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© 2015 Macmillan Publishers Limited. Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (∼50 mJm-2) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (

An electrostatic complexation of liposomes, composed of anionic palmitoyloleoyl phosphatidylserine (POPS1-) and zwitterionic dioleoylphophatidylcholine (DOPC), with bilayer vesicles composed of cationic poly(l-lysine)-b-poly(l-leucine) block copolypeptides has been investigated. The complexation was characterized by several physicochemical methods with the following main conclusions: (a) all added liposomes are totally adsorbed on the polypeptide vesicles up to a certain saturation concentration. (b) The calculated number of liposomes per a single polypeptide vesicle is about 60. (c) The liposomes remain intact (i.e., do not leak) after being complexed with the vesicles. (d) Complexes are stable in physiological ionic strength solution with [NaCl] = 0.15 M. (e) The vesicles are effectively digested by proteolytic enzyme trypsin even when covered by liposomes. These findings as well as the high potential for loading of anionic liposomes and cationic vesicles with biologically active compounds make these multi-liposomal complexes promising in the drug delivery field.

Abstract: An ABC type amphiphilic triblock copolymer poly(ethylene glycol)–b-poly(acrylic acid)–b-poly(styrene), PEG47–b-PAA126–b-PSt32, was successfully synthesized by reversible addition–fragmentation chain transfer (RAFT) controlled radical polymerization, and was characterized by 1H NMR and gel permeation chromatography (GPC). The pH and salt responsive micellization of the copolymer in aqueous solution was studied using dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (Cryo-TEM). The micelle is composed of a hydrophobic PSt core, PAA shell and PEG corona with hydrodynamic size (D h) of ∼80nm independent of the copolymer concentration at 30°C and pH=3.5. The complexation results from collapse of the polymer chains, which is induced by the contraction of PAA chains and the enhanced association between PAA and PEG chains. The changes in the D h of micelles at different pH and in the presence of two salts, sodium sulfate (Na2SO4) and calcium chloride (CaCl2) are reported. Both salts increase D h; CaCl2 interacts with PAA and Na2SO4 with PEG, making the respective polymer block less hydrophilic. We further find that in presence of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), micelle size decreased. Such stimuli-responsive block copolymers may be attractive candidates as “smart” pH- and salt-responsive drug delivery systems. [Copyright &y& Elsevier]

The term supramolecular polymer has been applied to polymeric materials in which the individual units, i.e., building blocks-are bound to each other via noncovalent interactions, including electrostatic or hydrogen bonding, as well as metal-ligand conjugation. The building blocks are generally low molecular weight amphiphiles. Methods for preparing biopolymers based on non-toxic, metal-ligand conjugation have been little studied; however, they offer significant potential for tuning the response of biologically relevant macromolecules. In this communication, we characterize the assembly and morphology of supramolecular biopolymers in which the building blocks are low- or medium-molecular weight globular proteins-ubiquitin and Cas9-interacting via metal-ligand conjugation. In each case, the protein gene was expressed in cell culture with the addition of hexa-His/linkers at both the N and C termini. Divalent cations investigated were Zn 2+ and Ni 2+ . We observe in cryo-TEM imaging an absolute requirement for divalent cations for the formation of supramolecular biopolymers. In the presence of Ni 2+ , 1D assembled fibers are predominant, while with Zn 2+ , the more frequently detected structures are sheet-like. We use gel electrophoresis and CD spectroscopy to monitor possible secondary and tertiary structural changes in the protein building blocks during conjugation., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

Alzheimer's disease (AD) is characterized by toxic protein accumulation in the brain. Ubiquitination is essential for protein clearance in cells, making altered ubiquitin signaling crucial in AD development. A defective variant, ubiquitin B + 1 (UBB +1 ), created by a non-hereditary RNA frameshift mutation, is found in all AD patient brains post-mortem. We now detect UBB +1 in human brains during early AD stages. Our study employs a 3D neural culture platform derived from human neural progenitors, demonstrating that UBB +1 alone induces extracellular amyloid-β (Aβ) deposits and insoluble hyperphosphorylated tau aggregates. UBB +1 competes with ubiquitin for binding to the deubiquitinating enzyme UCHL1, leading to elevated levels of amyloid precursor protein (APP), secreted Aβ peptides, and Aβ build-up. Crucially, silencing UBB +1 expression impedes the emergence of AD hallmarks in this model system. Our findings highlight the significance of ubiquitin signalling as a variable contributing to AD pathology and present a nonclinical platform for testing potential therapeutics., (© 2023. Springer Nature Limited.)

