Interaction between flavonoid, quercetin and surfactant aggregates with different charges

The interactions of flavonoid, quercetin with sodium dodecyl sulfate (anionic surfactant) and cetyltrimethyl ammonium bromide (cationic surfactant) micelles were investigated. The average location site of quercetin in different micelles was determined by the cyclic voltammetry method with the aid of molecular optimization. The interaction parameters of quercetin with micelles of different charges such as binding constant K and normal binding energy DeltaG were calculated. Furthermore, the morphologic change of the SDS and CTAB spherical micelles and rod-like micelles upon their interaction with quercetin was also observed.     

Specific Deuteration in Patuletin and Related Flavonoids via Keto–Enol Tautomerism: Solvent‐ and Temperature‐Dependent 1H‐NMR Studies

An H/D exchange process in patuletin ( 1 ) and its derivatives in D‐donor solvents (e.g., CF₃COOD), which occurs regioselectively at C(8) was observed for the first time during NMR studies. The effect of substituents and temperature on the deuteration of various flavonoids (see Fig. 1) which include apigenin, chrysin, galangin, kaempferol, luteolin, morin, myricetin, patuletin, patulitrin, and quercetin, as well as derivatives of patuletin was examined extensively under NMR conditions. The rate constant of deuteration at C(8) of patuletin ( 1 ) and two flavones, luteolin ( 3 ) and apigenin ( 12 ), was also determined in CF₃COOD. The D‐atom was introduced into the flavonoids via a keto–enol tautomerism (Scheme 1). During these studies, monodeuterated patuletin was also obtained as a new compound. The examined flavonoids have been reported to possess significant pharmacological activities, and their deuterated derivatives would be of importance for the identification and quantification of these compounds in biological matrices.     

Surfactant‐assisted dispersive liquid–liquid microextraction of nitrazepam and lorazepam from plasma and urine samples followed by high‐performance liquid chromatography with UV analysis

Surfactant‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with UV detection has been developed for the simultaneous preconcentration and determination of lorazepam and nitrazepam in biological fluids. In this study, an ionic surfactant (cetyltrimethyl ammonium bromide) was used as an emulsifier. The predominant parameters affecting extraction efficiency such as the type and volume of extraction solvent, the type and concentration of surfactant, sample pH, and the concentration of salt added to the sample were investigated and opted. Under the optimum conditions (extraction solvent and its volume, 1‐octanol, 70 μL; surfactant and its concentration, 1 mL of ultra‐pure water containing 2 mmol L^?1 cetyltrimethyl ammonium bromide; sample pH = 9 and salt content of 10% NaCl w/v), the preconcentration factors were obtained in the range of 202–241 and 246–265 for nitrazepam and lorazepam, respectively. The limits of quantification for both drugs were 5 μg L^?1 in water sample and 10 μg L^?1 in biological fluids with R² values higher than 0.993. The suitability of the proposed method was successfully confirmed by the extraction and determination of the target drugs in human urine and plasma samples in the range of microgram per liter.     

Statistical optimization of an RP‐HPLC method for the determination of selected flavonoids in berry juices and evaluation of their antioxidant activities

An isocratic RP‐HPLC method for the separation and identification of selected flavonoids (quercetin, rutin, luteolin‐7‐O‐glucoside, kaempferol and kaempferol‐3‐O‐glucoside) in commercial berry juices (blackcurrant, blueberry, red raspberry and cherry) was developed with the aid of central composite design and response surface methodology. The optimal separation conditions were a mobile phase of 85:15 (% v/v) water–acetonitrile, pH 2.8 (adjusted with formic acid), flow rate 0.5 mL min⁻¹ and column temperature 35°C. The obtained levels of bioflavonoids (mg per 100 mL of juice) were as follows: for quercetin, ca. 0.21–5.12; for kaempferol, ca. 0.05–1.2; for rutin, ca. 0.4–6.5; for luteolin‐7‐O‐glucoside, ca. 5.6–10.2; and for kaempferol‐3‐O‐glucoside, ca. 0.02–0.12. These are considerably lower than the values in fresh fruits. Total phenolic, flavonoid and anthocyanin contents were determined spectrophotometrically. Total flavonoid content varied as follows: blackcurrant > blueberry > red raspberry > cherry. The antioxidant activity of juice extracts (DPPH and ABTS methods) expressed as IC₅₀ values varied from 8.56 to 14.05 mg L⁻¹. These values are ~2.5–3 times lower than quercetin, ascorbic acid and Trolox®, but compared with rutin and butylhydroxytoluene, berries show similar or better antioxidant activity by both the DPPH and ABTS methods.     

