Distinctly Different Glass Transition Behaviors of Trehalose Mixed with Na2HPO4 or NaH2PO4: Evidence for its Molecular Origin

Abstract

Purpose The present study is aimed at understanding how the interactions between sugar molecules and phosphate ions affect the glass transition temperature of their mixtures, and the implications for pharmaceutical formulations. Methods The glass transition temperature (Tg) and the α-relaxation temperature (Tα) of dehydrated trehalose/sodium phosphate mixtures (monobasic or dibasic) were determined by differential scanning calorimetry and dynamic mechanical analysis, respectively. Molecular dynamics simulations were also conducted to investigate the microscopic interactions between sugar molecules and phosphate ions. The hydrogen-bonding characteristics and the self-aggregation features of these mixtures were quantified and compared. Results Thermal analysis measurements demonstrated that the addition of NaH2PO4 decreased both the glass transition temperature and the α-relaxation temperature of the dehydrated trehalose/NaH2PO4 mixture compared to trehalose alone while both Tg and Tα were increased by adding Na2HPO4 to pure trehalose. The hydrogen-bonding interactions between trehalose and HPO42− were found to be stronger than both the trehalose-trehalose hydrogen bonds and those formed between trehalose and H2PO4−. The HPO42− ions also aggregated into smaller clusters than H2PO4− ions. Conclusions The trehalose/Na2HPO4 mixture yielded a higher Tg than pure trehalose because marginally self-aggregated HPO42− ions established a strengthened hydrogen-bonding network with trehalose molecules. In contrast H2PO4− ions served only as plasticizers, resulting in a lower Tg of the mixtures than trehalose alone, creating large-sized ionic pockets, weakening interactions, and disrupting the original hydrogen-bonding network amongst trehalose molecules.

Effect of water content on the glass transition temperature of mixtures of sugars, polymers, and penetrating cryoprotectants in physiological buffer

“…Compared with binary trehalose-water mixtures, the trehalose-PBS mixtures had a substantially lower glass transition temperature at low water content, which suggests that PBS salts impair the glass forming ability of trehalose. This result is consistent with other studies on the effects of PBS and similar physiological buffers on the glass transition temperature of trehalose mixtures [ 31 , 37 , 44 , 46 ].…”

Cryoprotectant Toxicity: Facts, Issues, and Questions

“…Ca 2+ and Mg 2+ have been shown to increase the glass transition temperature of glycerol, 151 and HPO 4 2− has been shown to increase the glass transition temperature of trehalose. 152 As with the comparison of EG and PG, kosmotropes could assist CPA vitrification by weak hydrogen bonding, leaving more water available for hydration. Inadvertent kosmotropic enhancement may already be implemented by the use of carrier solutions, which can reduce CPA toxicity without reducing CPA concentration.…”

Effects of Water on Structure and Dynamics of Trehalose Glasses at Low Water Contents and its Relationship to Preservation Outcomes

“…The high level of interconnection among trehalose molecules can result in trehalose clusters of various sizes 22 23 . Therefore, we calculated the numbers of large and small clusters comprised of only trehalose molecules at different temperatures.…”

“…Hydrogen bonds in the aqueous trehalose mixtures were identified by the geometric criteria. A certain aggregate between two oxygen atoms was regarded as an H-bond only if the distance between them did not exceed 3.5 Å, which is the position of the first minimum of the radial distribution function ( g oo ( r )), and the angle O-H···O was greater than 150°, based on the preferential linearity of H-bonds 23 32 .…”