The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: A revision

Abstract

Saccharides are still commonly isolated from biological feedstock by crystallization from aqueous solutions. Precise thermodynamic data on solubility are essential to optimize the downstream crystallization process. Solubility modeling, in turn, requires knowledge of melting properties. In the first part of this work, following our previous work on amino acids and peptides, D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were investigated with Fast Scanning Calorimetry (FSC) in a wide scanning rate range (2000 K·s−1 to 10000 K·s−1). Using the experimental melting properties of saccharides from FSC allowed successfully modeling aqueous solubility for D-sucrose and D-α-galactose with the equation of state PC-SAFT. This provides cross-validation of the measurement methods to determine accurate experimental melting properties with FSC. Unexpectedly, the experimental FSC melting temperatures, extrapolated to zero scanning rates for thermal lag correction, were higher than results determined with DSC and available literature data. To clarify this inconsistency, FSC measurements towards low scanning rates from 10000 K·s−1 to 1 K·s−1 (D-α-glucose, D-β-fructose, D-sucrose) overlapping with the scanning rates of DSC and literature data were combined. At scanning rates below 1000 K·s−1, the melting properties followed a consistent non-linear trend, observed in both the FSC and the literature data. In order to understand the non-linear decrease of apparent melting temperatures with decreasing heating rate, the endothermic peaks were investigated in terms of isoconversional kinetics. The activation energies in the non-linear dependency region are in the range of $$300<{E}_{A}< 600 {\text{kJ}}\bullet {\text{mo}}{\text{l}}^{-1}$$ 300 < E A < 600 kJ ∙ mol - 1 . These values are higher than the enthalpy of sublimation for D-α-glucose, indicating that the non-linear behavior does not have a physical nature but attributes to chemical processes corresponding to the decomposition of molecular compounds within the crystal lattice before melting. The melting properties reported in the literature, commonly determined with conventional methods such as DSC, lead to inaccurate results due to the decomposition of these biomolecules at low heating rates. In addition, the FSC results at lower scanning rates coincide with results from DSC and literature in the overlapping scanning rate range, further validating the accuracy of FSC measurements to determine reliable melting properties of thermally labile biomolecules. The experimental FSC melting properties determined at higher scanning rates are considered as the correct equilibrium melting properties, which are not influenced by any chemical processes. The combination of FSC and PC-SAFT opens the door to model solubility of solid compounds that commonly decompose before melting.

Thermal dehydration of d-glucose monohydrate in solid and liquid states

“…When the sample was heated from room temperature to 343 K at b = 10 K min À1 without an isothermal holding section and subsequently to 423 K at b = 2 K min À1 with the 15 min isothermal holding sections at each 10 K (Fig. S6, ESI †), the XRD pattern at 353 K differed from that of DG-MH, and the XRD peaks disappeared between 413 and 423 K, which correspond to the melting point of anhydride (literature value: 412-448 K; [34][35][36][37][38][39][40][41][42] this study: 424.1 AE 0.4 K (Table S2, ESI †)) (Fig. S6(a), ESI †).…”

“…Two polymorphs of glucose anhydride are known as aand b-phases, with melting points at 412-448 K and 419-429 K, respectively. [34][35][36][37][38][39][40][41][42] In addition, amorphous D-glucose is formed by the quenching of its melt, which has a T g of 308-315 K. [35][36][37]41,[43][44][45] Thus, the anhydrate product produced during the thermal dehydration of DG-MH can exhibit a complex phase relationship and influence the thermal dehydration pathway and kinetics.…”

Determination of Melting Parameters of Cyclodextrins Using Fast Scanning Calorimetry

“…Native cyclodextrins (CDs) are pharmaceutically important biomolecules, which applications require a knowledge of their melting parameters. Melting points and fusion enthalpies are essential parameters used in theoretical models for prediction of solubility [ 1 , 2 , 3 ] and in correlations with dissolution rates [ 4 , 5 ], which are key physical values for pharmaceuticals [ 6 , 7 ]. CDs are used as excipients enhancing the solubility and dissolution rate of active pharmaceutical ingredients [ 8 , 9 ].…”

“…A state-of-the-art method for determination of melting parameters for compounds of low thermal stability is fast scanning calorimetry (FSC) [ 6 , 11 , 12 , 13 ]. FSC was used to determine melting properties of thermally labile biomolecules: proteins [ 14 ], peptides [ 15 ], amino acids [ 5 ], pharmaceuticals [ 16 , 17 ], mono and disaccharides [ 1 ], and nucleobases [ 18 ]. This method uses special chip sensors that are both sample holders and electrical circuits for sample heating and determination of its temperature and heat flow at scanning rates of several thousand K per second due to the extremely low addenda heat capacity and sample size [ 19 ].…”

“…FSC method was applied to find the scanning rate above which this correlation breaks resulting in relatively small further shift of the observed endothermic effect by temperature. Such marginal dependence on heating rate is intrinsic to fusion of biomolecules in FSC studies [ 1 , 15 , 18 ]. From the onset temperature of main thermal effect in this range of heating rates the melting points of native CDs were determined.…”