Comparison of Electrochemical Oxidation of Flavonols and Calculated Proton Affinity and Electron Transfer Enthalpy in Water

Flavonols, a class of flavonoids, are present in flowers, fruits and vegetables. They are jointly responsible for antioxidant activity as free radical acceptors. The redox behaviour of myricetin, quercetin, isorhamnetin, fisetin, morin and kaempferol is investigated using cyclic and differential pulse voltammetry. Quantum chemical calculations of proton affinities and electron transfer enthalpies were performed to identify possible reactive sites and radical species to compare them with measured oxidation potentials of the flavonols. Regarding to their chemical structure, these flavonols showed an oxidation order: myricetin > quercetin > isorhamnetin > fisetin > morin > kaempferol.     

Preparation of ionic liquid‐modified magnetic nanoparticles based on thiol‐ene click chemistry for the analysis of polycyclic aromatic hydrocarbons in water and smoked meat samples

In the present study, ionic liquid (IL)‐modified Fe₃O₄ magnetic nanoparticles (Fe₃O₄) were synthesized by the thiol‐ene click reaction for magnetic solid‐phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs) in water and smoked meat samples. An IL 1‐vinyl‐3‐butylimidazolium bromide was firstly synthesized, and then immobilized on the surface of thiol group‐functionalized Fe₃O₄ via a thiol‐ene click reaction. The as‐synthesized Fe₃O₄@ILs were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscopy. Various parameters (including the amount of adsorbent, extraction time, sample volume, and desorption conditions) affecting MSPE were optimized. Under the optimum conditions, the limits of detection of four PAHs in the range of 0.6–7.2 ng/L were obtained using high‐performance liquid chromatography–ultraviolet detection. The accuracy of the method was assessed by recovery measurements on spiked real samples and good recovery of 80–108% with relative standard deviations lower than 8.16% was achieved. The enrichment factors ranging from 699 to 858 were obtained for the analytes. This result indicated that the proposed method had great potential for sample preparation.     

Preparation and characterization of copper nanoparticles surface‐capped by alkanethiols

Cu nanoparticles surface‐capped by alkanethiols were synthesized using ligand exchange method in a two‐phase system. The effects of synthetic conditions, including the pH value of CuSO₄ solution, the ratio of cetyltrimethyl ammonium bromide to CuSO₄, and reaction temperature, on the size and shape of as‐synthesized Cu nanoparticles were investigated. As‐synthesized Cu nanoparticles surface‐capped by alkanethiols with different chain lengths (C_xS‐Cu) were characterized by means of X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and ultraviolet–visible light spectrometry. The tribological behavior of C_xS‐Cu as an additive in liquid paraffin was evaluated with a four‐ball machine. Results indicate that cetyltrimethyl ammonium bromide plays an important role in controlling the dispersion of Cu nanoparticles before adding modifier octanethiol into the reaction solution. C_xS‐Cu nanoparticles as additive in liquid paraffin possess excellent antiwear and friction‐reduction performance because of the deposition of nano‐Cu with low melting point on worn steel surface leading to the formation of a self‐repairing protective layer thereon. Copyright © 2013 John Wiley & Sons, Ltd.     

