Increasing the aqueous solubility of the anesthetic propofol through wormlike micelle formation

Propofol, a phenol derivative, is commonly employed as an intravenous anesthetic during clinical procedures, formulated as an oil/water emulsion due to its poor solubility in water. The stability limitations associated with emulsions have prompted research efforts towards developing aqueous formulations of propofol. In this work, we investigate the solubility enhancement of propofol in anionic and cationic surfactants. Our findings reveal that the solubility of propofol can increase significantly, up to 100-fold, depending on the nature of the micellar aggregate, as observed for alkylammonium halogenates CnTAB (for n = 12, 14 and 16), contrasting with the lower solubility with SDS. Interestingly, C14TAB and C16TAB demonstrate significantly higher solubility than C12TAB. This was attributed to the formation of wormlike micelles, in which the propofol molecules are positioned between the cationic heads of the surfactant molecules, changing the micellar curvature and the morphology of the aggregate. Therefore, the aromatic molecules in the micellar environment can be partitioned into the micellar cores and their palisades. Regarding C12TAB, the alkyl chain is too short to form wormlike micelles, thus, concentrating propofol molecules mainly into the micellar core, and consequently, leading to their aggregation. Solubility diagrams of propofol were constructed in conjunction with different surfactants. The systems exhibiting viscoelastic behavior, indicative of wormlike micelle formation, were further investigated using rheology. Additionally, the fluorescent properties of propofol enabled the examination of the anesthetic molecule within diverse micellar environments.

The effect of the molecular structure of hydroxypropyl methylcellulose on the states of water, wettability, and swelling properties of cryogels prepared with and without CaO2

Hydroxypropyl methylcellulose (HPMC) belongs to the cellulose ether family that has hydroxyl groups substituted by hydrophobic methyl groups (DS) and hydrophilic hydroxypropyl groups (MS). Herein, the interactions between water molecules and cryogels prepared with HPMC in the presence and absence of a linear nonionic surfactant, as well as CaO₂ microparticles, which react with water producing O₂, were systematically investigated by sorption experiments and Time-Domain Nuclear Magnetic Resonance. Regardless of the DS and MS, most water molecules presented transverse relaxation time t2 typical of intermediate water and a small population of more tightly bound water. HPMC cryogels with the highest DS of 1.9 presented the slowest swelling rate of 0.519 ± 0.053 g_water/(g.s) and the highest contact angle values 85.250^o ± 0.004^o, providing the best conditions for a slow reaction between CaO₂ and water. The presence of surfactant favored hydrophobic interactions that allowed the polar head of the surfactant to be exposed to the medium, resulting in a higher swelling rate and lower contact angle values. The HPMC with the highest MS presented the fastest swelling rate and the lowest contact angle. These findings are relevant for the formulations and reactions, where tuning the swelling kinetics is crucial for the final application.

Supramolecular Arrangement of Doxycycline with Sulfobutylether-β-Cyclodextrin: Impact on Nanostructuration with Chitosan, Drug Degradation and Antimicrobial Potency

Doxycycline (DX) is a well-established and broad-spectrum antimicrobial drug. However, DX has drawbacks, such as physicochemical instability in aqueous media and bacterial resistance. The inclusion of drugs in cyclodextrin complexes and their loading into nanocarriers can overcome these limitations. Thus, we studied the DX/sulfobutylether-β-CD (SBE-β-CD) inclusion complex for the first time and used it to reticulate chitosan. The resulting particles were evaluated by their physicochemical characteristics and antibacterial activity. DX/SBE-β-CD complexes were characterized by nuclear magnetic resonance, infrared spectroscopy, thermal analysis, X-ray diffraction, and scanning electron microscopy (SEM), whereas DX-loaded nanoparticles were characterized by dynamic light scattering, SEM, and drug content. The partial inclusion of the DX molecule in CD happened in a 1:1 proportion and brought increased stability to solid DX upon thermal degradation. Chitosan-complex nanoparticles measured approximately 200 nm, with a narrow polydispersity and particles with sufficient drug encapsulation for microbiological studies. Both formulations preserved the antimicrobial activity of DX against Staphylococcus aureus, whereas DX/SBE-β-CD inclusion complexes were also active against Klebsiella pneumoniae, indicating the potential use of these formulations as drug delivery systems to treat local infections.

Probing water mobility in confining channels of reverse wormlike micelles

Reverse wormlike micelles are a potential template for chemical reactions in confined environments. Here, we use time-domain NMR to demonstrate the solvent effect on the mobility of water molecules. The higher the cohesive energy of alkanes, the lower the water mobility, and the less viscous the solution.

