Dynamic covalent surfactants and their uses in the development of smart materials

Dynamic covalent chemistry, which leverages the dynamic nature of reversible covalent bonds controlled by the conditions of reaction equilibrium, has demonstrated great potential in diverse applications related to both the stability of covalent bonds and the possibility of exchanging building blocks, imparting to the systems the possibility of "error checking" and "proof-reading". By incorporating dynamic covalent bonds into surfactant molecular architectures, combinatorial libraries of surfactants with bespoke functionalities can be readily fabricated through a facile strategy, with minimum effort in organic synthesis. Consequently, a multidisciplinary field of research involving the creation and application of dynamic covalent surfactants has recently emerged, which has aroused great attention in surfactant and colloid science, supramolecular chemistry, self-assembly, smart materials, drug delivery, and nanotechnology. This review reports results in this field published over recent years, discusses the possibilities presented by dynamic covalent surfactants and their applications in developing smart self-assembled materials, and outlines some future perspectives.

Facile fabrication of self-reporting micellar and vesicular structures based on an etching-ion exchange strategy of photonic composite spheres of poly(ionic liquid)

Micellar and vesicular structures capable of sensing and reporting the chemical environment as well as facilely introducing user-defined functions make a vital contribution to constructing versatile compartmentalized systems. Herein, by combining poly(ionic liquid)-based photonic spheres and an etching-ion exchange strategy we fabricate micellar and vesicular photonic compartments that can not only mimic the structure and function of conventional micelles and vesicles, but also sense and report the chemical environment as well as introducing user-defined functions. Photonic composite spheres composed of a SiO2 template and poly(ionic liquid) are employed to selectively etch outer-shell SiO2 followed by ion exchange and removal of the residual SiO2 to afford micellar photonic compartments (MPCs). The MPCs can selectively absorb solvents from the oil/water mixtures together with sensing and reporting the adsorbed solvents by the self-reporting optical signal associated with the uniform porous structure of photonic spheres. Vesicular photonic compartments (VPCs) are fabricated via selective infiltration and polymerization of ionic liquids followed by etching of the SiO2 template. Subsequent ion exchange introduces desirable functions to the VPCs. Furthermore, we demonstrate that the thickness and the anisotropic functions of VPCs can be facilely modulated. Overall, we anticipate that the micellar and vesicular photonic compartments with self-reporting optical signals and user-defined functions could serve as novel platforms towards multifunctional compartmentalized systems.

Protein distribution in lupin protein isolates from Lupinus angustifolius L. prepared by various isolation techniques

Differences in the protein distribution of various protein isolates from Lupinus angustifolius L. Vitabor were identified as affected by the isolation procedure (alkaline and/or salt-induced extraction followed by isoelectric and/or dilutive precipitation). Protein isolates extracted in alkaline solution showed higher protein yields (26.4-31.7%) compared to salt-induced extraction (19.8-30.0%) or combined alkaline and salt-induced extraction (23.3-25.6%). Chemical variations among the protein isolates especially occurred within the albumins. Protein isolates precipitated isoelectrically showed the highest contents, whereas protein isolates precipitated by dilutive showed the lowest contents of conglutin δ. Furthermore, the alkaline subunits of conglutin α and conglutin γ decreased during alkaline extraction compared to salt-induced extraction. A decrease in protein-bound polar and basic amino acids was shown after protein isolation. In contrast, the amounts of nonpolar, aliphatic, aromatic, hydroxylated and sulfur-rich amino acids were higher in the lupin protein isolates compared to the lupin flakes. However, the functional side chains could not be related to the specific molecular arrangements of the protein isolates, as a similar amino acid composition was found among the protein isolates.

