17 May 2018

Characterization and Investigation of a Binuclear Manganese(III)-Peroxo Metastable Intermediate

Literature Discussion

Submitted by Anthony L. Fernandez, Merrimack College

In this literature assignment, students are asked to read an article from the primary literature on a binuclear manganese-peroxo complex that is similar to species proposed to be involved in photosynthetic water splitting and DNA biosynthesis. The assignment contains 25 questions that are intended to guide students through the article and help them extract important information about the work. The completed questions are then used as the basis for an in-class discussion of model complexes, which leads to a more advanced discussion on the topic.

While this assignment is geared towards an advanced course, aspects of this assignment (kinetics, structure, electron counting) would be suitable for a foundation-level course.

This literature discussion was created in memory of my friend, Elena Rybak-Akimova (one of the co-authors of the article), just after she passed away. I took a few minutes at the end of the class to talk about Elena and how her skill and knowledge in kinetics made much of this work possible.

Learning Goals: 

After completing this assignment, a student should be able to:

  • extract important information from the primary literature,
  • recall the importance of metal-peroxo complexes,
  • describe how the authors synthesized and characterized the complexes under investigation,
  • explain why unusual techniques needed to be used to study the kinetics of the reaction,
  • rationalize why model complexes are useful in the examination of biologically-active metals.
Implementation Notes: 

The assignment was given to the students about 1 week before the discussion was to take place in class. A Google Doc version of this assignment was distributed using Google Classroom. Students were expected to download the article through our library, read the article, and answer the guiding questions in the assignment. 

In the class preceding our discussion of the article, we covered model complexes, the difference between structural and functional mimics, and why studying the two types of model complexes is important. We also looked at a number of examples: hydrogenase mimics, Collman's picket fence porphyrin, B12 mimics, molybdenum-oxo compounds, B12 model complexes, and engineered metalloeznymes. We also talked about ligand design using examples from Andy Borovik.

This assignment is intended to prepare students for the in-class discussion of the article so students had to submit their answers (via a Google Doc) before the start of class to receive credit for the assignment. The dicussion was based upon student responses. (I peruse the student responses just before class to see what questions they struggled with and which they seem to understand quite well.) We did not go through every question in detail, but instead covered 15-17 questions. Students wanted to discuss the characterization and kinetics questions extensively. I came prepared to talk a bit about stopped flow kinetics and Eyring plots, which was good because students had questions about both of those topics.

After completing our discussion of the assignment, I asked the students to determine the type of model compound that this was and we looked at the proposed mechanism of water splitting by photosystem II. 

Time Required: 
1-2 hours (outside of class by student); 45-60 minutes in class (including discussion of related topics)
Evaluation Methods: 

This assignment is graded based upon effort and not on the submission of correct answers. To receive full credit for this assignment, students must make a honest effort to complete the assignment, turn it in on time, and participate in the in-class discussion. I expect students to attempt to answer almost all of the questions, but I am not concerned if they got every answer completely correct.

I use the in-class discussion to go over student responses and have them guide each other to the correct answers. I judge student understanding by the overall quality of the discussion.

Evaluation Results: 

Of my 8 students, 5 received full credit for the assignment. Of these 5 students, four answered every question and one answered about 3/4 of the questions. These 5 students particpated in the in-class discussion and had little trouble recalling facts from the article or discussing the findings. I was quite pleased overall with the student responses and their preparedness for the dicussion.

When I looked a bit more closely at the submitted answers, I found that students submitted correct or mostly correct answers to the vast majority of the questions. Several of the students struggled with question 18. While they could all calculate the number of unpaired electrons that would give rise to the observed magnetic moment, several struggled to explain the lack of coupling between the the metal centers. (It is worth noting that this is one of the few questions for which the answer could not be found directly in the article.)

In the discussion, it became apparent that while the students provided correct answers for questions 23 & 24 (activation parameters) they did not understand how to calculate them, which was disappointing, or how to use them to infer mechanistic details.

Creative Commons License: 
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