A first-order transition in the charge-induced conformational changes of polymers

Analytical mean-field theories and lattice model simulations have been used to study the charge-induced conformational changes of single polymer molecules. The compact-to-extended transition induced by charge is found to be first-order (i.e., two-state transition with a transition state) in the pres...

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Bibliographic Details
Published in:The Journal of chemical physics 2002-06, Vol.116 (22), p.9964-9974
Main Authors: Mao, Yi, Burin, Alexander L., Ratner, Mark A., Jarrold, Martin F.
Format: Article
Language:English
Subjects:
Biopolymers
Computer simulation
Crystal lattices
Electrostatics
Entropy
Mathematical models
Monte Carlo methods
pH effects
Phase transitions
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Summary:Analytical mean-field theories and lattice model simulations have been used to study the charge-induced conformational changes of single polymer molecules. The compact-to-extended transition induced by charge is found to be first-order (i.e., two-state transition with a transition state) in the presence of strong short-range interactions at low temperatures. Short-range interactions decay much faster than electrostatic energy so expansion below a minimal value cannot produce electrostatic compensation for short-range energy loss. This is the origin of a free energy barrier (transition state) between the compact and the extended states. If the short-range interactions are weak in comparison with attractive and repulsive Coulomb interactions, the transition is expected to be second-order (one-state transition without a transition state). The prediction is compared to the computer simulation of the exhaustive enumeration of all 12-mer cubic lattice polymer conformations using different potentials, and qualitative agreement is found. Implications for protein folding and unfolding are discussed.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.1478771