Ferrous carbon monoxide complex

Carbon monoxide has 14 electrons, which pair to give a net spin of zero. Carbon monoxide complexes of transition metals, like oxygen complexes, cannot convert an even electron system to an odd electron system. In the case of iron, CO usually binds only to ferrous ions, which have six 3d electrons. As a consequence, CO complexes and O2 complexes with iron-containing proteins are generally not detectable by EPR. 

E° = —196 mV) to the ferric P450CAM heme iron to produce the ferrous state of the protein, 3. Dioxygen binds to the ferrous heme iron to form the ferrous oxy complex, 4a/4b, whose valence structure can be presented either as the ferrous-02, 4a, or as the ferric superoxide, 4b, complex. Addition of carbon monoxide to 3 yields a ferrous carbon monoxide adduct, 5, with its characteristic absorbance peak at 450 nm [37],... 

Oxidations. Most oxidative processes take place in liver microsomes and are catalysed by mono-oxygenase enzymes known as mixed-function oxidases. These processes require reduced nicotinamide-adenine dinucleotide phosphate, molecular oxygen and a complex of enzymes in the endoplas-matic reticulum. The terminal oxidizing enzyme is cytochrome P450, a hemoprotein. The notation P450 refers to the ability of the reduced (ferrous) form of the hemoprotein to react with carbon monoxide, yielding a complex with absorption peak at 450 nm. For each molecule... 

The presence of a carbon in the core of the ring indicates that these macrocycles will form organometallic interactions upon metal binding. In biological systems, naturally occurring organometallic complexes are rare. The cobalamin cofactor is one of the more important examples, which possesses an axial metal-carbon bond in a cobalt porphyrinoid macrocycle (77). Another common example is seen in carbon-monoxide deactivated ferrous heme (22) ... 

The ferrous heme within Mb and Hb forms stable complexes with at least two other gaseous diatomic molecules, namely, carbon monoxide and nitric oxide. Since both CO and NO are produced naturally in the body," it is important for Mb/Hb to distinguish these two molecules from each other and from O2. How does Mb/Hb discriminate three molecules of such similar size and polarity Attempts to answer this question have occupied a number of investigators for many years, and several reviews on this topic are available. 

Carbon Monoxide. The facilitated transport of carbon monoxide by cuprous chloride in aqueous solution was first studied by Steigelroan and Hughes (j 8) and more recently by Smith and Quinn (J 9). Smith and Quinn found the cuprous ion to be very effective c2U"rier for carbon monoxide and increased the flux by two orders of magnitude over the purely diffusive case. The facilitation factor was measured as a function of carbon monoxide partial pressure, total copper concentration, and membrane thickness. Recently, Koval et al. (20) reported facilitated CO transport using a ferrous complex derived from the tetraimine macrocyclic ligand 2,3,9,10-tetramethyl-1,3,8,11-tetraazacyclo-tetradeca-1,3,8,10- tetraene(TIM) in benzoni-trile. They measured the kinetic and dlffusional constants and showed selectivity for CO over a variety of other gases. The experimental and mathematical procedures which they described can be used for any simple complexatlon reaction. 

---