Anionic Sodium Dodecyl Sulfate Micelles Research Articles

Capillary electrophoresis: Recent advancements and applications of micellar electrokinetic capillary chromatography

The article discusses capillary electrophoresis (CE) as an advanced technique used for the separation and detection of various pharmaceutical drugs. CE involves the application of high voltages across buffer-filled capillaries to produce separation based on various separation theories, including capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), capillary gel electrophoresis, and capillary isoelectric focusing. While traditional CZE is not suitable for the separation of neutral substances, MEKC was developed by Shigeru Terabe in the early 1990s to expand the use of CE to neutral analytes that cannot be separated using straightforward free solution CE. MEKC employs an ionic micellar solution that interacts with the analytes through partitioning processes like a chromatographic technique. To create a pseudostationary phase, a surfactant such as sodium dodecyl sulfate (SDS) is added to the buffer solution at a concentration higher than its critical micellar concentration. The anionic SDS micelles are electrostatically drawn towards the anode, while the electro-osmotic flow carries the bulk solution toward the negative electrode due to the negative charge on the inside surface of the silica capillaries. When a neutral analyte is introduced into the micellar solution, a portion is integrated into the micelle, while the remaining fraction of the analyte migrates with the electroosmotic velocity. Separation depends on the individual partitioning equilibrium of the various analytes between the micellar and the aqueous phase. The bigger percentage of analyte dispersed inside the micelle, the slower it will travel. This article provides an in-depth understanding of the separation principle and the mechanism involved in MEKC, highlighting its usefulness in separating neutral analytes that cannot be separated using traditional CZE.

Exploring cationic polyelectrolyte-micelle interaction via excited-state proton transfer. Signatures of probe transfer.

Excited-state proton transfer (ESPT) is a sensitive tool for the delicate monitoring of structural reorganization, hydration level, and confinement within surfactant and polymer assemblies. Here, we investigate the interaction of a cationic polyelectrolyte, poly(diallyl dimethylammonium chloride) (PDADMAC), with micelles of differently charged surfactants using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) as an ESPT probe. We used three surfactants: anionic sodium dodecyl sulfate (SDS), cationic dodecyl trimethylammonium bromide (DTAB), and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB12), possessing the same alkyl (dodecyl) chain but varying headgroup charges. The fluorescence of HPTS residing initially within the micellar medium modulates differently in the presence of PDADMAC. For the anionic SDS and cationic DTAB micelles, the emission spectrum of HPTS does not alter significantly; however, for SB12 micelles, the emission spectrum undergoes a strong modulation upon adding the polyelectrolyte. The emission intensities quench strongly at a low concentration of PDADMAC but recover at a higher concentration. The emission intensity ratio of the two emission bands also changes significantly, implying strong modulation of the ESPT process with varying PDADMAC concentrations. The time-resolved area normalized emission spectra (TRANES) disclose single isoemissive points in the SB12 micelle at low and high concentrations of PDADMAC but two different isoemissive points (one characteristic of the SB12 micelle at 500 nm and another characteristic of the PDADMAC interface at 480 nm) in the mixed assembly at an intermediate concentration. Detailed analysis suggests that the polyelectrolyte can enforce the transfer of the anionic probe HPTS from the zwitterionic micelle to the PDADMAC assembly above a specific PDADMAC concentration. The transfer of the molecular probe between two assemblies resembles a drug sequestration event, and the study reveals necessary emission signatures.

Spatial structure and oligomerization of viscotoxin A3 in detergent micelles: Implication for mechanisms of ion channel formation and membrane lysis

Thionins are the family of small (∼5 kDa) cationic cysteine-rich peptides involved in the immune response in plants. Viscotoxin A3 (VtA3) is the thionin from mistletoe (Viscum album) demonstrating antimicrobial and cytotoxic activity against cancer cells in vitro. VtA3 (charge +6) interacts with the membranes containing anionic lipids and forms cation-selective ion channels. Here we studied the VtA3 structure in membrane-mimicking media by NMR spectroscopy. Spatial structure of VtA3, consisting of a helical hairpin and a short β-sheet, was stable and did not undergo significant changes during micelle binding. VtA3 molecule bound with high affinity to the surface of zwitterionic dodecylphosphocholine (DPC) micelle by hydrophobic patch in the helical hairpin. Oligomerization of VtA3 was observed in the anionic micelles of sodium dodecylsulphate (SDS). No direct contacts between the peptide molecules were observed and the possible interfaces of detergent-assisted oligomerization were revealed. The data obtained suggest that the VtA3 membrane activity, depending on the concentration, obeys the ‘toroidal’ pore model or the ‘carpet’ mechanism. The model of the membrane disrupting complex, which explains the ion channel formation in the partially anionic membranes, was proposed.

