I The synthesis and coordination chemistry of novel 1,1,1-tris(aminomethyl)ethane (TAME) derived ligands and their use as size selective fluorescent zinc(II) sensors II The synthesis of strongly and weakly binding ligands with nitrogen, oxygen, and sulfur-donor groups to be used as receptors in fluorescent ratiometric indicators for transition metal ions

Abstract

The Ni(II)-mediated template synthesis of the novel chelator TAMEpyr, where TAMEpyr =N,N\u27,N -tris(2-pyridylmethyl)-1,1,1-tris(aminomethyl)ethane, and its coordination chemistry with a host of metal ions is presented. Structural data for [Zn(TAMEpyr)]2+ show the propensity of the ligand for an octahedral coordination geometry. Solution studies of TAMEpyr further illustrate the chelator\u27s flexibility. Lastly, the pyridyl groups of the parent ligand TAMEpyr were exchanged with a host of azaheterocycles affording a collection of novel TAME derived chelators. The Ni(II)-template chemistry developed to prepare the novel chelator TAMEpyr was exploited in the preparation of novel Zn(II)-selective fluorescent sensors. The molecules TAMEisoquin and 6,7-DMTI possess the fluorophore-spacer-receptor design motif that is evident in many photoinduced electron transfer (PET) based metal-ion sensors. These molecules display exquisite spectroscopic selectivity for Zn(II) with target-induced fluorescence enhancements of ca. 14 and 17 respectively. The measured quantum yield for [Zn(TAMEisoquin)]2+ was a dismal 1.2%. This was improved, however, to 20% for [Zn(6,7-DMTI)] 2+. The thermodynamic stability imparted to the target analyte from the polydentate N6-donor set was evidenced in the measured K d\u27 of 1.4 fM for [Zn(TAMEisoquin)]2+. Unlike many reported sensors, the TAME-based chelators display excellent selectivity for Zn(II) over Cd(II). Moreover, the synthetic flexibility of the TAME podand for additional functionalization may facilitate the development of novel bifunctional luminescent sensors. Work on TAME derived azacoumarins is presented. Lastly, swelling polymeric networks built from N-isopropylacrylamide (NIPA) have been prepared toward the sensing of Cu(II). The candidate\u27s role in this collaborative project was to synthesize strongly and weakly binding metal ion receptors to be copolymerized into the polyNIPA network. Fluorescent groups were also copolymerized into this network which acted as luminescent reporters upon analyte recognition. Depending on the charge of the bound metal-receptor complex the polymer either became swollen or shrank. Polymer shrinking brought the donor-acceptor pair closer together such that fluorescence resonance energy transfer (FRET) increased. Conversely, reduction of like charges within the polymeric network caused the polymer to swell thus attenuating the measured FRET. This section describes the ligating systems chosen to be incorporated into the polyNIPA systems and the results obtained for the sensing of Cu(II) is presented