Rapid, simple and sensitive determination of the apparent formation constants of trans-resveratrol complexes with natural cyclodextrins in aqueous medium using HPLC

Improvement of the Physicochemical Limitations of Rhapontigenin, a Cytotoxic Analogue of Resveratrol against Colon Cancer

It has been argued that methoxylated stilbenes are better candidates for oral administration than hydroxylated stilbenes, including resveratrol, as they share many biological activities but have better bioavailability. By contrast, they have a disadvantage to consider, i.e., their lower hydrophilic character that leads to precipitation issues in the final product. In this work, we analysed and compared the growth inhibition of colorectal cancer cells of the methoxylated stilbene rhapontigenin and some analogues and overcame potential problems in the development of fortified products by designing inclusion complexes. Among several cyclodextrins, we found the one that best fit the molecule by physicochemical and bioinformatics assays. The stoichiometry and the encapsulation constants with natural and modified cyclodextrins were determined by fluorescence spectroscopy. The most promising complexes were analysed at different temperature and pH conditions, determining the thermodynamic parameters, to discover the optimal conditions for the preparation and storage of the products. The results showed that rhapontigenin solubility and stability were significantly improved, achieving a sevenfold increase in water solubility and maintaining more than 73% of the stilbene after three months. These findings could be of great interest for industries that aim to deliver novel bioactive compounds with higher solubility and lower degradation.

Molecular encapsulation and bioactivity of gnetol, a resveratrol analogue, for use in foods

BACKGROUND

Gnetol is a stilbene whose characterization and bioactivity have been poorly studied. It shares some bioactivities with its analogue resveratrol, such as anti-inflammatory, anti-thrombotic, cardioprotective and anti-cancer activities. However, the low solubility of stilbenes may limit their potential applications in functional foods. Encapsulation in cyclodextrins could be a solution.

RESULTS

The antioxidant activity of gnetol was evaluated by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation and ferric reducing antioxidant power methods (Trolox equivalents 13.48 μmol L^-1 and 37.08 μmol L^-1 respectively at the highest concentration) and it was higher than that of resveratrol, and depending on the method, similar or higher to that of oxyresveratrol. Spectrophotometric and spectrofluorimetric characterization of gnetol is published for the first time. Moreover, its water solubility was determined and improved almost threefold after its molecular encapsulation in cyclodextrins, as well as its stability after storage for a week. A physicochemical and computational study revealed that cyclodextrins complex gnetol in a 1:1 stoichiometry, with better affinity for like 2-hydroxypropyl-β-cyclodextrin (K_F  = 4542.90 ± 227.15 mol^-1  L). Temperature and pH affected the encapsulation constants.

CONCLUSION

These results could increase interest of gnetol as an alternative to the most studied stilbene, resveratrol, as well as aid in the development of more stable inclusion complexes that improve its aqueous solubility and stability so that it can be incorporated into functional foods. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The kinetics of formation of resveratrol-β-cyclodextrin-NH2 and resveratrol analog-β-cyclodextrin-NH2 supramolecular complexes

The determination of the kinetics of inclusion processes is significant for the application of inclusion complexes as carriers for bioactive molecules. We determined the kinetic parameters of inclusion between modified β-cyclodextrin (β-CD-NH₂) and the polyphenols resveratrol (RES) and its structural analog (RESAn1), using the real-time analysis of surface plasmon resonance. The association and dissociation rate constants (k_a and k_d) showed that RESAn1 inclusion and its dissociation from β-CD-NH₂ were faster than a similar process for RES ( [Formula: see text]  = 3.10∙10⁴ ± 0.14 M^-1s^-1, [Formula: see text] =1.87∙10³ ± 0.11 M^-1s^-1; [Formula: see text] =0.39 ± 0.02 s^-1, [Formula: see text] =0.30 ± 0.02 s^-1, at 25 °C). The activated complex formation was also affected by the structural differences between the polyphenols, as showed by the activation energies of the association step ( [Formula: see text] 14.81 ± 0.64 kJ∙mol^-1, [Formula: see text] -15.01 ± 0.75 to 82.35 ± 4.47 kJ∙mol^-1). These effects of polyphenol structural differences are due to the desolvation process of interacting molecules. These results elucidate the role of small group to the dynamics of the molecular inclusion of β-CD.

