Self-assembly of model amphiphilic Janus particles

We apply molecular dynamics simulations to investigate the structure formation of amphiphilic Janus particles in the bulk phase. The Janus particles are modeled as (soft) spheres composed of a hydrophilic and hydrophobic part. Their orientation is described by a vector representing an internal degree of freedom. Investigating energy fluctuations and cluster size distributions, we determine the aggregation line in a temperature-density-diagram, where the reduced temperature is an inverse measure for the anisotropic coupling. Below this aggregation line clusters of various sizes depending on density and reduced temperature are found. For low densities in the range ρ? ≤ 0.3, the cluster size distribution has a broad maximum, indicating simultaneous existence of various cluster sizes between 5 and 10. We find no hint of a condensation transition of these clustered systems. In the case of higher densities (ρ? = 0.5 and 0.6), the cluster size distribution shows an extremely narrow peak at clusters of size 13. In these icosahedrons, the particles are arranged in a closed-packed manner, thereby maximizing the number of bonds. Analyzing the translational mean-square displacement we also observe indications of hindered diffusion due to aggregation.     

Self-assembly of an amphiphilic derivative of chitosan and micellar solubilization of puerarin

A kind of amphiphilic derivatives of chitosan (2-hydroxyl-3-butoxyl)-propylcarboxymethyl-chitosan (HBP-CMCHS), has been synthesized, and the critical micelle concentration (cmc) of HBP-CMCHS was detected by the fluorescence method. The puerarin-loaded HBP-CMCHS micellar system was prepared by physical entrapped method. Result showed that when adding the same amount of puerarin, the solubilizing capacity was enhanced by increasing the concentration of HBP-CMCHS and temperature. Puerarin-loaded micellar system of HBP-CMCHS was characterized by TEM and DLS. TEM photograph revealed that the micelles were spherical and puerarin was solubilized in the cores of the spherical polymeric micelles. DLS showed that after solubilization the size of the micelles became bigger. In vitro tests showed that puerarin was slowly released from micellar solution and the release lasted up to 60 h by means of the dialysis method.     

Self-assembly of facially amphiphilic dendrimers on surfaces

Facially amphiphilic dendrimers have been shown to provide significant difference in surface behavior due to subtle changes in structure. The monodendrons are capable of providing hydrophobic surfaces, while the didendrons provide superhydrophobic surfaces. This provides an example of how a molecular level change could result in significant changes in surface behavior. This difference is attributed to the conformational differences exhibited by these dendrimers on surfaces.     

Self-assembly and hydrophobic clusters of amphiphilic polysaccharides

The objective of this work was to synthesize and characterize new polymeric surfactants deriving from natural polymers and designed for membrane protein solubilization. For this purpose, a set of hydrophobically-modified pullulans (HMCMPs) of moderate molar mass and differing in hydrophobic modification ratio, charge ratio and the nature of the hydrophobic chains introduced, were prepared. Their behaviour in aqueous dilute solutions was investigated by surface tension measurement and with a polarity probe, the Coomassie Brilliant Blue dye. Two distinct critical concentrations were evidenced, demonstrating the complex behaviour of HMCMPs. Amphiphilic pullulan derivatives may indeed establish hydrophobic associations in bulk solution while adsorbing at the air  water interface. The structural parameters of the polymers influence their aqueous behaviour. Self-assembly of HMCMPs occurs at smaller concentrations when the hydrophobic modification ratio or the alkyl hydrophobic chain length increases. It seems to be governed by the concentration of hydrophobic grafts, rather than by polymer concentration. Probably because of steric hindrance, 3-phenylpropyl grafts do not favour self-assembly, and lead to HMCMPs that preferentially adsorb at the air  water interface.     

Self-assembly of amphiphilic glycoconjugates into lectin-adhesive nanoparticles

This work describes the synthesis and self-assembly of carbohydrate-clicked rod-coil amphiphilic systems. Copper-catalyzed Huisgen cycloaddition was efficiently employed to functionalize the hydrophilic extremity of PEG-b-tetra(p-phenylene) conjugates by lactose and N-acetyl-glucosamine ligands. The resulting amphiphilic systems spontaneously self-assembled into nanoparticles when dissolved in aqueous media, as evidenced by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The formation of highly monodisperse micelles having a mean diameter of 10 nm was observed for systems containing a PEG 900 core, and a decrease in the hydrophilic moiety (PEG 600) led to the formation of vesicles with a broader size distribution. The presence of carbohydrate residues on the surfaces of the micelles and their ability to establish specific interactions with wheat germ agglutinin (WGA) and peanut agglutinin (PNA) were further highlighted by light-scattering measurements, thus confirming the attractive applications of such sugar micelles in biosensor devices.     

Self-assembly of amphiphilic imidazolium-based hexa-peri-hexabenzocoronenes into fibreous aggregates

Imidazolium-based amphiphilic hexa-peri-hexabenzocoronenes were synthesized and shown to undergo ordered columnar self-assembly in solid-state as well as in solution to yield defined nanofibers upon solution drop casting onto solid substrate.     

