Clupeine is isolated from herring and is an example of a protamine, which are cationic antimicrobial peptides occurring in the sperm cells of some fish. Protamines are active against food-borne Gram-negative organisms, and the proposed experiments are a continuation of our work to achieve a better insight as to their mechanism of action. We will work with modified clupeines as follows: (i) hydrophobic modification with fatty acids (palmitic and myristic); (ii) charge modification with quantitative exposure to 1,2-cyclohexanedione to reduce cationic charge. The neutron reflectivity experiments on bilayer membrane models of E. coli will allow us to investigate the initial interactions leading to microbial death, toward the development of more cost-effective antimicrobial peptides.