Three crystal-hydration methods for high-pressure cryocooling. The scale bar in each figure indicates 100 µm. (a) Oil-coating method. The method can remove excess mother liquor, which is helpful to suppress water crystallization inside crystals. The image was taken at room temperature before high-pressure cryocooling. (b) Capillary-hydration method. Crystals are grown in a capillary and are hydrated by the surrounding mother liquor. The image was taken on the beamline at 100 K after high-pressure cryocooling. (c)–(f) Capillary-shielding method. The crystal is picked up in a cryoloop and inserted into a polyester capillary which has a plug of mother liquor in the other end. (c) The crystal is hydrated by vapor diffusion between the mother liquor and the cryoloop. A small cut in the enclosing capillary facilitates pressure equilibration during pressure cryocooling. The image was taken at room temperature before high-pressure cryocooling. (d) The image of a capillary-shielded crystal on the beamline (100 K) after high-pressure cryocooling, with the polyester capillary still attached. (e) The crystal in (d) was transferred back to liquid nitrogen to remove the polyester capillary and then reloaded on the beamline (100 K). (f) Another crystal on the beamline (100 K) prepared by the capillary-shielding method. The crystal was equilibrated with 10%(v/v) glycerol solution (in deionized water) before high-pressure cryocooling. (g) The same crystal as in (f) was quickly warmed to room temperature and refrozen back to 100 K in a nitrogen gas stream. The crystal is swollen with bubbles because of the release of compressed He gas captured in the sample during high-pressure cryocooling.