US EPA

8341746 

Journal Article 

Interaction of benzo[a]pyrene and 6-oxybenzo[a]pyrene with caffeine. Structures of the complexes as studied by nuclear magnetic resonance chemical shift and relaxation 

Nosaka, Y; Akasaka, K; Hatano, H 

1978 

1 

Journal of Physical Chemistry
ISSN: 0022-3654 

82 

26 

2829-2833 

English 

10.1021/j100515a017 

The interaction of caffeine with benzo[a]pyrene (BP) and with 6-oxybenzo[a]pyrene (OBP), a carcinogenic free-radical intermediate, has been studied with the proton nuclear magnetic resonance (NMR) method. Observation of ring current shift for both caffeine and BP molecules in CDCl3 led to the conclusion that caffeine associates with BP by a stacking arrangement in this solvent. The magnitude of the chemical shifts observed for BP solubilized by caffeine-d10 in D2O suggests the formation of a 1:2 BP-caffeine complex. The formation of a 1:2 complex is independently supported by the results of measurements of the spin-lattice relaxation time (T1) which shows that the rotational correlation time of the caffeine-BP complex is a factor of 3-4 longer than that of caffeine itself. The OBP radical is solubilized by caffeine in D2O and enhances the 1/T1 of the four kinds of protons of caffeine. With these enhancements, the average distances between the protons of caffeine and the electron spin of the radical in the complex were calculated. To determine probable structures of the complex, these distances were computer simulated for all possible intermolecular orientations. The most probable structure is such that an OBP molecule is sandwiched between two caffeine molecules in a parallel arrangement with a plane-to-plane distance of 0.33 nm, similar to that of the 1:2 complex between BP and tetramethyluric acid crystals. This structure is in qualitative agreement with the structure of the complex between the diamagnetic BP and caffeine expected from chemical shift measurements. © 1978 American Chemical Society.