CHASM (Chain Alignment on the Surface of Materials): An algorithm for predicting polymer and polypeptide conformations at interfaces

Herein, we describe a lattice-matching algorithm, adopted from the unimodular matrix coincident-site lattice approach, that can be used for determining the low-energy orientation(s) for a macromolecular chain (polymer, polypeptide) that adsorbs directly onto a well-defined periodic surface, such as an exposed inorganic crystal surface or an oriented organic film. The program, CHASM (for chain alignment on the surface of materials), utilizes transformation (S), rotation (R), and deformation (D) matrix operations to generate angular-dependent lattice overlap patterns for the two components. From the coincidence pattern generated from lattice overlap at a given angle of rotation, CHASM determines either the periodicity (N′) or a dislocation energy parameter (P), both of which are measurements of the stability of a given interface. In this report, we benchmark the CHASM algorithm against STM and X-ray diffraction data obtained for oriented polyethers, polyamides, poly(caprolactone), and lysozyme adsorbed onto periodic substrates. We find that the CHASM-predicted orientations exhibit excellent agreement with experimental data.