**5. Mechanism for the interaction of CD nanofibers/membranes with various species**

such as drug delivery, filtration, templates, biomedical, catalysis, water treatment, reinforcement, electronics, pharmaceuticals and optical devices [39, 98, 99]. Celebioglu and coworkers formed inclusion complexation using the antibacterial agent, triclosan, with two types of CD derivatives (HP-βCDs and HP-γCDs). The electrospun inclusion complexes were tested against Gram-negative (*Escherichia coli*) and Gram-positive (*Staphylococcus aureus*) bacteria. The antibacterial activity against the two bacteria strains was found to be higher for the inclusion complexes compared to the bare triclosan. The interactions of triclosan with the CD derivatives improved its antibacterial activity [100]. Li and coworkers used βCDs with maleic anhydride (MAH) and 3-(4-vinylbenzyl)-5,5-dimethylhydantoin (VBDMH) for antibacterial studies. The composite βCD-MAH-VBDMH was electrospun with cellulose acetate and the antibacterial activity was tested against *E. coli* and *S. aureus* bacteria. The nanofibers achieved 99.7 and 80.3% activity against *E. coli* and *S. aureus*, respectively, within 10–30 min contact time [20]. In another study, Dong and coworkers used ciprofloxacin hydrochloride (CipHCl) as the antibacterial agent with electrospun citric acid cross-linked cellulose and βCDs. The CipHCl loaded on the electrospun nanofibers demonstrated high antibacterial activity against

In drug delivery systems, CDs and their derivatives have also been used for targeted delivery and control of release rate as well as solubility control. Bazhban and coworkers electrospun a drug delivery system from carboxymethyl-βCDs and chitosan blended with PVA in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as the condensing agent and *N*-hydroxysuccinimide as a hydrolyzing agent. The electrospun nanofibrous mats were observed to have slower release rates of the entrapped salicylic acid compared to the nanofibrous mats without βCDs [64]. Canbolat and coworkers complexed naproxen (NAP) with βCDs and electrospun the inclusion complex with poly(ε-caprolactone) (PCL/NAP-βCDs). The electrospun PCL/NAP-βCDs had high release rates of NAP compared to the electrospun PCL/NAP [50]. Electrospun CD nanofibers have also been used in the syntheses of metal nanoparticles as reducing agents and size-controlling agents. Celebioglu and coworkers synthesized Ag nanoparticles in the presence of PVA/CD electrospun nanofibers. They obtained Ag nanoparticles of 2 nm in size without aggregation compared to the 8 nm aggregated nanoparticles obtained with the use of bare nanofibers [56]. Bai and coworkers used electrospun PVP/βCDs as stabilizing and reducing agents for the synthesis of Au nanoparticles. The Au nanoparticles were found to be evenly distributed and well dispersed in the nanofibers

By forming inclusion complexes with other materials, CDs can improve their stability and shelf life. Kayaci and coworkers enhanced the thermal stability of eugenol (EG) by means of inclusion complexation with β and γCDs. The inclusion complex EG-CD was incorporated and electrospun together with PVA. The complexed EG demonstrated thermal evaporation at high temperature and slowed release at temperatures as high as 100°C compared to poor thermal stability of pure EG [66]. Uyar and coworkers prepared inclusion complexes between menthol with α, β and γCDs and electrospun the complexes with polystyrene in order to enhance the thermal stability of menthol. The thermal stability of menthol was improved up

*E. coli* and *S. aureus* [101].

152 Cyclodextrin - A Versatile Ingredient

and induced antibacterial behavior on the nanofibers [47].

to 350°C by the electrospun nanofibers [65].

