We have performed optimizations of the ring dimers constrained to maintain the distance and relative orientations between the rings found in the peptides. Results are summarised in Figure . For comparison, we also evaluated the interaction energy of Phe-Phe dimers with analogous constraints. In all cases, the interaction between two mimosine rings was significantly higher than the interaction between two phenyl rings by roughly 1.5 kcal/mol for the interaction between Mms 1 -Mms 5 and Mms 5 -Mms 8 dimers. In the case of the Mms 1 -Mms 8 interaction, we also found a structure with mimosine sidechains in an antiparallel conformation, which led to the highest interaction among the dimers -8.0 kcal/mol, almost double the interaction between phenyl dimer analogs, -4.6 kcal/mol. In addition, we considered DFT calculations with a reduced model of the mimosine hexapeptide (see Figure ), which maintains the backbone atoms connecting both rings.