Critical Concentration Of Micelle Formation Research Articles

Mechanism of stearic acid adsorption to calcite

Abstract This paper presents the interpretation of binding mechanism of stearic acid for calcite surface in two modification methods. In the “dry” method, a surface dissociation of stearic acid is assumed where H + ion goes to a surface carbonate ion and stearic ion is chemisorbed on primary surface center of − Ca + ion which is only available for chemisorption. The structure of adsorbed layer indicates chemisorption of stearate, but due to steric effects, and the oblique or gauche conformation of hydrocarbon chains. A part of surface − Ca + centers can be blocked, which is explained by the result that physical adsorption dominates over 1.5%. In the “wet” method, by adding stearic acid, at concentration above the critical concentration of micelle formation in base solution, micelles are formed, and on the other side free stearic acid molecules or molecules from developed micelle dissociate. The resulting stearic ions can be chemisorbed on primary centers of − Ca + ions or participate in ion exchange with OH − ions from secondary surface centers. With increasing adsorption density, the adsorbed ions and molecules, due to interactions of hydrocarbon chains, and thickness of double electrical layer, achieve a vertical orientation and keep the trans-conformation of hydrocarbon chains.

Supramolecular system 4-aza-1-hexadecyl-1-azoniabicyclo[2.2.2]octane bromide—sodium salicylate. Aggregation and rheological properties

The system based on the cationic surfactant 4-aza-1-hexadecyl-1-azoniabicyclo[2.2.2]-octane bromide (DABCO-16) and the organic electrolyte sodium salicylate was studied by tensiometry, conductometry, pH-metry, dynamic and electrophoretic light scattering, and viscosimetry. The critical concentration of micelle formation of DABCO-16 and the electrokinetic potential decrease sharply and the hydrodynamic diameter of the aggregates increases as the concentration of sodium salicylate increases. The rheological properties of the studied solutions are well described by the Maxwell model for a viscoelastic liquid with one relaxation time. Aqueous solutions DABCO-16—sodium salicylate exhibit the properties of an elastic gel and can be used for the formation of compositions with the improved rheological properties.

The use of cationogenic SAS in pressure-driven processes of purification of water contaminated with Cr (VI) salts

The article has investigated the impact of cationogenic SAS on purification of contaminated waters of Cr (VI) by the methods of ultra and nanofiltration. We have determined the impact on these processes of the pH of the medium working pressure, and concentration of SAS concentration. The most effective results of water purification of Cr (VI) were obtained at pH 5 and SAS concentration close to its critical concentration of micelle formation.

Pluronic Block Copolymers Inhibit Low Density Lipoprotein Self‐Association

Little is known about exogenous inhibitors of low-density lipoprotein (LDL) aggregation. The search for nontoxic and bioavailable inhibitors of LDL aggregation is of interest, especially considering that the suppression of the aggregation of LDL might represent a therapeutic approach. We hypothesized that amphiphilic copolymers of propylene oxide and ethylene oxide, the so-called Pluronic block copolymers, can be used to influence the aggregation of LDL. In this work we used Pluronic® P85, L61 and F68. A comparative study of the effects of Pluronic block copolymers with various hydrophilic-lipophilic properties on the aggregation process of LDL showed that Pluronic copolymers with strong hydrophobic properties (P85 and L61) at concentrations close to or greater than the respective critical concentration of micelle formation inhibited the aggregation process of LDL; however, the "hydrophilic" Pluronic F68 had no effect on the aggregation of LDL at any concentration. Thus, the study demonstrated for the first time that Pluronic® block copolymers inhibit LDL self-association. The possibility of modulating the aggregation of LDL by various Pluronic copolymers can be regarded as a prerequisite in the creation of new types of anti-atherosclerotic drugs.