Molecular self-assembly forms structures of well-defined organization that allow control over material properties, affording many advanced technological applications. Although the self-assembly of molecules is seemingly spontaneous, the structure into which they assemble can be altered by carefully modulating the driving forces. Here we study the self-assembly within the constraints of nanoconfined closed spherical volumes of polymeric nanocapsules, whereby a mixture of polyester-polyether block copolymer and methacrylic acid methyl methacrylate copolymer forms the entrapping capsule shell of nanometric dimensions. We follow the organization of the organic dye indigo carmine that serves as a model building unit due to its tendency to self-assemble into flat lamellar molecular sheets. Analysis of the structures formed inside the nanoconfined space using cryogenic-transmission electron microscopy (cryo-TEM) and cryogenic-electron tomography (cryo-ET) reveal that confinement drives the self-assembly to produce tubular scroll-like structures of the dye. Combined continuum theory and molecular modeling allow us to estimate the material properties of the confined nanosheets, including their elasticity and brittleness. Finally, we comment on the formation mechanism and forces that govern self-assembly under nanoconfinement.

We report on the phase behavior of a technical grade and commercially available diglycerol monoisostearate, C41V, and its use for the preparation of nanostructured liquid crystal dispersions (hexosomes). C41V in water forms a reverse hexagonal liquid crystal at room temperature and in a wide range of concentrations (0.5-95 wt%); this hexagonal liquid crystal is stable up to 70 °C. A simple and effective method has been developed to disperse hexosomes with an encapsulated active molecule (Ketoprofen) that consists of (1) producing a nano-emulsion stabilized by an amphiphilic block copolymer (Pluronic F127) and containing ethyl acetate and C41V by using ultrasounds and (2) evaporating the solvent to produce hexosomes. The size of the hexosomes and ultrasound dispersion time is markedly reduced by using ethyl acetate as an auxiliary solvent with an optimal initial ratio of C41V:ethyl acetate of 50:50. Dynamic light scattering shows that the size of the hexosomes decreases as the concentration of stabilizer F127 or encapsulated Ketoprofen is increased. The lattice parameter in the hexagonal structure is calculated from small angle scattering data to be ca. 5.3  nm and is only slightly dependent on the amount of F127 and/or encapsulated Ketoprofen. Cryo electron microscopy reveals that the samples contain hexosomes and these coexist with spherical, likely F127 micelles. Lastly, hexosomes show a pH responsive release of Ketoprofen which could be useful for target delivery in the gastrointestinal tract., (Copyright © 2019 Elsevier Inc. All rights reserved.)

We report the first demonstration of nonionic detergent micelle conjugation and phase separation using purpose-synthesized, peptide amphiphiles, C 10 -(Asp) 5 and C 10 -(Lys) 5 . Clustering is achieved in two different ways. Micelles containing the negatively charged peptide amphiphile C 10 -(Asp) 5 are conjugated (a) via a water-soluble, penta-Lys mediator or (b) to micelles containing the C 10 -(Lys) 5 peptide amphiphile. Both routes lead to phase separation in the form of oil-rich globules visible in the light microscope. The hydrophobic nature of these regions leads to spontaneous partitioning of hydrophobic dyes into globules that were found to be stable for weeks to months. Extension of the conjugation mechanism to micelles containing a recently discovered, light-driven proton pump King Sejong 1-2 (KS1-2) demonstrates that a membrane protein may be concentrated using peptide amphiphiles while preserving its native conformation as determined by characteristic UV absorption. The potential utility of these peptide amphiphiles for biophysical and biomedical applications is discussed., (© 2019 European Peptide Society and John Wiley & Sons, Ltd.)

