Thermal Structure Transformation of Methylammonium Vanadate and it's Application as a Negative Staining Reagent for Observing SARS-CoV-2

Abstract

The solid-state thermal structure transformation of methylammonium vanadate, (CH₃NH₃)VO₃, from -150 °C to 350 °C is reported. Variable-temperature X-ray single-crystal structure analysis at 23, 0, -50, -100, and -150 °C reveal (CH₃NH₃)VO₃ comprises of methylammonium cations and "snake-like" ([VO₃]^-)_n anion chains propagating along the c-direction in the Pna2₁ space group. In between -150 and -100 °C, we observe a reversible structural transformation due to the re-orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V₂O₅ is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS-CoV-2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy.

Keywords: Negative staining reagents; Polyoxometalates; Polyoxovanadates; Structure elucidation; Thermochemistry.