Superparamagnetic Fe3O4@SiO2 core–shell composite nanoparticles for the mixed hemimicelle solid‐phase extraction of benzodiazepines from hair and wastewater samples before high‐performance liquid chromatography analysis

Magnetic Fe₃O₄/SiO₂ composite core–shell nanoparticles were synthesized, characterized, and applied for the surfactant‐assisted solid‐phase extraction of five benzodiazepines diazepam, oxazepam, clonazepam, alprazolam, and midazolam, from human hair and wastewater samples before high‐performance liquid chromatography with diode array detection. The nanocomposite was synthesized in two steps. First, Fe₃O₄ nanoparticles were prepared by the chemical co‐precipitation method of Fe(III) and Fe(II) as reaction substrates and NH₃/H₂O as precipitant. Second, the surface of Fe₃O₄ nanoparticles was modified with shell silica by Stober method using tetraethylorthosilicate. The Fe₃O₄/SiO₂ composite were characterized by X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. To enhance their adsorptive tendency toward benzodiazepines, cetyltrimethylammonium bromide was added, which was adsorbed on the surface of the Fe₃O₄/SiO₂ nanoparticles and formed mixed hemimicelles. The main parameters affecting the efficiency of the method were thoroughly investigated. Under optimum conditions, the calibration curves were linear in the range of 0.10–15 μgmL^?1. The relative standard deviations ranged from 2.73 to 7.07%. The correlation coefficients varied from 0.9930 to 0.9996.     

Effect of ionic micellar medium on kinetics and mechanism of oxidation of bovine serum albumin: A pulse radiolysis study

Effect of protein–micelle interaction on bovine serum albumin (BSA) oxidation by trichloromethyl peroxyl radical (CCl₃O₂^·) in anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethyl ammonium bromide (CTAB) micellar media has been studied using nanosecond pulse radiolysis technique. Viscosity measurement and light scattering studies have suggested that SDS and CTAB micelles produce BSA–micelle aggregates of different sizes and polydispersity. Oxidation kinetics and transients have been affected both by anionic SDS and cationic CTAB micelles but in a different manner. Tryptophanyl-CCl₃O₂^· adduct radical to tyrosyl radical transformation in BSA has been observed in anionic SDS micelles but not in cationic CTAB micelles. Similar studies have also been done with tryptophan and tyrosine amino acids, which undergo oxidation in BSA. The study suggests that Coulombic and hydrophobic interactions between micelles and protein affect the structure of the protein to shield its functional amino acids, like tryptophan and tyrosine, to neutral oxidizing radical.     

Molecular imprinted polymer for solid‐phase extraction of flavonol aglycones from Moringa oleifera extracts

Molecular imprinted polymer produced using quercetin as the imprinting compound was applied for the extraction of flavonol aglycones (quercetin and kaempferol) from Moringa oleifera methanolic extracts obtained using heated reflux extraction method. Identification and quantification of these flavonols in the Moringa extracts was achieved using high performance liquid chromatography with ultra violet detection. Breakthrough volume and retention capacity of molecular imprinted polymer SPE was investigated using a mixture of myricetin, quercetin and kaempferol. The calculated theoretical number of plates was found to be 14, 50 and 8 for myricetin, quercetin and kaempferol, respectively. Calculated adsorption capacities were 2.0, 3.4 and 3.7 μmol/g for myricetin, quercetin and kaempferol, respectively. No myricetin was observed in Moringa methanol extracts. Recoveries of quercetin and kaempferol from Moringa methanol extracts of leaves and flowers ranged from 77 to 85% and 75 to 86%, respectively, demonstrating the feasibility of using the developed molecularly imprinted SPE method for quantitative clean‐up of both of these flavonoids. Using heated reflux extraction combined with molecularly imprinted SPE, quercetin concentrations of 975 ± 58 and 845 ± 32 mg/kg were determined in Moringa leaves and flowers, respectively. However, the concentrations of kaempferol found in leaves and flowers were 2100 ± 176 and 2802 ± 157 mg/kg, respectively.     

Alcohol‐based deep eutectic solvent as a carrier of SiO2@Fe3O4 for the development of magnetic dispersive micro‐solid‐phase extraction method: Application for the preconcentration and determination of morin in apple and grape juices,diluted and acidic extract of dried onion and green tea infusion samples

