Question #fc785

1 Answer
Mar 15, 2015

The biuret reagent contains CuSO₄. The Cu²⁺ ion is a Lewis acid.

The biuret reaction is a test for the presence of peptide bonds.

The Cu²⁺ ion forms violet-colored coordination complexes with peptides in an alkaline solution.

The biuret reagent is made of NaOH and CuSO₄·5H₂O.

Potassium sodium tartrate is added to stabilize the Cu²⁺ ions and prevent their precipitation as Cu(OH)₂.

The Cu²⁺ ions are Lewis acids. They react with the lone pairs on the peptide N atoms and form a purple tetradentate chelate.