Aggregation Behavior In Aqueous Solution Research Articles

The influence of herbicidal anions on chemical shifts in NMR, phytotoxicity and surface properties of pyrrolidinium surface-active ionic liquids

Abstract Six surface-active ionic liquids (SAILs) with herbicidal anions were synthetized (with a yield of ≥ 88 %) and their structure was confirmed by NMR spectra. Subsequently, their surface properties, phytotoxicity and bulk aggregation behavior in aqueous solution investigated. The compounds studied have an amphiphilic structure and, due to the presence of two long alkyl chains in the cation, they displayed surface activity (CMC values, ranging from 0.13 mmol L−1 to 1.36 mmol L−1). Our results provide explanations for the role of counterions in the physical and chemical properties of SAILs. Indeed, the aromatic anion affects the hydrophilic charge of the surface-active compounds. The SAILs containing the [MCPA]− and [MCPP]− anions were the most phytotoxic to representatives of dicotyledonous plants compared to the other compounds. By analysis of the structure of SAILs, we demonstrate that counterions play an important role in self-assembly and adsorption processes in aqueous solutions, and therefore, in the potential biological application of these compounds.

Dendritic Glycerol-Cholesterol Amphiphiles as Drug Delivery Systems: A Comparison between Monomeric and Polymeric Structures.

The application of micelles as drug delivery systems has gained a great deal of attention as a means to overcome the current several drawbacks present in conventional cancer treatments. In this work, we highlight the comparison of polymeric and monomeric amphiphilic systems with a similar hydrophilic-lipophilic balance (HLB) in terms of their biocompatibility, aggregation behavior in aqueous solution, and potential in solubilizing hydrophobic compounds. The polymeric system consists of non-ionic polymeric amphiphiles synthesized via sequential RAFT polymerization of polyglycerol first-generation [G1] dendron methacrylate and cholesterol methacrylate to obtain poly(G1-polyglycerol dendron methacrylate)-block-poly(cholesterol methacrylate) (pG1MA-b-pCMA). The monomeric system is a polyglycerol second-generation [G2] dendron end-capped to a cholesterol unit. Both amphiphiles form spherical micellar aggregations in aqueous solution, with differences in size and the morphology in which hydrophobic molecules can be encapsulated. The polymeric and monomeric micelles showed a low critical micelle concentration (CMC) of 0.2 and 17 μg/mL, respectively. The results of our cytotoxicity assays showed that the polymeric system has significantly higher cell viability compared to that of the monomeric amphiphiles. The polymeric micelles were implemented as drug delivery systems by encapsulation of the hydrophobic small molecule doxorubicin, achieving a loading capacity of 4%. In summary, the results of this study reveal that using cholesterol as a building block for polymer synthesis is a promising method of preparation for efficient drug delivery systems while improving the cell viability of monomeric cholesterol.

Investigating the Influence of Aromatic Counterions on the Micellar Structure and Aggregation Behavior of Morpholinium-Based Surface-Active Ionic Liquids in an Aqueous Solution.

Two morpholinium-based surface-active ionic liquids (SAILs) with aromatic counterions were synthesized, namely, n-dodecyl-n-methylmorpholinium salicylate [C12mmor][Sal] and n-dodecyl-n-methylmorpholinium 3-hydroxy-2-naphthoate [C12mmor][3-h-2-n], and explored their aggregation behavior in aqueous solutions systematically. Electrical conductivity, small-angle neutron scattering (SANS), surface tension (ST), and UV-vis spectroscopy measurements were employed to determine various thermodynamic, micellar, and interfacial parameters, like the degree of counterion binding (β), critical micelle concentration (CMC), minimum area per molecule (Amin), surface excess concentration (Γmax), standard Gibbs free energy of adsorption (ΔGad0), aggregation number (Nagg), standard Gibbs free energy of micellization (ΔGm0), standard enthalpy of micelle formation (ΔHm0), and the standard entropy of micellization (ΔSm0) in an aqueous solution. Incorporating the aromatic counterions favors significantly excellent micellization properties over conventional halogenated SAILs such as [C12mmor][Br]. SANS analysis revealed that upon changing the counterion from salicylate to 3-hydroxy-2-naphthoate, the structure changed from prolate ellipsoidal micelles to large unilamellar vesicles. Also, increasing the concentration in the case of [C12mmor][Sal] resulted in a lower aggregation number.

