Metal Ion Binding by Amino Acids. Potassium Hydrogen L‐Glutamate Monohydrate K(L‐GluH)·H₂O

The title compound is obtained by neutralization of aqueous solutions of L‐glutamic acid with potassium hydroxide, and crystallization from aqueous methanol. The compound shows a pH of 7 in water at ambient temperature and an optical rotation [α]²⁰_D of ‐4.30 (c = 3.0). In the crystal (orthorhombic, space group P2₁2₁2₁) the potassium ion is in a distorted trigonal‐prismatic environment of six oxygen atoms of four different amino acids and of the water molecule. No nitrogen coordination is observed. Through the bridging function of some of the α‐carboxylate oxygen atoms (O1, O2) and through complexation of the metal through the γ‐carboxylate groups (O3), a layer‐coordination polymer, with strings of potassium ions running parallel, is formed. The layers are cross‐linked by hydrogen bonds involving the ammonium and γ‐carboxylate functions as well as the water molecule.