Ribbon-like Micelles Research Articles

Divergence Entropy-Based Evaluation of Hydrophobic Core in Aggressive and Resistant Forms of Transthyretin.

The two forms of transthyretin differing slightly in the tertiary structure, despite the presence of five mutations, show radically different properties in terms of susceptibility to the amyloid transformation process. These two forms of transthyretin are the object of analysis. The search for the sources of these differences was carried out by means of a comparative analysis of the structure of these molecules in their native and early intermediate stage forms in the folding process. The criterion for assessing the degree of similarity and differences is the status of the hydrophobic core. The comparison of the level of arrangement of the hydrophobic core and its initial stages is possible thanks to the application of divergence entropy for the early intermediate stage and for the final forms. It was shown that the minimal differences observed in the structure of the hydrophobic core of the forms available in PDB, turned out to be significantly different in the early stage (ES) structure in folding process. The determined values of divergence entropy for both ES forms indicate the presence of the seed of hydrophobic core only in the form resistant to amyloid transformation. In the form of aggressively undergoing amyloid transformation, the structure lacking such a seed is revealed, being a stretched one with a high content of β-type structure. In the discussed case, the active presence of water in the structural transformation of proteins expressed in the fuzzy oil drop model (FOD) is of decisive importance for the generation of the final protein structure. It has been shown that the resistant form tends to generate a centric hydrophobic core with the possibility of creating a globular structure, i.e., a spherical micelle-like form. The aggressively transforming form reveals in the structure of its early intermediate, a tendency to form the ribbon-like micelle as observed in amyloid.

Thermoresponsive Structure and Dye Encapsulation of Micelles Comprising Bolaamphiphilic Quercetin Polyglycoside.

A bolaamphiphile is a special member of amphiphilic molecules, which contains a hydrophobic skeleton and two water-soluble groups on both ends. Bolaamphiphiles form thermally stable associates in water under lower concentration than those of typical monoheaded amphiphiles, indicating the potential usefulness of bolaamphiphiles as the component of nanomaterials. However, the structural diversity of bolaamphiphiles is limited at this moment. We recently developed the synthesis of quercetin-3-O-polyglycoside (QP) as a new entry of bolaamphiphiles via a one-pot polymerization using sugar-based cyclic sulfite initiated by quercetin skeleton. Herein, we show the bolaamphiphilic properties of QP in detail. The micellization behaviors of QP are systematically investigated through comparison with those of quercetin (Que) and isoquercitrin (IQ) to evaluate the roles of glycone on the micellization of quercetin derivatives. The morphology of the micelles bearing QP is observed by cryo-transmission electron microscopy (cryo-TEM), suggesting the formation of bolaamphiphile-specific giant ribbon-like micelles in addition to spherical micelles. The thermoresponsive micellization behaviors are also discussed through the critical micelle concentration (CMC) values, the dynamic light scattering analyses at various temperatures, and thermal hysteresis of the micellizations. It is indicated that the polysaccharide chains integrated on the surface of micelles would serve as a steric protecting group to endow the micelles with kinetic stability. These results will shed light on natural glycoside skeletons to design a new class of micelles for advanced health applications in near future.

Effects of Sugar Chain Length of Quercetin-3-O-Glycosides on Micellization in Aqueous Media

