Ab initio structure analysis of copper perbromophthalocyanine

1992 ◽  
Vol 50 (2) ◽  
pp. 1446-1447
Author(s):  
W.F. Tivol ◽  
J.N. Turner ◽  
D.L. Dorset
Keyword(s):  
Electron Diffraction ◽  
Ab Initio ◽  
Structure Analysis ◽  
High Energy ◽  
Electron Dose ◽  
Heavy Atoms ◽  
Voltage Electron ◽  
High Energy Electrons ◽  
Diffraction Mode ◽  
Diffraction Patterns

The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Dynamical scattering from compounds containing heavy atoms may make such an analysis difficult or impossible with data obtained at conventional voltages. In the case that even high-energy electrons do not produce diffraction intensities sufficiently close to the kinematic values, criteria other than the simple minimization of the R-factor must be used to seek the correct structure solution.Copper perbromophthalocyanine (Cu-BrPTCY) was grown epitaxially from the vapor phase onto a clean KCl crystal face. Electron diffraction patterns were obtained from crystals tilted at 26.5° and oriented so that the electron beam was parallel to the c-axis. The AEI EM7 high-voltage electron microscope was used at a voltage of 1200 kV in diffraction mode with a 10 μm selected area aperture. The data were obtained using a minimal electron dose and recorded on DuPont Lo-dose Mammography film (See Fig. 1). Intensities were measured on a Joyce-Loebl MkIIIC flat bed microdensitometer by integrating under the peaks.

Electron diffraction of copper phthalocyanine on the HVEM

1993 ◽  
Vol 51 ◽  
pp. 660-661
Author(s):  
W. F. Tivol ◽  
J. N. Turner ◽  
M. P. McCourt ◽  
D. L. Dorset
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Ab Initio ◽  
Organic Compounds ◽  
Structure Analysis ◽  
Copper Phthalocyanine ◽  
High Energy ◽  
Radiation Resistant ◽  
Diffraction Patterns

The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Previous studies showed that ab initio analysis of copper perchlorophthalocyanine could be accomplished ; accelerating voltages at or above 1000 kV, but net at 400 kV for crystals which are about 10 nm thick. Copper perbromophthalocyanine could also be analyzed ab initio at 1200 kV, but the presence of severe dynamical scattering precluded such analysis at lower voltages.A study of copper perchlorophthalocyanine at accelerating voltages from 200 kV to 1200 kV showed that dynamical scattering accounted for the differences among the diffraction patterns which lead the failure of ab initio analysis at the lower voltages. The series of phthalocyanines offers a good model for the study of dynamical scatterin and direct phasing methods, since it consists of relatively radiation-resistant compounds for which high-resolution diffraction patterns can be obtained.

Electron diffraction of copper perfluorophthalocyanine on the HVEM

1995 ◽  
Vol 53 ◽  
pp. 158-159
Author(s):  
W. F. Tivol ◽  
J. R. Fryer
Keyword(s):  
Electron Beam ◽  
Electron Diffraction ◽  
Ab Initio ◽  
Vapor Phase ◽  
High Energy ◽  
Illumination Level ◽  
Objective Lens ◽  
Crystal Face ◽  
Correct Orientation ◽  
Diffraction Patterns

The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Previous studies showed that ab initio analysis of copper perchlorophthalocyanine could be accomplished at accelerating voltages at or above 1000 kV, but not at 400 kV for crystals which are about 10 nm thick. Copper perbromophthalocyanine could also be analyzed ab initio at 1200 kV, but the presence of severe dynamical scattering precluded such analysis at lower voltages.Copper perfluorophthalocyanine (Cu FPC) was grown epitaxially from the vapor phase onto a clean KC1 crystal face. Electron diffraction patterns were obtained from crystals tilted at 20° and oriented so that the electron beam was parallel to the c-axis.Electron doses were kept to a minimum by the use of a 100 μm condenser aperture and a highly excited first condenser lens. A video system allows scanning the specimen to find a crystal suitable for the correct orientation of the grid by rotating it within its own plane and focusing the objective lens, all at an illumination level below that necessary to distinguish anything by eye on the HVEM's phosphor screen.

Electron-diffraction studies in synthetic polymer materials

1983 ◽  
Vol 41 ◽  
pp. 362-365
Author(s):  
D.T. Grubb
Keyword(s):  
Electron Diffraction ◽  
Synthetic Polymer ◽  
Polymer Materials ◽  
Crystallographic Structure ◽  
High Dose ◽  
Electron Dose ◽  
Dose Rates ◽  
First Case ◽  
Diffraction Patterns ◽  
The Many

Diffraction studies in polymeric and other beam sensitive materials may bring to mind the many experiments where diffracted intensity has been used as a measure of the electron dose required to destroy fine structure in the TEM. But this paper is concerned with a range of cases where the diffraction pattern itself contains the important information.In the first case, electron diffraction from paraffins, degraded polyethylene and polyethylene single crystals, all the samples are highly ordered, and their crystallographic structure is well known. The diffraction patterns fade on irradiation and may also change considerably in a-spacing, increasing the unit cell volume on irradiation. The effect is large and continuous far C94H190 paraffin and for PE, while for shorter chains to C 28H58 the change is less, levelling off at high dose, Fig.l. It is also found that the change in a-spacing increases at higher dose rates and at higher irradiation temperatures.

