A highly selective pyridoxal-based chemosensor for the detection of Zn(ii) and application in live-cell imaging; X-ray crystallography of pyridoxal-TRIS Schiff-base Zn(ii) and Cu(ii) complexes.

In a simple, one-step reaction, we have synthesized a pyridoxal-based chemosensor by reacting tris(hydroxymethyl)aminomethane (TRIS) together with pyridoxal hydrochloride to yield a Schiff-base ligand that is highly selective for the detection of Zn(ii) ion. Both the ligand and the Zn(ii) complex have been characterized by 1H & 13C NMR, ESI-MS, CHN analyses, and X-ray crystallography. The optical properties of the synthesized ligand were investigated in an aqueous buffer solution and found to be highly selective and sensitive toward Zn(ii) ion through a fluorescence turn-on response. The competition studies reveal the response for zinc ion is unaffected by all alkali and alkaline earth metals; and suppressed by Cu(ii) ion. The ligand itself shows a weak fluorescence intensity (quantum yield, Φ = 0.04), and the addition of zinc ion enhanced the fluorescence intensity 12-fold (quantum yield, Φ = 0.48). The detection limit for zinc ion was 2.77 × 10-8 M, which is significantly lower than the WHO's guideline (76.5 µM). Addition of EDTA to a solution containing the ligand-Zn(ii) complex quenched the fluorescence, indicating the reversibility of Zn(ii) binding. Stoichiometric studies indicated the formation of a 2 : 1 L2Zn complex with a binding constant of 1.2 × 109 M-2 (±25%). The crystal structure of the zinc complex shows the same hydrated L2Zn complex, with Zn(ii) ion binding with an octahedral coordination geometry. We also synthesized the copper(ii) complex of the ligand, and the crystal structure showed the formation of a 1 : 1 adduct, revealing 1-dimensional polymeric networks with octahedral coordinated Cu(ii). The ligand was employed as a sensor to detect zinc ion in HEK293 cell lines derived from human embryonic kidney cells grown in tissue culture which showed strong luminescence in the presence of Zn(ii). We believe that the outstanding turn-on response, sensitivity, selectivity, lower detection limit, and reversibility toward zinc ion will find further application in chemical and biological science.

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.

We report here a series of heteroatom-substituted macrocycles containing an anthraquinone moiety as a fluorescent signaling unit and a cyclic polyheteroether chain as the receptor. Sulfur, selenium, and tellurium derivatives of 1,8-anthraquinone-18-crown-5 (1) were synthesized by reacting sodium sulfide (Na2S), sodium selenide (Na2Se) and sodium telluride (Na2Te) with 1,8-bis(2-bromoethylethyleneoxy)anthracene-9,10-dione in a 1 : 1 ratio. The optical properties of the new compounds are examined and the sulfur and selenium analogues produce an intense green emission enhancement upon association with Pb(II) in acetonitrile. Selectivity for Pb(II) is markedly improved as compared to the oxygen analogue 1 which was also competitive for Ca(II) ion. UV-Visible and luminescence titrations reveal that 2 and 3 form 1 : 1 complexes with Pb(II), confirmed by single-crystal X-ray studies where Pb(II) is complexed within the macrocycle through coordinate covalent bonds to neighboring carbonyl, ether and heteroether donor atoms. Cyclic voltammetry of 2-8 showed classical, irreversible oxidation potentials for sulfur, selenium and tellurium heteroethers in addition to two one-electron reductions for the anthraquinone carbonyl groups. DFT calculations were also conducted on 1, 2, 3, 6, 6 + Pb(II) and 6 + Mg(II) to determine the trend in energies of the HOMO and the LUMO levels along the series.

(BMI)3LnCl6 crystals as models for the coordination environment of LnCl3 (Ln = Sm, Eu, Dy, Er, Yb) in 1-butyl-3-methylimidazolium chloride ionic-liquid solution.

A series of (BMI)3LnCl6 (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions of LnCl3 dissolved in the ionic liquid, 1-butyl-3-methylimidazolium chloride (BMICl). Crystals with Ln = 5% Sm + 95% Gd and with Ln = 5% Dy + 95% Gd were also grown to assess the importance of cross-relaxation in the Sm and Dy samples. The crystals are isostructural, with monoclinic space group P21/c and four formula units per unit cell. The first coordination sphere of Ln(3+) consists of six Cl(-) anions forming a slightly distorted octahedral LnCl6(3-) center. The second coordination sphere is composed of nine BMI(+) cations. The emission spectra and luminescence lifetimes of both (BMI)3LnCl6 crystals and LnCl3 in BMICl solution were measured. The spectroscopic similarities suggest that crystalline (BMI)3LnCl6 provides a good model of the Ln(3+) coordination environment in BMICl solution.