Citrus sinensis peel waste assisted synthesis of AgNPs: effect of surfactant on the nucleation and morphology

Silver nanoparticles (AgNPs) were synthesized by using Citrus sinensis peel waste extract. Optical images and UV-visible spectroscopy reveals the appearance of yellow to brown-red color and surface plasmon resonance (SPR) band at 400–480 nm, respectively, due to the formation of AgNPs. The stable perfect transparent silver sols were formed in presence of cetyltrimethylammonium bromide (CTAB). The brownish precipitates appeared with sodium dodecyl sulphate (SDS) after 3 h. The nucleation, position of SPR band and intensity depends on the head group nature of cationic and anionic micelles of SDS and CTAB. The as-prepared AgNPs were characterized using conventional techniques such as Fourier-transform infra-red, energy dispersed X-ray detector, scanning electron microscope, transmission electron microscope, and X-ray diffractometer. Zeta potential of CTAB-AgNPs was calculated and found to be stable for ca. 1 week. Molar concentration (3.3 × 10−4 mol/L) and aggregation number (607,339.917) of DPE-AgNPs were calculated. Ascorbic acid, citric acid and total reducing sugars were estimated in dry and fresh peel extract. Gram positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria shows excellent antibacterial activities toward DPE-AgNPs.

Chemiluminescence Reactions of Luminol and N-Octyl Luminol with Hypochlorite in Anionic Surfactants

A comparative study of the kinetics of the chemiluminescent reaction of luminol, localized in the aqueous phase, and its hydrophobic analogue, N-octyl luminol, localized in the micellar phase, with the hypochlorite ion in anionic sodium dodecyl sulfate micelles at various surfactant concentrations is carried out. The dependence of the rate constant of the accumulation and decay of the intermediate product on the presence and concentration of the surfactant in the reaction mixture is determined.

Apelin conformational and binding equilibria upon micelle interaction primarily depend on membrane-mimetic headgroup

Apelin is one of two peptide hormones that activate the apelin receptor (AR or APJ) to regulate the cardiovascular system, central nervous system, and adipoinsular axis. Here, we apply circular dichroism (CD) spectropolarimetry and nuclear magnetic resonance (NMR) spectroscopy to characterize the potential membrane binding by the two longest bioactive apelin isoforms, apelin-55 and -36, using membrane-mimetic dodecylphosphocholine (DPC), sodium dodecyl sulfate (SDS), and 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] (LPPG) micelles. Pulsed field gradient diffusion NMR experiments demonstrated preferential interaction of both apelin-55 and -36 with anionic SDS and LPPG micelles over zwitterionic DPC micelles. Chemical shift perturbations and changes in ps-ns scale dynamics of apelin-55 in all micelles were similarly localized along the polypeptide backbone, demonstrating clear dependence upon detergent headgroup, while comparison of chemical shifts between apelin-55 and apelin-36 showed negligible differences indicative of highly similar modes of micelle interaction. Notably, the observed behaviour was consistent with an ensemble averaged pair of free and bound states in fast exchange on the NMR timescale proportional to the fraction of micelle-bound protein, implying a similar conformational equilibrium regardless of headgroup and tailgroup. Membrane catalysis of apelin-AR binding would thus give rise to analogous behaviour in the essential C-terminal region common to all apelin isoforms.

