The surfactant Dioctyl Sodium Sulfosuccinate (DOSS) exposure causes adverse effects in embryos and adults of zebrafish (Danio rerio).

Dioctyl Sodium Sulfosuccinate (DOSS, CAS 577-11-7) is a chemical emulsifying surfactant that is widely used in the food and the cosmetic industry, and it is also the major component of the crude oil chemical dispersant Corexit™. Despite of its wide use, the studies related to its negative effect have been evaluated mainly in marine environments showing that DOSS is highly bioactive, extremely low volatile, and potential to persist in the environment longer than other dispersant components. Up to date, there is no available information of DOSS concentration in freshwater environments, little is known about its downstream fate after excretion and its effect on freshwater organisms. The objective of this study was to evaluate the effect of DOSS at different concentrations in embryos and adults of zebrafish Danio rerio in an acute-static bioassays of 96 h. The median lethal concentration in embryos was 33.3 mg/L. Malformations started to be observed at 10 mg/L. In adults, the gene expression analysis in gill tissues showed a deregulation in genes associated with the antioxidant system and the nucleotide excision repair mechanism. Additionally, Micronuclei (DNA damage) in erythrocytes, and fat degeneration in liver, hypertrophy and hyperplasia in gills, and hyaline drops in kidney tissues were also observed. In conclusion, the concentrations of DOSS evaluated here would be of health relevance to fish based on morphological alterations in embryos and changes in the gene expression profile, DNA damage and tissue impairment in adults.

Biamphiphilic ionic liquid based aqueous microemulsions as an efficient catalytic medium for cytochrome c.

Considering the remarkable applicability of ionic liquids (ILs) in bio-catalysis involving enzymes, herein, we report new IL based aqueous microemulsions as a catalytic reactor for cytochrome c (Cyt-c). Microemulsions (µEs), comprising water as the polar component, imidazolium (cation) and dioctylsulfosuccinate (AOT) (anion) based biamphiphilic ionic liquid (BAIL) as the surfactant and a hydrophobic ionic liquid (HIL) as the non-polar component have been prepared and characterized. The use of BAIL has promoted the formation of µEs without any co-surfactant, owing to its higher surface activity. The effect of ester- or amide-functionalization of the alkyl chain of the imidazolium cation of BAILs on the phase behavior of µEs has been investigated. The prepared µEs have been characterized via conductivity, dynamic light scattering (DLS), UV-vis absorption and steady-state fluorescence (using external polarity probes) techniques. The prepared µEs have been employed as nano-reactors for exploring the catalytic activity of Cyt-c. The formed BAIL-water nano-interfaces in reverse µEs have exerted a positive effect on the catalytic activity of Cyt-c stored in a water pool of reverse µEs. A five-fold higher rate constant in µEs as compared to buffer establishes µEs as a better catalytic medium. Furthermore, the differing nature of nano-interfaces created by BAILs and water in reverse µEs, depending on the functionalization of the alkyl chain of the cationic part of BAIL, has exerted varying influence on the catalytic activity of Cyt-c. It is expected that the present work will result in providing a versatile platform for the creation of new IL and water based µEs for bio-catalytic applications.

Structure and conductivity of AOT solutions in n-hexadecane-chloroform mixtures.

The structure and conductivity of AOT (sodium bis(2-ethylhexyl) sulfosuccinate) solutions (2.5 × 10-4 -2.5 × 10-1 M) in n-hexadecane-chloroform mixture at the chloroform concentration from 50 to 100 vol% were studied. The diffusion ordered spectroscopy NMR study revealed that in the indicated range, the observed hydrodynamic diameter of micelles depends only on the AOT concentration and does not depend on the chloroform content. Molar fractions of free AOT molecules and those aggregated into micelles were calculated using the Lindman's law: at concentrations above 2.5 × 10-1 М, the solutions contain mostly the micelles, whereas at concentrations below 2.5 × 10-4 M, the solutions contain AOT molecules. The transition region contains both the AOT molecules and the micelles. Conductivity measurements were used to determine free charge carriers in the bulk of solutions and their contributions to conductivity.

The Influence of Anionic, Cationic Surfactant and AOT/Water/Heptane Reverse Micelle on Photophysical Properties of Crocin: Compare with RPMI Effect.

