3.1.1 ESP analysis
The ESP analysis can efficiently determine potential sites of
intermolecular interactions for the most stable geometric configuration
of a compound from a molecular level. The stable structures of DBU, EG,
DBU-EG, DBU-2EG and H2S and their corresponding
electrostatic potential distributions are conducted as shown in Figure
1(b). In which the blue and red colors represent positive and negative
electrostatic potentials in the colorimetric band,
respectively.22,36 In the ESP map of DBU, EG and
H2S, the region of nitrogen atoms (N), oxygen atom (O)
and sulfur atom (S) exhibits a local negative electrostatic potential
(see Figure 1(b)), respectively, while the hydrogen atom (H) attached
with O in EG or H in H2S displays a local positive
electrostatic potential. When DBU and EG interact to form DBU-EG or
DBU-2EG multimer absorbents, O and N exhibit more local negative
electrostatic potential, and H attached with O and N displays more local
positive electrostatic potential in the ESP map (red and blue in those
molecules deeper than DBU and EG). There are two types of N in the DBU
molecule, which can interact with two EG to form a trimer molecule.
Hirshfeld charge of DBU, EG, H2S, DBU-EG and DBU-2EG are
shown in Table S1, the N, O and H charge values changed more negatively
and positively in DBU-EG and DBU-2EG relative to DBU and EG,
respectively. Therefore, it can be deduced that four potential
interaction sites exist between DBU-2EG and H2S. In
literature, DBU was equimolar interacts with
monoalcohols.29-31 However, the interaction of two
moles EG and one mole DBU hasn’t been explored yet.