Contrary to everyday experience, where all liquid droplets assume rounded, near-spherical shapes, the temperature-tuning of liquid droplets to faceted polyhedral shapes and to spontaneous splitting has been recently demonstrated in oil-in-water emulsions. However, the elucidation of the mechanism driving these surprising effects, as well as their many potential applications, ranging from faceted nanoparticle synthesis through new industrial emulsification routes to controlled-release drug delivery within the human body, have been severely hampered by the micron-scale resolution of the light microscopy employed to date in all in situ studies. Thus, the thickness of the interfacially frozen crystalline monolayer, suggested to drive these effects, could not be directly measured, and the low limit on the droplet size still showing these effects remained unknown. In this study, we employ a combination of super-resolution stimulated emission depletion microscopy, cryogenic transmission and freeze-fracture electron microscopy, to study these effects well into the nanometer length scale. We demonstrate the occurrence of the faceting transition in droplets spanning an incredible 12 decades in volume from nanoliters to yoctoliters and directly visualize the interfacially frozen, few nanometer thick, crystalline monolayer suggested to drive these effects. Furthermore, our measurements allow placing an upper-limit estimate on the two-dimensional Young modulus of the interfacial nanometer-thick surface crystal in the smallest droplets, providing insights into the virtually unexplored domain of nanoelasticity.

We introduce a new concept and potentially general platform for antibody (Ab) purification that does not rely on chromatography or specific ligands (e.g., Protein A); rather, it makes use of detergent aggregates capable of efficiently capturing Ab while rejecting hydrophilic impurities. Captured Ab are then extracted from the aggregates in pure form without co-extraction of hydrophobic impurities or aggregate dissolution. The aggregates studied consist of conjugated "Engineered-micelles" built from the nonionic detergent, Tween-20; bathophenanthroline, a hydrophobic metal chelator, and Fe 2+ ions. When tested in serum-free media with or without bovine serum albumin as additive, human or mouse IgGs were recovered with good overall yields (70-80%, by densitometry). Extraction of IgGs with 7 different buffers at pH 3.8 sheds light on possible interactions between captured Ab and their surrounding detergent matrix that lead to purity very similar to that obtained via Protein A or Protein G resins. Extracted Ab preserve their secondary structure, specificity and monomeric character as determined by circular dichroism, enzyme-linked immunosorbent assay and dynamic light scattering, respectively.

Researchers have explored the ability of chitosan to form nanoparticles, to suit varying applications, ranging from wound-healing to gene delivery. Ionic gelation is a widely used method for formulating chitosan nanoparticles, where self-assembly plays a crucial role. This self-assembly is initially promoted by hydrophilic-hydrophobic parity amongst individual chitosan residues, along with electrostatic and Van der Waals interactions with the cross-linker. However, until now the intrinsic ability of chitosan to self-assemble is not widely studied; hence, we investigate the self-assembly of chitosan, based on proton balance between its protonated and deprotonated residues, to promote facile nanoparticle synthesis. This is one of the first reports that highlights subtle but critical influence of proton balance in the chitosan polymer on the formation of chitosan nanoparticles., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Ferritin turnover plays a major role in tissue iron homeostasis, and ferritin malfunction is associated with impaired iron homeostasis and neurodegenerative diseases. In most eukaryotes, ferritin is considered an intracellular protein that stores iron in a nontoxic and bioavailable form. In insects, ferritin is a classically secreted protein and plays a major role in systemic iron distribution. Mammalian ferritin lacks the signal peptide for classical endoplasmic reticulum-Golgi secretion but is found in serum and is secreted via a nonclassical lysosomal secretion pathway. This study applied bioinformatics and biochemical tools, alongside a protein trafficking mouse models, to characterize the mechanisms of ferritin secretion. Ferritin trafficking via the classical secretion pathway was ruled out, and a 2:1 distribution of intracellular ferritin between membrane-bound compartments and the cytosol was observed, suggesting a role for ferritin in the vesicular compartments of the cell. Focusing on nonclassical secretion, we analyzed mouse models of impaired endolysosomal trafficking and found that ferritin secretion was decreased by a BLOC-1 mutation but increased by BLOC-2, BLOC-3, and Rab27A mutations of the cellular trafficking machinery, suggesting multiple export routes. A 13-amino-acid motif unique to ferritins that lack the secretion signal peptide was identified on the BC-loop of both subunits and plays a role in the regulation of ferritin secretion. Finally, we provide evidence that secretion of iron-rich ferritin was mediated via the multivesicular body-exosome pathway. These results enhance our understanding of the mechanism of ferritin secretion, which is an important piece in the puzzle of tissue iron homeostasis.

