Construction of a highly sensitive detection platform for heparin based on a "turn-off" cationic fluorescent dye.

A highly sensitive detection platform for heparin was constructed via the utilization of a commercially available cationic fluorescent dye (cresyl violet acetate, CV) as a fluorescence probe. The electrostatic binding between CV and heparin quenched the fluorescence in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic (HEPES) buffer solution (10 mM, pH 7.1). CV was highly selective towards heparin over other potential inferring substances. The detection limit of heparin detection was 5.19 ng/mL, and the linear working range was 0 ∼ 1 µg/mL in HEPES solution. In 1 % serum, the detection platform based on the fluorescence "turn-off" behavior of CV was also successfully constructed with a detection limit of 5.86 ng/mL in the linear range of 0 ∼ 0.8 µg/mL. Moreover, the CV-heparin complex was considered a potential sensor platform for the detection of protamine because of its stronger affinity for heparin and protamine.

The Spontaneous Vesicle-Micelle Transition in a Catanionic Surfactant System: A Chemical Trapping Study.

Typically, the formation of vesicles requires the addition of salts or other additives to surfactant micelles. However, in the case of catanionic surfactants, unilamellar vesicles can spontaneously form upon dilution of the micellar solutions. Our study explores the intriguing spontaneous vesicle-to-micelle transition in catanionic surfactant systems, specifically cetyltrimethyl ammonium bromide (CTAB) and sodium octylsulfonate (SOS). To gain insights into the changes occurring at the interface, we employ a chemical trapping method to characterize variations in the molarities of sulfonate headgroups, water, and bromide ions during the transition. Our findings reveal the formation of ion pairs between the cationic component of CTAB and the anionic component of SOS, leading to tight interfacial packing in CTAB/SOS solutions. This interfacial packing promotes vesicle formation at low surfactant concentrations. Due to the significant difference in critical micelle concentration (cmc) between CTAB and SOS, an increase in the stoichiometric surfactant concentration results in a substantial rise in the SOS-to-CTAB ratio within the interfacial region. This enrichment of SOS in the aggregates triggers the transition from vesicles to micelles. Overall, our study may shed new light on the design of morphologies in catanionic and other surfactant systems.

Interfacial Composition of Surfactant Aggregates in the Presence of Fragrance: A Chemical Trapping Study.

In recent years, there has been increasing interest in daily-use chemical products providing a pleasant scent. The added fragrance molecules may induce microstructural transitions of surfactant aggregates, which further affect the physical and chemical properties of the products. Here, the effects of four types of aromatic alcohols (cinnamyl alcohol, phenyl ethanol, phenyl methanol and anisyl alcohol) on cetyltrimethylammonium bromide (CTAB)/KBr aggregates were studied. The combined results from rheology, dynamic light scattering, and transmission electron microscopy measurements showed that cinnamyl alcohol induced significant micellar growth, while increases in micellar growth were less obvious for the other aromatic alcohols. The changes in the interfacial molarities of water, aromatic alcohol, and bromide ions during such transitions were studied using the chemical trapping method. Transitions resulting from added cinnamyl alcohol were accompanied by significant declines in interfacial water and bromide ion molarities, and a rise in interfacial alcohol molarity. The marked decrease in interfacial water molarity was not observed in previous studies of the octanol induced formation of wormlike micelles and vesicles, indicating that a different mechanism was presented in the current system. Nuclear magnetic resonance investigation showed that π-π stacking between cinnamyl alcohols, but not cation-π interactions between alcohols and CTAB headgroups, facilitated the tight packing of alcohol molecules in CTAB aggregates and the repulsion of water from the interfacial region. The current study may provide a theoretical basis for the morphological regulation of surfactant aggregates in the presence of additives.

Ion-Specific Effects on Vesicle-to-Micelle Transitions of an Amino Acid Surfactant Probed by Chemical Trapping.

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+) on sodium lauroyl glycinate (SLG) aggregation were studied by dynamic light scattering (DLS) and transmission electron microscopy. Although previous studies have shown that the kosmotropic TAA+ ions tend to induce micellar growth or micelle-to-vesicle transitions of some anionic surfactants, TAA+ addition in the present study induced partial vesicle-to-micelle transitions in SLG solutions. The chemical trapping (CT) method was employed to estimate changes in the interfacial molarities of water, amide bonds, and carboxylate groups during such transitions. The vesicle-to-micelle transitions were accompanied by a marked rise in interfacial water molarity and a decline in interfacial amide bonds molarity, suggesting that the hydrated TAA+ entered the interfacial region and disrupted hydrogen bonding, thus preventing the SLG monomers from packing tightly. Molecular dynamic simulation was also performed to demonstrate the salt-induced cleavage of amide-amide bonds between SLG headgroups. Furthermore, both CT and DLS results show that the ability of tetraalkylammonium cations to induce such transitions increased with increasing size and hydrophobicity of the cation, which follows the Hofmeister series. The current study offers critical molecular-level evidence for understanding the specific effects of tetraalkylammonium ions on the aggregation transitions of an acyl amino acid surfactant.

