Self-Assembled Structures of Catanionic Associations: How to Optimize Vesicle Formation?

Like other amphiphilic compounds, bolaforms do not always possess surfactant properties; it depends on the spacer chain length and the nature of the polar head group (both sufficiently hydrophobic or hydrophilic, respectively, to intensify the amphiphilic properties). In this regard, unsymmetrical bolaamphiphiles bearing a sugar polar head group and a carboxylic acid function at the opposite ends of a hydrophobic binding spacer were synthesized. These biocompatible sugar-derived bolaforms were associated with basic fatty amines, by an acid–base reaction, to obtain catanionic mixtures. Associations with 1,7-lactobionamidoheptanoic acid and decylamine or octylamine spontaneously form stable 200–600 nm vesicles. This new type of association may find an application in drug delivery since catanionic vesicles can transport active substances inside the hydrophilic core, as well as hydrophobic drugs within the bilayer.     

Surface properties of N-alkanoyl-N-methyl glucamines and related materials

The surface properties [effectiveness of surface tension reduction (γ_CMC) critical micelle concentration (CMC), efficiency of surface tension reduction (pC ₂₀), maximal surface excess concentration (Γ_max), minimal area/molecule at the interface (A _min), and the (CMC/C ₂₀) ratio] of some well-purified N-alkanoyl-N-methyl glucamines and related polyol-based N-methyl amide-type surfactants, having the structural formula RC(O)N(Me)CH₂(CHOH)_xCH₂OH, where RC(O)=undecanoyl, lauroyl, tridecanoyl, myristoyl, and x=1,3, and 4, were investigated at 25°C in distilled water and 0.1 M NaCl. Water solubility of these compounds does not simply depend on the number of hydroxyl groups in the molecule but is associated with the balance between intermolecular hydrogen bonds and hydrogen bonds formed with water molecules. The fundamental interfacial properties, such as CMC and γ_CMC and two thermodynamic parameters, standard free energy of adsorption and standard free energy of micellization, were found to be significantly dependent on the hydrophobic acyl chain rather than on the number of CHOH groups in the hydrophilic moieties. By contrast, the practical performance properties were greatly dependent on the nature of the hydrophilic group. As a whole, these surfactants had desirable foaming properties and efficient wetting abilities. Furthermore, synergism in foaming and wetting abilities was observed in a binary mixture of these surfactants with an alkyloxyethylene sulfate.     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

水溶性润滑添加剂的分子结构与性能

讨论了水溶性润滑添加剂的分子结构与性能的关系,认为添加剂的同一分子中包含亲水性,吸附性,疏水性和反应性基团,则可能兼有油性剂,抗磨剂和极压剂多种作用。     

Nonionic amphiphilic compounds from lysine as molecular mimics of lecithins

New monodisperse nonionic surfactant molecules, based on lysine with two fatty acid chains in the hydrophobic part and one or two polyoxyethylene methoxycapped chains (EO _n −Me) in the hydrophilic headgroup, are synthesized as mimics of natural lecithins. Their surface-activity properties indicate that these compounds have surfactant behavior whose global hydrophobic contribution is comparable to that of one fatty chain.     

Gemini表面活性剂在固液界面的吸附及增溶作用

介绍了一类新型表面活性剂———Gemini表面活性剂。这类表面活性剂具有特殊的分(离)子结构,其分(离)子由两(或三)条疏水链、两个亲水基和一个连接基组成。综述了Gemini表面活性剂在固液界面的吸附及增溶作用,其在固液界面的吸附及增溶作用与固体表面的性质及其分(离)子结构有很大关系。     

The effect of glycols on the hydrophile-lipophile balance and the micelle formation of nonionic surfactants