Magnesium octa(benzo-15-crown-5)phthalocyaninate in the sodium dodecyl sulfate solutions: A study using electron and 1H NMR spectroscopy

The behavior of magnesium octa(benzo-15-crown-5)phthalocyaninate in water medium in the presence of sodium dodecyl sulfate was studied using both electronic and 1H NMR spectroscopy, including the method of two-dimensional 1H-1H correlation NOESY. In the microheterogeneous environment of the CH3(CH2)11OSO3Na solutions at the concentrations of the latter close to the CMC the phthalocyanine is in monomeric form, while at the concentration less than the critical micelle-formation concentration it becomes a dimer or even more aggregated. The results of the NMR spectroscopic investigation indicate that magnesium octa(benzo-15-crown-5)phthalocyaninate preferrably binds to the CH3(CH2)11OSO3Na micelle in the hydrophobic region of the latter.

Influence of the strong electrolyte on the aggregation behavior and catalytic properties of dicationic surfactants

The introduction of potassium chloride into an aqueous solution of dicationic (gemini) surfactants results in the partial neutralization of the surface charge of micelles, which is accompanied by an increase in their size, a decrease in the critical concentration of micelle formation, a decrease in the surface potential of the system, and a change in the micellar influence on the hydrolytic stability of solubilized carboxylic esters.

Optical tweezers based active microrheology of sodium polystyrene sulfonate (NaPSS)

We used oscillatory optical tweezers to investigate the microrheological properties of Sodium polystyrene sulfonate (NaPSS; Mw = 70 kDa) polymer solutions with different concentrations from 0.001 mM to 10 mM in terms of elastic modulus G'(ω) and loss modulus G"(ω) as a function of angular frequency (ω) in the range of 6 rad/s to 6000 rad/s. The viscoelastic properties (including zero-shear-rate viscosity, crossing frequency and transition frequency) as a function of polymer concentration, deduced from our primary data, reveal the subtle structural changes in the polymer solutions as the polymer concentration increases from dilute to semi-dilute regimes, passing through the critical micelle formation concentration and the polymer overlapping concentration. The experimental results are consistent with the Maxwell model in some regime, and with the Rouse model in other, indicating the transient network character and the micelles formation in different regimes.

Synthesis, self‐assembly, fluorescence, and thermosensitive properties of star‐shaped amphiphilic copolymers with porphyrin core

AbstractStar‐shaped amphiphilic poly(ε‐caprolactone)‐block‐poly(oligo(ethylene glycol) methyl ether methacrylate) with porphyrin core (SPPCL‐b‐POEGMA) was synthesized by combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Star‐shaped PCL with porphyrin core (SPPCL) was prepared by bulk polymerization of ε‐caprolactone (CL) with tetrahydroxyethyl‐terminated porphyrin initiator and tin 2‐ethylexanote (Sn(Oct)2) catalyst. SPPCL was converted into SPPCLBr macroinitiator with 2‐bromoisobutyryl bromide. Star‐shaped SPPCL‐b‐POEGMA was obtained via ATRP of oligo(ethylene glycol) methyl ether methacrylate (OEGMA). SPPCL‐b‐POEGMA can easily self‐assemble into micelles in aqueous solution via dialysis method. The formation of micellar aggregates were confirmed by critical micelle formation concentration, dynamic light scattering, and transmission electron microscopy. The micelles also exhibit property of temperature‐induced drug release and the lower critical solution temperature (LCST) was 60.6 °C. Furthermore, SPPCL‐b‐POEGMA micelles can reversibly swell and shrink in response to external temperature. In addition, SPPCL‐b‐POEGMA can present obvious fluorescence. Finally, the controlled drug release of copolymer micelles can be achieved by the change of temperatures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

The influence of micelle forming process in nonionic surface active substances on diclofenak-sodium release rate from ointments

The influence of the nonionic surface active substances (long-chain fatty alcohols) on the medicinal substances release rate has been studied on the pattern diclofenak-sodium ointments (1%). The increase of the surfactant quantity in the ointment has not been found to lead a direct increase of the diclofenak-sodium release rate. Two surfactant concentrations have been determined provoking the maximum diclofenak-sodium release rate they from the ointment. Liquid crystalline phase has been shown to form when surfactant concentration exceeded the second critical micelleformation concentration, diffusion through the phase being the lowest one.

