Amphiphilic Side Chains Research Articles

Synthesis and self-assembly of high grafting density core-shell bottlebrush polymer with amphiphilic side chain

Self-assembly of bottlebrush polymers are widely studied in photonic bandgap materials, biomedical materials and nanomaterial with different structures. In this work, high grafting density bottlebrush polymer with amphiphilic QPDMA[FeCl4]-b-PS side chains grafting on every carbon atom of the backbone are prepared via grafting from approach. The para-isocyanobenzoate monomer modified with chain transfer agent (CTA) is designed and synthesized to prepared polymer backbones with CTA grafting on each atoms. The core-shell bottlebrush block copolymer is prepared by sequential reversible addition-fragmentation chain transfer polymerization of dimethylaminoethyl methacrylate and styrene. The inner core follows quaternization and ion exchange to form water soluble QPDMA[FeCl4] magnetic block. The resulting core-shell bottlebrush magnetic polymer (PCN-g-[QPDMA[FeCl4]-b-PS]) self-assembles into nanowires with magnetic QPDMA[FeCl4] as core and PS as corona in the shell selected solvent dichloromethane, the length of nanowires increases with self-assembly time. While it self-assembles into nanoparticle clusters in core selected aqueous solution. And, the thermal and magnetic properties are affected by the self-assembly morphology. Especially, the as prepared PCN-g-[QPDMA[FeCl4]-b-PS] and the nanoparticles cluster self-assembly are paramagnetic, but the nanowire self-assembly is superparamagnetic.

Jellyfish-inspired smart tetraphenylethene lipids with unique AIE fluorescence, thermal response, and cell membrane interaction.

Smart lipids with fluorescence emission, thermal response, and polyethylene glycolation (PEGylation) functions can be highly valuable for formulation, image-traceable delivery, and targeted release of payloads. Herein, a series of jellyfish-shaped amphiphiles with a tetraphenylethene (TPE) core and four symmetrical amphiphilic side chains were conveniently synthesized and systematically investigated as smart lipids. Compared with regular amphiphilic TPE lipids and phospholipids, the unprecedented jellyfish-shaped molecular geometry was found to enable a series of valuable capabilities, including sensitive and responsive aggregation-induced emission of fluorescence (AIE FL) and real-time FL monitoring of drug uptake. Furthermore, the jellyfish-shaped geometry facilitated the concentration-dependent aggregation from unimolecular micelles at low concentrations to "side-by-side" spherical aggregates at high concentrations and a unique mode of AIE. In addition, the size and the arrangement of the amphiphilic side chains were found to dominate the aggregate stability, cell uptake, and thus the cytotoxicity of the amphiphiles. This study has unprecedentedly developed versatile smart TPE lipids with precise structures, and unique physicochemical and biological properties while the peculiar structure-property relationship may shed new light on the design and application of AIE fluorophores and functional lipids in biomedicine and materials science.

Rapidly SO2-responsive vesicles with intrinsic fluorescent indicators for membrane structure evolution

Stimuli-responsive vesicles (SRVs) have been widely exploited as smart nanocarriers for biomedical applications. Herein, high-performance SO2-responsive nanovesicles were reported to exemplify a new mode of SRVs. Structurally, the sensory vesicles were based on amphiphilic hydrogen-bonded (HB) polymers which can be facilely fabricated via modular self-assembly. The HB polymers are designed to consist of a melamine-barbituric acid HB skeleton with pendant anthracene fluorophores and amphiphilic side chains. Upon stimulation with increasing amount of SO2, the vesicles in aqueous solution undergo an unusual morphology evolution including rapid fission into small ones, swelling and final collapse of the offspring vesicles. During this process, the intrinsic fluorescence response of the vesicles allows intuitive tracking of the hierarchical structural evolution of the self-assembled membranes and straightforward quantitation of the stimuli. This work exemplifies a rational design of auto-recording stimuli-responsive nanovesicles.

Hysteresis in the thermally induced phase transition of cellulose ethers.

