Aqueous Sodium Dodecyl Sulfate Micelles Research Articles

Discerning the Structure Factor of Charged Micelles in Water and Supercooled Solvent by Contrast Variation X-ray Scattering.

Sodium dodecyl sulfate (SDS) is a well-known anionic surfactant that forms micelles in various solvents including supercooled sugar-urea melt. Here, we explore the application of contrast variation small-angle X-ray scattering (SAXS) in discerning the structure and interactions of SDS micelles in aqueous solution and in a room-temperature supercooled solvent. The SAXS patterns can be analyzed in terms of a core-shell ellipsoid model. For aqueous SDS micelles, at low volume fractions, the features due to intermicellar interaction, S(q), in the SAXS pattern are poorly resolved because of the prominent contribution from shell scattering. Increasing the electron density of the solvent by the addition of the urea or fructose-urea mixture (at a weight ratio of 6:4) permits the systematic variation of shell scattering without influencing the structure drastically. For a 10% solution of SDS in water, the contribution from the shell can be completely masked by the addition of 40% urea or fructose-urea mixture. The fructose-urea mixture is a preferred additive as it can vary the scattering length density over a wide range and serves as a matrix to form supercooled micelles. The structural parameters of micelles in supercooled fructose-urea melt are obtained from contrast variation SAXS, small-angle neutron scattering, and high-resolution transmission electron microscopy.

A Carbohydrate-Conjugated Deep Cavitand Permits Observation of Caviplexes in Human Serum

A deep cavitand was covalently modified with carbohydrates to provide solubility in biologically relevant environments and to investigate its receptor function. Specifically, a tetrakis(β-D-glucosyl) cavitand (1) that was soluble in neutral water or acid/base-buffered solutions was synthesized, and it formed complexes with hydrophobic small molecules. Extraction of the cavitand into aqueous sodium dodecyl sulfate micelles as simple membrane mimetics increased the scope of guests bound by 1 beyond that observed in only aqueous media. Complex formation was also detected in human serum. The findings show the functional compatibility of the receptor in both micelle-bound and serum-soluble forms.

Solubilization of Single‐Walled Carbon Nanotubes by using Polycyclic Aromatic Ammonium Amphiphiles in Water—Strategy for the Design of High‐Performance Solubilizers

We describe the design of polycyclic aromatic compounds with high performance that dissolve single-walled carbon nanotubes (SWNTs). Synthetic amphiphiles trimethyl-(2-oxo-2-phenylethyl)-ammonium bromide (1) and trimethyl-(2-naphthalen-2-yl-2-oxo-ethyl)-ammonium bromide (2) carrying a phenyl or a naphtyl moiety were not able to dissolve/disperse SWNTs in water. By contrast, trimethyl-(2-oxo-2-phenanthren-9-yl-ethyl)-ammonium bromide (3) solubilized SWNTs, although the solubilization ability was lower than that of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (4) (solubilization behavior observed by using 4 was described briefly in reference 4a). Transmission electron microscopy (TEM), as well as visible/near-IR, fluorescence, and near-IR photoluminescence spectroscopies were employed to reveal the solubilization properties of 4 in water, and to compare these results with those obtained by using sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) as solubilizers. Compound 4 solubilized both the as-produced SWNTs (raw-SWNTs) and purified SWNTs under mild experimental conditions, and the solubilization ability was better than that of SDS and HTAB. Near-IR photoluminescence measurements revealed that the chiral indices of the SWNTs dissolved in an aqueous solution of 4 were quite different from those obtained by using micelles of SDS and HTAB; for a SWNTs/4 solution, the intensity of the (7,6), (9,5), and (12,1) indices were strong and the chirality distribution was narrower than those of the micellar solutions. This indicates that the aqueous solution of 4 has a tendency to dissolve semiconducting SWNTs with diameters in the range of 0.89-1.0 nm, which are larger than those SWNTs (0.76-0.97 nm) dissolved in the aqueous micelles of SDS and HTAB.