Adsorption and Aggregation Behavior in Aqueous Solution of Tetrasiloxane-based Carboxylate Surfactants via "Thiol-ene" Photochemical Reaction.

Anionic silicone surfactants have long been a neglected field. In this paper three anionic silicone surfactants were synthesized first time from dichloromethylvinylsilane through hydrolysis-condensation, "thiol-ene" photo- chemical and then salting reaction. The critical aggregate concentration (CAC), surface tension, minimum surface area per surfactant molecule and surface pressure at CAC were studied by both surface tension and electrical conductivity. The results showed that they had significant surface activity at the gas/liquid interface and were capable to reduce the surface tension of water to approximately 20 mN m-1 . The results of transmission electron microscopy showed that the three silicone surfactants self-assembled into spherical aggregates of uniform size in aqueous solution above the CAC. The dynamic light scattering results demonstrated that the size of the aggregates was determined to be in the range from 60 to 300 nm at 0.05 mol L-1 and the order of the size of the aggregates is (Me3 SiO)3 SiCO2 Li<(Me3 SiO)3 SiCO2 Na<(Me3 SiO)3 SiCO2 K.

Aggregation of magnetic nanoparticles functionalized with trans-resveratrol in aqueous solution

In the framework of a protein–ligand-fishing strategy to identify proteins that bind to trans-resveratrol, a natural phenolic compound with pharmacological benefits, we have developed magnetic nanoparticles covalently linked to trans-resveratrol through three different derivatives and examined their aggregation behavior in aqueous solution. The monodispersed magnetic core (18 nm diameter) with its mesoporous silica shell (93 nm diameter) exhibited a notable superparamagnetic behavior useful for magnetic bioseparation. The hydrodynamic diameter, deduced from dynamic light scattering analysis, of the nanoparticle increased from 100 to 800 nm when the aqueous buffer changed from pH 10.0–3.0. A size polydispersion occurred from pH 7.0–3.0. In parallel, the value of the extinction cross section increased according to a negative power law of the UV wavelength. This was mainly due to light scattering by mesoporous silica, whereas the absorbance cross section remained very low in the 230–400 nm domain. The three types of resveratrol-grafted magnetic nanoparticles exhibited similar scattering properties, but their absorbance spectrum was consistent with the presence of trans-resveratrol. Their functionalization increased their negative zeta potential when pH increased from 3.0 to 10.0. The mesoporous nanoparticles were monodispersed in alkaline conditions, where their anionic surface strongly repulsed each other but aggregated progressively under van der Waals forces and hydrogen bonding when negative zeta potential decreased. The characterized results of nanoparticle behavior in aqueous solution provide critical insight for further study of nanoparticles with proteins in biological environment.

Volumetric Properties and Aggregation Behavior of Aqueous Solutions of Novel 1-Decyl-3-Methylimidazolium-Based Amino Acid Ionic Liquids

Volumetric Properties and Aggregation Behavior of Aqueous Solutions of Novel 1-Decyl-3-Methylimidazolium-Based Amino Acid Ionic Liquids

Layered silicate edge-linked perylene diimides: Synthesis, self-assembly and energy transfer

The control over intermolecular interactions between chromophores at nanomaterial interfaces is important for sensing and light-harvesting applications. To that aim, inorganic nanoparticles with anisotropic shape and surface chemistry can serve as useful supports for organic modification. Herein, novel asymmetric perylene diimides with aspartic acid and oleyl terminal groups were grafted to the edges of the layered silicate clay Laponite, a water-dispersible discoidal nanoparticle. The photophysical properties and solvent-dependent self-assembly of the nanoclay-grafted perylenes were investigated, revealing that the polarity of the terminating ligand dictates the aggregation behavior in aqueous solution, where increased water content generally led to the formation of perylene H-aggregates. The anionic basal surface of the nanoclay provided a binding site for a cationic fluorophore, leading to energy transfer from the face-bound donor to the edge-bound perylene acceptor. This study encourages further research on the use of functional ligands for the formation of organic–inorganic hybrids, particularly where inorganic template particles with specific surface chemistry can be exploited to study intermolecular interactions. Overall, these findings should advance further design and implementation of novel semiconducting ligands towards inorganic–organic hybrids, with potential applications in sensing and energy harvesting.

