We studied the interaction of four new penta-peptides with spherical silver nanoparticles. Our findings indicate that the combination of the thiol in Cys and amines in Lys/Arg residues are critical to providing stable protection for the silver surface. Molecular simulation reveals the atomic scale interactions that underlie the observed stabilizing effect of these peptides, while yielding qualitative agreement with experiment for ranking the affinity of the four penta-peptides for the silver surface.