Triton X-100 Molecules Research Articles

Investigation the adsorption mechanism of a non-ionic surfactant on graphene oxide and its derivatives (kinetic, isotherm curves, thermodynamic, and effect of salts studies)

In this work, the adsorption of Triton X-100 (TX-100), a non-ionic surfactant, on graphene oxide (GO)-based adsorbents was considered, and the adsorption mechanism, bonding between TX-100 molecules and GO derivatives, kinetic, isotherm, and thermodynamic studies were investigated. The adsorbents were GO, reduced GO (rGO), GO-humic acid (GO-HA), and GO-saponin (GO-SA) and their surface area of them were 261.8, 304.1, 348.1, and 458.6 m2/g, respectively. The results showed that the optimum pH and contact time for TX-100 adsorption were 3 and 60 min, respectively. The most significant factor in the adsorption process was the surface chemistry of the adsorbent, which affect the bonds between the adsorbate and the adsorbent. In other words, the amount of H-bonding, which was related to the amount of oxygen-containing functional groups, played an important role in TX-100 adsorption. With the reduction of oxygen-containing functional groups, the possibility of π – π and π-cationic bonds increased, and the adsorption capacity was related to the amount of π-bonding. Also, it was concluded that the pore-filling occurred and increased the adsorption capacity in mesoporous adsorbents. The surface area of the adsorbent and the electrostatic charge of its surface did not affect the adsorption capacity.

Aggregation Properties of Triton X-100 in a Mixture of Ordinary and Heavy Water

The dynamic and aggregation properties of Triton X-100 in a mixture of ordinary and heavy water in a wide temperature range from room temperature to the cloud point and above were studied. The ratio of ordinary and heavy water was calculated in such a way as to ensure equal densities of Triton X-100 and the water mixture. This made it possible to exclude the effects of sedimentation and study the evolution of Triton X-100 micelles and aggregates, without complication by the effects of spatial phase separation above the cloud point. Self-diffusion coefficients of Triton X-100 molecules were measured by NMR, and the effective hydrodynamic radii of micelles and aggregates were calculated using the Stokes–Einstein relation. The anomalous temperature behavior of the diffusion coefficient of Triton X-100 molecules is explained by changes in the sizes of diffusing objects during their evolution from micelles to dehydrated aggregates below the cloud point and by changes in the sizes of aggregates above the cloud point. The results of the NMR studies are confirmed by data obtained by dynamic light scattering.

Molecular mechanism of the effect of benzene ring structure in nonionic surfactants on the wettability of anthracite

Reducing coal dust is critical for environmental protection and energy efficiency, however anthracite has a high degree of coalification, high hydrophobicity, resulting in a poor dust removal effect. The addition of surfactants to water can improve the wetting of coal dust, resulting in a more effective dust reduction effect. In this investigation, Polyethylene glycol octyl phenyl ether (Triton X-100) and The lauryl polyoxyethylene ethers (C12(EO)9) were chosen as research subjects. Contact angle experience, Fourier Transform infrared spectroscopy experience (FTIR), and X-ray Photoelectron Spectroscopy experience (XPS) were used to compare the ability of two surfactants to improve the wettability of anthracite from a macro perspective. Molecular dynamics (MD) simulation was used to explain macroscopic experimental phenomena from a microscopic perspective. Due to the presence of the benzene ring structure in the hydrophobic group, the surface of anthracite following Triton X-100 adsorption is more hydrophilic. The network structure of Triton X-100 molecules on the surface of anthracite is loose owing to the presence of the benzene ring, which facilitates water molecule penetration.

Cooperative Adsorption of Nonionic Triton X-100 and Dodecyldimethylamine Oxide Surfactant Mixtures at the Hydrophilic Silica-Water Interface Studied by Total Internal Reflection Raman Spectroscopy and Multivariate Curve Resolution.

