Abstract
Trehalose dihydrate is a nonreducing disaccharide which has generated great interest in the food and pharmaceutical industries. However, it is well recognized that considerable batch to batch variation exists for supposedly identical samples, particularly in terms of the thermal response. In this investigation, two standardized forms of trehalose dihydrate were generated using two distinct crystallization pathways. The two batches were characterized using scanning electron microscopy, X-ray powder diffraction, and FTIR. The thermal responses of the two forms were then studied using modulated temperature differential scanning calorimetry (MTDSC) and thermogravimetric analysis (TGA). In particular, we describe the technique of quasi-isothermal MTDSC as a means of studying the change in equilibrium heat capacity as a function of temperature. Finally, variable temperature FTIR was utilized to assess the change in bonding configuration as a function of temperature. SEM revealed significant differences in the continuity and grain structure of the two batches. The TGA, MTDSC, and quasi-isothermal MTDSC studies all indicated significant differences in the thermal response and water loss profile. This was confirmed using variable temperature FTIR which indicated differences in bond reconfiguration as a function of temperature. We ascribe these differences to variations in the route by which water may leave the structure, possibly associated with grain size. The study has therefore demonstrated that chemically identical dihydrate forms may show significant differences in thermal response. We believe that this may assist in interpreting and hence controlling interbatch variation for this material.
Highlights
Α,α-Trehalose dihydrate (α-D-glucopyranosyl, α-D-glucopyranoside) is a nonreducing disaccharide, consisting of two α,α units of glucopyranose linked together by an α,α-1↔1-glycosidic linkage
In experiments where three endotherms have been observed, for example, in a study by McGarvey et al.,[12] the first two low temperature endotherms have been attributed to the initial partial dehydration of the dihydrate resulting in a mixture of the Tγ form and the stable anhydrate (Tβ), subsequent further dehydration of Tγ resulting in the full formation of Tβ, which melts at ca. 210 °C
Three endotherms have been observed in a study by Taylor and York,[14] where the first endotherm was ascribed to loss of water from the crystal lattice, the second to the melt of the Tα, and the third endotherm to the melt of the stable anhydrate Tβ
Summary
Α,α-Trehalose dihydrate (α-D-glucopyranosyl, α-D-glucopyranoside) is a nonreducing disaccharide, consisting of two α,α units of glucopyranose linked together by an α,α-1↔1-glycosidic linkage. It is apparent from these results that the rate of weight loss occurring in Th2 samples is most rapid over the temperature range corresponding to the endotherms identified in DSC studies between 90 and 125 °C, linking them to the dehydration of the dihydrate crystal. In order to support the observations obtained via scanning thermal methods, FTIR studies were conducted at a range of temperatures in order to identify structural changes to the samples on heating. Further analysis of Th2 spectra at 124 °C suggest that, on heating, Th2 samples undergo structural rearrangement from the dihydrate to another crystalline material, which our ATR-FTIR data suggests to be a mixture of the stable and unstable anhydrate This material undergoes amorphization at the lower temperatures. 30 to 116 °C, green spectra 118 to 134 °C, black spectra 136 to 198 °C)
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