Impact of urea on detergent micelle properties

Co-solvents, such as urea, can entail drastic changes in the micellization behavior of detergents. We present a systematic quantification of the impact of urea on the critical micellar concentration, the micellization thermodynamics, and the micelle size in three homologous series of commonly used non-ionic alkyl detergents. To this end, we performed demicellization experiments by isothermal titration calorimetry and hydrodynamic size measurements by dynamic light scattering on alkyl maltopyranosides, cyclohexyl alkyl maltopyranosides, and alkyl glucopyranosides at urea concentrations of 0-8 M. For all detergents studied, we found that the critical micellar concentration increases exponentially because the absolute Gibbs free energy of micellization decreases linearly over the entire urea concentration range, as does the micelle size. In contrast, the enthalpic and entropic contributions to micellization reveal more complex, nonlinear dependences on urea concentration. Both free energy and size changes are more pronounced for long-chain detergents, which bury more apolar surface area upon micelle formation. The Gibbs free energy increments per methylene group within each detergent series depend on urea concentration in a linear fashion, although they result from the entropic term for alkyl maltosides but are of enthalpic origin for cyclohexyl alkyl maltosides. We compare our results to transfer free energies of amino acid side chains, relate them to protein-folding data, and discuss how urea-induced changes in detergent micelle properties affect in vitro investigations on membrane proteins.

Spectral and electrochemical studies of bis(diimine)copper(II) complexes in anionic, cationic and nonionic micelles

The spectral and redox behavior of bis(diimine)copper(II) complexes, where diimine is bipyridine, 1,10-phenanthroline, 4-methyl-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 5-nitro-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline and dipyrido-[3,2-d:2',3'-f]-quinoxaline, are significantly different in aqueous and in aqueous SDS, CTAB and Triton X-100 micellar solutions. The (1)H NMR spectral study in aqueous (D(2)O) and aqueous micelles reveals that the Cu(II) complexes interact more strongly with SDS than with CTAB and Triton X-100 micelles and at sites on SDS micelles different from those on the latter. Ligand Field spectral studies reveal that the complexes exist as the dicationic aquated species [Cu(diimine)(2)(H(2)O)(2)](2+), which interacts strongly with the anionic SDS micelles through columbic forces. However, they exist as [Cu(diimine)(2)(H(2)O)Cl](+) and/or [Cu(diimine)(2)H(2)] located in the hydrophobic microenvironments in Triton X-100 and CTAB micelles. The attainment of reversibility of the redox systems in the micellar microenvironments is remarkable and this illustrates that the Cu(II) and Cu(I) species undergo stereochemical changes suitable for reversible electron-transfer. The remarkable differences in spectral and electrochemical properties of Cu(II) complexes in aqueous and aqueous micellar solutions illustrate that the complexes are nestled largely within the micellar environments and imply that the accessibilities of the complexes to electron-transfer are different and are dependent on the nature of micelles as well as the nature and hydrophobicity of the diimine ligands.

Photocatalytic events of CdSe quantum dots in confined media. Electrodic behavior of coupled platinum nanoparticles

The electrodic behavior of platinum nanoparticles (2.8 nm diameter) and their role in influencing the photocatalytic behavior of CdSe quantum dots (3.4 nm diameter) has been evaluated by confining both nanoparticles together in heptane/dioctyl sulphosuccinate/water reverse micelles. The particles spontaneously couple together within the micelles via micellar exchange processes and thus facilitate experimental observation of electron transfer reactions inside the water pools. Electron transfer from CdSe to Pt is found to occur with a rate constant of 1.22 × 10(9) s(-1). With the use of methyl viologen (MV(2+)) as a probe molecule, the role of Pt in the photocatalytic process is established. Ultrafast oxidation of the photogenerated MV(+•) radicals indicates that Pt acts as an electron sink, scavenging electrons from MV(+•) with a rate constant of 3.1 × 10(9) s(-1). The electron transfer between MV(+•) and Pt, and a drastically lower yield of MV(+•) under steady state irradiation, confirms the ability of Pt nanoparticles to discharge electrons quickly. The kinetic details of photoinduced processes in CdSe-Pt assemblies and the electrodic behavior of Pt nanoparticles provide important information for the development of light energy conversion devices.

