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. By using α-amino acids as monomers, poly(amidoaminoacid)s (PAACs) are obtained. PAACs maintain the chirality and the amphoteric properties of the starting monomers. In previous works, the PAAC obtained from the reaction of L-arginine and N,N’-methylenebisacrylamide, proved highly citycompatible with IC50 ≥ 8 mg/mL.[1] Cell internalization studies in Balb/3T3 cells demonstrated its preferential localization in the perinuclear region. Amphoteric PAAC isomers, named (D)-,(L)- and (D,L)-ARGO7, were synthesized at 50°C with 58% yield, Mn = 8500 and PDI = 1.40. Their β corrected pKa1 (COOH) and pKa2 (main chain tert-amine) values were evaluated using the modified Henderson-Hasselbach equation. Both β constants indicate deviation from the ideal behaviour, more pronounced for the carboxyl group. ARGO7 species distribution indicated isolectric point ≈10 and +0.25 net average charges per repeating unit at pH 7.4. The secondary structure in aqueous solution was studied by recording ARGO7 circular dichroism (CD) spectra at different pH values. Spectra showed pH-dependent bands in the 200-340 nm region with maximum values at 280 nm and strong absorption at pH>6.5. The (D)- and (L)- isomers had mirror-like CD spectra. The pH-dependent conformation and the high cytocompatibility of ARGO7 polymers let envisage a potential for stereochemical-governed intracellular localization and interactions with biocell components.