On the Origin of a Low Angle Spacing in Starch

The structure of starch granules from different botanical sources was studied by transmission electron microscopy and small‐angle X‐ray diffraction. Electron micrographs of negatively stained starch granule fragments show a rippled fibrous structure. The ripples are interpreted as being stacks of thin crystalline lamellae comprising the linear α‐(1→4) chains of the amylopectin. Optical diffraction analysis of the electron micrographs showed that the spacing of the ripples varies from 9.2 nm in potato starch to 10.4 nm in barley starch. This correlates well with the position of a Bragg peak at appr. 10 nm measured by small‐angle X‐ray diffraction. These observations indicate that the Bragg peak arises from the alternating amorphous and crystalline regions seen as ripples in the electron micrograph

Automation of specimen selection and data acquisition for protein electron crystallography

A system is presented for semi-automatic specimen selection and data acquisition for protein electron crystallography, based on a slow-scan CCD camera connected to a transmission electron microscope and control from an external computer. Areas of interest on the specimen are localised at low magnification and subsequently imaged on the CCD camera, using a dose which is small compared to the dose used in the exposure mode. The crystalline quality of the area is evaluated from the appearance of diffraction peaks in the calculated image Fourier transform. If the quality is considered good, images can then be recorded in different modes, both on film and using the CCD camera. Using this system a significant gain, both quantitatively and qualitatively, can be obtained in acquiring data for electron crystallography of beam-sensitive materials. (C) 1998 Elsevier Science B.V. All rights reserved

Cryoelectron microscopy of block-copolymers in an organic solvent

Solutions of the diblock copolymer polystyrene/poly-2-vinylpyridine (PS/P2VP) in toluene were studied by cryo-transmission electron microscopy following fast freezing of a thin film of the solution in liquid nitrogen. The block copolymer forms spherical micelles which can be visualized using phase contrast microscopy. From the measured diameter of copolymer micelles with different block lengths, it can be concluded that only the poly-2-vinylpyridine core is visible in the electron micrographs, whereas the polystyrene corona is not visible and is largely dissolved into the toluene. The block copolymer micelles are rather stable in the beam and provide enough contrast relative to the amorphous toluene, due to the higher density of the micelles relative to the toluene, to be visible without any staining. This opens the possibility to directly visualize the phase behavior of polymer systems in a volatile solvent, perform time-resolved microscopy, and thus study the dynamics of the formation of different morphologies

Recrystallization of amylopectin in concentrated starch gels.

The relation between the recrystallization of amylopectin and the increase in stiffness of starch gels during storage was studied by various techniques. From transmission electron microscopy it was concluded that the size of the crystalline domains in retrograded 30% w/w potato starch gels was about 5 nm, much smaller than those present in native starch. The super-helical structure formed by the crystalline domains in native starch granules was not seen. It may thus be concluded that in retrograded starch gels the long range ordering is not regained during retrogradation. The relation between the degree of recrystallization, as determined with differential scanning calorimetry (DSC), and the increase in stiffness, as measured in compression, was found to be closely related. Two mechanisms will be discussed which may explain these observations. Copyright (C) 1996 Elsevier Science Lt

Mixed Monolayers and Multilayers of Poly(Isocyanide)S with Nonlinear Optically-Active Side-Chains

