Effects of End Group Termination on Salting-Out Constants for Triglycine

Salting out constants for triglycine were calculated for a series of Hofmeister salts using molecular dynamics simulations. Three variants of the peptide were considered with both termini capped, just the N-terminus capped, and without capping. The simulations were supported by NMR and FTIR measurements. The data provide strong evidence that earlier experimental values of salting out constants assigned to the fully capped peptide (as previously assumed) should have been assigned to the half-capped peptide instead. Therefore, these values cannot be used to directly establish Hofmeister ordering of ions at the peptide backbone, since they are strongly influenced by interactions of the ions with the negatively charged C-terminus.