Self-assembly Behavior In Water Research Articles

Self-Assembly, In Vitro Gene Transfection, and Antimicrobial Activity of Biodegradable Cationic Bolaamphiphiles.

Bolaamphiphiles or bolaforms have drawn particular interest in drug and gene delivery, and studies of bolaforms have been growing continuously. Bolaforms, due to their unique structure, exhibit specific self-assembly behavior in water. The present work aims to develop biodegradable cationic bolaforms with a better gene transfection ability. In this work, a novel cationic bolaform (Bola-1) with head groups bearing hydroxyl (OH) functionality was designed and synthesized to investigate self-assembly and gene transfection efficiency. The self-assembly behavior of Bola-1 in water was compared with that of the hydrochloride salt (Bola-2) of its precursor molecule to investigate the effect of the -OH functionality on their solution properties. Several techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy, were employed for the physicochemical characterization of Bola-1 and Bola-2. Despite the presence of polar urea groups in the spacer chain, both bolaforms were found to form spherical or elongated micelles above a relatively low critical aggregation concentration (CAC). The presence of the OH group was found to significantly affect the CAC value. The results of calorimetric measurements suggested a thermodynamically favorable aggregate formation in salt-free water. Despite stronger binding efficiency with calf thymus DNA, in vitro gene transfection studies performed using adherent cell Hek 293 suggested that both Bola-1 and Bola-2 have gene transfection efficiency comparable to that of turbofectamine standard. Both bolaforms were found to exhibit significant in vitro cytotoxicity at higher concentrations. Also, the bolaforms showed beneficial antibacterial activity at higher concentrations.

Physico-chemical characterization of Synperonic™ 91/5 self-assembly behaviour in water

We studied the self-assembled aggregates of Synperonic™ 91/5 (SYN) in water solution. This surfactant presents the peculiarity of having an odd number of aliphatic carbons, with a tail composed of C9H19 and C11H23, and the headgroup having an average of 5 ethoxy units. While the general family of CiEOj nonionic surfactants has been widely studied, there is little knowledge for the case of surfactants with odd-number carbons. For this reason, we carried out an in depth physico-chemical characterization of water solutions containing SYN in the wide range of concentration from 2 % to 50 % (i.e. 0.05–1.4 M), considering that high concentrated systems are relevant for industrial applications. This class of surfactants is also interesting as remediation agent since they can incorporate different polluting molecules, both polar and nonpolar, such as volatile Organic Compounds (VOCs) and Dense Non Aqueous Phase liquids (DNAPLs). The rheological and transport properties of SYN solutions were investigated through diffusion coefficients and viscosity, while shape and size of self-assemblies were determined by Dynamic Light Scattering and by Small Angle Scattering of Neutrons (SANS) and X-rays (SAXS). Results show that SYN generally behaves as other nonionic surfactants in dilute solutions, but shows some peculiarity of aggregate packing at high concentration. We recently demonstrated the efficiency of the Synperonic™ family of surfactants in solubilising trichloroethylene (TCE), in particular above a critical concentration of 0.1 M, thus being a good candidate for remediation purposes. Here, the solubility of TCE was correlated with the number and the size of micelles at different surfactant concentrations. Our work helps filling a gap in the literature about technical grade surfactants with odd-number carbons, and the results can help in assessing the performances of Synperonic™ products for technical tasks.

Random ionic polymers: Salt-triggered reversible vesicular self-assembly in water

NaCl salt as an external stimulus triggers the self-assembly of ionic polymers and offers a convenient route to structuring vesicular reversible polymeric nanoparticles. In this contribution, amphiphilic random imidazolium ionic polymers are synthesized by roping the partial anion exchange and the choice of N-substituent. These polymers are evaluated for their self-assembly behavior in water, and it is strengthened by dye encapsulation application in water through self-assembly. The effects of salt and pH study demonstrated the reversibility of self-assembly. The self-assembled nano-aggregates are thermoresponsive at the upper critical solution temperature (UCST) (Cp 47 °C). The synergic balance between hydrogen bonding and ionic self-assembly is attributed to the constituents in the macromolecular structure, making these polyionic liquids (PILs) a “smart” responsive system in water upon the addition of external stimuli, such as NaCl and KPF6. This self-assembly is acquired with partial anion exchange and salt balance in the water. The unusual interfacial activity of polymer to form a regular shape eventually to surfaces organic dye molecule serving as a type of stabilizer or scavenger evidenced by nano-size and vesicular morphology analysis.