Recent advances in the treatment of Niemann pick disease type C: A mini-review

Niemann Pick disease Type C (NPC) is a recessive rare disease caused by the mutation on NPC1 and/or NPC2 genes changing the processing of the Low-density proteins (LDL) resulting in an accumulation of lipids in the cells. Until today there is not a cure, the current treatment is based on palliative affairs to reduce the symptoms and prevent its appearance. Among all the treatments proposed the use of cyclodextrins (CDs), nanocarriers which can complex cholesterol, is one of the most useful alternatives. Indeed, for several years 2-hydroxypropyl-β-CD (HPβ-CD) is approved as orphan drug for FDA and EMA to the treatment. However, different CDs based materials are created each year to improve the cholesterol uptake. This review is focused on the novelty of CD based materials for NPC treatment.

Study of oxyresveratrol complexes with insoluble cyclodextrin based nanosponges: Developing a novel way to obtain their complexation constants and application in an anticancer study

The complexation of the bioactive compound oxyresveratrol (OXY) with a polymer called cyclodextrin-based nanosponge (CD-NS) and its application was studied.A new methodology is used to calculate, an apparent inclusion complex constant (K_Fapp) between a ligand and CD-NSs. Moreover, the K_Fapp of resveratrol was also evaluated and compared. The complex of OXY with the nanosponge β-CDI 1:4, was studied in vitro using DSC, TGA and FTIR techniques and its drug loading and release behavior were studied. An in vitro digestion showed higher protection of OXY complexed than free OXY. The bioactivity enhancing capacity of OXY was also studied against prostate (PC-3) and colon (HT-29 and HCT-116) cancer cell lines, where it showed stronger cell viability inhibition than the free drug. The findings as a whole represent a new opportunity for studying the complexation of drugs in CD-NSs and the use of oxyresveratrol as an ingredient in nutraceutical products.

Antimicrobial Carvacrol Incorporated in Flaxseed Gum-Sodium Alginate Active Films to Improve the Quality Attributes of Chinese Sea bass (Lateolabrax maculatus) during Cold Storage

The objective of this research was to explore the antimicrobial activity and mechanism of carvacrol against Vibrio Parahemolyticus, Shewanella putrefaciens, Staphylococcus aureus and Pseudomonas fluorescens and evaluate the effect of the addition of carvacrol/β-cyclodextrin emulsions to flaxseed gum (FSG)-sodium alginate (SA) edible films on the preservation of Chinese sea bass (Lateolabrax maculatus) fillets during refrigerated storage. The minimum inhibitory concentration (MIC) of carvacrol against V. parahemolyticus, S. putrefaciens, S. aureus and P. fluorescens were 0.5, 0.5, 0.125, and 0.5 mg/mL, respectively. Alkaline phosphatase activity assay, nucleotide and protein leakage, and scanning electron microscope demonstrated that carvacrol damaged the external structure of the tested bacterial cells causing leakage of cytoplasmic components. At the same time, when FSG-SA films containing carvacrol used as coating agents for Chinese sea bass fillets cold storage, FSG-SA films containing 1.0 or 2.0 mg/mL carvacrol could significantly reduce TVB-N content, K-value, the degree of microbial deterioration and maintain quality of sea bass fillets according to organoleptic evaluation results.

Complexation of Danube common nase (Chondrostoma nasus L.) oil by β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin

β-Cyclodextrin- and 2-hydroxypropyl-β-cyclodextrin/Danube common nase (Chondrostoma nasus L.) oil complexes (β-CD- and HP-β-CD/CNO) have been obtained for the first time. The fatty acid (FA) profile of the CNO indicates an important content of polyunsaturated fatty acids, the most important being eicosapentaenoic acid (EPA, 6.3%) and docosahexaenoic acid (DHA, 1.6%), both ω-3 FAs. The complexes have been obtained by kneading method. The moisture content and successful of molecular encapsulation have been evaluated by thermal and spectroscopic techniques. Thermogravimetry and differential scanning calorimetry analyses reveals that the moisture content of CD/CNO complexes significantly decreased, compared to starting CDs. On the other hand, the crystallinity index was for the first time determined for such type of complexes, the β-CD/CNO complex having values of 43.9(±18.3)%, according to X-ray diffractometry. FA profile and CD/CNO characteristics sustain the use of these ω-3 based complexes for food supplements or functional food products, but further studies are needed.

