Cd 2+ -Specific Fluorescence Response of Methoxy-Substituted N , N -Bis(2-quinolylmethyl)-2-methoxyaniline Derivatives.

The N3O1 tetradentate ligand, TriMeOBQMOA ( N , N -bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyaniline), was developed as a Cd 2+ -specific fluorescent sensor. The structure of TriMeOBQMOA is half of TriMeOBAPTQ ( N , N , N ', N '-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-bis(2-aminophenoxy)ethane), which is a tetrakisquinoline derivative of the well-known calcium chelator BAPTA (1,2-bis(2-aminophenoxy)ethane- N , N , N ', N '-tetraacetic acid). The fluorescent Cd 2+ selectivity of TriMeOBAPTQ ( I Zn / I Cd = 5.3% in the presence of 3 equiv of metal ions in MeOH-HEPES buffer (9:1)) comes from the formation of fluorescent dinuclear cadmium (M 2 L) and nonfluorescent OH-bridged dizinc ((μ-OH)M 2 L) complexes. TriMeOBQMOA also exhibits excellent Cd 2+ specificity in fluorescence enhancement ( I Zn / I Cd = 2.3% in the presence of 5 equiv of metal ions in DMF-HEPES buffer (1:1, HEPES 50 mM, KCl 0.1 M, pH = 7.5)) via substantial formation of a highly fluorescent bis(μ-chloro)dinuclear cadmium complex ([Cd 2 (μ-Cl) 2 L 2 ] 2+ ), which is in equilibrium with the mononuclear Cd 2+ complex ([CdLCl] + ), and extremely poor stability of the TriMeOBQMOA-Zn 2+ complex. The all-nitrogen derivatives of BQMOA and BAPTQ, namely, N , N -BQDMPHEN ( N , N -bis(2-quinolylmethyl)- N ', N '-dimethyl-1,2-phenylenediamine) and BPDTQ ( N , N , N ', N '-tetrakis(2-quinolylmethyl)-2,2'-( N , N '-dimethylethylenediamino)dianiline), respectively, and their methoxy-substituted derivatives were also prepared, and the fluorescent metal ion sensing properties are discussed.