Presence Of Sodium Dodecyl Sulfate Micelles Research Articles

Time-resolved detection of SDS-induced conformational changes in α-synuclein by a micro-stopped-flow system.

An intrinsically disordered protein, α-synuclein (αSyn), binds to negatively charged phospholipid membranes and adopts an α-helical structure. This conformational change is also induced by interaction with sodium dodecyl sulfate (SDS), which is an anionic surfactant used in previous studies to mimic membrane binding. However, while the structure of the αSyn and SDS complex has been studied widely by various static measurements, the process of structural change from the denatured state to the folded state remains unclear. In this study, the interaction dynamics between αSyn and SDS micelles was investigated using time-resolved measurements with a micro-stopped-flow system, which has been recently developed. In particular, the time-resolved diffusion based on the transient grating technique in combination with a micro-stopped-flow system revealed the gradual change in diffusion triggered by the presence of SDS micelles. This change is induced not only by binding to SDS micelles, but also by an intramolecular conformational change. It was interesting to find that the diffusion coefficient decreased in an intermediate state and then increased to the final state in the binding reaction. We also carried out stopped-flow-kinetic measurements of circular dichroism and intramolecular fluorescence resonance energy transfer, and the D change was assigned to the formation of a compact structure derived from the helix bending on the micelle.

Extending the stability of red and blue colors of malvidin-3-glucoside-lipophilic derivatives in the presence of SDS micelles

Anthocyanins lipophilization recently emerged as an efficient tool to deliver oil-soluble dyes aiming to expand their applications in lipophilic matrices such as cosmetics formulations. Sodium dodecyl sulfate (SDS) micelles were used to solubilize malvidin-3-glucoside derivatives bearing an ester chain derived from dodecanoic and hexanoic fatty acids. Detailed investigations on the kinetic and thermodynamic behavior of the pigments towards pH variations was carried out by means of UV-Vis spectroscopy. It was found that the pH domain of the red flavylium cation is extended in ca 0.3–0.4 pH units. The mole fraction of the quinoidal base at neutral conditions increased by 40% when compared with malvidin-3-glucoside in the same micellar media, which provides a great blue color stabilization. The results presented herein report for the first time the blue color stabilization of these lipophilic anthocyanin bioactives, opening new application fields as novel colorants for lipid-based foods and cosmetics.

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.

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.

Membrane Mimetics Induce Helix Formation and Oligomerization of the Chloride Intracellular Channel Protein 1 Transmembrane Domain

Chloride intracellular channel protein 1 (CLIC1) is a dual-state protein that can exist either as a soluble monomer or in an integral membrane form. The transmembrane domain (TMD), implicated in membrane penetration and pore formation, comprises helix α1 and strand β2 of the N-domain of soluble CLIC1. The mechanism by which the TMD binds, inserts, and oligomerizes in membranes to form a functional chloride channel is unknown. Here we report the secondary, tertiary, and quaternary structural changes of the CLIC1 TMD as it partitions between an aqueous and membrane-mimicking environment. A synthetic 30-mer peptide comprising the TMD was examined in 2,2,2-trifluoroethanol, sodium dodecyl sulfate (SDS) micelles, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes using far-ultraviolet circular dichroism and fluorescence spectroscopy. Data obtained in the presence of SDS micelles and POPC liposomes show that Trp35 and Cys24 have reduced solvent accessibility, indicating that the peptide adopts an inserted orientation. The peptide assumes a helical structure in the presence of these mimetics, consistent with its predicted membrane conformation. This acquisition of secondary structure is concentration-dependent, suggesting an oligomerization event. Stable dimeric and trimeric species were subsequently identified using SDS-polyacrylamide gel electrophoresis. We propose that, in the vicinity of membranes, the mixed α/β TMD in CLIC1 rearranges to form a helix that then likely dimerizes via noncovalent helix-helix interactions to form a membrane-competent protopore complex. Such oligomerization would be essential for forming a functional ion channel, given that each CLIC1 monomer possesses only a single TMD. This work highlights the central role of the TMD in CLIC1 function: It is capable of promoting membrane insertion and dimerization in the absence of the C-domain and large portions of the N-domain.

