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Amino acid surfactants have been applied to numerous areas of science and are often used in the presence of electrolytes. In this study, the interfacial rheological behaviors of potassium N-cocoyl ...

Polyglycerol monolaurates are generally recognized as safe food additives and are commonly used as food emulsifiers. In this study, the antimicrobial effect of four polyglycerol monolaurates on two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative bacteria (Escherichia. coli and Pseudomonas aeruginosa) were investigated. The minimum inhibitory concentration (MIC) of diglycerol monolaurate (PG2ML), triglycerol monolaurate (PG3ML), hexaglycerol monolaurate (PG6ML), and decaglycerol monolaurate (PG10ML) against S. aureus was 0.16, 0.32, 0.63, and 1.25 mg/mL, respectively. The MIC of PG2ML, PG3ML, PG6ML, and PG10ML against B. subtilis was 0.32, 0.63, 1.25, and 3.75 mg/mL, respectively. No apparent antimicrobial effect of these four polyglycerol monolaurates on E. coli and P. aeruginosa was observed even up to 10.00 mg/mL. The underlying mechanism was investigated by assessing cell membrane permeability, the integrity of cell membrane, and morphology. We concluded that polyglycerol monolaurates might eliminate Gram-positive bacteria by disrupting the cell membrane, thereby increasing cell membrane permeability, releasing the cellular contents, and altering the cell morphology.

Three kinds of polyglycerol fatty acid esters were used as emulsifiers to produce curcumin-loaded nanoemulsions by low-energy emulsification. Characterization of nanoemulsions was performed by meas...

Ion-specific effects widely exist in biological and chemical systems and cannot be explained by classical theories. The complexity of ion-specific effects in protein systems at the molecular level necessitates the use of mimetic models involving smaller molecules, such as amino acids, oligopeptides, and other organic molecules bearing amide bonds. Therefore, it is of theoretical value to determine the effect of additional salts on the aggregation transitions of acyl amino acid surfactants. Herein, the effects of specific tetraalkylammonium ions (TAA

Herein, we report a Pd-catalyzed mono-α-arylation reaction for pyridine benzylic functionalization. This approach serves as an efficient alternative to synthesize di-heteroaryl acetates in good yields and selectivities. Moreover, the method is applicable to heteroaryl substrate combinations, and exhibits great functional group tolerance. A streamlined protocol also enables the rapid synthesis of diheteroaryl ketones. The synthetic value was also demonstrated by scale-up experiments

The transitions between surfactant aggregate structures are triggered by changes in chemical or physical stimulations, including addition of additives. Effects of added alcohols on aggregate morphologies correlate strongly with alcohol chain length. The local molarities of alcohol, water, and counterions in the interfacial regions play an important role in controlling the aggregate morphologies. However, direct experimental estimates of changes of interfacial alcohol molarities during alcohol induced micelle-to-vesicle transitions have never been reported. Ellipsoidal-wormlike micelle-vesicle transitions in CTAB/KBr aqueous solutions in the presence of long-chain octanol were characterized by using combined rheological, dynamic light scattering (DLS), transmission electron microscopy (TEM) and turbidity measurements. However, the transitions are absent with added butanol. The chemical trapping method (CT) was employed to understand the differences between medium- and long-chain alcohols in determining aggregate morphology. The CT method was used to estimate interfacial water, alcohol, and counterion molarities with increasing stoichiometric alcohol concentrations. With 55 mM alcohol added, the interfacial octanol molarity is 0.9 M, which is three times higher than that for butanol. With added octanol, the ellipsoidal-wormlike micelle-vesicle transition is accompanied by a concurrent sharp increase of interfacial water molarities and a decrease of interfacial counterion molarity, which is not observed with added butanol. The CT data was also employed to estimate the changes of Israelachvili's packing parameter with increasing added alcohol concentration. Our result provides critical molecular level information for understanding the morphological transitions of CTAB/additives.

The current research involves fabrication of a redox-responsive self-assembly system based on a ferrocene (Fc)-containing β-cyclodextrin (β-CD) derivative (βCD-EG-Fc). βCD-EG-Fc was synthesized, and its redox-sensitive self-assembly behavior was investigated using various techniques. On the basis of the intermolecular host–guest recognition between the β-CD group and the Fc moiety, βCD-EG-Fc primarily formed network-like structures and then vesicles following aging for a specified time. The formation of these structures was primarily driven by hydrogen bonding. Conversely, the oxidized molecules (βCD-EG-Fc+) self-assembled into cationic vesicles with the absence of host–guest complexation. Upon controlling the oxidation and reduction of Fc/Fc+, reversible aggregate transformation was achieved. The current study resulted in a deeper understanding of β-CD/Fc redox-responsive self-assemblies and contributed to the development of a single-component host–guest inclusion model.