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.

Differential sensing of Zn(II) and Cu(II) via two independent mechanisms.

Selective reduction of an anthracenone-quinoline imine derivative, 2, using 1.0 equiv of NaBH(4) in 95% ethanol affords the corresponding anthracen-9-ol derivative, 3, as confirmed by (1)H NMR, (13)C NMR, ESI-MS, FTIR, and elemental analysis results. UV-vis and fluorescence data reveal dramatic spectroscopic changes in the presence of Zn(II) and Cu(II). Zinc(II) coordination induces a 1,5-prototropic shift resulting in anthracene fluorophore formation via an imine-enamine tautomerization pathway. Copper(II) induces a colorimetric change from pale yellow to orange-red and results in imine hydrolysis in the presence of water. Spectroscopic investigations of metal ion response, selectivity, stoichiometry, and competition studies all suggest the proposed mechanisms. ESI-MS analysis, FTIR, and single-crystal XRD further support the hydrolysis phenomenon. This is a rare case of a single sensor that can be used either as a chemosensor (reversibly in the case of Zn(II)) or as a chemodosimeter (irreversibly in the case of Cu(II)); however, the imine must contain a coordinating Lewis base, such as quinoline, to be active for Cu(II).

A simple acrylic acid functionalized zinc porphyrin for cost-effective dye-sensitized solar cells.

A simple zinc porphyrin with an acrylic acid at the meso position exhibits an energy conversion efficiency of 5.1%, demonstrating its potential for cost-effective dye-sensitized solar cells.

Zinc(II) mediated imine-enamine tautomerization.

Reduction of imine-anthracenone compounds selectively produces secondary alcohols leaving the external imine group unreacted. Addition of the Zn(II) ion induces a metal-mediated imine-enamine tautomerization reaction that is selective for Zn(II), a new fluorescence detection method not previously observed for this important cation.

catena-Poly[1-butyl-3-methyl-imidazolium [[dichlorido(methanol-κO)(propan-2-ol-κO)lanthanate(III)]-di-µ-chlorido]].

The title compound, (C(8)H(15)N(2))[LaCl(4)(CH(3)OH)(C(3)H(7)OH)], consists of one 1-butyl-3-methyl-imidazolium (BMI(+)) cation and one hexa-hedral tetra-chlorido(methanol)(propan-2-ol)lanthanate anion. The La(III) ion is eight-coordinate, with the La(III) ion bridged by a pair of Cl atoms, so forming chains propagating along the a-axis direction. Each La(III) ion is further coordinated by two isolated Cl atoms, one methanol and one propan-2-ol mol-ecule. The coordinated methanol and propan-2-ol mol-ecules of the anion form O-H⋯Cl hydrogen bonds with the Cl atoms of inversion-related anions. The BMI(+) cation froms C-H⋯Cl hydrogen bonds with the Cl atoms of the anion. The anions are located in the C faces of the triclinic unit cell, with an inversion center in the middle of the La(2)Cl(2) ring of the polymeric chain.

BODIPY chromophores as efficient green light sensitizers for lanthanide-induced near-infrared emission.

A new boron dipyrromethene (BODIPY) modified 8-hydroxylquinoline ligand (8-HOQ-BODIPY) is synthesized for the sensitization of near-infrared emission of lanthanide(III) ions. The BODIPY unit, as revealed by single-crystal X-ray diffraction analysis, aligns almost perpendicularly to the 8-HOQ unit. The ligand exhibits strong absorption at ~506 nm and fluorescence at 510 nm in organic solvents with quantum yields ranging from ~0.45 in dichloromethane to 0.015 in ethanol. It forms stable ytterbium(III), erbium(III) and neodymium(III) complexes with 3:1 ligand-to-metal molar ratios. Upon excitation (~522 nm), the neodymium(III) and erbium(III) complexes emit weakly at 1060 and 1382 nm, respectively, whereas the ytterbium(III) complex exhibits strong emission at 976 and 1003 nm. The results demonstrate the potential of BODIPY dyes as efficient and robust visible light sensitizers for lanthanide-based NIR emitters in medical diagnosis.

Site-selective imination of an anthracenone sensor: selective fluorescence detection of barium(II).

