Which of the following is the non-physiological oxidant used by Robert Hill known as Hill reagent?
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To remember this: Robert Hill's original 1937 paper specifically utilized ferric oxalate as the non-physiological electron acceptor, establishing the fundamental proof of the light reaction of photosynthesis.
Step 1: Understanding the Concept:
In 1937, the British biochemist Robert Hill demonstrated that isolated chloroplasts could produce oxygen (\(O_2\)) in the presence of light if they were supplied with an artificial (non-physiological) electron acceptor.
This reaction is known as the "Hill Reaction," and the artificial electron acceptors are referred to as "Hill reagents." Step 2: Detailed Explanation:
Let us analyze the historical and scientific context of Robert Hill's experiments:
- In his pioneering experiments, Hill used leaf extracts containing isolated chloroplasts.
- Because the physiological electron acceptor NADP\(^+\) was washed out or diluted during the isolation process, the chloroplasts could not evolve oxygen on their own.
- To resolve this, Hill introduced artificial oxidants that could act as electron acceptors.
- The specific non-physiological oxidant used by Robert Hill in his early experiments was ferric oxalate (along with other ferric salts).
- In the presence of light, the ferric ions (\(Fe^{3+}\)) in ferric oxalate were reduced to ferrous ions (\(Fe^{2+}\)), and water was oxidized to release oxygen gas:
\[ 4\text{Fe}^{3+} + 2\text{H}_2\text{O} \xrightarrow{\text{light, chloroplasts}} 4\text{Fe}^{2+} + 4\text{H}^+ + \text{O}_2 \]
- Later, other artificial electron acceptors like potassium ferricyanide and DCPIP (2,6-dichlorophenolindophenol) were also utilized in laboratories, but ferric oxalate remains the classic Hill reagent used by Robert Hill himself to prove that light-driven water splitting is independent of carbon dioxide fixation. Step 3: Final Answer:
The correct option is (B).
