Thermodynamics of the encapsulation by cyclodextrins (original) (raw)
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Cyclodextrins: Structural, Chemical, and Physical Properties, and Applications
Polysaccharides, 2022
Due to their unique structural, physical and chemical properties, cyclodextrins and their derivatives have been of great interest to scientists and researchers in both academia and industry for over a century. Many of the industrial applications of cyclodextrins have arisen from their ability to encapsulate, either partially or fully, other molecules, especially organic compounds. Cyclodextrins are non-toxic oligopolymers of glucose that help to increase the solubility of organic compounds with poor aqueous solubility, can mask odors from foul-smelling compounds, and have been widely studied in the area of drug delivery. In this review, we explore the structural and chemical properties of cyclodextrins that give rise to this encapsulation (i.e., the formation of inclusion complexes) ability. This review is unique from others written on this subject because it provides powerful insights into factors that affect cyclodextrin encapsulation. It also examines these insights in great detail. Later, we provide an overview of some industrial applications of cyclodextrins, while emphasizing the role of encapsulation in these applications. We strongly believe that cyclodextrins will continue to garner interest from scientists for many years to come, and that novel applications of cyclodextrins have yet to be discovered.
Encapsulation of norharmane in cyclodextrin: formation of 1:1 and 1:2 inclusion complexes
Journal of Photochemistry and Photobiology B: Biology, 2005
Steady state absorption and fluorometric techniques have been used to investigate the photophysics of norharmane (NHM), a bioactive fluorophore, in aqueous as well as aqueous cyclodextrin (CD) environments. The absorption and steady state fluorescence spectral studies reveal the formation of two types of inclusion complexes between the fluorophore and b-cyclodextrin (b-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined monitoring the fluorescence data. a-and c-cyclodextrin (a-CD, c-CD) do not have appreciable effect on the spectral pattern of the fluorophore. The differential fluorimetric behavior of NHM in different CD environments has been rationalized from the variation of the relative dimensions of the probe and the CD cavities.
The Journal of Chemical Thermodynamics, 2012
The inclusion complexation of b-cyclodextrin with various surfactants, possessing the same alkyl chain length but differing in the hydrophilic headgroup, was investigated by isothermal titration microcalorimetry. Sodium dodecyl sulfate, sodium dodecyl sulfonate, dodecyltrimethylammonium bromide and dodecyl(dimethyl)amine oxide were investigated. The major aim of this study was to elucidate the effects of temperature and the nature of the headgroup on the complex formation. Thermometric titrations were effected between the temperatures (288 and 348) K. The results provided the stoichiometry, the equilibrium constant and the reaction enthalpy of complexation. Changes in Gibbs energy, entropy and van't Hoff enthalpy were additionally calculated.
The Journal of Physical Chemistry B, 2002
Steady-state, time-resolved fluorescence spectroscopy and Molecular Mechanics (MM) were used to study the inclusion complexes of Diethyl 2,6-naphthalenedicarboxylate (DEN) with Rand-cyclodextrins (CDs). The ratio, R, of intensities of two bands that are sensitive to the medium polarity and the average of lifetime, <τ>, which is more sensitive to the medium microviscosity surrounding the guest molecule, were obtained as a function of the CD concentration and temperature. Stoichiometries, formation constants, and the changes of enthalpy and entropy upon inclusion were also obtained. The complexes prefer 1:2 (DEN:CD) stoichiometries. MM calculations were employed to study the formation of different complexes of DEN with both Rand CDs. For the most stable structure of 1:1 complexes, an important portion of DEN is outside CD cavity, making it possible to stabilize them by adding another CD. Driving forces for 1:2 inclusion processes are dominated by nonbonded van der Waals DEN-CD interactions. Nevertheless, due to the different geometry of the 1:2 complexes, an important electrostatic interaction appears between both CDs in the DEN: CD 2 complex that does not exist between RCDs in the DEN:RCD 2 complex. Most of this contribution is due to the intermolecular hydrogen bonding formation between secondary hydroxyl groups of both CDs.
Cyclodextrin inclusion complexation and pharmaceutical applications
ScienceAsia, 2020
Cyclodextrins are widely used in pharmacy, chemistry and other scientific disciplines, due to their unique properties which are consequences of the special geometries of these compounds. The cyclic arrangements of glucopyranose rings form structures where small and medium-sized molecules can be included. This inclusion reaction is of high interest, because it may change the physico-chemical properties of the guest molecules and allows the application of the involved compounds like drugs for a better delivery. Another important feature is the fact, that a large number of cyclodextrin derivatives is existing, with different affinities to the guest molecules, different thermodynamic properties and consequently a broad variety of applications. In the present review a short overview will be given about the various structures, the applications, in particular as drug carriers.
‘Novel trends in cyclodextrins encapsulation. Applications in food science’
Current Opinion in Food Science
Cyclodextrins (CDs) are cyclic oligosaccharides composed of linked glucopyranose subunits. The main property of CDs is that their hydrophobic inner cavity forms inclusion complexes with a wide range of guest molecules, while the hydrophilic exterior enhances CD solubility in water. Because of their molecular inclusion capability, the properties of the materials with which they complex can be significantly modified. Particularly, solubility and stability of bioactive compounds to be used as nutraceuticals, could be improved by encapsulation in CDs. The available thermodynamic data are consistent with an exothermic and spontaneous inclusion processes. Phase solubility studies in liquid systems along with studies of physical properties of solids complex, help to elucidate complex stoichiometry and guest-CD interactions. The use of CD-complexes for improving molecules solubility and stability, for control release and as adjuvant in extraction processes, represents a promising innovative strategy in the food industry for the development of new ingredients and products.
Encapsulation of ethylene gas into α-cyclodextrin and characterisation of the inclusion complexes
Food Chemistry, 2011
Molecular encapsulation of various apolar compounds with a-cyclodextrin (a-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an a-CD under 0.2-1.5 MPa for 12-120 h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03 mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-a-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP-MAS 13 C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C 4 , C 3 and C 5 in NMR spectra, intensity changes of C-H bending and C@C stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans.
The Journal of Physical Chemistry B, 2011
Inclusion complexes based on native cyclodextrins are basic building blocks for the design of a new generation of promising materials. The design process can be optimized by maximizing the population of the desired chemical species. This is greatly facilitated by an accurate characterization of the thermodynamic parameters for their formation. A critically assessed literature review of equilibrium constants for cyclodextrin:sodium dodecyl sulfate (CD:SDS) complexes is reported. We performed multiple-temperature isothermal titration calorimetric (283À323 K) measurements for these systems, leading to the first reported heat capacity changes of binding. Data were analyzed using two thermodynamic models by homemade programs that also provide the distribution of chemical species as a function of the experimental variables. Assisted by earlier molecular dynamic simulations, a microscopic-level discussion of the contributions to the thermodynamic parameters is given. On the basis of our results, a number of recommendations to obtain reliable association parameters for CDbased inclusion complexes are listed.