The empirical hydrophile-liophile balance (HLB) value of nonionic surfactants is an important parameter used to predict performance as, e.g., emulsifiers, solubilizers and wetting agents. However, the HLB value is based on an original molecular structure and does not take into account all the factors affecting the performance of nonionics, such as presence of additives, type of solvent, temperature, degree of hydration, structural modifications of the surfactant molecule and decomposition of surfactants. On a performance basis, where these factors come into play, a given nonionic surfactant may exhibit a multiplicity of apparent HLB values. Accordingly, we recently introduced the term “effective HLB value” which is a performance value which incorporates into the HLB the parameters listed above. The HLB value thus becomes a variable depending on the physical and chemical conditions at the time of the measurement. In this work, we investigated the effect of adding glycols and diglycols on the HLB using 3 different methods: cloud point, phenol index and critical micelle concentration (cmc). We found that this type of additive increases the cloud point, phenol index, cmc and the “effective HLB” of a polyoxyethylated nonionic surfactant. The effectiveness of the glycols in causing these increases was in the following order; dipropylene glycol > 1,4-butanediol > 1,2-propanediol > diethylene glycol > ethylene glycol. The solvent effect of glycols and diglycols on the hydrophobic and hydrophilic portions of the surfactant molecule are discussed. On the hydrocarbon part of the surfactant molecule, the solvents cause a weakening of the hydrophobic bond and an increase in the cmc. On the polyoxyethylene part of the molecule, the solvent may cause either an increase or a decrease in the cmc. The effect on the hydro-philic portion is related to hydrogen bonding exhibited by the additives. The results obtained again suggest that the effective HLB value, which is a measure of the HLB under operative conditions, may be of greater practical significance than calculated HLB.     

Properties of ethoxylate derivatives of norrandom alkylphenols

Performance evaluation data for highly biodegradable C₈−C₁₈ nonrandom línear alkylphenol ethoxylates and ethoxysulfates are presented for typical heavy- and light-duty detergent formulations. The effect of the derivatives' molecular weight on performance characteristics is discussed, including variations in the hydrophobic and hydrophilic parts of the molecule. Presented at the AOCS Meeting, Cincinnati, October 1965.     

Protein structure and properties

Proteins are the most versatile of the bipolymers with respect to structure, properties and function. This versatility is a consequence of the chemical diversity of their amino acid monomers and of the infinite number of ways in which the amino acid composition, linear sequence and three-dimensional folding may be varied. The constituent amino acids include hydrophobic and hydrophilic, reactive and inert forms. Thetrans, planar nature of the amido (peptide) linkage between amino acids limits the conformational freedom of the resulting polypeptide chain. Portions of the chain usually occur as one of several regular forms such as helixes, stabilized by hydrogen bonds. Overall conformation of the molecule is maintained largely by noncovalent forces such as hydrogen bonds and hydrophobic interactions. Conformation of the protein is determined by the linear sequence of amino acids in the chain, but is readily interrupted by a variety of nonphysiological agents, with concurrent loss of biological function. This rearrangement of the polypeptide chains, denaturation, usually results in an alteration of the characteristic chemical and physical properties of the molecule. The observation that denaturation can sometimes be reversed leads to new concepts of protein structure and properties. Journal Paper No. 3780 of the Agriculture Experiment Station, Purdue University, Lafayette, Indiana 47907. Presented at the AOCS-AACC Joint Protein Short Course, French Lick, Indiana, July 13–16, 1969.     

Amphiphilic building blocks for self-assembly: from amphiphiles to supra-amphiphiles

The process of self-assembly spontaneously creates well-defined structures from various chemical building blocks. Self-assembly can include different levels of complexity: it can be as simple as the dimerization of two small building blocks driven by hydrogen bonding or as complicated as a cell membrane, a remarkable supramolecular architecture created by a bilayer of phospholipids embedded with functional proteins. The study of self-assembly in simple systems provides a fundamental understanding of the driving forces and cooperativity behind these processes. Once the rules are understood, these guidelines can facilitate the research of highly complex self-assembly processes. Among the various components for self-assembly, an amphiphilic molecule, which contains both hydrophilic and hydrophobic parts, forms one of the most powerful building blocks. When amphiphiles are dispersed in water, the hydrophilic component of the amphiphile preferentially interacts with the aqueous phase while the hydrophobic portion tends to reside in the air or in the nonpolar solvent. Therefore, the amphiphiles aggregate to form different molecular assemblies based on the repelling and coordinating forces between the hydrophilic and hydrophobic parts of the component molecules and the surrounding medium. In contrast to conventional amphiphiles, supra-amphiphiles are constructed on the basis of noncovalent interactions or dynamic covalent bonds. In supra-amphiphiles, the functional groups can be attached to the amphiphiles by noncovalent synthesis, greatly speeding their construction. The building blocks for supra-amphiphiles can be either small organic molecules or polymers. Advances in the development of supra-amphiphiles will not only enrich the family of conventional amphiphiles that are based on covalent bonds but will also provide a new kind of building block for the preparation of complex self-assemblies. When polymers are used to construct supra-amphiphiles, the resulting molecules are known as superamphiphiles. This Account will focus on the use of amphiphiles and supra-amphiphiles for self-assembly at different levels of complexity. We introduce strategies for the fabrication of robust assemblies through self-assembly of amphiphiles. We describe the supramolecular approach for the molecular design of amphiphiles through the enhancement of intermolecular interaction among the amphiphiles. In addition, we describe polymerization under mild conditions to stabilize the assemblies formed by self-assembly of amphiphiles. Finally, we highlight self-assembly methods driven by noncovalent interactions or dynamic covalent bonds for the fabrication of supra-amphiphiles with various topologies. Further self-assembly of supra-amphiphiles provides new building blocks for complex structures, and the dynamic nature of the supra-amphiphiles endows the assemblies with stimuli-responsive functions.     

