Phase transition of L ‐Ser monohydrate crystal studied by 13 C solid‐state NMR

We used gravimetric analysis (GA) and 13 C solid‐state nuclear magnetic resonance (NMR) to study solid‐phase transition from the transparent single crystal of L ‐serine ( L ‐Ser) monohydrate to a turbid powder. We found that L ‐Ser monohydrate loses water molecules and transforms into an anhydrate, thus experimentally demonstrating Frey's assumption ( Acta Cryst. , B29, 876, 1973). Application of a handmade cross‐polarization (CP) NMR probe with a saddle‐type coil to the oriented crystal of the L ‐Ser monohydrate revealed the dehydration mechanism. Furthermore, the chemical shift tensor components of the carboxyl carbon in L ‐Ser monohydrate were determined. The difference in the tensor component of δ 22 between the monohydrate and anhydrate forms was more than 7 ppm, probably owing to differences in the hydrogen‐bonding structure of each form. Copyright © 2006 John Wiley & Sons, Ltd.