Encapsulation of crocin (CN), having large nonlinear optical (NLO) properties, can be utilized in studies of photodynamic therapy (PDT). For this purpose, photo-physical and NLO properties of CN encapsulation with and without cell culture medium (CCM) were investigated. As well, nonlinear absorption (NLA) coefficient and nonlinear refractive (NLR) indices were found to be 10-7 (cm W-1) and 10-12 (cm2 W-1); respectively. The results revealed that NLO properties of CN had changed through its dipole moment. Reflecting on the theory of Bilot and Kawski, it was evidenced that the dipole moment of CN could change with a nano-droplet size. Furthermore, it was demonstrated that RPMI-1640 as a growth medium had failed to change NLO properties of CN encapsulated in nano-droplet. Accordingly, the encapsulated CN in nano-droplet in the form of a photosensitizer (PS) was suggested as a good candidate to examine PDT under in-vitro conditions.

Enhancing the Spreading Behavior on Pulmonary Mucus Mimicking Subphase via Catanionic Surfactant Solutions: Toward Effective Drug Delivery through the Lungs.

Effective and efficient spreading of drug formulations on the pulmonary mucosal layer is key to successful delivery of therapeutics through the lungs. The pulmonary mucus layer, which covers the airway surface, acts as a barrier against therapeutic agents, especially in the case of chronic lung diseases due to increased thickness and viscosity of the mucus. Therefore, spreading of the drug formulations on the airways gets harder. Although spreading experiments have been conducted with different types of formulations on mucus-mimicking subphases, a highly effective formulation is yet to be discovered. Adding surfactant to such formulations decreases the surface tension and triggers the Marangoni forces to enhance the spreading behavior. In this study, catanionic (cationic + anionic) surfactant mixtures composed of dodecyltrimethylammonium bromide (DTAB) and dioctyl sulfosuccinate sodium salt (AOT) mixed at various mole ratios are prepared and their spreading behavior on both mucin and cystic fibrosis (CF) mucus models is investigated for the first time in the literature. Synergistic interaction is obtained between the components of the DTAB/AOT mixtures, and this interaction has enhanced the spreading of the formulation drop on both the mucin and CF mucus models when compared with the spreading performances of selected conventional surfactants. It is proposed that the catanionic surfactant mixtures, especially when mixed at the molar ratios of 8/2 and 7/3 (DTAB/AOT), improve the spreading even on the cystic fibrosis sputum model. As it is vital to transport a sufficient amount of drug to the targeted region for the treatment of diseases, this study presents an important application of the fundamentals of colloidal science to pharmaceutical nanotechnology.

Structure Dependence of Pyridine and Benzene Derivatives on Interactions with Model Membranes.

Pyridine-based small-molecule drugs, vitamins, and cofactors are vital for many cellular processes, but little is known about their interactions with membrane interfaces. These specific membrane interactions of these small molecules or ions can assist in diffusion across membranes or reach a membrane-bound target. This study explores how minor differences in small molecules (isoniazid, benzhydrazide, isonicotinamide, nicotinamide, picolinamide, and benzamide) can affect their interactions with model membranes. Langmuir monolayer studies of dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylethanolamine (DPPE), in the presence of the molecules listed, show that isoniazid and isonicotinamide affect the DPPE monolayer at lower concentrations than the DPPC monolayer, demonstrating a preference for one phospholipid over the other. The Langmuir monolayer studies also suggest that nitrogen content and stereochemistry of the small molecule can affect the phospholipid monolayers differently. To determine the molecular interactions of the simple N-containing aromatic pyridines with a membrane-like interface, 1H one-dimensional NMR and 1H-1H two-dimensional NMR techniques were utilized to obtain information about the position and orientation of the molecules of interest within aerosol-OT (AOT) reverse micelles. These studies show that all six of the molecules reside near the AOT sulfonate headgroups and ester linkages in similar positions, but nicotinamide and picolinamide tilt at the water-AOT interface to varying degrees. Combined, these studies demonstrate that small structural changes of small N-containing molecules can affect their specific interactions with membrane-like interfaces and specificity toward different membrane components.

Mass Exchange and Equilibration Processes in AOT Reverse Micelles.

