Investigation of properties and structural characterization of the quercetin inclusion complex with (2-hydroxypropyl)-β-cyclodextrin

Quercetin: A Potential Polydynamic Drug

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.

Tuning the Pharmacokinetic Performance of Quercetin by Cocrystallization

Quercetin (QUE) is a widely studied nutraceutical with a number of potential therapeutic properties. Although QUE is abundant in the plant kingdom, its poor solubility (≤20 μg/mL) and poor oral bioavailability have impeded its potential utility and clinical development. In this context, cocrystallization has emerged as a useful method for improving the physicochemical properties of biologically active molecules. We herein report a novel cocrystal of the nutraceutical quercetin (QUE) with the coformer pentoxifylline (PTF) and a solvate of a previously reported structure between QUE and betaine (BET). We also report the outcomes of in vitro and in vivo studies of QUE release and absorption from a panel of QUE cocrystals: betaine (BET), theophylline (THP), l-proline (PRO), and novel QUEPTF. All cocrystals were found to exhibit an improvement in the dissolution rate of QUE. Further, the QUE plasma levels in Sprague-Dawley rats showed a 64-, 27-, 10- and 7-fold increase in oral bioavailability for QUEBET·MeOH, QUEPTF, QUEPRO, and QUETHP, respectively, compared to QUE anhydrate. We rationalize our in vivo and in vitro findings as the result of dissolution-supersaturation-precipitation behavior.

Application of Citrus and Apple Fibers for Formulation of Quercetin/Fiber Aggregates: Impact of Quercetin Concentration

Among flavonoids, quercetin has gained special attention due to its positive biological activities. Quercetin's disadvantages, such as its hydrophobic nature, poor solubility, and permeability, could be overcome by complexation with different polymers. Dietary fibers are known as carriers of polyphenols, which can protect them from environmental conditions and thus allow them to be absorbed. In this study, apple and citrus fibers (as applicable food by-products) were used as carriers of quercetin. A constant amount of fibers (1%) and different concentrations of quercetin solution (5 mM, 10 mM, and 20 mM) were complexed. Obtained fiber aggregates were subjected to HPLC to determine the quercetin concentration and antioxidant activity of aggregates (ABTS, DPPH, FRAP, and CUPRAC assays). IR spectra were recorded to confirm complexation of quercetin with selected fibers, and an additional DSC study was performed to evaluate the thermal stability of fiber aggregates. The results of HPLC analysis showed that quercetin had higher affinity towards apple fiber than citrus fiber, without proportional trends of adsorption. Consequently, apple fiber aggregates had higher antioxidant potential than citrus fiber aggregates. FTIR-ATR analysis showed the formation of new bands and the loss of existing bands when quercetin was present. Adsorption of quercetin also had an impact on the thermal stability of formulated fiber aggregates. For apple fiber, this impact was negative, while for citrus fiber, the impact was positive. These results could contribute to greater understanding of quercetin's behavior during the preparation of food additives based on polyphenols and fibers.

The challenge of flavonoid/cyclodextrin complexation in a complex matrix of the quercetin, luteolin, and 3-O-methylquercetin

The complexation of herbal constituents with cyclodextrin has been a useful tool to improve their aqueous solubility. However, the simultaneous complexation of these compounds still lacks detailed studies. The present study investigated the multicomplexation of quercetin (QCT), luteolin (LUT), and 3-O-methylquercetin (3OMQ) with (2-hydroxypropyl)-β-cyclodextrin (HPβCD), when they are simultaneously contained in a flavonoid-enriched fraction (FEF) of Achyrocline satureioides. The phase-solubility diagram revealed a linear correlation between the flavonoids solubility and the HPβCD concentration, demonstrating the formation of complexes with a 1:1 stoichiometric ratio, which was confirmed by ESI-MS. Negative ΔG⁰ values indicated that complexation was spontaneous. Flavonoids/HPβCD interactions were evidenced by FT-IR, DSC, SEM, and 1D and 2D NMR. The last one showed the formation of inclusion complexes by insertion of the B-ring of the flavonoids into the cavity of HPβCD. Unexpectedly, the FEF/HPβCD complex showed a radical scavenger potential lower than the FEF. The HPLC analysis revealed that the complex contained different flavonoid ratio than the fraction. Thus, the antioxidant capacity of the samples was demonstrated to be related to the ratio among the flavonoids, rather than to the total flavonoids. These new findings are very useful for developing herbal cyclodextrin-based products from A. satureioides or other herbal products.