Merging of electron-diffraction intensities acquired with a slow-scan CCD camera of crotoxin complex crystals to 3.5Å resolution

1994 ◽  
Vol 52 ◽  
pp. 104-105
Author(s):  
Jaap Brink ◽  
Wah Chiu
Keyword(s):  
Electron Diffraction ◽  
Ccd Camera ◽  
Crystal Thickness ◽  
Local Contrast ◽  
Camera Model ◽  
Data Set ◽  
3 Dimensional ◽  
Diffraction Mode ◽  
Diffraction Patterns ◽  
Complex Crystals

Crotoxin complex is the principal neurotoxin of the South American rattlesnake, Crotalus durissus terrificus and has a molecular weight of 24 kDa. The protein is a heterodimer with subunit A assigneda chaperone function. Subunit B carries the lethal activity, which is exerted on both sides ofthe neuro-muscular junction, and which is thought to involve binding to the acetylcholine receptor. Insight in crotoxin complex’ mode of action can be gained from a 3 Å resolution structure obtained by electron crystallography. This abstract communicates our progress in merging the electron diffraction amplitudes into a 3-dimensional (3D) intensity data set close to completion. Since the thickness of crotoxin complex crystals varies from one crystal to the other, we chose to collect tilt series of electron diffraction patterns after determining their thickness. Furthermore, by making use of the symmetry present in these tilt data, intensities collected only from similar crystals will be merged.Suitable crystals of glucose-embedded crotoxin complex were searched for in the defocussed diffraction mode with the goniometer tilted to 55° of higher in a JEOL4000 electron cryo-microscopc operated at 400 kV with the crystals kept at -120°C in a Gatan 626 cryo-holder. The crystal thickness was measured using the local contrast of the crystal relative to the supporting film from search-mode images acquired using a 1024 x 1024 slow-scan CCD camera (model 679, Gatan Inc.).

Calculation of Reflected Intensities for Medium and High Energy Electron Diffraction

1972 ◽  
Vol 27 (3) ◽  
pp. 390-395 ◽  
Author(s):  
A.R. Moon
Keyword(s):  
Electron Diffraction ◽  
Surface Structure ◽  
Incident Angle ◽  
High Energy ◽  
Numerical Calculations ◽  
High Energy Electron ◽  
Matrix Eigenvalue ◽  
High Energy Electrons ◽  
Experimental Values ◽  
Reflection Electron Diffraction

Abstract The Bethe theory of electron diffraction is used to calculate reflection electron diffraction intensities for medium and high energy electrons. A generalized Hill's determinant method is used for the numerical calculations instead of the more common but slower matrix-eigenvalue technique. Results of a "systematics" calculation of the specular intensity as a function of incident angle are compared with some experimental values for the Si (111) surface. The application of the Bethe theory to crystals where the surface structure differs from the bulk is also considered.

Reduction of Charging in Biological Electron Cryomicroscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 365-366
Author(s):  
M.B. Sherman ◽  
J. Brink ◽  
W. Chiu
Keyword(s):  
Electron Diffraction ◽  
Ion Beam ◽  
High Energy ◽  
Carbon Layer ◽  
Thin Layers ◽  
Biological Macromolecules ◽  
Electron Cryomicroscopy ◽  
Obvious Effect ◽  
Diffraction Patterns ◽  
The Stability

High resolution imaging in electron cryomicroscopy of biological macromolecules is strongly affected by beam-induced charging1. Charging is often expressed in frozen or glucose-embedded specimens as an increase in apparent mass-thickness of the irradiated area. Another obvious effect of charging is blurring of both the unscattered beam and reflections in electron diffraction patterns recorded from crystalline specimens. Coating of ice-embedded specimens with a carbon layer helps to improve the stability of the ice and probably reduce charging of the specimen. Coating in a Gatan ion-beam coater (model 681) of glucose-embedded specimens with thin layers of various conductive materials did reduce charging but the specimens were damaged by the high energy ions used for the coating. In general, coating resulted in much weaker reflections in electron diffraction patterns obtained from coated crystals and faster resolution fall-off.We modified the Gatan coater by outfitting it with a new chamber that replaced the ion-beam deposition capability for thermal evaporation of carbon rods (Fig. 1).

Comparative analysis of high energy electron diffraction patterns from LB films of Cd- and Pb-stearates

1996 ◽  
Vol 284-285 ◽  
pp. 208-210 ◽  
Author(s):  
V. Klechkovskaya ◽  
M. Anderle ◽  
R. Antolini ◽  
R. Canteri ◽  
L. Feigin ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Electron Diffraction ◽  
High Energy ◽  
Energy Electron ◽  
High Energy Electron ◽  
Lb Films ◽  
Diffraction Patterns
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