In this study, a hydrophilic deep eutectic solvent was synthesized as a carrier and disperser of magnetic nanoparticles based on ferrofluid and used to develop the dispersive micro‐solid‐phase extraction method. Ethylene glycol/tetramethylammonium chloride deep eutectic solvent and SiO₂@Fe₃O₄ were used to provide the highly stable ferrofluid with strong sorbing properties without any additional stabilizer, which was employed to extract and determine morin in apple and grape juices, diluted and acidic extract of dried onion, and green tea infusion samples. The dispersibility of SiO₂@Fe₃O₄ and prevention of its aggregation in the sample solution were improved using the deep eutectic solvent‐based ferrofluid. Also, it facilitated the fast injection of sorbent into the sample solution that led to an increase of the contact surface between the sorbent and analyte, and reduction of the extraction time and consumption of the sorbent. The important experimental parameters influencing the extraction efficiency of morin were examined. Under the optimal conditions, a linear calibration curve was obtained in the range of 3–500 µg/L with a determination coefficient of 0.9994. The limits of detection and quantification were of 0.91 and 2.98 µg/L, respectively. While an extraction recovery of 97.7% with relative standard deviation of 3.8% (interday) was obtained via three replicated measurements on a 30 µg/L of morin standard solution, the enrichment factor was 39.1. Finally, this method was successfully used to extract and preconcentrate morin in various samples, followed with their determination by high‐performance liquid chromatography with ultraviolet detection.     

Interaction of flavonoids,the naturally occurring antioxidants with different media: A UV–visible spectroscopic study

Quantitative parameters for interaction of flavonoids—the naturally occurring antioxidants, with solvents and surfactants are determined using UV–visible absorption spectroscopy. The availability of flavonoids; kaempferol, apigenin, kaempferide and rhamnetin in micelles of sodium dodecyl sulfate (SDS) is reflected in terms of partition coefficient, K_c. Thermodynamic calculations show that the process of transfer of flavonoid molecules to anionic micelles of SDS is energy efficient. A distortion in flavonoid's morphology occurs in case of kaempferol and apigenin in surfactant and water, exhibited in terms of a new band in the UV region of electronic spectra of these flavonoids. The partition coefficients of structurally related flavonoids are correlated with their antioxidant activities.     

Characterisation of an extract and fractions of Azadirachta indica flower on cholesterol lowering property and intestinal motility

Azadirachta indica has long been used in traditional medicine. This study focused on isolation and characterisation of active ingredients in the extract, its fractions (NF-EA, NF-AQ, NF-G) and its effect on the cholesterol absorption activity. The NF-EA fraction was identified by marker compounds by LC-ESI-QTOF/MS. Cholesterol absorption activity was performed by measuring the solubility and size of cholesterol micelles. The intestinal motility was also examined by isolated rat’s ileum to test the contraction. The extract and its fractions consist of flavonoids and phenolic compounds, like quercetin, kaempferol and myricetin. We found that A. indica extract and NF-EA increase cholesterol micelles size, while the extract, NF-AQ, myricetin and quercetin, reduced the solubility of cholesterol in micelles. The extract and quercetin inhibited the contraction induced by KCl up to 29 and 18%, respectively, and also decreased CaCl₂-induced contraction. This finding is in support to traditional uses of A. indica as cholesterol-lowering agents and regulator of gastrointestinal motility.     

Flavonoid glycosides from Persea caerulea. Unraveling their interactions with SDS‐micelles through matrix‐assisted DOSY,PGSE, mass spectrometry,and NOESY

Two flavonoid glycosides derived from rhamnopyranoside ( 1 ) and arabinofuranoside ( 2 ) have been isolated from leaves of Persea caerulea for the first time. The structures of 1 and 2 have been established by ¹H NMR, ¹³C NMR, and IR spectroscopy, together with LC–ESI–TOF and LC–ESI–IT MS spectrometry. From the MS and MS/MS data, the molecular weights of the intact molecules as well as those of quercetin and kaempferol together with their sugar moieties were deduced. The NMR data provided information on the identity of the compounds, as well as the α and β configurations and the position of the glycosides on quercetin and kaempferol. We have also explored the application of sodium dodecyl sulfate (SDS) normal micelles in binary aqueous solution, at a range of concentrations, to the diffusion resolution of these two glycosides, by the application of matrix‐assisted diffusion ordered spectroscopy (DOSY) and pulse field gradient spin echo (PGSE) methodologies, showing that SDS micelles offer a significant resolution which can, in part, be rationalized in terms of differing degrees of hydrophobicity, amphiphilicity, and steric effects. In addition, intra‐residue and inter‐residue proton–proton distances using nuclear Overhauser effect build‐up curves were used to elucidate the conformational preferences of these two flavonoid glycosides when interacting with the micelles. By the combination of both diffusion and nuclear Overhauser spectroscopy techniques, the average location site of kaempferol and quercetin glycosides has been postulated, with the former exhibiting a clear insertion into the interior of the SDS‐micelle, whereas the latter is placed closer to the surface. Copyright © 2016 John Wiley & Sons, Ltd.     

