Enhancement of Hydrate Stability through Substitutional Defects

Abstract

Cytosine monohydrate (CM) and anhydrate crystal forms reversibly interconvert under high temperatures or high humidity conditions. Here, we demonstrate through defect engineering the ability to expand the thermal stability range of CM through the targeted creation of quantifiable defects in low-level concentrations. Twelve different molecular dyes with a variety of core structures and charges were screened as potential dopants in CM. CM-dye phases prepared with Congo red (CR), Evans blue (EB), and Azocarmine G (AG) exhibited the highest inclusion levels (up to 1.1 wt %). In these doped isomorphous materials, each dye is presumed to substitute for 4–7 cytosine molecules within the low-rugosity (102) planes of the CM matrixes, thereby creating a quantifiable substitutional defect and an impediment to the cooperative molecular motions which enable the transformation to the anhydrate. Dehydration of materials with these engineered defects requires significantly higher temperatures and proceeds with slower kinetics compared to pure CM. The CM-dye phases also exhibit a reduction in the thermal expansion along key crystallographic axes and yield dehydration products with altered particle morphologies.

Long-Chain Bio-Based Nylon 514 Salt: Crystal Structure, Phase Transformation, and Polymerization

“…The As seen in Figure 1, hydrate-anhydrate phase transformations are complicated processes. Defining the environmental conditions to ensure that the material stays within an acceptable range is useful to minimize the risk of phase conversion during manufacturing or storage [27,28]. Moreover, the anhydrous forms and hydrates of a compound may sometimes differ greatly in terms of bulk density, hygroscopic properties, stability, and mechanical properties [29][30][31][32][33][34][35].…”