EPR Spin Probe Study of New Micellar Systems

Molecular dynamics, structure, and phase state of two new micellar systems were investigated using spin-probe electron paramagnetic resonance spectroscopy. While the local mobility of the new cationic long-chain detergents varies in micelles in a minor way when the length of a chain increases from 16 to 22 carbon atoms, the order parameter increases noticeably. The latter is caused by gain of hydrophobic interactions. It is worthwhile to note that the incorporation of the two hydroxyl groups into the polar head group of the C22 detergent influences particularly on the molecular dynamics and phase state of an aqueous solution of the detergent. Furthermore, not only the local mobility decreases and ordering factor increases, but also the phase state of the system changes, being transited from the solid to the micellar (liquid) state. Addition of the KCl salt in an aqueous solution of the long-chain detergents results in a decrease of local mobility and increase of ordering factor. The phase transitions are found to be caused by the addition of the salt. The cationic monomer [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate was shown to decrease the critical concentration of micelle formation of the anionic detergent sodium dodecyl sulfate (SDS). Most likely this is because, being the counterion, the cationic monomer forms a dense layer around the SDS micelle. Binding of SDS micelle with the monomer strongly reduces the local mobility of the detergent.

Preparation and characterization of thermosensitive and biodegradable PNDH- g-PLLA nanoparticles for drug delivery

A series of thermosensitive and biodegradable graft copolymers (PNDH- g-PLLA) were synthesized by the radical copolymerization of N-isopropylacrylamide, N,N-dimethylacrylamide and N-(hydroxymethyl)acrylamide, followed by the ring-opening polymerization of L-lactide. The molecular weight and chemical structure of these copolymers were determined by gel permeation chromatography (GPC), nuclear magnetic resonance ( 1H NMR) and Fourier transform infrared spectra (FT-IR). The resulting copolymers were temperature-sensitive and the lower critical solution temperature (LCST) was affected by their compositions. The graft copolymers obtained in this study exhibited low critical micelle formation concentration (CMC) values that were affected by the content of PLLA. Spherical nanoparticles with degradable cores were prepared from aqueous solutions of the amphiphilic graft polymers by a dialysis method. Dynamic light scattering (DLS) results indicated that the particle size increased with increase of PLLA content in the copolymer. The morphologies of prepared nanoparticles were observed by transmission electron microscopy (TEM). The prepared PNDH- g-PLLA nanoparticles with thermosensitive and biodegradable properties may have practical application in drug delivery and controlled drug release.

Supramolecular catalytic systems based on anionic amphiphiles and polyethyleneimine for hydrolytic cleavage of phosphorus ester bonds

Self-organization in individual and binary systems based on polyethyleneimine (PEI) and amphiphilic sulfonatocalix[4]resorcinarene was studied by conductometry, tensiometry, dynamic light scattering, and 1H NMR spectroscopy. The critical concentrations of micelle formation and aggregate sizes were determined. The enhancement of the catalytic effect on the hydrolysis of O-ethyl O-p-nitrophenyl chloromethylphosphonate was shown in the following series of the systems: PEI-water < PEI—calixarene-water < PEI—calixarene—LaIII—water.

Cleavage of RNA by an amphiphilic compound lacking traditional catalytic groups

Recently, in experiments with combinatorial libraries of amphiphilic compounds lacking groups, known as catalysts of transesterification reaction, we discovered novel RNA-cleaving compounds [N. Kovalev, E. Burakova, V. Silnikov, M. Zenkova, V. Vlassov, Bioorg. Chem. 34 (2006) 274–286]. In the present study, we investigate cleavage of RNA by the most active representative of these libraries, compound named Dp12. Sequence-specificity of RNA cleavage and influence of reaction conditions on cleavage rate suggested that Dp12 enormously accelerates spontaneous RNA cleavage. Light scattering experiments revealed that the RNA cleavage proceeds within multiplexes formed by assembles of RNA and Dp12 molecules, at Dp12 concentration far below critical concentration of micelle formation. Under these conditions, Dp12 is presented in the solution as individual molecules, but addition of RNA to this solution triggers formation of the multiplexes. The obtained data suggest a possible mechanism of RNA cleavage, which includes interaction of the compound with RNA sugar-phosphate backbone resulting in changing of ribose conformation. This leads to juxtaposition of the 2′-hydroxyl group and internucleotide phosphorus atom at a distance needed for the transesterification to occur.