Removal of anionic and cationic dyes from aqueous solution using thermo- and pH-responsive amphiphilic copolymers

Amphiphilic copolymers exhibiting thermally induced phase segregation in water hold great potential as smart flocculants for water purification. Herein, we report the preparation of thermo- and pH-responsive copolymers based on oligo(ethylene glycol) methacrylate (OEGMA), dimethylaminoethyl acrylate (DMAEA) and pentafluorostyrene (PFS), and their use as thermally induced adsorbents for the removal of anionic and cationic dyes from water. The copolymer self-assembly behaviour in water was first studied as a function of concentration and pH. Then, the potential to remove thiazole yellow G (TYG) and rhodamine B (RhB) was investigated as a function of pH and dye concentration, highlighting that dye removal is mediated by hydrophobic and electrostatic interactions. As regards TYG, at pH 4 a removal capacity (RC) of about 80 mg/g, corresponding to a 97 % dye removal efficiency, was achieved at 800 mg/L TYG. In the case of RhB, a maximum RC value of 32 mg/g was obtained at pH 10. The results reported herein show that these copolymers represent a versatile platform to remove water-soluble organic dyes depending on pollutant concentration and pH conditions.

Nanobowls from Amphiphilic Core–Shell Cyclic Bottlebrush Polymers

Cyclic bottlebrush polymers are macrocycles that contain pendent side-chain polymers on nearly every repeat unit. We leveraged a method to generate cyclic bottlebrush polymers utilizing ring-expansion polymerization (REP) followed by subsequent grafting-from via atom-transfer radical polymerization (ATRP) to produce core–shell cyclic bottlebrush polymers and investigated their self-assembly behavior in water. The bottlebrush polymers were comprised of a cyclic backbone with side chains composed of a hydrophobic polystyrene block and a hydrophilic poly(acrylic acid) block. A two-step morphological transformation from spheres to porous spheres to nanobowls (spheres with a single large pore) was observed with solvent exchange from tetrahydrofuran to water. In contrast, under identical experimental conditions, an analogous linear bottlebrush polymer with a similar backbone and side chain degrees of polymerizations did not aggregate into nanobowls but rather exhibited a porous sphere morphology. These unusual morphologies and their propensities to transform can be attributed to changes in the internal viscosity of the aggregates during the solvent exchange process. Additionally, the rate of solvent exchange was found to influence the propensity for shape transformation to occur.

Single-chain folding and self-assembling of amphiphilic polyethyleneglycol-modified fluorinated styrene homopolymers in water solution

Amphiphilic tetrafluorostyrene monomers (EFSn) carrying in the para position a polyethyleneglycol (PEG) chain with varied lengths (n = 3–13) were synthesized and polymerized by ARGET-ATRP to obtain the corresponding amphiphilic homopolymers pEFSn-x with controlled and tailored polymerization degrees (x = 8–135). All polymers presented a reversible thermoresponsive LCST-type behavior, in water/methanol mixture when n ≤ 4 or in pure water when n ≥ 8, with a cloud point (Cp) temperature in the range 30–40 °C strictly dependent on the length of the PEG side chain. Combined small angle X-scattering (SAXS) and dynamic light scattering (DLS) measurements were used to study the self-assembly behavior in water of the water-soluble amphiphilic homopolymers. SAXS confirmed the formation of compact-sized and spherical single-chain self-folded nanostructures below Cp, that generally presented small hydrodynamic diameters (Dh ≤ 11 nm) as proven by DLS analysis. Above Cp, much larger multi-chain aggregates were formed (Dh ≥ 800 nm), that reversibly turned back to collapsed nanostructures on cooling below the Cp temperature. By contrast, the polymers were not able to self-assemble in THF or DMF solutions, in which they adopted conventional random coil conformations.

Overcoming the Necessity of a Lateral Aggregation in the Formation of Supramolecular Polymer Bottlebrushes in Water

In article number 2000585 by Johannes C. Brendel and co-workers, 1,3,5-benzenetrisurea-polyethylene oxide conjugates equipped with different amino acids are examined for their self-assembly behavior in water. One amino acid unit per arm results in spherical micelles, whereas introducing two amino acid units, and thus increasing the number of hydrogen bonds per molecule, enables the formation of supramolecular polymer bottlebrushes despite the absence of any lateral aggregation.