Here we present a pH-responsive self-assembly based on a β-cyclodextrin (β-CD) derivative bearing a dansyl terminus (βCD-C6-Dns). Vesicular structures were formed over the entire studied pH range (8.5-0.7); however, the molecular configuration and packing within the vesicles were different at different pH values. Intramolecular host-guest complexation occurred mainly between the dansyl group and β-CD at pH values where the dansyl group was not protonated. The alkyl chain also acted as a competitive guest to form host-guest inclusions as confirmed by 2D 1H NMR measurements. The pH-responsive βCD-C6-Dns vesicles have potential application prospects in pH-controlled drug release based on the low cytotoxicity of βCD-C6-Dns.

Effect of the numbers of oxypropylene on dynamic interfacial tensions (IFT) of five extended surfactants C12-14PmE2S (m = 0, 3, 5, 8 and 12) were investigated. The effects of electrolyte (NaCl and CaCl2) concentration, salinity, surfactant concentration were studied in detail. The IFTs between C12-14PmE2S aqueous solutions and n-decane obtained ultralow range at optimum NaCl concentration expect C12-14E2S. The optimum salinity (S*) decreased with increase of number of oxypropylene. Also, the IFTs of C12-14P8E2S and C12-14P12E2S approached or obtained ultralow IFT in a wide range of CaCl2 concentrations. The IFTs between C12-14P12E2S aqueous solution and n-decane decreased as salinity increased. With increasing surfactant concentration, the values of IFT decreased initially and then increased.

N-lauroyl-L-Valine sodium (NLLVS) was synthesized and characterized by FT-IR, 1H-NMR spectrometry. Surface and interface tension were measured by wilhelmy plate and spinning drop method. The effect...

The effect of metal ions and surfactants on the enzymatic hydrolysis of pretreated wheat straw lignocellulose was investigated. Scanning electron microscopy, infrared spectrum analysis, dynamic light scattering, and fluorescence spectra analysis were used to characterize the influence of Fe3+/ polyoxyethylene (20) sorbitan monooleate (Tween 80). The interaction between Fe3+/Tween 80 and enzyme was further investigated by enzyme kinetics and enzyme activity measurements. The best synergistic effect was obtained when the ratio of Fe3+ and Tween 80 was 0.06. The scanning electron microscopy images showed that the Fe3+/Tween 80 combination was associated with high porosity substrates. The infrared spectrum analysis indicated that the components of the substrates depended on additive types. The highest relative enzymatic activity increase rate was obtained with added Fe3+/ Tween 80. The Vmax and Km values of the group with added Fe3+/Tween 80 were much higher than that of the group without additives. With the addition of Fe3+/ Tween 80, the intensity of the fluorescence emission peak decreased and the peak shifted towards a longer wavelength.

The development of amino acid surfactants which are considered to be biodegradable and less toxic than traditional surfactants has been a subject of growing interests among chemists for the past 20 years. Within this category, N-acyl amino acid surfactants are popular due to their excellent interfacial properties and antimicrobial activities. In the present work, six new N-acyl amino acid surfactants were synthesized using vegetable oils (castor oil and cottonseed oil) and amino acids (glycine, alanine, and serine). Surface active properties of these surfactants were investigated. With the amide bonds acting as hydrogen bond donors and acceptors, globular and tubular vesicles were observed in the aqueous solutions of some prepared surfactants. The results indicated that hydroxyl groups on the hydrophobic tails for castor oil derivatives were associated with spherical vesicles formation, whereas serine residues bearing hydroxyl groups may be associated with the tubular vesicles.

Ion specific effect, which is also known as Hofmeister effect, has been reported in numerous systems including ionic surfactant aggregates. Acyl amino acid surfactants have attracted growing attentions in the field of novel surfactants research due to their environmentally benign characteristics. The objective of this study was to investigate the effect of different salts containing NH4+ and tetraalkylammonium (TAA+), where alkyl = methyl (TMA+), ethyl (TEA+), and propyl (TPA+), cations on the dilational rheological properties of interfacial film are stabilized by potassium N-cocoyl glycinate (KCGl). The interfacial behaviors were studied using oscillating drop shape analysis method. The interfacial tensions (IFTs) and dilational rheological parameters results illustrate that KCGl in the presence of salts has better interfacial activity and stronger intermolecular interaction, indicating that added cations contribute to denser molecular packing at oil-water interface. Ion specific effects were observed in the system. Among the cations, KCGl shows highest dilational modulus in the presence of NH4+. The overall interaction between cations and headgroups of KCGl decreases in the sequence NH4+ >TMA+ >TEA+ ≈TPA+, which follows Hofmeister series. The increasing hydrophobicity of TAA+ prevents the interaction between cations and KCGl's headgroup, and therefore prevent amphiphiles from packing closely at interface. The results present a theoretical origin for useful application of KCGl in cosmetics, petroleum and daily chemical industries.

