New Fluorescent Chemosensors for Heavy Metal Ions Based on Functionalized Pendant Arm Derivatives of 7-Anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane

Abstract

Two new ligands 7-anthracenylmethyl-13-methylpyridyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L4) and 7-anthracenylmethyl-13-(2,2-dimethyl-2-hydroxyethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L(5)) have been synthesized and characterized. Both derive from 7-anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L(3)) and differ for having a differently functionalized pendant arm covalently attached to the remaining secondary nitrogen donor of the macrocyclic framework. The protonation and coordination behavior of L(4), L(5), and the unbranched L(3) with metal ions have been studied in MeCN/H2O (1:1 v/v, 298.1 K, I = 0.1 M) using potentiometric methods. The crystal structures of L(3), [(H2L(3))(HL(3))](ClO4)3, and the complex [CdL(3)(NO3)2] have been determined by single-crystal X-ray methods. The fluorescent behavior of L(3)-L(5) in the presence of Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been studied as a function of pH in MeCN/H2O (1:1 v/v). The presence of Cu(II), Hg(II), or Pb(II) does not affect the fluorescent behavior observed for the three free ligands upon changing the pH. Interestingly, the fluorescent emission of L(3) and L(5) is selectively enhanced only in the presence of Cd(II) at basic pH. The same effect is observed for L4 in the presence of Cd(II) or Zn(II) at about pH 7.

Terphenyl-phenanthroline conjugate as a Zn2+ sensor: H2PO4− induced tuning of emission wavelength

“…Interestingly, the addition of H 2 PO 4 − ions to the [5-Zn] complex regulates the binding site for additional Zn 2+ ions and hence leads to a blue-shifted band. In contrast to the reported sensors, 13,14,16 receptor 5 described herein is efficient in discriminating Zn 2+ and Cd 2+ ions on the basis of fluorescence and also showed improved binding with Zn 2+ ions.…”

“…Consequently, more attention is being focused on the development of fluorescent chemosensors for the detection of Zn 2+ ions. 9,10 A plethora of examples of Zn 2+ -based fluorescent sensors exist in the literature, [11][12][13][14][15][16] but in most of the cases discrimination between Zn 2+ and closely related metal ions like Cd 2+ is difficult due to their similar chemical properties. Thus optimized sensors are still needed to quantify nanomolar to micromolar Zn 2+ concentrations.…”

Optical methods for the detection of heavy metal ions

“…94 The use of crown ether fused to a conjugated system of bonds for the design of promising sensor 61 for cadmium ion has been reported. 95 This compound comprises two potential ionophores Ð the macrocycle and the exo-pyridine nitrogen atom.…”

Azathia crown ethers carrying pyrene pendant as receptor molecules for metal sensor systems

“…This result can also be explained by the hampered PET mechanism as mentioned above. However, there was a decrease in fluorescence intensity of L(2) with Fe 2 + , Cu 2 + and Pb 2 + cations, and this result can be attributed to ''heavy atom effect'' [33,34]. Fig.…”