Tuning lipid structure by bile salts: Hexosomes for topical administration of catechin

The delivery of bio-active molecules through the skin is challenging given the complex structure of its outer layer, the stratum corneum. Here we explore the possibility to encapsulate natural compounds into nanocarriers containing permeation enhancers that can affect the fluidity of the stratum corneum lipids. This approach is expected to facilitate dermal or transdermal release. For this purpose, the application of bile salts, which are natural surfactants involved in vivo in lipid digestion, was exploited.Bile salts were added to lipid liquid crystalline nanoparticles (NPs) made of monoolein for antioxidant topical delivery. Monoolein self-assembly behaviour in water was affected by the presence of bile salts molecules, giving a transition from a bicontinuous cubic to unilamellar vesicles dispersion. By adding oleic acid (OA), the change of curvature in the system led to a reverse hexagonal phase. The morphology, structure and size of the nanocarriers was investigated before the nanoparticles were loaded with catechin, a natural antioxidant occurring in plants and food. The encapsulation did not affect significantly the formulation phase behaviour. The formulation loaded with bile salts and catechin was thereafter tested in vitro on the skin from new-born pig. The results for two different lipid formulations without bile salts were compared under the same experimental conditions and with the same antioxidant. The formulation with bile salts showed the best performance, allowing a superior permeation of catechin in the different skin layers in comparison with formulations without bile salt.

Light-Gated Nano-Porous Capsules from Stereoisomer-Directed Self-Assemblies.

Structuring pores into stable membrane and controlling their opening is extremely useful for applications that require nanopores as channels for material exchange and transportation. In this work, nanoporous vesicles with aggregation-induced emission (AIE) properties were developed from the amphiphilic polymer PEG550-TPE-Chol, in which the hydrophobic part is composed of a tetraphenylethene (TPE) group and a cholesterol moiety and the hydrophilic block is a poly(ethylene glycol) (PEG, Mn = 550 Da). Two stereoisomers, trans-PEG550-TPE-Chol and cis-PEG550-TPE-Chol, were successfully synthesized. These thermally stable stereoisomers showed distinct self-assembly behavior in water: trans-PEG550-TPE-Chol formed classical vesicles, while cis-PEG550-TPE-Chol self-assembled into cylindrical micelles. Interestingly, trans/cis mixtures of PEG550-TPE-Chol (trans/cis = 60/40), either naturally synthesized without isomers' separation during the synthesis or intentionally mixed using trans- and cis-isomers, constructed perforated vesicles with nanopores. Moreover, under the illumination of high intensity UV light (365 nm, 15 mW/cm2), the classical vesicles of trans-PEG550-TPE-Chol were perforated by its cis counterparts generated from the trans-cis photoisomerization, while the cylindrical micelles of cis-PEG550-TPE-Chol interweaved to form meshes and nanoporous membranes due to the trans-isomers produced by cis-trans photoisomerization. All of these assemblies in water emitted bright cyan fluorescence under UV light, while their constituent molecules were not fluorescent when solubilized in organic solvent. The AIE fluorescent normal vesicles and nanoporous vesicles may find potential applications in biotechnology as light-gated delivery vehicles and capsules with nanochannels for material exchange.

PH-Induced Transition Between Single-Chain Macrocyclic Amphiphile and [c2]Daisy Chain-Based Bola-Type Amphiphile and the Related Self-Assembly Behavior in Water.

Macrocyclic amphiphiles, a type of amphiphiles synthesized based on macrocyclic compounds, have attracted much attention over the past decades due to their unique superiority in the construction of various functional nanomaterials. The regulation of the state of macrocyclic amphiphiles by introducing stimuli-responsive motif to macrocyclic amphiphiles is an efficient way to extend their applications in diverse fields. Herein, pillararene-based macrocyclic amphiphile H1 was prepared. H1 can act as single-chain amphiphile to self-assemble into micelles in water when the pH was ≥5.0. H1 can be protonated to turn into H2 when pH changed to <5.0. Interestingly, H2 formed [c2]daisy chain-based bola-type supramolecular amphiphile. This bola-type supramolecular amphiphile self-assembled into nanosheets in water. Therefore, pH-induced transition between single-chain macrocyclic amphiphile and bola-type amphiphile and the corresponding self-assembly system based on pillararene in water were constructed.

Visible-Light-Controlled Reaction-Separation for Asymmetric Sulfoxidation in Water with Photoresponsive Metallomicelles

Metallomicellar catalysis has gained increasing attention in recent years since it made water-incompatible organometallic catalysis highly efficient in water. However, a convenient approach to combine activity and recovery of metallomicelles from aqueous systems has remained challenging to date. Herein, we developed a series of nitrospiropyran-containing metallomicelles which possessed visible-light-responsivity, to realize the visible-light-controlled reaction and separation for asymmetric sulfoxidation in water. A series of nitrospiropyran-containing diblock chiral salen TiIV copolymers were thus prepared by copolymerizing photosensitive nitrospiropyran derivative with hydrophobic chiral salen TiIV monomer via free-radical polymerization. Characterization results suggested their visible-light-controlled self-assembly behavior in water due to the negative photochromism of nitrospiropyran block. The resultant light-responsive metallomicelles induced a micellar catalysis approach in the dark for asymmetric...

