**6.1. X-ray diffraction**

guests that can be altered during inclusion complexation include taste modification, solubility enhancement, physical isolation and stabilization of labile guests [108]. As shown by **Figure 16**, CDs and their derivatives can interact with other molecules to form supramolecular polymeric structures [109]. The high surface area and pore volume and permanent porosity of the

Marques et al. used CDs for the encapsulation of essential oils such as chamomile oil via inclusion complexation. Inclusion complexation of essential oils is used for various reasons such as avoiding degradation induced by oxygen, light or heat, improving water solubility and stabilizing fragrances [110]. βCDs were also used by others to enhance the solubility of Gliclazide by employing the coprecipitation and kneading methods. It was found that the complex prepared by kneading method was more suitable for the improvement of Gliclazide

By inclusion complexation, the CD moiety does not only bind the guest molecules but also brings them close to the functional groups for other reactions such as photocatalytic degradation to take place [112]. CDs can also alter the physicochemical properties of the guest molecules by making it easy to modify during that period. For example, it can promote fast dissolution rates, efficient absorption and short drug release times. As a result, CDs find application in cosmetics, food, drug delivery, bioconversion and environmental protection [103, 105]. It should be noted that complexation between the host and a guest depends mostly on several properties of the host and guest, dosage, thermodynamics and equilib-

The index of the change in physicochemical properties of guest can be shown by the stabil-

inclusion complexation toward equilibrium is assisted by four energetically favorable inter-

**i.** The displacement of water molecules from the hydrophobic cavity by nonpolar molecules. **ii.** The increasing number of hydrogen bonds formed when the displaced water is driven

**iii.** Reduced repulsive interactions between the nonpolar guest and the aqueous environment.

Clearly, the common interaction of CDs with other species in aqueous solutions is inclusion complexation. Kayaci and coworkers reported that the filtration efficiency of PET was improved after surface modification with α, β and γCD. The filtration process was tested against phenanthrene compounds and the improvement was credited to inclusion complexation between the CDs and phenanthrene [7]. Uyar and coworkers reported the use of PMMA nanofibers modified with βCD for molecular entrapment of organic vapors such as styrene, aniline and toluene. The reported interaction between the vapors and nanofibers was inclusion complexation (CD) and adsorption (PMMA and CDs). The interactions between the two were analyzed by direct pyrolysis mass spectrometry and thermogravimetric analysis [51].

**iv.** Increasing hydrophobic interactions as the guest inserts itself into the cavity [12].

) measurements. The formation of

) and dissociation constant (*K<sup>d</sup>*

porous CD polymer enable the rapid removal of the organic contaminants [109].

solubility compared to the one prepared by coprecipitation [111].

rium kinetics.

actions, which are:

ity, equilibrium constant (*Kc*

154 Cyclodextrin - A Versatile Ingredient

to the outer pool.

X-ray diffraction (XRD) is very useful for the analysis of CD materials in powder or microcrystalline states. This is simply because the XRD pattern of the parent CD will be different from that of the derivative or the inclusion complex, which will confirm successful modification, functionalization and/or inclusion complexation [110, 111]. This technique can be used on ground and homogenized samples even on unknown samples. The intensity of peaks helps understand the interactions between CDs and other materials as well as their degree of crystallinity [115].