For extremely asymmetric n-hexyl(n-decyl)phosphate (HDeP), n-hexyl(n-dodecyl)phosphate (HDoP), and n-hexyl(n-cetyl)phosphate (HCeP), the effect of the long-chains on the dynamic behavior of their aggregate structures in water was examined by cryo-TEM imaging, SANS, and X-ray diffraction techniques. The cryo-TEM images demonstrated the complex and dynamic behavior of the aggregates, and its dependence on the length of the long-chain. Application of the one-dimensional aggregate theory to the SANS results led to the conclusion that the existence of a limiting size also depended on the length of the main long-hydrocarbon chain and affected strongly the dynamic behavior of the aggregates, causing breakage of thread-like micelles or ribbon-like aggregates. The X-ray diffraction patterns of the lyotropic liquid crystalline samples of HDeP and HCeP were used to estimate the aggregate structures of this limited size.

The dearth of high quality, three dimensional crystals of membrane proteins, suitable for X-ray diffraction analysis, constitutes a serious barrier to progress in structural biology. To address this challenge, we have developed a new crystallization medium that relies on the conjugation of surfactant micelles via base-pairing of complementary hydrophobic nucleosides. Base-pairs formed at the interface between micelles bring them into proximity with each other; and when the conjugated micelles contain a membrane protein, crystal nucleation centers can be stabilized, thereby promoting crystal growth. Accordingly, two hydrophobic nucleoside derivatives - deoxyguanosine (G) and deoxycytidine (C), each covalently bonded to a 10 carbon chain were synthesized and added to an aqueous solution containing octyl β-d-thioglucopyranoside micelles. These hydrophobic nucleosides induced the formation of oil-rich globules after 2days incubation at 19°C or after a few hours in the presence of ammonium sulfate; however, phase separation was inhibited by 100mM GMP. The presence of the membrane protein bacteriorhodopsin in the conjugated - micellar dispersion resulted in the growth within the colorless globules of a variety of purple crystals, the color indicating a functional protein. On this basis, we suggest that conjugation of micelles via base-pair complementarity may provide significant assistance to the structural determination of integral membrane proteins., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The lipid liquid crystalline sponge phase (L3) has the advantages that it is a nanoscopically bicontinuous bilayer network able to accommodate large amounts of water and it is easy to manipulate due to its fluidity. This paper reports on the detailed characterization of L3 phases with water channels large enough to encapsulate bioactive macromolecules such as proteins. The aqueous phase behavior of a novel lipid mixture system, consisting of diglycerol monooleate (DGMO), and a mixture of mono-, di- and triglycerides (Capmul GMO-50) was studied. In addition, sponge-like nanoparticles (NPs) stabilized by Polysorbate 80 (P80) were prepared based on the DGMO/GMO-50 system, and their structure was correlated with the phase behavior of the corresponding bulk system. These NPs were characterized by dynamic light scattering (DLS), cryo-transmission electron microscopy (Cryo-TEM) and small angle X-ray scattering (SAXS) to determine their size, shape, and inner structure as a function of the DGMO/GMO-50 ratio. In addition, the effect of P80 as stabilizer was investigated. We found that the NPs have aqueous pores with diameters up to 13 nm, similar to the ones in the bulk phase.

Kappa-casein (κCN) and beta-casein (βCN) are disordered proteins present in mammalian milk. In vitro, βCN self-assembles into core-shell micelles. κCN self assembles into similar micelles, as well as into amyloid-like fibrils. Recent studies indicate that fibrillization can be suppressed by mixing βCN and κCN, but the mechanism of fibril inhibition has not been identified. Examining the interactions of native and reduced kappa-caseins (N-κCN and R-κCN) with βCN, we expose a competition between two different self-assembly processes: micellization and fibrillization. Quite surprisingly, however, we find significant qualitative and quantitative differences in the self-assembly between the native and reduced κCN forms. Specifically, thermodynamic analysis reveals exothermic demicellization for βCN and its mixtures with R-κCN, as opposed to endothermic demicellization of N-κCN and its mixtures with βCN at the same temperature. Furthermore, with time, R-κCN/βCN mixtures undergo phase separation into pure βCN micelles and R-κCN fibrils, while in the N-κCN/βCN mixtures fibril formation is considerably delayed and mixed micelles persist for longer periods of time. Fibrils formed in N-κCN/βCN mixtures are shorter and more flexible than those formed in R-κCN/βCN systems. Interestingly, in the N-κCN/βCN mixtures, the sugar moieties of N-κCN oligomers seem to organize on the mixed micelles surface in a manner similar to the organization of κCN in milk casein micelles.

