**6.3. Infrared spectroscopy**

Infrared spectroscopic techniques such as the Fourier transform infrared (FTIR) spectroscopy can be used to reveal CD functionalization and inclusion complexation. This can be validated by the appearance of new peaks, shift in peak position or change in peak intensity as a result of changes on pure CD molecules. Noticeable changes may include disappearance of the ─OH peak for functionalization with the appearance of new peaks depending on the type of functional groups introduced. For inclusion complexation, ─CO stretching peaks may be observed [110]. Vibrational modes of the host and guest can be studied using this technique to understand the process of complexation and/or functionalization. Vibrational modes can be restricted to a certain level during complexation and this can result in weak interatomic bonds due to the altered environment around the bonds [116, 117].

**6.7. Chromatography**

**6.8. Microscopic techniques**

[11, 43, 49, 69, 73, 77].

**6.9. Other characterization techniques**

the dose was excreted as CO<sup>2</sup>

dation factor Rf

Chromatographic analysis such as thin layer chromatography (TLC) can be very useful for the verification of complexation and modification by monitoring the alterations of the retar-

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

values. The complex of modified CDs is found between the Rf

CDs and that of the functional group or guest [110, 121]. Another way to study CDs and their complexes using chromatography is by monitoring their volatility using head-space chromatography. This chromatographic technique is specifically for volatile compounds. The increase or decrease in volatility can be observed as influenced by the host-guest interaction

Microscopic techniques such as SEM and TEM are used as complementary techniques to analyze the surface morphology, topography and composition of various samples including nanofibers and membranes containing CD species. These two techniques give critical details on the size, size distribution and alignment of fibers as well as the nature of the nanofiber or membrane surfaces. These microscopic techniques are mostly used in the analytic investigation of nanofibers and membranes because of their capability of imaging at high resolutions

Other popular techniques often used to study CDs, their derivatives and nanocomposites are thermogravimetric analysis to probe their thermal stability, circular dichroism spectroscopy to study inclusion complexation of ideally sized molecules in the CD cavity, contact angle analysis to understand the hydrophilicity of surfaces, nanosizer instruments for surface charge and Brunauer-Emmett-Teller (BET) to measure the surface area and pore volume.

Even though CDs have several advantages for applications in areas such as water treatment, tissue engineering and drug delivery, their toxicity, biological fates and safety issues need to be evaluated since they eventually find their way into animal and human bodies. The three most common natural CDs and their hydrophilic derivatives are known to only permeate lipophilic biological membranes, which include the gastrointestinal mucosa, skin and cornea of the eye with certain difficulty. CDs have been reported to be nontoxic to a certain level due to low absorption from the gastrointestinal track [12, 123, 124]. αCDs were found to bind with some lipids resulting in eye irritation in rats when they were orally administered, whereby 60% of

in urine and feces [12, 125]. Oral administration in rats showed that βCDs have less irritation compared to αCDs; however, small amounts were absorbed in the upper intestinal track [12, 126]. Even though they are nontoxic when administered orally, βCDs cannot be administered parenterally due to their low solubility in aqueous solutions and their nephrotoxicity [127].

, 26–33% as metabolite incorporation and 7–14% as metabolites

and the stability of the complex can be determined [110, 122].

**7. Toxicology and safety of CDs and their derivatives**

values of the

157

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