2-Hydroxypropyl-β-cyclodextrin (HP-β-CD) is a chemically modified derivative of β-cyclodextrin, a cyclic oligosaccharide composed of seven glucose units. It is widely used in pharmaceuticals, cosmetics, and research due to its ability to form inclusion complexes with hydrophobic molecules. Here’s a detailed breakdown:

Chemical Structure

• Core Structure: β-cyclodextrin (7 glucose units linked by α-1,4 glycosidic bonds) with 2-hydroxypropyl (-O-CH?-CHOH-CH?) groups attached to hydroxyl (-OH) sites on the glucose units.

• Degree of Substitution (DS): Varies (typically 0.6–1.5 hydroxypropyl groups per glucose unit).

• Molecular Formula: (C?H??O?)? modified with (C?H?O)? groups.

• Molecular Weight: ~1,400–1,600 g/mol (depending on DS).

Properties

• Solubility: Highly water-soluble (>50% w/v) compared to unmodified β-cyclodextrin (poor solubility).

• Hydrophobic Cavity: Forms inclusion complexes with lipophilic molecules via host-guest interactions.

• Biocompatibility: Non-toxic, biodegradable, and non-immunogenic.

• Thermal Stability: Stable at high temperatures (decomposes >200°C).

Applications

Pharmaceuticals:

• Drug Solubility Enhancement: Binds hydrophobic drugs (e.g., antifungals, steroids) to improve bioavailability.

• Stabilization: Protects sensitive drugs from oxidation, light, or enzymatic degradation.

• Taste Masking: Reduces bitterness of oral medications.

• Drug Delivery: Used in nasal sprays, eye drops, and injectables.

  Cosmetics:

• Encapsulates fragrances, vitamins, or UV filters for controlled release.

• Reduces irritation from active ingredients (e.g., retinol).

  Food Industry:

• Stabilizes flavors, colors, and nutraceuticals.

  Research:

• Solubilizes membrane proteins or hydrophobic compounds in lab assays.

Mechanism of Action

• The hydrophobic cavity traps non-polar guest molecules, while the hydrophilic exterior ensures water solubility. This "molecular encapsulation" enhances solubility, stability, and bioavailability of poorly soluble compounds.

Synthesis

• Produced by reacting β-cyclodextrin with propylene oxide under alkaline conditions.

• The hydroxypropyl groups are introduced via nucleophilic substitution at hydroxyl sites.

Safety & Regulation

• Toxicity: Low systemic toxicity; approved for use in injectables and oral formulations by regulatory agencies (FDA, EMA).

• Side Effects: High doses may cause renal toxicity (rare).

• Biodegradability: Degraded by environmental microbes.

Key Advantages

• Overcomes limitations of native β-cyclodextrin (e.g., poor solubility, nephrotoxicity).

• Versatile excipient for formulation scientists.

• Enhances drug efficacy and patient compliance.

HP-β-CD is a critical tool in modern formulation science, bridging the gap between hydrophobic actives and aqueous delivery systems.