Nonionic Surfactant Octyl Glucoside Research Articles

Application of Computer Simulation Free-Energy Methods to Compute the Free Energy of Micellization as a Function of Micelle Composition. 2. Implementation

In this paper, the implementation of the CS-FE/MT model introduced in article 1 is discussed, and computer simulations are performed to evaluate the feasibility of the new theoretical approach. As discussed in article 1, making predictions of surfactant/solubilizate aqueous solution behavior using the CS-FE/MT model requires evaluation of DeltaDeltaG for multiple surfactant-to-solubilizate or surfactant-to-cosurfactant transformations. The central goal of this article is to evaluate the quantitative accuracy of the alchemical computer simulation method used in the CS-FE/MT modeling approach to predict DeltaDeltaG for a single surfactant-to-solubilizate or for a single surfactant-to-cosurfactant transformation. A hybrid single/dual topology approach was used to morph the ionic surfactant sodium dodecyl sulfate (SDS) into the ionic solubilizate ibuprofen (IBU), and a dual topology approach was used to morph the nonionic surfactant octyl glucoside (OG) into the nonionic solubilizate p-aminobenzoate (PAB). In addition, a single topology approach was used to morph the nonionic surfactant n-decyl dimethylphosphine oxide (C10PO) into the nonionic cosurfactant n-decyl methyl sulfoxide (C10SO), the nonionic surfactant octylsulfinyl ethanol (C8SE) into the nonionic cosurfactant decylsulfinyl ethanol (C10SE), and the nonionic surfactant n-decyl methyl sulfoxide (C10SO) into the nonionic cosurfactant n-octyl methyl sulfoxide (C8SO). Each DeltaDeltaG value was computed by using thermodynamic integration to determine the difference in free energy associated with (i) transforming a surfactant molecule of type A into a cosurfactant/solubilizate molecule of type B in a micellar environment (referred to as DeltaG2) and (ii) transforming a surfactant molecule of type A into a cosurfactant/solubilizate molecule of type B in aqueous solution (referred to as DeltaG1). CS-FE/MT model predictions of DeltaDeltaG for each alchemical transformation were made at a number of simulation conditions, including (i) different equilibration times at each value of the coupling parameter lambda, (ii) different data-gathering times at each lambda value, and (iii) simulation at a different number of lambda values. For the three surfactant-to-cosurfactant transformations considered here, the DeltaDeltaG values predicted by the CS-FE/MT model were compared with DeltaDeltaG values predicted by an accurate molecular thermodynamic (MT) model developed by fitting to experimental CMC data. Even after performing lengthy equilibration and data gathering at each lambda value, physically unrealistic values of DeltaDeltaG were predicted by the CS-FE/MT model for the transformations of SDS into IBU and of OG into PAB. However, more physically realistic DeltaDeltaG values were predicted for the transformation of C10PO into C10SO, and reasonable free-energy predictions were obtained for the transformations of C8SE into C10SE and C10SO into C8SO. Each of the surfactant-to-cosurfactant transformations considered here involved less extensive structural changes than the surfactant-to-solubilizate transformations. As computer power increases and as improvements are made to alchemical free-energy methods, it may become possible to apply the CS-FE/MT model to make accurate predictions of the free-energy changes associated with forming multicomponent surfactant and solubilizate micelles in aqueous solution where the chemical structures of the surfactants, cosurfactants, and solubilizates differ significantly.

Octyl Glucoside-Mediated Solubilization and Reconstitution of Liposomes: Structural and Kinetic Aspects

Structural and kinetic aspects of the solubilization of phosphatidylcholine (PC) liposomes induced by the nonionic surfactant octyl glucoside (OG) and the reconstitution of PC vesicles by dilution ...

