Interaction of flavonoids within organized molecular assemblies of anionic surfactant

Drug-ionic surfactant interactions: density, sound speed, spectroscopic, and electrochemical studies

The failure of antibiotics against infectious diseases has become a global health issue due to the incessant use of antibiotics in the community and a lack of entry of new antibacterial drugs onto the market. The limited knowledge of biophysical interactions of existing antibiotics with bio-membranes is one of the major hurdles to design and develop more effective antibiotics. Surfactant systems are the simplest biological membrane models that not only mimic the cell membrane functions but are also used to investigate the biophysical interactions between pharmaceutical drugs and bio-membranes at the molecular level. In this work, volumetric and acoustic studies were used to investigate the molecular interactions of moxifloxacin (MXF), a potential antibacterial drug, with ionic surfactants (dodecyl-tri-methyl-ammonium bromide (DTAB), a cationic surfactant and sodium dodecyl sulfate (SDS), an anionic surfactant) under physiological conditions (phosphate buffer, pH 7.4) at T = 298.15-313.15 K at an interval of 5 K. Various volumetric and acoustic parameters were computed from the density and sound speed data and interpreted in terms of MXF-ionic surfactant interaction using electrostriction effect and co-sphere overlap model. Absorption spectroscopy and cyclic voltammetry were further used to determine the binding, partitioning, and related free energies of MXF with ionic micelles.

Interaction of sulphone based reactive dyes with cationic surfactant: a spectroscopic and conductometric study

Interaction of sulphone based reactive dyes, designated as dye-1 and dye-2, with cationic micellar system of cetyltrimethylammonium bromide (CTAB), has been investigated by spectroscopic and conductometeric measurements. Efficiency of the selected micellar systems is assessed by the values of binding constant (K b ), partition coefficient (K x ) and respective Gibbs energies. Critical micelle concentration (CMC) of surfactant, electrostatic and hydrophobic interactions as well as polarity of the medium plays significant role in this phenomenon. The negative values of Gibbs energies of binding (∆G b ) and partition (∆G p ) predicts the feasibility and spontaneity of respective processes. Similarly negative values of ∆G m and ∆H m and positive values of ∆S m , calculated from conductometeric data, further, revealed the exothermicity, spontaneity and, thus, stability of system. The results, herein, have disclosed the strong interaction between dye and surfactant molecules. The dye-2 has been observed to be solubilized to greater extent, as compared to dye 1, due to strong interaction ith hydrophiles of CTAB and accommodation of its molecules in palisade layer of micelle closer to the micelle/water interface.

Simulating Absorption Spectra of Flavonoids in Aqueous Solution: A Polarizable QM/MM Study

We present a detailed computational study of the UV/Vis spectra of four relevant flavonoids in aqueous solution, namely luteolin, kaempferol, quercetin, and myricetin. The absorption spectra are simulated by exploiting a fully polarizable quantum mechanical (QM)/molecular mechanics (MM) model, based on the fluctuating charge (FQ) force field. Such a model is coupled with configurational sampling obtained by performing classical molecular dynamics (MD) simulations. The calculated QM/FQ spectra are compared with the experiments. We show that an accurate reproduction of the UV/Vis spectra of the selected flavonoids can be obtained by appropriately taking into account the role of configurational sampling, polarization, and hydrogen bonding interactions.

Influence of micelles on protein's denaturation

To evaluate the role of micelles for protein-surfactant interaction, we have studied the binding modes of serum albumin proteins (human (HSA) and rabbit (RSA)) with anionic-surfactant, sodium dodecyl sulfate (SDS) by using UV-visible, fluorescence, circular dichroism, fluorescence lifetime, atomic force microscopy (AFM) techniques. The study performed with three different pHs (below (4.0), at (4.7), and above (7.0) isoelectric point). Hydrocarbon chain of the surfactant, dominant role of hydrophobic forces and electrostatic interactions helped in polar interaction on protein on binding surfaces. The change above and below the critical micelle concentration (CMC) in fluorescence spectra was due to polarity of the microenvironment. The CD spectra different binding aspects as below CMC and above CMC, explain about folding and unfolding in secondary structure. Surfactant's binding induces fluctuations in the microenvironment of aromatic amino acid's residues of both proteins at different pHs. AFM images clarify the structural changes in both proteins (HSA & RSA). AFM images also indicate some different interesting conformational and structural changes in both proteins below/above the CMC of the surfactant. The molecular docking studies indicate the binding energy -4.8 kcal mol^-1 and -4.7 kcal mol^-1 for HSA-SDS and RSA-SDS, respectively. Structural changes can be seen above and below the CMC.

