Effect of pH, counter ion, and phosphate concentration on the glass transition temperature of freeze-dried sugar-phosphate mixtures.
OBJECTIVE
The aim of the present work is to study the interaction of phosphate salts with trehalose and sucrose in freeze-dried matrices, particularly the effect of the salts on the glass transition temperature (Tg) of the sugars.


METHODS
Freeze-dried trehalose and sucrose systems containing different amounts of sodium or potassium phosphate were analyzed by differential scanning calorimetry to determine the Tg and by Fourier-transform infrared spectroscopy (FTIR) analysis to evaluate the strength of the interaction between sugars and phosphate ions.


RESULTS
Sucrose-phosphate mixtures show an increase in Tg up to 40 degrees C in a broad pH range (4-9) compared to that of pure sucrose. Sucrose-phosphate mixtures exhibit a higher Tg than pure sucrose while retaining higher water contents. Trehalose-phosphate mixtures (having a Tg of 135 degrees C at a pH of 8.8) are a better option than pure trehalose for preservation of labile materials. The -OH stretching of the sugars in the presence of phosphates decreases with increase in pH, indicating an increase in the sugar-phosphate interaction.


CONCLUSIONS
Sugar-phosphate mixtures exhibit several interesting features that make them useful for lyophilization of labile molecules; Tg values much higher than those observed for the pure sugars can be obtained upon the addition of phosphate.
Ohtake
Satoshi
S
Chemical and Biological Engineering Department, University of Wisconsin, Madison, Wisconsin 53706, USA. sohtake@students.wisc.edu
Schebor
Carolina
C
Palecek
Sean P
SP
de Pablo
Juan J
JJ
D002152:Calorimetry, Differential Scanning; D005612:Freeze Drying; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013395:Sucrose / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D014199:Trehalose / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D010710:Phosphates; D014867:Water; D013395:Sucrose; D014199:Trehalose