The adsorption of dimethyldodecylamine oxide (DDAO) and Triton X-100 (TX) as single components and mixed systems at the silica-water interface has been studied using total internal reflection (TIR) Raman spectroscopy combined with multivariate curve resolution (MCR). In this study, the mixtures of DDAO and TX indicate minimal synergism in the bulk solution; however, the cooperative adsorption behavior on the silica surface is shown with various mixtures of DDAO (up to 1.3 mM) and TX (up to 1.1 mM). Adding the DDAO (up to 0.3 mM) to TX solution, the surface excess of TX shows 30% enhancement, from 1.2 to 1.8 μmol m-2. Adding the DDAO also shifts the TX adsorption isotherms, resulting in the Gibbs free energy change of -2.87 ± 0.73 kJ mol-1. This free energy change is interpreted as the decrease in surface energy when the silica surface charged sites are screened by the DDAO adsorbed layer. Alternatively, when a DDAO solution contains a small amount of TX molecules, i.e., < 30 μM, its adsorption on the silica surface quickly equilibrates. In addition, the formation of a more ordered liquid-crystalline adsorbed layer, as in the case of single-component DDAO adsorption, is not observed.

Synthesis and wettability of cellulose based composites by aqueous solutions of nonionic surfactant

The synthesis and characterization of the new UV-cured polymeric composites with microcrystalline cellulose (MCC) as a bio-filler are presented. The different contents of MCC from 0% to 20% wt. were applied. The polymeric parts of the composites were: bisphenol A glycerolate diacrylate (BPA.DA) as a cross-linking monomer and N-vinylpyrrolidone (NVP) as an active diluent. Due to the application of bulk polymerization method and UV-initiator (2,2-dimethoxy-2-phenylacetophenone), regular plates with the dimensions of 60 × 50 × 3 mm were obtained. The surface properties of the obtained solids were determined by the infrared spectra (ATR-FTIR) and optical profilometer as well as the values of the solid surface tension calculated from those of the contact angle of model liquids and van Oss et al. approach to the solid-liquid interface tension. Next the contact angle measurements of aqueous solutions of the nonionic surfactant Triton X-100 (TX100) (C = 10−6–10−3 M) were performed in the time range from 0 to 12 min for each drop. It was proved that with the MCC addition the composites become more hydrophobic and the TX100 adsorption at the solid-water interface as well as the surface structure are not the same as at the water-air one. Also the wetting and the spreading processes depend on the amounts of hydroxyl groups on the composites surface and the surface roughness as well as on the conformation and hydration of hydrophilic parts of TX100 molecules.

Reverse flotation of non-coking coal fines using non-ionic surfactant triton X-100 as depressant

A novel approach to apply Triton X-100 (TX-100) surfactant as depressant in reverse flotation of non-coking coal fines, which is different from the conventional use of dextrin as an depressant. Fourier transformed infrared spectroscopy (FTIR), contact angle and induction time instruments were used to analyze the mechanism of high-concentration TX-100 depressing the floating of coal particle. FTIR results revealed that TX-100 could physically adsorb on the surface of coal. Contact angle results showed the higher concentration of TX-100 aqueous solution was more likely to wet the surface of TX-100-treated coal, slowing down the film thinning and rupture rate during bubble-coal adhesion. In high-concentration TX-100 aqueous solution, the bubble surface was modified by the coverage of TX-100 molecules, which makes bubble difficult to adhere to coal particle. Induction time results showed the adhesion probability of coal particle and bubble gradually decreases with the increase of TX-100 concentration.

Electrochemical growth of two-dimensional tin nano-platelet as high-performance anode material in lithium-ion batteries

A template free, single-step process is developed for fabrication two-dimensional tin nano-platelets by electrochemical deposition in the presence of Triton X100 (TX100). Electrochemical studies combined with structural characterization revealed that during electrodeposition, TX100 molecules adsorb preferentially on {022} planes of Sn and highly anisotropic growth promotes in [200] direction which results in the formation of platelet morphology. The deposited platelets exhibit a high aspect ratio of 30 (width to thickness) and thickness of 25±5nm that uniformly covered the substrate with a high platelet density of 9×108cm−2. The electrochemical performance of nano-platelets for lithium storage was studied in detail and compared with other morphologies of tin. Tin nano-platelets exhibited high reversible capacity and excellent cycling performance, the capacity was maintained at 820mAhg−1 for 100 cycles and more, far superior to the other structures. Excellent rate capability was also observed for nano-platelets up to 5 C, with the ability to be operated at 20 C without damage. The superior electrochemical performance of tin platelets is mainly attributed to its two-dimensional structure that efficiently distributes strain, allowing high mechanical stability even after 100 cycles, as confirmed by Scanning Electron Microscopy (SEM).

