Theoretic Insight into CO2 Reduction at Active Sites of Molybdenum and   Tungsten Enzymes: a {\pi} Interaction between CO2 and Tungsten Bis-Dithiolene   Complexes
  Active sites of molybdenum and tungsten enzymes, particularly mononuclear tungsten formate dehydrogenase (FDH) have been theoretically investigated towards their interaction with CO2. Obvious {\pi} interaction has been found between the 2e reduced metallodithiole moiety and the molecular CO2. This weak {\pi} bonding is predicated both at gas phase, noted as -6.0 kcal/mol and aqueous solvation level, -3.6 kcal/mol. Such interaction is not only limited to CO2, but also to the CO2 reduced product, i.e. formate, in the form of anion- {\pi} interaction, noted as -6.8 kcal/mol and -4.1 kcal/mol respectively in gas and aqueous solvation model. The Bailar twisted angles from 60o to 0o, governing structure preference of tungsten dithiolene from octahedron to triangle prism in their restricted structures, has been explored to evaluate such {\pi} in-terrelations with CO2 and formate. An octahedral structure with 3 kcal/mol energy lower is preferred over the triangle prismatic when such interactions are concerned. 
Yong Yan, Jing Gu
physics.chem-ph