Structural transitions of a semi-flexible polyampholyte

Polyampholytes (PAs) are charged polymers composed of positively and negatively charged monomers along their backbone. The sequence ofthe charged monomers and the bending of the chain significantly influence the conformation and dynamical behavior of the PA. Using coarse-grained molecular dynamics simulations, we comprehensively study the structural and dynamical properties of flexible and semi-flexible PAs.The simulation results demonstrate a flexible PA chain, displaying a transition from a coil to a globule in the parameter space of the chargesequence. In addition, the behavior of the mean-square displacement (MSD), denoted as <(Delta r(t))(2)>, reveals distinct dynamics, specificallyfor the alternating and charge-segregated sequences. The MSD follows a power-law behavior, where <(Delta r(t))(2)>similar to t(beta), with beta approximate to 3/5 and beta approximate to 1/2 for the alternating sequence and the charge-segregated sequence in the absence of hydrodynamic interactions, respectively. However, whenhydrodynamic interactions are incorporated, the exponent beta shifts to similar to 3/5 for the charge-segregated sequence and 2/3 for the well-mixedalternating sequence. For a semi-flexible PA chain, varying the bending rigidity and electrostatic interaction strength(Gamma e)leads to distinct,fascinating conformational states, including globule, bundle, and torus-like conformations. We show that PAs acquire circular and hairpin-like conformations in the intermediate bending regime. The transition between various conformations is identified in terms of the shapefactor estimated from the ratios of eigenvalues of the gyration tensor.Published under an exclusive license by AIP Publishing.https://doi.org/10.1063/5.0219070