properties and tailored functionalities. Ring opening polymerization (ROP) is a versatile, low cost, and well-established technique to synthesize polymers from N-carboxyl anhydrides (NCA), which has been successfully employed in the synthesis of long chain polymers.[5,6] Extensive control over the polymerization has been achieved by use of low temperatures, high pressures, and catalysts to enable the elimination of unwanted side reactions permitting the synthesis of highly monodisperse polypeptides.[7,8,9,10,11,12,13] While
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