Comparison of Microenvironments of Aqueous Sodium Dodecyl Sulfate Micelles in the Presence of Inorganic and Organic Salts: A Time-Resolved Fluorescence Anisotropy Approach

Microenvironments of aqueous sodium dodecyl sulfate (SDS) micelles was examined in the presence of additives such as sodium chloride and p-toluidine hydrochloride (PTHC) by monitoring the fluorescence anisotropy decays of two hydrophobic probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and coumarin 6 (C6). It has been well-established that SDS micelles undergo a sphere-to-rod transition and that their mean hydrodynamic radius increases from 19 to 100 A upon the addition of 0.0-0.7 M NaCl at 298 K. A similar size and shape transition is induced by PTHC at concentrations that are 20 times lower compared to that of NaCl. This study was undertaken to find out how the microviscosity of the micelles is influenced under these circumstances. It was noticed that the microviscosity of the SDS/NaCl system increased by approximately 45%, whereas there was a less than 10% variation in the microviscosity of the SDS/PTHC system. The large increase in the microviscosity of the former system with salt concentration has been rationalized on the basis of the high concentration of sodium ions in the headgroup region of the micelles and their ability to strongly coordinate with the water present in this region, which decreases the mobility of the probe molecules.

Surfactant−Polymer Aggregates Formed by Sodium Dodecyl Sulfate, Poly(N-vinyl-2-pyrrolidone), and Poly(ethylene glycol)

The interaction of sodium dodecyl sulfate (SDS) in aqueous solution with poly(N-vinyl-2-pyrrolidone) (M(w) = 55,000 g/mol) in the presence of poly(ethylene glycol) (M(w) = 8000 g/mol) is investigated by electrical conductivity, zeta potential measurements, viscosity measurements, fluorescence spectroscopy, and small-angle X-ray scattering (SAXS). The results indicate that SDS-polymer interaction occurs at low surfactant concentration, and its critical aggregation concentration is fairly dependent on polymer composition. The polymer-supported micelles have average aggregation numbers dependent on surfactant concentration, are highly dissociated when compared with aqueous SDS micelles, and have zeta potentials that increase linearly with the fraction of PVP at constant SDS concentration. The analysis of the SAXS measurements indicated that the PVP/PEG/SDS system forms surface-charged aggregates of a cylindrical shape with an anisometry (length to cross-section dimension ratio) of about 3.0.

Are Aqueous Sodium Dodecyl Sulfate Micelles in the Presence of Added Salt Polydisperse? A Time-Resolved Fluorescence Quenching Study with Global Analysis

Aggregation numbers of aqueous sodium dodecyl sulfate (SDS) in the presence of added salt were estimated using the time-resolved fluorescence quenching method. Tris (2,2‘-bipyridyl)ruthenium(II) and 1-ethylpyrene were used as probes and 9-methylanthracene, 3,4-dimethylbenzophenone, and 1-dodecylpyridinium chloride were used as quenchers. It was found that aqueous SDS micelles are monodisperse even in the presence of high salt concentrations contrary to what has been reported. Similar studies were carried out using the nonionic surfactant hexaethylene glycol mono-n-dodecyl ether (HEGDE) in water. Aqueous 33.1% (w/w) HEGDE solutions were found to be polydisperse.

Quenching kinetics of the acridine excited state by vinyl monomers in homogeneous and micellar solution

The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monomers is investigated in homogeneous (methanol), aqueous, and reverse micelles of sodium dodecyl sulfate (SDS). The fluorescence quenching of the dye by styrene derivatives in methanol as well as in aqueous SDS micelles is very efficient with quenching rate constants of the order of 10 10 M -1 s -1 and 5×10 7 s -1 , respectively. However, triplet quenching rate constants in methanol are much lower than the diffusion controlled limit, and no dye photoblenching is observed suggesting that a quenching process follows a reversible photoinduced charge-transfer mechanism. The fluorescence quenching of the dye by styrene derivatives in reverse SDS micelles is a pseudo-first-order process with no micellar quenching transient. It is shown that placing the dye inside a reverse micelle substantially reduces the quenching rate by styrene derivatives. The scope of this effect on photoinitiation efficiency for radical polymerization of styrene derivatives via a photoredox process of cationic dyes in reverse micelles is discussed. Association constants of vinyl monomers to SDS micelles, K, as well as partition coefficients in n-octanol/water have been also determined using the fluorescence quenching method. K is correlated with the boiling points of the vinyl monomers.

