Highly selective optical-sensing membranes, containing calix[4]arene chromoionophores, for Pb2+ ions

Exploring the design and performance of a tellurium optical sensor utilizing a plasticizer-free polymer inclusion membrane

A highly responsive, discerning, and uncomplicated technique has been devised for immobilizing reagents onto a plasticizer-free optical sensor membrane, employing polymer inclusion membranes (PIMs). This procedural strategy relies on a physical immobilization approach, specifically encapsulation, resulting in the creation of an optical sensing membrane. The responsive PIM is composed of poly(vinyl chloride) (PVC) as the fundamental polymer, Aliquat 336 as an extractant, and 4-(4 -chlorobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole (CBIMMT) as the reagent. The optimized sensor demonstrates a linear range of 6.00-156 ng/mL for Te(IV), along with detection and quantification limits of 1.75 and 5.60 ng/mL, respectively. The sensor response time is 3.0 min, confirming its reproducibility. Effective regeneration of the sensor is achieved using a 0.2 mol/L HCl solution. The sensor membrane's selectivity is evaluated against various interfering ions, underscoring minimal interference. The sensor membrane efficacy is demonstrated through successful applications in quantifying Te(IV) levels, including natural water, chalcogenides, milk, vegetables, and soil samples.

Development of a microplate-format direct optode sensor for ultra-high-throughput environmental and wastewater monitoring of Pb2

Although many Pb²⁺-selective optodes have been developed so far, methods using optical sensor membranes have not become widespread in environmental analytical practice. In order to create a bulk optode sensor, which can overcome all of the main drawbacks in the application of conventional optode membranes, - i.e., pH-dependence, long response time and the leakage of the ionic components - unusually thick PVC membrane was developed, embedded in microtiter plates and operated on a novel concept. This is the first reported work, which applies a plate-format optode as well as a direct optode-type sensing membrane for determination of Pb²⁺. We reported here also the first example for the application of an ionic component-free bulk optode membrane to avoid the membrane leakage, improve the regenerability and extend the lifetime of the membrane. The reported sensor has a LOD above 4.0 × 10^-7 M (∼83 μg L^-1), thus it is unsuitable for the effective monitoring of drinking waters, but considered to be a promising method for monitoring contamination episodes. On the other hand, the widest pH-independent working range of 4.3 < pH < 7.0 among bulk optodes reported in the literature was realized and an unprecedentedly fast response time of <10 s was achieved. The effectiveness of the applied method was investigated by measuring Pb²⁺-spiked multicomponent aqueous solutions as simulated environmental or wastewater samples containing near equimolar amounts of Ag⁺, Ca²⁺, Co²⁺, Cu²⁺, K⁺, Mg²⁺, Na⁺ and Zn²⁺ as acetate salts. In the presence of these potential competing ions with a concentration not greater than the typical ionic strength of surface freshwaters (∼10^-3 M) the reported sensor proved to be appropriate for the selective detection of Pb²⁺ without any preparation of the samples (e.g., preconcentration, buffering, addition of excipients, etc.) with a required sample volume of only 100 μL. An outstanding analytical performance could be achieved within an average time of less, than 5 s/sample. The reported fluorescent probe is considered to be a promising method for replacing atomic absorption spectroscopy- (AAS), anodic stripping voltammetry- (ASV) or inductively coupled plasma- (ICP) based techniques as well as conventional ion-selective bulk membranes in high-throughput preliminary environmental monitoring of Pb²⁺, as it provides a cheap and unprecedentedly fast qualitative analysis of contaminated surface and wastewaters.

Test Strips for Lead(II) Based on a Unique Color Change of PVC-film Containing O-Donor Macrocycles and an Anionic Dye

Glassy test strips partially coated with PVC-film including O-donor macrocyclic receptors (L), tetrabromophenolphthalein ethyl ester (TBPE(-)), and a plasticizer sensed Pb(2+) in aqueous solutions by a unique color change. Yellow films successively changed color to green, dark-blue and purple with increases of the Pb(2+) concentration. In contrast with the ordinary "optode", a characteristic absorption band at 525 nm was newly appeared independently of the protonation and deprotonation of HTBPE (yellow to blue). The unique color change occurred only when asymmetric receptors with respect to the basal plane were coupled with Pb(2+). This optical-structural correlation is likely to be induced by the H aggregate of two sets of TBPE(-) in the 1:2 ion-pair, [Pb-L](2+).(TBPE(-))(2). The color change, based on metachromasy, was exclusive for Pb(2+) among common metal cations (Ca(2+), Al(3+), Cd(2+), Zn(2+), Fe(3+), Co(2+), Hg(2+)) and anions (Cl(-), SO(4)(2-), PO(4)(3-), S(2)O(3)(2-)).

