Analysis of pH response for amphoteric Poly(O-methacryloyl-L-serine) and interaction with serum protein by fluorescence spectroscopy

The amphoteric polymer having L-serine residues in the side chain as a pH responsible hydrogel component was prepared as follows: L-serine with protected amino and carboxyl groups, N -tert-butoxycarbonyl-O -methacryloyl-L-serine diphenylmethyl ester (Boc-SerMA-Ph₂) and 2-(dansyloxy) ethyl methacrylate (DnsEMA) were copolymerized by a radical mechanism with 2,2' -dimethyl-azobisisobutyrate in tetrahydrofuran at 60 °C for 20 h. Deprotection of the resulting polymer was carried out in 80% trifluoroacetic acid aqueous solution to give amphoteric poly(SerMA labeled with a dansyl group [poly(SerMA-co-DnsEMA)]. The fluorescence spectral changes of a dansyl-labeled poly(SerMA) solution at pH ranging from 1.2 to 12.0 revealed that poly(SerMA) shows pH response. The interaction between a serum protein such as bovine serum albumin (Alb), human γ-globulin (Glo), or bovine serum fibrinogen (Fib), and poly(SerMA-co-DnsEMA) was also examined by means of fluorescence spectroscopy in a phosphate buffered solution at pH 5.7 for Alb and Fib, pH 6.2 for Glo. The interaction between Alb and poly(SerMA-co-DnsEMA) was observed, whereas no definite interaction was confirmed for Glo and Fib.