Cac Value Research Articles

Elucidating effect of dicarboxylate anions on nanostructural organization of dicationic imidazolium-based ionic liquids

This work reports the influence of the dicarboxylate anion (oxalate, malonate succinate, glutarate, adipate, pimelate) on the aggregation process of ionic liquids derived from 1,8-bis(3-methylimidazolium-1-yl)-octane [C8(MIM)2] and 1,10-bis(3-methylimidazolium-1-yl)-decano [C10(MIM)2] in water solution. The aggregation behavior was investigated using electrical conductivity, nuclear magnetic resonance, transmission electron microscopy, atomic force microscopy, and zeta potential. Results showed that the aggregates have a wormlike morphology. The CAC values for [C10(MIM)2]2+ increase in the following order: [Oxa] < [Suc] < [Mal] < [Glu] < [Adi] < [Pim], which indicates a direct relationship with the increase in the number of methylene groups of the dianion spacer. In the case of [C8(MIM)2]2+, there was no relationship between the CAC value and the anion’s alkyl spacer chain length, which was attributed to the flexibility and complexity of the dynamic behavior of the aggregates. Anions on the nanorganized structures of micelles are oriented in the way that carboxylate groups are at the aggregate surface (forming hydrogen bonds with cationic heads and water), and apolar alkyl chains are in the hydrophobic (downshift) region of the micelles making an arrangement where they also adopt the bend conformation of alkyl chains. The aggregation of dicationic ILs with dicarboxylate anions is a very innovative topic of investigation in the literature, and more research on different structures, system conditions, and techniques could be done to gain a better understanding of these systems.

Probing plausible role of anionic surfactants in inducing structural alternations in HEWL with Fe-containing metallo-catanionic aggregates

Through this report, we tend to provide insights into the role of anionic surfactant in aggregation and interactional behavior of Fe-containing metallo-catanionic aggregates. For this objective, two anionic surfactants sodium dodecyl surfactant (SDS) and sodium oleate (SO) were selected and their metallo-catanionic aggregates were synthesized with cationic metallosurfactant FeCTAC II in different molar ratios. Firstly, the effect of anionic surfactant on the aggregation behavior of metallo-catanionic surfactants was explored, where SDS containing aggregates were found to aggregate at a lower CAC value. The morphology on the other hand, was not affected with different anionic surfactant. The interactions of different aggregates have been explored with HEWL and with CD spectroscopic results it was confirmed that SO-containing aggregates behaved differently towards the secondary structure of HEWL. However, with 1° and 3° structure of protein, both types of aggregates behaved in an almost identical manner. The mode of interactions of aggregates with HEWL was further confirmed by experiments performed with ANS, pyrene, congo red, and thioflavin T. The role of anionic surfactant in the activity of HEWL was also studied with micrococcus lysodeikticus cell suspensions and at room temperature, higher activity was observed with SDS containing aggregates.

Noncovalent Association and Partitioning of Some Perfume Components at Infinite Dilution with Myelin Basic Protein Pseudophase in Normal Saline

Myelin basic protein (MBP), one of the major protein constituents of the myelin sheath, possesses unique ligand-binding features. We present a novel equilibrium headspace gas chromatographic technique to examine the thermodynamics of noncovalent interactions between common perfume components: Lilial, Hedione, Hexylcinnamic aldehyde, and Versalide with MBP monomers and its hexameric MBP-pseudophase. A general theoretical model is used to calculate the critical aggregation concentration (cac) of MBP, perfume component binding constants with monomeric MBP, K11, and MBP as pseudophase, Kn1, and free energies for perfume component binding with monomeric MBP, ΔGb,11, and MBP as pseudophase, ΔGb,n1. In addition, the pseudophase-water partition coefficients, Kx, the free energies of transfer of perfume from bulk water to the MBP-pseudophase, ΔGt, and the intra-aggregate activity coefficients, γm∞, at infinite dilution were also determined. The cac value measured by the method of fractional distribution is a unique and precise approach in understanding the aggregation phenomenon. Within the experimental error, the 1:1 binding free energies did not differ by more than 1 kJ/mol among the perfume components but favored the MBP pseudophase binding by 6 kJ/mol. Therefore, that protein aggregation can enhance the binding of small molecules is probably a general conclusion. While the magnitudes of K11, Kn1, ΔGb, Kx, and ΔGt show weak trends, the γm∞ values show a strong and distinct trend in interaction, spanning 4 orders of magnitude among the perfume components.

