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.