Copolyaspartates: Uncovering Simultaneous Thermo and Magnetoresponsiveness

• DOI: 10.1021/acs.macromol.0c02688
• Publication Date: 2021-02-11T15:16:26Z
• Authors: Max Hirschmann; Dominic S. Schirra; Christina M. Thiele
• Keywords: conformation; spectroscopy; Chemical Sciences not elsewhere classified; Biophysics; poly -β-benzyl co; 02 engineering and technology; Biochemistry; NMR; 2 H quadrupolar splittings; temperature-dependent; helix realignment; Virology; Medicine; copolymer composition; 0210 nano-technology; Physical Sciences not elsewhere classified; copolyaspartate

A series of poly-β-benzyl-l-aspartate-co-poly-β-phenethyl-l-aspartates varying in their copolymer composition as well as with selectively introduced deuterium labels in the backbone or the side-chain were synthesized and their temperature-dependent conformation and orientation with respect to an external magnetic field were characterized by measuring ²H quadrupolar splittings [nuclear magnetic resonance (NMR) spectroscopy] and circular dichroism. All copolymers demonstrate a temperature-dependent change of their helical conformation from right-handed to left-handed (helix reversal) and a change of their alignment from perpendicular to parallel with respect to the magnetic field in an anisotropic solution (helix realignment) at different temperatures. Both effects react differently to a change of copolymer composition, but are concentration, dispersity, and molecular weight independent as well as unaffected by the initiator used for polymerization. The helix realignment by 90° in a magnetic field has not been observed previously for these copolyaspartates. Its existence is proven directly by measurement of the quadrupolar splitting of the specifically labeled polymers and comparison to calculated quadrupolar splittings. Furthermore, the temperature of both transitions was found to be dependent on deuteration at the N-position. The uncovering of the thermo and magnetoresponsiveness will lead to an improved understanding and application scope of the copolyaspartates (e.g., in their use as alignment media in NMR spectroscopy).