Synthesis and properties of sodium carboxylate silicone surfactant via thiol-ene “click” reaction

The sodium carboxylate silicone surfactant (Si4-COONa)was synthesized via thiol-ene “click” reaction. Its chemical structure was confirmed by 1H NMR, and ESI-MS. The surface activity and aggregation behavior in aqueous solution were investigated by electrical conductivity, surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Si4-COONa exhibited admirable surface activity and could reduce the water's surface tension to 19.4 mN·m−1. The electrical conductivity showed that the counterion binding value of Si4-COONa increases with increasing temperature. By analyzing the thermodynamic parameters of micellization, it was found that the micellization of Si4-COONa is spontaneous and entropy driven. The addition of inorganic and organic salts in the aqueous solution decreases the critical micelle concentration remarkably. The TEM and DLS results indicated that the Si4-COONa in aqueous solution or salts solution formed spherical aggregates above the critical micelle concentration.

Synthesis and Performance of Double-Chain Quaternary Ammonium Salt Glucosamide Surfactants.

A series of double-chain quaternary ammonium salt surfactants N-[N′[3-(gluconamide)] propyl-N′-alkyl]propyl-N,N-dimethyl-N-alkyl ammonium bromide (CnDDGPB, where n represents a hydrocarbon chain length of 8, 10, 12, 14 and 16) were successfully synthesized from D (+)-glucose δ-lactone, N,N-dimethyldipropylenetriamine, and bromoalkane using a two-step method consisting of a proamine-ester reaction and postquaternization. Their surface activity, adsorption, and aggregation behavior in aqueous solution were investigated via measurements of dynamic/static surface tension, contact angle, dynamic light scattering, and transmission electron microscopy. An analysis of their application performance in terms of wettability, emulsifying properties, toxicity, and antibacterial properties was conducted. The results show that with increasing the carbon chain length of the CnDDGPB surfactants, their critical micelle concentration (CMC) increased and the pC20 and efficiency in the interface adsorption of the target product gradually decreased. Moreover, the influence of the hydrophobic carbon chain length on the surface of polytetrafluoroethylene (PTFE) was even greater for the wetting effect, reducing the contact angle to 32° within the length range of C8–C14. The results of the contact angle change and the wettability experiments proved that C10DDGPB exhibited the best wettability. The liquid paraffin and soybean oil emulsification ability of CnDDGPB showed an upward trend followed by a downward trend with the growth of the carbon chain, with C12DDGPB exhibiting the best emulsification performance. The Dlong/Dshort ratio was far lower than 1, which indicates mixed-kinetic adsorption. The surfactants formed spherical micelles and showed a unique aggregation behavior in aqueous solution, which showed an increase–decrease–increase trend with the change in concentration. A cell toxicity and acute oral toxicity experiment showed that the CnDDGPB surfactants were less toxic than the commonly used surfactant dodecyldimethylbenzyl ammonium chloride (1227). In addition, at a concentration of 150 ppm, CnDDGPB exhibited the same bacteriostatic effect as 1227 at a concentration of 100 ppm. The results demonstrate that sugar-based amide cationic surfactants are promising as environmentally friendly disinfection products.

Multiple strategies to control the hydrophilic-hydrophobic balance of P(DMA-co-DMAEMA-co-QDMAEMA) coatings.