Self-assembly of cyclodextrin complexes: detection, obstacles and benefits.

Cyclodextrins (CDs) are cyclic oligosaccharides that form water-soluble inclusion complexes of lipophilic molecules. They are commonly used as pharmaceutical excipients. Recently it has been observed that CDs and CD complexes self-assemble in aqueous solutions to form transient clusters, nanoparticles and small microparticles. The critical aggregation concentration (cac) of the natural αCD, βCD and γCD in pure aqueous solutions is about 25, 8 and 9 mg/ml, respectively. The cac of 2-hydroxypropyl-β-cyclodextrin (HPβCD), that consists of a mixture of isomers, in pure aqueous solutions is significantly higher or about 118 mg/ml. Formation of guest/ CD complexes can increase or decrease the cac value. Due to the transient nature of the CD clusters and nanoparticles they can be difficult to detect and their presence is frequently ignored. However, formation of such particulate matter in aqueous CD solutions can lead to erroneous analytical results and product rejections during drug manufacturing. On the other hand, they have also given rise to formation of novel drug delivery systems with exceptional properties.

Breakup versus coalescence of closely packed fluid drops in simple shear flows

Using computational fluid dynamic (CFD) simulations, based on an improved conservative level set method we investigated the dynamics of mechanically interacting fluid drops in closely packed drop systems under simple shear flow. Our 2D simulations show drop concentration (ψ) as a key factor, in addition to capillary number (Ca) in controlling the two competing processes: breakup and coalescence. For a given ψ, the breakup process governs the drop dynamics when Ca exceeds a critical value (Cac); this is replaced by the coalescence process as Ca < Cac. The Cac value is found to increase non-linearly with ψ. We observed varying modes of breakup as a function of ψ for different Ca values. Low concentrations (ψ ∼ 0) give rise to drop breakup by mid-point pinching, forming smaller daughter drops of nearly equal size. Increasing ψ transforms this breakup mode into another mode characterized by asymmetric capillary instability at the drop edges. On the other hand, high Ca promotes the capillary instability to develop uniformly in strongly flattened drops, resulting in their homogeneous breakup. We demonstrate that these three modes: mid-point pinching, edge breakup and homogeneous breakup yield characteristic drop size distributions (DSDs). Our multiple drop models provide a concentration limit (ψ < 0.4) for the breakup process; this is taken over by coalescence drop dynamics as ψ exceeds this limit. It is shown that two contrasting mechanisms: tension-driven interfacial burst and compression-driven interfacial wave instability operate in the coalescence processes under low (Ca < 0.2) and high (Ca > 0.2) capillary numbers, respectively under high concentrations (ψ > 0.4). The first coalescence mechanism develops a single bridge between two adjoining drops, which grows in diameter non-linearly with time. We predict distinctive non-linear relations for collision and pull-apart drop configurations. We finally synthesize the breakup and coalescence mechanisms in a ψ – Ca space.

Self-assembly of the mixed systems based on cationic surfactants and different types of polyanions: The influence of structural and concentration factors

Mixed systems based on cationic surfactants with a cyclic head group (morpholinium bromide (Mor-16) and triphenylphosphonium bromide (TPPB-16)) and pH-dependent polyanions with different natures (polyacrylic acid (PAA) and bovine serum albumin (BSA)) were formed. The critical aggregation concentration, sizes, zeta-potential, solubilization capacity, aggregation number of the mixed systems were determined by the complex of modern, complementary physicochemical methods. It has been shown that the nature of the polyanions and the head group of surfactant play important role in the formation of complexes. By several methods it has been shown that the addition of PAA to Mor-16 solution leads to a significant decrease in the CAC compared to single surfactant by one to two orders of magnitude, while the addition of fixed amount of BSA to Mor-16 system does not affect the aggregation threshold. For mixed PAA-TPPB-16 system only slight changes in CAC value compared to CMC of single TPPB-16 system were revealed by different techniques. The particle size in the mixed BSA-surfactant systems is about 10 nm, while in PAA-surfactant systems the size is determined by the nature of the surfactant head group. By the synchronous fluorescence method it has been shown that the interaction of BSA with surfactant occurred through the tryptophan residues of BSA. The presence of aromatic ring in the surfactant structure can be a key factor in increasing the binding efficiency in the surfactant-BSA systems.

