Effect of copolymer microstructure on single chain collapse
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)Abstract
We present dynamic Monte Carlo simulations of the collapse of copolymers containing monomers, m and 'sticky' comonomers, c. At poor solvent condition, decrease of the size of the chain is mainly driven by the net m-m and c-c attractions. The strong c-c attraction increases the overall solvophobicity of the copolymer chain relative to a homopolymer and as a result, copolymers collapse more abruptly and, at a higher effective temperature relative to homopolymers. There is a qualitative difference in the transition depending on c content. For c content greater than 50\%, copolymer collapse is qualitatively similar to that observed for homopolymers, when rescaled to account for comonomer solvophobicity. However, collapse of copolymers with c content less than 50\% is qualitatively steeper than for homopolymers. We show that the change in the nature of collapse is due to the formation of an intermediate structure comprising c-core and m-shell, after the theta-point. The pathway to collapse is also strongly influenced by the distribution of comonomers along the chain. For uniform copolymer chains (viz. equispaced c units along the chain), collapse happens at relatively lower temperatures than random copolymers. Further, uniform copolymers, but not random, appear to collapse cooperatively. Transition of uniform copolymer appears to be more abrupt (happens at a narrow temperature range) compared to random copolymer. Our results have relevance to protein folding where specific amino acid sequences lead to collapse and folding to a unique native structure.