Block copolymers of poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS) have recently emerged as a new macromolecular amphiphile capable of forming a wide range of morphologies when dispersed in water. To understand better the relationship between stability and morphology in terms of the relative and absolute block compositions, we have synthesized a collection of PEG-PPS block copolymers and quantified their critical aggregation concentration and observed their morphology using cryogenic transmission electron microscopy after thin film hydration with extrusion and after solvent dispersion from tetrahydrofuran, a solvent for both blocks. By understanding the relationship between aggregate character and block copolymer architecture, we have observed that whereas the relative block lengths control morphology, the stability of the aggregates upon dilution is determined by the absolute block length of the hydrophobic PPS block. We have compared results obtained with PEG-PPS to those obtained with poly(ethylene glycol)-bl-poly(propylene oxide)-bl-poly(ethylene glycol) block copolymers (Pluronics). The results reveal that the PEG-PPS aggregates are substantially more stable than Pluronic aggregates, by more than an order of magnitude. PEG-PPS can form a wide variety of stable or metastable morphologies in dilute solution within normal time and temperature ranges, whereas Pluronics can generally form only spherical micelles under the same conditions. On the basis of these results, block copolymers of PEG with poly(propylene sulfide) may present distinct advantages over those with poly(propylene glycol) for a number of applications.

The formation of 2D arrays of three small icosahedral RNA viruses with known 3D structures (tomato bushy stunt virus, turnip yellow mosaic virus and bromegrass mosaic virus) has been investigated to determine the role of each component of a negative staining solution containing ammonium molybdate and polyethylene glycol. Virion association was monitored by dynamic light scattering (DLS) and virus array formation was visualised by conventional transmission electron microscopy and cryo-electron microscopy after negative staining. The structural properties of viral arrays prepared in vitro were compared to those of microcrystals found in the leaves of infected plants. A novel form of macroscopic 3D crystals of turnip yellow mosaic virus has been grown in the negative staining solution. On the basis of the experimental results, the hypothesis is advanced that microscopic arrays might be planar crystallisation nuclei. The formation of 2D crystals and the enhancing effect of polyethylene glycol on the self-organisation of virions at the air/water interface are discussed.Synopsis: The formation of 2D arrays of icosahedral viruses was investigated by spectroscopic and transmission electron microscopic methods. (c) 2007 Elsevier Ltd. All rights reserved.

Cationic lipids and polymers are routinely used for cell transfection, and a variety of structure-activity relation data have been collected. Few studies, however, focus on the structural aspects of self-assembly as a crucial control parameter for gene delivery. We present here the observations collected for a set of cationic dendritic amphiphiles based on a stiff tolane core (1-4) that are built from identical subunits but differ in the number and balance of their hydrophobic and cationic hydrophilic moieties. We established elsewhere that vectors 3 and 4 have promising transfection properties. Scanning probe microscopy (AFM, STM), cryo-transmission electron microscopy (cryo-TEM), and Langmuir techniques provide insight into the self-assembly properties of the molecules under physiological conditions. Furthermore, we present DNA and pH "jump" experiments where we study the response of Langmuir films to a sudden increase in DNA concentration or a drop in pH. We find that the primary self-assembly of the amphiphile is of paramount importance and influences DNA binding, serum sensitivity, and pH response of the vector system.

Nanometer light source: Interaction between high-affinity binding sites on lipid-coated nanocrystals (NCs) and different proteins enables the controlled formation of supramolecular nanostructures on micropatterned surfaces (see picture; FRET=fluorescence resonant energy transfer, NTA=nitrilotriacetic acid, His6=hexahistidine). The NCs serve as local light sources emitting light over distances from 1 to more than 10 nm.

We explore the effects of preparation protocol on the morphology and stability of aggregates from a poly(ethylene glycol-b-propylene sulfide-b-ethylene glycol) triblock copolymer, PEG44−PPS76−PEG44. Fluorescence spectra and excimer formation of the probe molecule pyrene elucidated the various stages of aggregate formation, and cryo-TEM yielded insight into aggregate morphology. When prepared by direct hydration of polymer films, an extraordinary variety of morphologies was formed, ranging from spherical micelles to wormlike micelles, Y-junctions, blackberry micelles, and vesicles. Aging produced more uniform structural ensembles, including wormlike micelles with undulations and eventually spherical micelles, indicating the nonequilibrium nature of the system as initially formed. On the contrary, preparation by dilution from organic solvent yielded only structures that were closer to equilibrium distributions.