Mixed surfactant (altering chain length and head group) aggregates as an effective carrier for tuberculosis drug

Surface properties and aggregation behavior of cationic-cationic and cationic-non-ionic mixed surfactant systems viz. Dodecylethyldimethylammonium bromide (DDAB) with a series of double chain cationic surfactants (DiDDAB, DMDTAB, and DODAB) and non-ionic surfactants (Brij 96, Tyloxapol and Tween 80) were analysed using surface tension and transmission electron microscopy (TEM). The effect of chain length of cationic surfactant and hydrophilic-lypophilic balance (HLB) prominently observed in critical aggregation (cac) value. The aqueous solubility of anti-tuberculosis drug: rifampicin (RIF) was comparatively studied by UV–vis spectroscopy in presence of formulated micelles and vesicles. RIF was significantly solubilised in aqueous medium using all the formulated aggregates. RIF is very unstable in basic medium (above pH-7) and in oxidizing media. Therefore, stability at pH-13 as well as in strong oxidising environment was monitored using UV–vis spectroscopy. To trace the locus of the drug encapsulation in the micelles/vesicles, fluorescence spectroscopy and TEM studies were carried out. Both the techniques stemmed in complimentary results and confirmed that, RIF is majorly populated at polar medium in cationic-cationic vesicles and favour to reside at hydrophobic medium of the nonionic-cationic micelles.

The self-assemble of natural cyclodextrins in aqueous solutions: Application of miniature permeation studies for critical aggregation concentration (cac) determinations

Permeation techniques can be applied to determine the critical aggregation concentration (cac) of natural cyclodextrins (CDs) in aqueous solutions although the method is both laborious and time consuming. In the present study, the permeation technique was modified and the influence of osmotic pressure, sampling time, CD concentration and molecular weight-cut off (MWCO) of the membrane were investigated in two different permeation units, that is Franz diffusion cells and Slide-A-Lyzer™ MINI Dialysis. While both the osmotic pressure and CD concentration affect the steady state flux in both permeation units, effects of sampling time and the MWCO of the mounted membrane were only observed in the Franz diffusion cells. The osmotic effect was negligible in the Slide-A-Lyzer™ MINI Dialysis units. The modified permeation technique using Slide-A-Lyzer™ MINI Dialysis units was then used to determine the cac of natural CDs in water. The cac of αCD, βCD and γCD was 1.19±0.17, 0.69±0.05 and 0.93±0.04% (w/v), respectively. The results indicated that the cac values depended on their intrinsic solubility. Moreover, the cac value of γCD in aqueous hydrocortisone/γCD inclusion complex solution was identical to the γCD cac value determined in pure water.

Interaction of cationic dodecyl-trimethyl-ammonium bromide with oxy-HbGp by isothermal titration and differential scanning calorimetric studies: Effect of proximity of isoelectric point.

In this work, isothermal titration and differential scanning calorimetric methods, in combination with pyrene fluorescence emission and dynamic light scattering have been used to investigate the interaction of dodecyltrimethylammonium bromide (DTAB) with the giant extracellular Glossoscolex paulistus hemoglobin (HbGp) in the oxy-form, at pH values around the isoelectric point (pI ≈ 5.5). Our ITC results have shown that the interaction of DTAB with the hemoglobin is more intense at pH 7.0, with a smaller cac (critical aggregation concentration) value. The increase of protein concentration does not influence the cac value of the interaction, at both pH values. Therefore, the beginning of the DTAB-oxy-HbGp premicellar aggregates formation, in the cac region, is not affected by the increase of protein concentration. HSDSC studies show higher Tm values at pH 5.0, in the absence and presence of DTAB, when compared with pH 7.0. Furthermore, at pH 7.0, an aggregation process is observed with DTAB in the range from 0.75 to 1.5 mmol/L, noticed by the exothermic peak, and similar to that observed for pure oxy-HbGp, at pH 5.0, and in the presence of DTAB. DLS melting curves show a decrease on the hemoglobin thermal stability for the oxy-HbGp-DTAB mixtures and formation of larger aggregates, at pH 7.0. Our present data, together with previous results, support the observation that the protein structural changes, at pH 7.0, occur at smaller DTAB concentrations, as compared with pH 5.0, due to the acidic pI of protein that favors the oxy-HbGp-cationic surfactant interaction at neutral pH.

