A note here on a few recent Angew. Chem. articles of interest to readers of this blog. The first is a comment by Frenking¹ concerning the “trilogue” by Shaik, Hoffmann and Rzepa² which discusses the nature of C₂, especially the notion that this molecules may possess a quadruple bond (see this post for a previous post on this article.) Frenking argues that the force constant associated with the C-C stretch in C₂ is smaller than that in acetylene, so how can one argue that there is some quadruple bond character in C₂? A reply from the original authors³ accompanies the comment by Frenking, and they respond by noting that the PES for bond stretching is unusually flat. I had the generally sense, though, that the authors of both articles were really talking past each other and that an opportunity for a more fruitful discussion has been missed.

The other article of note is an excellent review of de novo enzyme design as performed by the Baker and Houk labs.⁴ This review, authored by leaders of this effort, highlights their approach to this “holy grail” problem. The general notion is to use standard tools of computational chemistry to design a theozyme. Next, this theozyme is placed into known protein motifs with the attempt to have it fit without too much steric clash. The protein is then mutated one residue at a time to optimize the fit and binding of the theozyme to substrate. Lastly, the best targets are synthesized and tested. (The reader can see my post one of their projects: synthetic Diels-Alderase.)

References

(1) Frenking, G.; Hermann, M. "Critical Comments on “One Molecule, Two Atoms, Three
Views, Four Bonds?”," Angew. Chem. Int. Ed. 2013, 52, 5922-5925. DOI: 10.1002/anie.201301485.

(2) Shaik, S.; Rzepa, H. S.; Hoffmann, R. "One Molecule, Two Atoms, Three Views, Four
Bonds?," Angew. Chem. Int. Ed. 2013, 52, 3020-3033, DOI: 10.1002/anie.201208206.

(3) Danovich, D.; Shaik, S.; Rzepa, H. S.; Hoffmann, R. "A Response to the Critical Comments on “One Molecule, Two Atoms, Three Views, Four Bonds?”," Angew. Chem. Int. Ed. 2013, 52, 5926-5928, DOI: 10.1002/anie.201302350.

(4) Kiss, G.; Çelebi-Ölçüm, N.; Moretti, R.; Baker, D.; Houk, K. N. "Computational Enzyme Design," Angew. Chem. Int. Ed. 2013, 52, 5700-5725, DOI: 10.1002/anie.201204077.