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X-ray Diffraction of Water in Polyvinylpyrrolidone
C J Benmore1, S R Benmore2, S K Wilke1,2
1X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Molecular Pharmaceutics
|June 12, 2023
Summary
Polyvinylpyrrolidone (PVP) water sorption was studied using X-ray scattering. Water molecules prefer bonding with each other over PVP, forming isolated clusters at higher concentrations.
Area of Science:
- Polymer science
- Materials science
- Physical chemistry
Background:
- Polyvinylpyrrolidone (PVP) is a hydrophilic polymer widely used in pharmaceutical formulations as an excipient.
- Understanding water-PVP interactions is crucial for predicting drug stability and release profiles.
Purpose of the Study:
- To investigate the structural changes and water sorption dynamics in PVP under varying humidity conditions.
- To quantify water-water and water-PVP interactions using advanced scattering techniques and computational modeling.
Main Methods:
- Time-resolved high-energy X-ray scattering experiments on PVP pellets at different humidity levels.
- Scattering measurements on PVP powders with controlled water content (2-12.3 wt % H2O).
- Empirical Potential Structure Refinement (EPSR) modeling to analyze structural data.
Main Results:
- A two-phase exponential decay in water sorption was observed.
- A peak at 2.85 Å in the differential pair distribution function indicates carbonyl oxygen-water oxygen hydrogen bonding.
- EPSR models revealed linear relationships between coordination numbers and water content, with a preference for water-water hydrogen bonding.
Conclusions:
- PVP structure evolves continuously with increasing water content.
- Water molecules exhibit a stronger preference for hydrogen bonding with each other than with PVP carbonyl groups.
- At approximately 12 wt % H2O, each water molecule is, on average, hydrogen-bonded to one other water molecule.
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