Enzyme-catalyzed regioselective modification of starch nanoparticles

The selective esterification of starch nanoparticles was performed using as catalyst Candida antartica Lipase B (CAL-B) in its immobilized (Novozym. 435) and free (SP-525) forms. The starch nanoparticles were made accessible for acylation reactions by formation of Aerosol-OT (AOT, bis(2-ethylhexyl)sodium sulfosuccinate) stabilized microemulsions. Starch nanoparficleS in microemulsions were. reacted with vinyl stearate, epsilon-caprolactone, and maleic anhydride at 40 degreesC for 48 h to give. Starch esters with degrees of substitution (DS) of 0.8, 0.6, and 0.4, respectively. Substitution occurred reposelectively at the C-6 position of the glucose repeat units. Infrared microspectroscopy (IMMS) revealed that AOT-coated starch nanoparticles diffuse into the outer 50 mum shell of catalyst beads. Thus. even ihough CAL-B is immobilized within a macroporous resin, CAL-B Is sufficiently accessible to the starch nanoparticleS. When free CAL-B was incorporated along with starch within AOT-coated reversed tnicelleS.. CAL-B was: also active and catalyzed the acylation with vinyl stearate (24 h, 40 degreesC) to give DS = 0.5. -Aliter removal of surfactant from the modified starch nanoparticles, the.), were dispersed in DMSO or water and were T shown to retain their nanodimensions.