Lecture 4 Flashcards
What is the dioxygen binding protien equalibrium?
Where does it typically lie?
Protien + O2 —-> Protien-O2
Lies to the RHS at ambient temperatures and partial pressures of O2
How do most animals get their energy?
‘Combustion’ of organic compounds, which requires a lot of oxygen
Why is oxygen diffusion inefficient?
- Surface to volume ratio of most higher organisms is too low for oxygen diffusion to be sufficient
- under stress, some tissues or organs require O2 very quickly and diffusion wouldn’t be fast enough
What two mechanisms have been developed for supply distribution?
- a circulatory system that actively delivers O2 to all cells
- the use of oxygen carrying molecules to overcome the low solubility of O2 in water
What are the 3 types of oxygen carrying proteins and where are they found?
What colour changes occur?
Haem proteins - red (oxy) to purple (deoxy) blood
Dicopper proteins- Blue to colourless, found in molluscs and anthropoids
Diiron proteins- violet to colourless, found in marine worms
Why are most reactions with dioxygen slow?
Due to O2 having a triplet ground state, which is spin forbidden from reacting with singlet molecules.
- a large input of energy is required to obtain singlet oxygen
How does oxygen interact with metal centres
- O2 pi* orbital interact with metal d orbitals
- a low energy pathway for overcoming the spin restrictions and kinetic inertness of O2
How are electrons transferred in O2- metal complexes?
- O2 is easily reduced and TMs have many oxidation states
- transfer from the metal to the dioxygen
- O2 bond is weakened due to donation so the bond becomes longer
What are Haemoglobin and Myoglobin?
Haemoglobin circulates through the body within red blood cells
Myglobin occurs in muscle tissue
Both are oxygen carrying proteins containing at least one Haem group
What is Haem?
A Haem group is an iron chelate of a tetrapyrrole macrocycle
approximately planar and highly rigid
Pi to Pi* electronics transitions give characteristic and intense absorption spectra
Both Fe(III) and Fe(II) ox states are available
What happens when oxygen binds with iron in a haem group?
Oxygen binds end on with the iron end on, and upon binding the iron moves into the same plan as the porphyrin ring, dragging the His group with it.
In deoxy Mb/Hb Fe(II) is high spin with a large covenant radius so it can’t fit in the plane of the ring.
The Fe(III)-O2- complex has a smaller covelant radius that can fit in the plane as it is low spin.
How many Haem groups do Hb/Mb have?
Mb- Monomer, Mw 17000, 1 Haem group
Hb- Tetramer, Mw 64500, 4 Haem groups
Describe the binding process in Hb
- A cooperative process
- As each O2 is bonded the affinity of the vacant sites to O2 increases (4th site is 300x more reactive than the first)
- Can be explained by conformational changes in the protein groups as oxygen binds to them. The movement of around 0.4 A by each Fe dramatically changes the structure due to pull on the proximal His group
CO and CN- toxicity
- CO binds to Haem instead of oxygen and is not easily lost
- CN- does not bind to Hb/Mb but binds to Fe(III) in cytochromes
Synthetic blood model 1:
- Cobalt and Schiff ligands. In te presence of DMSO or a non- coordinating solvent + Lewis acid
- rapid and reversible O2 uptake occurs up to 0 Celsius.
- square pyramidal favoured over square planar due to the unpaired electron being in the dz orbital so it can interact with the approaching dioxygen
