Interaction between cationic and conventional nonionic surfactants in the mixed micelle and monolayer formed in aqueous medium

Mixed micellization and surface properties of cationic and nonionic surfactants dimethyl decyl-, tetradecyl- and hexadecyl phosphineoxide mixtures are studied using conductivity and surface tension measurements. The models of Rubingh, Rosen, and Clint, are used to obtain the interaction parameter, minimum area per molecule, mixed micelle composition, free energies of mixing and activity coefficients. The micellar mole fractions were always higher than ideal values indicating high contributions of cationics in mixed micelles. Activity coefficients were less than unity indicating synergism in micelles. The negative free energies of mixing showed the stability of the surfactants in the mixed micelles.

Can affinity interactions influence the partitioning of glucose-6-phosphate dehydrogenase in two-phase aqueous micellar systems?

In this work, we provide an investigation of the role and strength of affinity interactions on the partitioning of the glucose-6-phosphate dehydrogenase in aqueous two-phase micellar systems. These systems are constituted of micellar surfactant solutions and offer both hydrophobic and hydrophilic environments, providing selectivity to biomolecules. We studied G6PD partitioning in systems composed of the nonionic surfactants, separately, in the presence and absence of affinity ligands. We observed that G6PD partitions to the micelle-poor phase, owing to the strength of excluded-volume interactions in these systems that drive the protein to the micelle-poor phase, where there is more free volume available.

Nanoemulsões óleo de laranja/água preparadas em homogeneizador de alta pressão

The objective of this work was to use the high-pressure homogenizer (HPH) to prepare stable oil/water nanoemulsions presenting narrow particle size distribution. The dispersions were prepared using nonionic surfactants based on ethoxylated ether. The size and distribution of the droplets formed, along with their stability, were determined in a Zetasizer Nano ZS particle size analyzer. The stability and the droplet size distribution in these systems do not present the significant differences with the increase of the processing pressure in the HPH). The processing time can promote the biggest dispersion in the size of particles, thus reducing its stability.

Interação tensoativo/hidrótropo em sistemas aquosos, utilizando ressonância magnética nuclear de ¹H e 13C

In this work, it was studied the behavior of the nonionic surfactant aqueous solutions, containing or not a hydrotropic agent, by resonance magnetic nuclear (NMR). We have studied monofunctional diblock copolymers of poly(propylene oxide-ethylene oxide) (R-PPO-PEO-OH, where R length is linear C4) as nonionic surfactant and sodium p-toluenesulfonate (NaPTS) as hydrotropic agent. The critical micelle concentration (CMC) of the aqueous copolymer solution was obtained from ¹H-NMR. The preliminary study of the interaction between the copolymer, under the unimer and micelle forms, and the hydrotrope, in aqueous solutions, was evaluated by ¹H-NMR and 13C-NMR.

A fluorescence probe study of gemini surfactants in aqueous solution: a comparison between n-2-n and n-6-n series of the alkanediyl-a,w-bis (dimethylalkylammonium bromides)

Two series of alkanediyl-a,w-bis (dimethylalkylammonium bromide (n-2-n and n-6-n; n=8, 10,12, and 16) have been synthesized and their micelles properties studied in aqueous solution using pyrene, pyrenecarboxaldehyde (PCA) and 1,8 anilinonaphtalene sulfonic acid sodium salt (ANS) as fluorescent probes. The micelles from these surfactants have been characterized on the basis of the information provided by micelle-solubilized fluorescent probes. The obtained results indicated that the surfactant concentration at which a marked decrease in l max parameter of pyrenecarboxaldehyde (PCA) occurs corresponds to the CMC determined by conductimetric measurements. Changes in the emission spectra of ANS and PCA observed in the submicellar range for both surfactants series (n-2-n and n-6-n) were interpreted as formation of pre-aggregates. It was found that the dimeric surfactants with long spacer (s= 6) form more hydrated aggregates when compared with those formed by the n-2-n and CnTAB surfactants series. This was attributed to a more difficult packing of n-6-n surfactant molecules to form micelles.

Isolation of an enriched plasma membrame subpellicular microtubule fraction of Leishmania mexicana amazonensis

A cell fractionation procedure previously developed for Trypanosoma cruzi was applied to isolated the plasma membrane of promastigotes of Leishania mexicana amazonensis. The cell, swollen in an hypotonic mediun, were disrupted in the presence of a nonionic detergent and the membrane fraction isolated by differencial centrifugation. Electron microscopy showed that the fraction consisted of pieces of the plasma membrane associated with subpellicular microtubules. It was also shown that this fraction is able to induce cell-mediated immune response in mice.