Glucamine-based gemini surfactants II: Gemini surfactants from long-chain <Emphasis Type="Italic">N</Emphasis>-alkyl glucamines and epoxy resins

Gemini surfactants were synthesized by reaction of long-chain N-alkyl glucamines with epoxy resins. Analogous to the synthesis of gemini surfactns from long-chain N-alkyl glucamines and α, ω-diepoxides (1), the reaction in methanol at 70°C could be used to convert the starting materials selectively and almost quantitatively. N-Octyl glucamine, N-decyl glucamine, and N-dodecyl glucamine were combined with several epoxy resins, mainly technical glycidyl ethers of diols. Syntheses involving equimolar amounts of amine resulted in quantitative conversion of the epoxy resins, and epoxide and products could be isolated quantitatively by removing the solvent. Gemini surfactants having hydrophobic or hydrophilic spacers were preparared according to their structures and the hydrophilic properties of the epoxy resin. Surface tensions were measured, and foaming propertiers were examined to characterize surface-active properties of these surfactants. The more hydrophilic products were of particularly high surface activity. Tensiometric studies showed a reduction of surface tension to 30–34 mN/m and critical micelle concentrations in the range of 2–35 mg/L. Comparison of gemini surfactants from long-chain N-alkyl glucamines and diepoxides of α,ω-diolefins (chain lengths: C₈, C₉, C₁₀, and C₁₄) with those based on epoxy resins showed similar or lower surface activities using hydrophobic epoxy resins and much better surface-active properties using hydrophilic epoxy resins (e.g., based on glycerol). This, together with the easier availability, makes the epoxy resin-based products interesting surfactants. Products having very good surface-active properties are available, especially using glycidyl ether of aliphatic diols or glycerol.     

Intelligent polymeric surfaces through molecular self-assembly

Recently, stimuli-responsive surfaces have gained considerable interest among coatings researchers in industry as well as in academe. To date, many switchable surfaces based on such external stimuli as temperature, electricity, pH, and many others have been designed and developed. Environmentally switchable surfaces have been among the most widely studied surfaces since they are known to exhibit smart behavior under external influence. In the present work, we report the synthesis of hydrophobic, hydrophilic, and amphiphilic polyurethane coatings with tethered hydrophilic and/or hydrophobic moieties. These coatings have been characterized and tested for mechanical properties and surface characteristics using such advanced instruments as the scanning probe microscope (SPM), dynamic contact angle analyzer (DCA), adhesion tester, and nanoindenter. The surfaces with tethered hydrophobic or hydrophilic moieties, when immersed in water, showed remarkable changes in the surface topography, hence, their dynamic surface characteristics. The amphiphilic surfaces, containing both hydrophobic and hydrophilic moieties, showed intelligent behavior in response to the external environment. The ability to tailor surfaces with predictable behavior upon exposure to the external environment opens up enormous opportunities for their potential end-use applications. This paper was presented at the FSCT FutureCoat! 2007 Conference, Toronto, Canada, October 3–5, 2007, and was selected as the “best student paper” for the A.L. Hendry Award.     

Protein-water interactions and functional properties

Hydration or rehydration is the first and perhaps most critical step in imparting desired functional properties to proteins in a food system. Water that interacts with the protein molecule exhibits different properties from those of “free” water. The types of water in protein-food systems are described in terms of structural, monolayers, unfreezable, hydrophobic hydration, imbibition or capillary condensation, and hydrodynamic hydration water. Protein functional properties such as swelling, solubility, gelation, water holding capcity, etc., are directly related to the manner in which the protein interacts with water. Methods for studying the protein-water interaction are discussed. The primary protein-water interaction is believed to take place at various water binding sites on the protein molecule. Theories that explain the mechanism of action of these different water binding sites are reviewed. Factors which affect the protein-water interactions include the number and nature of the binding sites on the protein molecule, protein conformation, plus environmental factors such as pH, salt, temperature and others. Finally, the protein-water interaction phenomenon and the physico-chemical and functional properties of proteins in protein isolate systems (dehydrated, solution, and gels) and in protein food systems are briefly examined.     

