Sodium Octyl Research Articles

Selective enrichment of albumin in biological samples by CE using segmental filling with sodium octyl sulfate in the background electrolyte

This paper shows that in CE, the peak efficiency and effective electrophoretic mobility of HSA and BSA were significantly enhanced by using a short plug (8 nL) of 1% w/w sodium octyl sulfate (SOS) and 1% w/v dextran sulfate as the additive. However, under identical conditions, other proteins did not exhibit the same phenomena. When the concentration of SOS was increased to 1.0% w/w SOS, a broad peak that corresponded to HSA transformed to a sharp peak. When the SOS concentration was more than 3.0% w/w, there was no shift in the effective electrophoretic mobility of HSA (10 microM), indicating that the binding of SOS to HSA is saturated. Through the specific interaction between SOS and HSA, the selective sweeping of HSA was accomplished using a short plug (24 nL) of 1% w/w SOS, followed by the injection of 190 nL of the sample. The excellent peak efficiency was still obtained for HSA and BSA upon the injection of a large-volume sample. As a result, the LOD for HSA (S/N=3) was 0.1 nM. In contrast to the normal injection without the SOS plug, approximately, a 4000-fold increase in the sensitivity of HSA was obtained by using the sweeping method. The proposed method has been successfully applied for the quantification of HSA in urine and erythrocytes as well as the quantification of BSA in milk.

Thermodynamic Study of Intermediate State of Papain Induced by n-Alkyl Sulfates at Two Different pH Values: A Spectroscopic Approach

The formation of the intermediate state of papain was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; and sodium dodecyl sulfate, SDS at different concentrations. A systematic investigation of n-alkyl sulfates induced conformational alteration in molten globule state under an acidic condition and the native state of papain was examined by tryptophan fluorescence, 1-anilino 8-naphtalene sulfonic acid (ANS) binding and UV absorbance. The addition of n-alkyl sulfates to molten globule state at pH 2 shows a decrease in tryptophan fluorescence intensity and quenched ANS fluorescence relative to the native state that leads to enhancement in tryptophan fluorescence and an increase in ANS fluorescence as well. In the presence of n-alkyl sulfates in various conditions, two intermediate (IA and IB) with different conformations were obtained at acidic and native states, respectively. Thus, we can assume that the intermediate states in folding and unfolding pathways in various conditions have different structures. The results show that SDS is much more effective than SDeS and SOS for the formation of the intermediate states for papain in the two different pathways due to the presence of its hydrophobic tail. Therefore, hydrophobic interactions play an important role in inducing the two different intermediates along the two various thermodynamic pathways.

Compositional effects on electrophoretic and chromatographic figures of merit in electrokinetic chromatography with cetyltrimethylammonium bromide/sodium octyl sulfate vesicles as the pseudostationary phase. Part 1: Effect of the phase ratio

The effect of the phase ratio on the electrophoretic and chromatographic properties of unilamellar vesicles comprised of cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) was investigated in EKC. The surfactant concentration of the vesicles was 0.9, 1.2, 1.5, and 1.8% w/v, with a mole ratio of 1:3.66 (CTAB/SOS). Results were compared to those obtained using SDS micelles at concentrations of 1.0% (w/v, 35 mM) and 1.5% (52 mM). The CTAB/SOS vesicles (0.9-1.8% w/v) provided a significantly larger elution range (5.7 < or = t(ves)/t(0) < or = 8.7) and greater hydrophobic (methylene) selectivity (2.8 < or = alpha(CH2) < or = 3.1) than SDS micelles (3.1 < or = t(mc)/t(0) < or = 3.3; alpha(CH2) = 2.2). Whereas the larger elution range can be attributed to the 25% reduction in EOF due to the interaction of unaggregated CTAB cations and the negatively charged capillary wall, the higher methylene selectivity is likely due to the lower concentration of water expected in the CTAB/SOS vesicle bilayer compared to the Palisades layer of SDS micelles. For a given phase ratio, CTAB/SOS vesicles are somewhat less retentive than SDS micelles, although retention factors comparable to those observed in 1.0-1.5% SDS can be obtained with 1.5-1.8% CTAB/SOS. A linear relationship was observed between phase ratio and retention factor, confirming the validity of the phase ratio model for these vesicles. Unique polar group selectivities and positional isomer shape selectivities were obtained with CTAB/SOS vesicles, with both types of selectivities being nearly independent of the phase ratio. For four sets of positional isomers, the elution order was always para < ortho < meta. Finally, the thermodynamics of solute retention was qualitatively similar to that reported for other surfactant aggregates (micelles and microemulsions); the enthalpic contribution to retention was consistently favorable for all compounds, whereas the entropic contribution was favorable only to hydrophobic solutes.

