SYNTHESIS AND AQUEOUS SOLUTION PROPERTIES OF GRAFT COPOLYMERS BASED ON SOY PROTEIN ISOLATE WITH AMINO-TERMINATED POLY(2-ACRYLANMIDO-2-METHYL PROPANE SULFONIC ACID)

Graft copolymers(SPI-g-NH-PAMPS)were prepared by a graft reaction between the free carboxylic acid groups of soy protein isolate(SPI)and the amino groups of poly(2-acrylanmido-2-methyl propane sulfonic acid)(H_2N-PAMPS)using 1-(3-(dimethylamino)propyl)-3-ethyl-carbodiimide hydrochloride/N-hydroxysuccinimide as the condensing agents in a buffer solution.H_2N-PAMPS and SPI-g-NH-PAMPS were fully characterized by 1H-NMR,FTIR and 13C-NMR spectroscopies.The aqueous solution properties of SPI and SPI-g-NH-PAMPS were studied by zeta potentiometer,UV-Visible spectroscopy,fluorescence spectrometer,dynamic laser light scattering(DLS).The charge of SPI-g-NH-PAMPS measured by zeta potentiometer was negative within the whole pH range studied,which was due to the ionization of sulfonic groups of grafted chains.UV-Visible spectroscopy measurements demonstrated that the solubility of SPI was improved after the graft reaction,especially around the isoelectric point of SPI where it was increased by about 40%,because of the grafted hydrophilic H_2N-PAMPS chains.Fluorescence probing studies with 1-anilinonaphthalene-8-sulfonic acid(ANS)in aqueous solution revealed that the surface hydrophobicity of SPI-g-NH-PAMPS was much weaker than that of SPI.The average hydrodynamic radius(R_h)of SPI aggregates measured by dynamic laser light scattering(DLS)was increased from about 140 nm to about 200 nm.TEM studies indicated that SPI-g-NH-PAMPS aggregates presented a unique core-shell structure because hydrophilic PAMPS long chains surrounded on the surface of SPI globulins,and formed more hydrophilic shell,and the average size of SPI-g-NH-PAMPS aggregates was also bigger than that of SPI aggregates.The graft reaction using EDC provides a new method to modify SPI and expands the application fields of SPI.