Cyclodextrins (CD) are a series of cyclic oligosaccharides obtained through amylase degradation and contain d-glucopyranose units. CDs have a basket-like or truncated cone-like structure, with cavities being their key structural feature. Based on the cavity, CD is capable of accommodating a variety of guest molecules and forming host-guest inclusion complexes, enabling them to be widely used in the pharmaceutical, cosmetics, food and other industries.
Alpha- (α), beta- (β) and gamma (γ)-CDs are native or natural CDs composed of 6, 7 and 8 glucopyranose subunits respectively. They share a common feature with all CD molecules, having a stable hydrophobic cavity and an external hydrophilic surface, since the primary hydroxyl groups are located on the outer surface of the molecule and the secondary hydroxyl groups are located on the interior. Because of their unique physicochemical properties, native CDs have received the most attention. There are certain differences between α, β and γ-CD molecules in terms of glucose subunits, molar mass, external diameter, internal diameter, and water solubility. The main properties of three native CDs are shown in Table 1 [1] [2].
Table 1. Main properties of α, β and γ-CDs [1].
| Property | α-CD | β-CD | γ-CD |
| Number of glucose subunits | 6 | 7 | 8 |
| Molar mass (g·mol-1) | 972 | 1135 | 1297 |
| External diameter (nm) | 1.4-1.5 | 1.5-1.6 | 1.7-1.8 |
| Internal diameter (nm) | 0.47-0.52 | 0.60-0.80 | 0.75-1.00 |
| Water solubility at 25°C (mg·mL-1) | 145 | 18.5 | 232 |
α-CD is composed of 6 d-glucopyranose subunits. Among the three native CDs, α-CD has the smallest internal diameter, ranging from 0.47 to 0.52 nm. It has moderate water solubility, almost eight times that of β-CD, but less than γ-CD. It also has relative thermal stability, stability in alkaline and acidic solutions, and slightly distinct sensory characteristics. Its chemical structure prevents it from being hydrolysed by human saliva and pancreatic amylase, giving it probiotic properties and enabling its use as a dietary fiber [2].
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β-CD is composed of 7 d-glucopyranose subunits with an inner diameter of 0.60-0.80 nm. Among the three types of native CD, β-CD has been studied and applied the most due to its low cost. β-CD has better complexing efficiency and larger cavity size than α-CD, allowing it to be used to encapsulate a large number of molecules. However, β-CD has poor water solubility, with the lowest solubility of 18.5 mg·mL−1 among the three native CDs. Based on the good inclusion property and poor water solubility of β-CD, it is often chemically modified to expand its application range [2].
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γ-CD is composed of 8 d-glucopyranose subunits. Compared with β-CD, it has a larger cavity with an internal diameter of 0.75-1.00 nm, so it can encapsulate a larger number of guest molecules than β-CD. Among the three native CDs, γ-CD has the highest water solubility at 232 mg·mL−1 and it can be used as a solubilizer to carry highly hydrophobic molecules. In addition, unlike α-CD, γ-CD does not easily penetrate biofilms and can be rapidly digested by gastrointestinal bacteria and metabolized by α-amylase in saliva, bile, and tears [2,3].
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Alfa Chemistry is one of the leading CD manufacturers. We offer kilograms of high-quality native CDs, including α-CD, β-CD and γ-CD, along with related services and support to meet customers' needs. We are committed to providing our customers with the best possible experience with our products and services. For more information, please feel free to contact us.
References
- Yousaf, R.; et al. Cyclodextrins: an overview of fundamentals, types, and applications. Cyclodextrins - Core Concepts and New Frontiers. 2022.
- Arruda, T. R.; et al. Native cyclodextrins and their derivatives as potential additives for food packaging: a review. Polysaccharides. 2021, 2(4): 825-842.
- Saokham, P.; Loftsson, T. γ-Cyclodextrin. Int J Pharm. 2017, 516(1-2): 278-292.
- Poulson, B. G.; et al. Cyclodextrins: structural, chemical, and physical properties, and applications. Polysaccharides. 2022, 3(1): 1-31.
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