Bioinorganic Chemistry.ppt

1、Bioinorganic Chemistry,Chapter 16,Bioinorganic Chemistry,Only a few representative examples will be presented for these bioinorganic compounds and their actions. Table 16-1 (mammalian biochemistry) Examine the importance of iron. A relatively new area of study for bioinorganic molecules is the incor

2、poration of MO calculations.,Porphyrins and Related Complexes in Bioinorganic Molecules,A porphine ring has a square planar geometry with a “pocket” in the center. Examine Fig. 16-1. A metalloporphyrin complex can result by incorporating a metal atom into the pocket (look at heme from Rasmol). Axial

3、 sites are available for other ligands. Structure, specificity, and reactivity are changed by differing the side chains, metal ions, and surrounding species.,Hemoglobin and Myoglobin,Oxygen transfer and storage agents in the blood and muscle tissue. Hemoglobin transports oxygen (O2) from the lungs/g

4、ills to tissues and muscles. Myoglobin stores oxygen (O2) in the muscles and tissues. Oxygen commonly transfers from the hemoglobin to the myoglobin for later use.,Hemoglobin,Made up of four globin protein subunits ( and ). Each protein partially encloses a heme group. Each heme group is in a porphy

5、rin pocket. One axial position of the iron is bound to an imidazole nitrogen from the protein. One axial position is available/vacant or has H2O bound to it. Dissolved O2 can bind reversibly to this axial position. http:/www.umass.edu/microbio/chime/hemoglob/,Hemoglobin,In hemoglobin, the Fe(II) doe

6、s not become oxidized to Fe(III) or Fe(IV). Occurs readily in simpler systems (see Figure on the next page). There needs to be reversible binding of the O2 without oxidation. A free heme also oxidizes in an aqueous environment. Why doesnt oxidation occur in hemoglobin by O2 or H2O?,Hemoglobin (Figur

7、es),Hemoglobin,In nonoxygenated hemoglobin, the Fe(II) is about 70 pm out of the plane of the porphyrin nitrogens (show with Chime). Bonding O2 or CO in the sixth position causes the iron to be come planar. Fe(II) becomes diamagnetic Oxygen bonds at an angle of 130 degrees (show with Chime). Explain

8、 these structural changes upon bonding.,Hemoglobin,There is a considerable amount of backbonding from the metal to the O2. Can be described as Fe(III)-O2- Why is the O2 bent? The energy changes very little with this angle. suggestions,Hemoglobin,Cooperativity The function of hemoglobin is to bind O2

9、 at high oxygen pressure and carry it through the blood to needed areas (and myoglobin for storage). Hb + 4O2 Hb(O2)4 Hb(O2)4 + 4Mb 4Mb(O2) + Hb As one iron binds an oxygen molecule in Hb, the molecular shape changes to make binding of additional oxygen molecules easier. In a similar fashion, initial removal of oxygen triggers the release of the remaining oxygens.,Hemoglobin,At low partial pressures of O2, Mb has a much greater affinity for O2.The Bohr effect. Increased acidity favors the release of O2 from Hb(O2)4,