Medium Dependent Dual Turn-On/Turn-Off Fluorescence System for Heavy Metal Ions Sensing

A dual turn-on/turn-off fluorescence sensing system based on <i>N</i>-alkylaminopyrazole ligands for heavy metal ions, where the response can be tuned upon medium change, is developed. The synthesis and characterization of Zn^II, Cd^II and Hg^II complexes with two <i>N</i>-alkylaminopyrazole ligands, used as metal receptors, are first presented. The acidity and complexation constants for a selected ligand (1-[2-(octylamino)ethyl]-3,5-diphenylpyrazole ligand (<b>L2</b>)) with Zn^II, Cd^II, and Hg^II are also determined. The fluorescent behavior of these complexes can be tuned by the different medium used (e.g., MeOH or HCl) giving rise to two different sensing mechanisms. The <b>L2</b> ligand can be applied as a global heavy metal warning chemosensor (for Pb^II, Zn^II, Cd^II, or Hg^II ions) for water samples achieving detection limits lower than the maximum concentration recommended by the environmental agencies (detection limit lower than 0.3 ng/mL for any of the mentioned metal ions). The utility of the developed sensing system for Hg^II detection in seawater without any previous sample pretreatment with interest for future in-field sensing kit like applications is also discussed

Different Nature of the Interactions between Anions and HAT(CN)₆: From Reversible Anion−π Complexes to Irreversible Electron-Transfer Processes (HAT(CN)₆ = 1,4,5,8,9,12-Hexaazatriphenylene)

We report experimental evidence indicating that the nature of the interaction established between HAT­(CN)₆, a well-known strong electron acceptor aromatic compound, with mono- or polyatomic anions switches from the almost exclusive formation of reversible anion−π complexes, featuring a markedly charge transfer (CT) or formal electron-transfer (ET) character, to the quantitative and irreversible net production of the anion radical [HAT­(CN)₆]^•– and the dianion [HAT­(CN)₆]^2– species. The preferred mode of interaction is dictated by the electron donor abilities of the interacting anion. Thus, weaker Lewis basic anions such as Br^– or I^– are prone to form mainly anion−π complexes. On the contrary, stronger Lewis basic F^– or ^–OH anions display a net ET process. The ET process can be either thermal or photoinduced depending on the HOMO/LUMO energy difference between the electron donor (anion) and the electron acceptor (HAT­(CN)₆). These ET processes possibly involve the intermediacy of anion−π complexes having strong ET character and producing an ion-pair radical complex. We hypothesize that the irreversible dissociation of the pair of radicals forming the solvent-caged complex is caused by the reduced stability (high reactivity) of the radical resulting from the anion

Ion-Directed Assembly of Gold Nanorods: A Strategy for Mercury Detection

Water-soluble gold nanorods (Au NRs) have been functionalized with an <i>N</i>-alkylaminopyrazole ligand, 1-[2-(octylamino)­ethyl]-3,5-diphenylpyrazole (PyL), that has been demonstrated able to coordinate heavy metal ions. The <i>N</i>-alkylaminopyrazole functionalized Au NRs have been characterized by electron microscopy and spectroscopic investigation and tested in optical detection experiments of different ions, namely, Zn²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Pb²⁺, and As³⁺. In particular, the exposure of the functionalized NRs to increasing amounts of Hg²⁺ ions has resulted in a gradual red-shift and broadening of the longitudinal plasmon band, up to 900 nm. Interestingly, a significantly different response has been recorded for the other tested ions. In fact, no significant shift in the longitudinal plasmon band has been observed for any of them, while a nearly linear reduction in the plasmon band intensity versus ion concentration in solution has been detected. The very high sensitivity for Hg²⁺ with respect to other investigated ions, with a limit of detection of 3 ppt, demonstrates that the functionalization of Au NRs with PyL is a very effective method to be implemented in a reliable colorimetric sensing device, able to push further down the detection limit achieved by applying similar strategies to spherical Au NPs

Palladium-Mediated Catalysis Leads to Intramolecular Narcissistic Self-Sorting on a Cavitand Platform

Palladium-catalyzed aminocarbonylation reactions have been used to directly convert a tetraiodocavitand intermediate into the corresponding carboxamides and 2-ketocarboxamides. When complex mixtures of the amine reactants are employed in competition experiments using polar solvents, such as DMF, no “mixed” products possessing structurally different amide fragments are detected either by ¹H or ¹³C NMR. Only highly symmetrical cavitands are sorted out of a large number of potentially feasible products, which represents a rare example of intramolecular, narcissistic self-sorting. Our experimental results along with thermodynamic energy analysis suggest that the observed self-sorting is a symmetry-driven, kinetically controlled process