Photoinduced Increase in Vesicle Size and Role of Photoresponsive Malachite Green Leuconitrile Derivative in Vesicle Fusion

The influence of photoirradiation on vesicles containing a Malachite Green leuconitrile derivative carrying a long alkyl chain, affording photogenerated amphiphilicity, was investigated. The photoresponsive Malachite Green leuconitrile derivative was embedded in the vesicle bilayer of two single-tailed amphiphiles with oppositely charged head groups consisting of cetyltrimethylammonium chloride (CTAC) and sodium octyl sulfate (SOS). Transmission electron microscopy, which was used for observing photoinduced structural change in the vesicles, demonstrated that photoirradiation of the vesicles containing the Malachite Green leuconitrile derivative increased the average size of the vesicle diameter from 116 to 243 nm in the [CTAC]/[SOS] = 0.48 system. The mechanism for vesicle enlargement was studied with fluorescent probe molecules. The photoinduced change in the vesicle size can be explained by the destabilization of the vesicle bilayer, which is perturbed by photogenerated amphiphilicity. In addition, it was shown that the fusion process arising from the destabilized bilayer contributed to the increase in vesicle size.

A Biophysical Investigation on the Binding and Controlled DNA Release in a Cetyltrimethylammonium Bromide−Sodium Octyl Sulfate Cat-Anionic Vesicle System

The interactions between cat-anionic (an acronym indicating surfactant aggregates (micelles and vesicles) formed upon mixing cationic and anionic surfactants in nonstoichiometric amounts) vesicles and DNA have been the subject of intensive studies because of their potential applications in biomedicine. Here we report on the interactions between DNA and cetyltrimethylammonium bromide (CTAB)-sodium octyl sulfate (SOS) cat-anionic vesicles. The study was performed by combining dielectric relaxation spectroscopy, circular dichroism, dynamic light scattering, ion conductivity, and molecular biology techniques. DNA is added to positively charged vesicles until complete charge neutralization of the complex and formation of lipoplexes. This occurs when the mole ratio between the phosphate groups of DNA and positive charges on the vesicle is about 1.8. Above this threshold the nucleic acid in excess remains free in solution. This very interesting new result shows that anionic surfactants are not expelled upon saturation, and therefore, no formation of micelles occurs. Furthermore, vesicle-bound DNA can be released in its native form, as confirmed by dielectric spectroscopy and circular dichroism measurements. The nucleic acid is released upon addition of SOS, which competes with the phosphate groups of the DNA: this results in the demolition of the CTAB-SOS cat-anionic vesicles. These results indicate the possibility of a controlled DNA release and might be of interest in biomedicine.

The association of DNA and stable catanionic amino acid-based vesicles

Cationic surfactants associate strongly to DNA and compact but are often toxic. The interaction of some novel cationic amino acid-based surfactants, which may enhance transfection and appear to be nontoxic, is described. A cationic arginine-based surfactant, ALA, gives in combination with anionic surfactants spontaneously stable vesicles, and special attention is given to the association of these catanionic vesicles, with a net positive charge, to DNA. The ability of this surfactant alone to compact DNA is compared in fluorescence microscopy studies to classical cationic surfactants. Addition of DNA to a solution of the catanionic vesicles results in associative phase separation at very low vesicle concentrations; there is a separation into a precipitate and a supernatant solution, which is first bluish but becomes clearer as more DNA is added. From studies using cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering it is demonstrated that there is a lamellar structure with DNA arranged within the surfactant bilayers. Analysis of the supernatant by means of proton nuclear magnetic resonance ( 1H NMR) showed that above the isoelectric point between ALA, anionic surfactant (sodium octyl sulfate, SOS) and DNA, anionic surfactant starts to be expelled from the bilayers on further incorporation of DNA. There appears to be a transition from a lamellar to a hexagonal liquid crystal structure when most of SOS has been expelled from the aggregate bilayers; at higher DNA-to-surfactant ratios, self-assembled SOS micelles and the excess of DNA added seem to coexist in solution. Regarding the phase-separating DNA–surfactant particles, cryo-TEM demonstrates a large and nonmonotonic variation of particle size as the DNA–surfactant ratio is varied, with the largest particles obtained in the vicinity of overall charge neutrality.

