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Electronic structures and spectra of halogenated purines and pyrimidines III.σ‐Electronic structure and some comments on the mechanism of the xanthine oxidase reaction of 2‐halopurines and related analogs
Author(s) -
Song PillSoon
Publication year - 1968
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560020209
Subject(s) - cndo/2 , chemistry , xanthine oxidase , purine , computational chemistry , molecular orbital , purine metabolism , molecule , xanthine , electron , spectral line , crystallography , enzyme , organic chemistry , physics , quantum mechanics
The extended HMO (EHMO) and Pople‐Segal SCF‐MO‐CNDO /2 calculations on purine, 8‐oxopurine, 2‐oxopurine, 2‐fluoropurine, and 2‐chloropurine indicate significant polarizations of the σ cores. It is shown that the polarizations of both σ and π frameworks are mutually opposing in some cases. The results from the two methods are compared for these complex biomolecules. It is found that the EHMO calculations tend to over‐polarize the σ and π frameworks. However, the CNDO shows anomalous π‐electron densities on N (7) and C (8) of the purine rings, and the reason for this anomaly is not certain. The application of the results to the xanthine oxidase system indicates that the substrate molecules are subject to a specific orientation on the enzyme surface to counteract the electronic reactivity, in support of the previous prediction based on the π‐electron calculations. The CNDO results appear to be more satisfactory than the EHMO in this respect.