A New Zinc(II) Fluorophore 2-(9-Anthrylmethylamino)ethyl-Appended 1,4,7,10-Tetraazacyclododecane

Abstract

A new 2-(9-anthrylmethylamino)ethyl-appended cyclen, L(3) (1-(2-(9-anthrylmethylamino)ethyl)-1,4,7,10-tetraazacyclododecane) (cyclen = 1,4,7,10-tetraazacyclododecane), was synthesized and characterized for a new Zn(2+) chelation-enhanced fluorophore, in comparison with previously reported 9-anthrylmethylcyclen L(1) (1-(9-anthrylmethyl)-1,4,7,10-tetraazacyclododecane) and dansylamide cyclen L(2). L(3) showed protonation constants log K(a)(i)() of 10.57 +/- 0.02, 9.10 +/- 0.02, 7.15 +/- 0.02, <2, and <2. The log K(a3) value of 7.15 was assigned to the pendant 2-(9-anthrylmethylamino)ethyl on the basis of the pH-dependent (1)H NMR and fluorescence spectroscopic measurements. The potentiometric pH titration study indicated extremely stable 1:1 Zn(2+)-L(3) complexation with a stability constant log K(s)(ZnL(3)) (where K(s)(ZnL(3)) = [ZnL(3)]/[Zn(2+)][L(3)] (M(-)(1))) of 17.6 at 25 degrees C with I = 0.1 (NaNO(3)), which is translated into the much smaller apparent dissociation constant K(d) (=[Zn(2+)](free)[L(3)](free)/[ZnL(3)]) of 2 x 10(-)(11) M with respect to 5 x 10(-)(8) M for L(1) at pH 7.4. The quantum yield (Phi = 0.14) in the fluorescent emission of L(3) increased to Phi = 0.44 upon complexation with zinc(II) ion at pH 7.4 (excitation at 368 nm). The fluorescence of 5 microM L(3) at pH 7.4 linearly increased with a 0.1-5 microM concentration of zinc(II). By comparison, the fluorescent emission of the free ligand L(1) decreased upon binding to Zn(2+) (from Phi = 0.27 to Phi = 0.19) at pH 7.4 (excitation at 368 nm). The Zn(2+) complexation with L(3) occurred more rapidly (the second-order rate constant k(2) is 4.6 x 10(2) M(-)(1) s(-)(1)) at pH 7.4 than that with L(1) (k(2) = 5.6 x 10 M(-)(1) s(-)(1)) and L(2) (k(2) = 1.4 x 10(2) M(-)(1) s(-)(1)). With an additionally inserted ethylamine in the pendant group, the macrocyclic ligand L(3) is a more effective and practical zinc(II) fluorophore than L(1).

A phenol-based compartmental ligand as a potential chemosensor for zinc(ii) cations

“…Based on such chelation enhanced fluorescence (CHEF) mechanism, many zinc chemosensors have been designed. [12][13][14][15][16] The structure of a typical cation chemosensor is usually composed of two parts: an ion recognition and a signal transduction units. 8 We herein report an atypical fluorescence chemosensor where only benzene rings act as fluorophores and alcoholic and phenolic hydroxyls as ion recognition units (Figure 1).…”

Imidazolium-Salt-Based Fluorescent Chemosensor for Cu(II), Zn(II) and Co(II)

“…Fluoroionophores can provide chemical information on ions; thus, they are important substances in metal ion analysis. Macrocyclic polyamine ligands possess many unique properties, for example, as a catalyst of DNA cleavage, (1) a fluorescent sensor for cations, (2,3) and as a small molecular sensor. (4) Fluorescent sensors have been widely applied in the detection of organic compounds and metal ions such as Pb 2+ and Cu 2+ .…”

“…(4) Fluorescent sensors have been widely applied in the detection of organic compounds and metal ions such as Pb 2+ and Cu 2+ . (2,3,5) Due to their high sensitivity, accuracy and efficiency, they are effective for determining trace amounts of pollutants in industrial sewage, textiles and paints, and they are often used in the field of online production analysis. (6)(7)(8)(9) 1,4,7,10-tetraazacyclododecane (Cyclen) is an excellent complex reagent with many transition-metal ions such as Cu(II), Zn(II) and Co(II).…”

“…(6)(7)(8)(9) 1,4,7,10-tetraazacyclododecane (Cyclen) is an excellent complex reagent with many transition-metal ions such as Cu(II), Zn(II) and Co(II). (2) Many derivatives of Cyclen are good metal-ion-chelating enhanced fluorophores. (3,5) Because of an additional ethylamine group in the pendant group, the macrocyclic ligand 2-(9-anthrylmethylamino)ethylappended Cyclen is a more effective and practical zinc(II) fluorophore than 9-anth rylmethylcyclen.…”

“…(3,5) Because of an additional ethylamine group in the pendant group, the macrocyclic ligand 2-(9-anthrylmethylamino)ethylappended Cyclen is a more effective and practical zinc(II) fluorophore than 9-anth rylmethylcyclen. (2,3) Therefore, complexes with a fluorescence response have received much attention from researchers. (10,11) Unfortunately, most complexes synthesized so far have been heterocyclic aromatics, whose solubility in water and biocompatibility are usually both very poor; thus, they cannot be used universally in practice.…”