Solid-state properties of creatine monohydrate

Creatine monohydrate (CM) is a nutritional supplement and an ergogenic aid for athletes. It appears to increase lean body mass, high-intensity power output and strength in healthy humans. The crystal structure of creatine monohydrate has previously been reported. However, little information is available on its solid-state properties. In this investigation, creatine monohydrate was subjected to Thermal Analyses, Karl-Fisccher Titrimetry (KFT), Scanning Electron Microscopy (SEM), and Variable Temperature X-ray Powder Diffractometry (VTXRD) to characterize its solidstate properties. The results of this study suggested that commercially available creatine monohydrate dehydrates at about 97-125°C. A phase transition after dehydration was confirmed by X-ray diffraction studies. This dehydrated phase at a temperature above 230°C undergoes intramolecular cyclization with a loss of an additional mole of water to form creatinine. Creatinine finally melts with decomposition at about 290°C. VTXRD, confirmed that the above solid-state thermal transformation was kinetically driven, and occurred within a narrow temperature range. Mass Spectrometric (MS) studies further indicated a possible dimerization of creatinine formed during the solid-state transformation.