Amorphous Inclusion Complexes: Molecular Interactions of Hesperidin and Hesperetin with HP-Β-CD and Their Biological Effects

This study aimed at obtaining hesperidin (Hed) and hesperetin (Het) systems with HP-β-CD by means of the solvent evaporation method. The produced systems were identified using infrared spectroscopy (FT-IR), X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC). Moreover, in silico docking and molecular dynamics studies were performed to assess the most preferable site of interactions between tested compounds and HP-β-CD. The changes of physicochemical properties (solubility, dissolution rate, and permeability) were determined chromatographically. The impact of modification on biological activity was tested in an antioxidant study as well as with regards to inhibition of enzymes important in pathogenesis of neurodegenerative diseases. The results indicated improvement in solubility over 1000 and 2000 times for Hed and Het, respectively. Permeability studies revealed that Hed has difficulties in crossing biological membranes, in contrast with Het, which can be considered to be well absorbed. The improved physicochemical properties influenced the biological activity in a positive manner by the increase in inhibitory activity on the DPPH radical and cholinoesterases. To conclude the use of HP-β-CD as a carrier in the formation of an amorphous inclusion complex seems to be a promising approach to improve the biological activity and bioavailability of Hed and Het.

Integrating diverse plant bioactive ingredients with cyclodextrins to fabricate functional films for food application: a critical review

The popularity of plant bioactive ingredients has become increasingly apparent in the food industry. However, these plant bioactive ingredients have many deficiencies, including low water solubility, poor stability, and unacceptable odor. Cyclodextrins (CDs), as cyclic molecules, have been extensively studied as superb vehicles of plant bioactive ingredients. These CD inclusion compounds could be added into various film matrices to fabricate bioactive food packaging materials. Therefore, in the present review, we summarized the extraction methods of plant bioactive ingredients, the addition of these CD inclusion compounds into thin-film materials, and their applications in food packaging. Furthermore, the release model and mechanism of active film materials based on various plant bioactive ingredients with CDs were highlighted. Finally, the current challenges and new opportunities based on these film materials have been discussed.

Electrospun poly (vinyl alcohol) nanofibers incorporating caffeic acid/cyclodextrins through the supramolecular assembly for antibacterial activity

Here, we prepared the solid inclusion complexes between Caffeic acid (CA) and Cyclodextrins (β- and γ-CDs) (CA/CDs) that were effectively embedded into Poly (vinyl alcohol) (PVA) electrospun nanofibers via electrospinning technique to enhanced solubility and antibacterial activity. In tested Cyclodextrins are β-and γ-CDs with CA in the ratio of 1:1 resulting in the formation of CA/CDs by co-precipitation method. The physical properties of CA/CDs were examined by FT-IR, UV, and Raman Spectroscopy. The phase solubility test showed a much higher solubility of CA due to inclusion complexes (ICs). Furthermore, CA/β-CD and CA/γ-CD perfected achieved 0.70:1 and 0.80:1 the molar ratio of ICs, confirmed by NMR studies. The fiber size distribution, average diameter, and morphology features were evaluated by SEM analysis. The dissolution profile of PVA/CA and PVA/CA/CDs were tested within 150 min, resulting in CA dissolved in PVA/CA/CDs slightly higher than PVA/CA nanofibers due to enhanced solubility of ICs. Moreover, PVA/CA/CDs exhibit high antibacterial activity against gram-positive bacteria of E-Coli and gram-negative bacteria of S. aureus. Finally, these results suggest that PVA/CA/CDs may be promising materials for active food packaging applications.

