Abstract
The synthesis and original thermoresponsive behavior of hybrid diblock copolypeptides composed of synthetic and recombinant polypeptides are herein reported. A thermoresponsive recombinant elastin-like polypeptide was used as a macroinitiator to synthesize a range of poly( l-glutamic acid)- block-elastin-like polypeptide (PGlu- b-ELP) diblock copolypeptides with variable PGlu block lengths. Their temperature-triggered self-assembly in water and in phosphate-buffered saline (PBS) was investigated at the macroscopic scale using complementary techniques such as turbidimetry, dynamic and static light scattering, small-angle neutron scattering, and at the molecular scale by 1H NMR and circular dichroism (CD). In deionized water, PGlu- b-ELP copolypeptides showed one transition from free soluble chains below the transition temperature ( Tt) of the ELP block to macroscopic aggregates above the Tt. In contrast, in PBS, four successive regimes were observed upon increasing temperature: below the Tt, copolypeptides were soluble, above the Tt, large aggregates appeared and fell apart into discrete and defined spherical nanoparticles at a temperature named critical micellization temperature (CMT), before finally reaching an equilibrium. During the last regime, neutron scattering experiments revealed that the micelle-like structures underwent a densification step and expelled water from their core. In addition, 1H NMR and CD experiments revealed, in deionized water, the formation of type II β-turns into the ELP block upon temperature increase. These β-turns are known to participate in the intrinsic thermoresponsive behavior of the ELPs. In contrast, in PBS, circular dichroism measurements showed an attenuation of folded structure during the self-assembly phase, leading to less cohesive aggregates able to reorganize into nanoparticles at the CMT.
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