Thermal study of water/β-cyclodextrin interactions (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.
Energetics of Water/Cyclodextrins Interactions
Journal of Inclusion Phenomena
The heat capacities of solid γ-CD, 8.1 H2O and α-CD, 6.0 H2O have been measured between 10 and 300 K by adiabatic calorimetry. Using earlier results obtained in similar experiments with anhydrous cyclodextrins and with β-CD, 9.7 H2O, a comparative analysis has been developed. The energetic behaviours of anhydrous and hydrated cyclodextrins (CDs) have been compared in order to investigate the role of water molecules in the stabilization of the cyclodextrin's rings and on their reactivities. Calculations, based on the additivity of thermodynamic properties, provide the energetic and entropic average contributions of water molecules in each cyclodextrin. From these results, we assumed that the water–water and water–CD interactions are rather different according to the cyclodextrin. In the (β-CD, 9.7 H2O) structure, the water molecules seem to be better organised in a relatively independent network. Concerning hydrated α-CD and γ-CD, stronger water–CD interactions probably prevent a...
β-Cyclodextrin hydration: a calorimetric and gravimetric study
Thermochimica Acta, 1995
The standard heat of solvation of [I-cyclodextrin @CD) with one mole of water is determined as -10.50 kJ per mol /1CD, after measurement of the heat of dissolution of flCD samples containing various amounts of water. This value is constant in the composition range flCD nH,O, with 0 <n < I I (n is the number of water molecules attached).
Vibrational Spectroscopy, 2003
b-Cyclodextrin (b-CD) hydrate was dehydrated under vacuum at room temperature (293 K) and the changes of its IR n(OH) band profile were observed. A curve fitting with Voigt functions to the band profile was able using information obtained from difference spectra. Four different fitting strategies gave similar band components. The behavior of the integrated intensities of these components upon dehydration was the basis for an assignment of these band components. The component a 3580 cm À1 is due to water molecules in the b-CD cavity and they leave very fast the macrocycle upon dehydration. Two components at 3530 and 3289 cm À1 are assigned to OH groups retained in b-CD despite dehydration, i.e. primary and secondary OH groups. The components at 3422 and 3185 cm À1 may be associated with water molecules in the interstices among b-CD molecules and linked by hydrogen bonds with them. Nevertheless, additional contributions from primary and secondary OH groups were found for these two bands.
Crystal Growth & Design, 2011
S ome hydrophobically modified cyclodextrins have been known to have negative temperature coefficients in water. 1 A typical example is heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD, Figure 1a). Unlike other types of cyclodextrin compounds, these molecules decrease their solubilities in water and finally crystallize (Figure 1b and c). Saenger and co-workers thoroughly investigated the structures of these CDs, and they proposed that large amounts of water molecules surround the CDs at low temperatures. 2,3 By contrast, at high temperatures, the molecules are completely dehydrated or only a few water molecules are remaining in the CDs. In addition, they also found that the crystallization of these CDs in water brought large endothermic heats, especially for DM-β-CD. 4 However, considering most compounds accompany exothermic heats during their crystallizations, the endothermic heat implies that more than two processes are involved in the crystallization of DM-β-CD. Moreover, the processes of crystallization for DM-β-CD in water are not clearly understood, although the mechanism will provide an important clue to expand the application of this molecule to a variety of biomedical fields.
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.
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.
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
Current Science, 2018
Studies of water contents of solid -cyclodextrin (-CD) in crystallized and vacuum dried conditions are reported. Water contents were estimated using Karl-Fischer (KF) titration and thermo-gravimetric analysis (TGA) techniques. It was found that the water contents for crystallized and vacuum-dried samples were 6.93 and 0.86 moles of water per -CD molecule respectively. TGA studies gave values of 6.83 and 0.52 moles of water per -CD molecule respectively. The results agree with those reported from X-ray diffraction studies. Also, the molecular weight of the vacuum dried sample was determined using vapour pressure osmometry, which agrees well with the actual molecular weight of -CD. The thermal profiles of -cyclodextrin (-CD) and -CD are presented. The differential scanning calorimetry data was used to calculate specific heat at constant pressure (C p) at different temperatures (338.15-468.15 K). These results are compared with similar data for -CD and discussed in terms of motional contribution to C p values and related conformational effects.
Hydration and dehydration processes of ?-cyclodextrin: A raman spectroscopic study
Journal of Inclusion Phenomena and Molecular Recognition in Chemistry, 1996
A linear relationship between the integrated intensity of the Raman OH stretching band (IoH) and ambient humidity in equilibrium with a sample of a crystalline 13-Cyclodextrin (13CD) hydrate, for humidities between 15% and 100%, was obtained. In addition, hydration and dehydration processes were monitored by measuring IOH as a function of time. For the normally hydrated crystal, both hydration and dehydration processes present essentially continuous and similar variations with hysteresis for times shorter than 20 rain.