Selective chromogenic reagents for lead

Abstract

The cryptands 3 and 5 are both selective reagents for lead, they also respond to other doubly charged cations including Ca2+, Sr2+ Hg2+ and Cd2+ but with significantly lower sensitivity; they show no significant response t o Zn2+, Cu2+ and Ba2+.

Multi‐Channel Receptors and Their Relation to Guest Chemosensing and Reconfigurable Molecular Logic Gates

“…A selective colour variation from red-pink to yellow-orange (hypsochromic shift from 520 to 475 nm) was observed upon addition of the heavy metal cation Pb 2+ (see Figure 4). [22] This result is in agreement with the larger radius of Pb 2+ , which apparently fits well into the large binding cavity of L 4 . The correct combination of ring and cation size would result in a suitable coordination to the nitrogen atom of the macrocyclic subunit, thus inducing the hypsochromic shift of the charge-transfer band.…”

Benzothiazolium styryl dyes containing a monoazacrown ether: Protonation and complexation with metal and ammonium cations in solution

“…The complexation of the azacrown ether of 1 at ca. 10~5 mol dm~3 was found here to occur only at metal and ammonium cation concentrations of [5 ] 10~3 mol dm~3 in acetonitrile ; the formation of dimer complexes is unlikely at these high relative cation concentrations.…”

“…It is difficult to distinguish dimer complexes using L 2 (Mn`) 2 UVÈVIS absorption spectroscopy. Such complexes of a zwitterion derivative of a benzothiazolium styryl benzo-15-crown-5 ether dye with Mg2`have been reported, even at very low concentration (5 ] 10~6 mol dm~3) of the dye in acetonitrile,36 although the cation concentration also was low (1.2 ] 10~4 mol dm~3). An increase in the cation concentration for a Ðxed, low ionophore concentration should disfavour their formation.…”

“…Third, di †erent heteroatoms may facilitate the synthesis of three-dimensional cavities which improve the receptor selectivity. 5,11,12 The substitution of nitrogen for oxygen atoms is known to reduce the affinity of 18-crown-6 ethers for the hard alkalimetal cation, K`, but to strengthen greatly their affinity for the soft cation, Ag`. 13 In general, the affinity of crown ethers for Ag`is high when the ratio of N : O heteroatoms within the ring is high, while their affinity for alkali-metal cations is higher than that for Ag`when this ratio is low.…”

A Cation-Specific, Light-Controlled Transient Chromoionophore Based on a Benzothiazolium Styryl Azacrown Ether Dye

“…Macrocyclic ionophores based on polyether derivatives have attracted much attention because of their selective affinity for cations − and their application as functional units within supramolecular systems. − The receptor and carrier characteristics of macrocyclic molecules enable metal or molecular ions to be recognized and transported and may facilitate the development of supramolecular ionic devices. Significant progress has been made in the development of sensing devices, with different types of response being available from ionophores with different functional properties, including ion-selective electrodes ,− and optrodes. ,, The majority of ion and molecular sensors are based on specific interactions which result in easily recognizable changes in the sensor molecule, commonly observed via absorption, luminescence, or redox potential properties. − ,− A strong interaction between the ionophore and a dye is necessary to produce a strong optical response, and this interaction may be either intermolecular − or intramolecular, as for chromo- or fluoroionophores. − Many chromo- and fluoroionophores which are sensitive to different ions have been investigated, mainly in solution ,,− but also in films. ,−…”