Effects of hypertonic solutions on two species of human intestinal parasites during fecal examination

Aim: Ova and parasite examination by flotation requires hypertonic solutions, which can damage the egg and cyst membranes, leading to false negatives. The authors investigated the harmful effects of ZnSO₄ and C₁₂H₂₂O₁₁ solutions on the ova and parasite examination. Materials & methods: The authors processed samples using the Three Fecal Test technique. Aliquots were floated in different pH levels, temperatures and solution densities. Results: Densities above 1.12 g/ml led structures to collapse after 6-10 min. pH neutralization of the ZnSO₄ solution did not prevent the parasites from changing. Conclusion: All structures were altered when standard methods were performed. To delay collapse, the parasite floating under 5 °C is highly desirable.

Detection of intestinal parasites in human faecal samples using dissolved air flotation

OBJECTIVE

Ova and parasite (O&P) examination is recommended for the laboratory diagnosis of agents causing parasitic infections; however, this exam requires scientific and technological improvements to enhance its diagnostic validity. Dissolved air flotation (DAF) is an efficient technical principle separating suspended solids in a liquid medium. We aimed to develop and validate a new procedure for intestinal parasite detection with DAF.

METHODS

In this study, we collected samples from 500 volunteers, screened them by direct examination, and transferred the material to tubes using the Three Faecal Test (TF-Test) for triplicate DAF tests. We evaluated physical-chemical parameters and DAF prototype components through quantifying parasites recovered from floated and non-floated regions of the flotation column. The DAF operation protocol was validated with the gold standard results.

RESULTS

The 10% saturated volume proportion and cationic surfactant showed regularity and high parasite recovery (80%). Modifications of the needle device did not influence parasite recovery (p > 0.05). Sensitivity, specificity, accuracy and kappa agreement obtained with the DAF protocol were 91%, 100%, 93% and substantial (k = 0.64), respectively.

CONCLUSION

The DAF principle could be used to process faecal samples in routine laboratory exams, enabling intestinal parasite detection.

Understanding the Performance of Plant Protein Concentrates as Partial Meat Substitutes in Hybrid Meat Emulsions

Hybrid meat products are an excellent strategy to incorporate plant proteins into traditional meat formulations considering recent market trends focusing on the partial reduction in red meat content. In this work, we evaluated the effects of different concentrated plant proteins (soy, pea, fava bean, rice, and sunflower) in partially replacing meat in meat emulsion model systems. Soy, pea, and sunflower proteins showed great compatibility with the meat matrix, giving excellent emulsion stability and a cohesive protein network with good fat distribution. Otherwise, adding rice and fava bean proteins resulted in poor emulsion stability. Color parameters were affected by the intrinsic color of plant proteins and due to the reduction in myoglobin content. Both viscoelastic moduli, G′ and G″ decreased with the incorporation of plant proteins, especially for rice and fava bean. The temperature sweep showed that myosin denaturation was the dominant effect on the G′ increase. The water mobility was affected by plant proteins and the proportion between immobilized and intermyofibrillar water was quite different among treatments, especially those with fava bean and rice proteins. In vitro protein digestibility was lower for hybrid meat emulsion elaborated with rice protein. It is concluded that soy, pea, and mainly sunflower proteins have suitable compatibility with the meat matrix in emulsified products.

Wormlike micelles of CTAB with phenols and with the corresponding phenolate derivatives - When hydrophobicity and charge drive the coacervation

HYPOTHESIS

Hydrophobicity and the presence or absence of charge in phenol derivatives are relevant on the rheology and phase behavior when they are assembled with a cationic surfactant, forming wormlike micelles. The incorporation of phenols with a greater number of rings into the micellar palisade is entropically favored, but a solubilization limit or coacervation are two paths followed by the solutions, depending on the electrical nature of the aromatic co-solutes.

EXPERIMENTS

The investigations were carried out with systems formed by a fixed concentration of hexadecyltrimethylammonium bromide (CTAB) and increasing concentrations of neutral phenols (1-naphthol, 2-naphthol, 2,3-dihydroxynaphthalene and R and S-binol) and with their corresponding phenolate derivatives. The monophasic limits of the systems were established, as well as their linear and non-linear rheology. The structural investigation of the coacervates formed with the phenolates were done using SAXS and Cryo-TEM.

FINDINGS

The zero-shear viscosity of the solutions reaches maxima values close to the solubility limit of the aromatics, which depends on the numbers of rings and hydroxyl groups (position and number). However, when the correspondent ionized phenols were investigated, beyond the maxima values for the zero-shear viscosity, liquid-liquid biphasic systems are formed, in which the upper phase contains a coacervate, associated with branched wormlike micelles. However, when the ratio between phenolate and CTAB is around 3:1 the coacervate evolves to a lamellar structure.

