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Lee J.W.,University of Illinois at Urbana - Champaign | Thomas L.C.,DSC Solutions LLC | Schmidt S.J.,University of Illinois at Urbana - Champaign
Journal of Agricultural and Food Chemistry | Year: 2011

Thermodynamic melting occurs at a single, time-independent temperature with a constant enthalpy value. However, substantial variation in the melting parameters (Tm onset, Tm peak, and ΔH) for sucrose, glucose, and fructose has been reported in the literature. Although a number of explanations have been put forth, they do not completely account for the observed variation. Thus, this research was performed to elucidate the fundamental mechanism underlying the loss of crystalline structure in the sugars using both thermal (Part I) and chemical (Part II) analysis approaches. A strong heating rate dependency observed in the melting parameters for the sugars implies the occurrence of a kinetic process during the loss of crystalline structure. The difference in heat capacity and modulated heat flow amplitude in the stepwise quasi-isothermal modulated differential scanning calorimetry experiments for the sugars compared to indium and mannitol (thermodynamic melting comparison materials) strongly suggests thermal decomposition as the kinetic process responsible for the loss of crystalline structure, which is the critical difference between our conclusion and others. We propose the term "apparent melting" to distinguish the loss of crystalline structure due to a kinetic process, such as thermal decomposition, from thermodynamic melting. © 2010 American Chemical Society. Source


Lee J.W.,University of Illinois at Urbana - Champaign | Thomas L.C.,DSC Solutions LLC | Jerrell J.,University of Illinois at Urbana - Champaign | Feng H.,University of Illinois at Urbana - Champaign | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2011

High performance liquid chromatography (HPLC) on a calcium form cation exchange column with refractive index and photodiode arrary detection was used to investigate thermal decomposition as the cause of the loss of crystalline structure in sucrose. Crystalline sucrose structure was removed using a standard differential scanning calorimetry (SDSC) method (fast heating method) and a quasi-isothermal modulated differential scanning calorimetry (MDSC) method (slow heating method). In the fast heating method, initial decomposition components, glucose (0.365%) and 5-HMF (0.003%), were found in the sucrose sample coincident with the onset temperature of the first endothermic peak. In the slow heating method, glucose (0.411%) and 5-HMF (0.003%) were found in the sucrose sample coincident with the holding time (50 min) at which the reversing heat capacity began to increase. In both methods, even before the crystalline structure in sucrose was completely removed, unidentified thermal decomposition components were formed. These results prove not only that the loss of crystalline structure in sucrose is caused by thermal decomposition, but also that it is achieved via a time-temperature combination process. This knowledge is important for quality assurance purposes and for developing new sugar based food and pharmaceutical products. In addition, this research provides new insights into the caramelization process, showing that caramelization can occur under low temperature (significantly below the literature reported melting temperature), albeit longer time, conditions. © 2010 American Chemical Society. Source


Chakravarty P.,Genentech | Bates S.,Triclinic Laboratories Inc. | Thomas L.,DSC Solutions LLC
Molecular Pharmaceutics | Year: 2013

GNE068, a small organic molecule, was obtained as an amorphous form (GNE068-A) after isolation from ethanol and as a partially disordered form (GNE068-PC) from ethyl acetate. On subsequent characterization, GNE068-PC exhibited a number of properties that were anomalous for a two phase crystalline-amorphous system but consistent with the presence of a solid state phase having intermediate order (mesomorphous). Modulated DSC measurements of GNE068-PC revealed an overlapping endotherm and glass transition in the 135-145 C range. ΔH of the endotherm showed strong heating rate dependence. Variable temperature XRPD (25-160 C) revealed structure loss in GNE068-PC, suggesting the endotherm to be an "apparent melt". In addition, gentle grinding of GNE068-PC in a mortar led to a marked decrease in XRPD peak intensities, indicating a "soft" crystalline lattice. Computational analysis of XRPD data revealed the presence of two noncrystalline contributions, one of which was associated with GNE068-A. The second was a variable component that could be modeled as diffuse scattering from local disorder within the associated crystal structure, suggesting a mesomorphous system. Owing to the dominance of the noncrystalline diffuse scattering in GNE068-PC and the observed lattice deformation, the mesomorphous phase exhibited properties consistent with a conformationally disordered mesophase. Because of the intimate association of the residual solvent (ethyl acetate) with the lattice long-range order, loss of solvent on heating through the glass transition temperature of the local disorder caused irrecoverable loss of the long-range order. This precluded the observation of characteristic thermodynamic mesophase behavior above the glass transition temperature. © 2013 American Chemical Society. Source


