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Thermoresponsive Alignment Media in NMR Spectroscopy: Helix Reversal of a Copolyaspartate at Ambient Temperatures
Author(s) -
Schwab Mira,
Schmidts Volker,
Thiele Christina M.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201803540
Subject(s) - helix (gastropod) , chemistry , side chain , copolymer , residual dipolar coupling , polymer , solvent , nuclear magnetic resonance spectroscopy , alpha helix , crystallography , circular dichroism , stereochemistry , organic chemistry , ecology , snail , biology
Poly(aspartic acid esters) are known to form either right‐or left‐handed α‐helices depending on the ester group in the side chain, on solvent and/or on temperature. Polyphenethyl‐ l ‐aspartates (PPLA) exhibit a helix reversal from the right‐ to the left‐handed form with increasing temperature. We have recently reported the application of polyphenethylaspartates as helically chiral alignment media. The thermoresponsivity observed for these polymers offers the possibility to measure different orientations of analytes before and after helix reversal of the alignment medium at 373 K. Herein we present a synthesized copolymer of phenethyl‐ and benzylaspartate as a new alignment medium undergoing this helix reversal at 303–313 K. Thus, the measurement of residual dipolar couplings (RDC) before and after the helix reversal is allowed for at ambient temperatures. A complete sign change of all 1 H– 13 C RDCs was observed, which is close to the highest possible difference in NMR spectra.