The pH Response of a Peptoid Oligomer

Polypeptoids are N-substituted glycine
polymers,
which differ from peptides in the placement of the side chain on the
amide nitrogen rather than the Cα carbon. A peptoid
with a chiral side chain containing both an aromatic group and carboxylic
acid has a structure that responds to pH changes. All-atom molecular
dynamics simulations using a force field specifically tuned for peptoids
were carried out with an advanced sampling method for the peptoid
(S)-N-(1-carboxy-2-phenylethyl)­glycine
in the high and low pH limits. The simulations show that the structure
changes from mostly cis amide bonds at low pH to
mostly trans bonds at high pH. The structural changes
are driven by side chain–backbone hydrogen bonds at low pH
and side chain repulsions and increased water contact at high pH.