Aza-crown-capped porphyrin models of myoglobin: Studies of the steric interactions of gas binding

James P. Collman*, Paul C. Herrmann, Lei Fu, Todd A. Eberspacher, Michael Eubanks, Bernard Boitrel, Pascal Hayoz, Xumu Zhang, John I. Brauman, Victor W. Day

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

72 Citations (Scopus)


A series of myoglobin active site analogues (1-6) has been synthesized and characterized. These synthetic models differ in their cavity dimensions, and have been designed to demonstrate the effects of steric factors on O2 and CO binding affinities. Quantitative gas titrations were employed to measure these affinities, yielding M values that are strikingly lower than those reported for hemoglobin and myoglobin. The 1,4,7-triazacyclononane-capped porphyrin 1 has about 1200 times the CO affinity but only about 10 times the O2 affinity of the cyclam-capped porphyrin 2, suggesting a more open gas binding cavity for 1. The cavity dimensions and conformation of 2 were determined by single-crystal X-ray structural analysis of the Zn analogue 7. This paper unequivocally demonstrates that steric effects can control the ratio of O2/CO binding constants.

Original languageEnglish
Pages (from-to)3481-3489
Number of pages9
JournalJournal of the American Chemical Society
Issue number15
Publication statusPublished - 1997
Externally publishedYes

Cite this