Effect of Pyrene Additive on the Growth of Gold Nanoparticles in Aqueous Sodium Alkyl Sulfate Micellar Solutions

AbstractGold nanoparticles (NPs) were synthesized by chemical reduction in sodium octyl sulfate (SOS), sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS) solutions. Gold NPs prepared in SDS solutions have the smallest size and the highest stability among them. The stability of gold NPs was reflected in the hydrophobic property of the protecting surfactant. Size‐controlled synthesis of gold NPs was further achieved with the addition of pyrene in all surfactant solutions. Experimental results indicated that the combination of SDS and pyrene has the extraordinary effect in decreasing the size and narrowing the dispersity of gold NPs. Micellar electrokinetic capillary chromatography (MEKC) showed that the chemical reaction between pyrene and gold complexes was attributed to the formation of gold NPs inside the micelles at the embryonic stage.

Determination of the dopamine agonist rotigotine in microdialysates from the rat brain by microbore column liquid chromatography with electrochemical detection

Rotigotine, an investigational dopamine agonist formulated as a patch, is being studied in Parkinson's disease. A microdialysis technique, in combination with microbore column liquid chromatography and electrochemical detection, was developed to monitor rotigotine levels in the brain. Microdialysis probes were inserted into the striata of anesthetized rats, and samples were collected during perfusion with Ringer's solution. Rotigotine was separated using a C18 reversed-phase column. The mobile phase consisted of 50 mM Na 2HPO 4·2H 2O, 2.5 mM sodium octyl sulfonate, and pH 4.5; 35% volume to volume acetonitrile. The flow rate was 30 μl/min, and the potential of the glassy carbon electrode was set to +850 mV. The method allowed monitoring of the time course of brain extracellular rotigotine levels with a detection limit of 1 nM following either intravenous (0.5 mg/kg) or subcutaneous (5.0 mg/kg) rotigotine injection.

Electrochemical behavior of phenol in alkaline media at hydrotalcite-like clay/anionic surfactants/glassy carbon modified electrode

The electrochemical behavior of phenol, using glassy carbon (GC) modified electrodes containing a hydrotalcite (HT)-like clay and anionic surfactants such as sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS), or sodium dodecylbenzenesulfonate (SDBS) in alkaline media, has been examined. Phenol oxidation at the modified electrodes, after a time accumulation under open circuit conditions, promotes increments of the current and shifts the oxidation potential to less positive values, compared to phenol oxidation at HT-GC or GC electrodes. The phenol oxidation is favored by the presence of surfactants in the films. The results suggest that the surfactant molecules intercalate between the HT layers, yielding a hydrophobic clay capable of preconcentrating phenol molecules. X-ray diffraction analyses showed a larger spacing of the HT layers when the surfactant intercalates between them. Cyclic voltammograms have shown that the SOS-HT-GC modified electrode exhibits short-lived activity for phenol oxidation as a consequence of surface fouling, while the SDS-HT-GC and SDBS-HT-GC modified electrodes showed a more stable behavior. The SDBS-HT-GC modified electrode was the most effective adsorbing phenol, since the charge ( Q), obtained from the integration of the anodic peak current of the phenol, is higher at this modified electrode. This is probably because the adsolubilization capacity of phenol on the SDBS-HT-GC electrode is higher than on SDS-HT-GC electrode.

Phase behavior of mixed solution of a glycerin-modified cationic surfactant and an anionic surfactant

The phase behavior of mixed solution of newly synthesized monoglycerylcetyldimethylammonium chloride (MGCA) and sodium octyl sulfate (SOS) in water was investigated by cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and fluorescence polarizing for evaluation of the microviscosity of bilayers. No precipitate was observed in the mixed solution except at concentrations below 20 mM over all mixing ratios, and stable vesicles were formed in a considerably wide range of mixing ratio, even at the equimolar ratio. Vesicles formed in aqueous 1/1 MGCA/SOS mixture were found to exhibit no phase transition, and fluorescence polarizing measurements showed that the vesicle bilayers have a high fluidity. This flexibility allows the bilayers to have a spontaneous curvature, and thus vesicles rather than flat lamellae can be stabilized in the mixture even at the equimolar ratio. In addition, because the glycerin group of MGCA interacts strongly with water, the hydration repulsion contributes to prevent the bilayers consisting of MGCA and SOS from adhering and flocculating even though the charge neutralization between MGCA and SOS occurs at the equimolar ratio.

