The thermodynamic constants of oxygen binding to cobalt "picket fence" porphyrin complexes, mejo-tetra(a,a,a,ao-pivalamidophenyl)porphyrinatocobalt(II)-1 -methylimidazole and 1,2-dimethylimidazole, are reported. In contrast to previously studied cobalt porphyrins, these complexes bind oxygen with the same affinity as cobalt substituted myoglobin and hemoglobin. Solvation effects are discussed as the source of this difference. The use of sterically hindered axial bases as models of T state hemoglobin is discussed.

In this laboratory experiment for precollege or first year courses, students find the stoichiometry of the reaction of citric acid with sodium hydroxide by mixing different acid/base ratios and finding which releases the most heat. Students collected the data cooperatively, in teams, reducing lab time to 90 minutes. The introduction, results, and conclusions are organized in a discovery format. The questions posed at the beginning of the laboratory about the number and kind of acidic H's in citric acid are answered by students in a discussion period at the end. Materials and equipment are simple and inexpensive, and the lab is short enough that students can design and carry out further experiments to test their initial conclusions within a single three hour laboratory period.

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