The association of building blocks into supramolecular polymers allows the fabrication of diverse functional architectures at the nanoscale. The use of minimal assembly units to explore polymer dynamics and phase transitions significantly contributes to the application of polymer physicochemical paradigms in the field of supramolecular polymers. We present a minimal model that displays spontaneous coordinated structural transitions between micro- and nanostructures, hydrogels with nanoscale order, and single crystals. The simple amphiphilic 9-fluorenylmethoxycarbonyl-3,4-dihydroxyphenylalanine (Fmoc-DOPA) modified amino acid undergoes a noninduced transition from spherical assemblies into nanofibrils followed by sol-gel transition, nanotube formation via intermediate assembly, and crystallization within the gel. Notably, the transition kinetics is slow enough to allow both multistage and multiscale characterization of the supramolecular arrangement using electron microscopy, vibrational and circular dichroism spectroscopies, nuclear magnetic resonance, and x-ray crystallography. This minimalistic system is the first comprehensive model for a complete spontaneous structural transition between diverse states governed by distinct molecular interactions.

β-Casein is a 24 kDa amphiphilic and unstructured protein that self-assembles into small core-shell micelles at a wide range of concentrations, pH values and temperatures. We recently developed the micelles as nanocarriers for oral delivery of hydrophobic drugs. In this paper we examined the effect of the hydrophobic non-steroidal anti-inflammatory drug (NSAID) ibuprofen on the micellar structure, as a function of temperature and loading. Using cryo-transmission electron microscopy (cryo-TEM) we find two routes of organization – mixed micellization and co-assembly (aggregation). The time-dependent events that characterize the second routes has been examined in detail. At 25 °C we find coexistence of small assemblies and larger aggregates of irregular (but defined) structures that contain the drug. Increasing the drug loading increases the relative number of the larger aggregates and their dimensions, leading eventually to the formation of long then branched structures, like in amphiphilic block copolymer solutions. Similar trends were identified for changes in the temperature. Combined, our results suggest that ibuprofen acts as a co-surfactant that possibly is localizes to the interface rather than being encapsulated in the micellar core as other NSAID hydrophobic drugs., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Spherical polycationic brushes (SPBs) were synthesized by grafting polycationic chains onto 100 nm polystyrene particles. These particles were exposed to unilamellar egg-lecithin (EL) liposomes with a mean diameter of 40 nm that had been rendered anionic via the presence of 10 molar% of phosphatidylserine (PS(1-)). The liposomes also contained 30 mole% of a morpholinocyclohexanol-based lipid (MOCH) that undergoes a conformational flip when the pH is decreased from 7.0 to 5.0. Mixtures of SPBs and liposomes at pH 7 gave an electrostatically-driven complex possessing, on average, about 40 liposomes for each SPB particle. It was found that the bound liposomes rapidly release much of their contents when the pH is reduced from 7.0 to 5.0 owing mostly to a MOCH conformational change that creates defects in the bilayer membrane. The drop in pH does not, however, induce a separation of the liposomes from the SPBs. Around 50-60% of the liposome contents escape before, it is reasoned, lateral and transmembrane motion of the membrane components heals the defects and prevents further release. Remarkably, the liposomes complexed with SPB release their cargo much faster than the identical but non-complexed liposomes.