Fluorescence and electron paramagnetic resonance studies of norfloxacin and N-donor mixed-ligand ternary copper(II) complexes: Stability and interaction with SDS micelles

The stability of ternary copper(II) complexes of a heterocyclic ligand, L (L being 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)) and the fluorescent antibacterial agent norfloxacin (NFX) as the second ligand was studied at pH7.4 and different ionic strengths. Fluorescence quenching upon titration of NFX with the binary complexes allowed to obtain stability constants for NFX binding, Kb, as a function of ionic strength. The Kb values vary by more than two orders of magnitude when buffer concentration varies from 0.5 to 100mM. It was observed that previously synthesized ternary complexes dissociate in buffer according with the obtained stability constants. This shows that equimolar solutions of NFX and binary complexes are equivalent to solutions of synthesized ternary complexes. The interaction of the ternary copper complexes with anionic SDS (sodium dodecyl sulfate) micelles was studied by fluorescence and electron paramagnetic resonance (EPR). Titration of NFX-loaded SDS micelles with the complexes Cu:L allowed to determine the stability constants inside the micelles. Fluorescence quenching demonstrated that SDS micelles increase the stability constants by factors around 50. EPR spectra gave details of the copper(II) local environment, and demonstrated that the structure of the ternary complexes inside SDS micelles is different from that in buffer. Mononuclear ternary complexes formed inside the micelles, while in buffer most ternary complexes are binuclear. The results show that anionic membrane interfaces increase formation of copper fluoroquinolone complexes, which can influence bioavailability, membrane diffusion, and mechanism of action of the antibiotics.

Stabilising phycocyanin by anionic micelles

Phycocyanins are pigment-protein complexes with potential application as natural food colourants. The perceived colour of phycocyanins varies with pH, and a method to stabilise the colour over a broad range of pH values is requested by the food industry. In this work, the stabilising effect of sodium dodecyl sulphate (SDS) micelles on pH-induced colour variations of phycocyanin was examined. SDS was shown to stabilise the blue conformation of phycocyanin, preventing formation of the green conformation, which is prevalent at low pH. The studies indicated that the stabilising effect occurred through interaction or entrapment of the non-protonated, circular helical (blue) structure of phycocyanin and the anionic SDS micelles. The interaction prevented conversion into protonated, partially unfolded (green) phycocyanin species. This information opens for new possibilities to stabilise the blue conformation of phycocyanin and to apply the stabilised form in food products as a natural blue food colourant.

Interaction of 6-methoxyquinoline with anionic sodium dodecylsulfate micelles: Photophysics and rotational relaxation dynamics at different pH

Interactions of different species of 6-methoxyquinoline (6MQ) with anionic micelles have been studied at different pre-micellar, micellar and post-micellar concentrations using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The sensitivity of fluorescence of 6MQ to change in its local environment was used to probe sodium dodecylsulfate (SDS) micelles. At post-micellar concentrations of SDS, the observed blue shift in the fluorescence spectrum and increase in quantum yield are attributed to the incorporation of solute molecule to micelles. 6MQ has been found to bind to the surface of the anionic micelles instead of penetrating inside the core of micelles. The binding constant (Kb) calculated for 6MQ revealed that the electrostatic forces mediate charged probe–micelle association, whereas, hydrophobic interaction allowed neutral 6MQ to associate with SDS micelles. The charged 6MQ gets inserted deeper into the micelle surface than its neutral form. The fluorescence anisotropy decay of 6MQ in SDS micelles studied at different pH allowed determination of restriction of motion of the fluorophore. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, ET(30), average fluorescence decay time, radiative and non-radiative rate constants, and rotational relaxation time. The micro-environment around the fluorophore reveals that the photophysics of 6MQ is very sensitive to the microenvironment of SDS and probe molecules reside at the water–micelle interface.

Interaction of quinine sulfate with anionic micelles of sodium dodecylsulfate: A time-resolved fluorescence spectroscopy at different pH

Photophysical behavior and rotational relaxation dynamics of quinine sulfate (QS) in anionic surfactant, sodium dodecylsulfate (SDS) at different pH have been studied using steady state and time resolved fluorescence spectroscopy. It has been observed that the cationic form of quinine sulfate (at pH 2) forms a fluorescent ion pair complex with the surfactant molecules at lower concentrations of surfactant. However, for higher concentrations of SDS, the probe molecules bind strongly with the micelles and reside at the water–micelle interface. At pH 7, QS is singly protonated in bulk aqueous solution. At lower concentrations of SDS aggregation between probe and surfactant molecules has been observed. However, for higher concentrations of SDS, an additional fluorescence peak corresponding to dicationic form of QS appears and this has been attributed to double protonation of the QS molecule in micellar solution. At pH 7, in the presence of SDS micelles, the photophysical properties of QS showed substantial changes compared to that in the bulk water solution. At pH 12, an increase in fluorescence intensity and lifetime has been observed and this has been attributed to the increase in radiative rate due to the incorporation of QS at the micelle–water interface. The local pH at micellar surface has been found different from the pH of bulk solution.

