Instructor: Dr. Keith M. Davies. Office 410 Occoquan (PW1)

1. CHEMISTRY 646 BIOINORGANIC CHEMISTRY SPRING 2011 Instructor:Dr. Keith M. Davies.     Office 410 Occoquan (PW1)                       kdavies@gmu.edu      703-993-1075  Office Hours: Tu 1:00-3:30; Th 1:30-2:30 (326B ST1) or by appointment M,W,F at 410 Occoquan (PW1). . Syllabus:http://osf1.gmu.edu/%7Ekdavies/646SYL-Spring-11.html

2. 1A class presentation of a “bioinorganic chemistry“ topic taken from journal articles in the "inorganic-biochemistry" literature and a 1-2 page written summary.

3. Textbook: Biological Inorganic Chemistry, Structure and Reactivity H. B. Gray, E. I. Stiefel, J. S. Valentine and I. Bertini, University Science Books, 2007.

5. Bioinorganic Texts in Johnson Center Library • Bertini, I.; Gray, H. B.; Lippard, S. J.; Valentine, J. S. Bioinorganic Chemistry (University Science Books; 1994) • Kaim, W. and Schwederski, B. Bioinorganic chemistry : inorganic elements in the chemistry of life : an introduction and guide (Wiley, 1994) • Cowan, J. A. Inorganic Biochemistry: An Introduction (Wiley-VCH: New York, 1997) • Lippard, S. J. and Berg, J. M. Principles of Bioinorganic Chemistry (University Science Books; 1994). •  Roat-Malone, R. M. Bioinorganic Chemistry: A Short Course (Wiley, 2002)

6. Course Outline and Objectives • Bioinorganic chemistry is concerned with the roles of • inorganic elements in biological processes. • In CHEM 646, we will apply fundamental principles of • inorganic chemistry, particularly transition metal • coordination chemistry and ligand field theory, to • understand the structure and function of metal ion • sites in biomolecules. • We will also consider bioinorganic topics including metal • toxicity, the use of metal complexes as drugs and the • bioregulatory functions of nitric oxide.  

7. The role of the metal center in biomolecules • Metal ions can have structural roles, catalytic roles, or both. • Metals that have catalytic roles will be present at the active site of the biomolecule which will likely be a metalloprotein (a metalloenzyme). • The reactivity of a metalloprotein is defined by the nature of the metal, particularly its electronic structure and oxidation state. • This, in turn, is determined by its coordination environment (ligand donor atoms) and molecular geometry, which is provided by the architecture of the protein surrounding the metal.

8. The importance of the electronic structure of the metal center • The electronic structure and spin state of a metal center defines its chemical reactivity as a redox center (i.e. it controls its efficiency at accepting or donating electrons) • The electronic structure of a metal center defines its chemical reactivity as a Lewis acid (electron-pair acceptor) which enables it to bind ligands (O2, N2, CO ..) for transport, activation and reaction. • The electronic structure and spin state of a metal center permits its investigation and characterization through electronic, Mossbauer and epr spectroscopy and through magnetic measurements.

9. Introduction • Occurrence, availability and biological roles of inorganic elements. Fundamentals of metal ion coordination chemistry. • Metal-ligand interactions, stability of metal complexes, chelation. Review of protein structure and metal ion binding in biomolecules.    Ligand field theory • Magnetic and spectral properties of transition metal ions. Thermodynamic stability, redox potentials and Latimer diagrams. Molecular orbital theory • Diatomic oxygen species. Metal-ligand s and Π-interactions. Π-unsaturated ligands, organometallic structures, 18-electron rule Biological transport and storage of metals • Iron transport by transferrin and storage in ferritin. Bacterial iron transport in siderophores. Zn and Cu transport in metallothionein and metallochaperones..

10. Dioxygen Transport: O2 carriers • Hemoglobin, hemerythrin and hemocyanin.Cooperativity in O2 binding, O2 and CO discrimination. Inorganic model compounds. Oxygen Metabolism: Dioxygen Activation • Oxygen atom transfer by cytochromes-P450, tyrosinase. Dioxygen Reactivity and Toxicity • Toxicity of reduced oxygen species. Oxidative stress from ROS and detoxification enzymes. Electron transfer in Biology • Metal cofactors. Iron cytochromes and iron sulfur proteins. Marcus theory. Electron transfer in proteins. Redox Cofactors • Cobalamins, nitrogenases, hydrogenases.

