| 초록 |
L-Histidine in protein has been shown to induce membrane fusion at endosomal pH values. Therefore, poly(L-histidine-co-L-phenyl alanine)-block-poly(ethylene glycol) (P(H-co-P)-b- PEG) diblock copolymers were synthesized to prepare pH-sensitive polymeric micelles. First, P(H-co-P) was synthesized by ring opening copolymerization of L-histidine and L-phenyl alanine N-carboxyanhydride, and then the resulting copolymer was coupled with poly(ethylene glycol). The block copolymer forms polymeric micelles on diafilteration and the dissociated pKa value of micelles was controlled by the histidine/phenyl alanine ratio. Dynamic light scattering and scanning electron microscopy show that the micelles are spherical in shape, with a unimodal distribution. The critical micelle concentration of P(H-co-P)(5.5K)-b-PEG is 2.8 mg/l at pH 7.1, as determined by fluorescence spectroscopy. Since pKa value of the block copolymer is 7.1, the block copolymer forms micelle above pH 7.1 while it does not form micelle below pH 7.1. This is because protonation of histidine residue converts the hydrophobic core into hydrophilic one at lower pH.
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