Functionalized cellulosics have shown promise as naturally derived thermoresponsive gelling agents. However, the dynamics of thermally induced phase transitions of these polymers at the lower critical solution temperature (LCST) are not fully understood. Here, with experiments and theoretical considerations, we address how molecular architecture dictates the mechanisms and dynamics of phase transitions for cellulose ethers. Above the LCST, we show that hydroxypropyl substituents favor the spontaneous formation of liquid droplets, whereas methyl substituents induce fibril formation through diffusive growth. In celluloses which contain both methyl and hydroxypropyl substituents, fibrillation initiates after liquid droplet formation, suppressing the fibril growth to a sub-diffusive rate. Unlike for liquid droplets, the dissolution of fibrils back into the solvated state occurs with significant thermal hysteresis. We tune this hysteresis by altering the content of substituted hydroxypropyl moieties. This work provides a systematic study to decouple competing mechanisms during the phase transition of multi-functionalized macromolecules.

Polybenzimidazole Ultrathin Anion Exchange Membrane with Comb-Shape Amphiphilic Microphase Networks for a High-Performance Fuel Cell.

A comb-shape amphiphilic cationic side chain is proposed to well-balance the water sorption in anion exchange membranes (AEMs), in which the cationic group is in between of an ether-containing hydrophilic spacer and an alkyl hydrophobic spacer. By fully grafting the amphiphilic side chains onto polybenzimidazole (PBI), comb-shape amphiphilic microphase networks are well-developed in the AEMs, in which the alkyl hydrophobic network greatly restricts water swelling and the ether-containing hydrophilic network keeps the hydration of the cationic groups and enlarges the ion conductive channel. The as-prepared membranes achieve a high conductivity of about 91.2 mS cm-1, an extremely low swelling ratio of about 8.1% at 80 °C, and good mechanical properties at a hydrated state (tensile strength and elongation at a break of about 14.6 MPa and 77.5%, respectively). Benefits from the balanced water sorption in AEMs, the H2/O2 fuel cell with a 10 μm ultrathin membrane could withstand 80 °C and 0.1 MPa back pressure and achieve a high open circuit voltage of about 1.0 V and a high peak power density of about 631.5 mW cm-2. This work provides a new insight into the design of high-performance AEM.

Biomimetic Asymmetric Polymer Brush Coatings Bearing Fencelike Conformation Exhibit Superior Protection and Antifouling Performance.

Antifouling surfaces with optimized conformation and compositional heterogeneities are presented with the goal of improving the efficacy of surface protection. The approach exploits the adhesive group (thiol or catechol chain end) to anchor asymmetric polymer brushes (APBs) bearing amphiphilic side chains with synergistic nonfouling and fouling-release abilities onto the surface. The conformation of the APB surface is close to the fencelike structure, which mimics lubricating protein lubricin, endowing the surface with capacity of enhanced protection and antiadhesivity, even facing the high compression of fouling. By utilizing a poly(Br-acrylate-alkyne) macroagent comprising alkynyl and 2-bromopropionate groups, we prepared a series of APB surfaces based on polyacrylate-g-poly(ethylene oxide)/poly(pentafluorophenyl methacrylate) (PA-g-PEO/PPFMA) APBs to explore the influence of the content of the fluorinated segment and bioinspired topological polymer chemistry on their antifouling performance. The APB surfaces can not only provide compositional heterogeneities of PEO and fluorinated segments in each side chain but also give a high surface coverage because of the characteristic of high grafting density of macromolecular brushes. It was found for the first time, as far as we are aware, the fencelike APB surface shows excellent antifouling performance with less protein adsorption (up to 91% off) and cell adhesion (up to 84% off) in comparison with the controlled substrate under relatively long incubation time.

Silicone Elastomer with Surface-Enriched, Nonleaching Amphiphilic Side Chains for Inhibiting Marine Biofouling

Silicone elastomer is one of the ecofriendly fouling release materials. However, it suffers from poor fouling resistant performance during idle periods. We developed a silicone elastomer with self-...