The foam and rheological properties of four extended surfactants C12–14PmE2S (m = 0, 3, 5, and 8) of four different concentrations were investigated in this paper. The foam properties, including, foamability, foam stability, liquid carrying ability, foam drainage and foam morphology were characterized. The rheological measurements were carried out through frequency sweep in the oscillation mode. The foamability and foam stability decreased with increasing numbers of PO groups embedded in those surfactants. At the same concentration, the longer the PO chain of the surfactant molecule, the larger the liquid carrying capacity of the foam. The foaming number decreases as the time increases, and longer PO chains were associated with faster foam number decline. The rheological measurements show that those surfactant solutions are “liquid-like”. With increasing surfactant concentration, the viscous modulus of C12–14P8E2S increases gradually, whereas that of C12–14E2S decreases.

A new series of gemini quaternary ammonium surfactants containing amide groups with the formula CnH2n+1CONH(CH2)2N+(CH3)2(CH2)2 N+(CH3)2(CH2)2NHCOCnH2n+1·2CH3CO3– (n = 11, 13, 15, 17) have been synthesized by the using green reagent dimethyl carbonate. The structures of these surfactants were confirmed by Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, and mass spectra. Their surface activities and aggregation properties were investigated by surface tension, conductivity, steady-state fluorescence, dynamic light scattering, and transmission electron microscope measurements. The results show that these synthesized gemini quaternary ammonium surfactants reduce the surface tension of water to a minimum value of 28.21 mN·m–1 at a concentration of 0.256 mmol·kg–1 and self-assemble spontaneously into double layer aggregates which are mostly single-room vesicles and multilamellar vesicles. Furthermore, with increasing alkyl chain length, their critical micelle concentration values and the degree of cou...

With the growing concern about safety and environmental issues, amino acid-based surfactants have great potential as sustainable and eco-friendly substances. In the present study, six N-acyl oligopeptide surfactants were synthesized using fatty acid methyl esters (i.e., methyl caprate, methyl laurate, and methyl myristate) and glycyl oligopeptides (i.e., glycylglycine and glycylglycylglycine). Surface active properties and aggregation behaviors of these surfactants were investigated using surface tension, fluorescence probe, dynamic light scattering, and microscopy measurements. The adsorption at the air-water interface and aggregation in the aqueous solution depend on the structure of both hydrophilic head-groups and hydrophobic tails. Spherical vesicles were observed in the aqueous solutions of glycylglycine derivatives, whereas short tubular aggregates were found in that of corresponding glycylglycylglycine products. Intermolecular hydrogen-bonding interaction between the amide head-groups might be responsible for the different self-assembly behavior and microstructure of N-acyl oligopeptide surfactants in the aqueous solution.

Denaturant effect of urea has been interpreted by two mechanisms, the direct interaction of the additive with biomolecules or lyophilic colloidal aggregates or the indirect mechanism via rupture of the water 3D structure. In contrast we focused that urea produces a higher polarity of aqueous mixtures that causes the denaturation. In the realm of this effect is how charges, dipoles and so in solutions and in suspensions are stabilized by urea addition. For example, ion association is in the center of the interactions that leads to ionic micelle formation. Here, using 79Br NMR line broadening and solubility data of bis (tri-methyl)-α,ω-alkanediammonium, (1-n-1)Br2 (n = 2-4) (bolaform salts) and of tetramethylammonium bromide and the effect of adding perchlorate, we demonstrated the effect of urea in weakening ion pair association and stabilizing solvent separated ions. The high association constant of perchlorate with ammonium salts was used to titrate the ammonium-bromide interactions. Bromide counterions in bolaform salts derivative having two, three, and four methylene spacers or in tetramethyl ammonium salts were replaced by perchlorate. Although addition of urea to water is well known to lead to an increase of the dielectric permittivity, urea leads to a decrease of anion selectivity and the new pairs bind unspecific both anions. Since ion pairing between ionic surfactants head groups and its counterions is directly correlated to the critical micelle concentration (CMC) values, “loss of selectivity” explains the increase in the ionic surfactants CMC’s with increase in urea concentration.

An efficient protocol for [2,3]-sigmatropic rearrangement of allyl and propargyl thioethers is reported. The key sulfonium ylide intermediate is in situ formed via S-arylation of arynes. This transition metal-free method allows for ready access to a wide array of functionalized thioether derivatives in good to excellent yields.

