TAMEisoquin, a novel tripodal fluorescent zinc sensor with high Zn(II) affinity and Zn(II)/Cd(II) selective fluorescence response: Synthesis, coordination geometry, spectroscopy, and comparative response to biometal ions

Herein we report a novel fluorescent zinc sensor 1,1,1-tris (aminomethylethane)N,N′,N″-(2-methylisoquinoline) (TAMEisoquin), [Zn(TAMEisoquin)]2+ complex and its structural and photophysical studies. TAMEisoquin was obtained from reduction of templated [Ni(TAMEisoquin-trisimine)]2+ complex to give [Ni(TAMEisoquin)]2+, which was subsequently decomposed with excess sodium cyanide to afford TAMEisoquin. A competition reaction between TAMEisoquin and the well-known Zn(II) chelator (N,N,N′, N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) at pH 7.2 indicated a conditional dissociation constant for [Zn(TAMEisoquin)]2+ of Kd = 1.4 × 10−15 M. The affinity of TAMEisoquin for Zn(II) is indicative of a ligand design exploiting ring size, preorganization and chelate effects to potentially detect picomolar and femtomolar zinc concentrations. X-ray crystallographic analysis of [Zn(TAMEisoquin)]2+ showed four unique cations that preferred a distorted octahedral geometry with trigonal twist angles that range between 34(2)° and 43.1(8)°. Moreover, [Zn(TAMEisoquin)]2+ complex showed Zn–N bond distances slightly similar to our previously reported [Zn(TAMEpyr)]2+ complex, being Zn–Nheterocyclic, 2.160(1) Å and Zn–Naliphatic, 2.178(4) Å versus 2.128(2) Å and 2.169(2) Å respectively for [Zn(TAMEpyr)]2+. The addition of Zn(II) to TAMEisoquin displayed 11-fold fluorescence enhancement, selective by comparison to divalent biometal ions and Cd(II) which induces only 16% of the Zn(II) response.

Herein we report a novel fluorescent zinc sensor 1,1,1-tris (aminomethylethane)N,N′,N″-(2-methylisoquinoline) (TAMEisoquin), [Zn(TAMEisoquin)]2+ complex and its structural and photophysical studies. TAMEisoquin was obtained from reduction of templated [Ni(TAMEisoquin-trisimine)]2+ complex to give [Ni(TAMEisoquin)]2+, which was subsequently decomposed with excess sodium cyanide to afford TAMEisoquin. X-ray crystallographic analysis of [Zn(TAMEisoquin)]2+ showed four unique cations that preferred a distorted octahedral geometry with trigonal twist angle that range between 34(2)° and 43.1(8)°. Moreover, [Zn(TAMEisoquin)]2+ complex showed Zn–N bond distance slightly similar to our previously reported [Zn(TAMEpyr)]2+ complex, being Zn–Nheterocyclic, 2.160 (1) Å and Zn–Naliphatic, 2.178(4) Å versus 2.128(2) Å and 2.169(2) Å respectively for [Zn(TAMEpyr)]2+. The addition of Zn(II) to TAMEisoquin displayed 11-fold fluorescence enhancement with selectivity of Zn(II) over other bioavailable divalent metal ions. The Zn(II)/Cd(II) selectivity studies showed that Cd (II) induces only 16% of Zn(II) response, and thus TAMEisoquin prefers Zn(II) over Cd(II). Additionally, a competition reaction between TAMEisoquin and a well-known Zn(II) chelator (N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine) (TPEN) indicated a conditional dissociation constant for [Zn(TAMEisoquin)]2+ of Kd=1.4 × 10−15 M at pH 7.2.Figure optionsDownload as PowerPoint slide