Dielectric study of the antiplasticization of trehalose by glycerol

Abstract

Recent measurements have suggested that the antiplasticizing effect of glycerol on trehalose can significantly increase the preservation times of proteins stored in this type of preservative formulation. In order to better understand the physical origin of this phenomenon, we examine the nature of antiplasticization in trehalose-glycerol mixtures by dielectric spectroscopy. These measurements cover a broad frequency range between 40 Hz to 18 GHz (covering the secondary relaxation range of the fragile glass-former trehalose and the primary relaxation range of the strong glass-former glycerol) and a temperature (T) range bracketing room temperature (220 K to 350 K). The Havriliak-Negami function precisely fits our relaxation data and allows us to determine the temperature and composition dependence of the relaxation time tau describing a relative fast dielectric relaxation process appropriate to the characterization of antiplasticization. We observe that increasing the glycerol concentration at fixed T increases tau (i.e., the extent of antiplasticization) until a temperature dependent critical "plasticization concentration" xwp is reached. At a fixed concentration, we find a temperature at which antiplasticization first occurs upon cooling and we designate this as the "antiplasticization temperature," Tant. The ratio of the tau values for the mixture and pure trehalose is found to provide a useful measure of the extent of antiplasticization, and we explore other potential measures of antiplasticization relating to the dielectric strength.

Local Mobility in Amorphous Pharmaceuticals—Characterization and Implications on Stability

“…Glycerol exerted antiplasticizing effect on the local motions in trehalose only below a critical temperature. 77 This critical temperature was found to be inversely related to the glycerol concentration. Thus, at lower glycerol concentrations, antiplasticization would occur at higher temperatures.…”

Structural and thermodynamic aspects of plasticization and antiplasticization in glassy encapsulation and biostabilization matrices

“…The impact of low-molecular weight diluents on the antiplasticization and plasticization was extensively investigated by experimental techniques probing the dynamics in the glassy state, such as inelastic neutron scattering [39,87,104,105] and dielectric spectroscopy (DES) [42,43] but also by molecular dynamics simulations [87][88][89]. These studies have mostly focussed on the trehalose-glycerol system, which is of relevance for the stabilization of sensitive pharmaceutical proteins.…”

“…These dynamic modes and their relation to pharmaceutical stability have primarily been explored for trehalose [34,39]. Using techniques, such as neutron scattering [39] and dielectric spectroscopy (DES) [40][41][42][43], it was observed that several of the dynamic modes in the glassy matrices could be partly suppressed or slowed down by the addition of limited amounts of a low-molecular weight hydrogen-bond forming diluent, such as glycerol or sorbitol. This phenomenon was identified as the antiplasticization of the matrix by the diluent [39,44].…”

The effect of complex solvents on the structure and dynamics of protein solutions: The case of Lysozyme in trehalose/water mixtures

“…Arginine being a strongly basic residue is typically found on the surface of a protein when immersed in water. However, when it is immersed in trehalose [75], a solvent less polar than water, Arginine tends to reduce the area of contact. The behavior of neutral residues however depends strongly on their spatial neighbors.…”