11. Metals in Medicine • Cisplatin and 2nd generation Pt anticancer drugs. • Metal toxicity and metal-related disease. Chelation therapy. Nitric Oxide Biochemistry • Physiological roles of NO in control of blood pressure, neuronal signaling and cytotoxicity. Nitric oxide synthase enzymes (NOS). Cobalamins • B12- coenzme dependant rearrangements. Hydrolytic Enzymes • Metal-dependant Zn hydrolase enzymes. Carbonic anhydrase, carboxypeptidase., alcohol dehydrogenase. Aconitase, urease. Biological roles and Transport of Na+, K+, Ca2+. • Na, K, Ca as biological messengers:membrane transport mechanisms. Ion channels

12. Occurrence, roles and classification of metallobiomolecules

13. Biologically Important Elements Which “inorganic” elements are important biologically? 99% of human body is comprised of 11 elements Bulk biological elements: H, C, N, O, P, S, Cl (as PO43-, SO42-, Cl-) Bulk metal ion nutrients: Na, Mg, K, Ca Essential elements for a wide range of bacteria/plants/animals Transition metals: V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo Non-Metals: (B), F, (Si), Se I, F.

14. Periodic Distribution of Biologically Important Elements

15. Evolution of biological roles for essential metals • Why have certain elements been "selected" for use in biological systems? • a. their abundance (availability in the earth’s crust or • oceans) • b. their basic fitness (intrinsic chemical suitability) • evolutionary adaption to realize critically required • specificity.

16. Lighter elements are more abundant in general and therefore utilized more. 3d metals, rather than 4d, are used as catalytic centers in metalloenzymes. • Why has Mo (4d) rather than Cr (3d) been utilized more biologically? Although Mo is rare in the earth’s crust, Mo is the most abundant transition metal in sea water as MoO4has fairly high solubility in water. Better correlation exists between the abundance of elements in in human body and in sea water than between the human body and the earth's crust. Taken as evidence for the oceans as the site of evolution of life. • Despite the high abundance of Si, Al and Ti (the 2nd, 3rd and 10th most abundant elements on earth). Why are they are not utilized biologically? • Because of the insolubility of their naturally occurring oxides (SiO2, Al2O3, TiO2) under physiological conditions. A lower oxidation state is unavailable for Si and Al and unstable for Ti in an aerobic environment and is readily oxidized to Ti(IV) at pH 7.

17. Why has iron been used so widely in biology although Fe3+, its most stable oxidation state, is highly insoluble at pH 7 Complex biological mechanisms have been developed to accommodate the low solubility of Fe(OH)3 (Ksp = 1 x 1038) ~ pH 7, and take advantage of its high "availability". • Co2+ and Zn2+ have very similar coordination chemistry and ionic size and can be interchanged in many Zn enzymes without loss of activity. Why is Co not utilized more biologically? Zn is much more abundant and therefore has been utilized more. • Why has cobalt been given an essential role in cobalamins despite its very low availability? • The unique properties of cobalt (e.g. its oxidation states, redox potentials and coordination chemistry) is needed to achieve essential functions of B12 coenzymes.

18. Indicators of Biologically Important Elements • Relative abundance of inorganic elements in earth's crust and in seawater. • Availability of elements from earth’s crust and sea water • Elemental composition of human body • Essential inorganic elements in food • Inorganic elements linked to deficiency symptoms

19. Elemental Composition of Human Body (70 kg adult) Element mass mass % __________________________________________________________________________________________________ Oxygen O 45.5 kg 65.0 Carbon C 12.6 18.0 Hydrogen H 7.0 10.0 Nitrogen N 2.1 3.0 Calcium Ca 1.1 1.5 Phosphorus P 0.700 1.0 Sulfur S 0.175 0.25 Potassium K 0.140 0.20 Chlorine Cl 0.105 0.15 Sodium Na 0.105 0.15 Magnesium Mg 35 g 0.020 Iron Fe 4.2 0.0060 Zinc Zn 2.3 0.0033 Silicon Si 1.4 0.0020 Rubidium Rb 1.1 0.0016 Fluorine F 0.8 0.0011 Zirconium Zr0.3 4.3 x 10-4 Bromine Br 0.2 2.9 x 10-4 Strontium Sr 0.14 2.0 x 10-4 Copper Cu 0.11 1.6 x 10-4 Aluminum Al 0.10 1.4 x 10-4 Lead Pb 0.080 1.1 x 10-4 Cadmium Cd 0.030 Iodine I 0.030 Manganese Mn 0.02 Vanadium V 0.02 Selenium Se 0.02 Barium Ba 0.02 Arsenic As 0.01 Nickel Ni 0.01 Chromium Cr 0.005 Cobalt Co 0.003 Molybdenum Mo < 0.00 ___________________________________________________________________________________________________

20. Mammals are believed to use only 25 of the known elements. • Eleven non-transition elements that make up 99.9% of the human body • (O, C, H, N, Ca, P, S, K, Cl, Na, Mg), • Three transition metals, Fe, Zn and Cu are needed in significant amounts. • “Trace quantities” of many other transition elements are required to • maintain proper physical functioning. • Other elements in the human body (e.g. Rb, Zr, Sr, Al, Pb, Ba) are not • essential but incorporated inadvertently because they share chemical • and physical properties with essential elements. • Other elements are added to the list of elements thought to be essential • as our knowledge of the chemistry of living systems increases.