A Way to Increase the Bioaccesibility and Photostability of Roflumilast, a COPD Treatment, by Cyclodextrin Monomers

Roflumilast is an orally available inhibitor of phosphodiesterase (PDE) type 4, which is widely used in chronic obstructive pulmonary diseases. However, it has low solubility and adverse effects include diarrhea and nausea. Since its solubilization may improve treatment and, dismissing any adverse effects, its interaction with cyclodextrins (CDs) was studied. The Higuchi-Connors method was used to determine the complexation constant with different CDs, pH values and temperatures. Molecular docking was used to predict interaction between the complexes. An in vitro digestion experiment was carried out to test roflumilast protection. Finally, the photostability of the complex was evaluated. The complex formed with β-CD had the highest K₁₁ value (646 ± 34 M⁻¹), although this value decreased with increasing temperature. Similarly, K₁₁ decreased as the pH increased. In vitro digestion showed that CDs protect the drug during digestion and even improve its bioaccessibility. Finally, CDs reduced the drug’s extreme photosensitivity, originating a fluorescence signal, which is described for first time. The kinetic parameters of the reaction were obtained. This study not only completes the complexation study of roflumilast-CD, but also points to the need to protect roflumilast from light, suggesting that tablets containing the drug might be reformulated.

Efficient monooxygenase-catalyzed piceatannol production: Application of cyclodextrins for reducing product inhibition

Piceatannol is a rare, costly plant-based stilbene derivative and exhibits various health-enhancing properties. Recently, we demonstrated that piceatannol could be produced from resveratrol through site-selective hydroxylation using Escherichia coli cells expressing the monooxygenase HpaBC. However, piceatannol production ceased at approximately 25 mM, even when sufficient levels of the substrate resveratrol remained in the reaction mixture. In this study, we found that high concentrations (>20-25 mM) of piceatannol significantly inhibited the HpaBC-catalyzed reaction. Cyclodextrins (CDs) reportedly encapsulate various hydrophobic compounds. We found that the addition of β-CD or γ-CD to the reaction mixture reduced the inhibition caused by the product piceatannol. The effects of β-CD on piceatannol production were more pronounced than those of γ-CD at high concentrations of the substrate resveratrol and CDs. The production of piceatannol reached 49 mM (12 g L^-1) in the presence of β-CD, a level twice that achieved in the absence of β-CD. The technique described here might be applicable to the bioproduction of other stilbenes and structurally related compounds.

Physico-chemical studies of resveratrol, methyl-jasmonate and cyclodextrin interactions: an approach to resveratrol bioproduction optimization

trans-Resveratrol (RSV) is a natural phenolic molecule of the stilbene family known for its anti-oxidant properties in the field of nutraceuticals and cosmetics. Its production by grapevine cell suspensions is induced by the addition to the culture medium of elicitor compounds, methyl jasmonate (MeJA) and cyclodextrins (CDs). Physico-chemical studies were performed to understand the mechanism of action of CDs on this bioproduction of RSV. Inclusion complexes of RSV in CDs were first observed and then interactions with MeJA were identified using various analytical techniques such as UV and nuclear magnetic resonance (NMR) spectroscopies, mass spectrometry (MS) and isothermal titration calorimetry (ITC).

The role of cyclodextrins in the bioproduction of resveratrol in the presence of methyl-jasmonate is rationalized, leading to solutions for the improvement of bioproduction.