From an EM study of thin sections, the rod-like microneme organelles within conventionally glutaraldehyde fixed Cryptosporidium parvum sporozoites have been shown to undergo a shape change to a more spherical structure when the sporozoites age in vitro for a period of approximately 12 to 24 h. This correlates with the shape change of intact sporozoites, from motile hence viable thin banana-shaped cells to swollen pear-shaped cells, shown by differential interference contrast light microscopy of unstained unfixed and glutaraldehyde-fixed samples, as well as by thin section EM of fixed sporozoites. From negatively stained EM specimens of unfixed and fixed sporozoites the cellular shape change has been confirmed as has the rod to sphere micronemal shape change. Intact micronemes released directly from sporozoites exclude negative stain and appear as smooth-surfaced electron transparent particles. Biochemically purified rod-shaped C. parvum micronemes are shown to be fragile organelles that inevitably undergo variable damage during isolation, storage and subsequent specimen preparation for EM study. In the absence of glutaraldehyde fixation, damaged micronemes allow the negative stain to enter and loose their contents and during storage undergo a rod-to-sphere shape transformation. Glutaraldehyde-fixed micronemes maintain the rod shape; intact fixed micronemes still exclude negative stain but damaged micronemes reveal a complex quasi-helical arrangement of internal protein within the rod-like micronemes. Loss of this internal organized structure appears to be responsible for the micronemal shape change. This interpretation has been advanced from mutually supportive data obtained from cryoelectron microscopy of unstained vitrified samples, conventional air-dry negative staining and cryo-negative staining. Attempts to biochemically solubilize the micronemal content by lysis and ultrasonication, and separate it from the micronemal membranes, have so far met with limited success as the internal material tends to remain as a disorganized cluster of particles upon release.

Proteins exist in one of two generally incompatible states: either membrane associated or soluble. Pore-forming proteins are exceptional because they are synthesized as a water-soluble molecule but end up being located in the membrane — that is, they are nonconstitutive membrane proteins. Here we report the pronounced effect of the single point mutation Y221G of the pore-forming toxin aerolysin. This mutation blocks the hemolytic activity of the toxin but does not affect its initial structure, its ability to bind to cell-surface receptors or its capacity to form heptamers, which constitute the channel-forming unit. The overall structure of the Y221G protein as analyzed by cryo-negative staining EM and three-dimensional reconstruction is remarkably similar to that of the wild type heptamer. The mutant protein forms a mushroom-shaped complex whose stem domain is thought to be within the membrane in the wild type toxin. In contrast to the wild type heptamer, which is a hydrophobic complex, the Y221G heptamer is fully hydrophilic. This point mutation has, therefore, converted a normally membrane-embedded toxin into a soluble complex.

Ordnung und Ästhetik kommen in neuartigen supramolekularen Architekturen zum Ausdruck, die aus präorganisierten starren stabförmigen Molekülen aufgebaut sind. Nach Selbstorganisation zu einer Fass-artigen Tertiärstruktur (links) bildet sich eine Quartärstruktur höherer Ordnung (rechts), die aus starren stabförmigen β-Fibrillen besteht.

Assemblyof the amyloid-beta peptide (Abeta) into fibrils and its deposition in distinct brain areas is considered responsible for the pathogenesis of Alzheimer's disease (AD). Thus, inhibition of fibril assembly is a potential strategy for therapeutic intervention. Electron cryomicroscopy was used to monitor the initial, native assembly structure of Abeta42. In addition to the known fibrillar intermediates, a nonfibrillar, polymeric sheet-like structure was identified. A temporary sequence of supramolecular structures was revealed with (i) polymeric Abeta42 sheets during the onset of assembly, inversely related to the appearance of (ii) fibril intermediates, which again are time-dependently replaced by (iii) mature fibrils. A cell-based primary screening assay was used to identify compounds that decrease Abeta42-induced toxicity. Hit compounds were further assayed for binding to Abeta42, radical scavenger activity, and their influence on the assembly structure of Abeta42. One compound, Ro 90-7501, was found to efficiently retard mature fibril formation, while extended polymeric Abeta42 sheets and fibrillar intermediates are accumulated. Ro 90-7501 may serve as a prototypic inhibitor for Abeta42 fibril formation and as a tool for studying the molecular mechanism of fibril assembly.

The behaviour in aqueous medium of cationic amphiphilic copolymers derived from 3-vinylpyridine has been studied. The ability of these polymers to form hydrophobic microdomains was shown by fluorescence spectroscopy using a molecular rotor as a fluorescent probe, and the resulting structure was visualized by cryo-transmission electron microscopy (cryo-TEM). The parameters (shape and size) obtained from cryo-TEM are discussed in relation to the copolymer composition and the local viscosity defined by the rotor fluorescence quantum yield. (C) 1999 Society of Chemical Industry.

The behaviour of new cationic amphiphilic copolymers derived from 3-vinylpyridine was studied in aqueous medium. The formation of hydrophobic microdomains was evidenced by fluorescence spectroscopy using a molecular rotor as a fluorescent probe and their structure was visualized by cryo-transmission electron microscopy (Cryo-TEM). The parameters (shape and size) obtained from Cryo-TEM were discussed in relation to the copolymers composition and to the local viscosity defined by the rotor fluorescence quantum yield.