The formation of hybrid materials consisting of membrane-coated silica nanoparticles (SiNPs) concentrated within small unilamellar vesicles (SUVs) of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) is described. They are formed by a simple self-assembly process resulting from invagination of the SiNPs into the SUVs and subsequent vesicle fusion, thereby retaining an almost constant size. This process was followed under conditions where it proceeds slowly and could be analyzed in structural detail. The finally formed well-defined SiNP-filled vesicles are long-time stable hybrid colloids and their structure is conveniently controlled by the initial mixing ratio of SiNPs and vesicles., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Conjugated engineered-micelles, i.e. micelles that are composed of nonionic detergents and hydrophobic chelators and subsequently conjugated in the presence of divalent metal ions, have been shown to be remarkably suited to the task of membrane protein purification, maintaining these proteins in their native state. They also efficiently solubilize highly hydrophobic antibiotics. To date, however, the morphological changes induced in the initially spherical or ellipsoidal micelles by conjugation have not been explored. In this study, the very rapid sample-vitrification protocol of cryogenic transmission electron microscopy (cryo-TEM) has been used to capture structural transformations that engineered-micelles undergo immediately following conjugation with the [(bathophenanthroline)3:Fe(2+)] hydrophobic complex. We found that condensed thread-like aggregates are formed when the detergents used are: octyl β-D-glucopyranoside (OG), octyl β-D-thioglucopyranoside (OTG) or pentaethylene glycol monododecyl ether (C12E5). However, with β-D-maltoside (DM), n-dodecyl β-D-maltoside (DDM) or β-D-glucopyranoside (DDG), lamellar structures, some of which appear as stacked lamellae or multilamellar vesicles (MLV's), were observed. Such architectural changes occur under very mild conditions i.e. low detergent concentration, no temperature or pH alterations and without the presence of any precipitants such as PEG or ammonium sulfate.

The influence of carbon nanotube (CNT) length on their macroscopic properties requires an accurate methodology for CNT length measurement. So far, existing techniques are limited to short (less than a few micrometers) CNTs and sample preparation methods that bias the measured values. Here, we show that the average length of carbon nanotubes (CNTs) can be measured by cryogenic transmission electron microscopy (cryo-TEM) of CNTs in chlorosulfonic acid. The method consists of dissolving at low concentration CNTs in chlorosulfonic acid (a true solvent), imaging the individual CNTs by cryo-TEM, and processing and analyzing the images to determine CNT length. By measuring the total CNT contour length and number of CNT ends in each image, and by applying statistical analysis, we extend the method to cases where each CNT is long enough to span many cryo-TEM images, making the direct length measurement of an entire CNT impractical. Hence, this new technique can be used effectively to estimate samples in a wide range of CNT lengths, although we find that cryo-TEM imaging may bias the measurement towards longer CNTs, which are easier to detect. Our statistical method is also applied to AFM images of CNTs to show that, by using only a few AFM images, it yields estimates that are consistent with literature techniques, based on individually measuring a higher number of CNTs.

A novel method for purifying membrane proteins is presented. The approach makes use of engineered micelles composed of a nonionic detergent, β-octylglucoside, and a hydrophobic metal chelator, bathophenanthroline. Via the chelators, the micelles are specifically conjugated, i.e., tethered, in the presence of Fe(2+) ions, thereby forming micellar aggregates which provide the environment for separation of lipid-soluble membrane proteins from water-soluble proteins. The micellar aggregates (here imaged by cryo-transmission electron microscopy) successfully purify the light driven proton pump, bacteriorhodopsin (bR), from E. coli lysate. Purification takes place within 15 min and can be performed both at room temperature and at 4 °C. More than 94% of the water-soluble macromolecules in the lysate are excluded, with recovery yields of the membrane protein ranging between 74% and 85%. Since this approach does not require precipitants, high concentrations of detergent to induce micellar aggregates, high temperature, or changes in pH, it is suggested that it may be applied to the purification of a wide variety of membrane proteins.

