Nature of O2 and CO binding to metalloporphyrins and heme proteins.

Abstract

The O2 vibration of dioxygen adducts of Fe and Co model complexes of a,a,ac,a-tetrapivalamidophenylporphyrin ("picket fence" porphyrin, TpivPP) with 1-methylimidazole and 1-tritylimidazole as axial bases are reported, obtained with difference techniques between 1'602,O180, 160-.80 A continuing controversy exists over the nature of ligand bonding to hemoproteins and metalloporphyrins. While it has been well established that both iron and cobalt bind dioxygen in a bent end-on fashion (1, 2), physical measurements (3-6) and theoretical calculations (7-10) have been used to support both the spin-paired dioxygen (M"1-02) (11) and the electron transfer superoxide (MIII-02-) (12) models. Here we present infrared data on dioxygen "picket-fence" porphyrin complexes of iron and cobalt. These results strongly support the MIn-02-formalism. The present data correct the preliminary report of an oxygen vibration at 1385 cm-' (3,13) which has since proved to be an artifact* (14). We are unaware of any previous reports of Po2 in model Fe and Co porphyrins. In addition, we discuss the nature of CO binding to ferrous porphyrins and the implication this has for the role of the apoprotein in biological oxygen carriers. It is our thesis that the distal binding site in hemoproteins functions to lower the carbon monoxide affinity.MATERIALS AND METHODS Benzene (spectroquality, Baker "Photrex") solutions of the "picket fence" porphyrin complexes (3, 14), FelImesotetra(a,a,a,a-o-pivalamidophenyl)porphyrinato (TpivPP) and Coll (aa,a,a-TpivPP), 17 mM and 19 mM containing 5 and 2 equivalents of 1-tritylimidazole (NTrIm), respectively, were Abbreviations: TpivPP, meso-tetra (a,a,a,a-o-pivalamidophenyl

Crystal Structures of the NO- and CO-bound Heme Oxygenase from Neisseriae meningitidis

“…Of the other two common Fe(II) ligands, CO and NO, NO is the best molecular mimic for O 2 binding. Both O 2 and NO prefer a bent geometry, whereas CO prefers a linear geometry when bound to Fe(II) porphyrins (25)(26)(27)(28). Moreover, high resolution structures of globins complexed with O 2 and NO show very similar binding geometries and local interactions in the heme pocket (29).…”

Assistance of the Iron Porphyrin Ligands to the Binding Interaction between the Fe Center and Small Molecules in Solution

“…5,8 Multiple effects from the protein have been identified, including steric hindrance, hydrogen bonding, and local polarity. 1,[13][14][15][16][17] However, due to the large size and the complex structure of protein, the interaction of protein with small molecules becomes extremely complicated. In addition, little attention has been paid to the small side ligands of porphyrin molecule itself.…”

Bonding and Correlation Analysis of Various SiCO Isomers

“…Because of the unsuitability of DFT and MP2 in treating 1 ∆ state of this system, the deviation among their theoretical results is large. By considering the bonding character of the 3 ∑ -state, it should be believed that the results obtained at the CASSCF/6-311+G* level are reliable, and perhaps the B3LYP and MP2 results (58-70 for ω 2 , 40-110 for ω 3 , and 2047-2122 cm -1 for ω 1 ) are fortunately reasonable. These small bending vibrational frequencies and small Si-OC stretching frequencies also imply that there should be similar PES character in the 1 ∆ state to that in the 3 ∑ -state.…”

“…In particular, for the studies on the CO species, much important information has been obtained. A recent survey of the stretching frequencies of CO bonded to the biological molecules has shown that there is an interesting change in the vibrational frequency for CO, 1 the affecting factors resulting in the frequency shift mainly involve the ring-ligand substituents, 2 CO ligand binding geometry and steric effects, [3][4][5] redox potentials, 6 CO binding affinities, 7 and the charge and polar interactions in the protein pocket. 1,8,9 To interpret the dependence of the CO binding on these effect factors, many interesting models have been established.…”

“…Another important contribution to the study of Si carbonyls should be referred to the Schaefer group works. [30][31][32][33] Using coupled-cluster with single and double excitations (CCSD), configuration interaction with single and double excitations (CISD), and many triple-basis sets, they investigated systematically the electronic structural characterization of silaketenylidene SiCO (carbonylsilene) and 2-silaketenylidene CSiO for their 3 ∑ -and 3 Π states, and indicated that there is obviously a Renner-Teller effect only for the linear 3 Π state. They also reassigned the structure of dicarbonyl Si (Si-(CO) 2 ) on the basis of theoretically predicted infrared spectra.…”