3.1.2 Trimer:
Two distinct possibilities, namely linear and cyclic forms, of cluster formation are possible for trimer. The linear variety can have three different conformers based on the relative orientation of the carbonyl groups in the adjacent monomeric units. Following the same nomenclature discussed in the previous section the conformers present here are named as CC, CT, and TT; the first one represents the relative orientation between first and second monomeric units, while the second letter does the same between second and third. The geometries of the conformers along with their name are provided in Figure S2. In case of the cyclic trimer, two different conformers are possible, namely trimer1 and trimer2. In trimer1 all three free carboxyl groups are in the same direction, while one is in the opposite direction in trimer2. The geometries of both the conformers are shown in Figure S2.
Binding energies of all the possible trimers are provided in Table 1. The three linear conformers are energetically very close to each other. The binding energies of CC, CT, and TT are -16.1, -16.4 and -16.2 kcal mol-1, respectively. Whereas binding energies for cyclic Trimer1 and Trimer2 were found to be -17.9 and -18.3kcal mol-1. Therefore, both the cyclic trimers are more stable than their linear counterparts. The difference in binding energies between most stable linear and least stable cyclic cluster being 1.5 kcal mol-1.