Reverse micelles (RMs) made with sodium bis(2-ethylhexyl)sulfosuccinate suspended in isooctane are commonly used experimental models of aqueous microenvironments. However, there are important unanswered questions about the very characteristic that makes them of interest, namely their size. To explore the factors that determine the size of RMs, all-atom molecular dynamics simulations of RMs with different sizes but the same water-loading ratio were performed. An Anton 2 machine was used so that systems of the necessary size could be extended into the microsecond timescale, and mass exchange processes could be observed. Contrary to hypothesis, there were no net gains or losses of water by diffusion between RMs of different size. However, gains and losses did occur following fusion events. RM fusion followed RM contact only when waters were present among the hydrophobic surfactant chains at the point of contact. The presence of an encapsulated 40-residue amyloid beta peptide did not directly promote RM fusion, but it quickly and efficiently terminated each fusion event. Before fusion terminated, however, the size of the peptide-containing RM increased without a corresponding change in its water-loading ratio. We conclude that the mass transfer between RMs is most likely accomplished through transient fusion events, rather than through the diffusion of component molecules through the organic phase. The behavior of the amyloid beta peptide in this system underscores its propensity to embed in, and fold in response to, multiple interactions with the surfactant layer.

Probing Human Telomeric DNA and RNA Topology and Ligand Binding in a Cellular Model by Using Responsive Fluorescent Nucleoside Probes.

The development of biophysical systems that enable an understanding of the structure and ligand-binding properties of G-quadruplex (GQ)-forming nucleic acid sequences in cells or models that mimic the cellular environment would be highly beneficial in advancing GQ-directed therapeutic strategies. Herein, the establishment of a biophysical platform to investigate the structure and recognition properties of human telomeric (H-Telo) DNA and RNA repeats in a cell-like confined environment by using conformation-sensitive fluorescent nucleoside probes and a widely used cellular model, bis(2-ethylhexyl) sodium sulfosuccinate reverse micelles (RMs), is described. The 2'-deoxy and ribonucleoside probes, composed of a 5-benzofuran uracil base analogue, faithfully report the aqueous micellar core through changes in their fluorescence properties. The nucleoside probes incorporated into different loops of H-Telo DNA and RNA oligonucleotide repeats are minimally perturbing and photophysically signal the formation of respective GQ structures in both aqueous buffer and RMs. Furthermore, these sensors enable a direct comparison of the binding affinity of a ligand to H-Telo DNA and RNA GQ structures in the bulk and confined environment of RMs. These results demonstrate that this combination of a GQ nucleoside probe and easy-to-handle RMs could provide new opportunities to study and devise screening-compatible assays in a cell-like environment to discover GQ binders of clinical potential.

Coarse-grained empirical potential structure refinement: Application to a reverse aqueous micelle.

Conventional atomistic computer simulations, involving perhaps up to 106atoms, can achieve length-scales on the order of a few 10s of nm. Yet many heterogeneous systems, such as colloids, nano-structured materials, or biological systems, can involve correlations over distances up 100s of nm, perhaps even 1µm in some instances. For such systems it is necessary to invoke coarse-graining, where single atoms are replaced by agglomerations of atoms, usually represented as spheres, in order for the simulation to be performed within a practical computer memory and time scale. Small angle scattering and reflectivity measurements, both X-ray and neutron, are routinely used to investigate structure in these systems, and traditionally the data have been interpreted in terms of discrete objects, such as spheres, sheets, and cylinders, and combinations thereof. Here we combine the coarse-grained computer simulation approach with neutron small angle scattering to refine the structure of a heterogeneous system, in the present case a reverse aqueous micelle of sodium-dioctyl sulfosuccinate (AOT) and iso-octane. The method closely follows empirical potential structure refinement and involves deriving an empirical interaction potential from the scattering data. As in traditional coarse-grained methods, individual atoms are replaced by spherical density profiles, which, unlike real atoms, can inter-penetrate to a significant extent. The method works over an arbitrary range of length-scales, but is limited to around 2 orders of magnitude in distance above a specified dimension. The smallest value for this dimension is of order 1nm, but the largest dimension is arbitrary. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Exploring the effect of formulation parameters on the particle size of carboxymethyl chitosan nanoparticles prepared via reverse micellar crosslinking.