Shear-thickening in aqueous surfactant-associative thickener mixtures

Associative thickeners represent an important class of rheology modifiers used in waterborne coatings. Understanding molecular level interactions between associative thickeners and surfactants has been the subject of a number of prior studies. Our recent studies focused on the behavior of a hydrophobically modified, aminoplast ether (HEAT) associative thickener and a highly hydrophobic ethoxylated octylphenol surfactant in aqueous solution. Aqueous blends of these two materials exhibit shear-thinning, as well as rarely reported, transient, shear-induced thickening behavior. In addition, the same compositions exhibit both thixotropy and antithixotropy. The shear-induced thickening is shown to be the result of transient aggregated structures formed under shear. Addition of a third component, β-cyclodextrin—a molecule known to disrupt hydrophobic associations—to the mixture helped us advance the understanding of the nature of associative thickener–surfactant interactions that cause the transient shear-thickening behavior. Results indicate that, while overall viscosity of the HEAT/surfactant mixtures is decreased by β-cyclodextrin, the shear-induced thickening is unaffected. An intermolecular interaction model to describe the transient thickening mechanism is presented.     

Surface activities,biodegradability and antimicrobial properties of n-alkyl glucosides,mannosides and galactosides

n-Alkyl α-and β-glucopyranosides, α-D-mannopyranosides and β-D-galactopyranosides with alkyl chains having from 8 to 12 carbon atoms were synthesized and their surface properties-such as static surface tension (γ), critical micelle concentration (CMC), occupation area of molecule, dynamic surface tension and foaming properties, biodegradability and antimicrobial activities—were evaluated. Alkyl glycosides containing C8 to C12 carbon chains showed surface activities and critical micelle concentrations. D-Glucoside, D-mannoside and D-galactoside having the same alkyl chain showed similar surface tension lowering at CMC (γ_CMC) and occupation area of the molecule at the surface. Among the alkyl glucosides, α-anomers were less hydrophilic than β-anomers. All alkyl glycosides tested in this study were readily biodegraded by activated sludge of a municipal sewage plant compared to those of ethoxylated nonionic alcohols. The difference of the hydrophilic glycopyranoside group in biodegradability was not seen clearly. n-Alkyl glycosides containing C8 to C12 alkyl chains showed a broad spectrum of increasing antimicrobial activity. n-Dodecyl α-D-mannopyranoside was the most effective, the order of antimicrobial activity being mannopyranoside > glucopyranoside > galactopyranoside group. Members of this class of compounds exhibit the physicochemical and biological properties needed both for a wide range of applications and for environmental acceptance.     

The Location of Phenolic Antioxidants and Radicals at Interfaces Determines Their Activity

To characterize parameters influencing the antioxidant activity at interfaces a novel ESR approach was developed, which facilitates the investigation of the reaction stoichiometry of antioxidants towards stable radicals. To relate the activity of antioxidants towards the location of radicals at interfaces NMR experiments were conducted. Micellar solutions of SDS, Brij and CTAB were used to model interfaces of different chemical nature. The hydrophilic Fremy’s radical was found to be solubilized exclusively in the aqueous phase of SDS micellar solution but partitioned partly into the hydrophilic headgroup area of Brij micelles. In contrast the hydrophobic galvinoxyl was exclusively located in the micellar phase with the increasing depth of intercalation in the order SDS < Brij < CTAB. Gallates revealed a higher stoichiometric factor towards galvinoxyl in CTAB systems, which is accounted to a concentration effect of antioxidant and radical being both solubilized in the palisade layer. In contrast, in SDS solutions hardly any reaction between galvinoxyl and gallates was found. SDS acted as a physical barrier between radical (palisade layer) and antioxidant (stern layer). The influence of the hydrophobic properties of the antioxidant was clearly seen in Brij micelles. Elongation of the alkyl chain in gallate molecule resulted in increasing stoichiometric factors in the presence of galvinoxyl being located in the deeper region of the bulky headgroup area. The reverse trend was found in the presence of Fremy’s radical being located in the hydrated area of the micelles.     

