Insights into the dehydration behavior of thiamine hydrochloride (vitamin B₁) hydrates: Part I

Thiamine hydrochloride (Vitamin B₁, THCl) can exist as a nonstoichio-metric hydrate (NSH) and as a hemihydrate (HH). NSH can contain up to ∼1 molar equivalent of water and be dehydrated to an isomorphic desolvate (ID) with minimal change in lattice structure. Crystallographic and spectroscopic techniques were used to characterize the influence of structure and mobility on NSH dehydration. Dehydration was accompanied by lattice contraction, as noted by a decrease in the d-spacings. Dehydration also led to the development of surface cracks parallel to the (101̄) and (102̄) planes in the NSH single crystal, as observed by hot stage microscopy. Step-wise dehydration of NSH produced gradual shifts in XRPD and SSNMR peaks, indicating that NSH (with ∼1 mole water) and ID represent the two extremes of a continuum in the hydration state. Variable temperature ¹³C SSNMR studies showed that water molecules move rapidly at room temperature within the NSH crystal lattice, and the thiamine molecules transiently exist in distinct hydrated and dehydrated states. It is hypothesized that, despite the lack of continuous hydration channels in the NSH crystal lattice, cooperative deformation of the thiamine molecules allows a nondisruptive departure of water molecules from the lattice during dehydration.