In this work we will explore how to use PolRef to study the binding of our rationally designed peptide amphiphiles onto floating lipid bilayers mimicking G- bacterial and red blood cell membranes. To help gain insight into the selective binding processes, we will select 2 representative peptides at 2 concentrations (below and above their MICs to typical bacteria) under 3 contrasts (d- and h-lipids and H2O/D2O), requesting 6 days of PolRef beam time. This work will provide valuable molecular insight of peptide selectivity to different membranes under different conditions.