The study of natural products as potential drug leads has gained tremendous research interest. Quercetin is one of those natural products. It belongs to the family of flavonoids and, more specifically, flavonols. This review summarizes the beneficial pharmaceutical effects of quercetin, such as its anti-cancer, anti-inflammatory, and antimicrobial properties, which are some of the quercetin effects described in this review. Nevertheless, quercetin shows poor bioavailability and low solubility. For this reason, its encapsulation in macromolecules increases its bioavailability and therefore pharmaceutical efficiency. In this review, a brief description of the different forms of encapsulation of quercetin are described, and new ones are proposed. The beneficial effects of applying new pharmaceutical forms of nanotechnology are outlined.

Quercetin (QUE) is a well-known natural product that can exert beneficial properties on human health. However, due to its low solubility its bioavailability is limited. In the present study, we examine whether its formulation with two cyclodextrins (CDs) may enhance its pharmacological profile. Comparative interaction studies of quercetin with 2-hydroxyl-propyl-β-cyclodextrin (2HP-β-CD) and 2,6-methylated cyclodextrin (2,6Me-β-CD) were performed using NMR spectroscopy, DFT calculations, and in silico molecular dynamics (MD) simulations. Using T1 relaxation experiments and 2D DOSY it was illustrated that both cyclodextrin vehicles can host quercetin. Quantum mechanical calculations showed the formation of hydrogen bonds between QUE with 2HP-β-CD and 2,6Μe-β-CD. Six hydrogen bonds are formed ranging between 2 to 2.8 Å with 2HP-β-CD and four hydrogen bonds within 2.8 Å with 2,6Μe-β-CD. Calculations of absolute binding free energies show that quercetin binds favorably to both 2,6Me-β-CD and 2HP-β-CD. MM/GBSA results show equally favorable binding of quercetin in the two CDs. Fluorescence spectroscopy shows moderate binding of quercetin in 2HP-β-CD (520 M⁻¹) and 2,6Me-β-CD (770 M⁻¹). Thus, we propose that both formulations (2HP-β-CD:quercetin, 2,6Me-β-CD:quercetin) could be further explored and exploited as small molecule carriers in biological studies.

Losartan potassium salt (LSR) is a well-known antihypertensive drug with proven beneficial effects on human health. Its formulation with the non-toxic 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) could improve its pharmacological profile. Thus, its molecular interactions are studied using a combination of Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD). First, its complexation is shown through Differential Scanning Calorimetry as lyophilization provided distinct thermal properties in comparison to the mixture. The complexation is further proved by utilizing the chemical shift changes in the complexation and T1 values. Furthermore, the reversible favorable complexation was shown by MD calculations. Such physical chemical properties provide evidence that this formulation must be further explored through biological experiments.

Donepezil (DH), a selective acetylcholinesterase inhibitor, is widely used to manage symptoms of mild to moderate Alzheimer’s disease by enhancing cholinergic neurotransmission and preventing acetylcholine breakdown. Despite the effectiveness of oral formulations, extensive hepatic metabolism and low systemic bioavailability have driven the search for alternative delivery systems. This study focuses on nasal delivery as a non-parenteral substitute, utilizing hydroxypropyl methylcellulose (HPMC) for its mucoadhesive properties and methyl-β-cyclodextrin (Me-β-CD) for its ability to enhance permeability and form inclusion complexes with drugs. Prior studies demonstrated the potential of HPMC-based nasal films for nose-to-brain delivery of donepezil and highlighted Me-β-CD’s role in improving drug solubility. Building on this, transparent gel formulations containing DH, HPMC, and 2,6 Me-β-CD were developed to investigate molecular interactions within two- and three-component systems. This study utilized a combination of nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) to provide detailed insights into the interactions between DH, 2,6-Me-β-CD, and HPMC. The findings provide critical insights into drug–excipient interactions, aiding the optimization of stability, solubility, and controlled release. This advances the rational design of nanotechnology-based drug delivery systems for enhanced therapeutic efficacy.