Cholesteryl moiety terminated amphiphilic polymethacrylates containing nucleic acid bases for drug delivery

AbstractPoly[9‐(2‐methacryloyloxyethyl)adenine] and poly[1‐(2‐methacryloyloxyethyl)thymine] with one pendant cholesteryl moiety at the polymer end (PMEA‐Chol, PMET‐Chol) and with two pendant cholesteryl moieties at both polymer ends as terminal groups (PMEA‐2Chol, PMET‐2Chol) were prepared by radical polymerization of 9‐(2‐methacryloyl‐oxyethyl)adenine (MEA) and 1‐(2‐methacryloyloxyethyl)thymine (MET) initiated with 4,4′‐azobis[(3‐cholesteryl)‐ 4‐cyanopentanoate] in the presence of 2‐mercaptoethanol or thiocholesterol as chain transfer reagents, respectively. The copolymers [PNiPAAm‐co‐PMEA‐nChol (n = 1,2)] composed of N‐isopropylacrylamide (NiPAAm) and MEA were also prepared in a similar manner. The self‐organization of these polymers and copolymers was confirmed by a fluorescence measurement, and then their critical concentrations of micelle formation (CMC) were determined. The mixture of PMEA‐2Chol and cholesterol as a lipophilic drug model formed a lamella type of complex with an interplaner spacing of d = 35.3 Å. The hypochromism based on the formation of a 1 : 1 interaction of adenine and thymine moieties was found to appear in the mixed aqueous solution of PMEA‐Chol and PMET‐Chol. Complementary interactions were also confirmed in the system of PMET‐2Chol and adenosine as well as PMEA‐2Chol and uridine. Cis‐dichlorodiammine platinum(II) (CDDP) was bound to PNiPAAm‐co‐PMEA‐Chol through the adenine moiety by ligand substitution atoms of CDDP. The amount of CDDP loaded on the copolymer was found to be 0.143 g g−1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3064–3075, 2007

Supramolecular systems formed by calix[4]resorcinarenes and surfactants in chlorophorm

Capacity titration and 1H NOESY 2D NMR were applied to investigation of intermolecular interactions and aggregation of amphiphilic calix[4]resorcinarenes (CRA 1, 2) modified with 1,2,4-triazine (1) and oxazine (2) functions in chloroform in the presence of cationic (3) and non-ionic (4) surfactants (SAA). Critical concentrations of micelle formation (CMC) indicate that the ability of CRA 1, 2 to form supramolecular aggregates like micelles or hybrid micelles with SAA 3, 4 only weakly depends on the constitution of CRA functional groups. In the case of the hybrid micelles, when CMC are defined by the nature of surfactants 3 or 4, the methyl and methylene groups of the hydrophobic fragments (CRA 1, 2) were found to interact with the hydroxy groups of SAA 3 and ethylene oxide moieties of SAA 4.

Hydrophobic fragments and the inhibiting effect of the functional derivatives of perfluoropolyethers

Functional derivatives (FDs) of perfluoropolyethers are studied as corrosion inhibitors in (PFPE) greases based on the corresponding polyethers. A lyophylic fluororganic radical is shown to affect the most important adsorption and colloid-chemical factors that determine the effectiveness of the FDs as the corrosion inhibitors (the high protonation of OH-acids, susceptibility to micelle formation in an organic phase, surface activity, hydrophobicity, etc.) in a low-polar environment. Depending on its size, a lyophobic aliphatic radical affects the inhibiting effect of an FD by increasing the hydrophobicity, surface activity, and critical concentration of micelle formation in nonpolar environments, as well as by sterically hampering the adsorption of functional groups and blockading the metal surface defects.

