Donald Voet

The Crystal Structures of Purines, Pyrimidines and Their Intermolecular Complexes

Publisher Summary This chapter is concerned with the structures and interactions of purines and pyrimidines in the crystalline state. However, because of their close similarity to the pyrimidines, it also discusses the crystal structure of the barbiturates. The chapter reviews the structure arid conformation of the sugar and the phosphate components of nucleosides, nucleotides, and nucleic acids, and their steric relationship to the purines and pyrimidines. It discusses relevance of single-crystal analysis of purine–pyrimidine interactions to the fiber analysis of polynucleotides. The chapter provides an overview on X-ray diffraction method. It presents a complete tabulation of the molecular geometry of the reliable structures for which there is three-dimensional diffraction information. It draws the conclusion that the structures of the individual purine and pyrimidine bases retain a fair amount of constancy in a variety of different crystal lattices. The chapter also focuses on the H-bonds that are formed between the purines and pyrimidines. In contrast to the narrow range of covalent bond lengths that are found within the molecules, there is considerable variation in both the length of H-bonds and their angles, a point that is emphasized in this presentation. As there is an appreciable range in the geometry of H-bonded interactions, it is likely that a greater variety of stable structures can be formed. An important variable in this connection is the variation in H-bond lengths, as the length of this bond characterizes the energy of H-bonding interactions in part. It reviews that purine and pyrimidine crystalIography underlines the diversity of the H-bonding potentiality of the nucleic acid bases; it is likely that this diversity has been utilized fully by nature in the evolution of the information-transferring system.