Imidazole is a five-membered aromatic heterocycle with nitrogen atoms at positions 1 and 3. In a neutral form, the two nitrogens have different lone-pair roles: one pair participates in the aromatic system and the other is available for proton acceptance or metal binding.
The ring occurs in the histidine side chain. Free imidazole can compete with histidine contacts during immobilized metal affinity chromatography, helping control protein retention and elution.
[ref]
Organic Chemistry by John McMurry. Chapter24, Amines and Heterocycles: imidazole and the distinct roles of nitrogen lone pairs
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