Spotted vesicles, striped micelles and Janus assemblies induced by ligand binding (original) (raw)
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Physical Chemistry Chemical Physics, 2013
We have studied the self-assembly of aqueous dispersions of amphiphilic di-and triblock copolyelectrolytes using static and dynamic light scattering. The hydrophobic blocks contained both ionisable and hydrophobic units rendering the association dynamic and thus ensuring that thermodynamic equilibrium was reached. The incorporation of ionisable units into the hydrophobic blocks caused the self-assembly to be strongly influenced by the pH and the ionic strength. As in the case of neutral block copolymers, diblock copolyelectrolytes self-assembled into star-like micelles and triblock copolyelectrolytes formed flower-like micelles. The latter was not predicted to occur for block copolyelectrolytes. At higher concentrations a system spanning network was formed. The structure of the systems could be quantitatively described by a model of purely repulsive spheres for the diblocks and attractive spheres for the triblocks. The polyelectrolyte effect expressed itself by a sensitivity of the structure to the pH and the ionic strength. The attraction increased with decreasing pH and increasing ionic strength leading at high ionic strength to phase separation.
Self-assembly based on hydrotropic counterion—single-chain amphiphile ion pairs
Colloid and Polymer Science, 2010
We investigate the effect of organic hydrotropic counterions on the self-assembled structures formed by pure counterion-single-chain amphiphile ion pairs. The effect of inorganic counterions on singlechain amphiphiles has been studied for years, taking into account the Hofmeister series that directly affects the micellization. Here, hexadecyldimethylbenzylammonium salicylate (C16Sal) in aqueous solution is used as a model for the influence of organic counterions, and the results have been compared with those previously published for inorganic counterions, specifically hexadecyldimethylbenzylammonium chloride (C16Cl). The studies have been performed by using conductivity, dynamic light scattering, as well as atomic force microscopy. We demonstrate the formation of vesicles and suggest the presence of a vesicle-to-micelle transition at higher concentrations. The Gibbs free energy associated with the self-assembly process has been estimated on the basis of the well-known massaction model. The main conclusion is that the use of hydrotropic counterions instead of classical inorganic ions dramatically changes the packing parameter of singlechain amphiphiles to higher values, resulting in bilayer structures. We propose that these systems are good and cheap alternatives to double-chain amphiphiles for forming more complex structures like vesicles.
Current Opinion in Solid …, 2011
Polymer micelles and vesicles form upon hydration of amphiphilic block copolymers in dilute aqueous solution. Present challenges with these self-assemblies include understanding how molecular structure and polydispersity determine nano-and mesoscopic shape and properties such as flexibility. With charged copolymers, divalent ionic ligands can rigidify polymer vesicle membranes and also induce microphase separation into domains of weak polyelectrolyte gels. In this review, we focus on the underlying physical and molecular questions concerning copolymer assembly and associated challenges and implications for nano-delivery materials. We also highlight molecular simulation techniques that can be used to investigate properties of assemblies, such as curvature, patterning, and other ionic effects in functional polymeric membranes and micelles.
Journal of Dispersion Science and Technology, 2018
We report herein, the aggregation behavior of 3, 4-di(dodecyloxy)benzoic acid-4-hydroxy phenyl ester (DDBE), a synthetic amphiphile and a true non-ionic surfactant system as per the geometrical considerations. The true surfactant nature of the system stems from its hydrophilic-lipophilic-balance (HLB ¼ 4.7), comparable to that of Span-60, also a true non-ionic surfactant. This compound undergoes spontaneous vesicle formation in THF:water binary solvent mixtures which further underwent fission at lower DDBE concentrations and fusion at higher concentrations, leading to giant vesicles of the order of 3000 nm. These vesicles are sensitive to the polarity of their environment. The predominant mode of interaction as observed from the molecular dynamics simulations were found to be p-p stacking with the phenyl rings of the molecule. Further, the system, upon complete extraction into water, formed spherical aggregates of size 50 nm based on the good solvent-poor solvent combination as the necessary condition for the vesicle formation.
Elastin-like polypeptides (ELPs) are a class of biopolymers consisting of the pentameric repeat (VPGαG) n based on the sequence of mammalian tropoelastin that display a thermally induced soluble-to-insoluble phase transition in aqueous solution. We have discovered a remarkably simple approach to driving the spontaneous self-assembly of high molecular weight ELPs into nanostructures by genetically fusing a short 1.5 kDa (XG y ) z assembly domain to one end of the ELP. Classical theories of self-assembly based on the geometric mass balance of hydrophilic and hydrophobic block copolymers suggest that these highly asymmetric polypeptides should form spherical micelles. Surprisingly, when sufficiently hydrophobic amino acids (X) are presented in a periodic sequence such as (FGG) 8 or (YG) 8 , these highly asymmetric polypeptides selfassemble into cylindrical micelles whose length can be tuned by the sequence of the morphogenic tag. These nanostructures were characterized by light scattering, tunable resistive pulse sensing, fluorescence spectrophotometry, and thermal turbidimetry, as well as by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). These short assembly domains provide a facile strategy to control the size, shape, and stability of stimuli responsive polypeptide nanostructures.
Bulletin of the American Physical Society, 2016
Chemistry-The ability to control the nano and the meso-scale architecture of molecular assemblies is one of the major challenges in nanoscience. Significantly, structural transformations of amphiphilic aggregates induced by variations in environmental conditions have attracted attention due to their biotechnological relevance. Here, we study the assembly in aqueous solution for a modular series of peptide amphiphiles with 3, 2 or 1 lysine groups conjugated to a C 16 carbon tail (C 16 K 3 , C 16 K 2, and C 16 K 1). This system design allow us to probe how the equilibrium structure of the self-assembly can be tuned by controlling the coupling between steric (via choice of headgroup: K3, K2, or K1) and electrostatic (via solution pH) interactions. Solution small-and wide-angle Xray scattering (SAXS/WAXS) and transmission electron microscopy (TEM) studies reveal that depending on pH and number of lysines in the lipid headgroup, amphiphiles can assemble into a range of structures: spherical micelles, bilayer ribbons and vesicles. We also perform detailed phase space mapping of pH-and headgroup size dependency of the structures of assembly over 0.1-100 nm length scales via SAXS/WAXS. The experimental results in conjunction with molecular dynamics (MD) simulations deduce quantitative relations between pH-dependent molecular charges, steric constraints and self-assembly morphologies, which is significant for developing experimental routes to obtain assembly structures with specific nanoand meso-scale features through controlled external stimuli.