Structural Modifications in the Stratum corneum by Effect of Different Solubilizing Agents: A Study Based on High-Resolution Low-Temperature Scanning Electron Microscopy

The action of different solubilizing agents (chloroform-methanol mixtures and the nonionic surfactant octyl glucoside, OG) on the structural organization of the stratum corneum (SC) was investigated by means of the double-layer high-resolution low-temperature scanning electron microscopy technique. Chloroform-methanol mixtures were able to remove mainly the lipid without a significant loss of cohesion in the SC tissue. However, OG treatment caused a partial disaggregation of the corneocytes and their envelopes and, at a macroscopic level, a loss of cohesion in the whole SC tissue. As for lipid domains, after OG treatment the formation of rough structures was detected, probably associated with the disorder in the lipid lamellae. The formation of these new structures could be attributable to the interaction of the lipids with the proteins liberated from the corneocytes. Hence, a direct correlation may be established between the preservation of the structure of the corneocytes and the corneocyte envelope and the cohesion of the whole SC tissue.

Liposomes as protective agents of stratum corneum against octyl glucoside: a study based on high-resolution, low-temperature scanning electron microscopy

The ability of phosphatidylcholine (PC) liposomes to protect pig stratum corneum (SC) against the action of the nonionic surfactant octyl glucoside (OG) was investigated “in vitro” using double-layer coating for high-resolution, low-temperature scanning electron microscopy. This technique has been useful in preventing drying artifacts in the study of biological materials. The treatment of SC with OG led to a perturbation mainly in the corneocytes. However, the incubation of the tissue with liposomes prior to the OG treatment resulted in a progressive decrease in these perturbations and, consequently, in the progressive protection of the SC against the action of the surfactant.

Ability of the exopolymer excreted by Pseudoalteromonas antarctica NF3, to coat liposomes and to protect these structures against octyl glucoside

The ability of an exopolymer of glycoproteic character (GP) excreted by a new gram-negative specie Pseudoalteromonas antarctica NF3, to coat phosphatidylcholine (PC) liposomes and to protect these bilayers against the action of the nonionic surfactant octyl glucoside (OG) has been investigated. TEM micrographs of freeze-fractured liposome/GP aggregates reveal that the addition of GP to liposomes led to the formation of a covering structure (polymer adsorbed onto the bilayers) that tightly coated PC bilayers. The complete coating was already achieved when the proportion of GP assembled with liposomes was approximately 10% (wt% vs total PC). Higher GP amounts resulted in a growth of this coating structure which exhibited at the highest GP proportion in the system (31 % of assembled GP) a multilayered structure. An increasing resistance of PC liposomes to be affected by OG both at sublytic and lytic levels occurred as the proportion of GP in the system rose; this protective effect being more effective when the proportion of assembled GP was 10-20% in weight. Thus, although a direct dependence was found between the growth of the enveloping structure and the resistance of the coated liposomes to be affected by OG, the best protection occurred when the proportion of assembled GP was about 10 wt%.

Partitioning of octyl glucoside between octyl glucoside/phosphatidylcholine mixed aggregates and aqueous media as studied by isothermal titration calorimetry

Stepwise dilution of lipid-surfactant mixed micelles first results in extraction of surfactant from the mixed micelles into the aqueous medium. Subsequently mixed micelles transform into vesicles, within a range of compositions that corresponds to equilibrium coexistence between these two types of aggregates. Further dilution results in extraction of surfactant from the resultant mixed vesicles. In the present study, we have investigated the heat evolution of these processes, as they occur in mixed systems composed of egg phosphatidylcholine (PC) and the nonionic surfactant octylglucoside (OG). A combined use of isothermal titration calorimetry (ITC) and photon correlation spectroscopy (PCS), capable of monitoring phase transformations, revealed that 1) The sum of all of the studied processes (i.e., extraction of OG from mixed micelles and vesicles and the phase transformation) is isocaloric at approximately 40 degrees C throughout the whole dilution. At lower temperatures, all of the dilution steps are exothermic, whereas at higher temperatures all of them are endothermic. 2) At all temperatures, the absolute value of the heat associated with each dilution step within the range of coexistence of micelles and vesicles is almost constant and larger than in either the micellar or the vesicular range. We give an interpretation of these calorimetric data in terms of the relationship between the composition of the mixed aggregates Re and the aqueous concentration of surfactant monomers Dw. Assuming that the main contribution to the heat evolution is due to extraction of surfactant from mixed aggregates to the aqueous solution, we deduce the relationship Dw(Re) characterizing the system over the whole range of compositions. We find that, in accord with thermodynamic expectations, Dw is almost constant throughout the range of coexistence of mixed micelles and vesicles.

