Download Lect. 10A

Extra credit
• Extra credit 1 – ionic radii trends
• Extra credit 2 – solving MIMT single crystal structures
• Work on these must be completed individually.
• Due date: May 14th
Exploring biological functionality
• Enzymes
– Complex systems that often contain metals at active site
– Metals are particularly import for redox enzymes
• Bio-inorganic chemistry
– Synthesis of model compounds
The biological nitrogen cycle
Nitrogenase
Nitrogenase consists of 2 proteins: dinitrogenase reductase and dinitrogenase
Overall reaction
dinitrogenase
reductase
dinitrogenase
16 ATP required for each reduction of N2 -> 2 NH3
Some bacteria fix nitrogen only when involved in a
symbiotic relationship with plants
Leghemoglobin protects nitrogenase by binding oxygen
A true cross-species collaboration:
Plant makes the globin protein and bacterium makes the heme cofactor
Industrial Haber process (N2 -> NH3)
T = 400-500 °C
p = 300-1000 atm
Dinitrogenase model compound
Oxygen binding in body
You will make model compound, Co(salen)
• Co(salen) can bind oxygen, just like the biological heme molecule
NH2 + 2
H2N
en
HO
HO
O
sal
O
N
OH
OH HO
N
salenH2
Co(II)
O
N
N
Co
O
N
N
Fe
N
N
N
Co
2+
O
O
N
Co(salen)
Ferrous Heme
O
Co(salen)
Oxygen binding depends on Co environment
• In crystals:
N
N
Co
O
O
O
O
Co
N
N
Active structure
Sol
• Solvated:
N
N
Co
O
O
O
O O O
Co
N
N
N
N
Co
O
O
O
O
Co
N
N
Inactive structure
Sol
N
N
Co
O
O
O
O
Sol
2:1 structure
1:1 structure
• Co(salen) exists with Co in a 4, 5, or 6 coordinate site
• Solvated Co(salen) only binds O2 when it is 5 or 6 coordinate
Experimental apparatus for measuring O2 binding
graduated
pipette
stopper
vac. flask
DMSO in tt
tubing
water
Co(salen)