Spontaneous Formation of Vesicles and Dispersed Cubic and Hexagonal Particles in Amino Acid-Based Catanionic Surfactant Systems

Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride (ALA) and N(alpha)-lauroyl-arginine-methyl ester hydrochloride (LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate (HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate (SOS) and sodium cetyl sulfate (SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure (cubosomes) and internal hexagonal structure (hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. (Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications.

Comparison of the conformational stability of the non-native α-helical intermediate of thiol-modified β-lactoglobulin upon interaction with sodium n-alkyl sulfates at two different pH

Bovine β-lactoglobulin assumes a dimeric native conformation at neutral pH, while the conformation at pH 2 is monomeric but still native. β-lactoglobulin has a free thiol at Cys121, which is buried between the β-barrel and the C-terminal major or α-helix. This thiol group was specifically reacted with DTNB (5,5′-dithiobis(2-nitrobenzoic acid)) at pH 7.5 and 2, producing a modified β-lactoglobulin containing a mix disulfide bond with 5-thio-2-nitrobenzoic acid (TNB). β-Lactoglobulin is a predominantly β-sheet protein, although it has a markedly high intrinsic preference for α-helical structure. The formation of non-native α-helical intermediate of thiol modified β-lactoglobulin (TNB- β-LG) was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at pH 7.5 and 2. The conformation and stability of non-native α-helical intermediate ( αI) state of TNB- β-LG were studied by circular dichroism (CD), fluorescence and differential scanning calorimetry (DSC) techniques. The effect of n-alkyl sulfates on the structure of αI state at both pH was utilized to investigate the contribution of hydrophobic interactions to the stability of αI intermediate. The present results suggest that the folding reaction of β-LG follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the native state of β-LG at pH 2 with more positive charges repulsion than at pH 7.5. Then TNB- β-LG will become a useful model to analyze the conformation and stability of the intermediate of protein folding.

Zero Spontaneous Curvature and Its Effects on Lamellar Phase Morphology and Vesicle Size Distributions

Equimolar mixtures of dodecyltrimethylammonium chloride (DTAC) and sodium octyl sulfonate (SOSo) show a vesicle phase at >99 wt % water and a single, fluid lamellar phase for water fractions below 80 wt %. This combination is consistent with the bilayer bending elasticity kappa approximately k(B)T and zero bilayer spontaneous curvature. Caillé line shape analysis of the small-angle X-ray scattering from the lamellar phase shows that the effective kappa depends on the lamellar d spacing consistent with a logarithmic renormalization of kappa, with kappa(o) = (0.8 +/- 0.1)k(B)T. The vesicle size distribution determined by cryogenic transmission electron microscopy is well fit by models with zero spontaneous curvature to give (kappa + (kappa/2)) = (1.7 +/- 0.1)k(B)T, resulting in kappa = (1.8 +/- 0.2)k(B)T. The positive value of kappa and the lack of spontaneous curvature act to eliminate the spherulite defects found in the lamellar gel phases found in other catanionic mixtures. Current theories of spontaneous bilayer curvature require an excess of one or more components on opposite sides of the bilayer; the absence of such an excess at equimolar surfactant ratios explains the zero spontaneous curvature.

Origin of peak asymmetry and isotherm nonlinearity in micellar electrokinetic chromatography: Variation of peak shape with buffer concentration

The diffuse fronts and sharp rears of peaks of nitrobenzene (nbz) solubilized at high concentrations in 50 mM SDS and 2.5, 25, and 50 mM sodium tetraborate buffers were modeled in MEKC by measurements of, and fits to, concave upward isotherms, and by numerical solution of the continuity equation. The isotherms varied with buffer concentration, with the smallest limiting slope and largest curvature found for the 50 mM tetraborate buffer. The Brunauer, Emmett, and Teller isotherm described the peak profiles in all buffers, with symmetrical peaks observed at sub- and low-mM levels of nbz, anti-Langmuirian peaks observed at 10-20 mM levels, and aquiline peaks resembling curved noses observed at 20-30 mM levels. The variation of the partition coefficient with nbz and buffer concentrations was shown to result from nonideal thermodynamics. High-buffer concentrations salt out nbz from the mobile phase, as quantified by a mobile-phase activity coefficient related to the Setchenov constant of nbz in sodium tetraborate. The activity coefficient of nbz in SDS micelles was shown to resemble that measured by other researchers for benzene in micelles of sodium octyl sulfate, i.e. it decreases with increasing solute concentration and increases with electrolyte concentration. Many examples from the literature are discussed, in which the variation of the intramicellar activity coefficient with solute mole fraction is consistent with peaks having diffuse fronts and sharp rears.