Dissolved air flotation as potential new mechanism for intestinal parasite diagnosis in feces

The parasitological examination of feces is recommended for the laboratory diagnosis of intestinal parasites due to its practicality, low-cost, and moderate diagnostic sensitivity. Dissolved Air Flotation (DAF) is an efficient technical principle used in other areas to separate dispersed solids. This study sought the preliminary evaluation of a proof-of-concept prototype as a tool for detecting species of parasites by adjusting DAF. Two DAF prototype units were developed to evaluate microbubbles' generation amidst fecal suspension and parasites' capture. For this evaluation, samples were screened and processed by the TF-Test technique (Control) and simultaneously by DAF device. The dimensional and attachment characteristics in the formation of the microbubbles were evaluated, and the percentage of parasitic recovery in floated and not-floated regions compared by Student's t-test. The second prototype unit proved to be more efficient in forming microbubbles with diameters between 34 and 170µm. The flotation tests showed a recovery of 73.27%, 58.12%, 37.85%, and 91.89% for Ascaris lumbricoides, Hymenolepis diminuta, Giardia duodenalis, and Strongyloides stercoralis, respectively. This study confirmed the selective interaction between microbubbles and parasite eggs and larvae during the flotation process using the DAF principle for the first time through imaging.

Urea induces (unexpected) formation of lamellar gel-phase in low concentration of cationic surfactants

HYPOTHESIS

The unexpected formation of a lamellar structure with concomitant gelation in solutions containing high urea concentration (40 wt%) and relatively low amount of cationic surfactant (3 wt%), indicates that a hierarchically structured complex is formed by both molecules.

EXPERIMENTS

Gels formed by combination of aqueous solutions of urea and C₁₂TAB, C₁₄TAB or C₁₆TAB were prepared in different proportions and their structures at microscopic and mesoscopic levels were investigated using XRD and SAXS, respectively. The elastic and viscous moduli and yield stress of the samples were determined and correlated with the composition and structuration of the gels. The lamellar structure is reversibly thermically destroyed and this process was investigated using DSC.

FINDINGS

XRD revealed that, at microscopic scale, the gels are formed through crystallization of adducts containing surfactant molecules loaded into the cavities of honeycomb-like urea assemblies. Such crystalline phase arranges itself in lamellae with interplanar distance around ∼20-30 nm, which were observed by SAXS. This hierarchical structure is independent of the chain length of the cationic surfactants. The blocks of lamellae dispersed in the continuous phase form a three-dimensional rigid particulate network structure, giving the characteristic rheological behavior of a hydrogel. DSC revealed a reversible thermal transition at around 20-25 °C, beyond which the adducts and the lamellar phase are destroyed and micelles are formed. The characteristic transition temperature is independent of the chain length of the surfactant, and thus, it is not associated with their Krafft temperatures. The structures of the gels indicate that they resemble alpha-gels formed by fatty-alcohols and surfactants, although they self-assemble by different driving forces.

Using inulin-based emulsion gels as fat substitute in salt reduced Bologna sausage

BACKGROUND

A high-fiber emulsion gel (EG) containing inulin, soy protein isolate, and soybean oil was applied as animal fat replacer in reduced salt and fat Bologna sausage containing mechanically deboned chicken meat, pork meat, and pork back fat. Technological and microbiological properties were evaluated for 60 days at 4 °C.

RESULTS

A reduction of 11 to 34% and 35 to 45% of fat and sodium were obtained in reformulated products, respectively. An increase in fiber content and polyunsaturated fatty acid was noticed in the formulations with EG. The addition of EG in Bologna increased L* (lightness) values and reduced a* (redness/greenness) values comparing to control treatment. Microstructural properties of sausages exhibited a denser network with the presence of EG. Softer, more elastic, cohesive and resilient samples with a higher intensity of lipid oxidation (P < 0.05) were observed in EG added sausages. The nuclear magnetic resonance (NMR) data shows that the presence of EG recovers the matrix that has been weakened due to reduction of fat and salt. Sensory evaluation showed that the incorporation of the EGs resulted in acceptable scores.

CONCLUSION

These results suggest that inulin-based EG is a potential fat substitute for developing healthier meat products, with better fatty acids composition and stable to chilled storage. © 2020 Society of Chemical Industry.

Inulin gelled emulsion as a fat replacer and fiber carrier in healthier Bologna sausage

The effects of gelled emulsions (GE) used as animal fat replacers in terms of the nutritional, technological, and sensory properties of Bologna sausages during 60 days of chilled storage have been studied. Samples with GE added exhibited a fat reduction of 31%. Sausages with GE had higher values of L* and lower values of a* compared to the control. Harder sausages were obtained by the addition of GE. Higher lipid oxidation rates were found with increasing amounts of GE in the reformulated products. In addition, the relaxation time was not affected by the reformulation. All samples were deemed acceptable by consumer tests. However, CATA (Check-all-that-apply) tests showed that Bolognas formulated with partial or total pork fat replaced with GE were described as rubbery, not very spicy and firm, appeared to be dry and opaque, and had an aftertaste. Chilled storage significantly affected the Thiobarbituric Acid Reactive Substances (TBARS) values and slightly affected the pH values, texture, color, and NMR data. An important result is that the panelists did not detect the oxidation results in relation to the TBARS values, and the addition of a GE with inulin as dietary fiber may be a good strategy to make Bologna sausage healthier.