Surface modification of activated carbon by surfactants mixtures

Adsorption of surfactants is widely used for surface modification of different materials. Using of the mixtures of the surfactants in many cases is more attractive compared with single surfactants, however composition of mixed adsorption layers at solid surface was not sufficiently studied yet. In this work, the mutual effect of anionic and nonionic surfactants on the composition of the mixed adsorption layer on the surface of activated carbon (AC) was studied. Sodium hexadecyl sulphate (SHS) and oxyethylated octylphenol Triton X100 (TX-100) were used as anionic and nonionic surfactants, respectively. Mixed SHS/TX-100 systems have been studied over a concentration range of 0.1-8.0 mmol/L and the molar fractions of SHS in the mixtures were within 0.2-0.8. It was shown that the adsorption isotherms of SHS or TX-100 surfactants at AC could be describe by the Langmuir equation. For surfactants mixtures at low equilibrium concentrations, it was found that adsorption of SHS increases when TX-100 is present in the solution. This might be explained by the decreasing of electrostatic interactions between the head groups of SHS molecules in the mixed adsorption layers due to incorporation of the molecules of the nonionic surfactant. At higher total surfactant concentrations, SDS adsorbed at AC surface is replaced by TX-100 molecules and as result the nonionic surfactants is preferentially adsorbed on AC.

ANALYSIS OF INTERMOLECULAR INTERACTIONS IN MIXED ADSORPTION LAYERS OF SURFACTANTS

The adsorption of the surfactants mixtures of different chemical nature such as Triton X-100 and sodium hexadecyl sulfate at the surface of graphitized carbon black was studied. Using the model of phase separation (the Rubi–Rosen approach), the composition of the mixed adsorption layers and parameters of interaction between the surfactant molecules in the adsorption layers were calculated. It was found that mixed adsorption layers are enriched with molecules of the non-ionic surfactant Triton X-100.&#x0D; The purpose of the work was to study the adsorption of binary mixtures of surfactants of various chemical nature on the surface of non-porous hydrophobic carbon sorbent at different SAS ratio in mixtures.&#x0D; The results of calculations show that the composition of the adsorption layer on the surface of the GC is significantly different from the ratio of surfactants in the solution. The value of the parameter χ indicates that the mixed adsorption layer on the surface of the GC is enriched with non-ionic surfactant molecules, even with a small its content in the solution (αTХ-100 = 0,2). With an increase in the ТХ-100 molar fraction in the binary solution from 0,2 to 0,8 its share in the adsorption layer increases in approximately 1.5 times. Negative values of the interaction parameters βs indicate excessive attraction of the molecules and ions of the mixture components in the mixed adsorption layers. An increase in the absolute value of the parameter βs with an increase in αTХ-100 in the solution characterizes the enhancement of the interactions between the components in the adsorption layer.&#x0D; Thus, in the course of experiments carried out for mixed systems of SHDS-ТХ-100, the existence of a synergistic effect in relation to an increase in the adsorption of surfactants on the GC surface was established. It is found that mixed adsorption layers are enriched with molecules of the non-ionic surface active substance of the triton X-100.

Synthesis and characterization of nano-sized hierarchical porous AuSAPO-34 catalyst for MTO reaction: Special insight on the influence of TX-100 as a cheap and green surfactant

