Showing papers on "Resolution (electron density) published in 1978"
TL;DR: The structure of the blue copper protein azurin (Mr 14,000) from Pseudomonas aeruginosa has been determined from a 3.0 A resolution electron density map computed with phases based on a uranyl derivative to 3 A resolution and a platinum derivative to3.7 A.
327 citations
TL;DR: The three-dimensional structure of the Fab fragment from human myeloma IgG New has been refined using “model building” and “real space” procedures and the relation between idiotypic determinants, antigen combining site and hypervariable regions, is discussed in terms of the refined model.
268 citations
223 citations
TL;DR: In this paper, it was shown that the variation of contrast with crystal thickness, microscope resolution and defocus has been faithfully reproduced by the calculations for some minerals and a binary oxide.
Abstract: It is now possible to compute images of crystal structures corresponding to experimental images produced by using high-resolution transmission electron microscopy (HRTEM). The variation of contrast with crystal thickness, microscope resolution and defocus has been faithfully reproduced by the calculations for some minerals and a binary oxide.
144 citations
TL;DR: If the various protective measures act cooperatively, they could increase the effective resolution of sensitive material by an order of magnitude, making possible electron microscopy of the atomic structure of, for instance, the nucleic acid bases and other macromolecules.
Abstract: SUMMARY
Radiation damage to a biological specimen arises from a variety of interactions between the illuminating electrons and the atoms in it. The relative probabilities of these events, and the amount of energy transferred, can be calculated from basic physical theory. The microscopic damage caused in a particular specimen in given operating conditions is more difficult to predict, but it can be measured by a number of macroscopic indicators, the chief of which are loss of mass and changes in the energy loss spectrum (or electron diffraction pattern, if any). For most biological material the observed rate of damage is such as to set a limit to the intensity of illumination, the maximum magnification and the minimum size of detail that can be made visible. Several techniques have been devised and tested for reducing the radiation sensitivity of a specimen, of which cooling to a very low temperature and encasing it in an inert medium are the most effective. If the various protective measures act cooperatively, they could increase the effective resolution of sensitive material by an order of magnitude, making possible electron microscopy of the atomic structure of, for instance, the nucleic acid bases and other macromolecules. The prospects for observing living cells at a resolution better than that of the best optical microscopes would remain very small.
126 citations
TL;DR: The three-dimensional structure of the lysozyme from bacteriophage T4 has been determined from a 2.4 A resolution electron density map and the approximate conformation of the molecule unambiguously is revealed.
126 citations
121 citations
TL;DR: In this article, the red system of the CN molecule emitted by a nitrous oxide-acetylene flame has been measured between 11 000 and 4000 cm−1 with a high resolution Fourier Spectrometer.
106 citations
TL;DR: The structure of 2-keto-3-deoxy-6-phosphogluconate aldolase has been extended to 2.8 A resolution and the nature of the interfaces of the two kinds of crystallographic trimers have been examined, from which it was concluded that the choice of trimers selected in the 3.5 A resolution work was probably correct for trimers in solution.
74 citations
TL;DR: A high resolution (2.6 A) X-ray diffraction analysis has been carried out of a modified form of the bacterial elongation factor Tu:GDP complex which plays an important role in protein biosynthesis.
72 citations
TL;DR: In this article, it was found that films must be grown above ∼850°C and doping profiles were distorted and Sb segregated strongly on the sample surface, which is impossible to achieve by CVD growth.
Abstract: Arbitrary doping profiles with abrupt transitions have been produced in n‐type Si MBE films. Changes in doping level were produced with a resolution unattainable by CVD growth and at depths inaccessible to ion implantation. It was found, however, that films must be grown above ∼850 °C. Below that temperature doping profiles were distorted and Sb segregated strongly on the sample surface.
TL;DR: In this article, the Si-SiO2 interface of a Si-MOSFET on a (911) surface by high-resolution electron microscopy was viewed edge-on parallel to [011] and the Si crystal lattice was directly resolved.
Abstract: We have studied the Si‐SiO2 interface of a Si‐MOSFET (metal‐oxide‐semiconductor field‐effect transistor) on a (911) surface by high‐resolution electron microscopy. The interface was viewed edge‐on parallel to [011] and the Si crystal lattice was directly resolved. The image shows the interface to be smooth to within 4 A and contains a possible indication of a transition layer (∼10 A) of nonstoichiometric oxides.
