Crystal structure of the most famous artificial sweetener determined after more than a century

Sodium saccharinate, NaC₇H₄NO₃S•xH₂O, listed in most catalogues as a dihydrate (x = 2), has been extensively used as a food additive and has constituted the basic component of the diabetics' diet for about 125 years. However, due to such factors as the instability of the crystal, the large unit cell and a very complex and heavily disordered structure, scientists have been unable to establish its composition with any certainty, until now. Dr. P. Naumov (Nat'l Inst for Mater. Sci., Japan) and his collaborators recently succeeded in the first determination of the crystal structure, by using special techniques for preserving unstable crystals during X-ray data collection. This crystal structure, which has as many as 16 formula units in the asymmetric unit (Z' = 16) as well as one of the largest unit cells, represents one of the most difficult cases for a small molecular species such as the saccharinate ion. It was found that, instead of being a dehydrate, the crystal is in fact a 1.875 hydrate, because of a structural misfit and the lack of two water molecules per asymmetric unit. The composition can be best described as Na₆₄(C₇H₄NO₃S)₆₄•120H₂O. At a meeting of the Asian Crystallographic Association held in Tsukuba, Japan, Dr. Naumov received the Best Presentation Award. For more information, see the paper, "Solid-state structure and temperature/evacuation-induced dehydration of sodium saccharinate 1.875 hydrate", P. Naumov et al., Angewandte Chemie, International Edition in English, 44, 1251 (2005).