Preface

Since Villiers first described "cellulosine" in 1891 and Schardinger laid out the fundamentals of cyclodextrins (also known as cycloamyloses) in the early nineteenth century, the chemistry of cyclodextrin (CD) and its congeners has continuously attracted interest from the scientific community worldwide. This valuable scaffold has numerous potential applications, including in solar cells, semiconductors, super-capacitors, polymers, drug delivery, sensors, ligands, nanotechnology, biomedicine, agriculture, dyes, food technology, cosmetics excipients, textiles, and the pharmaceutical industry, in addition to its role in the environmental, biological, supramolecular, and analytical horizons. The most distinctive signature of CDs is their capability to form inclusion complexes with a variety of small molecules through host–guest supramolecular interactions.

This book deals with core concepts and new perspectives on CDs. Chapter 1 describes the historical background of CDs along with their physiochemical characteristics, as well as provides a short overview of their diverse applications. Chapter 2 discusses the fundamental concepts of CDs, including their structure, properties, and host–guest interactions with a particular emphasis on molecular dynamics in addition to drug delivery uses. Chapter 3 highlights recent advancements in sensing diverse biologically important small molecules by CDs through colorimetric, fluorescence, electrochemical, and potentiometric responses. Chapter 4 describes the inclusion chemistry of various organic dyes with CDs. Finally, Chapter 5 focuses on CD-based polymers (both natural and synthetic) in solution as well as in gel states.

I am grateful to all the chapter authors for their excellent contributions. I also express my sincere thanks to my wife Saba Khan and my lovely daughters Naira Khan and Samaira Khan. Finally, I am also thankful to my family members, relatives, colleagues and friends for their continuous motivation and encouragement without which this book would not have been possible.

> **Rashid Ali** Department of Chemistry, Faculty of Natural Sciences, Jamia Millia Islamia, New Delhi, India

**1**

**Chapter 1**

*Rashid Ali*

**1. Introduction**

Introductory Chapter: Historical

Structural and Physiochemical

Properties of Cyclodextrins (CDs)

The discovery, by Antoine Villiers, of the biosynthetic cyclic oligosaccharides-based seminatural products consisting of 6, 7, and 8 chiral glucose units, arranged in a donut shape and connected *via* α-1,4-gycosidic bonds, is generally symbolized as α-, β-, and γ-cyclodextrins (or ACDs, BCDs, and GCDs), respectively. They seem to be the most investigated macrocyclic host molecules in the realm of supramolecular chemistry a study of the noncovalent interactions. Naturally, they are being obtained from the enzymatic degradation of one of the most indispensable polysaccharides, that is, potato starch in the bacteria (**Figure 1**) [1]. Sometimes, they also dubbed as the enzyme-modified starch derivatives. These macrocyclic systems comprise the lipophilic inner cavities as well as hydrophilic outer surfaces of the particular interest. Interestingly, the cyclodextrins (CDs) are produced "hundreds-of-thousands" of tons every year by means of environmentally friendlier, simple yet effective techniques and methods. The CDs belong to a family of "cage molecules" in which the core of their structures is unruffled of a very stable hydrophobic cavity, having the distinctive property of encapsulating the hydrophobic entities by virtue of the invaluable host-guest supramolecular interactions. The driving strengths that operate in the inclusion complex formation are van der Waals and electrostatic interactions besides the hydrogen bonding forces. Generally, the complex formation by the CDs depends on the shape and size of the cavities of CDs, chemical nature of the guests, expulsion of the high-energy H2O molecules, and CD-CD aggregation. More importantly, their vibrant properties can easily be altered significantly through their ability of forming the inclusion complexes and also by means of their apposite functionalizations, as they contain a groups of primary as well as secondary hydroxyl functionalities at the two rims (**Figure 2**) [2]. The chemical structures of the most popular cyclodextrins, i.e. α-, β-, and γ-CDs, are depicted in **Figure 3**. As shown in **Figure 3**, the CDs have "truncated cone shape" rather than the perfect cylindrical structures because of the chair conformations of the glucopyranose units present in these types of cyclic systems. The toroidal structure of the CDs contains a panel of secondary hydroxyl groups on the wider rim, whereas the primary hydroxyl groups are present at the narrower rim side. The hydrophobic cavity is clearly displayed with an arrow inside the truncated cone as displayed in **Figure 3**. On the other hand, different structural

Background – Fundamental