Micelle-induced versatile sensing behavior of bispyrene-based fluorescent molecular sensor for picric acid and PYX explosives.

The effect of surfactant micelles on the photophysical properties of a cationic bispyrene fluorophore, Py-diIM-Py, was systemically examined. The results from series of measurements including UV-vis absorption, steady-state fluorescence emission, quantum yield, fluorescence lifetime, and time-resolved emission spectra reveal that the cationic fluorophore is only encapsulated by the anionic sodium dodecyl sulfate (SDS) surfactant micelles and not incorporated in the cationic dodecyltrimethylammonium bromide (DTAB) and neutral Triton X-100 (TX100) surfactant micelles. This different fluorophore location in the micellar solutions significantly influences its sensing behavior to various explosives. Fluorescence quenching studies reveal that the simple variation of micellar systems leads to significant changes in the sensitivity and selectivity of the fluorescent sensor to explosives. The sensor exhibits an on-off response to multiple explosives with the highest sensitivity to picric acid (PA) in the anionic SDS micelles. In the cationic DTAB micelles, it displays the highest on-off responses to PYX. Both the sensitivity and selectivity to PYX in the cationic micelles are enhanced compared with that to PA in the anionic micelles. However, the poor encapsulation in the neutral surfactant TX100 micelles leads to fluorescence instability of the fluorophore and fails to function as a sensor system. Time-resolved fluorescence decays in the presence of explosives reveal that the quenching mechanism of two micellar sensor systems to explosives is static in nature. The present work demonstrates that the electrostatic interaction between the cationic fluorophore and differently charged micelles plays a determinative role in adjusting its distribution in micellar solutions, which further influences the sensing behavior of the obtained micellar sensor systems.

Lipid Composition-Dependent Membrane Fragmentation and Pore-Forming Mechanisms of Membrane Disruption by Pexiganan (MSI-78)

The potency and selectivity of many antimicrobial peptides (AMPs) are correlated with their ability to interact with and disrupt the bacterial cell membrane. In vitro experiments using model membranes have been used to determine the mechanism of membrane disruption of AMPs. Because the mechanism of action of an AMP depends on the ability of the model membrane to accurately mimic the cell membrane, it is important to understand the effect of membrane composition. Anionic lipids that are present in the outer membrane of prokaryotes but are less common in eukaryotic membranes are usually thought to be key for the bacterial selectivity of AMPs. We show by fluorescence measurements of peptide-induced membrane permeabilization that the presence of anionic lipids at high concentrations can actually inhibit membrane disruption by the AMP MSI-78 (pexiganan), a representative of a large class of highly cationic AMPs. Paramagnetic quenching studies suggest MSI-78 is in a surface-associated inactive mode in anionic sodium dodecyl sulfate micelles but is in a deeply buried and presumably more active mode in zwitterionic dodecylphosphocholine micelles. Furthermore, a switch in mechanism occurs with lipid composition. Membrane fragmentation with MSI-78 can be observed in mixed vesicles containing both anionic and zwitterionic lipids but not in vesicles composed of a single lipid of either type. These findings suggest membrane affinity and membrane permeabilization are not always correlated, and additional effects that may be more reflective of the actual cellular environment can be seen as the complexity of the model membranes is increased.