Influence of ion accumulation on the emulsion stability and performance of semi-synthetic metalworking fluids

The metalworking industry is one of the largest in the United States. Although metalworking fluids (MWFs) are ubiquitous in manufacturing as coolants and lubricants, these emulsified fluids have a significant environmental impact over their life cycle. Accordingly, it has become necessary to better understand emulsion destabilization mechanisms that lead to MWF deterioration and disposal so that MWF formulations can be designed for increased longevity. This paper investigates the impact of pH and a wide range of hard water salts on MWF emulsion stability. While expected trends from the emulsion science literature are observed, it is shown that MWF destabilization can lead to an increase in the microbial load that the MWF can sustain while only slightly improving manufacturing performance as measured by the tapping torque test. Experimental observations also indicate that these trends are strongly correlated with increased emulsion particle size, regardless of whether increased particle size is achieved by aging, by reductions in pH, or by the addition of hard water salts. In MWF systems, these conditions typically result from the accumulation of divalent and trivalent cations over time due to hard water additions and exposure to metal workpieces and tools. While MWFs are formulated with EDTA to avoid emulsion destabilization due to cation accumulation, it is shown that EDTA can be ineffective or highly inefficient for this purpose due to direct interactions between EDTA and the MWF emulsifier system. Given the ineffectiveness of EDTA and commonly utilized MWF emulsifier systems to maintain stable emulsion size in the presence of high concentrations of hard water salts, a more effective and environmentally preferable technological change to the MWF formulation design is proposed and successfully demonstrated.

Design of hard water stable emulsifier systems for petroleum- and bio-based semi-synthetic metalworking fluids

Metalworking fluids (MWFs) increase productivity and the quality of manufacturing operations by cooling and lubricating during metal forming and cutting processes. Despite their widespread use, they pose significant health and environmental hazards throughout their life cycle. An obvious environmental improvement to MWF technology would be to improve the lifetime of the fluid while utilizing more environmentally friendly and less energy-consuming materials without compromising existing performance levels. This investigation focuses on the design of mixed anionionc:nonionic emulsifier systems for petroleum and bio-based MWFs that improve fluid lifetime by providing emulsion stability under hard water conditions, a common cause of emulsion destabilization leading to MWF disposal. Experimental conditions were designed to evaluate the impact of emulsifier structural characteristics (straight chain, branched tail, branched head) and the molar ratios of anionic to nonionic surfactant and oil to total surfactant. Results from the 2500 formulations generated indicate that the use of a twin-headed anionic surfactant can provide improved hard water stability for both mineral oil- and vegetable oil-based formulations, even in the absence of a chelating agent and a coupler. Results also suggest that an oil:total surfactant molar ratio of 0.5 or less is necessary for particle size stability in hard water conditions for these systems. The newly developed petroleum and bio-based formulations with improved hard water stability are competitive with commercially available MWFs in performance evaluations for tramp oil rejection, contact angle, and tapping torque efficiency. These results can be used to design MWF formulations with fewer components and extended lifetime under hard water conditions, both of which would lead to a reduction in the life cycle environmental impact of MWFs.

Surfactant-assisted organic reactions in water. Effect of ultrasound on condensation reactions between active methylene compounds and arylaldehydes

A series of quaternary ammonium salts has been tested as phase transfer agents to promote condensation reactions in an aqueous solution of sodium hydroxide in the absence of any organic solvent. Methyltrioctylammonium chloride (Aliquat 336) emerges as the most efficient catalyst. Sonication of the reaction media has a poor but positive kinetic effect.

Physicochemical Properties of Dodecylammonium Picrate

A novel surfactant, dodecylammonium picrate (DDAP), was synthesized and its crystal structure was determined by X-ray diffraction analysis. DDAP's physicochemical properties were examined by spectral (infrared and nuclear magnetic resonance), thermal, microscopic, and conductometric studies. The results revealed the influence of counterion specificity on thermal solid-state transitions and solution properties: the Krafft point, the aqueous solubility, the critical micelle concentration, the degree of counterion binding, and thermodynamic parameters of micellization. Copyright 2000 Academic Press.