Synthesis of magnetic particles via a cationic–anionic surfactant vesicle method

In this work, a mixed cationic--anionic [i.e. cetyltrimethylammonium bromide–sodium octyl sulphate] surfactant system was used to synthesize the magnetite particles. The loading content of iron ions (Fe 3+ and Fe 2+) into the surfactant system was varied to study its effect on the formation of magnetite, magnetic and morphological properties of the magnetite particles encapsulated by the surfactant vesicles. It has been verified that the vesicle-encapsulated magnetite particles with sizes from 100 to 200 nm were formed, which were almost independent of the loading content of iron ions. However, the morphological structure of the magnetite particles was dependent on the loading content of iron ions and there existed an optimal loading content for a full packing of the surfactant vesicles with the magnetite particles.

Interactions between zwitterionic and conventional anionic and cationic surfactants

Critical micelle concentration (cmc) values have been determined for the mixed zwitterionic/anionic surfactant systems of N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/sodium dodecyl sulfate (SDS), N-dodecyl- N, N-(dimethylammonio)butyrate (DDMAB)/SDS, N-octyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-08)/sodium octyl sulfate (SOS), and the zwitterionic/cationic systems of ZW3-12/dodecyltrimethylammonium bromide (DTAB), DDMAB/DTAB. Conductivity studies and nuclear magnetic resonance (NMR) spectroscopy were the methods employed for cmc determinations. The degree of nonideality of the interaction in the micelle ( β m ), for each system, was determined according to Rubingh's nonideal solution theory. Evidence was found for the existence of strong interactions between zwitterionic and anionic surfactants in each of the zwitterionic/anionic systems. The ZW3-08/SOS and DDMAB/SDS systems behaved synergistically at all mole fractions studied while the ZW3-12/SDS system exhibited synergistic behavior above mole fractions of 0.30. Greater negative deviations from ideal behavior were demonstrated in the DDMAB/SDS system than in the other two zwitterionic/anionic systems. The zwitterionic/cationic systems of ZW3-12/DTAB and ZW3-08/OTAB displayed only slight deviations from ideal behavior, therefore indicating near ideal mixing.

Effect of surfactant counterion and organic modifier on the properties of surfactant vesicles in electrokinetic chromatography

Counterion and organic modifier are two parameters in EKC that can be varied in order to obtain improved solubility, selectivity, and efficiency. The effect of changing surfactant counterion and/or organic modifier on the chromatographic and electrophoretic properties of cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfate (SOS) vesicles is examined in EKC. The vesicles are prepared in a 1:3.66 cationic/ anionic mole ratio for a total surfactant concentration of 69 mM. The cationic CTAB is replaced by cetyltrimethylammonium chloride (CTAC) and the first use of CTAC/SOS vesicles is reported. The mean diameter of the CTAC/SOS vesicles is 96 nm while that of the CTAB/SOS vesicles is 85 nm. A class I modifier (2-amino-1-butanol) and a class II modifier (acetonitrile) have similar effects on the EOF, elution range, methylene selectivity, and the efficiency of the CTAB/SOS vesicles and the CTAC/SOS vesicles. Upon addition of 10% ACN, there is roughly a 10-fold increase in the efficiency of heptanophenone, a model hydrophobic compound, compared to the efficiency using unmodified vesicles. Linear free energy relationship (LFER) analysis using the Abraham solvation model is employed to characterize solute-vesicle interactions. The results suggest that organic modifier-vesicle interactions depend somewhat on the counterion.

Cooperative α-helix formation of β-lactoglobulin induced by sodium n-alkyl sulfates

It is generally assumed that folding intermediates contain partially formed native-like secondary structures. However, if we consider the fact that the conformational stability of the intermediate state is simpler than that of the native state, it would be expected that the secondary structures in a folding intermediate would not necessarily be similar to those of the native state. β-Lactoglobulin is a predominantly β-sheet protein, although it has a markedly high intrinsic preference for α-helical structure. The formation of non-native α-helical intermediate of β-lactoglobulin was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at special condition. The effect of n-alkyl sulfates on the structure of native β-lactoglobulin at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of non-native α-helical intermediate. The addition of various concentrations of n-alkyl sulfates to the native state of β-lactoglobulin (pH 2) appears to support the stabilized form of non-native α-helical intermediate at pH 2. The m values of the intermediate state of β-lactoglobulin by SOS, SDeS, SDS and STS showed substantial variation. The enhancement of m values as the stability criterion of non-native α-helical intermediate state corresponded with increasing chain length of the cited n-alkyl sulfates. The present results suggest that the folding reaction of β-lactoglobulin follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the non-native α-helical intermediate state.