Carboxymethyl chitosan (CMCh), as a non-toxic, biocompatible and biodegradable semi-synthetic biopolymer with mucoadhesive properties, is widely investigated for targeting drug or gene delivery applications. Here, fabrication of CMCh nanoparticles will be reported using a reverse (w/o) micellar system to provide particles with tuneable mean sizes. Reverse microemulsions were prepared by dispersing aqueous solution of CMCh in n-hexane using sodium-bis(ethylhexyl)-sulfosuccinate (AOT) and glutaraldehyde (GA) as an emulsifier and a crosslinking agent, respectively. The obtained particles were perfectly spherical in the nanometric size range (40-140 nm) with a narrow size distribution according to the FE-SEM images. To determine the effective parameters on the mean nanosphere size, CMCh, AOT and GA concentrations were varied according to a full-factorial, three-level design-of-experiments. After evaluating the results, it was found that AOT and CMCh concentrations had a significant effect on the mean nanosphere size while GA concentration surprisingly showed non-significant, minor effects on the same response.

Startling temperature effect on proteins when confined: single molecular level behaviour of human serum albumin in a reverse micelle.

The present work reports the effect of confinement, and temperature therein, on the conformational fluctuation dynamics of domain-I of human serum albumin (HSA) by fluorescence correlation spectroscopy (FCS). The water-pool of a sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelle has been used as the confined environment. It was observed that the conformational fluctuation time is about 6 times smaller compared to bulk medium when confined in a water-pool of 3.5 nm radius. On increasing the size of the water-pool the conformational fluctuation time was found to increase monotonically and approaches the bulk value. The effect of confinement is on par with the general belief about the restricted motion of a macromolecule upon confinement. However, the effect of temperature was found to be surprising. An increase in the temperature from 298 K to 313 K induces a larger change in the conformational fluctuation time in HSA, when confined. In the bulk medium, apparently there is no change in the conformational fluctuation time in the aforementioned temperature range, whereas, when HSA is present in an AOT water-pool of radius 3.5 nm, about an 88% increase in the fluctuation time was observed. The observed prominent thermal effect on the conformational dynamics of domain-I of HSA in the water-pool of an AOT reverse micelle as compared to in the bulk medium was concluded to arise from the confined solvent effect.

Dielectric depolarisation and concerted collective dynamics in AOT reverse micelles with and without ubiquitin.

In this computational study we present molecular dynamics (MD) simulations of reverse micelles, i.e. nano-scale water pools encapsulated by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and dissolved in isooctane. Although consisting of highly polar components, such micro-emulsions exhibit surprisingly low dielectric permittivity, both static and frequency-dependent. This finding is well supported by experimental dielectric measurements. Furthermore, the computational dielectric spectra of reverse micelles with and without the polar protein ubiquitin are almost identical. A detailed component analysis of our simulated systems reveals the underlying mechanism of the observed dielectric depolarisation. While each component by itself would make a remarkable contribution to the static dielectric permittivity, mutual compensation leads to the observed marginal net result. This compensatory behavior is maintained for all but the highest frequencies. Dielectric model theory adapted to the peculiarities of reverse micelles provides an explanation: embedding a system in a cavity engulfed by a low dielectric medium automatically leads to depolarization. In this sense experiment, simulation and theory are in accordance.

Safety Assessment of Dialkyl Sulfosuccinate Salts as Used in Cosmetics.

The Cosmetic Ingredient Review (CIR) Expert Panel (Panel) assessed the safety of 8 dialkyl sulfosuccinate salts for use in cosmetics, finding that these ingredients are safe in cosmetics in the present practices of use and concentration when formulated to be nonirritating. The dialkyl sulfosuccinate salts primarily function as surfactants in cosmetics. The Panel reviewed the new and existing available animal and clinical data in making its determination of safety. The Panel found it appropriate to extrapolate the data on diethylhexyl sodium sulfosuccinate to assess the safety of the entire group because all of the diesters are of a similar alkyl chain length, all are symmetrically substituted, and all have similar functions in cosmetic formulations.

Molecular dynamics simulation study of the association of lidocainium docusate and its derivatives in aqueous solution.

