β-Cyclodextrin hydration: a calorimetric and gravimetric study (original) (raw)
Related papers
1998
Heat capacities of-CD9.7H2O were measured by adiabatic calorimetry in the temperature range 10-300 K. Differential scanning calorimetry was used to follow the evolution of the thermal behaviour versus hydration ratio between 170 and 300 K. At least three different behaviours were observed, according to the number, n, of water molecules: 0 < n < 7, 7 < n < 10, and n > 10. These macroscopic results are discussed in terms of organization differences between the most or the least hydrated-CD. The structuring effect of the hydration water molecules is emphasised. The existence of two energetically distinct-CD hydrates (n < 10 and n > 10) seems to be confirmed. This hypothesis is discussed in comparison with previous spectroscopic and structural studies.
α -Cyclodextrin – Water binary system. New data on dehydration of α -cyclodextrin hexahydrate
The Journal of Chemical Thermodynamics, 2016
Cyclodextrins (CDs) are torous-like macrocycles composed of glucopyranose units. Due to their shapes, they are capable to include a wide variety of organic and inorganic guest molecules with formation of inclusion complexes in solid and liquid state. CDs crystallize from aqueous solution as hydrates (water molecules are located in the cavities and fill intermolecular space). The process of inclusion complex formation is, in fact, a replacement reaction of water molecules by hydrophobic guest molecules. Given the important role of water in the formation of CDs inclusion complexes, and the fact that the main commercial forms of cyclodextrins are the hydrated ones, the study of temperature (T)-composition (x) phase diagram of cyclodextrin-water binary system is of scientific and practical interest. This article reports an experimental study of the T, x-phase diagram of a-cyclodextrin-water binary system under isochoric conditions by differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Powder X-ray diffraction was used to identify the structures of different a-CD hydrates and to follow their phase transformations. It was shown that dehydration processes in isochoric and isobaric (open air) conditions differ significantly. In the temperature range of approximately 351 K-359 K the a-CD hexahydrate of known Form I structure transforms into the a-CDÁ5.3H 2 O of unknown structural type. It is found that the solid solution on the base of the structure a-CD hexahydrate Form I is formed within the limits of a-CDÁ6.1H 2 O-a-CDÁ2.1H 2 O. The above findings give new insight on dehydration processes in the a-CD-water binary system. Thermodynamic parameters of the dehydration process are derived from DSC data and tensimetric measurements of vapor pressure over a-CDÁ6.1H 2 O by static method. The data obtained represent new and valuable information which can be very helpful when choosing conditions of the gas-phase synthesis of a-CD complexes. Ó 2016 Elsevier Ltd. and inorganic guest molecules [1]. For this reason CDs inclusion complexes are widely used in the pharmaceutical and food industries, cosmetics, personal care, household and toiletry products, agricultural and chemical industries, in analytical separation methods, ets [1-3]. Water plays an important role in a formation of the CDs inclusion complexes. The process of complex formation is essentially a replacement reaction of water molecules located in CD cavities by hydrophobic guest molecules. The energy gain provides the spontaneity of these processes. Cyclodextrins form stable hydrates with varying water content. Currently five hydrates of a-CD are known: a-CDÁ6H 2 O (Form I) [4-6], a-CDÁ6H 2 O (Form II) [7], a-CDÁ7.57H 2 O (Form III) [8], a-CDÁ11H 2 O (Form IV) [9], and a-CDÁ6.8H 2 O (Form Ib) [10]. Forms I, II, III and Ib are based on differently hydrated cage-like packed a-CD molecules. The
Thermal study of water/β-cyclodextrin interactions
Solid State Ionics, 1993
It is shown that water/13-cyclodextrin system has a complex behaviour above room temperature, and displays phenomena which may be separately analyzed under carefully chosen conditions: in dry atmosphere, and/or below 60 ° C, the release of water occurs much faster than the expected structural transformation from the hydrated to the dehydrated structure. It is argued that this transition contributes substantially to the endothermic DSC peak usually attributed to dehydration. After completing its first transition to the dehydrated structure, a water grown sample undergoes a dramatic (~ 15%) and irreversible expansion, which apparently does not modify the crystal structure.
Hydration of beta-cyclodextrin: A molecular dynamics simulation study
Journal of Computer-Aided Molecular Design, 2000
We study by molecular dynamics simulations the hydration of β-cyclodextrin. Our simulations show that within these barrel-shaped molecules hydrophobicity dominates, while at the top and bottom sides of the barrel interactions with water are mostly hydrophilic in nature. These results agree with crystallographic data at 120 K and, in particular, with the spontaneous hydration process of a cyclodextrin crystal in wet atmosphere. The predicted structure of the hydration shells is discussed and compared with previous molecular mechanics calculations which report an overall hydrophobic behavior. Moreover, the temperature dependence of the hydration process is discussed.
Hydration of β-cyclodextrin: A molecular dynamics simulation study
Journal of Computer-aided Molecular Design, 2000
We study by molecular dynamics simulations the hydration of β-cyclodextrin. Our simulations show that within these barrel-shaped molecules hydrophobicity dominates, while at the top and bottom sides of the barrel interactions with water are mostly hydrophilic in nature. These results agree with crystallographic data at 120 K and, in particular, with the spontaneous hydration process of a cyclodextrin crystal in wet atmosphere. The predicted structure of the hydration shells is discussed and compared with previous molecular mechanics calculations which report an overall hydrophobic behavior. Moreover, the temperature dependence of the hydration process is discussed.
Inorganic salt modulation of the aqueous solubility of betabetabeta-cyclodextrin
a-, /~-and ~-Cyclodextrins have been shown to exist as aggregates in solution bound together by a network of hydrogen bonds. Removal of this network by ionisation of the hydroxyl groups leads to a greatly increased solubility and removal of aggregation. The presence of aggregates in solution of structure breaking solutes in which the solubility of/Lcyclodextrin is greatly enhanced, leads to a proposal that the abnormally low solubility of fl-CD may be explained by the presence of aggregates and the unfavourable interaction of these aggregates with the hydrogen bonded structure of water.
Inorganic salt modulation of the aqueous solubility of β-cyclodextrin
Supramolecular Chemistry, 1993
a-, /~-and ~-Cyclodextrins have been shown to exist as aggregates in solution bound together by a network of hydrogen bonds. Removal of this network by ionisation of the hydroxyl groups leads to a greatly increased solubility and removal of aggregation. The presence of aggregates in solution of structure breaking solutes in which the solubility of/Lcyclodextrin is greatly enhanced, leads to a proposal that the abnormally low solubility of fl-CD may be explained by the presence of aggregates and the unfavourable interaction of these aggregates with the hydrogen bonded structure of water.
Food Chemistry, 2012
The water sorption and physical properties of freeze-dried b-cyclodextrin (BCD) and 2-hydroxypropyl-bcyclodextrin (HBCD) were studied. The stability of the inclusion complexes of these cyclodextrins with different hydrophobic ingredients, such as myristic acid and a-terpineol, was investigated as a function of the storage time and water content of the systems. Besides increasing its solubility, BCD ring modification with hydroxypropyl groups conferred amorficity to the dehydrated matrices, and modified the sorption properties and their ability to form hydrates. Both ligands decreased BCD and HBCD water adsorption, in comparison with the pure cyclodextrins. The water adsorption data and glass transition values obtained are consistent with the displacement of water molecules from the inner cavity of the CDs when the ligand is included. Encapsulation of non-polar ligands of linear hydrocarbon chain, like myristic acid, was initially incomplete, depending on the ligand/CD ratio, and increased with the time of storage and water content.