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Calix[4]pyrroles (CPs) and polyammonium azacrowns (ACs) are well-known receptors for anions. CPs bind anions by directional hydrogen bonds that do not always work well for aqueous analytes. The positive charge in polyammonium ACs allows for a stronger but non-directional anion-ammonium electrostatic attraction but lack selectivity. Bridging the gap between CPs and ACs could increase affinity and potentially preserve the selectivity of anion binding. We have synthesized a flexible calixpyrrole-azacrown near isosteric receptor and incorporated an environmentally sensitive dansyl fluorophore to enable fluorescence measurements. Anion binding was evaluated using NMR and fluorescence titrations. The isosteric receptor shows a strong affinity for aqueous phosphates and phosphonates (Na + salts) in the order HAsO 4 2− > H 2 PO 4 − > H 2 P 2 O 7 2− > glyphosate 2− > AMP − > methylphosphonate − ≫ ADP 2− or ATP 3− but does not bind halides. This is in stark contrast to CP which shows a strong preference for halides over oxyanions. The anion binding by the new receptor was accompanied by analyte-specific changes in fluorescence intensity and spectral width and by a wavelength shift. These parameters were used in qualitative and quantitative sensing of aqueous anions. By applying machine-learning algorithms, such as linear discriminant analysis and support vector machine linear regression, this one sensor can differentiate between 10 different analytes and accurately quantify herbicide glyphosate and methylphosphonate, a product of sarin, soman or cyclosarin hydrolysis. In fact, glyphosate can be quantified even in the presence of competing anions such as orthophosphate (LODs were ≤ 1 μM).
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Increasing the selectivity of optical anion sensors with cationic extracting agents
Anions play an important role in our life, from storing our genetic code on the polyanion DNA, to being the active ingredient in agricultural fertilizers and other industrial processes. Consequently, chemists have been designing systems that can sense anionic species through a variety of methods, such as unimolecular chromophores or sensor arrays. Nonetheless, most existing sensing approaches still have some drawbacks, particularly related to obtaining adequate selectivity and achieving sensing of anions in aqueous environments. In this manuscript, we report a liquid-liquid extraction (LLE)-based sensing approach that allows the conversion of non-selective optical anion sensors that only work in organic media, into selective sensing systems that allow detection of anions in water. We tested this approach on deprotonation-based anion sensors (alizarin, naphthol AS, 4-nitrophenol, BI-Lawsone, and chromophore 1) and hydrogen bonding-based anion sensors (1,2-diaminoanthraquinone and 4-nitro-1,2-phenylenediamine). In general, the deprotonation-based sensors could be converted from a non-selective sensor for basic anions (NCO¯, H2PO4¯, AcO¯ and F¯) to a selective sensing system for NCO¯ with the aid of carefully chosen tetraalkylammonium salts as extracting agents. On the other hand, the hydrogen-bonding based sensors could be converted to a selective sensing system for the hydrophobic anion ClO4¯ using similar tetraalkylammonium salts.
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- Award ID(s):
- 2108699
- PAR ID:
- 10594086
- Publisher / Repository:
- Taylor & Francis
- Date Published:
- Journal Name:
- Supramolecular Chemistry
- Volume:
- 35
- Issue:
- 1-12
- ISSN:
- 1061-0278
- Page Range / eLocation ID:
- 42 to 54
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We report a combined theoretical and experimental effort to elucidate systematically for the first time the influence of anions of transition metal salt-decorated surfaces on the orientations of supported films of nematic liquid crystals (LCs) and adsorbate-induced orientational transitions of these LC films. Guided by computational chemistry predictions, we find that nitrate anions weaken the binding of 4′- n -pentyl-4-biphenylcarbonitrile (5CB) to transition metal cations, as compared to perchlorate salts, although binding is still sufficiently strong to induce homeotropic (perpendicular) orientations of 5CB. In addition, we find the orientations of the LC to be correlated across all metal cations investigated by a molecular anchoring energy density that is calculated as the product of the single-site binding energy and metal cation binding site density on the surface. The weaker single-site binding energy caused by nitrate also facilitates competitive binding of adsorbates to the metal cations, leading to more facile orientational transitions induced by adsorbates. Finally, our analysis suggests that nitrate anions recruit water via hydrogen bonding to the metal binding sites, modulating further the relative net binding energies of 5CB and adsorbates to surfaces decorated with metal nitrates. After accounting for the presence of water, we find a universal exponential relationship between the calculated displacement free energies and measured dynamic response of LCs to adsorbates for all metal salts studied, independent of the metal salt anion.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/10610278.2024.2426547