The regulation of the hydrophilic-hydrophobic balance of polymers has an important influence not only on their aggregation behavior in aqueous solution, but also on their adhesion properties on the surface of substrates and the applications of the modified surfaces. Based on this, a random copolymer poly(dopamine methacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(DMA-co-DMAEMA)) was synthesized as a starting polymer to generate P(DMA-co-DMAEMA-co-QDMAEMA) (PDDQ) derivatives by a programmable quaternization of the DMAEMA precursor. By adjusting the pH or temperature, both the aggregation behavior in aqueous solutions and the surface adhesive behavior on the substrate surfaces of PDDQ copolymers were regulated due to the hydrophilic-hydrophobic balance. Specifically, the surface adsorption of PDDQ copolymers on surfaces was enhanced by the increased hydrophobicity of PDDQ. Stainless steel meshes (SSM) modified with the PDDQ0 copolymer without quaternization showed a superoleophobicity in acidic aqueous media, which endowed it with improved oil-water separation performance. In addition, the hydrophilic-hydrophobic balance of PDDQs and their coatings could also be tuned by changing the ratio of DMAEMA to QDMAEMA in the copolymer. From PDDQ0 to PDDQ100, by increasing the hydrophilic QDMAEMA component of PDDQ copolymers, anti-protein properties and oil/water separation efficiency of the modified surfaces were also enhanced gradually. The results provided a reference for designing P(DMA-co-DMAEMA-co-QDMAEMA) coatings in different application environments.

Interfacial and Solution Aggregation Behavior of a Series of Bioinspired Rhamnolipid Congeners Rha-C14-Cx (x = 6, 8, 10, 12, 14).

Rhamnolipids are glycolipids produced by microorganisms with outstanding surfactant properties. They are a class of biosurfactants that are potential candidates for biodegradable and nontoxic replacements of current specialty synthetic surfactants. Building on our previous efforts in developing an efficient and practical chemical methodology to synthesize rhamnolipids allows us to now explore the tunability of rhamnolipid properties. Here, we explore the impact on solution self-assembly and adsorption at the air/water interface of symmetry of the two lipid tails for diastereomeric mixtures of a series of monorhamnolipids of the generic structure Rha-C14-Cx. Surface activity of the anionic forms of these molecules at pH 8 is described by surface tensiometry. Characteristics of their aggregation behavior in aqueous solutions including hydrodynamic radius, aggregation number, and aggregate morphology are determined using dynamic light scattering and time-resolved fluorescence quenching spectroscopy. The solution aggregation behavior of this series is found to unexpectedly vary in a nonmonotonic fashion. This is explained by molecular structural attributes of each series member that result in differences in the respective intermolecular interactions of various parts of these surfactants.

Synthesis and interfacial properties of glyco-lipophosphoramidates

Lipophosphoramidates are a class of amphiphilic molecules that are tunable; and are heavily explored for a variety of industrial and medicinal applications. Self-assembled structures derived from such molecules enhance the bioavailability, selectivity and pharmacokinetic properties of drug molecules. Herein we report the synthesis of novel glyco-lipophosphoramidates (GLP-3, GLP-4, GLP-5, GLP-6) with varying linear and branched hydrocarbon tails via the Staudinger-phosphite reaction. The incorporation of the carbohydrate moiety as the head group region of the amphiphile promotes biocompatibility and biodegradability. Surface activity, adsorption, and aggregation behavior in aqueous solution were examined using surface tension, Langmuir monolayers, and atomic force microscopy (AFM). The critical aggregation concentrations (CAC) and Langmuir isotherms showed the typical dependence on acyl chain structure. Gibbs adsorption profiles provided limiting molecular areas in the range 55–85 Å2. AFM imaging revealed the formation of large spherical aggregates in aqueous solution above the CAC. Dye encapsulation studies support the self-assembly into vesicles by GLP-3, GLP-4 and GLP-5; demonstrating the potential for drug delivery or nanocarrier applications.

Asphaltene Aggregation in Aqueous Solution Using Different Water Models: A Classical Molecular Dynamics Study.

The aggregation behavior of asphaltene in aqueous solution is systematically investigated based on a classical molecular dynamics study. In this work, a novel approach is adopted in order to investigate the structural and dynamical properties of the asphaltene nanoaggregates using different water models. The end-to-end distance of the asphaltene molecule is probed in order to understand the aggregation behavior in aqueous solution. The accuracy of different water models, that is, simple point charge, TIP4P-D, and TIP5P, is thoroughly investigated. In order to probe the dynamical properties of the asphaltene nanoaggregates, the transport coefficients, namely, diffusion coefficient and shear viscosity, are computed. The obtained results highlight the importance of using the appropriate water model in order to accurately study the aggregation behavior of asphaltene in aqueous solution.