As discussed earlier, CDs and their derivatives have the ability to form inclusion complexes with a number of liquid, solid or gaseous compounds [12], which can alter the physicochemical properties of the guest molecule [102]. This happens by taking up a whole or part of a guest molecule into the hydrophobic cavity, which is lined by skeletal carbons as well as the ethereal oxygen of the glucose units. During the formation, no covalent bonds are made or broken, and as a result the guest molecule is not permanently hosted, it is rather in a dynamic equilibrium with the host [103–105]. **Figure 16** shows an example of an inclusion complex between a CD molecule and an organic compound. The hydrophobic cavity provides an environment for appropriate guests to settle in and form a complexation with the CD molecule [12]. In solid-state inclusion complexation, guest molecules can be enclosed within the cavity or can aggregate outside the CD, while solution state inclusion complexation is controlled by equilibrium between the complexed and noncomplexed molecules [102, 106]. For successful inclusion complexation to occur the guest or part of the guest must have the size, polarity and shape that are compatible with those of the host [107]. Physicochemical properties of

**Figure 16.** Illustration of (a) interaction of βCD with an organic molecule forming a polymeric network, (b) N<sup>2</sup> adsorption and desorption and (c) pore volume measurements of the polymeric structure. Reproduced with permission from [109].

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

Chen and coworkers prepared a molecular filtration membrane using carbonaceous nanofiber membranes (CNFs) modified with βCDs for the filtration of phenolphthalein in aqueous solutions. Again, the removal of this compound was credited to complexation with CDs and absorption by both CDs and CNFs [63]. Workers reported the reduction of Ag and Fe supported on βCD/cellulose acetate nanofiber membranes for antibacterial studies. The CD molecules facilitated the charge transfer that occurred between ionized water molecules and

Cyclodextrin-Based Nanofibers and Membranes: Fabrication, Properties and Applications

http://dx.doi.org/10.5772/intechopen.74737

155

and Fe3+ since they were able to alter physicochemical properties of guest molecules (and

Several publications reported the use of CDs in various applications such as drug delivery, catalysis, water and air treatment, sensors and energy storage devices. The outstanding performance of all the materials is credited to inclusion complexation and absorption ability that are caused by hydrophobic and intermolecular interactions between the compounds of inter-

There are several methods that can be used to study and understand the properties and characteristics of CDs, CD-derivatives and CD-guest inclusion complexes. To study, understand and confirm changes on CD physicochemical properties during applications, analysis has to be conducted using a series of conventional techniques that can complement each other and give conclusive data. Some of the techniques are discussed in the subsections

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

Nuclear magnetic resonance (NMR) is mostly used to study inclusion complexation in solution and has been very useful in understanding the bonding configuration of functionalities present. This is mostly because when a guest is hosted the interior hydrogens are shielded by the guest resulting in a shift on the NMR spectroscopy [110]. NMR can also be used to determine the atoms that stabilize host-guest complexes using <sup>13</sup>C-NMR by monitoring the shifts of the carbon atoms involved [110, 115]. Furthermore, NMR can also provide information on

Ag<sup>+</sup>

below.

**6.1. X-ray diffraction**

crystallinity [115].

**6.2. Nuclear magnetic resonance**

the orientation of the guest within the host's cavity [115, 116].

in this case metal nanoparticles) [17].

**6. Characterization tools for CD materials**

est and CDs [16, 64, 113, 114].

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

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 equilibrium kinetics.

The index of the change in physicochemical properties of guest can be shown by the stability, equilibrium constant (*Kc* ) and dissociation constant (*K<sup>d</sup>* ) measurements. The formation of inclusion complexation toward equilibrium is assisted by four energetically favorable interactions, which are:


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]. Chen and coworkers prepared a molecular filtration membrane using carbonaceous nanofiber membranes (CNFs) modified with βCDs for the filtration of phenolphthalein in aqueous solutions. Again, the removal of this compound was credited to complexation with CDs and absorption by both CDs and CNFs [63]. Workers reported the reduction of Ag and Fe supported on βCD/cellulose acetate nanofiber membranes for antibacterial studies. The CD molecules facilitated the charge transfer that occurred between ionized water molecules and Ag<sup>+</sup> and Fe3+ since they were able to alter physicochemical properties of guest molecules (and in this case metal nanoparticles) [17].

Several publications reported the use of CDs in various applications such as drug delivery, catalysis, water and air treatment, sensors and energy storage devices. The outstanding performance of all the materials is credited to inclusion complexation and absorption ability that are caused by hydrophobic and intermolecular interactions between the compounds of interest and CDs [16, 64, 113, 114].