Lee J.W.,University of Illinois at Urbana - Champaign | Thomas L.C.,DSC Solutions LLC | Schmidt S.J.,University of Illinois at Urbana - Champaign
Journal of Agricultural and Food Chemistry | Year: 2011

The loss of crystalline structure in sucrose, glucose, and fructose has been shown to be due to the kinetic process of thermal decomposition (termed apparent melting), rather than thermodynamic melting. The purpose of this research was to investigate whether or not it is possible to scan quickly enough to suppress the kinetic process of thermal decomposition and reach the thermodynamic melting temperature of these sugars using a new rapid-scanning DSC. Indium, a thermodynamic melting material, and sucrose, glucose, and fructose were analyzed at three heating rates from 1 to 25 °C/min using standard DSC and at seven heating rates from 50 to 2000 °C/min using rapid-scanning DSC. Thermodynamic melting was achieved when the onset temperature (Tm onset) of the endothermic peak leveled off to a constant value independent of heating rate. The Tm onset for indium was constant (156.74 ± 0.42 °C) at all heating rates. In the case of fructose, the Tm onset increased considerably until a heating rate of approximately 698 °C/min, after which the average Tm onset for the remaining three heating rates was constant at 135.83 ± 1.14 °C. Thus, 135.83 °C is proposed to be the thermodynamic melting temperature of fructose. It is important to note that the heating rate at which this thermodynamic melting temperature is achieved is most likely influenced by the type and amount of trace components (e.g., water and salts) contained in the fructose, which are known to vary widely in sugars. In the case of sucrose and glucose, thermodynamic melting temperatures were not able to be obtained, because the upper limit heating rate used was not fast enough to suppress thermal decomposition and achieve thermodynamic melting, perhaps due to the higher apparent Tm onset for sucrose and glucose compared to that for fructose. © 2011 American Chemical Society. Source


Lee J.W.,University of Illinois at Urbana - Champaign | Thomas L.C.,DSC Solutions LLC | Schmidt S.J.,University of Illinois at Urbana - Champaign
Journal of Agricultural and Food Chemistry | Year: 2011

This research investigates the effects of heating conditions used to produce amorphous sucrose on its glass transition (Tg) parameters, because the loss of crystalline structure in sucrose is caused by the kinetic process of thermal decomposition. Amorphous sucrose samples were prepared by heating at three different scan rates (1, 10, and 25 °C/min) using a standard differential scanning calorimetry (SDSC) method and by holding at three different isothermal temperatures (120, 132, and 138 °C) using a quasi-isothermal modulated DSC (MDSC) method. In general, the quasi-isothermal MDSC method (lower temperatures for longer times) exhibited lower Tg values, larger ΔCp values, and broader glass transition ranges (i.e., Tg end minus Tg onset) than the SDSC method (higher temperatures for shorter times), except at a heating rate of 1 °C/min, which exhibited the lowest Tg values, the highest ΔC p, and the broadest glass transition range. This research showed that, depending on the heating conditions employed, a different amount and variety of sucrose thermal decomposition components may be formed, giving rise to wide variation in the amorphous sucrose Tg values. Thus, the variation observed in the literature Tg values for amorphous sucrose produced by thermal methods is, in part, due to differences in the heating conditions employed. © 2011 American Chemical Society. Source

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