Self-Ordering Secondary Structure of D - And L -Arginine-Derived Polyamidoamino Acids

This paper reports on synthesis, acid-base properties and pH-dependent structuring in water of D-, L- and D,L-ARGO7, bioinspired polymers obtained by polyaddition of the corresponding arginine stereoisomers with N,N'-methylenebis(acrylamide). The circular dichroism spectra of D- and L-ARGO7 showed a peak at 228 nm and quickly and reversibly responded to pH changes, but were nearly unaffected by temperature, ionic strength, and denaturating agents. Theoretical modeling studies of L-ARGO7 showed that it assumed a folded structure. Intramolecular interactions led to transoid arrangements of the main chain reminiscent of the protein hairpin motif. Torsion angles showed a quite similar distribution at pH 6 and 14 consistent with the similarity of the CD spectra from pH 6 upward.