Enhancement of Hydrate Stability through Substitutional Defects

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Cytosine monohydrate (CM) undergoes reversible interconversion with its anhydrate form under specific environmental conditions.
• Controlling phase transitions in crystalline materials is crucial for their stability and application.

Purpose of the Study:

• To investigate the potential of defect engineering in enhancing the thermal stability of cytosine monohydrate.
• To explore the use of molecular dye dopants to create quantifiable defects and impede phase transitions.

Main Methods:

• Screening of twelve molecular dyes as dopants for cytosine monohydrate.
• Preparation and characterization of CM-dye phases using techniques to quantify inclusion levels and crystal structure.
• Analysis of thermal stability, dehydration kinetics, thermal expansion, and product morphology of doped and undoped CM.

Main Results:

• CM phases doped with Congo red (CR), Evans blue (EB), and Azocarmine G (AG) showed high dye inclusion (up to 1.1 wt %).
• These doped phases exhibited increased thermal stability, requiring higher temperatures for dehydration with slower kinetics compared to pure CM.
• Engineered defects reduced thermal expansion and altered the morphology of dehydration products.

Conclusions:

• Targeted defect engineering via dye doping is an effective strategy to expand the thermal stability range of cytosine monohydrate.
• The presence of substitutional defects impedes the cooperative molecular motions necessary for anhydrate formation.
• This approach offers a method to control the solid-state transformations and properties of CM.