Crosslinking of latex polymers

The physicomechanical properties and processes of thermal crosslinking of latex acrylic polymer films containing functional groups of different chemical nature were studied. Improvement of properties characteristic of latex copolymers containing methylolamide groups is explained by orientated location of hydrophilic groups on the surface of latex particles during emulsion copolymerisation, that, in its turn, leads to a more ordered arrangement of macrochains. An optimum content of methylolamide groups as regards crosslinking processes was established and explained by steric location of these groups on the surfaces of latex particles. A similar optimum is not observed for crosslinking by watersoluble resin of latex copolymers containing groups of hydrophobic glycidylmethacrylate.     

Some characteristics of polyoxyethylene sorbitol tetra-oleate: Oligomer type emulsifier

Polyoxyethylene (P) sorbitol tetra-oleates with molecular weights of 2000 to 4000 were synthesized. They may be regarded as tetramers of those ordinary surfactants that consist of one hydrophilic and one hydrophobic group. Some emulsifying properties of the tetrameric surfactants were investigated including the phase inversion temperature (PIT, HLB-temperature). These surfactants are effective at relatively low concentration, they are stable for coalescence, and they are less irritating than conventional surfactants. Specifically, they proved to be good emulsifiers for unsaturated triglycerides such as olive oil. The mean droplet diameter of the emulsion was small, 1.5 microns. The emulsifying activity of these oligomer type surfactants for olive oil was improved markedly by the addition of 0.2–0.9 wt % of sodium oleate. Such effective performances of these surfactants have not been recognized in ordinary surfactants. It is expected that these oligomer type surfactants may find applications in various industrial fields.     

$$\pi$$-Conjugated Heterocyclic fused Bithiophene Materials

This article covers the developments on the synthesis and properties of heterocyclic fused π-conjugated bithiophene materials that are potentially applicable in molecular electronics and optoelectronics. This fairly young strategy to efficiently tuning the electronic properties generates materials with very narrow band gaps. The nature of the central bridging heteroatom has a significant impact on the electronic and luminescence properties of these materials leading to intriguing species that can be employed in organic light emitting diodes (OLEDs) or organic field effect transistors (OFETs). So far a variety of heteroelements of group 13–16 (B, Si, Ge, Sn, N, P, S) have been investigated and incorporated into molecular as well as polymeric systems. A significant number of these materials can potentially act as organic emitters, electron or hole transport materials in organic devices but further studies are needed to optimize the necessary properties for the utility of this young class of compound in molecular electronics.     

Synthesis, characterization and evaluation of amphiphilic star copolymeric emulsifiers based on methoxy hexa(ethylene glycol) methacrylate and benzyl methacrylate

Amphiphilic star copolymers were synthesized by sequential monomer and cross-linker additions using group transfer polymerization (GTP). Benzyl methacrylate (BzMA) and methoxy hexa(ethylene glycol) methacrylate (HEGMA) served as the hydrophobic and hydrophilic monomers, respectively, whereas the also hydrophobic ethylene glycol dimethacrylate (EGDMA) was used as the cross-linker. In total, twelve star copolymers were prepared, covering three different overall hydrophobic compositions, 39, 53 and 70% w/w, and four different architectures, AB star-block, BA star-block, heteroarm star and random star. The theoretical molecular weight of each arm was kept constant at 5000 g mol⁻¹. The molecular weights and molecular weight distributions of the linear precursors and of all the star copolymers were characterized by gel permeation chromatography (GPC) in tetrahydrofuran (THF), while their compositions were confirmed by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Moreover, all the star copolymers were characterized by static light scattering (SLS) in THF to determine the absolute weight-average molecular weight, M_w, and the weight-average number of arms. After polymer characterization, xylene-water and diazinon (pesticide)-water emulsions were prepared using these star copolymers as stabilizers at 1% w/w copolymer concentration and at different overall organic phase/water ratios. The most important factor in determining the emulsion type was the star copolymer composition in hydrophobic units. The four most hydrophilic star copolymers (39% w/w hydrophobic composition) always formed o/w emulsions, while the four most hydrophobic star copolymers (70% w/w hydrophobic composition) always formed w/o emulsions. The type of the emulsion in the case of the star copolymers with the more balanced composition, 53% w/w hydrophobic units, also depended on the emulsion content in the organic solvent, similar to particulate-stabilized emulsions. Considering that the best o/w emulsifier is that star copolymer which can emulsify the largest quantity of organic phase in water resulting in low viscosity, o/w emulsions without excess oil or water phase, it appeared that the most hydrophilic random copolymer star is the optimal emulsifier. Moreover, this star copolymer presented the smallest droplet size in its emulsions. It is also noteworthy that the resulting emulsions almost never had high viscosity, a feature attributable to the compact nature of star polymers.