Encompassment of Benzyl Isothiocyanate in cyclodextrin using ultrasonication methodology to enhance its stability for biological applications

The use of methodical and innovative sonication method has been explored for the fabrication of inclusion complex of Benzyl Isothiocyanate, a potential anticancer and -antimicrobial agent. The advancement involved investigation of inclusion behaviour, characterisation and an in-depth study of thermal and UV stability of Benzyl Isothiocyanate with cyclodextrins; β-CD and hp-β-CD. The sonication driven encompassment in cyclodextrins helped to overcome the hindrance of low solubility and high volatility. Investigations of physical and thermodynamic parameters using UV-visible spectroscopy, FTIR, XRD, TGA etc confirmed stability of inclusion complexes. Both β-CD and hp-β-CD based inclusion complexes retained the antimicrobial property of the free Benzyl Isothiocyanate, indicating their potential utility as antimicrobial agents. Haematological safety and cellular uptake data gives direction to in-depth analysis for its exploitation of anti-tumour activity.

Encapsulation Mechanism of Oxyresveratrol by β-Cyclodextrin and Hydroxypropyl-β-Cyclodextrin and Computational Analysis

In this study, the encapsulation mechanism of oxyresveratrol and β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied. As this research shows, oxyresveratrol and two cyclodextrins (CDs) were able to form inclusion complexes in a 1:1 stoichiometry. However, the interaction with HP-β-CD was more efficient, showing up as higher encapsulation constant (K_F) (35,864.72 ± 3415.89 M⁻¹). The K_F values exhibited a strong dependence on temperature and pH, which decreased as they increased. From the thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) of the oxyresveratrol loaded β-CD (oxyresveratrol-β-CD) and HP-β-CD (oxyresveratrol-HP-β-CD), it could be seen that the complexation process was spontaneous and exothermic, and the main driving forces between oxyrsveratrol and CDs were hydrogen bonding and van der waals force. Besides, molecular docking combined with ¹H-NMR were used to explain the most possible mode of interactions between oxyresveratrol and CDs.

Preparation and biological activity studies of resveratrol loaded ionically cross-linked chitosan-TPP nanoparticles

Nanoparticles with size range of 10-500nm can be efficiently delivered into cancer cells by the Enhanced Permeability and Retention (EPR) effect. Here, we prepared resveratrol (Res) loaded chitosan (CS) nanoparticles with the size of 172-217nm by an ionic cross-linking method, with sodium tripolyphosphate (TPP) as the cross-linking agent, to improve the stability, solubility and tumors targeting of the natural anti-cancer drug Res. The prepared Res loaded CS-TPP nanoparticles presented long-term storage stability and UV light stability. The cumulative drug release from nanoparticles in mimetic tumor tissue condition (pH 6.5) was higher than that in physiological condition (pH 7.4). Further, Res-loaded CS-TPP nanoparticles maintained the antioxidant activity of Res even after UV light irradiation. Cell viability study shows that the as prepared drug loaded nanoparticles had similar antiproliferative activity on hepatocellular carcinoma cells SMMC 7721 and lower cytotoxicity on normal hepatocyte cells L02 compared with free Res. Fluorescence microscopy observation revealed that the nanoparticles were efficiently taken in by SMMC 7721 cells. This work indicates the potential use of drug loaded CS-TPP nanoparticles for the efficient delivery of bioactive Res for chemotherapy.

Separating and Identifying the Four Stereoisomers of Methyl Jasmonate by RP-HPLC and using Cyclodextrins in a Novel Way

INTRODUCTION

Several authors have reported on the different bioactivities of methyl jasmonate (MeJA) stereoisomers. However, no simple, precise and cheap method for separating and identifying them using reversed-phase high performance liquid chromatography (RP-HPLC) has been developed.

OBJECTIVE

(1) To create a simple, precise and cheap method for separating and identifying the four stereoisomers present in commercial racemic mixtures of MeJA and (2) to identify the four stereoisomers using molecular docking techniques and coinjection. Materials and Methods - RP-HPLC using a 250 mm C18 column and different proportions of cyclodextrins (CDs) and organic solvents was applied to a commercial sample of racemic MeJA.