Interaction of piroxicam with micelles: Effect of hydrophobic chain length on structural switchover

Molecules, whose p K a values can be easily fine-tuned by their microenvironment, are expected to be profoundly affected by the heterogeneous environments of membranes. Membrane parameters can have a strong effect in choosing a particular structural form of a molecule for incorporation/interaction. A case study has been presented for piroxicam, a non-steroidal anti-inflammatory drug of oxicam group, whose targets are cyclooxygenases, which are membrane active proteins. The structural dynamism of piroxicam is reflected in the ease with which it can switchover or convert from one prototropic form to the other guided by its environment. In this work we have studied the effect of varying hydrophobic chain length and surface charges in fine-tuning the interaction of piroxicam with micelles. Interaction of piroxicam with three types of micelles with identical negatively charged head groups and varying tail lengths viz., sodium dodecyl sulfate (S12S), sodium decyl sulfate (S10S) and sodium octyl sulfate (S8S) shows that there is a shift in the apparent p K a in the direction that favors the switchover or conversion from the anionic form to the global neutral form. The binding constants of piroxicam with three micelles show a linear dependence on chain length. Interaction was also studied with micelles having oppositely charged head groups and different chain lengths viz., dodecyl N, N, N-trimethyl ammonium bromide (DTAB) and cetyl N, N, N-trimethyl ammonium bromide (CTAB). For micelles having identical chain lengths but oppositely charged head groups viz., S12S and DTAB, p K a shifts in two opposite directions compared to that in the absence of any surfactant. This is expected when electrostatic force is the only driving force. This case study demonstrates the effect of hydrophobic chain length and surface charges in fine-tuning the equilibrium between different structural forms of piroxicam. Our results also imply that for structurally dynamic drugs like piroxicam the nature of the biomembranes, characterized by different membrane parameters, should play a crucial role in choosing a particular structural form of the drug that will be finally presented to their targets.

Size Control of Styrene Oxide−Ethylene Oxide Diblock Copolymer Aggregates with Classical Surfactants: DLS, TEM, and ITC Study

The interactions between the diblock copolymer S(15)E(63) and the surfactants sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDeS), and sodium octyl sulfate (SOS) have been investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), and isothermal titration calorimetry (ITC). The surfactants with the same headgroup differentiate in their chain length. At 20 degrees C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6 nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO or E) corona. The different copolymer/surfactant systems have been studied at a constant copolymer concentration of 2.5 g dm(-3) and in a vast range of surfactant concentrations, from 7.5 x 10(-6) up to 0.75 M. When SDS and SDeS are added to the block copolymer solution, different regions are observed in the DLS data: at low surfactant concentrations (c < 1.0 x 10(-4) M), single surfactant molecules associate with the copolymer micelle, probably the former being solubilized in the micelle core, leading to a certain disruption of the mixed micelle due to repulsive electrostatic interactions between surfactant headgroups followed by a stabilization of the mixed micelle. At higher concentrations (1.0 x 10(-4) < c < 0.1 M), two types of copolymer-surfactant complexes coexist: one large copolymer-rich/surfactant complex and one small complex consisting of one or a few copolymer chains and rich in surfactants. At higher SDS and SDeS concentrations, complete disintegration of mixed micelles takes place. In contrast, SOS-S(15)E(63) interactions are less important up to surfactant concentrations of 0.05 M due to its higher hydrophilicity, reducing the hydrophobic interactions between surfactant alkyl chains and copolymer micelles. At concentration larger than the critical aggregation concentration (cac) of the system, 0.05 M, disruption of copolymer micelles occurs. These regions have been confirmed by transmission electron microscopy. On the other hand, the titration calorimetric data for SDS and SDeS present an endothermic increase indicating the formation of mixed copolymer-rich-surfactant micelles. From that point, important differences in the ITC plot for both surfactants are present. However, the ITC curve obtained after titration of a SOS solution in the copolymer solution is quite similar to that of its titration in water.