Ionic liquid active pharmaceutical ingredients (IL APIs) are novel materials in which the ions themselves are APIs, but the pure salt is a liquid under ambient conditions. It has been found that IL APIs can have superior performance relative to their conventional salt analogues, but the mechanism for this is unclear. We have used molecular simulations to estimate the aqueous phase association constants of the IL API lidocainium docusate and their sodium and chloride counterparts. Lidocainium is the cationic form of lidocaine, a local anesthetic, while the docusate anion is an emollient. From strongest to weakest, the calculated association constants are 10.1 M(-1) (lidocainium docusate); 0.77 M(-1) (sodium chloride); 0.086 M(-1) (sodium docusate); and 0.065 M(-1) (lidocainium chloride). These results suggest that the experimentally observed enhanced efficacy of lidocainium docusate relative to the traditional drug formulation as a lidocaine hydrochloride salt could result from association of the ions in aqueous solution and at the cell membrane, leading to a synergistic activity effect.

Sulfosuccinate and Sulfocarballylate Surfactants As Charge Control Additives in Nonpolar Solvents.

A series of eight sodium sulfonic acid surfactants with differently branched tails (four double-chain sulfosuccinates and four triple-chain sulfocarballylates) were studied as charging agents for sterically stabilized poly(methyl methacrylate) (PMMA) latexes in dodecane. Tail branching was found to have no significant effect on the electrophoretic mobility of the latexes, but the number of tails was found to influence the electrophoretic mobility. Triple-chain, sulfocarballylate surfactants were found to be more effective. Several possible origins of this observation were explored by comparing sodium dioctylsulfosuccinate (AOT1) and sodium trioctylsulfocarballylate (TC1) using identical approaches: the inverse micelle size, the propensity for ion dissociation, the electrical conductivity, the electrokinetic or ζ potential, and contrast-variation small-angle neutron scattering. The most likely origin of the increased ability of TC1 to charge PMMA latexes is a larger number of inverse micelles. These experiments demonstrate a small molecular variation that can be made to influence the ability of surfactants to charge particles in nonpolar solvents, and modifying molecular structure is a promising approach to developing more effective charging agents.

Biocompatible Polymeric Nanoparticles as Promising Candidates for Drug Delivery.

The use of polymeric nanoparticles (NPs) in pharmacology provides many benefits because this approach can increase the efficacy and selectivity of active compounds. However, development of new nanocarriers requires better understanding of the interactions between NPs and the immune system, allowing for the optimization of NP properties for effective drug delivery. Therefore, in the present study, we focused on the investigation of the interactions between biocompatible polymeric NPs and a murine macrophage cell line (RAW 264.7) and a human monocytic leukemia cell line (THP-1). NPs based on a liquid core with polyelectrolyte shells were prepared by sequential adsorption of polyelectrolytes (LbL) using AOT (docusate sodium salt) as the emulsifier and the biocompatible polyelectrolytes polyanion PGA (poly-l-glutamic acid sodium salt) and polycation PLL (poly l-lysine). The average size of the obtained NPs was 80 nm. Pegylated external layers were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). The influence of the physicochemical properties of the NPs (charge, size, surface modification) on viability, phagocytosis potential, and endocytosis was studied. Internalization of NPs was determined by flow cytometry and confocal microscopy. Moreover, we evaluated whether addition of PEG chains downregulates particle uptake by phagocytic cells. The presented results confirm that the obtained PEG-grafted NPs are promising candidates for drug delivery.

Effect of synergists on organic pigment particle charging in apolar media.

The current work investigates the apolar charging behavior of organic pigment particles and the role that synergists play in regard to particle charging. Organic pigments are often used in apolar paints, inks, and most recently electrostatic lithography. For electrolithography to work, the particles must be both stable and possess the correct polarity and magnitude of charge. It is therefore important to better understand the charging behavior and potential charging mechanisms of these particles that have received little or no attention in the literature. Unfortunately, these already complex systems are further complicated by the fact that the stability of organic pigments is often improved through the use of synergists. Synergists are designed to enhance the adsorption of steric stabilizers to the particles. However, their effect on particle charging has not been previously published. In this study, the particle zeta potential is determined for apolar dispersions of magenta and cyan particles in heptane (with and without synergist present). The particles are dispersed with three different surfactants commonly used in apolar charging studies: Span 80, Aerosol-OT, and OLOA 11000. Acid-base interactions appear to play an important role, particularly for cyan. However, due to the complexity of these systems, any general rule must be applied with caution as the particle, surfactant, and synergist chemistry all determine the nature of the particle charge.

