¹H‐ and ¹³C‐nmr studies on caffeine and its interaction with nucleic acids

The relative orientation of caffeine in stacks formed by self‐association in aqueous solution has been evaluated by both ¹H‐ and ¹³C‐nmr spectroscopy. The data, which were interpreted through the calculation of ring‐current and atomic diamagnetic anisotropic effects of the caffeine molecule, suggest two caffeine bases may stack in a nearly orthogonal manner. The interactions between caffeine and adenylyl‐3′,5′‐adenosine, polyadenylic acid, and ribo‐(A‐A‐G‐C‐U‐U)₂ helix were also studied by nmr at different caffeine/base ratios and at varying temperatures. The results show that caffeine tends to stack on the top of the terminal purine bases or to insert (the single‐stranded) or to intercalate (the double‐stranded) between purine bases.