Thermodynamic Characterization of Humic Acid-surfactant Interaction: New Insights into the Characteristics and Structure of Humic Acids

ABSTRACT Humic acids (HA) are a component of humic substances (HS), which are found in nearly all soils, sediments, and waters. They play a key role in many, if not most, chemical and physical properties in their environment. Despite the importance of HA, their high complexity makes them a poorly understood system. Therefore, understanding the physicochemical properties and interactions of HA is crucial for determining their fundamental role and obtaining structural details. Cationic surfactants are known to interact electrostatically and hydrophobically with HA. Because they are a very well-known and characterized system, they offer a good choice as molecular probes for studying HA. The objective of this study was to evaluate the interaction between cationic surfactants and HA through isothermal titration calorimetry in a thermodynamic manner, aiming to obtain information about the basic structure of HA, the nature of this interaction, and if HA from different origins show different basic structures. Contrary to what the supramolecular model asserts, HA structure is not loosely held, though it may separate depending on the conditions the HA are subjected to in their milieu. It did not show any division or conformational change when interacting with surfactants. The basic structure of the HA remains virtually the same regardless of the different sources and compositions of these HA.

Estudo microcalorimétrico da interação de tensoativos n-alquil-sulfato de sódio com tripsina a 298 k

Systematic study of the interactions of ionic surfactants with protein trypsin in buffer solution pH 3.5, 7.0 and 9.0, ionic strength 10 mM at 298 K was done using the microcalorimetric technique. In this study, anionic surfactant solutions of the sodium n-alkyl sulfates series (C8, C10, C12 and C14) were used. The enthalpy of interaction (ΔintHº) shows that the interaction of the surfactants C8, C10, C12 and C14 with trypsin in the solution pH 3.5 is an endothermic process with the value of ΔintHº decreasing linearly with increasing carbon chain length, which is attributed to the unfolding of the polypeptide chain. In the solution pH 7.0, we observed the same trend except for C14. In the solution pH 9.0, from C10 the enthapy of interaction didn't change with the increasing of the carbon chain length due to unfolding of the polypeptide. We concluded that when trypsin is folded, the enthalpy of interaction shows a linear relationship with the surfactant's hydrophobicity, in agreement with Traube's rule.

Ciência de espumas - aplicação na extinção de incêndios

The structural characteristics of foams are responsible for a broad range of applications of this system. Foams produced by aqueous solutions of surfactant concentrates are used in fire-fighting due to their special properties as extinguishing agents. In the present paper we discuss the main aspects involved in fire-fighting, based on some properties of foams. Thermal and chemical stability, good wetting of surfaces, cooling effect by water drained from the bubbles, isolation of the air from the burning surface and suppression of flammable vapors are some of the factors involved in the extinguishment of fire by foams.

Ambientes micelares em química analítica

This review deals with the general use of the surfactants in Analytical Chemistry. Principal characteristic of the micelle is the improvement in selectivity and/or sensitivity of the analytical determination with emphasis on the catalytic reaction and "cloud point" extraction.

Biossurfactantes: propriedades e aplicações

Chemically synthesized surfactants are widely used for many purposes in almost every sector of modern industry. Surface-active compounds of biological origin (biosurfactants) have been gaining attention in recent years because of some advantages such as biodegradability, low toxicity, diversity of applications and functionality under extreme conditions. Microbial biosurfactants are useful in bioremediation of water and soil, enhanced oil recovery, and in many formulations of petrochemical, chemical, pharmaceutical, food, cosmetic and textile industries. The importance of biosurfactants, their characteristics and industrial applications are discussed.

Adaptação no método do peso da gota para determinação da tensão superficial: um método simplificado para a quantificação da CMC de surfactantes no ensino da química

The discussion based on surfactant cleaning action is commonly used in chemistry classrooms for the comprehension of theoretical concepts related to surface tension and micelle formation. The experimental quantification of surface tension of aqueous solutions of surfactants provides the practical instruments for this discussion. The present paper describes a simplification on the common apparatus employed for the drop-weight method, making the determination of surface tension accessible to any chemistry lab. The surface tension of various liquids and the critical micelle concentration, CMC, of three commercial surfactants were measured with this modified method, and proved to be consistent with literature values.

Extração no ponto nuvem de compostos orgânicos homólogos e isômeros

In this work, the feasibility of employing micelle-mediated extraction for selective separation of homologous or isomeric organic compounds is demonstrated. Firstly, the main parameters controlling extraction performances, such as surfactant concentration and temperature were varied. A Scheffé-type experimental design was demonstrated as a novel and useful method to characterize the various experimental factors. At each point selected in the two-phase domain and for a given solute, extraction percentage (E%), concentration ratio, phase volume ratio, and equilibrium partition coefficient (K C) were determined. The values of E% and K C decrease in the following order: phenol > 1-phenylethanol ~ 2-phenylethanol > benzyl alcohol.