Density Functional and MP2 Calculations of Spin Densities of Oxidized 3-MethylIndole. Models for Tryptophan Radicals

摘要

Ab initio calculations have been carried out on 3-methyl indole, and the cationand neutral radicals of 3-methyl indole, using Density Functional Theory (DFT), the Becke3-Lee-Yang-Parr functional, and the 6-31G*, 6-31+G*, 3-21G*, and TZ2P basis sets. Optimized geometries, vibrational frequencies and, for the radicals, atomic spin densities are calculated. The latter are compared to experimental spin densities recently determined for the tryptophan-191 radical of compound ES of the enzyme cytochrome-c-peroxidase. The DFT spin densities for the cation radical of 3-methyl indole are in excellent agreement with the data for the tryptophan-l91 radical, which supports the conclusion that the tryptophan radical is a cation radical. The results are compared to calculations using second-order Moller-Plesset theory (MP2) and the 6-31G** basis set. The MP2 spin densities are in significantly worse agreement with the experiment spin densities. jg p3.