Light-Triggered Rheological Changes in a System of Cationic Wormlike Micelles Formulated with a Photoacid Generator

"Smart" fluids displaying large changes in their rheological properties in response to external stimuli have been of great interest in recent years. For example, "smart" wormlike micelles (WLMs) that respond to pH can be readily formulated by combining a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) with an aromatic compound such as 1,2-dihydroxybenzene (DHB). Here, we show that a pH-responsive aqueous formulation as mentioned above can be simultaneously made responsive to ultraviolet (UV) light by incorporating a photoacid generator (PAG) into the system. A commercially available PAG, diphenyliodonium-2-carboxylate, is used here. Upon exposure to UV light, this PAG irreversibly photolyzes into iodobenzene (IB) and benzoic acid (BA), with the formation of BA, leading to a drop in pH. WLMs formed by mixtures of CTAB, DHB, and the PAG are systematically characterized before and after UV irradiation. As the PAG photolyzes, an increase in the viscosity of WLMs occurs by a factor of 1000. We show that the ratio of the zero-shear viscosity η₀ (after UV/before UV) depends on the initial pH of the sample. The UV-induced increase in η₀ can be attributed to the growth of WLMs in solution, which in turn is influenced by both the ionization state of DHB and the presence of IB and BA.

The states of water in tryptophan grafted hydroxypropyl methylcellulose hydrogels and their effect on the adsorption of methylene blue and rhodamine B

Tryptophan (Trp) decorated hydroxypropyl methylcellulose (HPMC) cryogels were prepared by a one-step reaction with citric acid. The increase of Trp content in the 3D network from 0 to 2.18 wt% increased the apparent density from 0.0267 g.cm^-3 to 0.0381 g.cm^-3 and the compression modulus from 94 kPa to 201 kPa, due to hydrophobic interactions between Trp molecules. The increase of Trp content in HPMC-Trp hydrogels increased the amount of non-freezing water, estimated from differential scanning calorimetry, and the amount of freezing water, which was determined by time-domain nuclear magnetic resonance. The adsorption capacity of methylene blue (MB) and rhodamine B (RB) on HPMC-Trp hydrogels increased with Trp content and the amount of freezing water. HPMC-Trp hydrogels could be recycled 6 times keeping the original adsorptive capacity. The diffusional constants of MB and RB tended to increase with Trp content. RB adsorbed on HPMC-Trp hydrogels presented a bathochromic shift of fluorescence.

Reducing phosphate in emulsified meat products by adding chia (Salvia hispanica L.) mucilage in powder or gel format: A clean label technological strategy

This study evaluated the functional properties of chia mucilage powder (MCP) and gel (MCG) as a phosphate replacers in low-fat Bologna sausages. Four treatments were produced without phosphates (F1-2% MCP; F2-2% MCG; F3-4% MCP; F4-4% MCG) and two with 0.25% phosphate (F5-2% MCG and F6-4% MCG) besides control (20%-fat-0.5% phosphate). Samples containing mucilage were less firm and less chewy on day 0, except F3. Treatments containing 2% MCG were judged acceptable and provided better emulsion stability than those with MCP. Adding 4% MCP or MCG resulted in Bolognas with lower relaxation times and more restricted mobility and lowest sensorial acceptance characterized by the terms light brown and dark pink color (F4). The microscopy images exhibited less cohesive structure in treatments with 4% of MCG, suggesting the formation of a weaker bound protein network. Chia mucilage gel at 2%, due to its functional properties, has proven to be a feasible strategy to substitute 50% phosphate in low-fat Bologna sausages.

Probing the Formation of Wormlike Micelles Formed by Cationic Surfactant with Chlorobenzoate Derivatives

The energy released when tetradecyltrimethylammonium bromide (C₁₄TAB) is combined with different derivatives of chlorobenzoates in an isothermal titration calorimeter (ITC) allows a direct evaluation of the spontaneity of the threading of the aromatic anions into the micellar palisade. The comparison between the enthalpimetric curves with the ones for viscosity of the solutions, hydrodynamic radii of the aggregates (dynamic light scattering experiments), and the fraction of aromatic anions incorporated (diffusion-ordered spectroscopy experiments) allows the establishment of the variations of enthalpy with formation, growth, and decrease of the wormlike micelles (WLMs). The formation of WLMs with C₁₄TAB is very favored (very exothermic) for titrations of chlorobenzoate derivatives which present the chlorine atom in positions 3 or 4 of the aromatic ring. However, the aggregation is highly unfavorable if chlorine is at position 2 of chlorobenzoate. According to the results, the high potential of the ITC to determine critical concentrations and the energies associated with the aggregation of a cationic surfactant and aromatic anions for the formation of WLMs was demonstrated.

