Lanthanide Coordination in N-Acyl Diphenylalanine Organohydrogels

Abstract

Three different N-acylated diphenylalanine peptide conjugates with varying lengths of fatty acid tails were synthesized and characterized through 1H NMR, FT-IR, MS, and elemental analysis. The organo-hydrogelation of these peptides was studied, comprising of two organic solvents, DMF and DMSO, as well as in the presence of Tb3+, which resulted in successful gelation for 3 previously non-gelling conditions. The viscoelastic properties of these gels were also investigated through rheological frequency sweeps. The morphologies of the organo-hydrogel hybrids were also examined using TEM and SEM. Through mass spectrometry, we demonstrate a variety of Tb3+-peptide-solvent coordinated species owing to the variable geometries characteristic of lanthanides and the self-assembling nature of physical gels, driven by noncovalent interactions. A 1:1 peptide:Tb3+ ratio was found to yield the highest fluorescence intensity at 546 nm, though even 0.2 eq of peptide enhanced the innate fluorescent properties of Tb3+. Thus, through control of the peptide:Tb3+ ratio, a wide range of fluorescent gels with variable tunable viscoelastic properties can be developed.