Peptide Binding to Inorganic Surfaces and Thermal Transitions of Alkyl Chains on Nanoparticle Surfaces: Computation and Experiment
The self-assembly of peptides on the surfaces of metallic and layered silicate nanoparticles has been studied using classical MD simulation to understand experimental results of screening multibillion phage libraries (TEM, XRD, binding strength, spectroscopy etc). The binding of peptides (7 to 12 amino acids) is due to a unique combination of surface geometry (crystal facet, shape) and surface polarity to match complimentary amino acid sequences. Adsorption energies on even Au or Pd surfaces range from 0 to 80 kcal/mol and binding residues versus spacer residues are identified. Polarization at Pd-Au bimetallic junctions increases the binding energy by ~10 kcal/mol per peptide (7 to 12 amino acids). On layered silicate surfaces, a binding mechanism by ion exchange (Lys side chains) was directly observed in molecular simulation, and alternative mechanisms involve energetically favorable solvation by superficial sodium ions when no ion-exchange capability is available. The relation between packing density and reversible thermal transitions of alkyl chains grafted to surfaces of sheet silicates, metal surfaces, and oxide surfaces has been explained on the basis of extensive experimental (XRD, DSC, IR, NMR, etc) and simulation data. Packing densities (alkyl cross-sectional area per available surface area) between 0 and 0.2 lead to some ordering upon annealing, between 0.2 and 0.75 reversible melting transitions are seen, and above 0.75 no reversible transitions are observed due to quasi-crystalline order.