We will use neutron reflectivity measurements of lipopolysaccharide (LPS) layers at the air-water interface to help develop a realistic mimetic for the periphery of bacteria that will help us to understand the mode of action of antimicrobial peptides.These measurements will provide a structural link between molecular dynamics simulations and microbial growth and evolution experiments underway in Edinburgh. Specifically, by measuring the reflectivity from a deuterated LPS layer at the D2O-air and null reflecting water-air interfaces, we will determine the uptake of the AMP by the LPS layer, its distribution through the layer and any structural changes induced in the layer by the addition of Ca ions at a concentration observed to induce a significant decrease in the efficacy of the AMP.