Enhanced photodynamic therapy and effective elimination of cancer stem cells using surfactant-polymer nanoparticles.

Photodynamic therapy is a potentially curative treatment for various types of cancer. It involves energy transfer from an excited photosensitizer to surrounding oxygen molecules to produce cytotoxic singlet oxygen species, a process termed as type II reaction. The efficiency of photodynamic therapy is greatly reduced because of the reduced levels of oxygen, often found in tumor microenvironments that also house cancer stem cells, a subpopulation of tumor cells that are characterized by enhanced tumorigenicity and resistance to conventional therapies. We show here that encapsulation of a photosensitizer, methylene blue, in alginate-Aerosol OT nanoparticles leads to an increased production of reactive oxygen species (ROS) under both normoxic and hypoxic conditions. ROS generation was found to depend on the interaction of the cationic photosensitizer with the anionic alginate polymer. Dye-polymer interaction was characterized by formation of methylene blue dimers, potentially enabling electron transfer and a type I photochemical reaction that is less sensitive to environmental oxygen concentration. We also find that nanoparticle encapsulated methylene blue has the capacity to eliminate cancer stem cells under hypoxic conditions, an important goal of current cancer therapy.

In vitro interaction of polyelectrolyte nanocapsules with model cells.

The nanocapsules based on a liquid core with polyelectrolyte shells prepared by the technique of sequential adsorption of polyelectrolytes (LbL) were investigated to verify capsules bioacceptance. Using AOT (docusate sodium salt) as emulsifier, we obtained liquid cores, stabilized by the interfacial complex AOT/PLL (poly-l-lysine hydrobromide). These liquid cores were encapsulated by sequential adsorption of polyelectrolytes using biocompatible polyanion PGA (poly-l-glutamic acid sodium salt) and biocompatible polycation PLL. The average size of the formed capsules was 60-80 nm. The influence of a number of polyelectrolytes layer in the shell (thickness of polyelectrolytes shell), surface charge, and capsule doses on cell viability was studied in a cellular coculture assay. In order to improve nanocapsules biocompatibility, the PEG-ylated external layers were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). For the most toxic nanocapsules (with only one polycation layer) about 90% of cells could survive when the concentration of nanocapsules was below 0.2 × 10(6) per one cell. That suggests that they use as a delivery vehicles is quite safe for living cells. Analysis of internalization of AOT(PLL/PGA)4-g-PEG in HEK 293 cells indicates that tested nanocapsules can easily penetrate cells membrane.

Highly stabilized lipase in polyaniline nanofibers for surfactant-mediated esterification of ibuprofen.

Lipase (LP) from Candida rugosa was immobilized and stabilized in polyaniline nanofibers (PANFs) via a three-step process of enzyme adsorption, precipitation, and cross-linking, which generates the final immobilization called "EAPC". The activity of EAPC was 5.1 and 5.9 times higher than those of LP immobilizations via enzyme adsorption (EA) and enzyme adsorption/cross-linking (EAC), respectively. After incubation in an aqueous buffer under shaking (200 rpm) for 84 days, EAPC maintained 74% of its initial activity, while EA and EAC retained 11 and 24% of their initial activities, respectively. Highly stable and active EAPC was employed for the resolution of racemic ibuprofen via esterification of S-(+)-ibuprofen with 1-propanol in isooctane. The addition of 100 mM dioctyl sulfosuccinate (AOT) into the reaction medium increased the esterification activity by 61-fold, which can be explained by the better dispersion of EAPC in isooctane. EAPC showed 42% conversion in the esterification of racemic ibuprofen after 102 h, whereas EA and EAC showed only 1.2 and 1.4% conversion in the same condition, respectively. The EAPC approach increases both loading and stability of LP, and the combination of EAPC with the surfactant addition can be employed for efficient enzymatic reactions in organic solvents.