Dispersive liquid–liquid microextraction based on amine‐functionalized Fe3O4 nanoparticles for the determination of phenolic acids in vegetable oils by high‐performance liquid chromatography with UV detection

A novel dispersive liquid–liquid microextraction method based on amine‐functionalized Fe₃O₄ magnetic nanoparticles was developed for the determination of six phenolic acids in vegetable oils by high‐performance liquid chromatography. Amine‐functionalized Fe₃O₄ was synthesized by a one‐pot solvothermal reaction between Fe₃O₄ and 1,6‐hexanediamine and characterized by transmission electron microscopy and Fourier transform infrared spectrophotometry. A trace amount of phosphate buffer solution (extractant) was adsorbed on bare Fe₃O₄‐NH₂ nanoparticles by hydrophilic interaction to form the “magnetic extractant”. Rapid extraction could be achieved while the “magnetic extractant” on amine‐functionalized Fe₃O₄ nanoparticles was dispersed in the sample solution by vortexing. After extraction, the “magnetic extractant” was collected by application of an external magnet. Some important parameters, such as pH and volume of extraction and desorption solvents, the extraction and desorption time needed were carefully investigated and optimized to achieve the best extraction efficiency. Under the optimal conditions, satisfactory extraction recoveries were obtained for the six phenolic acids in the range of 84.2–106.3%. Relative standard deviations for intra‐ and inter‐day precisions were less than 6.3 and 10.0%, respectively. Finally, the established method was successfully applied for the determination of six phenolic acids in eight kinds of vegetable oils.     

A nanocomposite consisting of graphene oxide and Fe3O4 magnetic nanoparticles for the extraction of flavonoids from tea,wine and urine samples

We describe a single-step solvothermal method for the preparation of nanocomposites consisting of graphene oxide and Fe₃O₄ nanoparticles (GO/Fe₃O₄). This material is shown to be useful as a magnetic sorbent for the extraction of flavonoids from green tea, red wine, and urine samples. The nanocomposite is taking advantage of the high surface area of GO and the magnetic phase separation feature of the magnetic sorbent. The nanocomposite is recyclable and was applied to the extraction of flavonoids prior to their determination by HPLC. The effects of amount of surfactant, pH value of the sample solution, extraction time, and desorption condition on the extraction efficiency, and the regeneration conditions were optimized. The limits of detection for luteolin, quercetin and kaempferol range from 0.2 to 0.5 ng∙ mL⁻¹ in urine, from 3.0 to 6.0 ng∙mL⁻¹ in green tea, and from 1.0 to 2.5 ng∙mL⁻¹ in red wine. The recoveries are between 82.0 and 101.4 %, with relative standard deviations of <9.3 %.

The article describes a method for magnetic solid-phase extraction (MSPE) of trace amounts of natural substances in complex samples by using graphene oxide (GO)-Fe₃O₄nanoparticles as the sorbent.

     

Fe2+ and Co2+ Improved the Affinities of 7-Hydroxyflavone, Chrysin and Quercetin for Human Serum Albumin In Vitro

Chrysin, 7-hydroxyflavone, and quercetin were studied for their affinities with human serum albumin (HSA) in the presence and absence of Fe²⁺ and Co²⁺. The fluorescence intensities of HSA decrease remarkably with increasing concentration of the tested flavonoids. Chrysin resulted in a blue-shift of the emission line λ _em of HSA from 336 to 330 nm whereas quercetin showed an obvious red-shift of λ _em from 336 to 347 nm. However, the extents of the λ _em shifts induced by flavonoids in the presence of mental ions are much bigger than those of the corresponding systems in the absence of mental ions. Fe²⁺ and Co²⁺ increased the quenching constants of the tested flavonoids for HSA by 12.4–48.1 and 15.0–66.7 %, respectively. The affinities of 7-hydroxyflavone, chrysin and quercetin for HSA increased by about 6.42, 7.38 and 0.62 %, respectively, in the presence of Fe²⁺. Co²⁺ increased the affinities of 7-hydroxyflavone, chrysin, and quercetin for HSA about 8.43, 7.86 and 11.73 %, respectively.     