Naphthalene- and Anthracene-Based Aromatic Foldamers with Iminodicarbonyl Linkers: Their Stabilities and Application to a Chiral Photochromic System Using Retro [4 + 4] Cycloaddition

A circular dichroism (CD) spectral study on chiral aromatic chain imides possessing anthracene and naphthalene moieties with bulky N substituents showed that their helical chirality based on folding remained for a reasonably long time without racemization in solution. Racemization due to conformational equilibration occurred very slowly, requiring over 1 week at ambient temperature. Their CD spectra both in solution and in the solid state gave similar CD signals, suggesting retention of helicity observed in the solid state even after dissolving. As an application of this novel chiral folding of aromatic chain imides, a chiral photochromic system was investigated based on the photo [4 + 4] cycloaddition and its thermal cycloreversion of an anthracene-naphthalene system. The foldamer possessing an anthracene moiety in the center connected with two naphthalene moieties below and above it by iminodicarbonyl linkers was prepared for this purpose. Induced CD was observed for the foldamer with (S)-1-(1-naphthyl)ethyl substituents at the imide nitrogen atoms. Chiral photochromic cycles were monitored by CD spectral measurement.

Structural Insights into the Coordination and Extraction of Pb(II) by Disulfonamide Ligands Derived from o-Phenylenediamine

The o-phenylenediamine-derived disulfonamide ligands 1 and 2 complex and efficiently extract Pb(II) from water into 1,2-dichloroethane via ion-exchange, in combination with 2,2'-bipyridine (97.5% and 95.0%, respectively, for 1:1 ligand-to-Pb ratios). The corresponding Pb(II)-sulfonamido binary complexes of ligands 1 and 2 (3 and 4, respectively), and ternary complexes with 2,2'-bipyridine (5 and 6, respectively), were isolated and characterized. (1)H NMR spectra of the organic phases after extraction show the formation of ternary Pb-sulfonamido-bipy complexes. X-ray characterization of 3, 4, and the ternary complex 5 consistently demonstrates four primary coordination sites and a stereochemically active lone pair on Pb. The X-ray structure of 3 shows a pseudo trigonal bipyramidal configuration on Pb, with the lone pair occupying one of the equatorial sites, and the formation of an unusual "hemidirected" coordination polymer via axial S=O-Pb coordination. The same axial S=O-Pb coordination pattern with two DMSO molecules is observed in the structure of 4.[2(CH(3))(2)SO)], thus rationalizing the high solubility of the binary complexes in strongly coordinating solvents. In contrast, the X-ray structure of the ternary complex 5 reveals a distorted four-coordinate configuration with only weak S=O-Pb coordination leading to dimer formation, thus explaining its higher solubility in weakly coordinating solvents. FT-IR spectroscopy confirms the X-ray data, since the ligand nu(S)(=)(O) stretching frequencies shift to lower values in the binary Pb(II)-sulfonamido complexes and are again altered upon formation of the ternary Pb(II)-sulfonamido-bipy complexes, as would be expected for 2,2'-bipy complexation and hindered S=O-Pb coordination.

Upper Rim Allyl- and Arylazo-Coupled Calix[4]arenes as Highly Sensitive Chromogenic Sensors for Hg2+ Ion

The syntheses and chromogenic properties of calix[4]arenes, carrying 5,17-bisallyl-11,23-bis(p-X-phenyl)azo 3a-c, 5,11,17-triallyl-23-(p-X-phenyl)azo 4a-c, and 5,17-bis(hydroxypropyl)-11,23-bis(p-X-phenyl)azo groups on the upper rims 5a,b, are described. Unexpectedly, UV/vis spectra of the very popular 4-(4-nitrophenyl)azophenol-coupled calix[4]arenes 3c and 4c did not show any shift in lambda(max) when 10 different metal perchlorates were added separately to the host in a methanol-chloroform (v/v = 1/399) cosolvent. In contrast, the absorption spectra of calix[4]arenes with either 4-methoxyphenylazo (3b-5b) or 4-phenylazo (3a-5a) on the upper rim showed substantial bathochromic shifts (Deltalambda = 128-162 nm) upon the addition of soft metal ions (such as Hg(2+), Cr(3+), and Cu(2+)). The 4-(4-methoxyphenyl)azophenol-coupled calix[4]arenes (the 3b-5b series) are found to be highly sensitive for mercury ion (Hg(2+)) among the 10 different metal ions screened. Strong interactions between Hg(2+) ion and the 4-(4-methoxyphenyl)azophenol(s) as well as the p-allyl groups are corroborated by the (1)H NMR studies of 3a,b.Hg(2+) complexes. Furthermore, Job's plots revealed 1:1 binding stoichiometry for all these p-allyl- and arylazo-coupled calix[4]arenes with transition metal ions, and Benesi-Hilderbrand plots were used for the determination of their association constants.

Aromatic Foldamers with Iminodicarbonyl Linkers: Their Structures and Optical Properties

[structure: see text] Carboxamides possessing naphthalene rings connected by multiple iminodicarbonyl linkers were synthesized. These molecules forced the naphthalene rings to be placed in the positions facing each other, and they form helical foldamers both in solution and in the crystalline state. Their folding structures were investigated by single-crystal X-ray analysis and (1)H NMR spectroscopy. Their absorption and fluorescence spectra showed a red shift as the number of naphthalene moieties increased. This remarkable change is based on the intramolecular interaction between naphthalene moieties. Helicity of the foldamer can be controlled by the introduction of chiral auxiliaries at imide nitrogen atoms, which results in an observation of induced circular dichroism.