Upper Critical Solution Temperature‐Type Thermal Response of Soluble Multi‐l‐Arginyl‐Poly‐l‐Aspartic Acid (cyanophycin) Conjugated with Maltodextrin

Abstract

ABSTRACTMulti‐l‐arginyl‐poly‐l‐aspartic acid (MAPA), also known as cyanophycin, can incorporate lysine into the side‐chain position of arginine when being prepared with recombinant Escherichia coli. The soluble fraction (sMAPA) is known to display both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) responses at the physiological condition. In an attempt to alter the UCST thermal response, maltodextrin was employed to conjugate onto the amine group of lysine of sMAPA via the formation of Schiff base. In phosphate buffered saline, the UCST of the conjugates appeared around 50–62°C, depending on the extent of conjugation. In contrast to the unmodified sMAPA, the UCST of the conjugate became independent of pH ranging from 1 to 11. Heating the conjugate solution to complete transparent caused a delayed and partial recovery of the original turbidity during subsequent cooling. However, the turbidity can be restored by further precipitation with ethanol or isopropanol followed lyophilization and re‐dissolution. At room temperature, below UCST, the agglomerates exhibited a size of around 200–400 nm under TEM and DLS. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2048–2055