Micellar effects on aromatic nucleophilic substitution by the ANRORC mechanism. Hydrolysis of 2‐chloro‐3,5‐dinitropyridine

The hydrolysis of 2‐chloro‐3,5‐dinitropyridine by sodium hydroxide in the presence of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and sodium dodecyl sulfate (SDS) has been studied. The reaction follows a consecutive reaction path involving the formation of a long‐lived intermediate 3 and finally giving the product, 3,5‐dinitro 2‐pyridone 2. The mechanism follows an addition of the nucleophile, ring opening and ring closure (ANRORC) reaction path. The rate constant was observed to be first‐order dependent on [OH−]. The rate of reaction increased on increasing [CTABr] and, after reaching to the maxima, it started decreasing. The anionic SDS micelles inhibited the rate of hydrolysis. The results of the kinetic experiments were treated with the help of the pseudophase ion exchange model and the Menger–Portnoy model. The added salts, viz. NaBr, Na‐toluene‐4‐sulphonate, and (CH3)4NBr on varying [CTACl] and [SDS] inhibited the rate of reaction. The various kinetic parameters in the presence and absence of salts were determined and are reported herewith. Copyright © 2011 John Wiley & Sons, Ltd.

Quantitative Analysis of Dye Decolourization Reactions in Mixed Micellar Systems of Sodium Dodecyl Sulfate with Tween-20, Tween-80, and Triton X-100

The reaction of triphenylmethane dye (ethyl violet) with hydroxyl ion has been investigated in absence and presence of micelles. In micellar solutions, the solubilization of dye carbocation is observed. The reaction rate constant follows pseudo-first order kinetics with respect to the nucleophile. In presence of sodium dodecyl sulfate (SDS) micelles, an inhibitory effect is observed due to repulsion of the nucleophile to the strongly bound dye carbocation in the negatively charged SDS aggregate. The presence of nonionic surfactant reduces the inhibitory effect of the anionic SDS micelles. Quantitative analysis of the micellar data obtained has been done by applying a positive cooperativity model of enzyme catalysis. The value of n (index of cooperativity) has been found to be greater than 1 for all systems under study. The presence of solvents such as ethanol, n-propanol, and n-butanol reduces the inhibitory effect of the micelles.

Micelle to solvent stacking of organic cations in micellar electrokinetic chromatography with sodium dodecyl sulfate

The on-line sample concentration technique, micelle to solvent stacking (MSS), was studied for small organic cations (quaternary ammonium herbicides, β-blocker drugs, and tricyclic antidepressant drugs) in reversed migration micellar electrokinetic chromatography. Electrokinetic chromatography was carried out in fused silica capillaries with a background solution of sodium dodecyl sulfate (SDS) in a low pH phosphate buffer. MSS was performed using anionic SDS micelles in the sample solution for analyte transport and methanol or acetonitrile as organic solvent in the background solution for analyte effective electrophoretic mobility reversal. The solvent also allowed for the separation of the analyte test mixtures. A model for focusing and separation was developed and the mobility reversal that involved micelle collapse was experimentally verified. The effect of analyte retention factor was observed by changing the % organic solvent in the background solution or the concentration of SDS in the sample matrix. With an injection length of 31.9 cm (77% of effective capillary length) for the 7 test drugs, the LODs (S/N = 3) of 5–14 ng/mL were 101–346-fold better when compared to typical injection. The linearity ( R 2, range = 0.025–0.8 μg/mL), intraday and interday repeatability (%RSD, n = 10) were ≥0.988, <6.0% and <8.5%, respectively. In addition, analysis of spiked urine samples after 10-fold dilution with the sample matrix yielded LODs = 0.02–0.10 μg/mL. These LODs are comparable to published electrophoretic methods that required off-line sample concentration. However, the practicality of the technique for more complex samples will rely on dedicated sample preparation schemes.

Ionic Quenching of Naphthalene Fluorescence in Sodium Dodecyl Sulfate Micelles

Micellar effects on luminescense of organic compounds or probes are well established, and here we show that quenching is highly favored in aqueous sodium dodecyl sulfate (SDS) micelles, which concentrate a naphthalene probe and cations of lanthanides, transition metals, and noble metals. Interactions have been studied by steady state and time-resolved fluorescence in examining the fluorescence suppression of naphthalene by metal ions in anionic SDS micelles. The quenching is collisional and correlated with the unit charge and the reduction potential of the metal ion. The rate constants, calculated in terms of local metal ion concentrations, are close to the diffusion control limit in the interior of SDS micelles, where the microscopic viscosity decreases the transfer rate, following the Stokes-Einstein relation.

