Crystallographic studies rearrangements

The conversion of the kinetic data into AAG -values (Table 4.2) assumes that the rate-limiting step is the same in wild type and variant. It also assumes that the mutation does not cause structural rearrangements. Only in very few cases have the kinetic studies on the transition state stabilization by the oxyanion hole contributions been complemented by protein crystallographic studies of the liganded wild-type and mutated variant. One such example, discussed in more detail below, concerns the studies on the Ser42Ala variant of cutinase, in which case it was found that the structural changes are minimal [19]. 

Pyrolysis of the 2-(2-azidobenzoyl)pyridines 334 (R and R = H or Br) at llO C gives the benzisoxazoles 335, which rearrange to the mesomeric betaines 338 in good yield at higher temperatures (215°C). The yellow, crystalline betaines (v q 1640 cm ) are stable compounds whose structure is supported by an X-ray crystallographic study of the bromo derivative 338 (R = H, = Br). The following reactions of the parent system (338 R = R2 = H) have been reported (Scheme 13) (i) Nitration gives the 2-nitro... 

X-ray crystallographic studies during the course of the reaction have demonstrated that the reaction is a typical topochemical process involving a direct rearrangement of the monomer crystal to the polymer crystal having an extended rigid rod-like structure. By x-ray analysis and DSC on the thermal depolymerization of the polymer crystal, a reversible topochemical process has been demonstrated for monomer and polymer crystals. 

The diazotization of 5-amino-4-carbamoyl-l-(a-styryl)-l,2,3-triazole (30) gave 5-phenyl-1.2,3-triazolo[l,5-h][l,2,4]triazine-3-carboxamide (32) as a result of rearrangement of the initially formed 7-phenyl-l,2,3-triazolo[5,J-c][l,2,4]triazine-3-carboxamide (31). Compound 32 is favored thermodynamically and its structure was confirmed by an X-ray crystallographic study (88BSB179) (Scheme 10). 

Wong MW (2003) Quantum-Chemical Calculations of Sulfur-Rich Compounds. 231 1-29 Wrodnigg TM, Eder B (2001) The Amadori and Heyns Rearrangements Landmarks in the History of Carbohydrate Chemistry or Unrecognized Synthetic Opportunities 215 115-175 Wu N, Pai EP (2004) Crystallographic Studies of Native and Mutant Orotidine 5 phosphate Decarboxylases. 238 23-42... 

Modem surface crystallographic studies have shown that on the atomic scale, most clean metals tend to minimize their surface energy by two kinds of surface atom rearrangements - relaxation and reconstmction [22-26]. In this review, the term surface reconstruction applies to the case in which there is lateral (i.e. in the surface plane) movement of surface atoms such that the surface layer has a symmetry that is different from that of the underlying bulk of the crystal. Hence, the surface layer has a two-dimensional unit cell that is different from the corresponding two-dimensional unit cell of a layer in the bulk. The periodicity of the surface can be defined by Woods notation for example, an unreconstructed surface would be termed as (1x1), whereas if the surface unit cell size was doubled in one of the primary vector directions, it would be termed as (2 x 1), and so on. On the other hand, surface relaxation apphes to the case in which the surface layer is in a (1 x 1) state but the layer is displaced along the surface normal direction from the position expected for bulk termination of the crystal lattice. In this section, both surface reconstruction and surface relaxation effects are described with specific examples chosen to illustrate the phenomena as they are observed in the electrochemical environment. 

The pyridils are not especially remarkable. Some examples have been reported to undergo the benzilic acid rearrangement , but others with ethanolic potash give an aldehyde (which subsequently undergoes the Cannizzaro reaction) and a carboxylic acid . Heated with lead oxide, 2,2 -pyridil gives di-(2-pyridyl) ketone . An x-ray crystallographic study of 2,2 -pyridil has been made" . 

---