Water-Soluble Chiral Cyclic Peptoids and Their Sodium and Gadolinium Complexes: Study of Conformational and Relaxometric Properties

Cyclic peptoids are
macrocyclic oligomers of N-substituted glycines
with specific folding abilities and excellent metal binding properties.
In this work, we show how strategic positioning of chiral (S)- and (R)-(1-carboxyethyl)glycine units
influences the conformational stability of water-soluble macrocyclic
peptoids as sodium complexes. The reported results are based on nuclear
magnetic resonance spectroscopy, extensive computational studies,
and X-ray diffraction analysis using single crystals grown from aqueous
solutions. The studies include 1H relaxometric investigations
of hexameric cyclic peptoids in the presence of the Gd3+ ion to assess their thermodynamic stabilities and relaxivities.