Cu2+-Induced Micellar Charge Selective Fluorescence Response of Acridine Orange: Effect of Micellar Charge, pH, and Mechanism

Photophysical properties of cationic Acridine Orange (AO) have been studied in different micellar environments [anionic SDS (sodium dodecyl sulfate), nonionic TX (TritonX-100), and cationic CTAB (cetyl trimethyl ammonium bromide)] at different pH, in the presence of a metal ion (Cu(2+)). At pH ∼ 8, addition of Cu(2+) results in AO fluorescence quenching in the presence of SDS micelle, enhancement of the same in the presence of TX micelle, and remaining unaltered in the presence of CTAB micelle. At pH ∼ 2, addition of Cu(2+) results in AO fluorescence quenching only in the presence of SDS micelle, and it remains mostly unaffected in the presence of TX and CTAB. Availability of Cu(2+) toward AO and binding of Cu(2+) with AO at the charged micellar interface are responsible for this pH-dependent Cu(2+)-mediated micellar charge selective fluorescence pattern.

Synthesis and antimicrobial activity of truncated fragments and analogs of citropin 1.1: The solution structure of the SDS micelle-bound citropin-like peptides

Citropin 1.1 is a basic, highly hydrophobic, 16-amino acid peptide (GLFDVIKKVASVIGGL-NH(2)), displaying wide-spectrum antimicrobial activities. In this paper we describe the synthesis and antimicrobial properties of citropin 1.1 and its 18 analogs constituting mostly truncated fragments of citropin 1.1. Moreover, we examined conformational properties of citropin 1.1 and its two analogs, (1-12)citropin and (1-13)[Ala(4)]citropin, using FTIR, CD and NMR spectroscopies. Three-dimensional structures of the peptides were determined using molecular dynamics (MD) simulations with time-averaged (TAV) restraints obtained from NMR spectra measured in micellar concentration of sodium dodecyl sulfate (SDS). Earlier investigations showed that in TFE solution, citropin 1.1 is a single helix all along the backbone. However, this structure is not retained in the presence of SDS micelle. In H(2)O/SDS-d(25) solution, citropin 1.1 adopts two alpha-helices in the fragments 4-7 and 10-16, respectively, separated by betaIV-turn at position 8, 9. The (1-12)citropin adopts an alpha-helical structure along the entire backbone. In turn, (1-13)[Ala(4)]citropin demonstrates the tendency to adopt only a short alpha-helix in the middle part. Moreover, the conversion of alpha-helix to 3(10)-helix has been noticed in about 30% of conformations. The 3(10)-helical units could be thermodynamic intermediates during folding and unfolding of the alpha-helical segment of the peptide.

Test films for test-determinations on the base of reagents, immobilized in gelatinous gel

Gelatinous solidified layers of the photographic film were used for the immobilization of analytical reagents for detection and determination of reductants and primary aromatic amines. It was shown, that the films with immobilized iron(III)-Dipy or iron(III)-Phen complexes as test films for reductants and films with immobilized aldehydes (vanillin, p-dimethylaminobenzaldehyde) as the test films for primary aromatic amines can be used. The improving of reagents immobilization in the presence of sodium dodecylsulfate micelles was obtained. Metrological characteristics of visual detection and photometric determination using test films were evaluated on the basis of statistical approach and investigation of detection probability distribution in the concentration range of unreliable reaction. The suggested test films for the determination of ascorbic acid, analgin (dipyrone), novocaine and streptocide in drugs were examined successfully.

