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Undergraduate Research at UMass Dartmouth
depend on interactions between their side chains
while the cyclic dipeptides have increased interactions
between their cyclized backbones.
To investigate the interaction between the dimers
in more detail, an energy decomposition calculation
was carried out using the Hartree-Fock,
HF/6-31G*, level of theory. It showed that for each
dimer, electrostatic energy, charge transfer energy,
and electrostatic energy acted as attractive forces
between dimers and exchange energy acted as a
repulsive force (Figure 3). The electrostatic energy
implies the importance of the polar interactions
between monomers, the exchange energy implies
the importance of overlapping orbital mixing, the
dispersion energy implies the importance of weak
Van der Waals interactions between monomers, and
the charge transfer energy implies the importance
of attractive orbital interactions, as in π-π stacking
or hydrogen bonding. Altogether, this demonstrates
how several different weak forces come together to
drive dimerization.
In the third stage of the study, hexamer rings of
each of the dipeptides were studied, again using
DFTB. The lowest-energy conformers from stage one
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