Use of the aqueous biphasic system as an alternative for concentration of Ascaris lumbricoides eggs, with non-toxic separation of faecal residues and fats

OBJECTIVES

Human enteroparasites are considered a serious public health problem in underdeveloped countries located in world regions with tropical, subtropical and equatorial climates. These parasites are commonly diagnosed by the Parasitological Examination of Faeces (PEF), performed by conventional techniques and/or commercial kits that result in tests with low-to-moderate sensitivity, due to the use of destructive chemical solvents to parasite structures, and to present excess adipose substance and digestive residues in their microscopic slides. In order to improve the efficacy of these tests/examinations, this study aimed to investigate a new alternative for the PEF, with the use of Aqueous Biphasic System (ABS).

METHODS

For this, four ABSs containing poly (ethylene glycol), PEG (PEG-4000 and PEG-6000), dipotassium phosphate and sodium citrate at different concentrations in the biphasic systems were evaluated with faecal samples containing eggs of Ascaris lumbricoides.

RESULTS

The ABS consisting of PEG-4000 and dipotassium phosphate, at concentrations of 55% w/w and 20% w/w, respectively, achieved 100% satisfactory results compared to the conventional TF-Test technique in terms of preservation and concentration of A. lumbricoides eggs, with adequate separation of digestive residues, without using a centrifuge or chemical solvents that may cause harm to the parasites.

CONCLUSIONS

This study presents ABS as a new low-cost technical principle for the detection of parasite eggs in PEF. The new technique is simple, fast, non-toxic, not harmful to the parasite and does not require a centrifuge.

A new interpretation of the mechanism of wormlike micelle formation involving a cationic surfactant and salicylate

HYPOTHESIS

When tetradecyltrimethylammonium bromide, TTAB, is added to aqueous solution of sodium salicylate, NaSal, the threading of the aromatic anion into the micellar palisade leads to the formation of wormlike micelles. Based on the calorimetric titration of NaSal with TTAB, and on the lifetime of fluorescence of salicylate, we propose that the aggregation of the two components directly leads to the formation of wormlike micelles, without any pre-aggregation.

EXPERIMENTS

By using an isothermal titration calorimeter, aliquots of TTAB were added to a dilute solution of NaSal. The energy involved in each addition was then integrated and the variation of enthalpy was determined. In the same range of concentrations and molar ratios, the surface tensiometry and time-resolved emission spectroscopy experiments were performed.

FINDINGS

A very characteristic calorimetric signal associated with wormlike micelle formation was obtained, being the enthalpy variation of this process, Δ_WLMH₂₉₈⁰ < 0. When 1.2 mmol L^-1 of NaSal is titrated with 11.0 mmol L^-1 of TTAB at 298.15 K, Δ_fH₂₉₈⁰ = -10.31 kJ per mol of injectant. By adding TTAB to NaSal solution, two fluorescence lifetimes of salicylate were observed solely after wormlike micelle being formed. The correspondent lifetime values of 4.0 ns and 7.2 ns are respectively associated with the free and associated species of salicylate. The new results demonstrated that wormlike micelles are the first aggregate formed when TTAB is added to salicylate. This aspect is relevant for understanding the mechanism of wormlike micelles formation.

Effect of the Hydrophobic Tail of a Chiral Surfactant on the Chirality of Aggregates and on the Formation of Wormlike Micelles

The micellization of chiral enantiopure surfactants, dodecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide and hexadecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide, was investigated by circular dichroism spectroscopy and isothermal titration calorimetry. The formation of wormlike micelles (WLMs) upon the addition of sodium salicylate to the aqueous solutions of the surfactant was observed only in the case of hexadecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide. The presence of WLMs was assessed by cryogenic transmission electron microscopy, rheology, and isothermal titration calorimetry experiments, and their supramolecular chirality was investigated by circular dichroism spectroscopy. Depending on the length of the hydrophobic tail, molecular chirality is transferred into a different chiral supramolecular trait. Our findings demonstrate that hydrophobic interactions by controlling the organization and functions of self-assemblies also control the transcription of the chiral information from molecules to complex supramolecular systems.

