Crystal structures of amino acids: from bond lengths in glycine to metal complexes and high-pressure polymorphs

After the discovery of X-ray diffraction by crystals, amino acids were among the first organic compounds to have their solid-state structures investigated. The Cambridge Structural Database now contains more than 3500 entries for α-amino acids alone. After a short introduction dealing with the early history of X-ray structure determination, this review provides a classification of amino acid structures, describes essential structural elements, especially hydrogen bonding preferences and coordination to metal ions, and considers recent investigations on phase transitions as the result of extreme temperatures or pressure.