Imaging of poly(N-isopropyl acrylamide-co-acrylic acid) amino acid conjugates with scanning tunnelling microscopy

A copolymer of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AAc), Mw 1,400, AAc content of 3.1 mmol carboxylic acid groups per gram of the copolymer, was synthesised by a free radical polymerisation. Mono-, di-, and tripeptide conjugates of this copolymer were prepared by using the carboxyl-protected alanine, glycine and serine, with a water-soluble carbodiimide. Scanning tunnelling microscope images of the conjugates were taken after each synthesis step. The average length and width of the copolymer with no amino acid were measured as 17 and 2.5 nm, respectively. The lengths of the mono-, di-, and tri-peptide conjugates were similar to the length of the copolymer chain while the widths were in the range of 3.0-3.2, 3.5-4.0 and 4.2-4.4 nm, respectively.