Effect of salt and urea on complexation behavior of pharmaceutical excipient gelatin with phenothiazine drug promazine hydrochloride

An evaluation of the interactions of cationic phenothiazine drug promazine hydrochloride (PMZ) with gelatin in aqueous solution as well as in the presence of 50mM NaCl and 100mM urea, investigated through different physicochemical measurements is presented in the present study using conductometric method. PMZ is used for the control of mania and schizophrenia. The drug interacts with gelatin similar to the interaction of surfactants and polymers. The plots of specific conductivity versus concentration of the drug were nonlinear with three different linear regions with two clear breaks. The first break point, i.e., critical aggregation concentration (cac), appeared well below the typical critical micelle concentration (cmc). The second break point is considered as polymer saturation point (psp) that is akin to cmc. The cac value decreases on increasing the gelatin concentration, whereas the psp value increases for all fixed concentrations (%w/v) of gelatin which is a clear signal of the interaction of the drug with gelatin. As inorganic salts increase the ionic strength, the solubility of amphiphile (drug) is lowered by ionic screening effects, ensuing in a greater tendency to aggregates at lower concentration. As a result, both the cac and psp/cmc values decrease. By the addition of urea an increase in the surface charge of the micelles was observed followed by halt of the aggregation of the drug hence both the cac and psp/cmc values increase. Free energies of aggregation (ΔGagg), micellization (ΔGmic), polymer saturation (∆Gpsp) and transfer (ΔGt) were also evaluated.

Optimization of copper electrowinning from synthetic copper sulfate solution using a pulsed bed electrode

This paper concludes a series of investigations concerning the use of pulsed bed electrodes (PBEs) for copper electrowinning. In previous papers, the main operational parameters affecting the current efficiency (CE), space–time yield (Y), and energy consumption (EC) were identified and their effects on the performance of the process were analyzed. In light of the results, the fluidized bed time was set at 2s and it was found that the electrode thickness should be reduced in order to achieve values of CE and EC lower than those obtained in conventional industrial processes using flat plate electrodes. In this work, the electrode thickness was reduced from 3.4 to 2.4cm and the process was optimized using factorial experimental design and the Derringer desirability method to obtain current density (i), acid concentration (Cac), and pulsed bed time (tp) values that maximized CE and Y and minimized EC. The best Cac value was 100mgL−1 (a low level), while the optimum i and tp values were 2600Am−2 and 60s, respectively (high levels). Use of these values avoided short circuit and minimized copper dissolution during fluidization. The overpotential distribution within the porous cathode was improved using the 2.4cm electrode, and values of 100% (CE), 102kgm−3h−1 (Y), and 1.7kWhkg−1 (EC) were achieved under the optimized conditions. These values are better than those found for flat plate electrodes.

Complexation behavior of mixed monolayer/mixed micelle formation between cationic noble surfactant-nonionic conventional surfactant in the presence of biocompatible polymer

Herein, we are reporting the interaction of biocompatible polymer polyvinylpyrrolidone (PVP), with gemini, pentamethylene-1,5-bis(hexadecyldimethylammonium bromide) (G5) and TX-114 surfactant mixture. Various thermodynamic parameters are evaluated with the help of regular solution theory (RST) and pseudo-phase separation model. By the addition of PVP, the critical aggregation concentration (cac) value of G5 as well as mixture decreases. A decrease in the cac value mainly credited to the interactions between the polymer and surfactant. The partial negative charged oxygen atoms, present in the amide group of PVP, were believed to be responsible for interaction with cationic head group of gemini surfactant.

