Spectroscopic and Structural Investigations of Quercetin/Sulfobutylether-β-Cyclodextrin Inclusion Complex Incorporated pH – responsive Electrospun Nanofibers for Colon

Abstract

The present study deals with development and characterization of quercetin (QCT) – loaded sulfobutylether-β-cyclodextrin (SBE-β-CD) inclusion complex (IC) incorporated into eudragit S100 (ES100) nanofibers (NF) for colon specific delivery. The ¹H – NMR and 2D – NOESY experiments revealed key spatial correlations between the H-5 protons of SBE-β-CD (host) and the aromatic protons of QCT [ring A: H-8, H-6 and ring B: H-6ʹ and H-2ʹ]. The solid – state characterizations of IC and NF (FTIR, XRD, and TGA/DSC) demonstrated molecular interactions among QCT, SBE-β-CD and ES100, phase transition of crystalline QCT to a more stable amorphous form with improved thermal stability. The morphological evaluation of IC loaded NF revealed a uniform, smooth, bead-free NF structure, whereas, water contact angle (WCA) measurements indicated hydrophobic nature of NFs (WCA above 90°). The in–vitro release studies of ES100/QCT/SBE-β-CD-IC-NF demonstrated colon-specific release of QCT and approximately 81.85 ± 0.27% of QCT was released in colonic phase. Furthermore, both the IC and ES100/QCT/SBE-β-CD-IC-NF exhibited superior DPPH and ABTS radical scavenging potential (P ˂0.05) as compared to native QCT. Overall, this study presents a synergistic strategy of utilizing inclusion complexation and electrospinning technique for colon-specific release of QCT.

Highlights

SBE-β-CD demonstrated strong binding and solubility for QCT.

NMR confirmed host–guest interaction between QCT and SBE-β-CD molecules

Solid-state analysis demonstrated QCT amorphization and enhanced thermal stability

Nanofibers were smooth, bead-free, and hydrophobic with WCA > 90°

Nanofibers had antioxidant potential and pH – dependent colonic release

Introduction

Quercetin (QCT) is a hydrophobic dietary flavonoid derived from various fruits and vegetables (including apples, almonds, berries, broccoli, buckwheat, olives, onions, red grapes and green tea) [1]. It exhibits a plethora of therapeutic properties, including antioxidant, anticancer, and antibacterial activities [2]. Several in vitro and in vivo reports have elucidated QCT’s positive modulatory effects on colon health, garnering significant interest from the food and medicinal sector [3,4]. Nevertheless, the poor aqueous solubility, limited thermal stability and susceptibility to degradation in the upper digestive tract of QCT significantly hinder its colonic absorption [5]. Hence, there is an imperative need to develop a controlled delivery system that not only augments solubility but also prevents rapid release in non-target areas, thereby enhancing the bioavailability and therapeutic efficacy of QCT in the colonic phase.
In recent years, various site-specific colon delivery systems have been explored to improve the bioavailability and efficacy of QCT, including liposomes, microspheres, polymeric nanoparticles, and nanoemulsions [[6], [7], [8]]. Despite their promising potential, these nanotechnological strategies encounter significant challenges related to stability, encapsulation efficiency, premature release, reliance on potentially toxic surfactants and emulsifiers, and prone to aggregation under fluctuating pH, heat and salt conditions [9].

The use of cyclodextrin inclusion complex incorporated electrospun nanofibers (NFs) has emerged as a promising strategy, offering numerous advantages for the efficient delivery of bioactive compounds [10]. Unlike conventional encapsulation methods, the electrospinning technique can fabricate well-defined, fine porous nanofibers that surmount these limitations [11,12]. Cyclodextrin inclusion complexes are pivotal in ameliorating the stability and stability related issues of hydrophobic bioactive molecules [13]. The SBE-β-CD is chemically modified form of β-CD (USFDA approved GRAS excipient) with superior safety profile in terms of biocompatibility, negligible nephrotoxicity and reduced hemolytic potential relative to β-CD. Additionally, SBE-β-CD has about 50 times more water solubility than native β-CD, primarily due to the extended butyl chain in the lipophilic cavity and its enhanced dissociation constant, which collectively improve its solubility profile [14,15]. Furthermore, SBE-β-CD has been demonstrated to have a superior capacity to establish host-guest assembly with a wide range of bioactive substances (including phloretin, β-lapachone, and chrysin) compared to other modified forms of β-cyclodextrin derivatives [[16], [17], [18]]. Eudragit S100 (ES100, USFDA – approved, GRAS excipient) is a colon-specific, pH responsive, synthetic enteric copolymer composed of methyl methacrylate and methacrylic acid in a 1:2 ratio [19]. It is known to preserve structural integrity under acidic conditions (pH < 7.0) and dissolves in an alkaline environment (pH > 7.0). This dual behavior makes it particularly suitable for the colon specific delivery of bioactive molecules [[19], [20], [21]].

Considering these aspects, in this study we have incorporated QCT/SBE-β-CD-IC into ES100 electrospun nanofibers to facilitate the site-specific colonic delivery of QCT (Figure 1). It is anticipated that the IC formation between SBE-β-CD and QCT will enhance its stability and water solubility. On the other side, ES100, known for its resistance to acid and digestive enzymes, is expected to protect the QCT complex from undesirable interactions within the gastric and small intestinal environments. To our knowledge, the incorporation of QCT into electrospun ES100 nanofibers for enhancing solubility and stability via inclusion complex formation, coupled with site specific colonic release through enteric encapsulation, has not been investigated.

In the present work, the molar stoichiometry and solubilizing efficiency of different β-CD derivatives [(2-Hydroxypropyl)-β-CD, Methyl-β-CD and Sulfobutylether-β-CD] were obtained by phase solubility experiment. Subsequently, lyophilization technique was used to obtain QCT/SBE-β-CD-IC. Further, QCT/SBE-β-CD-IC incorporated ES100 nanofibers (ES100/QCT/SBE-β-CD-IC-NFs) were prepared via electrospinning technique. For comparative analysis, pristine ES100 nanofibers (ES100-NF), ES100 nanofibers loaded with only QCT (ES100/QCT-NF), and ES100 nanofibers with QCT and SBE-β-CD in non-complexed form (ES100/QCT/SBE-β-CD-NF) were also prepared. Both ICs and NFs were characterized by using XRD, FTIR and TGA/DSC. The surface morphology and hydrophobicity of NFs were determined using SEM and water contact angle measurements, respectively. Finally, the release profile of NFs in simulated gastrointestinal fluids and antioxidant potential have also been evaluated.

Materials

Quercetin (QCT, C15H10O7, MW: 302.24 g/mol, 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one, Cas No: 117-39-5, yellow powder, purity: ≥ 95%, melting point: 316.5°C), (2-Hydroxypropyl)-β-CD (Average Mn: ∼1460 g/mol, Cas No: 128446-35-5, white powder, melting point: 267°C), Methyl-β-CD (Average Mn: 1310, Cas No: 128446-36-6, white powder), Deuterium oxide (D2O, ‘‘100 %”, ≥ 99.96 atom %D, Cas No: 7789–20-0), Deuterated dimethyl sulfoxide (DMSO-d6, ‘‘100 %”, ≥ 99.96 atom %D, Eudragit S 100

Nabab Khan, Ankit Saneja, Spectroscopic and Structural Investigations of Quercetin/Sulfobutylether-β-Cyclodextrin Inclusion Complex Incorporated pH – responsive Electrospun Nanofibers for Colon – Specific Delivery, Journal of Molecular Structure, 2025, 142652, ISSN 0022-2860, https://doi.org/10.1016/j.molstruc.2025.142652.