Two different pathways for assembling bis-urea in benzene and toluene

The thermodynamic stability of assemblies formed by a bis-urea-based supramolecular polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT), was investigated in solutions using either benzene or toluene as the solvent. Starting from a higher temperature in which EHUT was soluble in both solvents, molecules spontaneously self-organized into tubular assemblies upon cooling and these assemblies were stable in a wide range of temperatures. However, the systems followed different paths below a specific temperature: while the supramolecular polymer remained stable in toluene, EHUT molecules underwent precipitation in benzene. The causes for these different behaviors were explored by molecular dynamics simulations, which provided support for stronger enthalpic stabilization of the tubular assemblies in toluene as compared to benzene. This stabilization was due mainly to the better interaction energy of trapped toluene molecules instead of benzene ones. For both cases, lowering the temperature makes the solvent penetration inside the tubes less favorable, which reduces the stability of supramolecular structures upon cooling. Graphical abstract Different EHUT solubilities.

Stabilization of spherical nanoparticles of iron(III) hydroxides in aqueous solution by wormlike micelles

HYPOTHESIS

The low K_sp value of Fe(OH)₃ (3 × 10^-38 at 298 K) explain the immediate coagulation when the pH of a solution of Fe(III) is adjusted to 7. However, stable dispersions of Fe(OH)₃ can be formed when the pH is adjusted to 7 in the presence of wormlike micelles formed by cetyltrimethylammonium bromide and sodium salicylate. The formation of a structure containing Fe(OH)₃ nanoparticles decorating wormlike micelles is responsible for the high stability of the dispersions.

EXPERIMENTS

Fe(OH)₃ nanoparticles were obtained by increasing the pH of solutions of cetyltrimethylammonium bromide and Fe(III), previously complexed with salicylate at pH 3. The interaction between nanoparticles and the chains of wormlike micelles was investigated by DLS, SAXS, TEM and Cryo-TEM.

FINDINGS

DLS revealed higher scattering contrast and slower diffusion for wormlike micelles in the presence of nanoparticles. These results were interpreted as the decoration of the chains of wormlike micelles by nanoparticles of Fe(OH)₃. A pearl-necklace model was successfully used to adjust SAXS curves, revealing nanoparticles with ∼3 nm of diameter, spaced ∼2 nm apart along the string. This result agrees with TEM and Cryo-TEM images. The formed structure prevents the coagulation of nanoparticles, assuring high stability to the dispersion.

Generation of a Chiral Giant Micelle

Over the past few years, chiral supramolecular assemblies have been successfully used for recognition, sensing and enantioselective transformations. Several approaches are available to control chirality of discrete assemblies (e.g., cages and capsules), but few are efficient in assuring chirality for micellar aggregates. Optically active amino acid-derived surfactants are commonly used to generate chiral spherical micelles. To circumvent this limitation, we benefited from the uniaxial growth of spherical micelles into long cylindrical micelles usually called wormlike or giant micelles, upon the addition of cosolutes. This paper describes the unprecedented formation of chiral giant micelles in aqueous solutions of cetyltrimethylammonium bromide (CTAB) upon increasing addition of enantiopure sodium salt of 1,1'-bi-2-naphthol (Na-binaphtholate) as a cosolute. Depending on the concentrations of CTAB and Na-binaphtholate, chiral gel-like systems are obtained. The transition from spherical to giant micellar structures was probed using rheology, cryo-transmission electron microscopy, polarimetry, and electronic circular dichroism (CD). CD can be effectively used to monitor the incorporation of Na-binaphtholate into the micelle palisade as well as to determine its transition to giant micellar structures. Our approach expands the scope for chirality induction in micellar aggregates bringing the possibility to generate "smart" chiral systems and an alternative asymmetric chiral environment to perform enantioselective transformations.

Calorimetric and Light Scattering Investigations of the Transition from Spherical to Wormlike Micelles of C₁₄TAB Triggered by Salicylate

Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.

Molecular variations in aromatic cosolutes: critical role in the rheology of cationic wormlike micelles

Wormlike micelles formed by the addition to cetyltrimethylammonium bromide (CTAB) of a range of aromatic cosolutes with small molecular variations in their structure were systematically studied. Phenol and derivatives of benzoate and cinnamate were used, and the resulting mixtures were studied by oscillatory, steady-shear rheology, and the microstructure was probed by small-angle neutron scattering. The lengthening of the micelles and their entanglement result in remarkable viscoelastic properties, making rheology a useful tool to assess the effect of structural variations of the cosolutes on wormlike micelle formation. For a fixed concentration of CTAB and cosolute (200 mmol L(-1)), the relaxation time decreases in the following order: phenol > cinnamate> o-hydroxycinnamate > salicylate > o-methoxycinnamate > benzoate > o-methoxybenzoate. The variations in viscoelastic response are rationalized by using Mulliken population analysis to map out the electronic density of the cosolutes and quantify the barrier to rotation of specific groups on the aromatics. We find that the ability of the group attached to the aromatic ring to rotate is crucial in determining the packing of the cosolute at the micellar interface and thus critically impacts the micellar growth and, in turn, the rheological response. These results enable us for the first time to propose design rules for the self-assembly of the surfactants and cosolutes resulting in the formation of wormlike micelles with the cationic surfactant CTAB.

