[Adsorption Behavior of Water on Virgin and Modified Cyclodextrin]

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Cyclodextrins (CD) are cyclic oligosaccharides with a hydrophobic cavity and hydrophilic exterior, widely used in drug delivery and food industries.
• Hydroxypropylation (HP) modifies cyclodextrins, altering their solubility and interaction properties.
• Understanding water molecule interactions with cyclodextrins is crucial for optimizing their applications.

Purpose of the Study:

• To investigate and compare the water adsorption behavior of parent cyclodextrins (CD) and hydroxypropylated cyclodextrins (HP-CD).
• To elucidate the structural and thermodynamic differences in water interactions between CD and HP-CD.
• To provide data for the rational design of cyclodextrin-based systems involving water.

Main Methods:

• Ad-desorption isotherm analysis to quantify water uptake.
• Determination of molar hydration ratio (R-value) for various cyclodextrins.
• X-ray diffraction (XRD) to assess structural changes under different water activities.
• Calculation of sorption entropy and heat of sorption.

Main Results:

• HP-CD demonstrated significantly higher water adsorption capability than CD.
• Ad-desorption isotherms of CD exhibited hysteresis, unlike HP-CD.
• Molar hydration ratios (R-values) were higher for HP-CDs (12.5-16.7) compared to CDs (7.1-13.5).
• XRD patterns revealed amorphous structures for HP-CDs at various water activities, contrasting with CDs.
• Thermodynamic parameters (sorption entropy and heat of sorption) were calculated.

Conclusions:

• Hydroxypropylation enhances the interaction of cyclodextrins with water molecules.
• The structural modifications induced by hydroxypropylation lead to distinct water sorption behaviors.
• These findings are valuable for optimizing the use of cyclodextrins in moisture-sensitive applications.