Extraction and Application of Natural Rutin From Sophora japonica to Prepare the Novel Fluorescent Sensor for Detection of Copper Ions

Rutin (R), a representative flavonoid found in various biomasses, can be used to prepare different fluorescent sensors for environmental, biological and medical fields. In this work, the natural R in Sophora japonica was extracted and purified to prepare fluorescent-responding sensor systems intended to recognize copper ions with both strong selectivity as well as appropriate sensitivity. Results showed that neat R had no obvious fluorescent emission peak in PBS buffer solution. However, when R and (2-hydroxypropyl)-β-cyclodextrin (CD) were introduced within buffer solution, fluorescent emission intensity was significantly increased due to the resultant R-CD inclusion complex. In addition, the formed R-CD inclusion complex was shown to behave as the aforementioned fluorescent sensor for copper ions through a mechanism of quenched fluorescent emission intensity when R-CD became bound with copper ions. The binding constant value for R-CD with copper ions was 1.33 × 10⁶, allowing for quantification of copper ions between the concentration range of 1.0 × 10^–7–4.2 × 10^–6mol⋅L^–1. Furthermore, the minimum detection limit was found to be 3.5 × 10^–8mol⋅L^–1. This work showed the prepared R-CD inclusion complex was both highly selective and strongly sensitive toward copper ions, indicating that this system could be applied into various fields where copper ions are of concern.

Novel Electrospun Pullulan Fibers Incorporating Hydroxypropyl-β-Cyclodextrin: Morphology and Relation with Rheological Properties

Fibers produced by electrospinning from biocompatible, biodegradable and naturally occurring polymers have potential advantages in drug delivery and biomedical applications because of their unique functionalities. Here, electrospun submicron fibers were produced from mixtures containing an exopolysaccharide (pullulan) and a small molecule with hosting abilities, hydroxypropyl-β-cyclodextrin (HP-β-CD), thus serving as multi-functional blend. The procedure used water as sole solvent and excluded synthetic polymers. Rheological characterization was performed to evaluate the impact of HP-β-CD on pullulan entanglement concentration (CE); the relationship with electrospinnability and fiber morphology was investigated. Neat pullulan solutions required three times CE (~20% w/v pullulan) for effective electrospinning and formation of bead-free nanofibers. HP-β-CD (30% w/v) facilitated electrospinning, leading to the production of continuous, beadless fibers (average diameters: 853-1019 nm) at lower polymer concentrations than those required in neat pullulan systems, without significantly shifting the polymer CE. Rheological, Differential Scanning Calorimetry (DSC) and Dynamic Light Scattering (DLS) measurements suggested that electrospinnability improvement was due to HP-β-CD assisting in pullulan entanglement, probably acting as a crosslinker. Yet, the type of association was not clearly identified. This study shows that blending pullulan with HP-β-CD offers a platform to exploit the inherent properties and advantages of both components in encapsulation applications.

Introducing nano/microencapsulated bioactive ingredients for extending the shelf-life of food products