Synthesis of Amphiphilic meso-Aryl­porphyrins in Organic Solvents and Aqueous Micellar Medium

Amphiphilic porphyrins find a remarkable place in chemistry of new materials due to their unique aromatic structure and spectral properties. Porphyrins and their metalloderivatives can be used as photoelectronic materials, sensors, electronics, photosensitized solar cells and organic light-emitting devices. Supramolecular synthetic methods and strategies rapidly develop, and porphyrins are particularly amenable to the design of complex and robust architectures because of their rigid framework. Architectural arrangement of the substituents plays an important role in such materials. Hydroxyl group side by side with carboxyl-group is often used to form supramolecular systems, and, at the other hand their asymmetry can provide interesting properties. Elaborations of the synthetic methods and obtaining of porphyrins in sufficient quantities are still in object of many researchers. In this study we have synthesized symmetrical and unsymmetrical amphiphilic tetraphenylporphyrins containing available hydroxylgroups and hydrophobic long chains. Two methods were explored – monopyrrole condensation in organic solvents mixture and in aqueous micellar medium. Initially both methods were used to produce meso-tetra(4-hydroxyphenyl) porphyrin. First method consists of the condensation of p-substituted benzaldehyde with pyrrole in mixed solvents (propionic acid, acetic acid and nitrobenzene). In this system nitrobenzene plays a role not only of the solvent, but of the efficient oxidant – the yields of porphyrins were doubled compared with those of the reaction system without nitrobenzene. The yields of this method were higher than from other general methods such as Adler method. Methodology of the isolation using mixed-solvents was fine-tuned. Yields were 39-43%. After that we have investigated the application of this method to the synthesis of the unsymmetrical amphiphilic porphyrins containing fatty alkyl residues. The aldehydes, 4-hydroxybenzaldehyde and 4-oxytetradecylbenzaldehyde, were condensed with pyrrole in ratio 3:1 and 1:3. Yields of the desired porphyrins were 10-13%, also the symmetrical porphyrins were obtained with sufficient yields 9-12%. The preparation of the meso-tetra(4-hydroxyphenyl)porphyrin using anionic sodium dodecyl sulfate micelles was the next step. Micelles act as potential wells, binding products more tightly than reactants, and may also catalyze condensation reactions. Choosing a micellar approach for the synthesis of amphiphilic porphyrins with long-chain substituents, we relied on the ability of these compounds to be embedded in micelles of various detergents, which are widely described in literature. By using this method meso-tetra(4hydroxyphenyl)porphyrin was obtained with 40% yield. In comparison with more hydrophilic aldehydes (like in the case of 4-hydroxybenzaldehyde), hydrophobic aldehydes gave much lower yields in micellar synthesis. For the first time we have proved a satisfiability of this method in condensation of the unsymmetrical aldehydes having hydroxylgroups and long alkyl substituents in phenyl rings. Yields of the porphyrins were 5-8% that is lower relatively the mixed solvents method. But it should be noted that monopyrrole condensation method in the micellar environment is easer in practice and more ecological. In the next stage of work it is planned to study the properties of these porphyrins, including liquid crystalline, and use them as syntons for subsequent functionalization of porphyrins.

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 (CCl 3O 2 · ) 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-CCl 3O 2 · 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.

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.

Salt effect on self-aggregation of sodium dodecylsulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB): Physicochemical correlation and assessment in the light of Hofmeister (lyotropic) effect

Amphiphile micellization is a well explored physicochemical process that can be affected by environmental conditions (temperature, pressure and additives). Salts have power to appreciably influence the water activity and self-association of ionic micelles; their effects on physicochemical processes are often examined in terms of Hofmeister or lyotropic series. In this work, physicochemical investigations on the self-association of sodium dodecylsulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB) in aqueous medium in presence of a number of monovalent, bivalent and trivalent inorganic and organic salts at μ = 0.01 at 303 K has been undertaken. Their critical micellar concentration (CMC), counter ion binding of micelles, and energetics of micellization have been estimated by the methods of conductometry and microcalorimetry. The ion effects on the physicochemical parameters have been found to poorly or loosely obey Hofmeister or lyotropic series; for a correlation, the lyotropic number ( L n) has been found to be better than both the effective hydrodynamic radius ( R h) and the polarizability ( α) of the counter ions (cations for anionic SDS micelles, and anions for cationic TTAB micelles).