Time-Resolved Fluorescence in Micellar Systems: A Critical Application to the Partitioning of Naphthalene in Aqueous Sodium Dodecyl Sulfate

Static and dynamic aspects of the partitioning of naphthalene into the hydrocarbon phase in aqueous sodium dodecyl sulfate micelles have been critically examined by nanosecond time-resolved pulse fluorometry. It is shown that, in such a system, a properly detailed analysis of the excited-state decay behavior as a function of progressive partitioning of the solute into increasing concentrations of micelles is capable of revealing and directly quantitating the underlying kinetics of the reversible transfer of naphthalene in its excited state between aqueous and micellar phases. The time-resolved data indicate that, in the aqueous sodium dodecyl sulfate system, the partition coefficient for excited-state naphthalene can differ only marginally from that for the ground state. From the estimate obtained for the rate coefficient for entry of excited-state naphthalene into micelles, it would appear that any barrier to the crossing of excited naphthalene into the micelle, given that a collision has taken place, is likely to be rather small. The contrasting time-resolved behavior of a system in which the basis lifetime of the fluorescence probe in the micellar environment is shorter than that in the bulk environment rather than longer, as in the case examined experimentally, is also modeled. The effects of quenching of the fluorescence at the interface between the micellar and aqueous phases are also examined and discussed in the context of the aqueous cetyltrimethylammonium bromide system.

Counterion association to aqueous sodium dodecyl sulfate micelles in the presence of organic additives

The effect of polar, nonpolar, and mixed polar-nonpolar additives on the counterion association, the structure, and the size of aqueous sodium dodecyl sulfate micelles has been examined by measuring the conductivity, the viscosity, and the electromotive force at 298.15 K. Octane does not affect the degree of counterion association, but the mobility of the micelles decreases. This is mainly due to an increased micellar volume. Small quantities of 1-butanol and 1-hexanol decrease the degree of counterion association. At higher hexanol molalities larger micellar aggregates, rod- or disk-like micelles are formed. Long-chained α,ω-alkanediols, 1,9-nonanediol and 1,10-decanediol, also reduce the degree of counterion association. The shorter diols apparently affect the micellar system mainly through their effect on the solvent. The effect of the mixed additives is intermediate to that of pure components. Changes in the aggregation number, the micellar radius, and the number of associated counterions have been estimated from the conductivity and electromotive force measurements. Addition of octane does not affect the degree of associated counterions, but the micellar aggregation number increases. Addition of hexanol lowers both the micellar aggregation number and the fraction of associated counterions.

Heats of solution of aliphatic and aromatic, linear, branched, and cyclic alcohols in aqueous sodium dodecyl sulfate micelles at 298°K

We have determined the heat of solution ΔH s o of 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 2-butanol, 2-pentanol, 3-pentanol, cyclohexanol, benzylalcohol, and phenol in aqueous sodium dodecyl sulfate (SDS) solutions as a function of surfactant concentration. A constant ΔH s o value is obtained in all cases (except 3-pentanol) at higher surfactant concentration corresponding to dilute alcohol molecules in spherical micelles. The standard enthalpy of transfer ΔH t o of the aliphatic alcohols from water to these diluted solutions, corrected for the fraction of solubilized solute, is a decreasing linear function of their molecular surface of contact (MSC). The same linear behavior is found for the corresponding free energy and entropy functions. At the same MSC value ΔH t o is much less positive for the aromatic than for the aliphatic molecules. Comparison of ΔH t o from water to SDS and to 1-octane solutions shows that the specificity observed for the aromatic molecules is three times larger for the transfer to 1-octane than to SDS solutions. These observations support the two-state model of solubilization of aromatic molecules in micelles through surface and interior localization. A parallel situation is pointed out using the magnitude of pairwise thermodynamic coefficients in classical solution chemistry.