| Purines play a central role in all living systems. They are not only constituens of nucleic acids but also interact with enzymes and other proteins. Their biological and pharmacological effects are connected with the ability to form supramolecular complexes with biological targets. The hydrogen bonds play crucial role in such supramolecular interactions. 15N NMR spectroscopy has been found essential to furnish information about the protonation site(s) on the purine ring, the proton-transfer equilibria and the hydrogen-bond formation. 15N NMR chemical shifts and 1H-15N coupling constants are obtained by using inverse-detected multiple bond chemical shift correlation techniques at 15N natural-abundance level. Low temperature measurements of 13C and 15N chemical shifts and 3JH,C a 2JH,N coupling constants are used for determining the proton-transfer proceses and interactions of purines with metal ions. The solid-state NMR, x-ray diffraction, and quantum chemical calculations are also extensively used in the structural analysis. |