Self-Assembled Biradical Ureabenzene Nanoparticles for Magnetic Resonance Imaging

As part of a series of investigations related to the construction of metal-free magnetic resonance imaging (MRI) contrast agents as alternatives to gadolinium agents, water-soluble biradicals, denoted as 1-AMP and 2-HEG, were prepared, in which two stable radicals were introduced to a ureabenzene framework. We found that 1-AMP possessed an amphiphilic side chain that consisted of an alkyl group and a hexaethylene glycol (HEG) chain, whereas 2-HEG possessed only an HEG chain. Accordingly, the biradicals showed self-assembly behavior due to multiple intermolecular interactions through which nanoparticles were formed in a water solution. Magnetic interaction took place in both biradicals, and the estimated interaction strength was J = 5.4 mT. Through MRI measurement, the water proton relaxivities, r1, were estimated to be 0.12 and 0.41 mM–1 s–1 for 1-AMP and 2-HEG, respectively; in other words, the r1 value for 2-HEG was approximately twice as high as that of monoradical-based contrast agents.

Effect of Hydrophobicity on the Self-Assembly Behavior of Urea Benzene Derivatives in Aqueous Solution

Urea benzene derivatives (UBD) with amphiphilic side chains showed self-assembly behavior in aqueous solution to form nanoparticles ~100 nm in size. Subsequent thermal treatment led to additional self-assembly of the nanoparticles due to dehydration of the amphiphilic side chains, producing microparticles. This self-assembly process was accompanied by a lower critical solution temperature (LCST) behavior, as revealed by the abrupt decrease in solution transmittance. In this study, three UBD (UBD-1–3) with different lengths of the alkyl segment in the amphiphilic side chain (namely, hexyl, heptyl, and octyl, respectively) were prepared to investigate the self-assembly behavior in aqueous solution. UBD-1–3 formed identical nanoparticles, with sizes in the 10~80 nm range but with different LCST values in the order 3 < 2 < 1. These results suggest a relationship between the hydrophobicity and the self-assembly behavior of UBD.

Water-Proton Relaxivities of Radical Nanoparticles Self-Assembled via Hydration or Dehydration Processes

Nanoparticles capable of accumulating in tumor tissues are promising materials for tumor imaging and therapy. In this study, two radical nanoparticles (RNPs), denoted as 1 and 2, composed of self-assembled ureabenzene derivatives possessing one or two amphiphilic side chains were demonstrated to be candidates for metal-free functional magnetic resonance imaging (MRI) contrast agents (CAs). Because of the self-assembly behavior of 1 and 2 in a saline solution, spherical RNPs of sizes ∼50-90 and ∼30-100 nm were detected. In a highly concentrated solution, RNP 1 showed considerably small water-proton relaxivity values (r1 and r2), whereas RNP 2 showed an r1 value that was around 5 times larger than that of RNP 1. These distinct r1 values might be caused by differences in the self-assembly behavior by a hydration or dehydration process. In vivo studies with RNP 2 demonstrated a slightly enhanced T1-weighted image in mice, suggesting that the RNPs can potentially be used as metal-free functional MRI CAs for T1-weighted imaging.

Design of Amphiphilic Polymers via Molecular Dynamics Simulations

Extensive all-atom molecular dynamics simulations were carried out on three novel amphiphilic homopolymers in explicit polar and nonpolar solvent environments. These nonlinear polymers have potential applications in drug delivery and consisted of 32 repeating bifurcated amphiphilic side chains bound to an alkynyl functionalized cyclic framework. All of the polymer systems investigated have the same backbone and hydrophobic dodecyl side chains and differ only in the nature of the hydrophilic side chains. This report focuses on the solvent polarity induced conformational changes exhibited as a result of the different hydrophilic modifications. Our simulations of polymer microenvironment provides useful information about the amphiphilic phase segregation that drives the formation of normal micelle-like and reverse micelle-like nanostructures that are expected to occur in response to solvents of varying polarities.

Aggregation of 4,8,12-Triazatriangulene Cation with Amphiphilic Side Chains: Emission Properties in Solution, in Aggregates, and in the Solid State

A 4,8,12-triazatriangulene (TATA) cation derivative bearing tetra(ethylene glycol) group was synthesized by direct functionalization of the TATA framework at the 2-, 6-, and 10-positions. Emission properties of the amphiphilic TATA derivative in three different environments—in the monomer state, in aggregates formed in aqueous media, and in the solid state—were carefully analyzed based on the radiative (kf) and nonradiative (knr) rate constants. We found that the fluorescence quenching of the TATA cation derivative upon aggregation is dominantly attributed to the decrease in the kf value but not to the change in the knr value.