Following our in vitro reassociation of keyhole limpet hemocyanin subunits in the presence of high concentrations (100mM each) of calcium and magnesium chloride (Harris et al., 1997a, Micron 28, 31–41; 1997b, Micron 28, 43–56), we have now extended our investigations by using a buffer system containing a lower concentration of the two divalent cations (10mM each). Reassociation of mixed KLH subunits present in the commercially available product Immucothel® was performed using a standardized buffer solution containing 50mM Tris–HCl, 150mM NaCl, 10mM CaCl2 and 10mM MgCl2 (pH 7.4) over a minimum period of one week, at 4°C. This solution was selected as being close to our KLH stabilizing buffer (used routinely for the 4°C storage of native KLH), but with a slightly elevated concentration of both divalent cations (i.e. 10mM instead of the usual 5mM) to potentiate KLH reassociation. The reformation of the higher molecular mass oligomeric and polymeric forms of KLH was monitored throughout from air-dried negatively stained specimens prepared on continuous carbon support films and across the small holes of holey carbon support films, and also by cryo-negative staining. Compared to our previous studies, KLH reassociation has been found to be much slower, but a high percent recovery of total KLH (ca. 87%, produced by centrifugal pelleting), was achieved after a period of seven–ten days reassociation at 4°C. In vitro production of naturally occurring oligomeric forms of KLH1 and KLH2 now predominates, and the proportion of smaller diameter tubular polymeric forms is much less. After reassociation of the mixed KLH1 and KLH2 subunits present in Immucothel®, separation of intact KLH1 from dissociated KLH2 was achieved by gel filtration chromatography after dialysis against 1% ammonium molybdate–0.2% PEG (Mr 1000) at pH 5.7 and monitored by native PAGE. This purification enabled the reassociation characteristics of the two purified KLH subunits (from a 130mM glycine–NaOH buffer solution at pH 9.6) to be investigated in our 10mM divalent cation-supplemented Tris–saline buffer. In both cases, the second reassociation, performed over a period of one–two weeks at 4°C, led to the production of the characteristic decameric oligomeric forms; for KLH1 the didecamer predominates, and for KLH2 didecamers and short multidecamers predominate, but in both cases a small quantity of the previously described helical/tubular polymers is also present. Subsequent centrifugal pelleting of this reassociated KLH1 and KLH2, with resuspension and storage at −70°C in stabilizing buffer containing 10% (w/v) trehalose, has been found to provide a biochemically and structurally characterized stock of purified KLH oligomers. The prolonged time-periods required by the overall reassociation and purification procedure do not appear to detract from the quality or stability of the high molecular mass forms of KLH1 and KLH2 so produced.

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTCationic Polyamphiphiles in Aqueous Media: Evidence for a Fingerprint-like Structure by Cryo-Transmission Electron MicroscopyA. Benjelloun, A. Brembilla, P. Lochon, M. Adrian, and J. GhanbajaView Author Information Laboratoire de Chimie-Physique Macromoléculaire (LCPM), Unité associée au CNRS No. 494, ENSIC-INPL, BP 451, 1 Rue Grandville, 54001 Nancy Cedex, France Laboratoire d'Analyse Ultrastructurale, Université de Lausanne, Bât. de biologie, CH-1015, Lausanne, Switzerland Service de Microscopie Electronique en Transmission, Faculté des Sciences, Université Henri Poincaré, Boulevard des Aiguillettes, BP 239, 54506 Vandœuvre-lès Nancy Cedex, France Cite this: Langmuir 1997, 13, 21, 5770–5773Publication Date (Web):October 15, 1997Publication History Received10 March 1997Revised22 July 1997Published online15 October 1997Published inissue 1 October 1997https://pubs.acs.org/doi/10.1021/la970268chttps://doi.org/10.1021/la970268cbrief-reportACS PublicationsCopyright © 1997 American Chemical SocietyRequest reuse permissionsArticle Views152Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Chemical structure,Fluorescence,Hydrophobicity,Physical and chemical processes,Solution chemistry Get e-Alerts

The organization of turnip yellow mosaic virus has been investigated by neutron small angle scattering at 300 K and 80 K in buffers containing various amounts of D2O. We confirm that in native virions, no substantial part of the RNA is located at a radius larger than ca. 100-110 A, i.e., that there is very little interpretation of the RNA into the capsid. At 80 K, scattering curves do not depend much upon contrast, from 40% D2O to 100% D2O buffers, but are strongly affected by interparticle interference. We could, however, show that it is not the case for the subsidiary intensity maximum at q approximately 0.06 A-1. From the position of this maximum, we conclude that upon freezing, the radius of the capsid expands by c.a. 3.5% and the RNA penetrates deeply into the protein shell. Biological implications of this conformational change immediately preceding decapsidation are discussed.