Predict the glass transition temperature and plasticization of β-cyclodextrin/water binary system by molecular...

Area of Science:

• Materials Science
• Computational Chemistry
• Physical Chemistry

Background:

• Beta-cyclodextrin (β-CD) is a cyclic oligosaccharide with diverse applications.
• Understanding the physical properties of amorphous β-CD and its mixtures is crucial for material design.
• Water's plasticizing effect on amorphous polymers is well-documented but requires specific investigation for β-CD.

Purpose of the Study:

• To investigate the glass transition temperature (Tg), diffusion behavior, and plasticization of amorphous β-CD and its water mixtures.
• To elucidate the role of water as a plasticizer in β-CD systems using molecular dynamics simulations.
• To analyze the intermolecular interactions and molecular mobility within β-CD/water mixtures.

Main Methods:

• Molecular dynamics (MD) simulations were employed using the COMPASS force field.
• Isothermal-isobaric (NPT) ensembles were used to model amorphous β-CD and its mixtures with 3%, 5%, and 10% water.
• Calculations included specific volume as a function of temperature, radial distribution functions, diffusion coefficients, and fractional free volume.

Main Results:

• Glass transition temperatures (Tg) decreased with increasing water content: 334.25 K (0% water) to 305.41 K (10% water).
• Water molecules form stronger hydrogen bonds with hydroxyl groups than acetal groups in β-CD.
• Water molecule mobility significantly increased above Tg and showed minimal change below Tg.

Conclusions:

• Water acts as an effective plasticizer for amorphous β-CD, lowering its Tg.
• The plasticization effect is attributed to increased intermolecular interactions and enhanced molecular mobility of water.
• These findings provide insights into the structure-property relationships of β-CD/water systems relevant to material science and drug delivery.