A spherical polycationic brush (SPB) is made by graft-polymerizing a cationic monomer onto the surface of a 100 nm polystyrene bead. It is possible to adsorb anionic liposomes (40-60 nm diameter) onto the SPBs while maintaining the liposome integrity. The liposomes were constructed with phosphatidyl choline (PC) admixed with 0.05-0.4 mol fraction of an dianionic lipid, cardiolipin (CL(2-)). As shown by electrophoretic mobility measurements, SPB-to-liposome complexation leads to a conversion from the initial positive charge of the copolymer to a negative charge. The higher the CL(2-) content of the liposomes, the lower the concentration needed for charge neutralization. Dynamic light scattering (DLS) revealed that multicomplex aggregates are formed with a maximum size at the SPB/liposome charge-equivalence point. Experiments with fluorescent-labeled liposomes show that at low CL(2-) content about 80 liposomes are adsorbed per SPB. As the mole fraction of CL(2-) increases from 0.05 to 0.4, fewer liposomes adsorb owing to electrostatic repulsion among neighboring liposomes. The effect of added NaCl also depends upon the CL(2-) content. With 0.05 mol fraction CL(2-), the SPB/liposome complex dissociates into its components at 0.15 M NaCl. With a mole fraction of >0.1, complexes fail to dissociate even at 1.2 M NaCl. Additional information about the SPB/liposome morphology was obtained from cryo-TEM. For example, cryo-TEM data confirm liposome integrity upon complexation, a behavior that contrasts with the liposome destruction as found with adsorption to many other types of surfaces.

Like-charged solid interfaces repel and separate from one another as much as possible. Charged interfaces composed of self-assembled charged-molecules such as lipids or proteins are ubiquitous. The present study shows that although charged lipid-membranes are sufficiently rigid, in order to swell as much as possible, they deviate markedly from the behavior of typical like-charged solids when diluted below a critical concentration (ca. 15 wt %). Unexpectedly, they swell into lamellar structures with spacing that is up to four times shorter than the layers should assume (if filling the entire available space). This process is reversible with respect to changing the lipid concentration. Additionally, the research shows that, although the repulsion between charged interfaces increases with temperature, like-charged membranes, remarkably, condense with increasing temperature. This effect is also shown to be reversible. Our findings hold for a wide range of conditions including varying membrane charge density, bending rigidity, salt concentration, and conditions of typical living systems. We attribute the limited swelling and condensation of the net repulsive interfaces to their self-assembled character. Unlike solids, membranes can rearrange to gain an effective entropic attraction, which increases with temperature and compensates for the work required for condensing the bilayers. Our findings provide new insight into the thermodynamics and self-organization of like-charged interfaces composed of self-assembled molecules such as charged biomaterials and supramolecular assemblies that are widely found in synthetic and natural constructs.

Spherical polycationic brushes, consisting of polystyrene particles with linear cationic macromolecules grafted onto their surfaces, were electrostatically complexed with small unilamellar anionic liposomes. Complexation was monitored using a multimethod approach that included laser electrophoresis, dynamic light scattering, fluorescence, cryogenic transmission electron microscopy, and conductivity. Liposomes adsorb onto the outer edges of the brushes rather than penetrate into their dense polycationic layer. The integrity of the liposomes remains unaltered when the liposomes reside on the polycationic brushes. The resulting complexes (roughly 40 liposomes per brush) do not dissociate into their components upon exposure to physiological solutions. The system is potentially useful in that liposomes are gathered into well-defined clusters with a high encapsulating potential. Multicomponent constructs can be easily prepared if polycationic brushes are allowed to bind to a mixture of liposomes that encapsulate different guests. This work provides an example of "systems chemistry" whereby as many as eight components, each with its own particular location and function (i.e., polystyrene core, polycationic graft, egg lecithin, cardiolipin, two fluorescent dyes, water, and buffer), collectively self-assemble.

Cryo-TEM and NaCl-leakage experiments demonstrated that the cationic polymer polylysine induces fusion of anionic liposomes but that the cationic polymer poly(N-ethyl-4-vinylpyridinium bromide) (PEVP) does not, although both polymers bind strongly to the liposomes. The difference was traced to the thickness of the coatings at constant charge coverage. Polylysine is believed to form planar β-sheets that are sufficiently thin to allow membrane fusion. In contrast, looping and disorganization among adsorbed PEVP molecules physically prevent fusion. A similar effect is likely to be applicable to important polycation-induced fusion of cell membranes.

Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, β-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO(101)PO(56)EO(101)), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled β-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above β-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/β-casein micelles. The negative enthalpy of micelle formation (ΔH) and cooperativity increase with raising β-casein concentration in solution. ζ-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of β-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.

