Investigations into the polymorphic properties of N,N-dimethyltryptamine by X-ray diffraction and differential scanning calorimetry

Abstract

The powerful psychoactive features of N,N-dimethyltryptamine (DMT) have sparked the imagination of many research disciplines for several decades. One of the key chemical features associated with compound identity is the determination of melting points. The descriptions of both melting points and morphology associated with DMT free base have long been a source of interest and discussion, especially when considering that these values encountered in the scientific literature range dramatically between 38–40 °C and 73–74 °C, respectively. Such variations in reported melting points suggest that DMT may exist in two or more polymorphic forms and it was the aim of this study to examine the potential polymorphism of DMT via X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC), including fast scan DSC. DMT samples were prepared following extraction from Mimosa tenuiflora inner barks or by laboratory synthesis and then its crystals were recrystallized from solutions of the alkaloid using either hexane or acetonitrile. Irrespective of source, crystals originating from synthesis were predominantly white crystals obtained using crystallization from hexane, whereas yellow samples following recrystallization with acetonitrile. Irrespective of source or solvent, two polymorphs appeared to exist with melting points, determined by DSC, of 57 °C to 58 °C for Form I and 45 °C to 46 °C for Form II. Estimates for their enthalpies were 91.9 ± 2.4 J g− 1 for Form I and 98.3 ± 2.8 J g− 1 for Form II. Form II converted to Form I during DSC; conversion was thus prevented by fast scanning rates of 100 °C min− 1. A transition temperature (Tg) in the range − 21 °C (2 °C min− 1) to − 13 °C (100 °C min− 1) was determined depending on DSC scanning rate. Its closeness to the melting point indicates a tendency of Form II to convert to Form I on storage, a phenomenon that was also facilitated by grinding. This study indicates that the presence of differently colored DMT free base crystals obtained from recrystallization might also point towards the existence of polymorphs rather than just the presence of impurities.