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J R Fryer

Publications and source records attributed to J R Fryer.

8 recordsLinked to original sources
PubMed1995

The Sayre equation in electron crystallography.

The Sayre equation was evaluated as a technique for phase refinement in electron crystallography. Atomic-resolution electron diffraction data from copper perchlorophthalocyanine were assigned phase values from the Fourier transforms of various experimental electron micrographs, including one at 2.3 A, containing errors due to lens astigmatism. In each case, an atomic-resolution structure could be found after Fourier refinement. In addition, it was possible to begin with a basis set derived from symbolic addition for phase extension. Such a source of phases was also found to be useful for extending zonal electron diffraction sets from six polymer crystals, even though there was considerable overlap of atomic positions in the projection down the chain axes. Other tests of the Sayre equation were made with zonal protein data sets (bacteriorhodopsin, halorhodopsin) to evaluate what difficulties are to be expected when direct phasing techniques are to be used in macromolecular electron crystallography. Comparison to known values indicated that the low-resolution range (e.g. to 6 A) was reasonably stable for phase extension from a 10-15 A resolution image. Only when a minimum in average intensity was approached (near 5 A) did the direct extension encounter serious difficulties. If this minimum was treated as a "phase node" to generate two possible solutions, a model more similar to the true phase set was found. In general, this rather simple convolutional technique for phase extension seems to be particularly suitable for a variety of electron crystallographic applications.

Crystallography↗
PubMed1990

Why do polyethylene crystals have sectors?

High-resolution (3.7 A in optical diffraction) electron microscope images have been obtained from a series of n-paraffin monolamellar crystals with chain lengths from n-C36H74 to n-C82H166. The higher molecular weight specimens, which do not undergo chain folding, form sectorized crystals and the molecular packing is found to include alternate bands of untilted and tilted chains along <130>. Their widths are consistent with those of Bragg fringe widths in bright-field images obtained at lower magnification. The chain tilt axis is near d*110. Lower molecular weight paraffins form nonsectorized crystals where the chains are generally untilted with occasional small inclinations around nonspecific axes. Surface decoration of the longer alkanes with polyethylene crystallites, first of all, reveals three preferred polyethylene crystal rod orientations ([100] plus two perpendicular to [110]) instead of the two commonly found for the lower alkane. Control studies on solid-solution crystals reveal that the third [100] orientation is a result of slight surface roughness due to unequal chain lengths or surface protrusions of chains; the new decoration is also randomly distributed. For pure n-C60H122 lamellae, however, suggestions of regular bands containing rods along [100], due to surface discontinuities along <130>, can also be seen. In contrast with polyethylene, these data suggest that crystal sectorization may be a function of chain-stem packing alone and that chain folds may play merely a secondary role in the polymer--e.g., by directing the collapse of pyramidal crystals on a flat surface.

Journal Article↗
PubMed1989

High-resolution imaging of organic crystals.

The history of high-resolution imaging of organic crystals is summarized, followed by a discussion of radiation damage which reflects current thinking. Methods of specimen preparation and the experimental techniques for high-resolution imaging are described. The results show the application of these techniques to aromatic hydrocarbons, phthalocyanines, and linear-chain aliphatic molecules. Artefacts and image interpretation are also discussed.

Chemistry, Organic↗
PubMed1987

Direct imaging of paracrystalline phospholipid structure in the electron microscope.

A long chain amphiphilic molecule--the phospholipid 1,2-dihexadecyl sn glycerophosphoethanolamine--has been crystallized epitaxially so that the interlamellar molecular periodicity is parallel to the substrate and hence normal to the electron beam in the electron microscope. This has permitted the direct resolution of the 55.6 A lamellae in unstained crystals at room temperature. The lattice images have shown the presence of line dislocations and lenticular cracks in the crystals. Of significance to their biological properties is that the lattice is undulating with a periodicity of 0.1-0.5 micron. This would also account for the difficulties encountered by X-ray and electron diffraction techniques when examining these crystals.

Crystallization↗
PubMed1984

The "quasi-thermal" mechanism for electron beam damage of n-paraffins.

Electron diffraction patterns from epitaxially grown microcrystals of n-hexatriacontane, which are slightly damaged by the electron beam, strongly resemble those from the same material when it is warmed just below the pre-melt hexagonal phase. The identity of these diffraction patterns, which display a marked attenuation of lamellar 001 reflections but much less alteration of the strongest reflections, implies that both processes occur via the induction of chain defects which, in turn, generate chain-end voids in the crystal packing. Such defects, however, need not be identical for the two events. With warming they are probably the gtg-1 kink and the gauche chain conformers identified by infrared spectroscopy. The creation of trans vinylene groups during radiation damage will also increase chain flexibility, and perhaps induce the production of gtg-1 kinks.

Microscopy, Electron↗
PubMed1975

The ultrastructural localization of calcium in the avian shell gland.

Fluctuating concentrations of calcium in the blood supplying the avian shell gland are not reflected at tissue level. Analyses of oviducal mucosa throughout the laying cycle show that the concentration of calcium remains relatively unaltered even at peak activity thereby implying a rapid transfer process. These experiments describe the use of potassium pyroantimonate as a localizing agent. The precipitate produced by injecting the latter via the aorta was identified as calcium pyroantimonate by electron diffraction and the efficiency of the precipitant estimated by neutron activation analysis of eggshells present in the shell gland at the time of operation. Results indicate that calcium is transferred across the surface epithelial cells of the shell gland (tubular and pouch regions). Its localization in the former is taken as an indication of the involvement of this region in the production of the mammillary mantle.

Animals↗