The self-assembling zwitterionic form of L-phenylalanine at neutral pH

The title zwitterion (2S)-2-azaniumyl-1-hydroxy-3-phenylpropan-1-olate, C9H11NO2, also known as l-phenylalanine, was characterized using synchrotron X-rays. It crystallized in the monoclinic space group P2(1) with four molecules in the asymmetric unit. The 0.62 angstrom resolution structure is assumed to be closely related to the fibrillar form of phenylalanine, as observed by electron microscopy and electron diffraction. The structure exists in a zwitterionic form in which pi-pi stacking and hydrogen-bonding interactions are believed to form the basis of the self-assembling properties.