Chemistry and Crystal Structures of Complexes of Caffeine and Tea Catechin - Caffeine: Chemistry, Analysis, Function and Effects - page 64

d n 0 t 2 n g | 3

Figure 4.12

Layer of the 2 : 1 complex of caffeine and Cg. Crystal solvent and
hydrogen atoms are omitted for clarity. Black arrows indicate the
distance between planes.

indicated that both B and B' rings of Cg were both in equatorial positions with
respect to the C ring of the Cg molecule. The layer structure of 2 : 1 complex of
caffeine and Cg was investigated. In the layer structure of the 2 : 1 complex of
caffeine and Cg, units of the 2 : 1 complex piled up parallel to the a-axis
(Fig. 4.12). The distances between A rings of Cgs, and B ' rings of Cgs were
7.013s and 6.763s, respectively. Two caffeine molecules were located in
almost the middle of the A rings of Cgs and B' rings of Cgs. The A and B' rings
of the upper Cg and the B' rings of the lower Cg slightly shifted to the six-
membered rings of caffeine, and the A rings of the lower Cg were face to face
with six-membered rings of caffeine.
Intermolecular interactions between caffeine and Cg moieties to form the 2 :
1 complex were investigated. The two caffeine molecules were sandwiched
between the A and B' rings of Cgs by offset p-p interactions (black dotted
arrows in Fig. 4.13), except between six-membered rings of caffeine and the A
ring of Cg marked by black arrow in Fig. 4.13. The molecular interaction of
the black arrow was face-to-face p-p interaction. As shown in Fig. 4.13 and
Table 4.6, six O-H...O hydrogen bonds were observed in the 2 : 1 complex of
caffeine and Cg.