Ethylene glycol-rich thermosensitive poly(ß-hydroxyl amine)s

This work illustrates a new molecular design for preparing amphiphilic ethylene glycol-rich poly(ß-hydroxyl amine) polymers. In this design, the backbone and the termini of the side-chain represents hydrophilic parts of the polymer chain. Incorporation of a short hydrophobic alkyl segment between the hydrophilic parts endows an amphiphilic character to the material. Due to this amphiphilic nature, the polymer chains show alkyl-length-dependent thermoresponsive aggregation behavior in aqueous solutions.

Novel dicationic pyrimidine-based nucleolipid bearing piperidine head groups: Synthesis, aggregation behavior, solubilization capacity and interaction with DNA decamer

Novel dicationic nucleolipid bearing piperidine head groups has been synthesized. Using various physico-chemical methods (tensiometry, conductometry, pH-metry, fluorescence spectroscopy, spectrophotometry) its aggregation behavior in aqueous solutions has been examined. It has been revealed, that replacement of ammonium head group by piperidine results in a decrease in aggregation thresholds (critical micelle concentration equals 1.1 mM), as well as affects morphological behavior dramatically. In particular, existence of aggregates with both hydrodynamic diameters of 2 nm and ∼100 nm depending on the amphiphile concentration has been demonstrated. Spectrophotometric analysis has revealed, that fabricated aggregates of nucleolipid exhibit high capability to increase the solubility of lipophilic azodye Orange OT in water. Using dynamic and electrophoretic light scattering techniques interaction of this nucleolipid with double-stranded DNA decamer has been performed. It has been shown, that nucleolipid binds with DNA decamer electrostatically (isoelectric point was found at Camphiphile / Coligonuceotide ∼ 0.5) and forms lipoplexes with hydrodynamic diameter in the range of 300−400 nm.

The Role of Surface Properties on Protein Aggregation Behavior in Aqueous Solution of Different pH Values.

This study aimed to investigate the effect of pH-mediated surface properties of bovine serum albumin (BSA) on protein aggregation and the changes of protein structure and colloidal stability at different solution pH levels. The hydrophobicity of BSA surface was characterized by endogenous fluorescence spectroscopy, fluorescence quenching of acrylamide, and fluorescence probe. The results showed that the hydrophobicity of BSA surface was similar at pH5, 6, 7.4, followed by pH4, 8, 9, 10, and finally by pH3 and 11 with strong acidity and alkalinity. The positive charge on the BSA surface was increased gradually with the decrease of solution pH, while the negative charge on protein surface was increased gradually with the increase of solution pH. The degree of protein aggregation was examined by turbidimetry, flow cytometry, and SDS-PAGE. The results showed that the oscillating aggregation of BSA did not change with the solution pH, but was partially dependent on the relative contribution of electrostatic and hydrophobic interactions between the protein molecules. In addition, the secondary structure, conformational stability, unfolding degree, and colloidal stability of proteins were investigated by circular dichroism, fluorescence spectroscopy, protein pulse hydrolysis, and dynamic light scattering, respectively. The results suggested that the solution pH could change the structure and stability of the protein at different levels. Solution pH has distinct effects on the structural stability of protein at different levels. The change of protein surface properties mediated by solution pH is related to protein aggregation.

Deconstructing poloxamer and poloxamine block copolymers to access poly(ethylene glycol) and poly(propylene oxide)-based thermoresponsive polymers

Poloxamer (Pluronic®) and poloxamine (Tetronic®) are commercially important block copolymers composed of polypropylene oxide (PPO) and polyethylene glycol (PEG) segments. Due to the difference in chemical polarity of the two blocks, the copolymers exhibit amphiphilicity and thermally induced aggregation behavior in aqueous solutions. The present work shows that block copolymer architecture is not necessary to achieve an amphiphilic character in PPO and PEG-based polymers. Instead a simple molecular tweaking by adding a very short hydrophilic or hydrophobic side-chain allows for attaining amphiphilicity and consequential thermoresponsiveness in PEG and PPO-rich polymers.