TL;DR: In this article, a tilt-compensated triple-pass system for use with previously built Fourier spectrometers to increase the resolution by 3 is described. But the resulting width of the apparatus function of the third-generation interferometer is better than 10−3 cm−1 and can be meaningfully expressed in frequency units.
Abstract: The contribution of the third-generation Fourier spectrometer, built at the Laboratoire Aime Cotton and currently at the Laboratoire d'Infrarouge, to meteorological and high resolution Doppler-limited measurements is reported citing typical examples and the latest instrumental improvements. A tilt-compensated triple-pass system for use with previously built Fourier spectrometers to increase the resolution by 3 is described. The resulting width of the apparatus function of the triple-pass third-generation interferometer is better than 10−3 cm−1 and can be meaningfully expressed in frequency units. Its actual value is 27 MHz. For the first time a spectrometer is able to give very wide spectral range information with a resolving power sufficient to analyze sub-Doppler spectra.
TL;DR: In this paper, a numerical deconvolution procedure was developed to measure X-ray diffraction data from partially oriented specimens to the highest possible resolution by measuring all the optical densities on an Xray film and placing them on a polar grid.
Abstract: A numerical deconvolution procedure has been developed to measure X-ray diffraction data from partially oriented specimens to the highest possible resolution. The resolution to which X-ray data from non-crystalline specimens can be measured is limited by the disorientation of the particles in the specimen. The distribution of particle orientations causes the X-ray reflections to be smeared into arcs about the center of the diffraction pattern. At sufficiently high diffraction angles, this arcing results in the overlap of adjacent reflections. Conventional methods of densitometry used to measure intensities from X-ray films cannot be used in this region. By measuring all the optical densities on an X-ray film and placing them on a polar grid, an angular deconvolution can be performed to correct for the disorientation and separate the intensities from overlapping reflections. This calculation results in a determination of the X-ray intensities and background, and a quantitative measurement of the highest possible resolution to which the data can be reliably measured. X-ray data from partially oriented specimens of several macromolecular aggregates have been collected with this method.
TL;DR: Differential optical oscillator strengths in CFCl3, CF2Cl2, CF3Cl and CF4 have been measured for incident 'photon' energies up to 36 eV as discussed by the authors.
Abstract: Differential optical oscillator strengths in CFCl3, CF2Cl2, CF3Cl and CF4 have been measured for incident 'photon' energies up to 36 eV. The resolution and statistical significance of the data has been good enough to enable many new features to be identified and classified. Comparison with previous less extensive studies has been made where possible.
TL;DR: Microcrystals of the lipoprotein–phosphoprotein complex which are found in the oocytes of Xenopus laevis were examined using electron microscopy and analysis of Fourier transforms of the images showed the space group to be P21221.
Abstract: Microcrystals of the lipoprotein–phosphoprotein complex which are found in the oocytes of Xenopus laevis were examined using electron microscopy. Analysis of Fourier transforms of the images of the (010) and (001) projections showed the space group to be P21221. Ten projections were combined to produce a map of the complex having about 20 A resolution. The lipoprotein complex consists of two subunits related by a local twofold symmetry axis. The density was averaged around the local symmetry and reasonably well defined structural domains can be seen in the resulting model.
TL;DR: The crystal structure of methemerythrin from Themiste dyscritum has been determined at 2.8-Angstrom resolution by single isomorphous replacement technique combined with anomalous scattering from a K2HgI4 derivative.
Abstract: The crystal structure of methemerythrin from Themiste dyscritum has been determined at 2.8-Angstrom resolution by single isomorphous replacement technique combined with anomalous scattering from a K2HgI4 derivative. Noncrystallographic symmetry relating the four subunits in the asymmetric unit was used to obtain an average electron density map of the hemerythrin monomer, and a computer graphics system was used to fit a polypeptide model to the electron density. The average map was of sufficient quality to locate most of the amino acid side chains and to confirm the assignment of His-25, His-54, Glu-58, His-73, His-77, His-101, Asp-106, and Tyr-109 as the iron ligands. One of the mercury sites in the heavy atom derivative is located between two Cys-9 residues related by a noncrystallographic twofold axis, although no intersubunit disulfide bond is present in the native structure. The residues responsible for the binding of the subunits to form the octamer are identified.