Removal of Ni(II) ions from wastewater by micellar-enhanced ultrafiltration

The feasibility in the use of a sodium dodecyl sulfate anionic surfactant and nonionic monoalkylphenol polyetoxilate to purify contaminated waters of Ni(II) ions has been studied. Both the retention coefficients and the transmembrane fluxes have been determined at purification of the different systems containing Ni(II) ions, anionic, and nonionic surfactants. A choice has been made of the most effective ultrafiltration membrane for its following use in the micellar-enhanced ultrafiltration process. An optimum value of the operating pressure has been determined. As has been shown on an example of the Ni(II) ions, micellar-enhanced ultrafiltration may make use of purified wastewaters from heavy metal ions. The most effective application of this process to remove the heavy metal ions from wastewaters takes place when concentration of the surfactants (both ionic and nonionic ones) is equal to the critical concentration of micelle formation and/or it is lower than that.

Kinetics of Reactions of α,β-Unsaturated Surfactants with Secondary Amines in a Solution

The kinetics of reactions of acrylamide derivatives (acrylamidotrihydroxymethylmethane (TA), sodium 4-acrylamidobutanoate (AA3), sodium 6-acrylamidohexanoate (AA5), and sodium 11-acrylamido-undecanoate (AA10)) with piperidine and morpholine in water (for TA, also in DMF, DMSO, and formamide) is studied at 293 K. These compounds are weak surfactant monomers. The critical concentrations of micelle formation (CCM) for them are determined. The self-association of AA3, AA5, and AA10 producing micelles results in a decrease in their reactivity compared to the monomeric forms. The rates of the reactions of surfactant monomers (SM) with morpholine and piperidine are described by the second-order rate law w0 = k[SM]0[Amine]0. An empirical equation is derived that relates the CCM values to the rate constant for the reaction of a surfactant monomer with a secondary amine with charges on the β-carbon and oxygen atoms of the amide group of a surfactant monomer. The rates of the reactions of TA with piperidine and morpholine are determined by the electrophilicity (acidity) of the medium, which is favorable for the Michael reaction.

Association of diphilic chains near the solvent critical region

By means of computer simulation the association process of diphilic macromolecules with strongly attractive head units (stickers) in the vicinity of the critical point of the solvent is studied. The calculations were carried out by means of Monte Carlo simulation with the bond-fluctuation model of polymer modified by us to mimic the hexagonal packing of monomer units. It was found that the critical concentration of micelle formation and average aggregation number depend crucially not only on the attraction between stickers but on the quality and state of solvent. The average aggregation number can demonstrate nonmonotonic behavior with change in temperature.

Circular Dichroic Properties of Phosphatidylcholine Micelles

The circular dichroic (CD) properties of aqueous and methanolic solutions of a series of short-chain phosphatidylcholinesranging from 1,2-dipropionyl-sn-glycero-3-phosphocholine (diC3PC) to 1,2-dioctanoyl-sn-glycero-3-phosphocholine (diC8PC)have been studied. In methanol, the CD spectrum is characterized by a negative peak centered around 210 nm. The peak intensity decreased with increasing acyl chain length. In aqueous solution, not only did the CD spectra recorded at concentrations below the critical concentration for micelle formation (cmc) show a clear dependency on the acyl chain length, but they were also slightly different from the corresponding spectra recorded above the cmc. The latter findingat least qualitativelyconfirms earlier extensive NMR investigations [e.g., Roberts; et al. Biochemistry 1978, 17, 935; Hauser; et al. Biochemistry 1988, 27, 9166]. The experimentally determined cmc for diC6PC in water at 25 °C was 15 mM. The conformation of micellar lipids (above the cmc) was more “rigid”i.e., was characterized by a higher degree of conformational restrictions involving the glycerol backbonethan in the case of monomers (below the cmc). Furthermore, the CD measurements indicate that monomeric phosphatidylcholines start to become more rigid if longer than diC4PC. In addition, the dependency of the conformational rigidity on the acyl chain length correlates with published data on the chain length dependency of the rate constants for pancreatic phospholipase A2 [Berg; et al. Biochemistry 1997, 36, 14512].