Abstract Hierarchical SAPO-34 and AuSAPO-34 were synthesized as a catalyst in methanol to olefins (MTO) reaction by utilizing gold (Au) as a novel promoter and Triton X-100 (TX-100) as a cheap, non-toxic and innovative mesoporogen. In this work, independent and simultaneous effects of introducing different amounts of TX-100 and Au to the SAPO-34 framework were studied by XRD, ICP-AES, UV–vis/DRS, FESEM, HRTEM, BET, NH3-TPD, FTIR and TGA-DTA analyses. The characterization results revealed that when the concentration of TX-100 is lower than the critical micelle concentration (CMC), the effects of surfactant are only limited to the covering and steric effects and its result can only be seen on the size of SAPO-34 crystals. Nevertheless, when the concentration of the surfactant exceeds CMC, in addition to the mentioned effects, micellization of the TX-100 molecules effectively occurs and results in the formation of small SAPO-34 crystals with hierarchical porosity. The presence of a small amount of gold demonstrates a significant effect on acidic properties and coke deposition rate of the samples. Consequently, the simultaneous presence of TX-100 and Au is accompanied with a superior catalytic performance of about 97% selectivity towards light olefins and 331 min lifetime.

The interaction between diesel and surfactant Triton X-100 and their adsorption on coal surfaces with different degrees of oxidation

Poor flotation of oxidised coals is a major challenge confronting coal preparation plants worldwide. Despite a number of studies to improve the flotation of oxidised coals using surfactants to adsorb on oxidised coal surfaces, the industry continues to use diesel as the dominant collector to float oxidised coals with a low efficiency. Following the previous study employing a composite collector consisting of diesel and surfactant Triton X-100 to improve the surface hydrophobicity of oxidised coals with diesel targeting un-oxidised surface areas while Triton X-100 targeting oxidised surface areas (Chang et al., 2017 [1]), the current study investigated the synergistic interaction between Triton X-100 and diesel and their adsorption on coal surfaces with different degrees of oxidation in flotation. It was found that the superior performance of the composite collector in the flotation of oxidised coals was attributed to the emulsification of diesel by Triton X-100 and the adsorption of Triton X-100 on oxidised surface areas. Triton X-100 molecules which adsorbed at the oil/water interfaces emulsified the diesel, significantly decreasing the size of diesel droplets and facilitating the adsorption of diesel on un-oxidised surface areas. On oxidised surface areas, Triton X-100 adsorbed through a “head-on” adsorption, rendering the hydrophilic surface hydrophobic.

Influence of surfactant for improving dewatering of brown coal: A comparative experimental and MD simulation study

Abstract Experimental method and molecular dynamics (MD) simulations were used to investigate the filtration dewatering process of brown coal in the presence of the surfactant TRITON X-100 (TX-100). A significant reduction in filter cake moisture content was observed upon addition of TX-100 in the dewatering experiments. It was observed that a narrow TX-100 concentration range of below the critical micelle concentration (CMC) was best for dewatering. The enhancement in filtration dewatering characteristics could be attributed to the wetting characteristic changes of the brown coal surface caused by surfactant adsorption, as indicated by measurement of contact angles. Monolayer adsorption of TX-100 at the lignite surface was investigated by MD simulations. The TX-100 molecules repelled water molecules near the coal surface and adsorbed at the water-lignite interface with the ethoxylate closer to the coal surface than the octylphenol. The mobility of water molecules was enhanced in presence of TX-100 according to the results of mean square displacement (MSD) and diffusion coefficient. It was inferred that adsorption of TX-100 resulted in a more hydrophobic brown coal surface, in agreement with the dewatering and contact angle experiments.

Thixotropic bulk elasticity versus interfacial elasticity in Xanthan Gum surfactant mixed solutions

Dynamic surface behavior and interfacial rheology of Xanthan Gum (XG) polymer and surfactant mixed aqueous solutions have been investigated in this work using Profile Analysis Tensiometry (PAT). The interactions of XG with anionic sodium dodecyl sulfate (SDS) and nonionic triton X100 surfactants were studied. The results demonstrate a significant influence of the XG thixotropic bulk rheology behavior on dynamic surface tension measurements. The time dependent thixotropic force (due to the movement and rearrangement of XG molecules under applied shear and relaxation time afterwards) was evaluated using a high precision buoyancy force measurement system. This extra thixotropic force can affect the expected balance of gravity and surface forces in the Gauss-Laplace equations and causes an abnormal increasing dynamic surface tension for aqueous XG solutions versus time in absence of surfactants. It is shown that the thixotropic property of this polymer can also induce an additional surface elasticity which can be measured by drop oscillation experiments via PAT. Therefore, surface elasticity measurements can be proposed as a novel method for determining the extent of fluid thixotropy. The results also showed strong interaction between XG and SDS molecules. At SDS concentrations below critical micelle concentration (CMC), the equilibrium surface tension of XG-SDS solution decreased considerably with increasing XG concentration. This interaction originates from the anionic nature of both XG and SDS molecules. The surface tension behavior of mixed solutions of XG and Triton X100 molecules did not show significant interactions. The obtained results allow improving the ability of the Gauss-Laplace Equation to calculate more accurately the dynamic surface tension of thixotropic fluids.