21. Essential Inorganic Elements in Adult Diet ____________________________________________________________ Recommended Daily Allowance (mg) ____________________________________________________________ K2000 - 5500 Na1100 - 3300 Ca800 - 1200 Mg300 - 400 Zn15 Fe10 - 20 Mn 2.0 - 5.0 Cu1.5 - 3.0 Mo 0.075 - 0.25 Cr 0.05 - 0.2 Co ~ 0.2 Cl 3200 PO43- 800 - 1200 SO42- 10 I 0.15 Se 0.05 - 0.07 F 1.5 - 4.0 _____________________________________________________________

22. Symptoms of Elemental Deficiency in Humans __________________________________________________________ Ca Retarded skeletal growth Mg Muscle cramps Fe Anemia, immune disorders Zn Stunted growth, skin damage, retarded maturation Cu Liver disorders, secondary anemia Mn Infertility, impaired skeletal growth Mo Retarded cellular growth Co Pernicious anemia Ni Depressed growth, dermatitis Cr Diabetes symptoms Si Skeletal growth disorders F Dental disorders I Thyroid disorders Se Cardiac muscular weakness As Impaired growth (in animals) ________________________________________________________

24. Biological Roles of Metallic Elements. Structural Skeletal roles via biomineralization Ca2+, Mg2+, P, O, C, Si, S, F as anions, e.g. PO43, CO32. Charge neutralization. Mg2+, Ca2+ to offset charge on DNA - phosphate anions Charge carriers:Na+, K+, Ca2+ Transmembrane concentration gradients ("ion-pumps and channels") Trigger mechanisms in muscle contraction (Ca). Electrical impulses in nerves (Na, K) Heart rhythm (K). Hydrolytic Catalysts: Zn2+ , Mg2+ Lewis acid/Lewis base Catalytic roles. Small labile metals. Redox Catalysts: Fe(II)/Fe(III)/Fe(IV), Cu(I)/Cu(II), Mn(II)/Mn(III)/(Mn(IV), Mo(IV)/Mo(V)/Mo(VI), Co(I)/Co(II)/Co(III) Transition metals with multiple oxidation states facilitate electron transfer - energy transfer. Biological ligands can stabilize metals in unusual oxidation states and fine tune redox potentials. Activators of small molecules. Transport and storage of O2 (Fe, Cu) Fixation of nitrogen (Mo, Fe, V) Reduction of CO2 (Ni, Fe) Organometallic Transformations. Cobalamins, B12 coenzymes (Co), Aconitase (Fe-S)

25. Transition Metals in Biomolecules Iron. Most abundant metal in biology, used by all plants and animals including bacteria. Some roles duplicated by other metals, while others are unique to Fe. Iron use has survived the evolution of the O2 atmosphere on earth and the instability of Fe(II) with respect to oxidation to Fe(III). Zinc. Relatively abundant metal. Major concentration in metallothionein (which also serves as a reservoir for other metals, e.g. Cd, Cu, Hg). Many well characterized Zn proteins, including redox proteins, hydrolases and nucleic acid binding proteins. Copper Often participatse together with Fe in proteins or has equivalent redox roles in same biological reactions. Reversible O2 binding, O2 activation, electron transfer, O2- dismutation (SOD). Cobalt. Unique biological role in cobalamin (B12-coenzymes) isomerization reactions. Manganese Critical role in photosynthetic reaction centers, and SOD enzymes. Molybdenum Central role in nitrogenase enzymes catalyzing N2 NH3, NO3 NH3 Chromium, Vanadium and Nickel Small quantities, uncertain biological roles. Sugar metabolism (Cr); Ni only in plants and bacteria (role in CH4 production) and SOD enzymes.

26. Biochemical Classification of Metallobiomolecules Transport and storage proteins : Transferrin (Fe) Ferritin (Fe) Metallothionein (Zn) O2 binding/transport: Myoglobin (Fe) Hemoglobin (Fe) Hemerythrin (Fe) Hemocyanin (Cu) Enzymes (catalysts) Hydrolases: Carbonic anhydrase (Zn) Carboxypeptidase (Zn) Oxido-Reductases: Alcohol dehydrogenase (Zn) Superoxide dismutase (Cu, Zn, Mn, Ni) Catalase, Peroxidase (Fe) Nitrogenase (Fe, Mo) Cytochrome oxidase (Fe, Cu) Hydrogenase (Fe, Ni) Isomerases: B12 coenzymes (Co) Aconitase (Fe-S) Oxygenases: Cytochrome P450 (Fe) Nitric Oxide Synthases (Fe) Electron carriers: Cytochromes (Fe) Electron transferases Iron-sulfur (Fe) Blue copper proteins (Cu) Non Proteins Transport Agents: Siderophores (Fe)