Purine crystallographic studies

X-Ray crystallographic studies of purine and its various substituted derivatives have been of special value in providing (a) fine structural details of the ring system of simple molecules in their various neutral and protonated, and to a lesser extent, deprotonated forms (b) a source of molecular geometries for theoretical calculations and related purposes and (c) information about the precise arrangement of purine (and pyrimidine) bases in the various nucleic acids, and the way in which interaction of such bases with extraneous materials including intercalated or absorbed compounds occurs. 

Molecular orbital theory indicates that there is little difference between the stability of the two tautomers of purine, 42 and 43.40 Molecular orbital calculations indicate that purine forms a monocation by protonation at N-341 or at N-l.42 A precise X-ray crystallographic study indicates that theophylline exists in the 7H form 44.43... 

C - For powder diffraction data determination the key step is the generation of reliable trial structures for final refinement. The subject of the study reported here is the pharmaceutical material anhydrous theophylline (3,7-dihydro-1,3-dimethyl-l//-purine-2,6-dione), which contains both oxygen and nitrogen as possible hydrogen bond acceptor atoms. Solid-state NMR spectra of a commercial sample not only confirmed immediately that there was only one molecule in the crystallographic asymmetric unit but also produced distinctive and chemical shifts. 

Evidence for the /3-d configuration of the anomeric center (C-1) of the purine nucleosides derived from the nucleic acids was obtained by Fur-berg, using x-ray crystallographic analysis, and by Todd and coworkers, whose studies of the anhydronucleosides (7 and 8) derived from... 

Xanthine oxidase (XO) catalyzes the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid. It plays an important role in the catabolism of purines.As shown in Figure 7.11, this reaction is slightly more complicated than the pure oxo-transfer reaction catalyzed by the other two enzymes discussed in this review. The structure of the XO active site has also been more controversial than for the other two enzymes. However, using a combination of crystallographic, EXAFS and computational studies it has been shown that the oxidized state has the structure MoOS(OH)(MPT), with the 0x0 group in the axial position. " Extensive experimental and theoretical investigations have been performed on XO and related enzymes " and the latter are summarized in Table 7.3. 

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