Continuous measurement of oxygen consumption by linoleic acid membranes exposed to free radicals generated by gamma-radiation

Vesicles enclosed by membranes prepared from linoleic acid were exposed in the chamber of an oxygen electrode to free radicals generated by 60Co gamma-rays. Oxidation was observed by oxygen consumption, conjugated diene formation, and tri-iodide assay for hydroperoxides. There was a dose-dependent lag period before the onset of rapid peroxidation. The radiation chemical yields (G-values) ranged from 4.45 to 19.37 mu-mol J-1 for maximum rates of oxygen consumption and from 2.18 to 16.37 mumol J-1 for maximum rates of hydroperoxide production when the radiation dose-rate was varied between 5.39 and 0.14 Gy min-1. The magnitudes of these G-values and the linear relationship between yield of hydroperoxide and (dose-rate)1/2 were indicative of a chain mechanism for peroxidation operating in membranes. The lack of congruence between the amount of oxygen consumed and hydroperoxide formed suggested that the oxygen consumed in membrane oxidation led to the formation of oxidized derivatives of linoleic acid additional to the hydroperoxides.

Effect of surfactants and dispersed components on the activity and reactivity of sorbic acid

In common with many other carboxylic acids, sorbic acid shows significant solubility in aqueous and non-aqueous solvents. The presence of a non-aqueous phase (e.g. fat) can markedly affect the concentration of the preservative in the aqueous phase. Solute distribution between the two phases is pH- and concentration-dependent. The presence of dissolved surfactants in the aqueous phase will also affect the activity of sorbic acid. This effect is due to the partitioning of the solute into surfactant micelles. The presence of dispersed components and surfactant micelles also has a marked effect on the reactivity of sorbic acid. Whereas thiols react slowly with sorbic acid, the rate of reaction is increased many-fold by the addition of low molecular weight surfactants. The mechanism of this catalysis will be explained. It has been suggested that sorbic acid inhibits enzymes by reacting with sulphydryl groups of the proteins. Kinetic data from model system studies suggest that the sorbic acid-thiol reaction may be too slow for it to be an obvious means of enzyme inhibition. However, this does not take account of possible catalysis of the reaction in the microenvironment of the protein, perhaps in a manner similar to that identified with low molecular weight surfactants.

Ionization and phase behavior of fatty acids in water: application of the Gibbs phase rule

The phase behavior of several medium-chain (10- and 12-carbon) and long-chain (18-carbon) fatty acids in water was examined as a function of the ionization state of the carboxyl group. Equilibrium titration curves were generated above and below fatty acid and acid-soap chain melting temperatures and critical micelle concentrations, and the phases formed were characterized by X-ray diffraction, 13C NMR spectroscopy, and phase-contrast and polarized light microscopy. The resulting titration curves were divided into five regions: (i) at pH values less than 7, a two-phase region containing oil or fatty acid crystals and an aqueous phase; (ii) at pH approximately 7, a three-phase region containing oil, lamellar, and aqueous (or fatty acid crystals, 1:1 acid-soap crystals, and aqueous) phases; (iii) between pH 7 and 9, a two-phase region containing a lamellar fatty acid/soap (or crystalline 1:1 acid-soap) phase in an aqueous phase; (iv) at pH approximately 9, a three-phase region containing lamellar fatty acid-soap (or crystalline 1:1 acid-soap), micellar, and aqueous phases; and (v) at pH values greater than 9, a two-phase region containing micellar and aqueous phases. Interpretation of the results using the Gibbs phase rule indicated that, for oleic acid/potassium oleate, the composition of the lamellar fatty acid/soap phase varied from approximately 1:1 to 1:3 un-ionized to ionized fatty acid species. In addition, constant pH regions observed in titration curves were a result of thermodynamic invariance (zero degrees of freedom) rather than buffering capacity. The results provide insights into the physical states of fatty acids in biological systems.(ABSTRACT TRUNCATED AT 250 WORDS)