A delicate balance-of-forces governs the interactions responsible for surfactant self-assembly and chemical reactivity within them. Chemical reactions in micellar media generally occur in the interfacial region of micelles that is a complex mixture of: water, headgroups, counterions, co-ions, acids or bases, organic solvents, and the reactants themselves. We have carried out a detailed study of a complex chemical reaction in mixed CTAB/C12E6 micelles by using the chemical kinetic (CK) and chemical trapping (CT) methods. The results provide a detailed quantitative treatment of the reaction of the anion of the antioxidant t-butylhydroquinone, TBHQ−, with 4-hexadecylbenzenediazonium, 16-ArN2+, within the interfacial region of the mixed micelles in the C12E6 mole fraction range of 0 to 1 at three different total surfactant concentrations. CK experiments showed that this reaction is monophasic in C12E6 micelles, but biphasic in mixed micelles. The results were fully consistent with a complex mechanism in which TBHQ− reacts with 16-ArN2+ to give a transient diazoether intermediate that competitively breaks down into products and or reverts to starting materials. The kinetics are the same in mixed micelles of CTAB/C12E6 (grow) and CTAB/C12E8 (don’t grow) showing that the rates only depend on micelle composition, not shape. CT results provided estimates of interfacial molarities of H2O are approximately constant at ca. 39 and Br− decreases from ca. 2.75 to 0.05 moles per liter of interfacial volume as C12E6 mole fraction increases from 0 to 1. Combined CK/CT results provided values for interfacial pH, ranging from ca. 4.25 in cationic micelles to 1.5 in nonionic micelles despite a constant bulk pH of 1.5 and the TBHQ interfacial pKa = 3.8 at all C12E6 molar fractions. In totality, these results yielded an extraordinary amount of quantitative information about the relationships between the chemical reactivity and interfacial compositions of the mixed micelles.

Decaglycerol laurates have been widely used as emulsifiers in food, medicine, and cosmetic industries for many years. Currently, they are synthesized using alkaline catalysts under stringent conditions. Here, decaglycerol laurates were prepared through a green lipase-catalyzed process, employing the transesterification of methyl laurate with decaglycerol by the immobilized lipase (Novozym 435). Single-factor experiments and orthogonal test were used for reaction optimization. The optimum conditions were obtained as follows: reaction temperature of 65°C, a laurate/decaglycerol molar ratio of 2 : 1, an oscillating speed of 180 rpm, an enzyme dosage (based on amount of methyl laurate) of 8 wt.%, initial water content (based on the total substrate mass) of 5.0 wt.%, and reaction time of 4.5 h with 84.4% conversion of methyl laurate. The transesterification products were identified by electrospray ionization mass spectrometer. In addition, the surface activity of decaglycerol laurates was also characterized, and the surface tension of water was reduced to 33 mN·m−1 at a concentration magnitude of 10−5 g/mL.

Polyimide (PI) films with ultralow coefficient of thermal expansion (CTE) and high glass transition temperature (Tg) are in great demand for applications as substrates in flexible displays. Furthermore, trade-off between CTE and toughness is highly concerned due to strategies for reducing CTE always result in weakness of toughness. In this work, we developed a facile method to improve dimension stability and toughness of PI containing benzimidazole units via regulating entanglement density based on controlling molecular weight and solid content of precursor polyamic acid (PAA) solution. As a result, the Tg of PI films increased from 394.3 to 441.4 °C and the in-plane CTE (40–350 °C) decreased from 65.7 to 3.9 ppm/K with entanglement density increasing from 253.3 to 2868.6 mol/m3. Moreover, mechanical properties especially toughness of PI films were enhanced significantly (from 7% to 18%) as entanglement density increased. In short, we delineated the effects of entanglement on the properties of PI films and found that the decrease of CTE mainly arises from the increase of entanglement density. Our studies provide new insights into the future design of flexible PI substrates with low CTE.

Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with increasing alkyl chain length of a particular AO. We conclude with perspectives and prospects.

A delicate balance-of-forces governs the interactions responsible for surfactant self-assembly and chemical reactivity within them. Chemical reactions in micellar media generally occur in the interfacial region of micelles that is a complex mixture of: water, headgroups, counterions, co-ions, acids or bases, organic solvents, and the reactants themselves. We have carried out a detailed study of a complex chemical reaction in mixed CTAB/C

Herein, a photo-responsive mono-component self-assembly system based on host-guest inclusion complexation is presented. An azobenzene group was linked to a β-cyclodextrin by an alkyl chain, generating a novel amphiphile βCD-C6-Azo. The prepared βCD-C6-Azo molecules showed reversible aggregate behavior due to photo-isomerization of azobenzene. In the case of trans-form βCD-C6-Azo system, intermolecular host-guest complexes between β-CD and azobenzene were formed, which were verified by 2D 1H NMR analysis, and further self-assembled into curved linear structures in water driven mainly by hydrogen bonding. Dissociation of cis-azobenzene group from β-CD cavity was achieved upon irradiated by UV light, leading to the aggregate transformation into vesicles.