Fluorescence response of TICT-active aminostilbenes to copper(II) ions: redox reaction vs ion recognition

Cu(II)-selective fluorescence enhancement (1, 2, and 4) or fluorescence quenching (3) was observed for aminostilbenes 1–4 in acetonitrile. The fluorescence responses result from efficient Cu(II)-mediated oxidation of 1–4 that forms new fluorescent species rather than from any specific noncovalent interactions. Evidence of redox reactions includes irreversible Cu(II) titration spectra, spectroscopic observation of the radical cations, and isolation of oxidized aminostilbene dimers. These results provide a new method for synthesis of tetrasubstituted tetrahydrofurans and suggest that aminostilbenes with twisted intramolecular charge-transfer activity are potential fluorescence-enhanced Cu(II) chemodosimeters. The role of Cu(II)-mediated redox reactions should be always taken into account in mechanisms for sensing of arylamine-based Cu(II)-selective fluoroionophores.     

Selective detection of Fe(III) ions in aqueous solution with a 1,8-diacridylnaphthalene-derived fluorosensor

The syn-isomer of 1,8-bis(4,4′-diisopropyl-9,9′-diacridyl)naphthalene, 1, has been prepared by two consecutive Pd(PPh₃)₄-catalyzed Stille cross-coupling steps. This highly congested sensor undergoes Fe(III)-selective fluorescence quenching in water/acetonitrile even in the presence of excess of other metal ions.     

Cu(II)-selective green fluorescence of a rhodamine-diacetic acid conjugate

A new rhodamine derivative (1) containing an ethylenediamine-N,N-diacetic acid moiety exhibits Cu(II)-selective strong green fluorescence, while showing very weak orange fluorescence with other metal cations.     

Tuning the selectivity of two chemosensors to Fe(III) and Cr(III)

Two rhodamine-based chemosensors (1 and 2) were designed, and their sensing behavior toward metal ions was investigated by fluorescence spectroscopies. 1 and 2 achieved tuning the selectivity to Fe(III) and Cr(III) in 100% aqueous solution, whereas other ions including Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I) induced basically no spectral change, which constituted a Fe(III)-selective and a Cr(III)-selective fluorescent chemosensor, respectively.     

A highly selective ‘off-on’ fluorescence chemosensor for Cr(III)

An ‘off-on’ fluorescence chemosensor for the selective signalling of Cr(III) has been designed exploiting the guest-induced inhibition of the photoinduced electron transfer signalling mechanism. The system shows an approximately 17-fold Cr(III)-selective chelation-enhanced fluorescence response in tetrahydrofuran and the system is highly selective against the background of environmentally and biologically relevant metal ions.     

An off-on fluorescent sensor with high selectivity and sensitivity for Fe(III)

A new fluorescent derivative (1) containing coumarin exhibits Fe(III)-selective strong yellow-green fluorescence in ethanol. This compound could be used as an “off-on” chemosensor and allow the detection of Fe³⁺ by monitoring changes in absorption and fluorescence spectra. Upon addition of Fe³⁺, an overall emission change of 125-fold was observed. High selectivity and sensitivity were observed over other metal ions, mainly due to the spirolactam ring-opening power of Fe³⁺. The detection limit was as low as 5.6?ppb. Photo-induced electron transfer, coupled with intramolecular charge transfer are proposed to account for the observed spectral response.     

Hydroxynitrile lyase catalysed synthesis of heterocyclic (R)- and (S)-cyanohydrins

Heterocyclic saturated five- and six-membered ring ketones sometimes bearing a methyl substituent were reacted with HCN under enzyme catalysis using recombinant hydroxynitrile lyase from Hevea brasiliensis, as a rule (S)-selective, and Prunus amygdalus, (R)-selective. The resulting cyanohydrins were stereochemically characterised. The steric outcome of these transformations was interpreted by molecular modelling.     

An rhodamine-based fluorescence probe for iron(III) ion determination in aqueous solution

An “off-on” rhodamine-based fluorescence probe for the selective signaling of Fe(III) has been designed exploiting the guest-induced structure transform mechanism. This system shows a sharp Fe(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Al(III), Cd(II), Fe(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Fe(III) concentration from 6.0 × 10⁻⁸ to 7.2 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.4 × 10⁻⁸ mol L⁻¹.     

Cu(II)-selective fluorescence of a bis-quinolylimine derivative

A new bis-quinolylimine ligand containing an azadiene moiety, 1,4-bis(2-quinolyl)-2,3-diaza-1,3-buthadiene (1), was synthesized by one-step facile condensation. This simple ligand, when dissolved in acetonitrile, shows a Cu²⁺-selective fluorescence enhancement. Coordination of 1 with Cu²⁺ produces two kinds of complexes with 1:1 and 1:2 stoichiometries. The 1:2 complex shows a strong fluorescence (Φ_F = 0.37), while the 1:1 complex does not (Φ_F < 0.01). Ab initio molecular orbital calculation reveals that the 1:1 complex has a distorted structure, while the 1:2 complex has a planar structure. The planar configuration of the 1:2 complex, therefore, allows an extended π-conjugation over the entire molecule and, hence, results in fluorescence enhancement.     