Contains fulltext : 10551.pdf (publisher's version ) (Open Access

An electron microscopic investigation of the structure of Alfalfa mosaic virus

Original article can be found at: http://www.sciencedirect.com/science/journal/00222836 Copyright Elsevier Ltd. DOI: 10.1016/0022-2836(81)90544-1 [Full text of this article is not available in the UHRA]Minimum beam electron microscopy and the three-dimensional reconstruction technique were used to analyse negatively stained Alfalfa mosaic virus particles and polymers of reassembled coat protein. Three strains of the virus were investigated: strains 425, 15/64 and VRU. The quaternary structure of the protein coat is based on a hexagonal net; in the VRU strain the orientation of this P6 lattice with respect to the cylindrical axis is not unique, so that different structures exist. In all strains the so-called “stacked” form is present, whereas in the VRU strain the “helical” forms of the lattice also appear. The hexagonal cell dimension is 84 Å. In those instances where cylindrical structures are formed by reassembling coat protein with or without the presence of nucleic acid, the quaternary structure of these products is similar to the parent virus structure. Image reconstruction shows that at low resolution (30 Å) the density distribution in negatively stained VRU virus particles, reassembled VRU coat protein tubes and VRU coat protein structures assembled in the presence of nucleic acid is similar. The protein is distributed in the P6-cell so that stain-accumulating centres exist at the symmetry positions, especially at the outside part of the cylindrical structure. The data suggest that the coat protein molecules are arranged in a relatively open network.Peer reviewe

Oxidative Coupling Polymerization in a Langmuir Monolayer of Octadecyl 3,5-Diaminobenzoate

In a Langmuir monolayer of the surface active monomer octadecyl 3,5-diaminobenzoate (ODDB), stabilized at a surface pressure of 10 mN/m and a temperature of 23.7 °C at the air-water interface, oxidative coupling polymerization occurs when copper(II) chloride was added or already was present in the subphase. Even in the absence of the catalyst this reaction takes place. Deposition of the polymerized monolayer onto glass, zinc sulfide, or gold substrates, using the vertical dipping method, gave transfer ratios between 0 and 0.4 on the downstroke and 1 on the upstroke. The multilayer films on zinc sulfide and gold substrates were characterized by means of Fourier transform IR spectroscopy, and multilayer films on quartz were characterized by means of UV/vis spectroscopy. Collected monolayers were characterized by means of size exclusion chromatography and again Fourier transform IR and UV/vis spectroscopy. During the stabilization of the monolayer without addition of copper(II) chloride to the subphase, the area per molecule decreased very slowly. Addition of copper(II) chloride enhanced this effect. The reduction of the area per molecule is probably caused by the polymerization itself accompanied by a reorientation of the molecules in the monolayer at the air-water interface. After stabilization the area per molecule was found to be about 27 Å2 and electron micrographs showed the formation of a smooth monolayer. From this it has been concluded that a closely packed monolayer was formed. Fourier transform IR and UV/vis spectra of polymerized multilayer materials are analogous to the spectra of the azo polymer of ODDB prepared in bulk solution. Size exclusion chromatography revealed that the molecular weight and the molecular weight distribution of the coupling product with and without copper(II) chloride in the subphase were the same. The average molecular weight was somewhat lower than the high-molecular-weight part of the corresponding material prepared in bulk solution.

Mechanism of formation of multilayered 2D crystals of the Enzyme IIC-mannitol transporter

AbstractWe have recently reported the crystallization by reconstitution into lipid bilayer structures of Enzyme IICmtl, the transmembrane C-domain of the mannitol transporter from E. coli. The projected structure was determined to a resolution of 0.5 nm [J. Mol. Biol. 287 5 (1999) 845]. However, further investigation proved that these crystals were multilamellar stacks instead of 2D crystals, and therefore were unsuitable for three-dimensional structural analysis by electron crystallography. Understanding the crystallogenesis of these crystals could reveal the mechanism of formation of multilayers. In the present study, cryo-electron microscopy (cryo-EM) and turbidimetry are used to study the successive steps of reconstitution of Enzyme IICmtl into phospholipid-containing structures and its crystallization under different conditions. Our experimental approach enabled us to distinguish the separate steps of reconstitution and crystallization. The salt concentration especially influenced the nature of the vesicles, either half open unilamellar or aggregated multilamellar, formed during reconstitution of Enzyme IICmtl. The presence of DOPE and DOPC and the temperature influenced the type of lipid structures that were formed during the crystallization phase of Enzyme IICmtl. Cryo-EM showed that protein crystallization is closely associated with the formation of isotropic lipid (cubic) phases. We believe that DOPE is responsible for the formation of these lipid cubic phases, and that crystallization is driven by exclusion of protein from these phases and its concentration into the lamellar phases. This mechanism is inextricably associated with the formation of multilayers