Condensation properties of vesicles formed from an amphiphilic N-phosphorylamino acid

Stable unilamellar vesicles were formed in water under appropriate pH from dispersions of N-(O,O-di-n-hexadecyl)phosphorylalanine, an amphiphilic N-phosphorylamino acid. We found that condensation occurred in the vesicle solution after incubated at 40 degrees C, which may contribute to the stability of the vesicular system. Dipeptide derivative in the vesicle solution was identified by electrospray ionization mass spectrometry (ESI-MS), which suggests the peptide formation without any coupling reagents. Hydrogen bond and electrostatic interactions play important roles in the process of vesicle formation, while the suitable orientation and packing of the amphiphilic molecules at the vesicle/water interface together with certain conformational freedom in the vesicular bilayer are considered to be most favorable for the condensation in ordered systems as vesicles.     

On the twist-bend nematic phase formed directly from the isotropic phase

The intriguing twist-bend nematic (N_TB) phase is formed, primarily, by liquid crystal dimers having odd spacers. Typically, the phase is preceded by a nematic (N) phase via a weak first-order transition. Our aim is to obtain dimers where the N_TB phase is formed directly from the isotropic (I) phase via a strong first-order phase transition. The analogy between such behaviour and that of the smectic A (SmA)–N–I sequence suggests that this new dimer will require a short spacer. This expectation is consistent with the prediction of a molecular field theory, since the decrease in the spacer length results in an increase in the molecular curvature. A vector of odd dimers based on benzoyloxybenzylidene mesogenic groups with terminal ethoxy groups has been synthesised with spacers composed of odd numbers of methylene groups. Spacers having 5, 7, 9 and 11 methylene groups are found to possess the conventional phase sequence N_TB–N–I; surprisingly, for the propane spacer, the N_TB phase is formed directly from the I phase. The properties of these dimers have been studied with care to ensure that the identification of the N_TB phase is reliable.     

A self-assembly phase diagram from amphiphilic perylene diimides

Supramolecular forces govern self-assembly and further determine the final morphologies of self-assemblies. However, how they control the morphology remains hitherto largely unknown. In this paper, we have discovered that the self-assembled nanostructures of rigid organic semiconductor chromophores can be finely controlled by the secondary forces by fine-tuning the surrounding environments. In particular, we used water/methanol/hydrochloric acid to tune the environment and observed five different phases that resulted from versatile molecular self-assemblies. The representative self-assembled nanostructures were nanotapes, nanoparticles and their 1D assemblies, rigid microplates, soft nanoplates, and hollow nanospheres and their 1D assemblies, respectively. The specific nanostructure formation is governed by the water fraction, R(w) , and the concentration of hydrochloric acid, [HCl]. For instance, nanotapes formed at low [HCl] and R(w) values, whereas hollow nanospheres formed when either the HCl concentration is high, or the water fraction is low, or both. The significance of this paper is that it provides a useful phase diagram by using R(w) and [HCl] as two variables. Such a self-assembly phase diagram maps out the fine control that the secondary forces have on the self-assembled morphology, and thus allows one to guide the formation toward a desired nanostructure self-assembled from rigid organic semiconductor chromophores by simply adjusting the two key parameters of R(w) and [HCl].     

Small-angle neutron and X-ray scattering from amphiphilic stimuli-responsive diamond-type bicontinuous cubic phase

The structural evolution of a diamond-type bicontinuous lipid cubic phase upon application of thermal and chemical (hydration agent) stimuli is investigated by means of small-angle neutron (SANS) and X-ray scattering (SAXS). The soft-matter cubic architecture responds by dramatic swelling (DLarge cubic structure) upon incorporation of a hydration-enhancing guest component (octyl glucoside) at low and ambient temperatures, the aqueous channel diameter increasing twice to approximately 7 nm. DLarge appears to be built up from an assembly of cubosomic domains, which may coexist with an amphiphilic lamellae domain at low temperatures. The chemical stimulus concentration can be selected as to tune the hydration of the nanochannels in the DLarge phase and its transformation into a DNormal phase at temperatures above the body temperature. Two-dimensional SANS images recorded upon heating scan reveal growth of spontaneously oriented domains of single-crystal cubic nature. Phase separation and squeezing out the guest-hydrating agent from the higher-curvature regions of the amphiphilic bilayer suggest a possible mechanism for the established transformations. The order-order structural transition, cubic DLarge-cubic DNormal, is found to be reversible upon cooling. The obtained results put forward a structure-based concept for release of encapsulated guest molecules from stimuli-responsive and self-regulated cubosomic nanocarriers.     

The preparation and characterization of amphiphilic core/shell particles

Colloidal amphiphilic particles were prepared with hydrophilic polyacrylamide cores encapsulated by hydrophobic poly(butyl methacrylate) shells. The hydrophobic shell possessed a porous structure, which made the hydrophilic core accessible to the outside liquid. The amphiphilicity of the particles was characterized by their water and diesel oil absorbabilities. The effect of the polymerization conditions on the structure and thickness of the hydrophobic layer was investigated in some detail. Such amphiphilic particles can be dispersed in both water and hydrophobic liquids, and the dispersions have a long life in water and a more moderate one in oil.     