A bolaamphiphile contains a hydrophobic skeleton and two water-soluble groups on the both ends. Bolaamphiphile forms thermally stable associates in water under lower concentration than those of typical mono-headed amphiphiles, indicating the potential usefulness of bolaamphiphile as the component of nano-materials. However, the structural diversity of bolaamphiphiles is limited at this moment. Herein, we show the bolaamphiphilic properties of naturally occurring quercetin glycosides. In addition to natural flavonoids, quercetin (Que) and isoquercitrin (IQ), we have prepared quercetin polyglycoside (QP) via one-pot grafting polymerization using sugar-based cyclic sulfite as a monomer, which plays a crucial role to elucidate the effects of sugar chain length on the micellization. The micellization behaviors of QP are systematically investigated through the comparison with those of Que and IQ. The polyphenolic structures of quercetin derivatives exhibit unique pH-dependency of critical micelle concentration (CMC). While Que hardly forms micelles in pH 10.0 aqueous medium, the solutions of IQ and QP form micelles in the same medium, indicating that the sugar chain would endow the micelles with pH-tolerance. The effects of sugar chain length on the micellization behaviors are discussed through the time-course of UV-vis spectra and the profiles of dynamic light scattering (DLS) analyses. The morphology of the micelles bearing QP is observed by transmission electron microscopy (TEM), suggesting the formation of bolaamphiphile-specific helical ribbon-like micelles. It is indicated that the polysaccharide chains integrated on the surface of micelle would serve as a steric protecting group to afford kinetically stable micelles.

Alternative Structures of α-Synuclein.

The object of our analysis is the structure of alpha-synuclein (ASyn), which, under in vivo conditions, associates with presynaptic vesicles. Misfolding of ASyn is known to be implicated in Parkinson’s disease. The availability of structural information for both the micelle-bound and amyloid form of ASyn enables us to speculate on the specific mechanism of amyloid transformation. This analysis is all the more interesting given the fact that—Unlike in Aβ(1–42) amyloids—only the central fragment (30–100) of ASyn has a fibrillar structure, whereas, its N- and C-terminal fragments (1–30 and 100–140, respectively) are described as random coils. Our work addresses the following question: Can the ASyn chain—as well as the aforementioned individual fragments—adopt globular conformations? In order to provide an answer, we subjected the corresponding sequences to simulations carried out using Robetta and I-Tasser, both of which are regarded as accurate protein structure predictors. In addition, we also applied the fuzzy oil drop (FOD) model, which, in addition to optimizing the protein’s internal free energy, acknowledges the presence of an external force field contributed by the aqueous solvent. This field directs hydrophobic residues to congregate near the center of the protein body while exposing hydrophilic residues on its surface. Comparative analysis of the obtained models suggests that fragments which do not participate in forming the amyloid fibril (i.e., 1–30 and 100–140) can indeed attain globular conformations. We also explain the influence of mutations observed in vivo upon the susceptibility of ASyn to undergo amyloid transformation. In particular, the 30–100 fragment (which adopts a fibrillar structure in PDB) is not predicted to produce a centralized hydrophobic core by any of the applied toolkits (Robetta, I-Tasser, and FOD). This means that in order to minimize the entropically disadvantageous contact between hydrophobic residues and the polar solvent, ASyn adopts the form of a ribbonlike micelle (rather than a spherical one). In other words, the ribbonlike micelle represents a synergy between the conformational preferences of the protein chain and the influence of its environment.

The Amyloid as a Ribbon-Like Micelle in Contrast to Spherical Micelles Represented by Globular Proteins.

Selected amyloid structures available in the Protein Data Bank have been subjected to a comparative analysis. Classification is based on the distribution of hydrophobicity in amyloids that differ with respect to sequence, chain length, the distribution of beta folds, protofibril structure, and the arrangement of protofibrils in each superfibril. The study set includes the following amyloids: Aβ (1–42), which is listed as Aβ (15–40) and carries the D23N mutation, and Aβ (11–42) and Aβ (1–40), both of which carry the E22Δ mutation, tau amyloid, and α-synuclein. Based on the fuzzy oil drop model (FOD), we determined that, despite their conformational diversity, all presented amyloids adopt a similar structural pattern that can be described as a ribbon-like micelle. The same model, when applied to globular proteins, results in structures referred to as “globular micelles,” emerging as a result of interactions between the proteins’ constituent residues and the aqueous solvent. Due to their composition, amyloids are unable to attain entropically favorable globular forms and instead attempt to limit contact between hydrophobic residues and water by producing elongated structures. Such structures typically contain quasi hydrophobic cores that stretch along the fibril’s long axis. Similar properties are commonly found in ribbon-like micelles, with alternating bands of high and low hydrophobicity emerging as the fibrils increase in length. Thus, while globular proteins are generally consistent with a 3D Gaussian distribution of hydrophobicity, the distribution instead conforms to a 2D Gaussian distribution in amyloid fibrils.