Enhancement of Ostwald Ripening by Depletion Flocculation

The time dependence of the dynamic mobility and the ultrasonic attenuation of octane and decane oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS) was measured. The emulsions grew to larger droplets due to Ostwald ripening. The growth rate measured by attenuation depends on the surfactant concentration and the polydispersity of the emulsion. At surfactant concentrations below the critical micelle concentration (cmc) of SDS, the growth was linear with time and the rate was dependent on the polydispersity of the drops; the rate was several times faster than that predicted on the basis of a diffusion growth mechanism. Above the cmc, however, as the droplets grew in size there was a point at which the rate of growth increased, which corresponds to the droplet size at which depletion forces due to the surfactant micelles become significant. Under these conditions both the electroacoustic dynamic mobility and the acoustic attenuation spectra displayed characteristics of flocs: a large decrease in the phase lag at higher frequencies in the dynamic mobility spectrum and a decrease in the attenuation coefficient at low-megahertz frequencies with an increase at higher frequencies. This depletion flocculation enhancement in ripening rates in the presence of SDS micelles provides another, alternative, and self-consistent mechanism for the effect of surfactant micelles on Ostwald ripening.

Dediazoniation of 1‐naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

AbstractWe have measured the rates and product yields of dediazoniation of 1‐naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV–vis spectroscopy and high‐performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1‐naphthol (NOH), and the observed rate constants (kobs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase kobs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic DN + AN mechanism that involves the rate‐determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301–309, 2008

The Lipid-Associated 3D Structure of SPA, a Broad-Spectrum Neuropeptide Antagonist with Anticancer Properties

[D-Arg 1, D-Trp 5,7,9, Leu 11] substance P (SPA) belongs to a family of peptides including antagonist G and SpD that act as broad-spectrum neuropeptide antagonists at several peripheral receptors. The lipid-induced structure of these peptides may be important for the receptor interactions of these analogs. Thus we describe the tertiary structure of SPA in the presence of sodium dodecylsulfate micelles at pH 5.0, and 25°C as determined from two-dimensional 1H-NMR data recorded at 500 MHz. The resulting three-dimensional structure can be generally described as two type IV nonstandard turns around Arg 1*, Pro 2, Lys 3, and Pro 4 and Gln 6, Trp 7*, Phe 8, and Trp 9* residues, respectively, inserted into the interfacial region of the micelles (the asterisks denote D-form amino acid). These turns juxtapose the N- and C-termini of SPA and may form the basis of this peptide’s unique ability to inhibit peptide receptor interactions at multiple receptor types.

Modification of Crystal Violet – Sulfite Ion Equilibrium Induced by Sds Micelles

The presence of sodium dodecylsulfate micelles was found to displace the equilibrium between crystal violet and sulfite ion in the direction of the former and lead to complete recovery of the dye. The underlying mechanism for this anomalous behaviour was elucidated and the rate of the reversal process determined.

Selective Entrapment of the Cationic Form of Norfloxacin within Anionic Sodium Dodecyl Sulfate Micelles at Physiological pH and its Effect on the Drug Photodecomposition†

The binding of the photosensitizing fluoroquinolone (FQ) antibiotic norfloxacin (NX) to sodium dodecyl sulfate (SDS) micelles and the photoreactivity of the NX/SDS complex under physiological pH conditions are investigated by means of absorption and emission spectroscopy, steady-state and laser flash photolysis. It is shown that the photolabile zwitterionic form of NX, which is dominant at physiological pH, is not the most abundant species in the presence of SDS micelles. This medium exhibits a high preference for the cationic form of the drug, which is selectively and successfully entrapped within the micellar cage (K(ass) = 6 x 10(4) M(-1) +/- 3000), becoming the largely dominant species at neutral pH. The effect of this trapping is drastically reflected on both efficiency and nature of the drug photodecomposition. It is observed that the photostability of NX incorporated in the micellar pseudophase increases of more than one order of magnitude if compared to that of the "free" drug. Furthermore, the radical photodecomposition mechanism occurring in phosphate buffered solution is suppressed by the micellar medium and the low photodegradation observed seems to take place preferentially through an ionic pathway. Hopefully, the results presented herein may contribute to a better understanding of the bio-distribution of NX in biological systems and provide helpful and stimulating information in order to get the control of FQ photoreactivity under physiological pH conditions.