Developing and Validating a Method for Separating Flavonoid Isomers in Common Buckwheat Sprouts Using HPLC-PDA

Buckwheat sprouts that are synthesized during the germination process are rich in flavonoids, including orientin, vitexin, rutin, and their isomers (isoorientin, isovitexin, and quercetin-3-O-robinobioside, respectively). The purpose of this study was to optimize and validate an analytical method for separating flavonoid isomers in common buckwheat sprout extract (CSE). Factors, such as range, linearity, precision, accuracy, limit of detection, and limit of quantification, were evaluated for each standard using high-performance liquid chromatography (HPLC). On the basis of resolution and symmetry, a column temperature of 40 °C with 0.1% (v/v) acidic water and acetonitrile as mobile phases, at a flow rate of 1 mL min⁻¹ were determined to be the optimal analytical conditions. Calibration curves for orientin, isoorientin, vitexin, isovitexin, and rutin exhibited good linearity with correlation coefficients of 0.9999 over the 6.25–100.00 μg mL⁻¹ range. Recovery values of 96.67–103.60% confirmed that the method was accurate for all flavonoids. The relative standard deviations of intra-day repeatability and inter-day reproducibility confirmed method preciseness, with values of less than 5.21% and 5.40%, respectively. The developed method was used to analyze flavonoids in CSE, with isomers satisfactorily separated and simultaneously quantified. We demonstrated that the developed HPLC method can be used to monitor flavonoids in buckwheat sprouts.

The Differential Spectroscopic Investigation of Partitioning of Reactive Dyes in Micellar Media of Cationic Surfactant, Cetyl Trimethylammonium Bromide (CTAB)

This manuscript reports the solubilization of two reactive dyes viz. reactive black-5 (RB-5) and reactive black-8 (RB-8) in the micellar media of cationic surfactant, cetyl trimethylammonium bromide (CTAB) by differential UV/visible spectroscopy. Absorption spectra of said dyes in the presence of CTAB provide strong evidence about dye–surfactant interaction. In premicellar region ion association pair is formed between dye and surfactant while in post micellar region dye molecules get accommodated within the micelles. The values of critical micelle concentration (CMC) of CTAB in the presence of dyes, partition coefficient; Kx , free energy of partition, ∆Gp , binding constant, Kb and free energy of binding, ∆Gb were determined and compared for both dyes. It is, thus, concluded that RB-5 is solubilized to greater extent than RB-8 because of its incorporation in palisade layer of micelle close to micelle-water interface.

Partitioning of reactive yellow 86 between aqueous and micellar media studied by differential absorption spectroscopy

The present study describes the partitioning of a reactive dye, reactive yellow 86, between aqueous and micellar media of a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB), as well as an anionic surfactant (sodium dodecyl sulphate, SDS). In a systematic investigation, we have recorded the UV–vis absorption spectra of the dye as a function of surfactant’s concentration above and below the critical micelle concentration (CMC). Absorption spectra display a red shift in the case of CTAB and a hypochromic shift upon using SDS. The partition coefficient (Kx) was calculated using differential absorption data, and the value of free energy of partition (ΔGp) was calculated using this Kx value. The results revealed that the dye is solubilized in CTAB micelles to a greater extent than in SDS micelles.

Quercetin solubilisation in bile salts: A comparison with sodium dodecyl sulphate

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Quercetin partitions into bile salt and SDS micelles.

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Quercetin’s UV–visible spectra reflect its environment and micelle formation.

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Quercetin’s binding site is more hydrophobic in bile salt micelles.

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Pyrene fluorescence confirms quercetin’s spectral data.

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The results contribute to understanding quercetin’s low bioavailability.

To understand the bioaccessibility of the flavonoid quercetin we studied its interaction with bile salt micelles. The environmental sensitivity of quercetin’s UV–visible absorption spectrum gave information about quercetin partitioning. Two quercetin absorption peaks gave complementary information: Peak A (240–280 nm) on the intermicellar phase and Peak B (340–440 nm) on the micellar phase. Thus, by altering pH, we showed that only non-ionised quercetin partitions into micelles. We validated our interpretation by studying quercetin’s interaction with SDS micelles. Pyrene fluorescence and the quercetin UV–visible spectra show that the adsorption site for pyrene and quercetin in bile salt micelles is more hydrophobic than that for SDS micelles. Also, both quercetin and pyrene reported a higher critical micelle concentration for bile salts than for SDS. Our method of using a flavonoid as an intrinsic probe, is generally applicable to other lipophilic bioactives, whenever they have observable environmental dependent properties.