The shelf-life of foods is affected by several aspects, mainly chemical and microbial events, resulting in a considerable decline in consumer's acceptance. There is an increasing interest to substitute synthetic preservatives with the plant-based bioactive ingredients which are safe and natural. However, full implementation of this replacement is postponed by some challenges associated with bioactive ingredients, including their low chemical stability, off-flavor, low solubility, and short-term effectiveness. Encapsulation could overcome these limitations. The present review explains current trends in applying natural encapsulated ingredients for food preservation based on a classified description including essential oils, plant extracts, phenolics, carotenoids, etc. and their application for extending food shelf-life mostly dealing with antimicrobial, ant-browning and antioxidant properties. Encapsulation techniques, especially nanoencapsulation, is a promising strategy to overcome their limitations. Moreover, better results are obtained using a combination of proteins and polysaccharides as wall materials than single polymers. The encapsulation method and type of encapsulants highly influences the releasing mechanism and physicochemical properties of bioactive ingredients. These factors together with optimizing the conditions of encapsulation process leads to a cost-effective and well encapsulated ingredient which is more efficient than its free form in shelf-life improvement. It has been shown that the well-designed encapsulation systems, finally, boost the shelf-life-promoting functions of the bioactive ingredients, mostly due to enhancing their solubility, homogeneity in food matrices and contact surface with deteriorative agents, and providing their prolonged presence over food storage and processing via increasing the thermal and processing stability of bioactive compounds, as well as controlling their release on food surfaces, or/and within food packages. To this end and given the numerous wall and bioactive core substances available, further studies are needed to evaluate the efficiency of many encapsulated forms of both conventional and novel bioactive ingredients in food shelf-life extending since the interactions and anti-spoiling behaviors of the ingredients in various encapsulation systems and foodstuffs are highly variable that should be optimized and characterized before any industrial application.

Quercetin Loaded Monolaurate Sugar Esters-Based Niosomes: Sustained Release and Mutual Antioxidant-Hepatoprotective Interplay

Flavonoids possess different interesting biological properties, including antibacterial, antiviral, anti-inflammatory and antioxidant activities. However, unfortunately, these molecules present different bottlenecks, such as low aqueous solubility, photo and oxidative degradability, high first-pass effect, poor intestinal absorption and, hence, low systemic bioavailability. A variety of delivery systems have been developed to circumvent these drawbacks, and among them, in this work niosomes have been selected to encapsulate the hepatoprotective natural flavonoid quercetin. The aim of this study was to prepare nanosized quercetin-loaded niosomes, formulated with different monolaurate sugar esters (i.e., sorbitan C12; glucose C12; trehalose C12; sucrose C12) that act as non-ionic surfactants and with cholesterol as stabilizer (1:1 and 2:1 ratio). Niosomes were characterized under the physicochemical, thermal and morphological points of view. Moreover, after the analyses of the in vitro biocompatibility and the drug-release profile, the hepatoprotective activity of the selected niosomes was evaluated in vivo, using the carbon tetrachloride (CCl₄)-induced hepatotoxicity in rats. Furthermore, the levels of glutathione and glutathione peroxidase (GSH and GPX) were measured. Based on results, the best formulation selected was glucose laurate/cholesterol at molar ratio of 1:1, presenting spherical shape and a particle size (PS) of 161 ± 4.6 nm, with a drug encapsulation efficiency (EE%) as high as 83.6 ± 3.7% and sustained quercetin release. These niosomes showed higher hepatoprotective effect compared to free quercetin in vivo, measuring serum biomarker enzymes (i.e., alanine and aspartate transaminases (ALT and AST)) and serum biochemical parameters (i.e., alkaline phosphatase (ALP) and total proteins), while following the histopathological investigation. This study confirms the ability of quercetin loaded niosomes to reverse CCl₄ intoxication and to carry out an antioxidant effect.

[6]-Shogaol/β-CDs inclusion complex: preparation, characterisation, in vivo pharmacokinetics, and in situ intestinal perfusion study

Aims: The aim was to improve the absorption and bioavailability of [6]-shogaol with β-cyclodextrin (β-CD) prior to in vitro and in vivo evaluation. Methods: [6]-Shogaol/β-CDs inclusion complexes (6-S-β-CDs) were developed using saturated aqueous solution method and characterised with appropriate techniques. The absorption and bioavailability potential of [6]-shogaol was evaluated via in vivo pharmacokinetics and in situ intestinal perfusion. Results: The results of characterisation showed that 6-S-β-CDs (drug loading, 7.15%) were successfully formulated. In vitro release study indicated significantly improved [6]-shogaol release. Pharmacokinetic parameters such as Cmax, AUC0-36 h, and oral relative bioavailability (about 685.36%) were substantially enhanced. The in situ intestinal perfusion study revealed that [6]-shogaol was markedly absorbed via passive diffusion in the intestinal segments, and duodenum followed by ileum and jejunum. Conclusions: Cyclodextrin inclusion technology could enhance the intestinal absorption and oral bioavailability of hydrophobic drugs like [6]-shogaol.