The heat of transfer of lipid and surfactant from vesicles into micelles in mixtures of phospholipid and surfactant

We study the heat associated with the transformation of vesicles into micelles in mixtures of bilayer-forming phospholipids and micelle-forming surfactants. We subdivide the total heat evolution deltaQ(coex) within the range of coexistence of vesicles and micelles into three contributions related to the transition of dN(D)m-b molecules of surfactant and dN(L)m-b molecules of lipid from micelles to vesicles and to the extraction of dN(D)m-w molecules of surfactant from micelles to the aqueous solution, so that deltaQ(coex) = deltaH(D)m-w x dN(D)m-w + deltaH(D)m-b x dN(D)m-b + deltaH(L)m-b x dN(L)m-b where deltaH(D)m-w, deltaH(L)m-b, and deltaH(D)m-b are the respective molar "transfer" enthalpies. We design a method for the evaluation of all three molar enthalpies, from isothermal calorimetric titrations conducted according to two different protocols of titration of lipid-surfactant mixtures. In the first protocol the mixture is titrated with an aqueous solution of pure lipid vesicles, and in the second the mixture is titrated with an aqueous solution of pure surfactant. Titration of the mixed systems by a buffer solution serves to verify the results obtained under these protocols. In addition to the values of molar enthalpies, our method yields the cmc value of the pure surfactant. We apply our method to investigating the heat evolution in mixtures of egg yolk phosphatidylcholine and the nonionic surfactant octylglucoside in a phosphate-buffered saline solution at 28 degrees C. These studies gave the following values: deltaH(D)m-w = -1732 cal/mol, deltaH(L)m-b = -592 cal/mol, deltaH(D)m-b = 645 cal/mol, and cmc = 23.5 mM. We discuss the possible physical insight of these values and the perspectives of applications of the proposed method.

SELECTIVE SOLUBILIZATION OF THE STRATUM CORNEUM COMPONENTS USING SURFACTANTS

ABSTRACT The selective solubilization of pig stratum corneum (SC) by the nonionic surfactant octyl glucoside (OG) was investigated. The use of OG concentrations lower than its critical micelle concentration (CMC) led to a progressive solubilization of SC membranes whereas OG concentrations higher than its CMC provided an increase in its solubilizing power. In these conditions, some amino acids building the SC keratinocyte envelopes and bound to the lipids by covalent bonds were extracted. TEM revealed during and after surfactant incubation the type of structures formed which may be correlated with the formation of some colloid association between SC components and OG. The OG may be considered as a more suitable solubilizing agent than solvents to obtain more specific and selective solubilization of SC components without a protein denaturing effect.

Study of the composition and structure of pig stratum corneum based on the action of different solubilizing agents

The composition and structure of pig stratum correum (SC) tissue were investigated using different solubilization methods. Whereas chloroform-methanol mixtures resulted in an almost complete removal of the intercellular lipids of the SC tissue and a small amount of proteins, the action of the nonionic surfactant octyl glucoside (OG) at concentrations lower and higher than its critical micelle concentration (CMC) led to the disaggregation of the SC tissue due to the solubilization of the corneocyte envelope. From a structural viewpoint, the intercellular lipids were bound one to another by means of hydrophobic interactions and the amino acids building the keratinocyte envelopes were linked covalently to these lipids (predominantly ceramides). The material extracted by organic solvents was able to form liposomes (proteoliposomes), whereas that solubilized using OG surfactant (richer in proteins) did not form these structures. Two different approaches may be envisaged in the interaction of the OG and organic solvents with the SC tissue. On the one hand, the OG can be considered as a preferential and selective agent with respect to the use of organic solvents to obtain more specific information on the assembly properties of the lipids and amino acids building the corneocyte lipid envelope. On the other hand, the organic solvents appear to be specifically suitable for studying the lipid building the intercellular SC matrix. In addition to the generally accepted assumption that organic solvents exert a protein denaturing influence, it was demonstrated that the action of chloroform-methanol mixtures does not affect the architecture of the SC tissue, whereas the OG leads to its disaggregation.