Construction of a pH-sensitive self-assembly in aqueous solutions based on a dansyl-modified ß-cyclodextrin.

Here we present a pH-responsive self-assembly based on a ß-cyclodextrin (ß-CD) derivative bearing a dansyl terminus (ßCD-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 ß-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 ßCD-C6-Dns vesicles have potential application prospects in pH-controlled drug release based on the low cytotoxicity of ßCD-C6-Dns.

In vitro Antibacterial Effect of Polyglycerol Monolaurates against Gram-Bacteria and Understanding the Underlying Mechanism.

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.

Effect of Added Tetraalkylammonium Counterions on the Dilational Rheological Behaviors of N-Cocoyl Glycinate.

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.

Simultaneous determination of interfacial molarities of an alcohol, bromide ion, and water during an alcohol induced microstructural transition: the difference between medium and long chain alcohols.

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.

Fabrication of a ß-cyclodextrin-based self-assembly containing a redox-responsive ferrocene.

The current research involves fabrication of a redox-responsive self-assembly system based on a ferrocene (Fc)-containing ß-cyclodextrin (ß-CD) derivative (ßCD-EG-Fc). ßCD-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 ß-CD group and the Fc moiety, ßCD-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 (ßCD-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 ß-CD/Fc redox-responsive self-assemblies and contributed to the development of a single-component host-guest inclusion model.

Highly Selective Synthesis of Monolaurin via Enzymatic Transesterification under Batch and Continuous Flow Conditions.

This study aimed to investigate the highly selective production of monolaurin via enzymatic transesterification of methyl laurate and glycerol. It was determined that a binary solvent system (tert-butanol/iso-propanol, 20:80, wt./wt.) was suitable for the enzymatic production of monolaurin, especially in the continuous process. The highest mass fraction of monolaurin in the product mixture (80.8 wt.%) was achieved in a batch mode under the following conditions: a methyl laurate-to-glycerol molar ratio of 1:6, a substrate concentration (methyl laurate in the binary solvent) of 15 wt.%, an enzyme dosage of 6 wt.% of the amount of methyl laurate, and a reaction time of 1.5 h at 50°C. Compared with the results under the batch conditions, a slightly higher yield of monolaurin (82.5 ± 2.5 wt.%) was obtained in a continuous flow system at a flow rate of 0.1 mL/min, while the mass fraction of dilaurin in the product mixture was only 0.7 ± 0.6 wt.%. In addition, the yield of monolaurin remained almost unchanged during the 18 tested days of the continuous experiment.

Effects of interfacial specific cations and water molarities on AOT micelle-to-vesicle transitions by chemical trapping: the specific ion-pair/hydration model.

Salt induced micelle-to-vesicle transitions of ionic surfactants depend on the surfactant chain length, headgroup structure, counterion type and concentration, but the interfacial molarities of counterions and water that balance the hydrophobic effect are difficult to determine. In anionic micelles of twin-tailed sodium bis(2-ethylhexyl)sulfosuccinate (AOT), the chemical trapping (CT) method provides estimates of the interfacial molarities of anionic headgroups (RSO3-m) and neutral (H2Om) nucleophiles during salt induced transitions of AOT micelles to vesicles. Product yields were measured by HPLC from the competitive dediazoniation reaction using a specially designed hydrophobic probe, 4-hexadecyl-2,6-dimethylbenzenediazonium cation, 16-ArN2+. The reactions were run at constant concentration of 15 mM AOT mixed with 0 to 50 mM added salts, containing cations of different sizes and valences including tetraalkylammonium cations (MR4+, R = 1-4) and metal cations (M1-3+). Parallel reactions in aqueous salt solutions with a short chain analog, 1-ArN2+, were used as references to calculate interfacial molarities. Aggregates were structurally characterized by TEM and DLS. Typically, interfacial RSO3- molarities increase with added salts from 1 to 2 M and water molarities decrease from about 40 to 20 M with the micelle to vesicle transition. These changes are consistent with the ion-pair/hydration model, in which the added cations form neutral but polar ion-pairs with RSO3- that have a lower demand for hydration and water was released into the surrounding aqueous phase. The extent of ion-pairing increases with cation size, charge and hydrophobicity and decreases with interfacial water molarity, which permits tighter interfacial packing and vesicle formation at lower added salt concentrations.

Aryne triggered [2,3]-sigmatropic rearrangement of allyl and propargyl thioethers.

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 novel combined chemical kinetic and trapping method for probing the relationships between chemical reactivity and interfacial H2O, Br- and H+ ion molarities in CTAB/C12E6 mixed micelles.

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.

To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.

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.