$\mathrm{Fe}^{2+}$-porphyrins fail to exhibit reversible oxygen transport and cannot differentiate CO from $\mathrm{O}_{2}$. However, the hemoglobin is free from both these pit falls. Among the following
\[ \begin{array}{l} \text{(A) } \mathrm{Fe^{2+}}\text{-porphyrins undergo } \mu\text{-oxodimer formation and the same is prevented in case of the hemoglobin.} \\ \text{(B) Fe-CO bond strength is much low in case of hemoglobin when compared to the } \mathrm{Fe^{2+}} \text{ porphyrins.} \\ \text{(C) While Fe-CO is linear, } \mathrm{Fe\text{-}O_2} \text{ is bent and is recognized by hemoglobin} \\ \text{(D) The interlinked four monomeric units in the hemoglobin are responsible to overcome the pitfalls.} \end{array} \]
The correct set of statements is
(a)A and B
(b)A and C
(c)C and D
(d)B and D
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Free Fe(II) porphyrins form irreversible μ-oxo dimers, which the protein pocket prevents in hemoglobin. The distal histidine favours bent Fe–O₂ and disfavours linear Fe–CO, which reduces CO affinity. A and C (b).