The Synthesis, Self-Assembled Structures, and Microbicidal Activity of Cationic Gemini Surfactants with Branched Tridecyl Chains

Cationic gemini surfactants with polymethylene spacer and linear alkyl chains containing an even number of carbon atoms have been extensively studied in the recent past, with the emphasis put on the determination of their aggregation behaviour in aqueous solution and their biological properties. However, the information on the aggregation of branched gemini surfactants with an odd number of carbon atoms in their alkyl chains is only sparsely reported in the literature. To help cover this gap in the research of cationic gemini surfactants, a series of branched bisammonium cationic gemini surfactants with an odd number of carbon atoms in alkyl chains (tridecane-2-yl chains) and a polymethylene spacer with a variable length ranging from 3 to 12 carbon atoms have been synthesized and investigated. Critical micelle concentration, which was determined by three methods, was found to be in the order 10−4 mol/L. A comparison of the obtained data of the novel series of tridecyl chain geminis with those of gemini surfactants with dodecyl chains and an identical spacer structure revealed that structural differences between both series of gemini surfactants result in different aggregation and surface properties for surfactants with 6 and 8 methylene groups in the spacer (N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethylhexane-1,6-diaminium dibromide and N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethyloctane-1,8-diaminium dibromide) with the cmc values 8.2 × 10−4 mol/L and 6.5 × 10−4 mol/L, respectively, as determined by surface tension measurements. Particle size analysis showed the formation of small stable spherical micelles in the interval between 2.8 and 5 nm and with zeta potential around +50 mV, which are independent of surfactant concentration and increase with the increasing spacer length. Microbicidal activity of 13-s-13 gemini surfactants was found to be efficient against Gram-positive, Gram-negative bacteria and yeast.

Micellar Aggregation Behavior of Alkylaryl Sulfonate Surfactants for Enhanced Oil Recovery.

Alkylaryl sulfonate is a typical family of surfactants used for chemically enhanced oil recovery (EOR). While it has been widely used in surfactant–polymer flooding at Karamay Oilfield (40 °C, salinity 14,000 mg/L), its aggregation behavior in aqueous solutions and the contribution of aggregation to EOR have not been investigated so far. In this study, raw naphthenic arylsulfonate (NAS) and its purified derivatives, alkylaryl monosulfonate (AMS) and alkylaryl disulfonate (ADS), were examined under simulated temperature and salinity environment of Karamay reservoirs for their micellar aggregation behavior through measuring surface tension, micellar size, and micellar aggregation number. It was found that all three alkylaryl sulfonate surfactants could significantly lower the surface tension of their aqueous solutions. Also, it has been noted that an elevation both in temperature and salinity reduced the surface tension and critical micellar concentration. The results promote understanding of the performance of NAS and screening surfactants in EOR.

Aggregation properties of siloxane surfactants with phenyldimethylsiloxyl groups in aqueous solution

Two siloxane surfactants (Ph-Si3-EO16 and Ph-Si4-EO16) with two or three phenyldimethylsiloxyl groups were successfully synthesized by Piers-Rubinsztajn and thiol-ene reaction. The aggregation behavior in aqueous solution was investigated by surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and freeze-fracture transmission electron microscopy (FF-TEM). Owing to the steric hindrance and hydrophobicity of phenyldimethylsiloxyl groups, Ph-Si3-EO16 (40.4 mN·m−1) and Ph-Si4-EO16 (35.4 mN·m−1) have higher γCMC values. In comparison with Ph-Si3-EO16, Ph-Si4-EO16 has smaller CMC, γCMC, and Amin values attributed to the three phenyldimethylsiloxyl groups and intermolecular interaction. In the aqueous solution of Ph-Si4-EO16, the coexistence of spherical and rodlike aggregates resulting from intermolecular interaction (π-π interactions) was confirmed by TEM and FF-TEM. The results show that phenyldimethylsiloxyl groups play a vital role in the aggregation behavior of siloxane surfactants.