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Calculated electron-density map

When small crystal structures are studied, all Bragg reflection data are used, and relative phase angles are derived by one of the methods described in Chapter 8, and electron-density maps are calculated to the maximum possible resolution that the wavelength of the X rays permit. On the other hand, because isomorphous replacement methods are used to obtain relative phase angles for macromolecular structures, it is usual to calculate electron-density maps at low resolution initially, and to increase the resolution as more phases from isomorphous replacement data become available. Traditionally the structure determination is divided into three resolution shells that correspond to the minima of the radial distribution of intensities. ... [Pg.366]

FIGURE 30.11 The phase problem. The experimental data obtained in an X-ray experiment are the intensities of the reflections. By using an inverse Fourier transform, it is possible to calculate electron-density maps from these intensities. However, it is essential for this calculation to know the phase associated with each reflection. Approximate initial phases can be obtained from heavy-atom derivatives, anomalous dispersion or molecular replacement (see text). More accurate phases can be derived from the refined model, once it has been obtained. [Pg.617]

B3LYP/6-311++G(fi ,/>)//AMl level is displayed in Fig. 9. The bond properties obtained at this level reveal a moderately strong interaction (calculated electron density maps, including an analysis of atomic energies [131]. [Pg.362]

The best calculated electron density map for the native protein is ... [Pg.46]

Intensities Phasing — Density map Retrieve phases to calculate electron density map Heavy atom methods MAD, SAD, MIR Molecular replacement Use structural ... [Pg.67]

Calculated Electron Density Maps at Medium Resolution Application to Shape Analysis of Zeolite-Like Systems. [Pg.203]

Figure 10 shows the calculated electron density map that slices through the four C centers of the transition state. Again it verifies that the transition state is quite productlike there is almost no electron overlap between the two P carbon centers. The left two C centers show the characteristics of an ethylene (double bond) while the right two C centers look like an ethyl radical. [Pg.405]

Figure 28. Modeling water assisted cleavage of a C-O-C ether bond calculated electron density map of H2O and HsO adsorption on a dimethyl ether. Figure 28. Modeling water assisted cleavage of a C-O-C ether bond calculated electron density map of H2O and HsO adsorption on a dimethyl ether.
Fig. 5.18 X-ray diffraction data of the two columnar phases, a 2D diffraction pattern of an aligned sample with two domains at 70 °C and 5.5 wt% of water in the Coli phase. The Miller indices of the reflexes originating from one of the domains are inserted in red. Reflexes which belong to other than the two main domains are marked with a green circle, b 2D diffraction pattern of the same sample at 60 °C in the C0I2 phase together with the Miller indices, c Calculated electron density map, which suggests a possible stmcture for the Coli phase, d Cell parameters corresponding to the X-ray diffraction data shown in (a) and (b)... Fig. 5.18 X-ray diffraction data of the two columnar phases, a 2D diffraction pattern of an aligned sample with two domains at 70 °C and 5.5 wt% of water in the Coli phase. The Miller indices of the reflexes originating from one of the domains are inserted in red. Reflexes which belong to other than the two main domains are marked with a green circle, b 2D diffraction pattern of the same sample at 60 °C in the C0I2 phase together with the Miller indices, c Calculated electron density map, which suggests a possible stmcture for the Coli phase, d Cell parameters corresponding to the X-ray diffraction data shown in (a) and (b)...
Fig. 1. Calculated electron density map of a 5 A thick section of a hypothetical RNA structure at 3 A resolution. A skeletal model of the structure is superimposed to aid in the interpretation of the map. At 3 A resolution the sugars and phosphates both appear as individual peaks, with the phosphate group almost spherical and the sugar more ellipsoidal in shape. The bases are easily resolved, appear planar, and it is possible to distinguish purine bases from pyrimidines. Fig. 1. Calculated electron density map of a 5 A thick section of a hypothetical RNA structure at 3 A resolution. A skeletal model of the structure is superimposed to aid in the interpretation of the map. At 3 A resolution the sugars and phosphates both appear as individual peaks, with the phosphate group almost spherical and the sugar more ellipsoidal in shape. The bases are easily resolved, appear planar, and it is possible to distinguish purine bases from pyrimidines.

See other pages where Calculated electron-density map is mentioned: [Pg.17]    [Pg.201]    [Pg.142]    [Pg.48]    [Pg.500]    [Pg.293]    [Pg.379]    [Pg.84]    [Pg.324]    [Pg.324]    [Pg.325]    [Pg.67]    [Pg.418]    [Pg.88]    [Pg.971]    [Pg.203]    [Pg.111]    [Pg.25]   
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