The mechanism of bensulfuron-methyl complexation with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin and effect on soil adsorption and bio-activity

In this work, the inclusion complexes of hydrophobic herbicide bensulfuron-methyl (BSM) with β-cyclodextrin (β-CD) and (2-hydroxypropyl)-β-CD (2-HP-β-CD) were prepared and characterized. Phase solubility study showed that both β-CD and 2-HP-β-CD increased the solubility of BSM. Three-dimensional structures of the inclusion complexes were simulated by the molecular docking method. The docking results indicated that guest BSM could enter into the cavities of host CDs, folded, and centrally aligned inside the inclusion complexes. The benzene ring of the guest molecule was close to the wide rim of the host molecules; the pyrimidine ring and side chains of the guest molecule were oriented toward the narrow rim of the host molecule. The inclusion complexes were successfully prepared by the coprecipitation method. The physiochemical characterization data of 1H NMR, FT-IR, XRD, and DSC showed that the guest and host molecules were well included. BSM had lower soil adsorption and higher herbicidal activity in the complexation form with β-CD or 2-HP-β-CD than in the pure form. The present study provides an approach to develop a novel CDs-based formulation for hydrophobic herbicides.

A review of microencapsulation methods for food antioxidants: Principles, advantages, drawbacks and applications

Bioactivities and numerous health benefits against a number of oxidative stress related diseases have been attributed to the role of dietary antioxidants. The development of physical (spray drying, lyophilization, supercritical fluid precipitation and solvent evaporation), physico-chemical (coacervation, liposomes and ionic gelation) and chemical encapsulation techniques (interfacial polymerization and molecular inclusion complexation) enable to obtain healthier and acceptable bioactive compounds. This review focuses on the impacts of microencapsulation techniques on the encapsulation characteristics of food antioxidants. Additionally, this study also provides detailed information on the principles, effective parameters, advantages, disadvantages and applications of microencapsulation techniques.

Preparation and Characterization of Butachlor/(2-Hydroxypropyl)-β-cyclodextrin Inclusion Complex: Improve Soil Mobility and Herbicidal Activity and Decrease Fish Toxicity

A water-soluble inclusion complex for butachlor was prepared by complexation with (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD). Phase solubility results indicated a 1:1 stoichiometric ratio with an apparent stability constant of 864.3 M^-1 in the obtained solid complex. The formation of the complex was confirmed by ¹H nuclear magnetic resonance, Fourier transform infrared, and differential scanning calorimetry spectra. Coupled with the molecular docking results, butachlor was considered to be completely included in HP-β-CD cavity. Butachlor complexation with HP-β-CD decreased its adsorption capacity and enhanced its mobility in soil. The inclusion complex displayed better herbicidal activities than free butachlor. The 96 h median lethal concentration values of the inclusion complex and free butachlor was 2.30 and 0.65 mg L^-1, respectively, for zebrafish, indicating that the complexation could significantly reduce toxicity to fishes. The present study provides an approach to develop environment-friendly formulations using CDs for herbicides.