Interactions of Cationic, Anionic and Nonionic Surfactants with Cresol Red Dye in Aqueous Solutions: Conductometric, Tensiometric, and Spectroscopic Studies

Abstract The interaction of cresol red (CR) with cetylpyridinium bromide (CPB), sodium dodecyl sulphate (SDS), and Triton X-100 (TX-100) was studied in aqueous solutions employing conductometric, tensiometric, and spectroscopic methods. Various micellar and interfacial parameters were calculated in absence and in presence of CR. The interactions suggest the formation of a CR-CPB adduct, an association of CR with the micelle of TX-100 while no adduct is formed between CR and SDS. Appreciably low critical micelle concentration, CMC value of TX-100 compared with those of CPB and SDS in pure water and drastic reduction of CMC of CPB (about one-twelfth of its value in pure water) than SDS and TX-100 in the presence of CR were observed. Higher negative values of Gibbs free energy of micellization, ΔG m 0, for all the three surfactants indicate that micellization process is spontaneous. The values of maximum surface excess concentration, Γ max, and minimum area per molecule, A min, suggest that in the presence of CR, the air-solution interface is closely packed and the orientation of surfactant molecules is almost perpendicular to the surface. UV-visible spectra suggest the formation of ion-pair complex between the dye CR and the monomers of CPB in the pre-micellar region, while above the CMC a breaking up of the ion-pair complex takes place and the dye is solubilized in the micelles of CPB. In the case of SDS the absorption spectra indicate weak interaction between CR and SDS molecules formation of H-bonding, short range dispersive forces, and hydrophobic interactions between CR and TX-100 molecules in the solution.

Composition of Surface Layer at the Water\u2013Air Interface and Micelles of Triton X-100\xa0+\xa0Rhamnolipid Mixtures

Measurements of the surface tensions, densities and viscosities of aqueous solutions of Triton X-100 (TX-100) and rhamnolipid (RL) mixtures, at constant concentration of RL or TX-100, were carried out. The measured values of the surface tension were compared to those determined using different theoretical models and on the basis of the surface tension of aqueous solutions of individual surfactants. From the surface tension isotherms, the Gibbs surface excess concentration of TX-100 and RL, the composition of surface layer and the standard Gibbs free energy of adsorption at the water–air interface were determined. Moreover, on the basis of surface tension, density and viscosity isotherms, the CMC of surfactants mixtures were evaluated. From the density isotherms, apparent and partial molar volumes of TX-100 and RL were also determined. These volumes were compared to those calculated from the sizes of TX-100 and RL molecules. There was observed a synergetic effect in the reduction of water surface tension and micelle formation, which was confirmed by the intermolecular interactions parameter. In the case of micelle formation, this effect was discussed based on the standard Gibbs free energy of micellization as well as of TX-100 and RL mixing in the micelles. The synergism of TX-100 and RL mixtures in the reduction of water surface tension and micelle formation was explained on the basis of electrostatic interactions between the hydrophilic part of TX-100 and RL molecules; this was supported by pH measurements.