Supramolecular redox-responsive substrate carrier activity of a ferrocenyl Janus device

Supramolecular Janus compounds have recently attracted increasing attention owing to their dynamic reversible properties, distinct topological structures, and remarkable physicochemical characteristics, e.g., amphiphilicity, heterofunctionality, and high-density of terminal groups. Herein, a new redox-responsive supramolecular Janus device was designed and synthesized involving β-cyclodextrin and 2-fold ferrocene host-guest interactions. The complex formation was analyzed via one-dimensional 1H NMR and two-dimensional Nuclear Overhauser Enhancement Spectroscopy. FeCl3 and ascorbic acid were used as oxidation and reduction triggers, respectively, to modulate the self-assembly behavior in water through complexation/dissociation of β-cyclodextrin inclusion compounds resulting from redox-conversion of the ferrocenyl guest moieties. The redox-responsiveness of the obtained supramolecular micelles was studied via scanning electron microscopy and dynamic light scattering. Substrate-loading ability of the supramolecular micelles was confirmed with Rhodamine B, and the oxidation of ferrocenyl groups led to the release of the loaded cargos. The present work illustrates a valuable design example of supramolecular Janus systems using the host-guest complexation between β-cyclodextrin and ferrocenyl structures. The present supramolecular micelle may be used as a promising molecular vehicle for application in the field of stimuli-responsive drug delivery.

Porphyrin-functionalized coordination star polymers and their potential applications in photodynamic therapy

We present a new family of porphyrin-functionalized coordination star polymers prepared through combination of coordination-driven self-assembly and post-assembly polymerization. Their self-assembly behaviour in water and potential for photodynamic therapy were demonstrated.

Controlled ROMP synthesis of side-chain ferrocene and adamantane-containing diblock copolymer for the construction of redox-responsive micellar carriers

We present the controlled synthesis of the polynorbornene-based well-defined block copolymer PNFc-b-PNAd side-chain containing ferrocene (Fc) and adamantane (Ad) units by the ring-opening metathesis polymerization using the 3rd generation Grubbs catalyst. A polycationic amphiphilic block copolymer PNFcium-b-PNAd was then fabricated by the stoichiometric oxidation of Fc into ferricinium (Fcium) cations, and its redox-controlled reversible self-assembly behavior in water was demonstrated by SEM and DLS with glutathione as reductant and FeCl3 as oxidant. By using benzocaine (BA) as model cargo, the loading ability of the cationic micelles formed by PNFcium-b-PNAd was investigated and confirmed, and the reduction of Fcium could lead to the rapid release of loaded payloads. A new supramolecular copolymer PNFc-b-PNAd@β-CD was further prepared by simply mixing PNFc-b-PNAd and β-cyclodextrin (β-CD) with equimolar quantity to Ad units, in which host-guest interactions were mainly observed between β-CD and pendant Ad. Owing to the formation of hydrophilic inclusion complexes, PNFc-b-PNAd@β-CD possesses amphiphilic property and exhibits redox-controlled self-assembly behavior in water, too. The oxidation-triggered release of loaded-BA from the supramolecular micelles was observed in a slow and durable way. The present novel redox-responsive micelles provide innovative examples of rational design for stimuli-responsive carriers by using Fc-containing polymers.

A comparison of the self-assembly behaviour of sodium N-lauroyl sarcosinate and sodium N-lauroyl glycinate surfactants in aqueous and aqueo-organic media

Self-assembly of surfactants is influenced by various intermolecular interactions and molecular structure, which dictate packing of molecules in the aggregate and its microstructure. Hydrogen-bonding between amide groups plays a key role in the self-assembly process of N-acyl amino acid surfactants (NAAS). The self-assembly properties of two NAAS, sodium N-lauroyl sarcosinate (SLS) and sodium N-lauroyl glycinate (SLG) that differ only in the head-group structure were compared in aqueous and aqueo-organic media by using a number of methods, including surface tension fluorescence, dynamic light scattering, calorimetry, and microscopy. It was observed that aggregate formation is more favoured in SLG. Studies revealed that while SLS formed small spherical micelles, SLG produced unilamellar vesicles in pH 7 buffer above critical micelle concentration at 25 °C. The stability of SLG vesicles with respect to pH and temperature was also investigated. Furthermore, both SLG and SLS were found to gelify aquo-organic mixtures of varying composition upon heat-cool treatment. Their gelation behaviour was compared by measuring minimum gelation concentration, molecular packing, and morphology and mechanical stability of the thermoreversible gels. The difference in self-assembly behaviour in water as well as in aqueo-organic mixtures was attributed to the steric repulsion and hydrogen-bonding interaction at the head-group of the molecules.