RESULTS

The results show that the best conditions for separating the MeJA stereoisomers are: 20% methanol in the mobile phase, a temperature of 45 °C and a 16 mM concentration of methyl-β-cyclodextrin (M-β-CD). A simple C18 250 mm column and a flow rate of 1.25 mL/min were used. The reduction in the retention time of MeJA observed when M-β-CD is added to the mobile phases was used to determine the complexation constants of the guest/CD complex and compared with the obtained when other CDs were used. The K_F for M-β-CD (117.49 ± 5.9 1/M) was obtained with a 1:1 stoichiometry. The four stereoisomers were identified by molecular docking techniques and coinjection of a commercially available rosemary essential oil.

CONCLUSION

The new method identified and classified the four stereoisomers of MeJA in the following ordination: (-)epiMeJA, (-)MeJA; (+)MeJA and (+)epiMeJA. These results could be used to improve the elicitation of cell cultures with only the best isomer. Copyright © 2016 John Wiley & Sons, Ltd.

The inclusion complex of oxyresveratrol in modified cyclodextrins: A thermodynamic, structural, physicochemical, fluorescent and computational study

The interaction between oxyresveratrol (a type of stilbene with high biological activity) and modified cyclodextrins (CDs) was studied. Using HPLC-RP, was seen to form a 1:1 complex with all the CDs tested. The best CD in this respect was MβCD (K_F=606.65±30.18M^-1), the complexation showing a strong dependence on pH and temperature: The complexation constant (K_F) decreased as the pH and temperature increased. The thermodynamic parameters studied (ΔH°, ΔS° and ΔG°) showed negative entropy, enthalpy and Gibbs free energy change at 25°C. In addition, fluorescence signal of oxyresveratrol increased when MβCD was added. The oxyresveratrol emission and excitation spectra were obtained for first time. A ¹H NMR was carried out to study the structure of the complex and, DSC studied demonstrated the complexation. A computational study by molecular docking was made to complement the structural study.

Moisture evaluation of β-cyclodextrin/fish oils complexes by thermal analyses: A data review on common barbel (Barbus barbus L.), Pontic shad (Alosa immaculata Bennett), European wels catfish (Silurus glanis L.), and common bleak (Alburnus alburnus L.) living in Danube river

The moisture content of β-cyclodextrin/Danube fish oils complexes (common barbel, Pontic shad, European wels catfish, common bleak) was evaluated by thermal methods. Saturated and monounsaturated fatty acids were the most concentrated in fish oils (25.3-30.8% and 36.1-45.0%). ω-3 And ω-6 fatty acids were identified in low concentrations of 2.8-12.1% and 4.1-7.1%. The moisture content was significantly lowered after β-CD complexation, as revealed by thermogravimetric (TG) analysis (13.3% for β-CD, 2.5-6.5% for complexes). These results are consistent with the differential scanning calorimetry (DSC) data for the peaks corresponding to dissociation of water (calorimetric effect of 536Jg^-1 for β-cyclodextrin and 304-422.5Jg^-1 for complexes). Furthermore, both TG and DSC results support the formation of inclusion complexes. This is the first study on the nanoencapsulation of Danube fish oils in β-cyclodextrin.

Encapsulation of piceatannol, a naturally occurring hydroxylated analogue of resveratrol, by natural and modified cyclodextrins

In this work, an in-depth study of the interaction between piceatannol (a type of stilbene with high biological activity) and different natural and modified cyclodextrins (CDs) is made, using steady state fluorescence. This bioactive molecule forms a 1 : 1 complex with all the natural (α-CD, β-CD and γ-CD) and modified (HP-β-CD, HE-β-CD and M-β-CD) CDs tested. Among natural CDs, the interaction of piceatannol with β-CD was the most efficient. However, the modified CDs showed higher encapsulation constants (KF) than β-CD, except M-β-CD; the highest KF being found for HP-β-CD (14 048 ± 702 M(-1)). The encapsulation of piceatannol in the internal cavity of CDs showed a strong dependence on pH and temperature. The interaction between HP-β-CD and piceatannol was less effective in the pH region where the stilbene begins to suffer the deprotonation of its hydroxyl group. Moreover, the values of KF decreased as the system temperature increased. To obtain information on the mechanism involved in the piceatannol affinity for CD, the thermodynamic parameters of the complexation (ΔH°, ΔS° and ΔG°) were studied, the results showed a negative entropy (-3.7 ± 0.2 J mol(-1) K(-1)), enthalpy (-24.6 ± 1.2 kJ mol(-1)) and Gibbs free energy change at 25 °C (-23.5 ± 1.2 J mol(-1)). Finally, molecular docking calculations provided further insights into how the different interactions influence the complexation constant. A high degree of correlation was observed between the computed scores and experimental values.

