Interaction with metal salts of homopolymer or copolymers of a vinyl compound carrying linear tripeptide as a substituent

A vinyl compound carrying a linear tripeptide as a substituent, $\text{t-butyloxycarbonylsarcosyl}\text{-N}{}^{\mathrm{?}}\text{-}\text{acryloyl-}\text{l}\text{-lysylsarcosine}$ ethyl ester (Boc-Sar-N^?-AcrLys-Sar-OEt) (LP), was synthesized. By radical polymerization, the homopolymer (PLP) and the copolymers with styrene [P(LP-ST)] or 4-vinylpyridine [P(LP-VP)] of Boc-Sar-N^?-AcrLys-Sar-OEt were synthesized. The interaction of the homopolymer and the copolymers with alkali or alkaline-earth metal salts in nonpolar organic solvents was investigated. PLP showed a higher complexation ability towards alkali and alkaline-earth metal salts than the corresponding linear tripeptide, which indicates the enhancement of the complexation ability by the intramolecular cooperation of the linear tripeptide substituents in PLP. The interaction of P(LP-ST) with metal salts was much weaker than PLP, which indicates an inhibitory effect of styrene units upon the intramolecular cooperation of the linear tripeptide substituents. The interaction of P(LP-VP) with metal salts was much stronger than PLP, indicating a cooperation of pyridyl group for the coordination of the linear tripeptide ligand with metal ion. The permeation of metal salt across a blend film of cellulose acetate and PLP was enhanced by blending PLP and fastest for K⁺, indicating a participation of PLP in the ion transport. The permeation of metal salt across a blend film of cellulose acetate and P(LP-ST) was decelerated by blending P(LP-ST) and did not show any ion selectivity, reflecting the hydrophobicity and the low ability of complexation of P(LP-ST) copolymer. The permeation of metal salt across a blend film of cellulose acetate and P(LP-VP) was decelerated by blending P(LP-VP) and did not show any ion selectivity, although P(LP-VP) copolymer is very hydrophilic and strongly coordinative to metal salt. This anomaly may be a reflection of ion trapping by the P(LP-VP) component.