US EPA

1178039 

Journal Article 

C-H bond activation in ribonucleotide reductases - Do short, strong hydrogen bonds play a role? 

Mohr, M; Zipse, H 

1999 

Yes 

Chemistry: A European Journal
ISSN: 0947-6539
EISSN: 1521-3765 

5 

10 

3046-3054 

WOS:000083059400031 

The hydrogen-transfer reactions between methyl thiyl radical and methanol, ethylene glycol, and 3,4-dihydroxytetrahydrofuran have been studied as model systems for the C-H bond activation step in ribonucleotide reductases with DFT methods. In all three cases, the overall reaction is endothermic. The lowest reaction barrier and the smallest endothermicity has been found for the tetrahydrofuran substrate. The influence of hydroxide, formate, hydronium, and neutral formic acid on the C-H bond activation in ethylene glycol has also been studied. Taking the reduction of the intrinsic barrier height as a measure of catalytic activity, the negatively charged formate group is the most effective catalyst. This catalytic effect is based on the formation of a strong anionic hydrogen bond, which achieves its maximum strength in the transition state of the C-H bond activation step. The observed modulation of the hydrogen bond strength along the reaction pathway is ultimately traced back to the electrophilic nature of the methyl thiyl radical. 

C-H bond activation; density functional calculations; radicals; ribonucleotide reductase; sulfur