Photoionization access to cyclodextrin-encapsulated resveratrol phenoxy radicals and their repair by ascorbate across the phase boundary

Photoionization with UV-A generates phenoxy radical ResO˙ of the famous red-wine antioxidant resveratrol inside cyclodextrin cavities without the participation of auxiliary reactants. This permits the isolated exploration of the ResO˙ repair by ascorbate at the water–cyclodextrin interface.

The main potentialities of resveratrol for drug delivery systems

Resveratrol (RSV), a natural polyphenol found in grapes, was found to be effective in the prevention and therapy of several diseases, however, it does have unfavourable physicochemical properties. In this context, an increasing number of studies have aimed at developing novel therapeutic systems for its delivery to overcome these disadvantages. This review focuses on the mechanisms of action and therapeutic applications. Finally, it also describes some tested formulations for RSV administration, controlled release and targeting, developed with the purpose of increasing RSV bioavailability.

Resveratrol production in bioreactor: Assessment of cell physiological states and plasmid segregational stability

Resveratrol is a plant secondary metabolite commonly found in peanuts and grapevines with significant health benefits. Recombinant organisms can produce large amounts of resveratrol and, in this work, Escherichia coli BW27784 was used to produce resveratrol in bioreactors while monitoring cell physiology and plasmid stability through flow cytometry and real-time qPCR, respectively. Initially, the influence of culture conditions and precursor addition was evaluated in screening assays and the data gathered was used to perform the bioreactor assays, allowing the production of 160 μg/mL of resveratrol. Cellular physiology and plasmid instability affected the final resveratrol production, with lower viability and plasmid copy numbers associated with lower yields. In sum, this study describes new tools to monitor the bioprocess, evaluating the effect of culture conditions, and its correlation with cell physiology and plasmid segregational stability, in order to define a viable and scalable bioprocess to fulfill the need for larger quantities of resveratrol.

Theoretical study of complexation of resveratrol with cyclodextrins and cucurbiturils: structure and antioxidative activity

The inclusion complexation of resveratrol with cyclodextrins and cucurbiturils and the influence of complexation on the antioxidative activity of resveratrol have been theoretically studied.

Energy efficient, facile and cost effective methodology for formation of an inclusion complex of resveratrol with hp-β-CD

A stable inclusion complex was obtained by using a greener, energy proficient approach via an ultrasonic method.

Physicochemical and thermodynamic characterization of the encapsulation of methyl jasmonate by natural and modified cyclodextrins using reversed-phase high-pressure liquid chromatography

Although the combinations of methyl jasmonate (MeJA) and cyclodextrins (CDs) have been used by different authors to stimulate the production of several metabolites, no study has been published about the possible formation of MeJA-CD complexes when these two molecules are added together to the reaction medium as elicitors. For this reason and because knowledge of the possible complexation process of MeJA with CD under different physicochemical conditions is essential if these two molecules are to be used in cell cultures, this paper looks at the complexation of MeJA with natural and modified CDs using a reversed-phase high-pressure liquid chromatography (RP-HPLC) system. The interaction of MeJA with β-CD was more efficient than with α- and γ-CDs. However, a modified CD, HP-β-CD, was the most effective of all of the CDs tested. Moreover, MeJA formed complexes with CD with a 1:1 stoichiometry, and the formation constants of these complexes were strongly dependent upon the temperature of the mobile phase used but not the pH. To obtain information about the mechanism of the affinity of MeJA for CD, the thermodynamic parameters ΔG°, ΔH°, and ΔS° were calculated. Finally, molecular modeling studies were carried out to propose which molecular interactions are established in the complexation process.

