Selective luminescence detection of cadmium(II) and mercury(II) utilizing sulfur-containing anthraquinone macrocycles (part 2) and formation of an unusual -crown ether dimer via reduction of Hg(II) by DMF

Anthraquinone-1,8-Derived (Pseudo-) Crown and Lariat Ethers: Design and Applications as Fluorescent and Chromogenic Ion (Pair) Sensors

Cyclic polyamine/ethers embedded with anthraquinone moieties and functional pendants, are structural analogues of crown ethers and (oxo-) cyclams, and could be utilized as sensitive and selective chemosensors towards metal cations. Those pseudo- (similar but geometrically distinct) crown and lariat ethers show various cation-binding patterns and stoichiometry, being modulated by donor type, cavity size and pendants' chelating ability. The luminescent and chromogenic properties also differ a lot along with the derivation of the parental macrocycle. Methodological designing including synthesis and post-functionalization through nucleophilic substitution, Mannich condensation etc., as well as the sensing performance of those pseudo- crown and lariat ethers are summarized in this review, basing on the spectroscopic, voltammetric and X-ray crystallographic determinations. Anion effect in sensing cations is evaluated according to the ion-pair recognition theory. Those results shed some light on exemplifying the anions' role in bioinorganic systems including metalloenzymes.

Cd2+-selective fluorescence response of TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives bearing ether oxygen-binding sites

Introduction of a methoxymethyloxy (MOMO) group at one of the four quinoline rings of TQEN (N,N,N′,N′-tetrakis-(2-quinolylmethyl)ethylenediamine) affords Cd2+-selective fluorescence enhancement.

A Hg(i) corrugated sheet assembled by auxiliary dioxole groups and Hg⋯π interactions

Comproportionation between Hg0 and Hg2+ resulted in the formation of [Hg2(Pip)2] supported by Hg⋯Odioxole and Hg⋯π interactions. Structural and computational assessment determined the tendency of Hg(i) to partake in Hg⋯π interactions.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

Detection of cyanide ions in aqueous solutions using cost effective colorimetric sensor

Cyanide (CN̄) is one of the most toxic material to the human and environment. It is very important to develop the diagnostic tools for the detection of CN̄ ions. Moreover, detection of the ions in an aqueous medium is a challenging task as water molecules interfere with the sensing mechanism. In this context, we prepared chemical sensor, S1, having anthraquinone as a signaling unit and thiourea as a binding site. This sensor exhibited distinct visual color and spectral changes in response to CN̄ ion over other testing anions in 50% aq. DMSO solution. However, in 20% aq. DMSO solution, S1 exhibited obvious spectral and color changes in response to CN̄, fluoride (F̄), acetate (Ac̄) and benzoate (Bz̄). Another sensor, S2, having a same signaling unit with that of S1, but a different binding site of urea group. In contrast to S1, S2 exhibited obvious spectral and color changes to F̄ in 2.5% aq. DMSO solution. NMR titration results suggested that the spectral and colorimetric responses were due to the formation of host-guest complex and deprotonation events. Finally, economically viable paper-based colorimetric "test stripes" of S1 were fabricated to detect the CN̄ ions in 100% aqueous solution.

Transition metal coordination complexes of chrysazin

Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction.

Improved selectivity for Pb(ii) by sulfur, selenium and tellurium analogues of 1,8-anthraquinone-18-crown-5: synthesis, spectroscopy, X-ray crystallography and computational studies

Selectivity for toxic Pb(ii) ion is improved by changing donor heteroatoms in the host.

Amino-ether macrocycle that forms CuII templated threaded heteroleptic complexes: a detailed selectivity, structural and theoretical investigations

Self-sorting behavior of a newly synthesized macrocycle with divalent metal ions and aromatic ligands via pseudorotaxane formation has been described.

Selective fluorescence sensing of copper(II) and water via competing imine hydrolysis and alcohol oxidation pathways sensitive to water content in aqueous acetonitrile mixtures

Addition of hydrazines to a 1,8-disubstituted anthraquinone macrocycle containing a polyether ring produces site-selective imination, where hydrazone formation produces the more sterically hindered adduct. Reduction of the remaining carbonyl group to a secondary alcohol followed by addition of copper(II) ion causes intense yellow fluorescence to occur, which is selective for this metal cation and allows this system to be used as a fluorescence sensor. In the presence of water, a green-fluorescent intermediate appears, which slowly decomposes to produce the original starting anthraquinone. The addition of a large amount of water radically changes the reaction pathway. In this case, oxidation of the secondary alcohol is kinetically faster than hydrolysis of the hydrazone, although the same anthraquinone product is ultimately produced. Stern-Volmer data suggest that dioxygen quenches the green emission through both dynamic and static mechanisms; the static ground-state effect is most likely due to association of oxygen with the copper-bound fluorescent intermediate.

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn(2+) or Cd(2+) is a worldwide concern. Developing an inexpensive and facile detection method for Zn(2+) and Cd(2+) is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn(2+) and Cd(2+) in aqueous media was reported. The proposed probe worked in fluorescence "turn-on" mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S(2-)). The presence of Zn(2+) (or Cd(2+)) can "turn-on" the weak fluorescence of QDs quenched by S(2-) due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn(2+) (or Cd(2+)) could be obtained in the range from 1.6 to 35 μM (1.3-25 μM for Cd(2+)). The limit of detection (LOD) for Zn(2+) and Cd(2+) were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn(2+) and Cd(2+) over other metal ions and was successfully used in the detection of Zn(2+) or Cd(2+) in real water samples.

Large amplitude, proton- and cation-activated latch-type mechanical switches: O-protonated amides stabilized by intramolecular, low-barrier hydrogen bonds within macrocycles

Large amplitude molecular switches have been developed using oxonium ions as the novel switching mechanism. Macrocycles that contain a polyether ring that are preorganized and of optimum geometry such that strong, linear Low-Barrier Hydrogen Bonds (LBHB, 2.4 to 2.6 A in length) are formed between a protonated amide oxygen and a cyclic ether, that lend significant iminol character to the amide. Deprotonation yields a large conformational change between closed and open forms, mindful of a new hinged, latch-type mechanical proton switch. Numerous open and closed forms have been characterized by X-ray crystallography, and the intramolecular hydrogen bond that forms between the protonated amide oxygen and the cyclic polyether oxygen accounts for the stability of these new acids. The open form of the deprotonated adducts persist in solution as indicated by the magnitude of coupling constants and other Nuclear Overhauser Effect experiments. Different saturated and unsaturated solid acids have been characterized including products derived from acetonitrile, propionitrile, caprylonitrile, acrylonitrile and adiponitrile, and also by reaction with primary amides in the case of phenyl and norbornene derivatives. We have also demonstrated that metal cations can replace the proton in the switching mechanism, characteristic of nascent synthetic pores.

Formation of organometallic species, [M - H](+) ions and radical cations upon mass spectrometric fragmentation of mercury-crown ether complexes

Mass spectrometric fragmentation pathways of [M + HgClO(4)](+) (M - crown ether molecule), determined by tandem mass spectrometry experiments, are discussed in detail. The decomposition of [M + HgClO(4)](+) proceeds along three fragmentation pathways: formation of [M - H](+) ions, formation of organometallic species, namely [M - H + Hg](+) ions, and formation of radical cations [M](+*). The factors influencing these processes, namely crown ether cavities and the presence of electron withdrawing/electron donor groups, have been discussed.