An OFF-ON chemosensor for biological and environmental applications: sensing Cd2+ in water using catanionic vesicles and in living cells.

A new OFF-ON fluorescent chemosensor (L(1)) for Cd(2+) recognition based on a 5-chloro-8-hydroxyquinoline pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN3) will be presented and its photochemical features in an MeCN-H2O 1 : 1 (v/v) mixture, in pure water, after inclusion within catanionic vesicles, and in living cells will be discussed. The coordination properties of L(1) both in solution and in the solid state were preliminarily studied and its selectivity towards Cd(2+)versus a set of different metal ions (Cu(2+), Zn(2+), Cd(2+), Pb(2+), Al(3+), Hg(2+), Co(2+), Ni(2+), Mn(2+), Mg(2+), K(+), Ca(2+), Ag(+), and Na(+)) was verified in MeCN-H2O 1 : 1 (v/v). In water, upon addition of increasing amounts of Cd(2+) to L(1) an enhancement of the fluorescence emission was detected. To overcome this serious drawback, L(1) was dissolved in an innovative catanionic vesicular solution based on sodium bis(2-ethylhexyl) sulfosuccinate, a traditional surfactant, and 1-dodecyl-3-methylimidazolium bromide, an ionic liquid. When enclosed within the vesicle bilayers in water, L(1) restored its fluorescence emission property upon addition of Cd(2+). Remarkably, L(1) enters the cellular membrane of living cells thus allowing the detection of intracellular Cd(2+). These findings encourage the application of this new fluorescent chemosensor in real samples for histological and environmental analyses.

Zn2+/Cd2+ optical discrimination by fluorescent chemosensors based on 8-hydroxyquinoline derivatives and sulfur-containing macrocyclic units.

Four new fluorescent chemosensors for metal ions based on 8-hydroxyquinoline (8-HDQ) derivatives and sulfur-containing macrocyclic units were synthesized and characterized, namely 1-(5-chloro-8-hydroxy-7-quinolinylmethyl)-1-aza-4,7,10-trithiacyclododecane (L1), 1-(5-chloro-8-hydroxy-7-quinolinylmethyl)-1-aza-4,13-dithia-7,10-dioxacyclopentadecane (L2), 1-(8-hydroxy-2-quinolinylmethyl)-1-aza-4,7,10-trithiacyclododecane (L3), and 1-(8-hydroxy-2-quinolinylmethyl)-1-aza-4,13-dithia-7,10-dioxacyclopentadecane (L4). Preliminary fluorimetric titrations indicated L1 as the only member of the family of ligands to give a selective CHEF-type response to the presence of Zn(2+) in MeCN-H2O (1:1, v/v) solutions, which allowed imaging of this metal ion in Cos-7 cells in vitro. The other ligands either did not show any fluorescence response (L3, L4) to any of the metal ions considered (Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+)) or gave (L2) a CHEF-type response also to the presence of Cd(2+). The coordination properties of L1 towards Zn(2+) were, therefore, fully investigated by potentiometric measurements and absorption and emission spectroscopy at different pH values, which indicated that the formation of 2:1 L1/Zn(2+) complexes is responsible for the CHEF-type effect observed. The complexes [Zn(L1)2H2O](BF4)2 and [Zn(L3)](ClO4)2 were characterized in the solid state by X-ray crystallography, and DFT calculations were performed to understand the origin of the Zn(2+)/Cd(2+) optical discrimination of the 8-HDQ-based "conjugate" fluorescent chemosensors reported.

Tuning the emission properties of fluorescent ligands by changing pH: the unusual case of an acridine-containing polyamine macrocycle.

Synthesis and characterization of a new macrocyclic compound, composed by a triethylentetraamine chain linking the 4 and 5 positions of an acridine moiety, are reported. The molecule, devised as a fluorescent chemosensor for anions, has revealed an intriguing pH-dependent spectroscopic behavior, whose features are the specific object of this article. Ligand protonation in aqueous solution has been analyzed by means of potentiometric, (1)H NMR, UV-vis, and fluorescence emission measurements. The molecule binds up to four protons in the pH range 2-11. Protonation takes place on the aliphatic tetraamine chain, while the acridine nitrogen does not participate to proton binding even at very low pH. Differently from acridine, the UV-vis spectra are almost unaffected by the pH. On the opposite, the emission spectra are strongly pH-dependent. In fact, at low pH values, the spectra show a blue-shifted emission, resembling that of unprotonated acridine, while at slightly acidic and alkaline pH the fluorescence features a red-shifted band similar to that of acridinium cation. This unusual behavior occurs in the mono-, bi-, and triprotonated forms of the compound and is interpreted as due to an excited state proton transfer from an aliphatic ammonium group adjacent to the acridine moiety to the acridine nitrogen. In the fully protonated state, this process is prevented owing to unfavorable molecular arrangements mainly determined by electrostatic repulsions. This interpretation is supported by quantum mechanical calculations as well as molecular dynamics simulations.

A BINOL-based chiral polyammonium receptor for highly enantioselective recognition and fluorescence sensing of (S,S)-tartaric acid in aqueous solution.

A chiral ditopic polyammonium receptor featuring two [9]aneN(3) moieties separated by a (S)-BINOL linker is able to selectively bind and sense in water (S,S)-tartaric acid over its (R,R)/meso forms.

Selective binding and fluorescence sensing of diphosphate in H2O via Zn(2+)-induced allosteric regulation of the receptor structure.

A terpyridine-based receptor featuring two [9]aneN(3) units is able to selectively bind and sense diphosphate over mono- and triphosphate in aqueous solution at pH 7, thanks to the conformational change of its structure induced by Zn(2+) coordination to the polypyridyl moiety.