A study of interaction between antidepressant drug nortriptyline hydrochloride with gelatin

The effect of gelatin on the micellization behavior of amphiphilic drug nortriptyline hydrochloride (NOT) in aqueous as well as aqueous urea (250mM) solutions has been studied using conductimetric technique. NOT is indicated for the relief of symptoms of depression. It is a tricyclic antidepressant drug. The drug interacts with gelatin similar to the interaction of surfactants and polymers. The plots of specific conductivity versus concentration of drug were nonlinear with three different linear regions with two clear breaks. The first break point, i.e., critical aggregation concentration (cac), appeared well below the typical critical micelle concentration (cmc). The second break point is considered as polymer saturation point (psp) that is similar to cmc. The cac value decreases on increasing the gelatin concentration, whereas psp value increases for all fixed concentrations (%, w/v) of gelatin which is a clear signal of the interaction of the drug with gelatin. Free energies of aggregation (ΔGagg) and micellization (ΔGmic) were also evaluated. In the presence of urea the increase in the surface charge of the micelles was observed followed by halt of the aggregation. Effect of NOT (drug) on the secondary structure of gelatin in aqueous solutions was also examined using CD measurements. The measurements verified that the random coil content of gelatin increases with increasing the NOT concentration.

PEG-Stabilized Micellar System with Positively Charged Polyester Core for Fast pH-Responsive Drug Release

To design functional drug carriers for fast pH-responsive drug release. Functional diblock terpolymers of monomethoxy poly(ethylene glycol)-block- copoly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione-co-ε-caprolactone) [mPEG-b-poly(ADMC-co-CL)] were fabricated via biosynthetic pathway. The self-assembled nanosphere and drug-loaded micelles of the copolymers were further prepared by dialysis method. The pH-tunable morphology variation and drug release pattern were observed at different pH. A collection of three PEGylated terpolymers with varied compositions in poly(ADMC-co-CL) block was designed with high cell-biocompatibility. The copolymers could readily self-assemble into nanoscale micelles (~ 100 nm) in aqueous medium and exhibit high stability over 80-h incubation in different mediums including deionized water, neutral NaCl solution, and heparin sodium solution. Due to the protonation-deprotonation of tertiary amine groups in ADMC units, acid-induced structural deformation of micelles was disclosed in terms of the variation in CAC value and hydrodynamic size at different pH. Drug loading efficiency was comparable to that of reported PEG-polyester micelles with specifically designed structures purposed for drug-loading improvement. Remarkably accelerated drug release triggered by acidity was distinctly detected for ibuprofen-loaded mPEG-b-poly(ADMC-co-CL) micelle system, suggesting a fast pH-responsive characteristic. Functional PEG-stabilized micellar carriers with positively charged polyester core were successfully developed for fast pH-responsive drug release.

The use of a kinetic process as sensor to determine DNA conformation changes in solution

The study of the processes [Ru(NH 3) 5pz] 2+ + S 2 O 8 2 - and [Fe(bpy) 3] 2+ + S 2 O 8 2 - (pz = pyrazine, bpy = 2,2′-bipyridine) was carried out in the presence of calf thymus DNA and hexadecyltrimethylammonium bromide (CTAB) as surfactant at different concentrations of polymer and surfactant. Results show a different kinetic behaviour depending on the molar relation [surfactant]/[DNA], that is, on the conformation of the polynucleotide. The conclusion obtained was that the cac value, that is, the surfactant concentration necessary to produce condensation of the DNA, can be estimated from kinetic data. In the authors’ opinion, it is the first time that this type of study has been used to determine the conformation change of a polymer.

Synthesis and physico-chemical characterization of bolaamphiphiles derived from alkenyl d-xylosides

The two step synthesis of a new series of bolaamphiphiles derived from alkenyl D-xylosides is described. Yields between 57 and 90% have been reached. Aggregation behavior and membrane interaction properties of a particular sugar-bolaform composed of two xylose heads connected by an ether link to a hydrophobic chain comprising 18 carbon atoms and an insaturation were studied. Its CAC value (∼0.05 mM) is low compared to those of conventional surfactants. Thermodynamic analysis has revealed that the aggregation phenomenon is mainly driven by an entropy process. The compound is able to interact with DPPC monolayers, in particular if their surface pressure is ≥15 mN m−1. Our results highlight the potential of this bolaamphiphile as surfactant and membrane interacting agent.

