Conformational Changes in Complexes of Two Homogeneous Polypeptides on the Surface of a Carbon Nanotube at Different pH Values

The conformational rearrangement of single or paired homogeneous polypeptide macromolecules of the same length, including those with different types of units, lying on the surface of a carbon nanotube were studied by molecular dynamics simulation at different pH levels. A mathematical model of macrochain conformations is presented, which allows for interactions in the complex of two similar polypeptides on the surface of the carbon nanotube, at different pH values of the solvent. When pH departed from the isoelectric point, the single polypeptide uncoiled and wound around the nanotube, while the two identical polypeptides repelled each other, shifting to the opposite ends of the nanotube. When two oppositely charged polypeptides were adsorbed on the surface of the carbon nanotube, they became tightly intertwined, forming a generally neutral polyelectrolyte complex. If the electric charge of one of the polypeptides in the complex did not change with a change in the pH level, while the electric charge of the other polypeptide decreased in magnitude, then the first polypeptide unfolded, dragging the second one along with it, and together they wound around the carbon nanotube.