ABSTRACT
The solid-state heating of methylammonium monomolybdate, (CH3NH3)2[MoO4] (prepared by dissolving MoO3 in an aqueous methylamine solution), in air released methylamine and water to produce (CH3NH3)6[Mo7O24] and followed by (CH3NH3)8[Mo10O34] before transformation to MoO3. We report the first single-crystal X-ray structural analysis of (CH3NH3)2- [MoO4] and (CH3NH3)6[Mo7O24] and demonstrate that the decamolybdate structure is different from that obtained from ammonium molybdates. Furthermore, (CH3NH3)6[Mo7O24] is a good negative staining reagent for transmission electron microscopy observations of viruses, such as SARS-CoV-2 and influenza virus. © 2023 The Chemical Society of Japan.
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.
ABSTRACT
Spike (S) glycoprotein of SARS-CoV2 exists chiefly in two conformations, open and closed. Most previous structural studies on S protein have been conducted at pH 8.0, but knowledge of the conformational propensities under both physiological and endosomal pH conditions is important to inform vaccine development. Our current study employed single-particle cryoelectron microscopy to visualize multiple states of open and closed conformations of S protein at physiological pH 7.4 and near-physiological pH 6.5 and pH 8.0. Propensities of open and closed conformations were found to differ with pH changes, whereby around 68% of S protein exists in open conformation at pH 7.4. Furthermore, we noticed a continuous movement in the N-terminal domain, receptor-binding domain (RBD), S2 domain, and stalk domain of S protein conformations at various pH values. Several key residues involving RBD-neutralizing epitopes are differentially exposed in each conformation. This study will assist in developing novel therapeutic measures against SARS-CoV2.