Preparation and properties of new micellar drug carriers based on hydrophobically modified amylopectin

Hydrophilic amylopectin was modified by grafting hydrophobic poly (lactic acid) chains. The 13C NMR and X-ray diffraction (XRD) analyses confirmed the modification reaction. For the resultant amphiphilic derivatives with various grafting yields, their self-association behavior and micellar aggregates were investigated by fluorometry, transmission electron microscopy and dynamic light scattering. The critical aggregation concentration (cac) was found to be in the range from 0.038 to 0.190 mg/L and the mean diameter (MD) was observed to be in the range from 20.7 to 77.2 nm in aqueous solutions at 25 °C. With the increase of the grafting yield, the cac value decreased while the MD value increased. For the resultant micellar aggregates, their drug loading and in vitro drug release characteristics were studied using indomethacin as the model drug. It was found that such micellar aggregates could be used as potential nanocarriers for drug delivery.

Multislice Computed Tomography in the Exclusion of Coronary Artery Disease in Patients With Presurgical Valve Disease

Background— Multislice computed tomography (MSCT) has shown high negative predictive value in ruling out obstructive coronary artery disease. Preliminary studies in patients with valvular heart disease (VHD) have demonstrated the potential of MSCT angiography (CTA) in such patients, precluding need for invasive angiography (XA). However, larger prospectively designed studies, including patients with atrial fibrillation and incorporating dose reduction algorithms, are needed. Methods and Results— To evaluate the clinical utility of 64-slice CT in the preoperative assessment in patients with VHD, we prospectively studied 452 consecutive patients undergoing routine cardiac catheterization for eligibility. Two hundred thirty-seven patients underwent both MSCT and XA. Segment-based, vessel-based, and patient-based agreement between CTA and XA was estimated assuming that “nonevaluable” segments were positive for significant coronary stenosis. In a patient-based analysis, sensitivity, specificity, positive predictive value, and negative predictive values of CTA were 95%, 89%, 66%, and 99%, respectively; in vessel-based analysis, 90%, 92%, 48%, and 99%, respectively; and in segment-based analysis, 89%, 97%, 38%, and 100%, respectively. No significant differences were found between patients with or without atrial fibrillation. A CAC value of 390 was the best cutoff for the identification of patients with positive or inconclusive CTA (which would not be exempted from XA in the clinical setting). Conclusions— In the preoperative assessment of patients with predominant VHD, the diagnostic accuracy of 64-slice CTA for ruling out the presence of significant coronary artery disease is very good even when including patients with irregular heart rhythm. Using this approach, CAC quantification before CTA can be successfully used to identify patients who should be referred directly to XA, sparing unnecessary exposure to radiation.

Aggregation behavior of novel hyaluronan derivatives—a fluorescence probe study

Aggregation properties of hydrophobized hyaluronan with different molecular weights and degrees of substitution were studied using pyrene and perylene as fluorescence probes. Both probes in contrast to native biopolymer confirmed aggregation of modified hyaluronan. The critical aggregation concentration (cac) was determined by the pyrene I1/I3 and perylene fluorescence intensity method. The cac value varied both with the molecular weight and the degree of substitution and was between 0.610 and 0.003 g·L−1. Pyrene polarity scale confirmed formation of hydrophobic domains.

Effect of Hydrogen Bonding on the Physicochemical Properties and Bilayer Self-Assembly Formation ofN-(2-Hydroxydodecyl)-l-alanine in Aqueous Solution

The aggregation behavior of N-(2-hydroxydodecyl)-L-alanine (C12HAla) and N-(n-dodecyl)-L-alanine (C12Ala) was studied in aqueous buffer (pH 12) over a concentration range above their critical aggregation concentration (cac). The C12HAla amphiphile has two cacs in contrast to only one cac value for C12Ala. The micropolarity and microviscosity of the aggregates were studied by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene, respectively, as fluorescent probes. Dynamic light scattering was used to measure the average hydrodynamic diameter and size distribution of the aggregates. Large size, high microviscosity, and low micropolarity values of the aggregates suggested the formation of bilayer structures in dilute solutions of C12HAla. In contrast, C12Ala was observed to form micelles. Transmission electron micrographs of dilute and moderately concentrated solutions of C12HAla revealed the existence of spherical vesicles and branching tubular structures, respectively. Comparison of the aggregation behavior of these amphiphiles to that of C12Ala and the FT-IR spectrum suggested that intermolecular hydrogen-bonding interactions between adjacent hydrocarbon chains through the -OH and -NH- groups of C12HAla are responsible for bilayer formation. The mechanism of nanotube formation was discussed. The temperature dependence of aggregate formation of the amphiphile also was investigated.