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Related Experiment Videos

Enthalpy relaxation in binary amorphous mixtures containing sucrose

S L Shamblin1, G Zografi

  • 1University of Connecticut, School of Pharmacy U-92, Storrs 06269, USA.

Pharmaceutical Research
|January 19, 1999
PubMed
Summary
This summary is machine-generated.

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Additives reduce sucrose molecular mobility below its glass transition temperature (Tg). Co-lyophilized mixtures showed decreased enthalpy relaxation compared to pure amorphous sucrose, indicating suppressed molecular motion.

Area of Science:

  • Physical chemistry
  • Materials science
  • Amorphous solid state science

Background:

  • Amorphous solids exhibit molecular mobility below their glass transition temperature (Tg).
  • Enthalpy relaxation is a key indicator of molecular mobility in amorphous systems.
  • Understanding molecular mobility is crucial for stabilizing amorphous pharmaceuticals and materials.

Purpose of the Study:

  • To compare enthalpy relaxation in amorphous sucrose and co-lyophilized sucrose-additive mixtures.
  • To quantify the effect of various additives on sucrose molecular mobility near its Tg.
  • To investigate the role of additive Tg in influencing sucrose mobility.

Main Methods:

  • Preparation of amorphous sucrose and co-lyophilized sucrose-additive mixtures (PVP, PVPNA, dextran, trehalose) via lyophilization.

Related Experiment Videos

  • Differential scanning calorimetry (DSC) to measure enthalpy recovery endotherms after aging.
  • Comparison of enthalpy relaxation in co-lyophilized mixtures versus a physical mixture of sucrose and PVP.

    • Main Results:

    • Co-lyophilized mixtures exhibited reduced enthalpy relaxation compared to pure amorphous sucrose.
    • The order of reduced relaxation was: dextran ≈ PVP > PVPNA > trehalose.
    • Calculated equilibrium enthalpy changes (ΔH∞) were consistent across sucrose and mixtures, aligning with long-term aging data.

    Conclusions:

    • Additives with Tg > sucrose Tg reduce sucrose molecular mobility below Tg.
    • Molecular dispersion, even at 10% additive, significantly lowers sucrose mobility.
    • Coupling of molecular motions via interactions between sucrose and additives explains the observed reduction in mobility.