Eco-friendly separation of catechins using cyclodextrins as mobile phase additives in RP-HPLC

BACKGROUND

New mobile phases for RP-HPLC were developed for the separation of catechin compounds in tea. Cyclodextrin mobile phase additives decreased the use of toxic and inflammable organic solvents without compromising resolution or separation efficiency.

AIMS

To develop a simple greener method for analyzing five tea catechins in RP-HPLC, the mobile phase condition was optimized and the lowest organic modifier proportion with content resolutions and retention factors were obtained.

MATERIALS & METHODS

Eco-friendly cyclodextrins were used as mobile phase additives to decrease the proportion of organic modifier and improve resolutions and retention factors.

RESULTS

The effects of several physico-chemical parameters on the retention factors were investigate d and the optimum conditions were obtained on a conventional C₁₈ column, where the mobile phase consisted of acetonitrile/water (12/88, v/v) with 1.5 mmol/L β-cyclodextrin at a flow rate of 1.0 mL/min.

DISCUSSION

Cyclodextrins can separate analytes through host-guest complexation, where a transient diastereomeric complex is formed between the cyclodextrin and the analyte. β-Cyclodextrin is the most accessible, the least expensive and generally the most useful cyclodextrin.

CONCLUSION

This work developed a simple eco-friendly method with the lowest concentration of organic solvents. Under the optimal condition, five catechins could be baseline separated within 17 minutes in the isocratic mode. This research exhibited the potential for the separation and determination of other active compounds from natural plants by a greener method.

Comparative study of three methods for affinity measurements: capillary electrophoresis coupled with UV detection and mass spectrometry, and direct infusion mass spectrometry

We present affinity capillary electrophoresis and mass spectrometry (ACE-MS) as a comprehensive separation technique for label-free solution-based affinity analysis. The application of ACE-MS for measuring affinity constants between eight small molecule drugs [ibuprofen, s-flurbiprofen, diclofenac, phenylbutazone, naproxen, folic acid, resveratrol, and 4,4'-(propane-1,3-diyl) dibenzoic acid] and β-cyclodextrin is described. We couple on-line ACE with MS to combine the separation and kinetic capability of ACE together with the molecular weight and structural elucidation of MS in one system. To understand the full potential of ACE-MS, we compare it with two other methods: Direct infusion mass spectrometry (DIMS) and ACE with UV detection (ACE-UV). After the evaluation, DIMS provides less reliable equilibrium dissociation constants than separation-based ACE-UV and ACE-MS, and cannot be used solely for the study of noncovalent interactions. ACE-MS determines apparent dissociation constants for all reacting small molecules in a mixture, even in cases when drugs overlap with each other during separation. The ability of ACE-MS to interact, separate, and rapidly scan through m/z can facilitate the simultaneous affinity analysis of multiple interacting pairs, potentially leading to the high-throughput screening of drug candidates.

Extraction of phenolic compounds from grapes and their pomace using β-cyclodextrin

Use of aqueous cyclodextrins (CD) for recovery of selected bioactive phenolic compounds from grapes and their pomace was evaluated. When α, β and γ forms of CD were compared, β-CD was the most effective in recovering stilbenes, flavonols, and flavan-3-ols from grape pomace. The maximum quantified phenolics were obtained from the powder and the slurry of grape pomace when extracted with 2.5% (w/v) aqueous β-CD solutions at 60°C for 12-24h. With β-CD, total quantified phenolics obtained from the dry powder were 123 mg/100g (DW) while from the slurry, they were 35.8 mg/100g (FW). Incorporation of β-CD to grape mash prior to pressing for juice enhanced the recovery of phenolics in juice. Incorporation of β-CD was more effective in recovering flavan-3-ols than flavonols. Aqueous CD can effectively be used in recovering phenolics from by-products of fruit processing and therefore for functional foods and nutraceutical applications.