Synergistic effect of triton X100 and 3-hydroxybenzaldehyde on Zn-Mn electrodeposition from acidic chloride bath

The effect of two non-complexing additives, namely Triton X100 and 3-hydroxybenzaldehyde (3-HBA) on Zn-Mn alloy deposition was investigated. The study was carried out using a simple KCl-based bath. To this end, cyclic voltammetry associated to the switching potential method, bulk electrolyses and scanning electron microscopy were used. Electrochemical study, from additives-free bath, showed that the potential of beginning Zn-Mn alloy deposition (E = −1.52 V vs. Ag/AgCl) stands between those of Zn (E = −1.03 V) and Mn (E = −1.65 V) alloying elements. The coatings obtained from this bath are Mn-poor alloys with dendritic structure, and the current efficiency is low (60%). It was found that the conjunction of triton X100 ad 3-HBA suppresses completely the individual electrodeposition of Zn. The synergistic effect of additives favors Zn and Mn co-deposition, but Mn-rich alloys are deposited only from E = −1.8 V vs. Ag/AgCl. The coatings obtained at lower cathodic potentials are adherent, smooth and bright. The current efficiency is enhanced and reaches 85%. Voltammogram data, from a comparative study using polyethylene glycol (PEG8000) instead of triton X100, display prominently the vital role that plays the hydrophobic head of triton X100 molecule in enhancing Mn incorporation into Zn matrix. Moreover, the switching potential technique demonstrated that at cathodic potentials higher than −1.8 V, the hydrogen evolution reaction is catalyzed when Mn-rich are deposited such that it gives rise to a higher pH increase at the cathode surface. This pH increase leads to an intense precipitation of hydroxides that blocks the alloy deposition process.

Study of Ionic Liquid Microemulsions: Ethylammonium Nitrate/TritonX-100/Cyclohexane

Abstract In this study, ionic liquid (IL), specifically ethylammonium nitrate (EAN), was used instead of water to form nonaqueous microemulsions with cyclohexane and the nonionic surfactant Triton X-100 (TX-100). The phase behavior of the ternary system was investigated, and the microemulsions of ionic liquid-in-oil (IL/O) and oil-in-ionic liquid (O/IL) and the bicontinuous microregion were identified through traditional electrical conductivity measurement. The micropolarities of the IL/O microemulsions were determined via UV–Vis spectroscopy with methyl orange as an absorption probe. Results indicated that the polarity of the reverse micelles remained constant but that of the IL/O microemulsions increased when IL pools were formed. Fourier transform infrared spectroscopy was used to study the interaction mechanism between TX-100 and EAN molecules in IL/O microemulsions. We demonstrated that IL/O microemulsions may be promising for application due to the unique features of ILs and microemulsions.

High transmittance cadmium oxysulfide Cd(S,O) buffer layer grown by triton X-100 mediated chemical bath deposition for thin-film heterojunction solar cells

Polycrystalline 100–190 nm Cd(S,O) n-type semiconductor thin films of high transparency in the visible range are deposited by a surfactant Triton X-100 mediated chemical bath deposition process. The crystalline structure of the films revealed by X-ray diffraction data shows a cubic-CdO phase signified by (111) and (200) planes alongside the (002), (220), and (110) planes from hexagonal-CdS. The invariance of the 2θ position of the (002) CdS diffraction is interpreted in terms of the growth of the composite film essentially by the formation of a dilute interstitial alloy of CdO and CdS. This is confirmed by Raman spectra which, besides the CdS 1LO and 2LO modes at 300 and 600 cm−1, also show Raman lines from CdO at 1098 cm−1 and 952 cm−1 assigned as overtone of 2LO phonon modes and 556 cm−1 due to band crossing between LO and TO modes of CdO. Optical spectra of Cd(S,O) films show a median transmittance of &amp;gt;85% compared to ∼70% for CdS films in the 550–1000 nm wavelength range. The Cd(S,O) films show optical bandgap varying from 2.34 to 2.26 eV with increasing CdO fraction but retain high sub-bandgap transmission and sharp band edge threshold. The Cd(S,O) films thus offer an alternative to the CdS buffer layer in the heterojunction solar cells, which has major shortcoming of poor stability and high sub-bandgap absorption. The photoluminescence spectra of Cd(S,O) films show three green bands, of which one is the near band edge transition at 511.5 nm, the same as in CdS, the second band at 526.0 nm that red shifted from the CdS position is due to shallow donor-acceptor defects arising from structural change due to CdO, and the third band at 543.6 nm (2.28 eV) originates from direct band transition in CdO. The growth mechanism of Cd(S,O) films is described, which invokes that the Triton X-100 molecule modifies the microenvironment around adsorbed [Cd(NH3)4]2+ species, thereby inducing two concurrent reactions, one with SH− species that cause CdS formation and the other controlled Cd(OH)2 deprotonation reaction that forms CdO.

