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Determination of the Absorption, Translocation, and Distribution of Imidacloprid in Wheat
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Characterizing Phase Separation of Amorphous Solid Dispersions Containing Imidacloprid.

Ali Mansuri1,2, Philipp Münzner3, Anrika Heermant1

  • 1Department of Biochemical and Chemical Engineering, TU Dortmund University, 44227 Dortmund, Germany.

Molecular Pharmaceutics
|March 10, 2023
PubMed
Summary

Amorphous-amorphous phase separation (AAPS) in amorphous solid dispersions (ASDs) was characterized using dielectric spectroscopy (DS). DS detected phase separation, domain size, and molecular mobility, confirming AAPS in imidacloprid-polystyrene systems.

Keywords:
amorphous phase separationconfocal fluorescence microscopydielectric spectroscopydomain sizemolecular interactionsrelaxationsolid dispersion

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Area of Science:

  • Materials Science
  • Pharmaceutical Science
  • Physical Chemistry

Background:

  • Amorphous solid dispersions (ASDs) are crucial for drug delivery, but amorphous-amorphous phase separation (AAPS) can compromise their performance.
  • Characterizing AAPS is essential for understanding and controlling the stability and efficacy of ASDs.

Purpose of the Study:

  • To develop a sensitive dielectric spectroscopy (DS) approach for characterizing AAPS in ASDs.
  • To detect AAPS, determine active ingredient (AI) domain size, and assess molecular mobility within each phase.
  • To validate DS findings using complementary techniques like confocal fluorescence microscopy (CFM).

Main Methods:

  • Dielectric spectroscopy (DS) to detect decoupled molecular dynamics (α-dynamics) of AI and polymer phases.
  • Confocal fluorescence microscopy (CFM) utilizing imidacloprid's autofluorescence for AAPS visualization.
  • Oscillatory shear rheology and differential scanning calorimetry (DSC) for thermal transitions.
  • Exploitation of interfacial and electrode polarization in DS for domain size estimation.
  • Mid-infrared spectroscopy to probe AI-polymer interactions.

Main Results:

  • DS successfully detected decoupled α-dynamics, indicating macroscopic phase separation in imidacloprid-polystyrene ASDs.
  • CFM confirmed AAPS, with domain size estimates from DS aligning well with CFM stereological analysis.
  • DSC and rheology identified the polymer's glass transition but not the AI's, consistent with phase separation.
  • Crystallization experiments showed poor inhibition of imidacloprid crystallization within the ASD, supporting AAPS.

Conclusions:

  • Dielectric spectroscopy provides a sensitive and versatile method for characterizing AAPS in ASDs.
  • The study demonstrates the utility of DS in determining domain size and molecular mobility in phase-separated systems.
  • The findings highlight the importance of AAPS in influencing ASD stability and drug crystallization behavior, paving the way for rational ASD design.