The dipeptides are a class of organic molecules that form hexagonal crystalline structures (space group P61) with one-dimensional chiral channels of tunable pore diameters in the range 3-6 Å. They have shown interesting selective properties in the adsorption and transport of water and solutes, and gases. We propose to use IRIS for the study of methane absorbed in porous dipeptides. We propose to compare L-isoleucyl-Lvaline, that was already studied via inelastic and quasi-elastic neutron scattering, with L-valyl-L-alanine. These two compounds have similar methane adsorption characteristics but differ in pore sizes and gas selective properties. We expect that the study of the diffusion of methane molecules in the two systems can allow a better comprehension of the interactions between the pore walls and adsorbed molecules.