pH-Responsive release from polypeptide microcapsules

Microcapsules were prepared from [Glu(OMe)](m)(Sar)(n) (m=21, n=19) and [Lys(Z)](m)(Sar)(n) (m=27, n=15), and were chemically modified to obtain a pH-responsive releasing membranes. One membrane was prepared by partially deprotecting the ester groups of [Glu(OMe)](m)(Sar)(n). The other membrane was prepared by connecting of poly(Glu) to side chain amino groups that were generated by a partial deprotection of [Lys(Z)](m) (Sar)(n). Consequently, two types of polypeptidic microcapsules were prepared; Glu residues in the main chain, and Glu residues in the graft chains on the positively charged main chain. Both microcapsules showed pH-responsive release of FITC-dextran encapsulated in the microcapsules. The release rate became slower in the medium at pH 3.0 than pH 7.5. Optical microscope observation revealed that partially deblocked [Glu(OMe)](m)(Sar)(n) microcapsules swelled more at pH 7.5 than at pH 3.0; hence, enhanced permeation through the polypeptide membrane at pH 7.5. However, the shape of poly(Glu)-grafted [Lys(Z)](m)(Sar)(n) microcapsules changed a little by changing pH of the medium. It is suggested that ion-pairing between carboxylate groups of poly(Glu) and ammonium groups of Lys acts as crosslinking to give the shape stability. (C) 1997 John Wiley & Sons, Inc.