Effect of counterion on the structural switchover and binding of piroxicam with sodium dodecyl sulfate (SDS) micelles

Addition of an electrolyte such as NaCl to ionic micelles such as sodium dodecyl sulfate (SDS) alters the ionic atmosphere of the bulk solvent, thereby changing both the micellar properties and the interaction pattern of micelles with a molecule in the solvent. In this study, we show how added NaCl in the presence of SDS micelles modulates the surface charge of the micelles, which in turn fine-tunes the switchover equilibrium between anionic and global neutral forms of piroxicam. The presence of salt alters the CMC and aggregation number of SDS micelles. The binding of the global neutral form of piroxicam with SDS is found to be strongly modulated by the presence of counterion in the bulk solvent.

Role of manganese(II), micelles, and inorganic salts on the kinetics of the redox reaction of L‐sorbose and chromium(VI)

AbstractThe kinetics of the reduction of chromium(VI) to chromium(III) by L‐sorbose in HClO4 was studied between 30 and 80°C at various concentrations of reactants and acidities in both aqueous and micellar sodium dodecyl sulfate (SDS)/TritonX‐100(TX‐100) solutions. Under pseudo‐first‐order conditions the reaction rate is fractional‐order in [L‐sorbose] and [H+], and first‐order in [CrVI] both in the absence and in the presence of surfactant micelles. The reaction is accelerated by addition of manganese(II) and is routed through the same mechanism as shown by the kinetic studies in the absence and presence of surfactants. The rate enhancement in presence of SDS/TX‐100 micelles indicates that essentially all the reactive species are bound to micelles under the experimental conditions. The observed catalyses are explained with the modified Menger and Portnoy model. Inorganic salts (NaBr, LiBr, NH4Br) inhibit the reaction in presence of SDS micelles, which confirms exclusion of the reactive species of chromium(VI) from the reaction site. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 543–554, 2003

A Comparison of Atmospheric and Electrochemical Oxidation of Vitamin C in SDS Systems

ABSTRACT Ascorbic acid (AA, H2A) can be solubilized up to 60% by weight into a microemulsion formed by water, pentanol, and sodium dodecylsulfate (SDS). Addition of AA to the aqueous solution caused systematic reduction of the microemulsion region in the phase diagrams of the system. Ascorbic anion interacts with dodecylsulfate association structures changing W/O microemulsions towards O/W systems. The polar part of AA is exposed to the aqueous solution and subject to oxidation. The results of kinetic determination of AA decomposition are in accordance with a suggested model. They show enhanced oxidation of AA with increasing pentanol concentration in the system. The system aqueous AA solution/SDS, of concentration in excess of critical micellization concentration (cmc), was found to be more resistant to oxidation in air than aqueous AA solution. This was confirmed by electrochemistry studies of the anodic oxidation of AA on glassy carbon electrode. Sodium dodecylsulfate shifted the AA oxidation potential E pa to more positive values and decreased the peak current I pa . Antioxidation activity of AA was diminished in the presence of SDS micelles.

Conformations of platypus venom C-type natriuretic peptide in aqueous solution and sodium dodecyl sulfate micelles

Nuclear magnetic resonance spectroscopy was used to investigate the conformations of the platypus venom C-type natriuretic peptide A (OvCNPa) in aqueous solutions and in solutions containing sodium dodecyl sulfate (SDS) micelles. The chemically synthesized OvCNPa showed a substantial decrease in flexibility in aqueous solution at 10 °C, allowing the observation of medium- and long-range nuclear Overhauser enhancement (NOE) connectivities. Three-dimensional structures calculated using these data showed flexible and reasonably well-defined regions, the locations of which were similar in the two solvents. In aqueous solution, the linear part that spans residues 3–14 was basically an extended conformation while the cyclic portion, defined by residues 23–39, contained a series of β-turns. The overall shape of the cyclic portion was similar to that observed for an atrial natriuretic peptide (ANP) variant in aqueous solution. OvCNPa adopted a different conformation in SDS micelles wherein the N-terminal region, defined by residues 2–10, was more compact, characterised by turns and a helix, while the cyclic region had turns and an overall shape that was fundamentally different from those structures observed in aqueous solution. The hydrophobic cluster, situated at the centre of the ring of the structure in aqueous solution, was absent in the structure in the presence of SDS micelles. Thus, OvCNPa interacts with SDS micelles and can possibly form ion-channels in cell membranes.