Compared with quaternary ammonium cationic surfactants with saturated alkyl chains, quaternary ammonium cationic surfactants with one double-bond in their alkyl chains, when mixed with appropriate counterions (in certain molar concentration ratios, ξ), can reach much lower effective drag-reduction temperatures, while maintaining the upper drag-reduction temperature limit of the corresponding saturated drag reducing surfactant solutions. No previous study has compared the effects of cis- vs. trans-unsaturated alkyl hydrocarbon tail configurations (oleyl vs. elaidyl) trimethyl ammonium chloride cationic surfactants at different counterion/surfactant concentration ratios on micellar nanostructures, (1)H NMR spectra and on rheological and drag-reduction behavior of their solutions. Since neither pure oleyl (cis-) nor elaidyl (trans-) trimethyl ammonium chloride surfactants are commercially available, they were synthesized and their 5mM solutions with NaSal counterion at concentrations of 5mM, 7.5mM and 12.5mM were studied., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Complexes of curdlan and genistein were prepared using four different methods. The total amount of genistein in curdlan-genistein complexes prepared at 40 degrees C (system I) was significantly higher (2.3 mg/100 mg dry matter) than that in other systems studied: curdlan-genistein complexes prepared at 60 degrees C (system II; 1.8 mg/100 mg dry matter); curdlan-genistein gel complexes (system III; 1.0 mg/100 mg dry matter); and curdlan-genistein dimethyl sulfoxide complexes (system IV; 1.8 mg/100 mg dry matter). x-ray diffraction results indicate that complexation of curdlan with genistein changes the crystalline nature of the pure components. Particle size analysis, atomic force microscopy and scanning electron microscopy imaging of curdlan-genistein complexes showed strong difference in particle size, surface and distribution in comparison with pure curdlan, confirming our assumption of a molecular interaction between curdlan and genistein and the formation of a new structure, which was revealed at the nanoscale level. All the curdlan-genistein complexes showed prolonged genistein release of up to 72 h, enhanced upon enzymatic digestion of curdlan by lyticase, thus opening the possibility of release regulation by the incorporation of lyticase in the delivery system. It is therefore suggested that the complexes could be used as a delivery system for the protection and slow release of genistein in the digestive tract.

For the first time, cryo-TEM imaging is used to directly show spontaneous filling of carbon nanotubes immersed in a solvent in the native state at ambient conditions. Multi-walled carbon nanotubes are dissolved in chlorosulfonic acid, and the high contrast between the acid and the carbon shows the difference between filled and unfilled nanotubes.

We report that chlorosulfonic acid is a true solvent for a wide range of carbon nanotubes (CNTs), including single-walled (SWNTs), double-walled (DWNTs), multiwalled carbon nanotubes (MWNTs), and CNTs hundreds of micrometers long. The CNTs dissolve as individuals at low concentrations, as determined by cryo-TEM (cryogenic transmission electron microscopy), and form liquid-crystalline phases at high concentrations. The mechanism of dissolution is electrostatic stabilization through reversible protonation of the CNT side walls, as previously established for SWNTs. CNTs with highly defective side walls do not protonate sufficiently and, hence, do not dissolve. The dissolution and liquid-crystallinity of ultralong CNTs are critical advances in the liquid-phase processing of macroscopic CNT-based materials, such as fibers and films.

A new composition of a fully water-dilutable microemulsion system stabilized by natural surfactants is presented as a template for preparation of celecoxib nanoparticles. Nanoparticles are obtained as a dry powder upon rapid conversion of microemulsion droplets with dissolved celecoxib into nanoparticles, followed by evaporation of all the liquid in a spray dryer. The resultant powder is easily re-dispersible in water to form a clear, transparent dispersion. The celecoxib nanoparticles are amorphous and their average size in the dispersion is 17 nm, in agreement with cryo-TEM results and concentration measurements after filtration. As a result of the nanometric size and amorphous state, about 10-fold increase in dissolution of the powder was obtained, compared to that for particulate celecoxib in the presence of surfactants., (2010 Elsevier B.V. All rights reserved.)

Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as approximately 2 mg ml(-1), which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations ( approximately 20-30 mg ml(-1)). Transparent, conducting films are produced from these dispersions at 1,000 Omega square(-1) and approximately 80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.