Solubilization and reconstitution of vesicular stomatitis virus envelope using octylglucoside

Reconstituted vesicular stomatitis virus envelopes or virosomes are formed by detergent removal from solubilized intact virus. We have monitored the solubilization process of the intact vesicular stomatitis virus by the nonionic surfactant octylglucoside at various initial virus concentrations by employing turbidity measurements. This allowed us to determine the phase boundaries between the membrane and the mixed micelles domains. We have also characterized the lipid and protein content of the solubilized material and of the reconstituted envelope. Both G and M proteins and all of the lipids of the envelope were extracted by octylglucoside and recovered in the reconstituted envelope. Fusion activity of the virosomes tested either on Vero cells or on liposomes showed kinetics and pH dependence similar to those of the intact virus.

Solubilizing effects caused by the nonionic surfactant octyl glucoside in phosphatidylcholine liposomes

AbstractThe mechanisms governing the interaction of the nonionic surfactant octyl glucoside (OG) on phosphatidylcholine (PC) liposomes were investigated. Permeability alterations were detected as a change in 5(6)‐carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was determined as a decrease in the static light scattered by liposome suspensions. A direct relationship was established in the initial interaction steps (10–50% CF release) between the growth of vesicles, the leakage of entrapped CF, and the effective molar ratio of surfactant to phospholipid in bilayers (Re). This dependence was also detected during the solubilization range of Re values between 1.3 and 3.0, where the decrease in the surfactant‐PC aggregate size and in the light scattering of the system depended on the Re parameter and, hence on the composition of these aggregates. The free OG concentrations at subsolubilizing and solubilizing levels showed lower and similar, respectively, values than its critical micelle concentration (CMC). These findings indicated that the alterations in bilayer permeability were due to the action of surfactant monomers, whereas bilayer solubilization was determined by the formation of mixed micelles. This finding supports the generally accepted assumption that the concentration of free surfactant must reach the CMC for solubiliation to occur.

Structural phase transitions involved in the interaction of phospholipid bilayers with octyl glucoside.

The transitional stages induced by the interaction of the nonionic surfactant octyl glucoside (OcOse) on phosphatidylcholine liposomes were studied by means of transmission electron microscopy (TEM), light scattering and permeability changes. A linear correlation was observed between the effective surfactant/lipid molar ratio (Re; three-stage model proposed for liposome solubilization) and the OcOse concentration in the initial and final interaction stages, despite showing almost a constant value during bilayer saturation. The bilayer/aqueous phase partition coefficient (K) decreased in the subsolubilizing interaction steps and increased during solubilization. Thus, whereas a preferential distribution of surfactant monomers in the aqueous phase with respect to the lipid bilayers took place in the initial interaction steps, a larger association of OcOse molecules with these lipids in bilayers occurred during solubilization. The initial steps of bilayer saturation (50-70% permeability) were attained for a lower free surfactant (Sw) than that for its critical micellar concentration (cmc). When Sw reached the OcOse cmc, solubilization started to occur (Resat). Large unilamellar vesicles began to form as the OcOse exceeded 60 mol/100 mol, exhibiting for 65 mol/100 mol (50% permeability) vesicles of approximately 400 nm. TEM pictures for 100% permeability (72 mol/100 mol) and Resat still showed unilamellar vesicles, albeit that the Resat TEM picture showing traces of smaller structures. Exceeding surfactant amounts led to a decrease in static light scattering; the vesicle-size curve began to show a bimodal distribution. The TEM picture showed tubular structures together with bilayer fragments. Thereafter, the open structures were gradually affected by the surfactant and the scattered intensity gradually decreased to a constant low value.