Nanoribbons with semicrystalline core dispersed in a visible-light photopolymerized epoxy network

It has been well documented that self-assembly of block copolymers (BCP) in selective solvents, where the core-forming block is a crystallizable polymer, results in micelle structures with exceptional aggregation morphologies determined mainly by the crystallization energy from the core. In this contribution, we apply this concept to create ribbon-like nanostructures dispersed in an epoxy network. The selected system was a polyethylene-b-poly(ethylene oxide) (PE-b-PEO) diblock copolymer in an epoxy monomer based on diglycidyl ether of bisphenol A (DGEBA). This system was selected on the bases that PEO is an epoxy-philic block which is completely miscible with DGEBA before and after curing reaction whereas PE is a crystallizable epoxy-phobic block. Under these conditions, we access to self-assembled nanostructures with semicrystalline core before curing reaction. With the aim of preserving the structural features of these micelles, the epoxy monomers were cured at room temperature (i.e., below the melting transition of the core-forming PE block) by photoinitiated cationic ring-opening polymerization. Long nanoribbons dispersed in the cured epoxy matrix were obtained, as characterized by SAXS patterns and TEM images. These ribbon-like micelles present a tendency to aggregate resulting in the formation of face-to-face stacking of parallel micelles. We demonstrated that while the stacking number decreases with decreasing BCP concentration, the arrangement of the nanoribbons within one stack becomes less organized.

Stimulus-Responsive Self-Assembly: Reversible, Redox-Controlled Micellization of Polyferrocenylsilane Diblock Copolymers

In depth studies of the use of electron transfer reactions as a means to control the self-assembly of diblock copolymers with an electroactive metalloblock are reported. Specifically, the redox-triggered self-assembly of a series of polystyrene-block-polyferrocenylsilane (PS-b-PFS) diblock copolymers in dichloromethane solution is described. In the case of the amorphous polystyrene(n)-b-poly(ferrocenylphenylmethylsilane)(m) diblock copolymers (PS(n)-b-PFMPS(m): n = 548, m = 73; n = 71, m = 165; where n and m are the number-averaged degrees of polymerization), spherical micelles with an oxidized PFS core and a PS corona were formed upon oxidation of more than 50% of the ferrocenyl units by [N(C(6)H(4)Br-4)(3)][SbX(6)] (X = Cl, F). Analogous block copolymers containing a poly(ferrocenylethylmethylsilane) (PFEMS) metalloblock, which has a lower glass transition temperature, behaved similarly. However, in contrast, on replacement of the amorphous metallopolymer blocks by semicrystalline poly(ferrocenyldimethylsilane) (PFDMS) segments, a change in the observed morphology was detected with the formation of ribbon-like micelles upon oxidation of PS(535)-b-PFDMS(103) above the same threshold value. Again the coronas consisted of fully solvated PS and the core consisted of partially to fully oxidized PFS associated with the counteranions. When oxidation was performed with [N(C(6)H(4)Br-4)(3)][SbF(6)], reduction of the cores of the spherical or ribbon-like micelles with [Co(η-C(5)Me(5))(2)] enabled full recovery of the neutral chains and no significant chain scission was detected.

Phase behavior and microstructure evolution in aqueous mixtures of cetyltrimethylammonium bromide and sodium dodecyl tri-oxyethylene sulfate

Abstract The phase behavior and microstructural changes in aqueous mixtures of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl tri-oxyethylene sulfate (C12E3S) are reported. The mixing behavior of the two surfactants is investigated via surface tension measurements and the regular solution approximation yielded a β value of −13, indicating attractive interaction. The difference in the growth behavior of the micelles on the CTAB-rich and C12E3S-rich sides of the phase diagram is studied using viscosity, quasielastic light scattering, small angle neutron scattering, and cryogenic transmission electron microscopy (cryoTEM). Branched micelles are formed close to the phase boundary and are more prevalent in CTAB-rich micelles. A shear-induced transition of cylindrical to ribbon-like micelles is observed by cryoTEM in CTAB-rich micelles near the phase boundary. A temperature-induced phase transition is observed for C12E3S-rich micelles due to the dehydration and/or conformational changes of the hydrophilic oxyethylene part of C12E3S in the mixed micelles.

