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GATE 2020 CY – Question 20

Inorganic Chemistry · Bioinorganic Chemistry: Ion (Na+ and K+) transport, oxygen binding, transport and utilization, electron transfer reactions, nitrogen fixation, metalloenzymes containing magnesium, molybdenum, iron, cobalt, copper and zinc. · 1 mark · Multiple choice

For oxyhemocyanin, select the copper coordination number, oxygen-binding mode, colour and net magnetic behaviour. Cu atomic number is 29.

  1. Four; $\mu-\eta^1:\eta^1-O_2^{2-}$; colourless; paramagnetic.
  2. Five; $\mu-\eta^2:\eta^2-O_2^{2-}$; colourless; paramagnetic.
  3. Five; $\mu-\eta^2:\eta^2-O_2^{2-}$; blue; diamagnetic.
  4. Four; $\mu-\eta^1:\eta^1-O_2^{2-}$; blue; diamagnetic.

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Correct answer: (C) Five; $\mu-\eta^2:\eta^2-O_2^{2-}$; blue; diamagnetic.

Explanation

Oxygen binds as a side-on peroxide bridge between two copper centres, μ-η²:η². Each Cu has three histidine nitrogen donors plus two peroxide oxygen contacts, giving coordination number five. Oxygenation produces the blue dicopper(II)–peroxide centre; antiferromagnetic coupling gives a net diamagnetic state. These four features identify C.

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