Self-assembly behavior of carbon nanotubes modified by amphiphilic block copolymer

Block copolymers of poly(tert-butyl methyacrylate) (PtBMA) and polystyrene (PSt) were grafted onto multi-walled carbon nanotubes (MWNTs) by the reaction of azide groups at the copolymer chain end with the surface of MWNTs. After hydrolysis, PtBMA block was transformed to polymethyacrylic acid (PMAA) block, and amphiphilic diblock copolymer-modified MWNTs were finally obtained. The modified MWNTs were characterized by XPS, TGA, FTIR, and Raman, and the results showed that the amphiphilic diblock copolymers were grafted onto MWNTs by the covalent bond. The TEM and SEM observation showed that PMAA-b-PSt copolymer modified MWNTs (S2) formed self-assembly tube bundles with the size up to 20 μm in both ethanol and chloroform. However, PtBMA-b-PSt copolymer modified MWNTs (S1) only formed small-size aggregates or dispersed as single-modified MWNTs. The dispersion stability tests showed that S1 had good dispersion stability in several solvents (water, ethanol, acetone, and chloroform) even after 20 days. Due to the big-size tube bundles formed by self-assemble S2, the dispersion stability of S2 in above all solvents decreased, but it was still much better than that of pristine MWNTs.     

Self-assembly of amphiphilic alkyloligosiloxanes within cylindrically and spherically confined spaces

The self-assembly of amphiphilic alkyloligosiloxane molecules within cylindrically and spherically confined spaces has been investigated. Hydrolyzed solutions of the precursors consisting of an alkylsiloxane core and three branching trimethoxysilyl groups (C n H 2 n+1 Si(OSi(OMe) 3) 3, n = 10 and 16) were impregnated into the cylindrical pores of porous anodic alumina membranes (PAAMs), leading to the formation of rod- and tubelike hybrids. A two-dimensional (2D) hexagonal mesostructure with a circular orientation and a lamellar mesostructure with a multitubular orientation were confirmed for n = 10 and 16, respectively. The pore diameters of PAAMs ranging from 30 to 400 nm did not significantly affect the mesostructures of the hybrids. The self-assembly in the spherical droplets was also performed by spray-drying of the hydrolyzed solutions. At high temperature, vesicular lamellar mesostructures were formed, independent of the alkyl chain length of the precursors ( n = 10 or 16). Spherical hybrids with a core-shell structure (a 2D hexagonal core and a lamellar shell) were also prepared by lowering the drying temperature in the case of n = 10. These are the first findings on the confined assembly of single siloxane-based amphiphiles that will lead to the fabrication of novel hierarchically ordered hybrid materials having Si-C covalent bonds at the interfaces.     

Self-assembly of amphiphilic perylene-cyclodextrin conjugate and vapor sensing for organic amines

An asymmetric, amphiphilic perylene bisimide derivative 1 was synthesized by grafting permethyl-β-cyclodextrin at one side and an octadecyl chain at the other side. Its aggregation capability and morphology, which attract intense interest, were carefully examined by combination of UV-vis, NMR, and fluorescence spectroscopy, DLS, XRD, TEM, and SEM. By adjusting the volume ratio of water and methanol, we are able to control the morphology, benefiting from the amphiphilicity of 1. Furthermore, the particular resulting aggregates were employed as solid-state fluorescence sensing for organic amines. An improvement of both selectivity and sensitivity is achieved compared to previous publications.     

Self-assembly of ABA amphiphilic triblock copolymers into vesicles in dilute solution

Self-assembly of an ABA amphiphilic triblock copolymer into vesicles in dilute solution was studied by successfully combining experimental methods and a real-space self-consistent field theory in three-dimensional space. It was found experimentally that vesicle size was sensitive to the initial copolymer concentration in the organic solvent. Also, the aggregate morphologies and vesicles sizes were found to be dependent on the annealing time. A number of complex vesicles, such as global, long-style, trigonal, and necklacelike vesicles, were obtained in our experiments. Moreover, the corresponding microstructures were produced in our simulations. The results show that various vesicles in dilute solution are formed solely on account of the inhomogeneous density distribution in the local region in nature. Our simulations confirm that the structural complexity coexisting behavior in the single-amphiphile systems is largely attributed to the metastability rather than the polydispersity of the triblock copolymer. These metastable states should strongly depend on the pathway of the system on the free energy landscapes, which is governed by the initial condition.     

Self-assembly and micellization of amphiphilic rod-coil block oligomer at the mica-water interface

In this paper, in situ atomic force microscopy has been used to investigate the micellization and self-assembling structure of an amphiphilic rod-coil block oligomer (EO16OPV) containing a conjugated oligo(phenylene vinylene) dimer and poly(ethylene oxide) at the mica-water interface. It is found that EO16OPV molecules have strong adsorption and aggregation properties on mica. In the wide concentration range from above the critical micelle concentration (cmc) to far below the cmc, a closely packed layer of stripe-like micelles with two preferred orientations can be formed at the mica-water interface. A cylindrical micelle structure for the stripes is proposed. We demonstrate that the stripe-like micelles formed on mica originate from different micellization processes at solution concentrations above and below the cmc. The origins of the strong micellization properties and oriented arrangement of the stripes are also discussed.     

