Effect of residual side chain blocking groups and side chain charge on polypeptide conformation in aqueous solution

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Abstract
The circular dichroism (CD) spectrum of poly‐L‐lysine and poly‐L‐glutamic acid has been investigated in the presence of a small percent of side‐chain blocking groups. The blocking groups benzyl, methyl, and carbobenzoxy show qualitatively similar effects. Less than five mole percent of aromatic blocking groups alters the CD spectrum. Consequently, unsuspected blocking groups may account for the variation observed in CD spectra of these polymers. A weak CD band at 235–240 nm was observed for the disordered unblocked polymer even in the absence of electrolyte. Viscosity data indicate that in salt‐free solutions these chains at neutral pH still behave as random coils though with reduced conformational freedom, in contrast to some polyelectrolytes which behave as rigid rods in the absence of electrolyte. The viscosity data bring into question the relevance of isolated molecule conformational calculations to experimental CD spectra.

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