Water-driven thermoresponsive peptohelical cushion

Oligopeptides were conjugated to the thermoresponsive polymer poly(N-vinylbutyramide) (PNVIBA) by the graft polymerization of the corresponding N-carboxyamino acid anhydrides from the amino side groups of P(NVIBA-co-vinylamine)s. The P{NVIBA-graft-(L)-aspartic acid (LAA)} with random-coiled graft chains showed a quick coil-globule transition accompanied by an endotherm due to chain dehydration across its low critical solution temperature (LCST) upon heating. In contrast, the P{NVIBA-graft-(L)-glutamic acid (LGA)}s with alpha-helical graft chains showed a slow transition accompanied by not only an endotherm but also an exotherm. A circular dichroism (CD) study indicated that the oligoLGA grafts changed their conformation accompanying the coil-globule transition of the PNVIBA backbone but recovered the a-helix at just above the exothermic temperature. H-1 nuclear magnetic resonance (H-1 NMR) indicated that the proton signals from the PNVIBA backbones and oligoLGA grafts were clearly detected just above the LCST, but only the PNVIBA protons reduced their intensity above the exotherm temperature. Thus, the present peptide grafts with a cc-helical conformation interfered with the thermoresponsive shrinking of the PNVIBA backbone by acting like spring cushions.