The effect of methylmercury(II) binding on the conformation of poly( L ‐glutamic acid) and poly( L ‐lysine): A raman spectroscopic study

The binding of the methylmercury cation CH3Hg+ by poly(L‐glutamic acid) (PGA) and by poly(L‐lysine) (PLL) has been investigated by Raman spectroscopy. Coordination on the side‐chain COO− and NH groups of these polypeptides gave characteristic ligand–Hg stretching modes at ca. 505 and 450 cm−1, respectively. Precipitation generally occurred upon formation of the complexes and changes of conformation were common. The solid complex obtained from PGA at pH 4.6 was found to have a mostly disordered conformation, which differed from the respective α‐helical and β‐sheet structures of the dissolved and precipitated uncomplexed polypeptide in the same conditions. An α‐helical structure was generally adopted by the complex formed with PLL, even in pH and temperature conditions where the free polypeptide normally exists in another conformation. The addition of a stronger complexing agent, glutathione, to the PLL/CH3Hg+ complex caused a migration of the bound cations and a restoration of the polypeptide to its original state.