Chemistry and Crystal Structures of Complexes of Caffeine and Tea Catechin - Caffeine: Chemistry, Analysis, Function and Effects - page 60

d n 0 t 2 n g | 3

Figure 4.7

Layer of the 1 : 1 complex of caffeine and EC. Crystal solvent and
hydrogen atoms are omitted for clarity. Black arrows indicate the

distances between planes.

of the A rings of ECs. The A rings of both upper and lower ECs faced the six-
membered ring of the caffeine (Fig. 4.7).
Non-covalent interactions are weaker forces than a covalent bond, but play
a very important role in forming complexes; therefore non-covalent interac-
tions among caffeine and catechin moieties in the complexes were investigated.
In the 1 : 1 complex of caffeine and EC, face-to-face p-p stacking interaction
formed between a six-membered ring of caffeine and the A ring of EC
(Fig. 4.8). Two O-H...O intermolecular hydrogen bonds were also observed
(Table 4.4).

Table 4.4 Hydrogen bonds in 1 : 1 complex of caffeine and EC.

D-H A D…A D-H H…A /D-H…A
OH(2O) a O(7) 2.721(6) 0.83 1.89 177.95
OH(6O) O(4) 2.719(7) 0.83 1.91 166.47
a Atom label in ORTEP drawing. D, H and A indicate hydrogen-bonding donor, hydrogen atom
and hydrogen-bonding acceptor, respectively. A unit of length is s.