Bending Energetics of Tablet‐Shaped Micelles: A Novel Approach to Rationalize Micellar Systems

A novel approach to rationalize micellar systems is expounded in which the structural behavior of tablet-shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H0), bending rigidity (k(c)), and saddle-splay constant (k(c)). As a result, experimentally accessible micellar properties, such as aggregation number, length-to-width ratio, and polydispersity, may be related to the different bending elasticity constants. It is demonstrated that discrete micelles or connected cylinders form when H0 > 1/4xi, where xi is the thickness of a surfactant monolayer, whereas various bilayer structures are expected to predominate when H0 < 1/4xi. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet-shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critical surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydisperse elongated micelles (large length-to-width ratio) form as the bending rigidity is lowered, approaching the critical point at k(c) = 0, whereas monodisperse globular micelles (small length-to-width ratio) are expected to be present at large k(c) values. The spontaneous curvature mainly determines the width of tablet-shaped or ribbonlike micelles, or the radius of disklike micelles, whereas the saddle-splay constant primarily influences the size but not the shape of the micelles.

Multicompartment micelles and vesicles from π-shaped ABC block copolymers: a dissipative particle dynamics study

Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartment micelles and vesicles formed from pi-shaped ABC block copolymers in water. By varying the chain architecture and the composition of copolymers, a rich variety of morphologies were observed, such as oblate vesicles, trumpet vesicles, layered ribbon-like micelles and Y-shaped micelles. The simulations show that the hydrophilic block length and the distance between the two grafts play important roles in the control of the morphology. Since pi-shaped ABC block copolymers can reduce to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles or vesicles. Thus, the knowledge obtained in this work as well as the new morphologies identified provides useful information for future rational design and synthesis of novel multicompartment micelles and vesicles.

A Small-Angle Neutron Scattering (SANS) Study of Tablet-Shaped and Ribbonlike Micelles Formed from Mixtures of an Anionic and a Cationic Surfactant

Micelles formed in mixtures of an anionic (SDS) and a cationic (DTAB) surfactant, i.e., two surfactants with identical hydrocarbon C12 chains, in either pure (heavy) water or 0.1 M NaBr brine at 40...

Formation of Tablet-Shaped and Ribbonlike Micelles in Mixtures of an Anionic and a Cationic Surfactant

SANS experiments demonstrate the formation of tablet-shaped micelles in aqueous mixtures of an anionic (SDS) and a cationic (DTAB) surfactant. The micelles grow in size as equimolar composition is approached at a given surfactant concentration or when the mixtures are diluted at low concentrations at a given surfactant composition. In the absence of added salt, both the width and the length of the micelles increase significantly, whereas, using 0.1 M NaBr brine as a solvent, the micelles grow dramatically in length but only very slightly in width. As a result, ribbonlike micelles as long as several thousand angstroms form in the latter case.

Micellar structures in lyotropic liquid crystals and phase transitions

The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.

“Cross-β” conformation in proteins

A structure is proposed to explain the X-ray diffraction pattern of a naturally occurring cross-β fibrous protein. The well-oriented fibres contain ribbon-like micelles about 25 Å thick with their longest dimension parallel to the fibre axis. The ribbons are packed face to face with a variable interfacial separation around a mean of 15 ± 4 Å. The inner structure of the ribbons is basically that of the Tussah silk model as described by Marsh, Corey & Pauling (1955), but in the cross-β conformation the extended parts of the polypeptide chains run at right angles to the fibre axis. In the protein studied these extended parts are linked together by short “bend” regions to form continuous folded polypeptide chains which lie in planes normal to the surface of the ribbon-like micelles and parallel to their long axis.