The elasticity of soap bubbles containing wormlike micelles

Slow-motion imaging of the rupture of soap bubbles generally shows the edges of liquid films retracting at a constant speed (known as the Taylor-Culick velocity). Here we investigate soap bubbles formed from simple solutions of a cationic surfactant (cetyltrimethylammonium bromide - CTAB) and sodium salicylate. The interaction of salicylate ions with CTAB leads to the formation of wormlike micelles (WLM), which yield a viscoelastic behavior to the liquid film of the bubble. We demonstrate that these elastic bubbles collapse at a velocity up to 30 times higher than the Taylor-Culick limit, which has never been surpassed. This is because during the bubble inflation, the entangled WLM chains stretch, storing elastic energy. This extra energy is then released during the rupture of the bubble, yielding an additional driving force for film retraction (besides surface tension). This new mechanism for the bursting of elastic bubbles may have important implications to the breakup of viscoelastic sprays in industrial applications.

Before and beyond the micellization of n-alkyl glycosides. A water-1H NMR relaxation study

The interactions between the headgroups of n-alkyl glycoside (AG) and water molecules were studied by nuclear magnetic transverse relaxation times (T2) of the water protons before and beyond the micellization. Despite the low concentration of the surfactants (mM), their micellization induce strong effect on the T2 values of bulk water when the AG molecules self-aggregate into micelles. This is associated with the decreasing of the fraction of OH headgroups of AG to exchange protons with water molecules due to the OH headgroups intermolecular interactions of AG at the micelle surface. These findings support the computational results described in the literature, which indicate that the water hydrogen bonding to OH headgroups is perturbed at AG micelle surfaces.

More on polypseudorotaxanes formed between poly(ethylene glycol) and α-cyclodextrin

A new interpretation for the mechanism associated with the spontaneous threading of α-CD, onto a PEG chain followed by the supramolecular hydrogel formation, is described. Beyond a specific stoichiometry, the complexation of α-CD and PEG results in the formation of a two-phase system. Besides the phase separation, for PEG with a molecular weight higher than 6000 Da, part of the polymer chains are unthreaded by the α-CD, leading to the formation of a supramolecular hydrogel. The kinetics for the complexation and the determination of the yield for equilibrated systems consisting of PEG (linear and star) are used to investigate the number of α-CD threaded before and after the phase separation. The results are compared with the prediction obtained from the application of the Poisson distribution and reveal the ratio between α-CD and PEG in each step of the process. Additionally, the kinetics for the hydrogel formation and its inner structure are investigated by using the proton NMR spin-spin relaxation of water.

Tuning the viscoelastic properties of bis(urea)-based supramolecular polymer solutions by adding cosolutes

Polymers formed by the self-assembly of a bis(urea)-based polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT), in organic solvents such as octane are promising systems with remarkable rheological properties. This is the first self-assembled polymer recently reported as a hydrodynamic drag reducer for hydrocarbons. The rheology of diluted and semidiluted EHUT solutions can be tuned by specific interactions between the chains, modulated by the nature of the solvent and the presence of additives. In this article, rheological, thermal and SANS measurements were performed in order to investigate the competition between EHUT self-assembly and its interaction with specific molecules (benzene, benzyl alcohol, and ethanol) that can interact with EHUT unimers via hydrogen bonds and π-π interactions. No substantial rheological, thermal, or structural effect is observed when benzene is added to the systems. However, ethanol and benzyl alcohol interact with EHUT unimers through hydrogen bonds, drastically decreasing the viscoelasticity of the solutions. In addition, benzyl alcohol can interact with EHUT polymers by π-stacking interactions, playing an important role in tuning the rheological properties of the systems.

The gelling of κ-carrageenan in light and heavy water

Gels of κ-carrageenan were prepared in H₂O and D₂O. Rheological measurements revealed that in heavy water the elastic modulus is substantially higher. From the rheological view point, this result indicates the formation of a higher number of physical-crosslinking points in the structure of the gel. These crosslinking points are mainly associated with the aggregation of the double-helix of the κ-carrageenan, which is enhanced in D₂O. The thermal stability of the gels in both solvents (relative to the sol-gel transition) was also investigated by using polarimetric measurements (to measure the relative fraction of helix-coil) and micro-differential scanning calorimetry (micro-DSC). The results obtained using these techniques are very consistent and allow us to propose a model to explain the differences for the gels formed in light and heavy water based on the degree of double-helix aggregation.