Selective dendritic fluorescent sensors for Zn(II)

A series of dendritic 8-hydroxyquinoline (8-HQ) and 5-dialkyl(aryl)aminomethyl-8-HQ derivatives were synthesized and their fluoroionophoric properties toward representative alkali, alkaline earth, group IIIA and transition metal ions were investigated. Among the selected ions, Zn(II) enhanced the fluorescence of N-di-(methoxycarbonylethyl)aminoethyl-3-[4-(8-hydroxyquinolin-5-ylmethyl)piperazin-1-yl]-propanoic amide] (7) by 31-fold, while Al(III) caused enhancement to some extent. The absence of any significant fluorescence enhancement by the other ions examined renders 7a highly useful Zn(II)-selective fluorescent sensor.     

A BODIPY-based fluorescent chemodosimeter for Cu(II) driven by an oxidative dehydrogenation mechanism

A boradiazaindacene (BODIPY) derivative containing a simple NO bidentate ligand shows a Cu(2+)-selective fluorescence in aqueous media. This is promoted via a coordination of Cu(2+) followed by oxidative dehydrogenation of an amine moiety, leading to a formation of a fluorescent Cu(+)-Schiff base complex.     

Stereoselective synthesis of either (E)- or (Z)-silyl enol ether from the same acyclic α,β-unsaturated ketone using cationic rhodium complex-catalyzed 1,4-hydrosilylation

The stereoselective synthesis of either (E)- or (Z)-silyl enol ether from the same acyclic α,β-unsaturated ketone is reported. Highly (Z)-selective conditions were the use of [Rh(cod)₂]BF₄/DPPE at room temperature with no solvent, whereas (E)-selective conditions were the use of [Rh(cod)₂]BF₄/P(1-Nap)₃ (1-Nap = 1-naphthyl) under refluxing dichloromethane.     

Microbial deracemisation of N-(1-hydroxy-1-phenylethyl)benzamide

Microbial deracemisation of racemic N-(1-hydroxy-1-phenylethyl)benzamide to give the (R)-enantiomer is described using whole cells of Cunninghamella echinulata NRRL 1384. The deracemisation involves fast highly (S)-selective oxidation followed by slower partially (S)-selective reduction of the intermediate ketone. The yield and ee of (R)-N-(1-hydroxy-1-phenylethyl)benzamide were optimised (82%, 98% ee) by removal of a competing extracellular amidase/protease activity by using static cells at pH 5. Use of the protease inhibitor PMSF with growing cells leads to a slower deracemisation (82% ee) but a very high (98%) overall recovery of alcohol and ketone.     

Ratiometric chemosensing of Mg ions by a calix[4]arene diamide derivative

A new chemosensor with a phenanthroimidazole subunit based upon calix[4]arene-diamide has been synthesized, and its Mg²⁺-selective fluoroionophoric properties were investigated in an aqueous DMSO solution. The compound exhibited a pronounced Mg²⁺-selective fluoroionophoric behavior over other physiologically relevant metal ions. A significant red shift in fluorescence emission (Δλ = 86 nm) provided the ratiometric determination as well as naked-eye detection of Mg²⁺ ions.     

Synthesis of 5-dialkyl(aryl)aminomethyl-8-hydroxyquinoline dansylates as selective fluorescent sensors for Fe3+

A series of 5-dialkyl(aryl)aminomethyl-8-hydroxyquinoline dansylates were synthesized and their fluoroionophoric properties toward representative alkali ions, alkaline earth ions and transition metal ions were investigated. Among the selected ions, Fe3+ caused considerable quenching of the fluorescence, while Cr3+ caused quenching to some extent. The absence of any significant fluorescence quenching effects of the other ions examined, especially Fe2+, renders these compounds highly useful Fe3+-selective fluorescent sensors.     

The formation and properties of mixed cadmium sulfide—silver sulfide,and mixed mercury sulfide—silver sulfide membranes for electrodes selective to cadmium(II) and mercury(II)

The preparation and behavior of cadmium(II)-selective and mercury (II)-selective electrodes made from mixed metal sulfide-silver sulfide precipitates are discussed. The performance of the cadmium-selective electrode is satisfactory in accordance with similar electrodes described in the literature. Responses to cadmium(II), alone as well as in the presence of complexing agents such as EDTA, NTA, trien and tetren, were determined as a function of pH. Selectivity coefficients are presented. The mercury(II)-selective electrodes generally did not behave reproducibly; at best, the limit of detection was about 10^-5 M.     

Synthesis of (sulfonyl)methylphosphonate analogs of prenyl diphosphates

Syntheses of several (sulfonyl)methylphosphonate analogs of geranyl, neryl, and farnesyl diphosphates are described. Key steps include utilization of an (E)-selective Horner-Wadsworth-Emmons olefination which couples an aldehyde to the sulfone phosphonate moiety, and a selective reduction of the resulting dienyl sulfone phosphonate substrates.     

Molybdenum(II)-catalyzed alkylation of electron-rich aromatics with allylic acetates

The molybdenum(II) complex [Mo(CO)₄Br₂]₂ has been found to catalyze allylic substitution with aromatic ethers, e.g., anisole (7), as nucleophiles. The reaction is remarkably para-selective (e.g., 7 + 8 → 11).     

Coated-wire ion-selective electrode for the determination of gold(III)

A coated-wire gold(III)-selective electrode based on the 1,2,4,6-tetraphenyl-pyridinium tetrachloroaurate(III) ion-pair is described. The response is Nernstian in the gold concentration range 10^?2–3 × 10^?6 (slope 59.0 mV/pAu). Of the 22 ions tested, only the interference of thallium(III) is important. The electrode is applied to the determination of gold in an Ag-Pd-Au alloy with satisfactory results.