|Chemistry and Environmental Studies 247
|| Assignment 03
Read (and reread!) the scheduled chapters of the text in order to keep up with class.
Submit your response to the queries and problems below by 1:00 PM, Saturday, 22 January 2011. You may hand in your work at Science Hall 131, if it is open, or at the faculty mailboxes in Briggs.
- Which element used by, or associated with, biological systems best matches each of the following clues? Do not use H, C, N, or O; do not name any element more than once.
- accumulation is associated with Alzheimer’s disease
- bonded to oxygen atoms in nucleic acids
- higher concentration inside cells than outside
- kidney stones
- nitrogen fixation
- role in acid-base catalysis
- soft acid as a +1 ion
- soft base
- stored in association with sulfur
- tooth of the shark
- twenty-first amino acid
- vitamin B12
- Give an example of:
- a low-spin metal ion
- a metal ion with a strongly preferred coordination geometry
- an anion that exists at a relatively high concentration in the cytoplasm
- Consider the Frost diagrams for copper, for O2|H2O, and for H+|H2 at pH 7. You will need Kw. Explain whether Cu+ or Cu2+ is expected to be the predominant form of aqueous copper at pH 7 in the absence of complexing agents.
- Consider valinomycin, an uncharged natural product that has also been synthesized in the laboratory, which very selectively binds K+ (and Rb+ and Cs+) in marked preference to Na+ (and Li+). The empirical crystal radius of NH4+, the ammonium ion, is 1.48 in the usual Ångstrom units.
- Which cation(s), including NH4+ and those for which data can be found on pages 43 and 50 of the text, would you nominate as the most likely to compete with K+ for binding to valinomycin?
- Which do you think may be of greater importance here, size or charge? Can you suggest why?
- In partitioning from an aqueous phase into the cavity in valinomycin, a metal ion will have to relinquish its hydration sphere. What are the enthalpic and entropic consequences of that?
You should begin to identify the chapter(s) from the latter portion of the book for which you would especially like to develop your major class presentation(s).
Note that the final deadline for all written work in this course will be 1:00 PM, Thursday, 10 March 2011.