Bis-urea-based supramolecular polymer: the first self-assembled drag reducer for hydrocarbon solvents

The hydrodynamic drag reduction phenomenon, also termed the Toms effect, is an unusual case involving macromolecules in solution in which the resistance to flow is reduced comparatively to that of the pure solvent. Although the effect is relatively well characterized, it is still unclear from the molecular viewpoint. The presence of some amount of a polymer with high molecular weight can produce large levels of drag reduction in turbulent flow as a result of the interactions of the long structures with the small vortices developed during the flow. For this reason, the effect is very attractive in the pumping process because a significant amount of energy can be saved. In aqueous systems, giant micelles can be spontaneously formed, driven by the hydrophobic effect, and are effective drag reducers. Giant micelles are interesting in promoting drag reduction because the noncovalent and reversible aggregation of the surfactant molecules avoids mechanical degradation, which typically occurs with classical polymers, due to irreversible scission of the backbone. In this letter, we present the first hydrodynamic drag reducer for hydrocarbons based on a self-assembled polymer formed from the reversible aggregation of bis-urea monomers. This system forms two competitive polymeric structures--the tube (T) and the filament (F) forms--which are in equilibrium with each other. Our rheology results in octane and toluene are fully consistent with calorimetry data and show that only the longest form, T, is able to promote the drag reduction effect.

Worm-like micelles of CTAB and sodium salicylate under turbulent flow

Polymers with high molecular weight and worm-like micelles are drag-reducing agents under turbulent flow. However, in contrast to the polymeric systems, the worm-like micelles do not undergo mechanical degradation due to the turbulence, because their macromolecular structure can be spontaneously restored. This very favorable property, together with their drag-reduction capability, offer the possibility to use such worm-like micelles in heating and cooling systems to recirculate water while expending less energy. The formation, growth, and stability of worm-like micelles formed by cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) were investigated using the self-fluorescence of salicylate ions and the ability of the giant micelles to promote hydrodynamic drag reduction under turbulent flow. The turbulence in solutions of CTAB-Sal was produced within the double-gap cell of a rotational rheometer. Detailed diagrams were obtained for different ratios of Sal and CTAB, which revealed transitions associated with the thermal stability of giant micelles under turbulent flow.

Catastrophic antiphospholipid syndrome: report of 4 cases

Catastrophic antiphospholipid syndrome (CAPS), described by Asherson in 1992, is a rare form of antiphospholipid syndrome resulting in multiorgan failure with a mortality rate of about 50%. The syndrome occurs in patients with either systemic lupus erythematosus and other rheumatic diseases (systemic sclerosis, rheumatoid arthritis, primary Sjogren syndrome) or alone. Whereas in "classic" antiphospholipid syndrome (APS), medium-large vessels are involved, a diffuse small vessel ischemia and thrombosis (microangiopathic disease) leading to a severe multiorgan dysfunction is predominant in CAPS. "Trigger" factors have been demonstrated in 45% of patients, but in the majority, they remain unknown. Not infrequently, CAPS arises in patients without any previous thrombotic history. The kidney is the organ most commonly affected, followed by the lung, the central nervous system, the heart and the skin. Disseminated intravascular coagulation occurs in approximately 13% of patients. The present study reports the clinical and serological features of 4 patients affected by this rare form of antiphospholipid syndrome. Nephrologists should be aware of the possibility of this syndrome as a cause of multiorgan failure since prompt recognition is essential for effective treatment.

Description of the Thermospray Formed at Low Flow Rate in Thermospray Flame Furnace Atomic Absorption Spectrometry Based on High-Speed Images

The mechanism of the thermospray formed at low flow rates using a peristaltic pump in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) is described here for the first time. The study was based on magnified images of the thermospray formed inside the hot tube furnace by using a high-speed CMOS camera. For this purpose different image acquisition speeds were used (from 1000 to 18,000 frames/s), revealing that the thermospray obtained under such conditions is quite different from those already reported. The frames of the thermospray evolution indicate that the Leindenfrost effect plays an important role and allow us to propose a mechanism for its formation. The analysis of the images contributed to calculation of parameters related to thermospray formation, such as pulse incidence average (110 +/- 10, 320 +/- 50, and 1200 +/- 150 pulses per second) and pulse speed (6 +/- 1, 10 +/- 1, and 14 +/- 2 m s(-1)) for 0.1, 0.4, and 1.0 mL min(-1) flow rate, respectively, for both parameters. Additionally, the evaporation constant (lambda) of 10(-4) m2 s(-1) was estimated, and the present thermospray was correlated to the conventional sprays using the Sauter mean diameter (SMD) parameter, which ranged from ca. 2 to 44 microm. In order to correlate the information obtained through images with analytical parameters employing the thermospray, the sensitivities for cadmium determination at each condition (0.12, 0.11, and 0.069 s L microg(-1) for 0.1, 0.4, and 1.0 mL min(-1) flow rate, respectively) were taken into account.