Pulsed‐field gradient NMR study of sodium dodecyl sulfate micelle–peptide association

AbstractPulsed‐field gradient (PFG) NMR spectroscopy was used to characterize the interactions between a series of small peptides and sodium dodecyl sulfate (SDS) micelles. The study was undertaken because peptide–micelle interactions are often exploited in the chromatographic analysis of complex mixtures, and therefore an accurate knowledge of peptide–micelle association constants is essential for a thorough understanding of the separation mechanism in these techniques. In the PFG‐NMR experiment, diffusion coefficients for each peptide were measured in free solution and in the presence of SDS micelles. These diffusion coefficients allowed the mole fraction of peptide molecules associated with SDS micelles and the peptide–micelle association constants, Keq, to be calculated. In a study of dipeptides derived from the leucine enkephalin (YGGFL) and D‐(Ala)2‐leucine enkephalin (YAGFL) amino acid sequences, only Phe–Leu was found to associate strongly with the micellar aggregates. The equilibrium constant for this dipeptide was found to be 69 ± 6 M−1. The dipeptides Tyr–Gly, Tyr–Ala, Gly–Gly and Gly–Phe exhibited little to no micelle binding, whereas Tyr–Leu had an association constant that was a factor of four less than the Phe–Leu value. Furthermore, the association constants for the pentapeptides leucine enkephalin and D‐(Ala)2‐leucine enkephalin (130 ± 8 and 584 ± 38, respectively) were both higher than the Keq values for all dipeptides investigated. These results suggest that micelle–induced changes in peptide conformation and peptide hydrophobicity both play important roles in governing peptide–micelle binding. Copyright © 2001 John Wiley & Sons, Ltd.

Templating peptide folding on the surface of a micelle: nucleating the formation of a β-hairpin

NMR spectroscopy is used to show that a 20-residue β-hairpin peptide sequence derived from ferredoxin I, with a Pro-Asp two-residue type I turn which is uncommon in β-hairpins, is unstructured in aqueous solution but shows NOE evidence for partial folding in the presence of sodium dodecylsulphate micelles. The peptide has a number of lysine residues in the N-terminal β-strand capable of interacting with the micelle surface and templating the partial folding of the hairpin by reducing the entropic cost of ordering the peptide backbone.

Effects of anionic micelles on intramolecular general base-catalysed aminolysis of ionized phenyl salicylate (PS−3)

The effects of micelles of sodium dodecyl sulphate (SDS) on the rates of reactions of ionized phenyl salicylate (PS ˇ ) with n-butylamine, piperidine and pyrrolidine were studied at 35 °C. Pseudo-first-order rate constants (kobs) show a linear increase with increase in the total concentration of amine ((Am) T) at a constant (SDS). An increase in the total concentration of SDS from 0.0 to 0.2 mol dm ˇ3 results in a decrease in the observed nucleophilic second-order rate constants by the factors of ca 2.6, 5.2 and 3.9 for the reactions of PSwith n-butylamine, piperidine and pyrrolidine, respectively. The rate constants, kobs, show a non-linear increase with increase in (NaOH) from 0.0 to 0.04 mol dm ˇ3 at a constant (SDS) and (Am)T. The observed results of aminolysis of PSin the presence of SDS micelles are rationalized in the light of the pseudophase model of micelles. Copyright © 1999 John Wiley & Sons, Ltd.