Sensitive fluorescent assay for copper(ii) determination in aqueous solution using quercetin-cyclodextrin inclusion

Environmentally friendly probe materials for detecting copper ions were studied in this research. Fluorescent emission of quercetin (Q) was observed in the buffer solution (pH = 7.40), and (2-hydroxypropyl)-β-cyclodextrin (CD) could enhance the fluorescence intensity of Q. The UV/Vis spectrum showed that the Q-CD system was formed. After adding copper ions into the Q-CD system, the fluorescent emission intensity of Q-CD system generated quenching, and other metal ions could not bring change, which meant the Q-CD system showed good selectivity to copper ions. The fluorescence titration spectra showed that the concentration of copper ions was inversely proportional to fluorescence intensity, and gave a good linear change in fluorescence emission intensity in response to the concentration of copper ions ranging from 5.0 × 10-8 to 8.3 × 10-6 mol L-1. The calibration curve of the relationship between the intensity and copper ions concentration was y = -9.24x + 844.51 (R 2 = 0.997). The detection limit of copper ions was measured to be 2.3 × 10-8 mol L-1. The probable mechanism was studied by UV/Vis spectrum and Job's plot method. The results indicated that Q-CD-Cu(ii) complex was formed and intramolecular charge transfer (ICT) took place. At last, the probe was successfully applied for determination of copper ions in water bodies, vegetables and fruits with good recovery. The study showed that Q-CD system could detect copper ions as a fluorescent probe with high selectivity, sensitivity and larger linearity range.

Preparation, characterization and antimicrobial activity of inclusion complex of biochanin A with (2-hydroxypropyl)-β-cyclodextrin

Objectives

An inclusion complex of biochanin A (BCA) with (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) was prepared in the ethanol solution to improve its water solubility.

Methods

Using the FTIR, 1H-NMR, XRD, DSC and SEM methods, the structural characterization of the prepared complex was analysed.

Key findings

The phase-solubility study has shown that the solubility of BCA was increased twofold in 42% (v/v) ethanol solution after complexation with HP-β-CD. The complex between BCA and HP-β-CD was prepared in the molar ratio of 1 : 1. The antibacterial activity of the inclusion complex was investigated against the various bacteria, fungus and yeast using the microdilution method. The minimal inhibitory concentration values for the analysed strain of bacteria were in the range of 0.84–1.69 mg/cm3, whereby the prepared inclusion complex exhibited less effect on the reduction of the number of Escherichia coli and Klebsiella pneumoniae species compared to pure BCA. The inclusion complex of BCA was significantly more active against Candida albicans than pure BCA. Biochanin A and its inclusion complex has not expressed the activity against Aspergillus niger.

Conclusions

Based on the obtained results, it can be concluded that the antimicrobial activity of BCA was remained unchanged after complexation.

Effect of sulfobutyl ether-β-cyclodextrin and propylene glycol alginate on the solubility of clozapine

Clozapine (CLZ) is an atypical antipsychotic medication used in the treatment of schizophrenia and is poorly soluble in water (0.05 mM). In this study, we have investigated the effect of β-cyclodextrin (CD) and its derivatives on the solubility of CLZ. The solubility of the CLZ was measured to generate a phase solubility diagram, and the interaction between CLZ and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) in aqueous solution was observed by ¹H- and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY)-NMR methods. Moreover, the synergistic effect of SBE-β-CD and water-soluble polymers, including polyvinylpyrrolidone, hydroxypropyl methylcellulose, carboxymethylcellulose sodium salt, polyvinyl alcohol, sodium alginate, and propylene glycol alginate (PGA), on the solubility of CLZ was investigated. The results show that the solubility of CLZ with 1 w/v% PGA was 7.6 mM, which was almost four times greater than that of CLZ without PGA in a 15 mM SBE-β-CD solution. In contrast, the solubility of CLZ with 1 w/v % PGA in an aqueous solution decreased by one-third relative to that of CLZ in a 15 mM SBE-β-CD solution. 2D ROESY-NMR indicated that a CLZ/SBE-β-CD/PGA ternary complex formed. It was found that the combination of PGA and SBE-β-CD enhanced the solubility of CLZ.