The Crystal Structure of the Intermolecular Complex between 9-Ethyladenine and Indole

The crystal structure of a 1: 1 complex of 9-ethyladenine and indole has been determined by the X-ray method. The crystal system is monoclinic with the space group of P21/c. The cell dimensions are a=15.712(2), b=8.098(1), c=11.838(1)Å, and β=103.90(1)°C. Adenines form walls made of double layer. An overlap of adenines is found between layers. The adenine molecule in the front layer is found to be joined by the hydrogen bond with the molecule in the back layer. An intermolecular hydrogen bond is found between adenine and indole rings. The significance of these observations in the interaction of adenine with tryptophan in biological systems is discussed.