In this literature discussion, students read a paper about a cobalt metallopeptide that imitates the active site of the enzyme nitrile hydratase. Specifically, the model complex is oxidized by air to produce a coordination sphere with both cysteine thiolate and sulfinic acid ligands, much like the post-translationally oxidized cysteine ligands in the biological system. This paper also provides an introduction to a variety of physical methods used to characterize the structure, including X-ray absorbance spectroscopy, magnetic susceptibility using the Evans method, IR spectroscopy, electronic absorbance spectroscopy, and electron paramagnetic resonance spectroscopy. This LO was created for the 2014 TUES Viper Workshop on bioinorganic chemistry.
Students will be able to:
Identify the oxidation state, coordination number, and approximate geometry of the cobalt complexes presented in this paper
Give the overall reaction catalyzed by the enzyme
Identify sites of potential ligand coordination in an oligopeptide
Compare two cobalt metalloenzyme active sites using the Protein Data Bank
Explain how X-ray absorbance spectroscopy can be used to identify the oxidation state of an atom
Assign ligand field or LMCT electronic transitions based on molar absorptivity
Compare and contrast thiolate, sulfenate, and sulfinate ligands with respect to charge, donor ability, and oxidation state
Predict how Lewis basicity and redox potential change as the ligand becomes more oxidized
- Evaluate the effectiveness of a model complex for reproducing a metalloenzyme active site
Students should read the paper and complete the reading guide before the literature discussion.
We hope that instructors will mix and match questions that are appropriate to their classes. In particular, instructors may want to remove questions 9-12 depending on the desired emphasis on experimental methods.