Intramolecular Folding or Intermolecular Self-Assembly of Amphiphilic Random Copolymers: On-Demand Control by Pendant Design

Amphiphilic random copolymers comprising different hydrophilic poly(ethylene glycol) (PEG, average number of oxyethylene units = 4.5 or 8.5) and hydrophobic butyl or dodecyl pendants were designed to investigate self-folding and self-assembly behavior in water. The copolymers with controlled composition and chain length were synthesized by ruthenium-catalyzed living radical copolymerization. We revealed that the pendant design was one of the most critical factors to selectively induce intramolecular self-folding or intermolecular self-assembly. In the case of 30 mol % hydrophobic monomers, random copolymers bearing short PEG (on average 4.5 oxyethylene units) and butyl pendants intramolecularly self-folded into unimer micelles in water, independent of chain length. The size of unimer micelles thus increased with increasing chain length. In contrast, random copolymers bearing long dodecyl pendants intermolecularly self-assembled into uniform multichain micelles; the size depended on composition and PEG len...

Chromonic self-assemblies in a series of dialkyl-thiacarbocyanine dyes and generalization of a facile route for the synthesis of fluorescent nanostructured silica fibers

Abstract In the search for new chromonic liquid crystals, we have explored the self-assembly behavior in water of a series of high-purity dialkylthiacarbocyanine dyes with different alkyl chain lengths and acetate as counterion. The dimer model was used to fit the UV–vis spectra and estimate the dissociation energy between molecules, which increases with the alkyl chain length suggesting that not only aromatic π–π interactions but also entropic/steric effects contribute to the aggregation process. NMR spectra suggest the existence of aromatic stacking interactions within the aggregates. At high concentrations, the dyes form nematic and hexagonal chromonic liquid crystals (CLC) in water within a limited range of alkyl chain lengths (ethyl to butyl); for longer lengths (pentyl) no liquid crystals were observed because of insufficient dye solubility. From small angle X-ray scattering patterns, it can be inferred that dye aggregates have cylindrical morphology with a multimolecular cross-section. The dye aggregates template the formation of silica nanofibers synthetized via sol–gel method in alkaline media. After removing excess dye, the silica/dye nanofibers showed high fluorescence emission with superb photochemical stability. The present report demonstrates a generalized route for the wet synthesis of nanostructured silica nanofibers with tunable optical properties.

A new amphiphilic pillar[5]arene: synthesis and controllable self-assembly in water and application in white-light-emitting systems.

A new amphiphilic pillar[5]arene with excellent surface activity was designed and synthesized successfully for the first time. Interestingly, this pillar[5]arene shows controllable self-assembly behaviour in water and can be applied in white-light-emitting systems.

A Useful Method for Preparing Mixed Brush Polymer Grafted Nanoparticles by Polymerizing Block Copolymers from Surfaces with Reversed Monomer Addition Sequence

The preparation of well-defined block copolymers using controlled radical polymerization depends on the proper order of monomer addition. The reversed order of monomer addition results in a mixture of block copolymer and homopolymer and thus has typically been avoided. In this paper, the low blocking efficiency of reversed monomer addition order is utilized in combination with surface initiated reversible addition-fragmentation chain-transfer polymerization to establish a facile procedure toward mixed polymer brush grafted nanoparticles SiO2 -g-(PS (polystyrene), PS-b-PMAA (polymethacrylic acid)). The SiO2 -g-(PS, PS-b-PMAA) nanoparticles are analyzed by gel permeation chromatography deconvolution, and the fraction of each polymer component is calculated. Additionally, the SiO2 -g-(PS, PS-b-PMAA) are amphiphilic in nature and show unique self-assembly behavior in water.

Supramolecular amphiphilies based on water-soluble pillar[5]arene/paraquat derivatives and their self-assembly behaviour in water

Supramolecular amphiphilies based on water-soluble pillar[5]arene/paraquat derivatives were successfully prepared. We found that when the length of the alkyl chain on guest molecules shorter than C12, it formed micelles, on the other hand, when the alkyl chain longer than C12, vesicles were obtained. Furthermore, we have demonstrated that the resulting vesicles can respond to multiple external stimuli, including temperature, host–guest inclusion and pH. Methods of warming, decreasing the pH of the system and inclusion of α-cyclodextrins were then employed to disrupt the vesicle architecture. Finally, controlled release experiments were performed to evaluate the vesicles which could encapsulate calcein within their interiors under neutral conditions and release it in response to a decrease in pH.