The Preparation of Isomorphous

The fourth step is the preparation of isomorphous crystals of heavy metal-containing derivatives. The heavy metal may be allowed to react with the protein before crystallization or may be diffused into preformed crystals. A variety of both cationic and anionic metal complexes, even large Ta6Br122+ tantalum clusters, have been used 405 Two or more different heavy metal derivatives are often required for calculation of the phases. The heavy metal atoms must be present at only a very small number of locations in the unit cell. 

A number of studies have been performed with methyl picolinimidate (Benisek and Richards 1968 Plapp et al. 1971) aimed at exploring the usefulness of the metal-chelating properties of such derivatives in the preparation of isomorphous heavy atom derivatives of proteins for X-ray diffraction studies. 

The chemical preparation step in which the protein is isolated, purified, and crystallized is critical in that the protein preparation must be chemically homogeneous otherwise, the resulting disorder will muddle the electron-density map. The preparation of isomorphous derivatives by soaking native protein crystals in various mercury, platinum, lead, uranium, etc., solutions also is critical since several crystals of each derivative are required for x-ray data collection (because of irradiation damage) and all the crystals should have the same heavy-atom distribution and concentration. The protein structure documentation should provide evidence that the preparative protein chemistry is sound. 

The preparation of isomorphous heavy-atom derivatives. If only one iso-morphous derivative is prepared, the method is known as a single isomorphous replacement if more than one derivative is prepared the method is known as multiple isomorphous replacement. 

Recently, the preparation of metallosilicates with MFI structure, which are composed of silicone oxide and metal oxide substituted isomorphously to aluminium oxide, has been studied actively [1,2]. It is expected that acid sites of different strength from those of aluminosilicate are generated when some tri-valent elements other than aluminium are introduced into the framework of silicalite. The Bronsted acid sites of metallosilicates must be Si(0H)Me, so the facility of heterogeneous rupture of the OH bond should be due to the properties of the metal element. Therefore, the acidity of metallosilicate could be controlled by choosing the metal element. Moreover, the transition-metal elements introduced into the zeolite framework play specific catalytic roles. For example, Ti-silicate with MFI structure has the high activity and selectivity for the hydroxylation of phenol to produce catechol and hydroquinon [3],... 

Cs2BkCl6 is not isomorphous with Cs2PuCl6 or CsaCeCU 408 this compound would provide a useful starting material for the preparation of oxygen donor complexes of BkCLt, which are at present unknown, by the methods used to prepare PuCU complexes of this type (p. 1161). 

For the preparation of the isomorphic trioxalatomanga-state (III) (K salt, 8-hydrate) see reference 2 ... 

The physical properties of the aqueous solutions were studied by Bucknall and coworkers 14 Ray and Bharls studied the magnetic susceptibility of the hexachloro complex. Potassium pentachloroaquomolybdate(III) exists as rhombic crystals and is isomorphous with potassium pentachloroaquoferrate(III).16 Potassium hexachloromo-lybdate(III) has been used for the preparation of potassium hexathiocyanatomolybdate(III), potassium heptacyano-aquomolybdate(III),17and potassium octacyanomolybdate-(IV).18... 

We report (i) isomorphous substitution of boron, by secondary synthesis, into silicalite and into highly siliceous (Si/Al>400) ZSM-5 and (ii) an improved direct synthesis of zeolite (Si,B) -ZSM-5. The chemical status of B in die boronated products depends upon reaction conditions. Careful control of the concentration of the base, the borate species and of die duration of treatment, allows the preparation of samples containing only 4-coordinated B or a mixture of 3- and 4-coordinated B in various relative concentrations. The products were characterized by magic-angle-spinning (MAS) NMR and infrared (IR) spectroscopies and by powder x-ray diffraction (XRD). 

Zirconate pyrochlores have a low isomorphic capacity with respect tetravalent actinides. However the amount of isomorphic substitution can be increased by coupled substitution of Ca, according to the scheme 2REE = An" -i- Ca. Production of single phase ceramic can be attained only for actinide waste streams with rather simple chemical compositions. In the case of a complex waste stream composition, extra phases occur [129]. Finally, zirconate matrices require high temperatures for their synthesis. In order to prepare REE-zirconates from oxide mixtures, sintering at 1500-1600 for about 50 hours is required... 

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