TQPHEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)-1,2-phenylenediamine) derivatives as highly selective fluorescent probes for Cd²⁺

Abstract

TQPHEN (N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-phenylenediamine) and its methoxy-substituted derivatives, 6-MeOTQPHEN (N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-phenylenediamine) and TriMeOTQPHEN (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-phenylenediamine), were examined as fluorescent Cd(2+) sensors. Although the TQPHEN exhibits a negligible fluorescence response toward Zn(2+) due to weak binding affinity in DMF-H2O (1:1), a 6-fold fluorescence enhancement at 392 nm was observed in the presence of 1 equiv. of Cd(2+). Comprehensive X-ray crystallographic analyses of TQPHEN-Zn(2+) and TQPHEN-Cd(2+) complexes reveal that significant distortion in the Zn(2+) complex plays a key role in the Cd(2+) specificity of TQPHEN. The TriMeOTQPHEN exhibits excellent sensitivity and selectivity for Cd(2+) detection (ICd/I0 = 44, ICd/IZn = 20 and LODCd = ∼10 nM (LOD = limit of detection)). On the other hand, the trans-1,2-cyclohexanediamine derivative TQDACH (N,N,N',N'-tetrakis(2-quinolylmethyl)-trans-1,2-cyclohexanediamine) exhibits high Zn(2+) specificity in the fluorescence response and extremely high Zn(2+) binding affinity (Dalton Trans., 2013, 42, 9688). Subtle differences in the PHEN and DACH backbone significantly alter the stability with a specific metal and the fluorescence response of tetrakisquinoline-based fluorescent probes.

Facile Synthesis of Galactosamine‐Stabilized Gold Nanoparticles with Sensitive Cd2+ Sensing

“…Compared with those of other optical Cd 2+ sensors reported previously, the detection sensitivity of the proposed method is higher or comparable. [38][39][40][41] This result indicates that the Galn-GNPs could function as a colorimetric probe for Cd 2+ ions with a high detection limit.…”

N,N,N′,N′‐Tetrakis(3‐isoquinolylmethyl)‐2,6‐lutidylenediamine (3‐isoTQLN): A Fluorescent Zn2+/Cd2+ Dual Sensor as a Hybrid of 2‐Quinolyl/1‐Isoquionolyl Counterparts TQLN/1‐isoTQLN

“…[7][8][9] The differential detection of zinc and cadmium is challenging because differences in these two group 12 metal ions are quite small. [10][11][12][13] There are limited examples of fluorescent probes that enable differential detection of Zn 2 + and Cd 2 + in a single molecule. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Strategies to discriminate Zn 2 + from Cd 2 + via fluorescence signals utilize (1) different ligand donor atoms, [14][15][16][17] (2) mononuclear/dinuclear complex formation, [18] (3) test strip, [19] (4) difference in metal binding affinity highlighted by appropriate auxiliary reagent, [20][21] and (5) different emission mechanism based on small structural difference in metal complexes.…”

N,N-bis(2-quinolinylmethyl)benzylamine

“…Additionally imposed on one of the faces of the aforementioned Pt(II) complexes was a significant aerial steric effect due to the near orthogonal orientation of the benzyl group on one side of the square plane of the complexes. Mikita et al [7][8][9][10] fabricated Zn(II)/Cd(II) off/on-fluorescence sensors using the bqma-derived hexadentates, linked by 1,2-ethylenediamine [6] and lately by 1,2-phenyl-/cyclohexyldiamines [7,8]. They also reported the crystal structure of tris(isoquinolinemeth-1-yl)amine [10], an analogue of 1, which has an iso-structural tridentate N-donor chelate and a closely related isoquinolinemeth-1-yl as a pendant group at the amine position.…”