Site-selective imination of anthraquinone-based macrocyclic crown ethers using titanium tetrachloride as the catalyst yields imines where only the external carbonyl group of the anthraquinone forms Schiff-bases. The following aromatic amines yield monomeric compounds (aniline, 4-nitroaniline, 4-pyrrolaniline, and 1,3-phenylenediamine). Reaction of 2 equiv of the macrocyclic anthraquinone host with 1,2- and 1,4-phenylenediamine yields dimeric imine compounds. The 1,2-diimino host acts as a luminescence sensor, exhibiting enhanced selectivity for Ba(II) ion. Spectroscopic data indicate that two barium ions coordinate to the sensor. Due to E/Z isomerization of the imine, the monomeric complexes are nonluminescent. Restricted rotation about the 1,2 oriented C═N groups or other noncovalent/coordinate-covalent interactions acting between neighboring crown ether rings may inhibit E/Z isomerization in this example, which is different from current examples that employ coordination of a metal cation with a chelating imine nitrogen atom to suppress E/Z isomerization and activate luminescence. The 1,4-diimino adduct, where the crown rings remain widely separated, remains nonluminescent.

4-tert-Butyl-pyridinium triiodide-4-tert-butyl-pyridine (1/1).

The title compound, C(9)H(14)N(+)·I(3) (-)·C(9)H(13)N, consists of monoprotonated 4-tert-butyl-pyridinium cations and triiodide anions. The triiodide ion has near-symmetric linear geometry, with bond lengths of 2.9105 (4) Š(I-I) and a bond angle of 177.55 (3)° (I-I-I). For this room-temperature structure, the butyl group on the pyridine ring is disordered and has been treated as a rigid rotator, modeled in three separate positions with 1/3, 1/3, 1/3 occupancies. The cations assemble into dimeric forms by way of N-H⋯N hydrogen bonds.

Substitution of thiophene oligomers with macrocyclic end caps and the colorimetric detection of Hg(II).

Alkyl substitution at the α position(s) of mono-, bi-, and terthiophenes via electrophilic addition of macrocyclic end caps combines linear, π-conjugated aromatic compounds and annular macrocycles. Addition of the Hg(II) ion to terthiophene adducts produces intense color changes, allowing for the selective, colorimetric detection of mercury(II). Chemical oxidation of the asymmetric terthiophene adduct produces the sexithiophene oligomer.

Di-µ-pivalato-κO,O':O';κO:O,O'-bis-[(methanol-κO)bis-(2,2,6,6-tetra-methylhepta-ne-3,5-dionato)praseo-dymium(III)].

In the centrosymmetric dimeric title compound, [Pr(2)(C(5)H(9)O(2))(2)(C(11)H(19)O(2))(4)(CH(3)OH)(2)], the two praseodymium(III) atoms are eight-coordinate and are bridged by O atoms from the two pivalate anions. Each Pr(III) ion is further coordinated by two chelating 2,2,6,6-tetra-methyl-3,5-hepta-nedionate (thd(-)) ligands and one methanol mol-ecule. The distance between the two Pr(III) ions is 4.273 (5) Å. Intra-molecular hydrogen bonds exists between the methanol hy-droxy group on one Pr(III) atom and a chelating O atom of a thd(-) ligand coordinated to the symmetry-related Pr(III) atom.

Hybridization of near-infrared emitting erbium(III) and ytterbium(III) monoporphyrinate complexes with silica xerogel: synthesis, structure and photophysics.

The new erbium(III) and ytterbium(III) monoporphyrinate complexes were synthesized and hybridized into silica xerogel frameworks though the coordination of 5-(N,N-bis(3-propyl)ureyl-1,10-phenanthroline to the lanthanide ions. The complexes are eight-coordinate with strong emissions in solution in the near-infrared region. The resulting silica films are transparent, homogenous, and exhibit strong mechanical strength. The scanning electron microscope and atomic force microscope study reveals that the surface of the film is porous with the silica in particulate or rod shapes. Upon visible light excitation, the fluorescence of the porphyrin at approximately 649 nm with lifetimes of approximately 3.4 and 3.8 ns for erbium(III) and ytterbium-hybridized films were observed, respectively. The erbium- and ytterbium-hybridized films gave characteristic emissions at 1538 nm with a lifetime of 0.6 micros and at 980 nm with a lifetime of 6.6 micros, respectively. They exhibited a 50 to 70% decrease in lifetime compared to their parent complexes in toluene.

Drag force on an impurity below the superfluid critical velocity in a quasi-one-dimensional Bose-Einstein condensate.

The existence of frictionless flow below a critical velocity for obstacles moving in a superfluid is well established in the context of the mean-field Gross-Pitaevskii theory. We calculate the next order correction due to quantum and thermal fluctuations and find a nonzero force acting on a delta-function impurity moving through a quasi-one-dimensional Bose-Einstein condensate at all subcritical velocities and at all temperatures. The force occurs due to an imbalance in the Doppler shifts of reflected quantum fluctuations from either side of the impurity. Our calculation is based on a consistent extension of Bogoliubov theory to second order in the interaction strength, and finds new analytical solutions to the Bogoliubov-de Gennes equations for a gray soliton. Our results raise questions regarding the quantum dynamics in the formation of persistent currents in superfluids.

