Characteristics of Crystal Transitions Among Pseudopolymorphs

Abstract

Reversible phase transitions among the pseudopolymorphs of nucleoside and nucleotide hydrates were induced by humidity (vapor pressure of water) and temperature conditions. A single crystal state at a high frequency was retained after these transitions, and the original, the final, and in some cases the intermediate crystal structures were determined. On the basis of the determined structures and information from complementary methods (e.g., Raman spectroscopy and molecular dynamics simulation), the characteristics of the transitions (i.e., conformational changes, sliding of molecular layers, and cyclic and bifurcated transitions) were revealed. The transition schemes and mechanisms are discussed.