Amino acid-deriving chiral polymers with potential for biotechnological applications

Polyamidoamines (PAAs) represent a well-known family of soluble synthetic functional polymers with a recognized potential for biotechnological applications. PAAs are obtained by stepwise Michael-type polyaddition of prim-monoamines or sec-diamines with bisacrylamides. The reaction occurs in aqueous solution at pH = 8–9 and at room temperature. The amine groups involved in the polyaddition pass from primary or secondary to tertiary preserving their amine character. By using -amino acids as monomers, poly(amidoaminoacid)s (PAACs) are obtained. PAACs maintain the chirality and the amphoteric properties of the starting monomers. These properties may affect their interactions with biological structures as proteins and living cells. A PAAC named L-ARGO7 was synthesized from L-arginine and methylenebisacrylamide.1 The acid/base properties of L-ARGO7 show an isolectric point of ≈10 and positive net average charges per repeating unit at pH 7.4 of +0.25. In vitro tests with mouse embryo fibroblasts balb/3T3 clone A31 show that L-ARGO7 polymers are endowed with effective cell internalization ability combined with minimal cytotoxicity. PAACs can be also obtained from D-enantiomers of amino acids, as in the case of D-arginine. The secondary structure of D-, L-, and D,L-ARGO7 in aqueous solution was studied by recording its circular dichroism (CD) spectra at different pH values. The spectra showed characteristic peaks at well-defined wavelengths. In particular, L-ARGO7 shows broad signals in the 250-340 nm region, indicating structuring. At pH = 5, these peculiar signals are minimized, clearly demonstrating that structuring in solution is pH-dependent. Comparison between D- and L-ARGO7 polymers is being performed in order to determine their differences in cell internalization.