Magnetically complexed collagen nanocomposites

Rare-earth ions with unfilled 4f shells, Gd3+ (J = ) and Dy3+ (J = ) are bound to glutamic acid residues at the ends of long linear oligopeptides derived from those in naturally occurring collagen proteins. The peptide, which folds into a triple helix about 10 nm long, consists of a sequence 36 amino acids long. The rare-earth–collagen complex self-assembles into layers through a smectic A liquid crystalline phase. The smectic layered structure is retained on drying, and the acidic peptide end blocks localize the rare-earth ions in sheets approximately 1–2 nm thick separated by the collagen-like peptide of the complex. X-ray crystallographic, scanning electron microscopy and optical studies demonstrate the liquid crystallinity of the peptides and the incorporation of the rare-earth ions into sheets between the smectic layers. Magnetic susceptibility (2 K ≤ T ≤ 300 K) and low-temperature isothermal magnetization (0 T ≤ H ≤ 5 T) show the rare-earth–collagen complexes are paramagnetic in the rare-earth concentration range studied (not more than 0.3–0.4 Gd or Dy ion per molecule). This technique of bonding rare-earth ions to oligopeptides, and using the oligopeptide mesophase behaviour to organize attached ions, can be used to tether other rare-earth and/or transition-metal ions, creating layered magnetic structures. The interlayer spacing is dictated solely by the intervening oligopeptide length.