Amphiphilic Schiff base organogels: metal-ion-mediated chiral twists and chiral recognition

Abstract

New amphiphilic gelators that contained both Schiff base and L-glutamide moieties, abbreviated as o-SLG and p-SLG, were synthesized and their self-assembly in various organic solvents in the absence and presence of metal ions was investigated. Gelation test revealed that o-SLG formed a thermotropic gel in many organic solvents, whilst p-SLG did not. When metal ions, such as Cu(2+), Zn(2+), Mg(2+), Ni(2+), were added, different behaviors were observed. The addition of Cu(2+) induced p-SLG to from an organogel. In the case of o-SLG, the addition of Cu(2+) and Mg(2+) ions maintained the gelating ability of the compound, whilst Zn(2+) and Ni(2+) ions destroyed the gel. In addition, the introduction of Cu(2+) ions caused the nanofiber gel to perform a chiral twist, whilst the Mg(2+) ions enhanced the fluorescence of the gel. More interestingly, the Mg(2+)-ion-mediated organogel showed differences in the fluorescence quenching by D- and L-tartaric acid, thus showing a chiral recognition ability.