Ultrasonic-assisted extraction of pigments from Hylocereus undatus flowers: optimization, antioxidant activity, and HPLC analysis

Optimization extraction, antioxidant activity, and HPLC analysis of pigments fromHylocereus undatusflowers.

Thermodynamic and spectroscopic investigation of interactions between reactive red 223 and reactive orange 122 anionic dyes and cetyltrimethyl ammonium bromide (CTAB) cationic surfactant in aqueous solution

The present study describes the conductometric and spectroscopic study of the interaction of reactive anionic dyes, namely, reactive red 223 and reactive orange 122 with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB). In a systematic investigation, the electrical conductivity data was used to calculate various thermodynamic parameters such as free energy (ΔG), enthalpy (ΔH), and the entropy (ΔS) of solubilization. The trend of change in these thermodynamic quantities indicates toward the entropy driven solubilization process. Moreover, the results from spectroscopic data reveal high degree of solubilization, with strong interactions observed in the cases of both dyes and the CTAB. The spontaneous nature of solubilization and binding was evident from the observed negative values of free energies (ΔG_p and ΔG_b).

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.

Chemical analysis of the resinous exudate isolated from Heliotropium taltalense and evaluation of the antioxidant activity of the phenolics components and the resin in homogeneous and heterogeneous systems

H. taltalense (Phil.) Johnst. (Heliotropiaceae) is an endemic species of the northern coast of Chile that produces a resinous exudate that covers its foliar surface and stems. Its chemical composition was analyzed for the first time, and two aromatic geranyl derivatives: filifolinol and filifolinyl senecionate and three flavonoids – naringenin, 3-O-methylgalangin and 7-O-methyleriodictiol – were isolated. The antioxidant activity of the flavonoids and the resinous exudates was carried out by measuring the 1,1-diphenyl-2-picrylhydrazyl (DPPH) bleaching effect in ethanolic solution and in sodium dodecyl sulfate (SDS) micelles. The influence of the reaction medium was analyzed. The initial velocity reactions for the pure compounds and for the extract were higher in SDS media than in ethanolic solution. The velocity of reaction observed was interpreted in terms of the reaction medium environment in the micelle.

Effect of spectroscopic properties on photostability of tamoxifen citrate polymorphs

The photostability of tamoxifen citrate polymorphs, forms A and B, was investigated by chromatographic and spectroscopic analyses including high-pressure liquid chromatography (HPLC), colorimetry and UV/vis solid-state absorption spectroscopy. On the basis of the results of photostability studies under irradiation by visible light and both UVA (320-400 nm) and a fraction of UVB (290-320 nm) light, form A was chemically unstable, whereas form B was stable against light irradiation. The surface color of pellets prepared with any of these crystal forms turned from white to brown; however, the extent of color change in cross-sections of form A pellet was deeper than that of form B pellet. The maximum peak of UV/vis solid-state absorption spectra of form A was observed at 337 nm within the UVA range and was in longer wavelength regions than form B, which exhibited the strong UV absorption mainly in UVB and UVC region. The results obtained suggested that the photodegradation followed by surface color change of form A crystal was caused by the selective absorption of photoenergy of UVA light irradiated by a xenon lamp.

Optimization of the separation of flavonoids using solvent-modified micellar electrokinetic chromatography

In this work the separation of eighteen flavonoids was attempted using reduced-flow micellar elektrokinetic chromatography (RF-MEKC) electrolytes modified by selected solvents with differing properties: methanol (MeOH), acetonitrile (ACN) and tetrahydrofuran (THF). Structural aspects such as unsaturation of the C ring, number and position of OH groups, methylation and glycosylation as well as solvent effects and their impact on the electrophoretic behavior of flavonoids were addressed. By evaluating the electropherograms obtained from mixture-designed electrolytes and searching for changes in the critical pairs, a favorable separation condition was achieved using 20 mmol/L phosphate buffer at pH 2.5 containing 50 mmol/L sodium dodecyl sulfate (SDS), 15% ACN and 5% THF (one critical pair) in less than 12 min with 1.5% coefficient of variation (CV) for retention factor and 3% CV for peak area (n = 5). The applicability of the proposed separation condition was demonstrated by the inspection of flavonoids in herbal extracts of Neem.