Synthesis and self-assembly of "tree-like" amphiphilic glycopolypeptides

Novel synthetic tree-like oligosaccharides-grafted-polypeptides were prepared by using Huisgen 1,3-dipolar cycloaddition between poly(γ-benzyl-L-glutamate)-block-poly(propargylglycine) and two different oligosaccharides, dextran or hyaluronan. By direct solubilisation in water, these tree-like glycopeptides spontaneously form very small assemblies with sizes below 50 nm and low polydispersity.     

Nematic phase formed by banana-shaped molecules

Most mesogens formed by banana-shaped molecules exhibit liquid-like smectic phases. Here we present the synthesis and properties of homologous series of derivatives of resorcinol and 2,6-disubstituted pyridine. One of these classes of bent-core molecules displays the nematic phase.     

Formation of reversible shell cross-linked micelles from the biodegradable amphiphilic diblock copolymer poly(L-cysteine)-block-poly(L-lactide)

A novel biodegradable diblock copolymer, poly(L-cysteine)-b-poly(L-lactide) (PLC-b-PLLA), was synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride of beta-benzyloxycarbonyl-L-cysteine (ZLC-NCA) with amino-terminated poly(L-lactide) (NH 2-PLLA) as a macroinitiator in a convenient way. The diblock copolymer and its precursor were characterized by (1)H NMR, Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS) measurements. The length of each block polymer could be tailored by molecular design and the ratios of feeding monomers. The cell adhesion and cell spread on the PZLC-b-PLLA and PLC-b-PLLA films were enhanced compared to those on pure PLA film. PLC-b-PLLA can self-assemble to form micelles in aqueous media. A pyrene probe is used to demonstrate the micelle formation of PLC-b-PLLA in aqueous solution. Due to the ease of disulfide exchange with thiols, the obtained micelles are reversible shell cross-linked (SCL) micelles. The morphology and size of the micelles are studied by dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM).     

Nematic phase formed by banana-shaped molecules

Most mesogens formed by banana-shaped molecules exhibit liquid-like smectic phases. Here we present the synthesis and properties of homologous series of derivatives of resorcinol and 2,6-disubstituted pyridine. One of these classes of bent-core molecules displays the nematic phase.     

Morphology of polytetrafluoroethylene coatings formed from the active gas phase and its thermal modification

Changes in the morphology and surface energy of polytetrafluoroethylene coatings in the course of their growth and after annealing were determined.     

Silver baits for the "miraculous draught" of amphiphilic lanthanide helicates

The axial connection of flexible thioalkyls chains of variable length (n=1–12) within the segmental bis‐tridentate 2‐benzimidazole‐8‐hydroxyquinoline ligands [ L12 ^Cn?2 H]^2? provides amphiphilic receptors designed for the synthesis of neutral dinuclear lanthanides helicates. However, the stoichiometric mixing of metals and ligands in basic media only yields intricate mixtures of poorly soluble aggregates. The addition of Ag^I in solution restores classical helicate architectures for n=3, with the quantitative formation of the discrete D₃‐symmetrical [Ln₂Ag2( L12 ^C3?2 H)₃]²⁺ complexes at millimolar concentration (Ln=La, Eu, Lu). The X‐ray crystal structure supports the formation of [La₂Ag₂( L12 ^C3?2 H)₃][OTf]₂, which exists in the solid state as infinite linear polymers bridged by S‐Ag‐S bonds. In contrast, molecular dynamics (MD) simulations in the gas phase and in solution confirm the experimental diffusion measurements, which imply the formation of discrete molecular entities in these media, in which the sulfur atoms of each lipophilic ligand are rapidly exchanged within the Ag^I coordination sphere. Turned as a predictive tool, MD suggests that this Ag^I templating effect is efficient only for n=1–3, while for n>3 very loose interactions occur between Ag^I and the thioalkyl residues. The subsequent experimental demonstration that only 25 % of the total ligand speciation contributes to the formation of [Ln₂Ag₂( L12 ^C12?2 H)₃]²⁺ in solution puts the bases for a rational approach for the design of amphiphilic helical complexes with predetermined molecular interfaces.     

Amphiphilic antioxidants from "cashew nut shell liquid" (CNSL) waste

Hydrogenated cardanol and cardols, contained in industrial grade cardanol oil and obtained by distillation of the raw "cashew nut shell liquid" (CNSL), are easily transformed into efficient 4-thiaflavane antioxidants bearing a long alkyl chain on A ring and a catechol group on B ring.     

"Micro-pottery"--marangoni effect driven assembly of amphiphilic fibers

We report spontaneous supra-assembly of fibrous surfactant crystallites at the air-solution interface resulting in spectacular arrays of two-dimensional spiral and three-dimensional "micro-pottery"-like superstructures. Surface pressure differential driven bending of the embryonic fiber nuclei and Marangoni convection driven fiber migration/alignment appear to be the causal factors behind this phenomenon. The assemblies form at specific crystal-growth velocities dictated by the relative time scales for fiber bending/alignment and their rigidification/immobilization as they grow. Although our studies are restricted to a specific class of amphiphiles, namely, alkaline metal salts of linear fatty acids, the phenomenon should be generic to amphiphilic molecules that crystallize into flexible fibers.