Elastic and hydrostatic behaviour of a zinc dietary supplement, zinc glycinate hydrate†

Coordination polymer based dietary supplement tablets are commonly consumed in our daily life and play an important role in the pharmaceutical industry. To fully understand their tableting process, their mechanical properties need to be comprehensively studied. In this work, the elastic and hydrostatic behaviour of a zinc supplement, zinc glycinate hydrate (Zn[O₂CCH₂NH₂]₂·H₂O), have been studied via density functional theory (DFT) calculations and high-pressure synchrotron powder X-ray diffraction. This material has a pseudo-layered structure and can be successfully exfoliated into nanosheets. The DFT calculated elastic moduli along the principal axes (13.84–36.11 GPa) indicate a significant elastic anisotropy of ZnG as expected for a layered system, and the directional dependent elastic modulus can be corroborated with the underlying atomic structure. In addition, the calculated B/G ratios (1.30–3.83) according to Pugh’s criterion reveal that ZnG could be brittle under uniaxial stress (B and G are bulk modulus and shear modulus, respectively). Furthermore, the measured B is ∼31 GPa, which lies in the middle of the values between inorganic dietary supplements and small organic drug crystals. These results provide some quantitative information about the tableting process of the hybrid dietary supplement which could be different from their inorganic and organic pharmaceutical counterparts.