Self-assembly of amphiphilic peptides to construct activatable nanophotosensitizers for theranostic photodynamic therapy

A variety of nano-engineered photosensitizers have been developed for photodynamic therapy (PDT) of cancer diseases. However, traditional nano-engineering methods usually cannot avoid drug leakage and premature release, and have disadvantages such as low drug load and inaccurate release. The self-assembly strategy based on amphiphilic peptides has been considered to be more attractive nano-engineering method. Here we developed novel acid-activatable self-assembled nanophotosensitizers based on an amphiphilic peptide derivative. The peptide derivative was synthesized from a fluorescein molecule with thermally activated delayed fluorescence (TADF). The self-assembled nanophotosensitizers can specifically enter the tumor cells and disassemble inside lysosomes companied with “turn-on” fluorescence and photodynamic therapy effect. Such smart nanophotosensitizers will open new opportunities for cancer theranostics.     

Self-assembly in mixed aqueous solutions of amphiphilic block copolymers and vesicle-forming surfactant

The self-assembly behavior of mixed solutions consisting of poly(isoprene-b-ethylene oxide) (IEO) copolymer micelles and vesicle-forming didodecyldimethylammonium bromide (DDAB) was investigated. Dynamic light scattering indicated the presence of two populations of nanoassemblies in the solutions. By aid of atomic force microscopy, the larger ones were identified as block copolymer modified surfactant vesicles (BCMSVs) and the smaller ones as surfactant-modified block copolymer micelles (SMBCMs). This identification is based on the amphiphilic character of the low and high molecular weight molecules and the notion that exchange of unimers of both types can take place between the initial nanoassemblies in aqueous solution. Electrophoretic light scattering experiments showed that the nanostructures carry positive charges originating from the surfactant. The sizes of the nanoassemblies depend on the relative concentrations of both components. The behavior of the mixed systems was also found to depend on block copolymer composition and temperature. Nanoassemblies of smaller sizes were formed at higher temperatures. BCMSVs and SMBCMs are thermosensitive, in contrast to the temperature stability of pure block copolymer micelles. On the other hand, BCMSVs showed lesser sensitivity to temperature increase compared to the pure DDAB vesicles. This indicates that incorporation of macromolecules into the DDAB bilayer increases the stability of the vesicles.     

Self-assembly of uncharged amphiphilic porphyrins and incorporation of C60 fullerenes in water

We synthesised an uncharged amphiphilic porphyrin, meso-tetrakis-(3,5-di-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-phenyl)-porphyrin, and investigated the supramolecular self-assembly of the porphyrins and the incorporation of C₆₀ molecules into the assembly in aqueous solutions. Spectroscopic and dynamic light scattering studies on the assembly of the amphiphilic porphyrin support that the amphiphilic porphyrins are likely held together through enhanced π–π interactions by pronounced hydrophobic effects in aqueous solutions. It was also found that C₆₀ molecules are efficiently incorporated into the assembly. The fluorescence emitted from the porphyrin ring of the porphyrin/C₆₀ co-assembly in aqueous solution is largely quenched, implying the presence of strong electronic interactions between C₆₀ and porphyrin molecules in the supramolecular assembly.     

Self-assembly of peptide-amphiphile nanofibers: the roles of hydrogen bonding and amphiphilic packing

The role of hydrogen bonding and amphiphilic packing in the self-assembly of peptide-amphiphiles (PAs) was investigated using a series of 26 PA derivatives, including 19 N-methylated variants and 7 alanine mutants. These were studied by circular dichroism spectroscopy, a variety of Fourier transform infrared spectroscopies, rheology, and vitreous ice cryo-transmission electron microscopy. From these studies, we have been able to determine which amino acids are critical for the self-assembly of PAs into nanofibers, why the nanofiber is favored over other possible nanostructures, the orientation of hydrogen bonding with respect to the nanofiber axis, and the constraints placed upon the portion of the peptide most intimately associated with the biological environment. Furthermore, by selectively eliminating key hydrogen bonds, we are able to completely change the nanostructure resulting from self-assembly in addition to modifying the macroscopic mechanical properties associated with the assembled gel. This study helps to clarify the mechanism of self-assembly for peptide amphiphiles and will thereby help in the design of future generations of PAs.     

Self-assembly of amphiphilic molecules: A review on the recent computer simulation results

We provided a short review on the recent progresses in computer simulations of adsorption and self-assembly of amphiphilic molecules. Owing to the extensive applications of amphiphilic molecules, it is very important to understand thoroughly the effects of the detailed chemistry, solid surfaces and the degree of confinement on the aggregate morphologies and kinetics of self-assembly for amphiphilic systems. In this review we paid special attention on (i) morphologies of adsorbed surfactants on solid surfaces, (ii) self-assembly in confined systems, and (iii) kinetic processes involving amphiphilic molecules.