Use of reversed phase high pressure liquid chromatography for the physicochemical and thermodynamic characterization of oxyresveratrol/beta-cyclodextrin complexes

Knowledge of the complexation process of oxyresveratrol with beta-cyclodextrin (beta-CD) under different physicochemical conditions is essential if this potent antioxidant compound is to be used successfully in both food and pharmaceutical industries as ingredient of functional foods or nutraceuticals, despite its poor stability and bioavailability. In this paper, the complexation of oxyresveratrol with natural CDs was investigated for first time using RP-HPLC and mobile phases to which alpha-, beta-, and gamma-CD were added. Among natural CDs, the interaction of oxyresveratrol with beta-CD was more efficient than with alpha- and gamma-CD. The decrease in the retention times with increasing concentrations of beta-CD (0-4 mM) showed that the formation constants (KF) of the oxyresveratrol/beta-CD complexes were strongly dependent on both the water-methanol proportion and the temperature of the mobile phase employed. However, oxyresveratrol formed complexes with beta-CD with a 1:1 stoichiometry in all the physicochemical conditions tested. Moreover, to obtain information about the mechanism of the oxyresveratrol affinity for beta-CD, the thermodynamic parameters DeltaG degrees, DeltaH degrees and DeltaS degrees were obtained. Finally, to gain information on the effect of the structure of different compounds belonging to the stilbenoids family on the KF values, the complexation of other molecules, resveratrol, pterostilbene and pinosylvin, was studied and compared with the results obtained for the oxyresveratrol/beta-CD complexes.

Physicochemical study of the complexation of pterostilbene by natural and modified cyclodextrins

In this paper, the interaction between pterostilbene and cyclodextrins (CDs) is described for the first time using steady-state fluorescence. It was seen that pterostilbene forms a 1:1 complex with all of the natural (alpha-, beta-, and gamma-CDs) and modified (HP-beta-CD, methyl-beta-CD, and ethyl-beta-CD) CDs tested. Among natural CDs, the interaction of pterostilbene with beta-CD was the most efficient. However, all of the modified CDs showed higher complexation constants (K(F)) than beta-CD. The highest K(F) was found for HP-beta-CD (17520 +/- 981 M(-1)), in which its value showed a strong dependence upon pH in the region where the pterostilbene begins the deprotonation of its hydroxyl group. Moreover, the values of K(F) decreased as the system temperature increased. To obtain information on the mechanism of pterostilbene affinity for CD, the thermodynamic parameters of the complexation (DeltaH degrees , DeltaS degrees , and DeltaG degrees ) were studied. Finally, a comparison of the K(F) values obtained for three types of stilbenes revealed that both the stoichiometry and the K(F) values of the complex are dependent upon the structure of the guest molecule. While the trans-resveratrol-HP-beta-CD and pterostilbene-HP-beta-CD complexes showed a 1:1 stoichiometry with a higher K(F) value for the trans-resveratrol-HP-beta-CD complexes, trans-stilbene showed a 1:2 stoichiometry.

Effect of protonation and aggregation state of (E)-resveratrol on its hydroperoxidation by lipoxygenase

The protonation and aggregation states of (E)-resveratrol were used as tools to investigate the kinetic properties of lipoxygenase (LOX). It was found that the deprotonation of the 4'-hydroxyl group at pH values higher than the pK(a1) of (E)-resveratrol produced an increase in the LOX activity, with an optimum pH of 8.5. Moreover, the results show how LOX activity is strongly affected by the aggregation state of (E)-resveratrol. When the enzyme uses monomers of (E)-resveratrol as substrate, LOX shows a Michaelian behavior and the K(m) value can be determined (44.39 microM). However, when (E)-resveratrol concentration is increased to values higher than the critical concentration determined by fluorescence methods (35 microM at pH 8.5), LOX shows strong inhibition. These results can be interpreted as a previously unreported aggregate-induced enzyme inhibition, which can be modified by the use of different modulators of the aggregation state of (E)-resveratrol, such as cyclodextrins or ethanol. Finally, when the reaction was kinetically characterized in the optimum conditions of both aggregation and protonation state, a typical induction period was observed, along with a dependence of the hydroperoxidation rate with the hydrogen peroxide concentration.