Crystal structure studies of amino acids and peptides.

This chapter discusses the crystal structure studies of amino acids and peptides. It describes the structures, as elucidated by single-crystal X-ray investigations, of the crystalline amino acids and peptides. The chapter also deals with the powers and limitations of present-day X-ray diffraction techniques. This chapter illustrates that in earlier times only two amino acids and DL-alanine, one Dipeptide, and one cyclic dipeptide has been investigated, and these by X-ray diffraction techniques that were crude by present-day standards. Moreover, the conclusions drawn from these early investigations—that resulted in the formulation of the stable configurations of polypeptide chains—including the a-helix and the pleated sheet and in the derivation of detailed structures for many fibrous proteins are valid. Moreover, the advent of high-speed digital computers has been responsible for a tremendous improvement in the accuracy of crystal-structure investigations; moreover, it has resulted in a parallel increase in the complexity of the molecules.