Highly Emissive Excimers by 2D Compression of Conjugated Polymers.

Interactions between π-conjugated polymers are known to create ground-state aggregates, excimers, and exciplexes. With few exceptions, these species exhibit decreased fluorescence quantum yields relative to the isolated polymers in liquid or solid solutions. Herein, we report a method to assemble emissive conjugated polymer excimers and demonstrate their applicability in the detection of selected solvent vapors. Specifically, poly(phenylene ethynylene)s (PPEs) with amphiphilic side chains are organized in a Langmuir monolayer at the air-water interface. Compression of the monolayer results in the reversible conversion from a face-on organization of the π-system relative to the water to what appears to be an incline-stack conformation. The incline-stack organization creates a bright yellow emissive excimeric state with increases of 28% in relative fluorescence quantum yields to the face-on monolayer conformation. Multilayers can be transferred onto the glass substrate via a Langmuir-Blodgett method with preservation of the excimer emission. These films are metastable and the fluorescence reverts to a cyan color similar to the spectra obtained in solution and spin-cast films after exposure to selected solvent vapors. This behavior has practical utility as a fluorescence-based indicator for selected volatile organic compounds.

Copolymer films containing amphiphilic side chains of well-defined fluoroalkyl-segment length with biofouling-release potential

Novel methacrylate copolymers containing polysiloxane (SiMA) and mixed poly(ethyleneglycol)-perfluorohexyl side chains (MEF) were synthesised and dispersed as surface-active additives in crosslinked PDMS films.

Antibacterial Activity of Geminized Amphiphilic Cationic Homopolymers.

The current study is aimed at investigating the effect of cationic charge density and hydrophobicity on the antibacterial and hemolytic activities. Two kinds of cationic surfmers, containing single or double hydrophobic tails (octyl chains or benzyl groups), and the corresponding homopolymers were synthesized. The antimicrobial activity of these candidate antibacterials was studied by microbial growth inhibition assays against Escherichia coli, and hemolysis activity was carried out using human red blood cells. It was interestingly found that the homopolymers were much more effective in antibacterial property than their corresponding monomers. Furthermore, the geminized homopolymers had significantly higher antibacterial activity than that of their counterparts but with single amphiphilic side chains in each repeated unit. Geminized homopolymers, with high positive charge density and moderate hydrophobicity (such as benzyl groups), combine both advantages of efficient antibacterial property and prominently high selectivity. To further explain the antibacterial performance of the novel polymer series, the molecular interaction mechanism is proposed according to experimental data which shows that these specimens are likely to kill microbes by disrupting bacterial membranes, leading them unlikely to induce resistance.

Consecutive incorporation of functionalized nucleotides with amphiphilic side chains by novel KOD polymerase mutant.

Recently, 7-substituted 7-deazapurine nucleoside triphosphates and 5-substituted pyrimidine nucleoside triphosphates (dN(am)TPs) were synthesized to extend enzymatically using commercially available polymerase. However, extension was limited when we attempted to incorporate the substrates consecutively. To address this, we have produced a mutant polymerase that can efficiently accept the modified nucleotide with amphiphilic groups as substrates. Here we show that the KOD polymerase mutant, KOD exo(-)/A485L, had the ability to incorporate dN(am)TP continuously over 50nt, indicating that the mutant is sufficient for generating functional nucleic acid molecules.