Effect of Triton X-100 on the stability of titania nanoparticles against agglomeration and sedimentation: A masked depletion interaction

The sedimentation half-times ts of suspensions of polydisperse titania particles in aqueous Triton X-100 (TX100) solutions with concentrations cTX100 ranging from 0.05 to 250mM were measured. Three regions of TX100 concentrations with different settling behavior were observed. In region A, or for cTX100 below its cmc (ca. 0.24mM in water at 25°C), the ts-values increase with increasing surfactant concentration. In region B, or for cmc≤cTX100<c**, where c** was determined to be 30mM experimentally, the ts-values do not vary with the surfactant concentration. In region C, or for cTX100≥c**, as cTX100 increases, the ts-values increase. In regions A and B, little or no viscosity effect on the sedimentation was observed. By contrast, in region C, the viscosity of the micellar solution increases with increasing cTX100 and accounts partially for the slower particle sedimentation rate. The surface densities of adsorbed TX100 molecules on the particle surfaces were measured to probe their effects on the steric interactions, which are responsible for the increase in the ts-values in region A. The maximum adsorbed densities on the particle surfaces, which are presumed to be hydrophilic, were found to be much smaller than those on other hydrophobic surfaces, as expected. Nonetheless, the adsorbed densities are high enough to induce strong steric interactions in region B, preventing the particles from agglomerating. In region C, the increase in viscosity slows down not only the particle sedimentation, but also the particle agglomeration, resulting in an apparently weaker micellar depletion effect. Our inference is that depletion-induced flocculation in region C is masked by the high solution viscosity. This inference is supported by several different lines of evidence. First, the once corrected half-times, tsI, which are the measured half-times divided by the relative viscosities, start to decrease at cTX100≅ 160mM, suggesting the formation of particle clusters, and reveals a micelle-induced depletion effect. The twice corrected half-times, tsII, which are tsI divided by the viscosity of the solution to account for the effect of viscosity on the agglomeration rate, are consistent with these inferences. In addition, the DLS data support our inference that the clusters in region C are flocs, which can be de-agglomerated with some mild agitation. A recently published model of agglomeration and sedimentation (Yang et al., 2016) is used to fit the data for estimating the effective Fuchs-Smoluchowski stability ratio W for flocculation. W-values are inferred to be over 106 at cTX100<160mM, but only ca. 500–1000 at higher concentrations, supporting the hypothesis of a depletion-induced flocculation that is masked by the solution viscosity.

A Surfactant-Induced Functional Modulation of a Global Virulence Regulator from Staphylococcus aureus

Triton X-100 (TX-100), a useful non-ionic surfactant, reduced the methicillin resistance in Staphylococcus aureus significantly. Many S. aureus proteins were expressed in the presence of TX-100. SarA, one of the TX-100-induced proteins, acts as a global virulence regulator in S. aureus. To understand the effects of TX-100 on the structure, and function of SarA, a recombinant S. aureus SarA (rSarA) and its derivative (C9W) have been investigated in the presence of varying concentrations of this surfactant using various probes. Our data have revealed that both rSarA and C9W bind to the cognate DNA with nearly similar affinity in the absence of TX-100. Interestingly, their DNA binding activities have been significantly increased in the presence of pre-micellar concentration of TX-100. The increase of TX-100 concentrations to micellar or post-micellar concentration did not greatly enhance their activities further. TX-100 molecules have altered the secondary and tertiary structures of both proteins to some extents. Size of the rSarA-TX-100 complex appears to be intermediate to those of rSarA and TX-100. Additional analyses show a relatively moderate interaction between C9W and TX-100. Binding of TX-100 to C9W has, however, occurred by a cooperative pathway particularly at micellar and higher concentrations of this surfactant. Taken together, TX-100-induced structural alteration of rSarA and C9W might be responsible for their increased DNA binding activity. As TX-100 has stabilized the somewhat weaker SarA-DNA complex effectively, it could be used to study its structure in the future.