TL;DR: The present report describes the results of an X-ray study of RNase S in complex with a non-hydrolysed analogue of UpA, 2’-deoxy-2”-fluoro uridilyl-3’,5’adenosine, abbreviated further as 2‘-FidUpA, to establish the position of the analogue in the active site of the enzyme, to deduce the conformation of 2�’
TL;DR: In this paper, a total of 112 individual vibration-rotation lines in the P and R branches of the three isotopic species were calibrated against stimulated emission lines from a highvoltage CO2 gain cell, and used to determine three scalar and two tensor spectroscopic constants for each species; an additional scalar constant was obtained from an analysis of the Q branch of 192OsO4.
Abstract: The ν3 bands of 187Os16O4, 189Os16O4, and 192Os16O4 have been recorded using both a Michelson interferometer (resolution 0.06 cm−1) and a tunable semiconductor diode laser (resolution limited by the Doppler width, ∼0.0007 cm−1). The rotational fine structure differs from that of most other spherical‐top molecules, for only rotational levels of A symmetry exist. A total of 112 individual vibration–rotation lines in the P and R branches of the three isotopic species were calibrated against stimulated emission lines from a high‐voltage CO2 gain cell, and were used to determine three scalar and two tensor spectroscopic constants for each species; an additional scalar constant was obtained from an analysis of the Q branch of 192OsO4. The strength of P (11) A2 0 was measured for 192OsO4 and yields a vibrational transition moment for ν3 of 0.17±0.02 D. Transitions of all isotopic species that are expected to fall near CO2 laser lines in the region 949–972 cm−1 are tabulated as an aid in the interpreation of satu...
TL;DR: In this article, the superconducting parameters of a weak superconductor surface layer, most probably NbO, were derived from tunneling data from thermally oxidized Nb junctions.
TL;DR: This chapter presents a series of images reconstructed from different combinations of diffraction spots, in which the interpretation is illustrated.
Abstract: Publisher Summary This chapter provides information on the image reconstruction in electron microscopy. Electron microscopy can routinely provide images of negatively stained biological specimens at a resolution of 1.5–3 nm, and of embedded and sectioned specimens at a resolution of 3–5 nm. This resolution, in particular with negative stain, is sufficient for the visualization of individual protein molecules and to show some details of subunit arrangement and shape. One approach to understanding the results of image reconstruction is to ask what each diffraction spot contributes to the image. The answer to this question follows directly from the theory of Fourier analysis and physical optics, but without going into the theory, the chapter presents a series of images reconstructed from different combinations of diffraction spots, in which the interpretation is illustrated. In addition, the optical diffraction pattern provides a direct criterion for distinguishing between the desired periodic features and the granular noise: all the information related to the periodic structures is contained in the discrete diffraction spots, whereas the noise produces a background of weak spots spread over the whole diffraction plane.
TL;DR: In this article, high-resolution (0·3 nm) images of platelets in diamond have been obtained using ultra-high resolution pole-pieces with spherical aberration coefficient C s = 0·7 mm.
Abstract: High-resolution (0·3 nm) images of platelets in diamond have been obtained using ultra-high resolution pole-pieces with spherical aberration coefficient C s = 0·7 mm. A through-focal series of images of a (100) defect, viewed edge-on in the [001] zone, shows phase contract which may be interpreted, using the projected-charge-density approximation, as arising from a thin lamella 2 ± 1 atomic layers thick having charge density, as seen by electrons, only slightly less dense than diamond. Image matching, using full-scale N-beam dynamical theory and the method of periodic continuation (MacLagan, Bursill and Spargo 1977) was undertaken using a number of structural models designed to probe the width and charge density of the patelets. The calculation included the effects of beam divergence, crystal tilt and phase changes caused by spherical aberration and objective lens defocus. Models included the nitrogen platelet proposed by Lang (1964), interstitial carbon (also with hydrogen to complete tetrahedra...
Journal Article•
Journal Article•
TL;DR: In this article, the resolution problem in X-ray energy-dispersive diffractometry is discussed, and it is shown that for a given characteristic of the solid-state detector system and a given range of interplanar spacings, an optimum scattering angle can be easily found for any divergence of the incident and scattered beams.
Abstract: The resolution problem in X-ray energy-dispersive diffractometry is discussed. It is shown that for a given characteristic of the solid-state detector system and a given range of interplanar spacings, an optimum scattering angle can be easily found for any divergence of the incident and scattered beams.