Anomolous scattering

Alternative methods of solving the phase problem are also used now. When a transition metal such as Fe, Co, or Ni is present in the protein, anomolous scattering of X-rays at several wavelengths (from synchrotron radiation) can be used to obtain phases. Many protein structures have been obtained using this multiple wavelength anomalous diffraction (MAD phasing) method.404 407 408 Selenocysteine is often incorporated into a protein that may be produced in... 

Early crystallographic studies of TMADH provided data from two derivatives at 6 resolution that revealed the domain structure and certain elements of secondary structure (Lim et al., 1982 Lim et al., 1984). Higher resolution data at 2.4 resolution have been collected and the structure solved by the multiple isomorphous replacement method with anomolous scattering (Lim et al., 1986). Analysis of the diffraction pattern lead to the identification of ADP as the third cofactor in TMADH. At the time the 2.4 data set was analysed, there was no sequence information available for TMADH (Lim et al., 1986), except for a 12 residue peptide which contained the covalently bound flavin (Kenney et al., 1978). Gas-phase sequencing of isolated peptides initially provided 80% of the primary sequence of... 

Refractive index consists of two parts, a real part that describes the refracted light and an imaginary (complex) part that describes absorption. In the case of very small particles, or particles where the complex part of the refractive index is near zero, light is transmitted through the partieles and interferes with the diffracted radiation. The interaction between the transmitted and diffracted radiation results in anomolous scattering and can be catered for in the Fraunhofer theory if both parts of the refractive index are known. 

Conformationally Controlled Gas-Solid Brominations in Racemic and Enantiomeric Crystals.—The above approach is elegant because any observed asymmetric induction is a direct consequence of the chirality of the crystal. However, the method does not permit a systematic analysis for the following reasons (/) only a small percentage of non-chiral molecules form chiral crystals, (//) it is not always feasible to prepare large homochiral crystals needed for the experiment, (m) the absolute configuration of both the starting crystal and the products formed requires application of the Bijvoet method of anomolous X-ray scattering, which is sometimes difficult to apply for molecules that do not contain heavy atoms. 

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