Office: CHB 108 Phone: (405) 325-6401 Email: grichteraddo@ou.edu Full Publications List Click here for full CV as a pdf file.	George B. Richter-Addo Professor and OU Presidential Professor & Department Chair Ph.D. University of British Columbia B.Sc. (Hons) University of Cape Coast, Ghana Dip. Ed. University of Cape Coast, Ghana
Division: Inorganic chemistry Research Interests Bioinorganic Chemistry, Inorganic Chemistry, Nitric Oxide, Metalloporphyrins, Heme Models, Heme Biomolecules, Myoglobin, Cytochrome P450

We have established a broad-based research program in the inorganic and bioinorganic chemistry of nitric oxide (NO). In particular, we have examined the role that synthetic metalloporphyrins, myoglobin, and cytochrome P450 play in the binding and activation of NO and various organic nitroso compounds containing N-nitroso (nitrosamines (R₂NNO), NONOates (X[N(O)NO)), C-nitroso (nitrosoarenes (ArNO)), S-nitroso (thionitrites (RSNO), and O-nitroso (alkyl nitrites (RONO) functional groups.

We have prepared discrete nitrosyl metalloporphyrin complexes of Fe, Fe, Mn, Ru, Os, and Co. The NO ligand adopts a linear geometry in most of the complexes, the exceptions being those of Fe^II, Ru^II (with some ligands), and Co^II.  In collaboration with the Coppens and Bagley research groups, we have demonstrated that isonitrosyl and side-on NO groups can exist in mestable complexes of iron and ruthenium nitrosyl porphyrins.  We are currently investigating the spectroelectrochemistry of representative compounds in an attempt to determine the controlling factors that allow a linear-to-bent geometry change. Such a geometry change should have a corresponding chemical reactivity change of the bound nitrosyl ligand: the nitrosyl-N of the linear NO group is susceptible to attack by nucleophiles, whereas the nitrosyl-N of the bent NO group is susceptible to attack by electrophiles.

Research in our laboratory has shown that organic X-N=O compounds (X = NR₂, Ar, SR, OR) can bind in a variety of ways to the metal center in metalloporphyrins (Fig. 2), depending on the metal (and its oxidation state) and X.  We have established the nature of the interactions of N-nitroso groups (h¹-O), C-nitroso groups (h¹-N or h¹-O), S-nitroso groups (h¹-X), and O-nitroso groups (h¹-X) with metalloporphyrins.  When we started this work just over six years ago, such a delineation of binding modes for XNO compounds had not been reported.  We succeeded in isolating discrete adducts of N-nitroso and C-nitroso compounds with metalloporphyrins; however, we were not successful in isolating the analogous (discrete) complexes of S-nitroso or O-nitroso compounds.  Curiously, these latter nitroso compounds are those that interact with the metal centers via the non-nitrosyl heteroatoms (releasing NO).  This new-found dichotomy of the N- and C-nitroso compounds versus the S- and O-nitroso compounds provides grounds for further study of their diverse reaction chemistry.  Clearly, factors that determine the binding modes of XNO groups need to be examined in a systematic way, and the reactivity patterns need to be investigated and established.

NO and organic nitroso compounds display varied biological activities ranging from dilation of blood vessels to cancer. The enzyme that synthesizes NO in vivo contains heme, and the enzyme that is the receptor for NO also contains heme. Thus, detailed information on the interaction of NO and organic nitroso compounds with heme and heme models is valuable in aiding our understanding of the complex pathways of NO bioactivity.  Our biochemistry projects (in collaboration with Professor Ann West) with myoglobin and cytochrome P450 examine these issues.

1.         "Synthesis, Characterization, and Molecular Structures of Six-Coordinate Manganese Nitrosyl Porphyrins."  Zahran, Z. N.; Lee, J.; Alguindigue, S. S.; Khan, M. A.; Richter-Addo, G. B.  Dalton Trans. 2004, (1), 44-50.

2.         "Synthesis and Molecular Structures of Nitrosoarene Metalloporphyrin Complexes of Ruthenium."  Lee, J.; Twamley, B.; Richter-Addo, G. B.  Dalton Trans. 2004, (2), 189-196.

3.         "Crystal Structures of Ferrous Horse Heart Myoglobin Complexed with Nitric Oxide and Nitrosoethane."  Copeland, D. M.; West, A. H.; Richter-Addo, G. B. PROTEINS:  Structure, Function, and Genetics 2003, 53(2), 182-192.

4.         "Synthesis, Characterization, and Molecular Structures of Nitrosyl Nitrito Complexes of Osmium Porphyrins:  Disproportionation of Nitric Oxide in Its Reactions with Os(P)(CO) (P = porphyrinato dianion)."  Leal, F. A.; Lorkovic, I. M.; Ford, P. C.; Lee, J.; Chen, L.; Torres, L.; Khan, M. A.; Richter-Addo, G. B.   Can. J. Chem. 2003, 81(7), 872-881.

5.         "Interactions of Organic Nitroso Compounds with Metals."  Lee, J.; Chen, L.; West, A. H.; Richter-Addo, G. B. Chem. Rev.  2002, 102(4), 1019-1065.

6.         "Unexpected Nitrosyl-Group Bending in Six-Coordinate {M(NO)}⁶ s-Bonded Aryl(iron) and -(ruthenium) Porphyrins."  Richter-Addo, G. B.; Wheeler, R. A.; Hixson, C. A.; Chen, L.; Khan, M. A.; Ellison, M. K.; Schulz, C. E.; Scheidt, W. R.  J. Am. Chem. Soc. 2001, 123(26), 6314-6326.

7.         "First Observation of Photoinduced Nitrosyl Linkage Isomers of Iron Nitrosyl Porphyrins."  Cheng, L.; Novoszhilova, I.; Kim, C.; Kovalevsky, A.; Bagley, K. A.; Coppens, P.; Richter-Addo, G. B. J. Am. Chem. Soc., 2000, 122(29), 7142-7143.

8.         "Binding and Activation of Nitric Oxide by Metalloporphyrins and Heme." Cheng, L.; Richter-Addo, G. B. In The Porphyrin Handbook; Kadish, K. M.; Smith, K.; Guilard, R., Eds.; Academic Press: San Diego, 2000;  Volume 4.  Chapter 33 (pp 219-291).