Extraction of diclofenac by SiO2‐NH2@Fe3O4 and its determination: Central composite design

In this work, magnetic nanoparticles (Fe₃O₄) were prepared by simple co‐precipitation method in aqueous medium and then subsequently modified with tetraethyl orthosilicate and 3‐aminopropyl triethylenesilane. The properties of the particles were characterized by FTIR spectroscopy X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy. The SiO₂‐NH₂@Fe₃O₄ particles were successfully applied to simultaneously enrich and separate diclofenac from water, urine, and plasma samples. The method, which takes the advantages of both nanoparticle adsorption and magnetic phase separation from the sample solution, could avoid some of the time‐consuming experimental procedures related to the traditional solid phase extraction. The main parameters affecting extraction and desorption efficiency such as pH, amount of SiO₂‐NH₂@Fe₃O₄, volume of desorption solvent, and extraction time were screened. The significant variables were optimized by using central composite design. At optimum conditions values of variables set as pH = 4, 10 mg SiO₂‐NH₂@Fe₃O₄, 0.5 mL methanol, and 15 min extraction time and then the extracted diclofenac were injected to HPLC for analysis. The linear response (r² > 0.9992) was obtained in the range of 0.004–15 µg/mL with detection limit 0.0012 µg/mL and extraction recovery was in the range of 92–96% with RSD < 5% (n = 6).     

Carbon Aerogels Synthesizd with Cetyltrimethyl Ammonium Bromide (CTAB) as a Catalyst and its Application for CO2 Capture

A series of carbon aerogels were synthesized by polycondensation of resorcinol and formaldehyde using cetyltrimethyl ammonium bromide (CTAB) as a catalyst. The structure and properties of carbon aerogels were characterized by X‐ray diffraction (XRD), Raman, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), and N₂ adsorption‐desorption technologies. Besides, the CO₂ capture behavior of carbon aerogels was also investigated. It was found that the amount of CTAB affected the structure and morphology of carbon aerogels, thus influenced the CO₂ adsorption behavior. The sample CA‐125 (the ratio of resorcinol and CTAB is 125) had the highest CO₂ adsorption capacity (63.71 cm³ · g^–1 at 1 bar and 24.14 cm³ · g^–1 at 0.15 bar) at 25 °C. In addition, the higher CO₂ adsorption capacity was ascribed to the higher surface area, pore volume and appropriate pore size, as well as the more defects over carbon aerogels.     

Determination of thermodynamic parameters for cloud point extraction of Arsenazo-III and Magdala Red dyes using mixed micelles: An essential requirement for high performance

A simple and low cost method for extraction and preconcentration of Arsenazo-III (ARS-III) and Magdala Red (MR) was developed by an efficient cloud point extraction (CPE) method using mixed micelles of Triton X–114 (TX–114) and cetyltrimethyl ammonium bromide (CTAB). Various parameters, such as pH/concentration of H₂SO₄, surfactant concentrations (TX-114 and CTAB), equilibrium temperature and time have been studied to maximise efficiency. Thermodynamic quantities like change in Gibbs free energy (ΔG⁰), change in enthalpy (ΔH⁰) and change in entropy (ΔS⁰) were calculated. The results show that the CPE of ARS-III and MR dye is feasible, spontaneous, and endothermic in the temperature range of (50–80) °C indicating good recoveries for the developed method. The effect of temperature, surfactant concentration and dye concentration on various thermodynamic quantities was investigated and it was found that ΔG⁰ values increased with temperature but decreased with surfactant and dye concentration. ΔH⁰ and ΔS⁰ values increased as surfactant concentration increased and decreased as dye concentration decreased. The recoveries were found to be the range from 90.02 – 101.03 % for ARS-III and 86.07–99.46 % for MR dyes which proves that the method is highly efficient.