Amphiphilic oligopeptides grafted to PDMS‐based diblock copolymers for use in antifouling and fouling release coatings

Amphiphilic surfaces, having both hydrophobic and hydrophilic properties, have been considered for marine antifouling and fouling release applications, as they may provide an environmentally friendly non‐biocidal alternative for surface coating. Here, we report a new class of polymers modified with amphiphilic side chains constructed from non‐natural oligopeptides. These non‐natural amino acids have a diverse array of functionalities and polarities that can be arranged in any sequence to optimize antifouling and fouling release behavior. Because of advances in solid state peptide synthesis, these peptides can be prepared on a multiple gram scale in a short period of time. Different sequences of non‐natural amino acids were synthesized to determine the effect on the physical and antifouling properties of the surface. These oligopeptide sequences were attached to a PS‐b‐P(DMS‐stat‐MVS) diblock copolymer using thiol‐ene “click” chemistry. The modified polymers were spray coated onto treated glass slides and characterized using water bubble contact angle measurements and near‐edge X‐ray absorption fine structure. The coatings were tested for antifouling and fouling release performance against spores and sporelings (young plants), respectively, of the green seaweed (alga) Ulva linza and also for non‐specific protein absorption. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of acidic aqueous alcohol solution on template sol-gel synthesis of phosphorescent hexagonal mesoporous silica film nanocomposite

Here novel mesoporous silica film nanocomposite with a hexagonal structure is successfully synthesized by using phosphorescent columnar assembly of a trinuclear gold(I) pyrazolate complex bearing amphiphilic side chains [Au3Pz3], formed via a weak AuI-AuI metallophilic interaction, as a functional template in the sol-gel synthesis. By controlling the molar ratios of alcohol to acid in an acidic aqueous alcohol solution, the sol-gel synthesis of columnar assembled [Au3Pz3] with a silica source can provide highly ordered hexagonal mesoporous silica film composite [Au3Pz3]/silicahex consisting one-dimensional molecular assembly in the nanoscopic channels. The as-fabricated silica film nanocomposite [Au3Pz3]/silicahex with red emission have phosphorescent properties with luminescence emission centered at 693 nm (ext = 276 nm; Stokes shift,  = 417 nm) and lifetime at 7.8 s (ext = 266 nm, em = 690 nm).

Cationic brush‐like terpolymer with pH responsive thickening behavior in a surfactant system

A new kind of cationic brush‐like terpolymer was synthesized by copper(I)‐mediated atom transfer radical polymerization (ATRP) of methyl ether poly(ethylene glycol) methacrylate (mPEGMA), poly(propylene glycol) methacrylate (PPGMA) and dimethylaminoethyl methacrylate (DMAEMA) in the presence of ethyl α‐bromoisobutyrate as ATRP initiator. The poly(PEG/PPG/DMAEMA) terpolymer was featured with a cationic backbone containing PDMAEMA segments and amphiphilic side chains composed of hydrophilic PEG and hydrophobic PPG short branches. The copolymer was characterized by 1H NMR, Fourier transform IR and gel permeation chromatography. The thickening behavior of this copolymer in a surfactant system (sodium dodecyl sulfate, SDS) was extensively investigated by a rheological study. It was found that the copolymer can effectively thicken the SDS surfactant system at low concentrations of both copolymer and surfactant. More interestingly, the thickened SDS system by this copolymer showed dramatic pH responsive rheological behavior in the pH range 4–10. Thus the rheological behavior of the thickened SDS system was tunable by pH value. Based on our findings, a novel thickening mechanism is proposed for this kind of cationic brush‐like terpolymer. This kind of cationic brush‐like copolymer would be a new type of rheology modifier for advanced hair/skin care systems. © 2014 Society of Chemical Industry

Self-assembly and phase separation of amphiphilic dyads based on 4,7-bis(2-thienyl)benzothiodiazole and perylene diimide

To get highly ordered organic structures at the nanoscale, a series of new electronic donor–acceptor (D–A) dyads were synthesized. The dyads bearing different side chains (lipophilic or amphiphilic) or linkers (Long or Short) showed variable self-assembly behaviour. Long-linker dyads can fold in dilute solution, but the folding of short-linker dyads was not observed. Intermolecular D–A interactions and acceptor–acceptor (A–A) aggregation were proved to co-occur in chloroform for all four dyads. In the bulk state, amphiphilic dyads could overcome the intrinsic D–A interactions and achieve better D–A phase separation than lipophilic ones due to the incompatibility of the side chains. The dyad with a short-linker and amphiphilic side chains, Samphi, had the ability to form a gel, and both of the amphiphilic dyads could form nanofibres.