Comparative relaxation dynamics of glucose and maltitol.
OBJECTIVE
To demonstrate the utility of differential scanning calorimetry (DSC) for determining activation energy landscape in amorphous pharmaceutical systems throughout the sub-Tg and Tg regions.


METHODS
DSC was employed to determine the effective activation energies (E) of the relaxation in sub-Tg and Tg regions as well as the sizes of cooperatively rearranging regions in glassy maltitol and glucose.


RESULTS
It has been found that in the sub-Tg region E decreases with decreasing T reaching the values approximately 60 (glucose) and approximately 70 (maltitol) kJ mol(-1) that are comparable to the literature values of the activation energies for the beta-relaxation. In the Tg region E decreases (from approximately 250 to approximately 150 kJ mol(-1) in maltitol and from approximately 220 to approximately 170 kJ mol(-1) in glucose) with increasing T as typically found for the alpha-relaxation. From the heat capacity measurements the sizes of cooperatively rearranging regions have been determined as 3.1 (maltitol) and 3.3 (glucose) nm.


CONCLUSIONS
DSC can be used for evaluating the energy landscapes. The E values for maltitol are somewhat greater than for glucose due to the added impeding effect of the bulky substitute group in maltitol. The comparable sizes of the cooperatively rearranging regions suggest a similarity of the heterogeneous glassy structures of the two compounds.
Vyazovkin
Sergey
S
Department of Chemistry, University of Alabama at Birmingham, 901 S. 14th Street, Birmingham, AL 35294, USA. vyazovkin@uab.edu
Dranca
Ion
I
D002152:Calorimetry, Differential Scanning; D002240:Carbohydrate Sequence; D005947:Glucose / Q000737:chemistry*; D007202:Indicators and Reagents; D008320:Maltose / Q000031:analogs & derivatives* / Q000737:chemistry; D008969:Molecular Sequence Data; D011143:Polyvinyl Chloride; D013402:Sugar Alcohols / Q000737:chemistry*; D013696:Temperature
D007202:Indicators and Reagents; D013402:Sugar Alcohols; D008320:Maltose; D011143:Polyvinyl Chloride; C010745:maltitol; D005947:Glucose