Elucidation, by X-ray diffraction

The successful use of these X-ray crysallographic techniques in studying the enzyme-substrate interactions of lysozyme (21) and chymotrypsin (22) has recently been reviewed by Blow and Steitz (16) and Blow (23). To date, however, these methods have had only limited application, since the detailed structures of only about ten enzymes have been elucidated by X-ray diffraction... 

During the addition of Ph2CN2 to a solutions of 44a in toluene at -78°C, the intense purple color of the diazomethane disappeared, yielding the yellow, crystalline [2+ l]-cycloadduct 52 (Eq. 15).14 Its molecular structure was elucidated by X-ray diffraction analysis (Fig. 15). 

Compound 12 represents the first aggregate of a solvent-free sodium polyarsanide that has been elucidated by X-ray diffraction analysis (Fig. 13) (24). 

The synthesis of this salt started with the enantiomerically pure 1,2-diamine 106, that was converted into the corresponding thiourea derivative 107 (Scheme 12). Exposure of the thiourea 107 to oxalyl chloride in toluene at 60 °C cleanly afforded the desired imidazolinium chloride 108. These two salts were used to produce new palladium and nickel carbene complexes. The structure of both palladium carbene complexes 96a and 96b has been elucidated by X-ray diffraction <2005CEJ1833>. 

Configuration and conformation, elucidation by X-ray diffraction, 22, 51 (1983) Corynantheine, yohimbine, and related alkaloids, 27, 131 (1986)... 

Ribonucleases are a widely distributed family of en-zymes that hydrolyze RNA by cutting the P—O ester bond attached to a ribose 5 carbon (fig. 8.12). A good representative of the family is the pancreatic enzyme ribonuclease A (RNase A), which is specific for a pyrimidine base (uracil or cytosine) on the 3 side of the phosphate bond that is cleaved. When the amino acid sequence of bovine RNase A was determined in 1960 by Stanford Moore and William Stein, it was the first enzyme and only the second protein to be sequenced. RNase A thus played an important role in the development of ideas about enzymatic catalysis. It was one of the first enzymes to have its three-dimensional structure elucidated by x-ray diffraction and was also the first to be synthesized completely from its amino acids. The synthetic protein proved to be enzymatically indistinguishable from the native enzyme. 

The molecular structures of several polysulfane tetroxides of this type have been elucidated by X-ray diffraction on single crystals. The S-S bonds between the sulfone groups and the neighboring sulfane sulfur are weaker (210-214 pm) than ordinary S-S single bonds (205 pm). ... 

The first secondary stibine, the structure of which was elucidated by X-ray diffraction, was MeSjSbH . This hydride is exceptionally stable and possesses (as expected) a trigonal pyramidal structure (CSbC, 101.7°). Reaction according to equation 26 formed the planar (X-ray) Cu2Sb2 heterocycle containing essentially identical Cu-Sb distances of 270 pm in agreement with a real Cu-Sb single bond (sum of covalent radii = 268 pm) . 

The total synthesis described here is the first enantioselective synthesis of 1. Previously, only one racemic total synthesis was known, which was published by the same authors." One purpose of accomplishing this total synthesis was to determine the absolute configuration of naturally occurring 1. The absolute configuration of the synthesized (+)-l was elucidated by X-ray diffraction. The amount of optical rotation for the natural product has not yet been published, so its absolute configuration is still unknown. 

Treatment of the acetylene complexes Cp2Ti( 72-C2R2) (R = SiMe3 or Ph) with C02 at room temperature resulted in the formation of the dimeric cr-alkenylcarboxylate complexes 131 and 132 (Equation (35)).102 The magnetic moment of both complexes was 1.6 /xB per titanium atom indicating that they contained trivalent Ti centers. The structure of 132 was elucidated by X-ray diffraction, and the presence of two fused metallacyclic rings was confirmed. 

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