Structure and photophysics of near-infrared emissive ytterbium(III) monoporphyrinate acetate complexes having neutral bidentate ligands.

Substitution reactions between [Yb(TPP)(OOCCH3)(CH3OH)2] (1) and neutral bidentate ligands NN led to the formation of monoporphyrinate ytterbium(III) complexes [Yb(TPP)(OOCCH3)(NN)] (TPP = 5,10,15,20-tetraphenylporphyrinate anion; NN = 4-methyl-1,10-phenanthroline (2), 1,10-phenanthroline (3), 4,7-dimethyl-1,10-phenanthroline (4), 5,6-epoxy-5,6-dihydroxy-1,10-phenanthroline (5) and 2,2'-dipyridylamine (6)). Single-crystal X-ray diffraction analysis revealed that ytterbium(III) ions in 1 and 6 were seven-coordinate with OOCCH3- in monodentate coordination, whereas those in 2, 3, 4 and 5 were eight-coordinate with OOCCH3- in bidentate coordination. The visible emission (650 and 720 nm) from the porphyrin and near-infrared (NIR) emission (980 and 1003 nm) from ytterbium(III) ion were observed for all complexes. The eight-coordinate complexes exhibited stronger NIR emission and longer lifetimes in toluene solution than the seven-coordinate complexes. The NIR emission of complexes with decreased lifetimes was also observed when they were blended into organic polymer PMMA.

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.

Luminescence detection of transition and heavy metals by inversion of excited states: synthesis, spectroscopy, and X-ray crystallography of Ca, Mn, Pb, and Zn complexes of 1,8-anthraquinone-18-crown-5.

A lumophore composed of anthraquinone attached to a macrocyclic polyether ring containing an intraannular carbonyl is capable of selectively detecting Pb(2+)() ion in solution using an alternative photophysical detection mechanism. Of the various methods available for detection of ions in solution, a mechanism involving inversion of excited states has not been previously employed for the detection of transition and heavy metals. In this mechanism, nonradiative n-pi transitions are replaced by radiative pi-pi transitions upon complexation by a suitable guest cation. Optimum fluorescence enhancement is achieved using cations of high charge, large cations that form long bonds within the host, and cations which do not coordinate solvent or the counteranion, all of which are necessary for inversion of excited states to occur. Photophysical properties and binding constants of this new class of luminescence sensors are provided, as well as the X-ray crystallographic results for Pb(2+), Mn(2+), and Zn(2+) complexes of 1,8-oxybis(ethylene-oxyethyleneoxy)anthracene-9,10-dione (1), referred to as 1,8-anthraquinone-18-crown-5. ([1.Pb](ClO(4))(2) (2) (monoclinic, P21/n, a = 8.0303(6) A, b = 25.976(2) A, c = 12.1616(9) A, beta = 94.956(1) degrees , Z = 4, 4980 reflections [I > or = 2sigma(I)], R1 = 0.0266, wR2, 0.0500, 173(2) K). [1.Mn(H(2)O)(NCCH(3))](ClO(4))(2) (5) (monoclinic, P21/c, a = 10.132(2) A, b = 11.8030(4) A, c = 23.999(7) A, beta = 95.75(2) degrees , Z = 4, 3000 reflections [I > or = 2sigma(I)], R1 = 0.0488, wR2, 0.0938, 203(2) K). [1.Zn(H(2)O)(NCCH(3))](ClO(4))(2) (6) (monoclinic, P21/c, a = 10.177(10) A, b = 11.977(6) A, c = 24.166(4) A, beta = 95.83(4) degrees , Z = 4, 3061 reflections [I > or = 2sigma(I)], R1 = 0.0673, wR2, 0.1729, 295(2) K).).

Luminescence and structural comparisons of strong-acid sensor molecules. 2.

Anthraquinone-containing cyclic polyether hosts form 1:1 complexes with hydronium ion, producing large enhancements in luminescence via inversion of npi* and pipi* exited states. We have characterized the binding of hydronium ion within these host molecules and have synthesized a large variety of analogous hosts that contain different structural and electronic features that allow better understanding of what controls binding and luminescence capacity in this class of fluorescent sensor molecules. X-ray crystallography of an anthraquinone host that contains terminal amine functional groups rather than terminal ether groups is investigated, and complete proton transfer to carbonyl groups is observed in concentrated sulfuric acid media that also produces a previously unobserved luminescence.