Selective sensing of Hg2+ by a proton-ionizable calix[4]arene fluoroionophore.

A fluorogenic derivative of a calix[4]arene with two proton-ionizable N-(phenyl)sulfonyl carboxamide-containing side arms in the 1,3-positions on the lower rim is employed for the selective sensing of Hg(2+) at low concentration levels in water/MeCN (1:1, v/v) solutions containing Pb(2+) and Cd(2+). All three metal ions quench the fluorescence of the ligand in pure MeCN. However, in water/MeCN mixed solvent, the recognition of such cations occurs differently as only Hg(2+) complexation quenches the fluorescence of the calixarene. Experiments carried out in the presence of an acid and a bulky non-complexing cation shows that the quenching of the calixarene fluorescence upon Hg(2+) addition is likely due to proton displacement from the proton-ionizable side arms of the ligand. The system may be employed as a simple tool for the selective and efficient mercury sensing in mixed water/organic solvent.

Nanostructural organization in acetonitrile/ionic liquid mixtures: molecular dynamics simulations and optical Kerr effect spectroscopy.

The nanostructural organization and subpicosecond intermolecular dynamics in mixtures of acetonitrile and the ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(5)mim][NTf(2)]) are studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The MD simulations show the IL to be nanostructurally organized into an ionic network and nonpolar domains, with CH(3)CN molecules localized in the interfacial region between the ionic network and nonpolar domains, as found previously by other researchers. The MD simulations indicate strong interactions between CH(3)CN and the hydrogen atoms on the imidazolium ring of the cation. The low-frequency (0-200 cm(-1)) intermolecular part of the reduced spectral densities (RSDs) of the mixtures narrows and shifts to lower frequency as the concentration of CH(3)CN increases. These spectral changes can be partly attributed to the increasing contribution of the low-frequency intermolecular modes of CH(3)CN to the RSD. At a given composition, the RSD of a mixture is found to be broader and higher in frequency than the corresponding ideal RSD given by the volume-fraction-weighted sum of the RSDs of the neat liquids. This difference is rationalized in terms of the competition between CH(3)CN-cation interactions and solute-induced disruption of the ionic networks.

Nanostructural organization in carbon disulfide∕ionic liquid mixtures: molecular dynamics simulations and optical Kerr effect spectroscopy.

In this paper, the nanostructural organization and subpicosecond intermolecular dynamics in the mixtures of CS(2) and the room temperature ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(5)mim][NTf(2)]) were studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. At low CS(2) concentrations (<10 mol.% CS(2)/IL), the MD simulations indicate that the CS(2) molecules are localized in the nonpolar domains. In contrast, at higher concentrations (≥10 mol.% CS(2)/IL), the MD simulations show aggregation of the CS(2) molecules. The optical Kerr effect (OKE) spectra of the mixtures are interpreted in terms of an additivity model with the components arising from the subpicosecond dynamics of CS(2) and the IL. Comparison of the CS(2)-component with the OKE spectra of CS(2) in alkane solvents is consistent with CS(2) mainly being localized in the nonpolar domains, even at high CS(2) concentrations, and the local CS(2) concentration being higher than the bulk CS(2) concentration.

Intermolecular vibrational motions of solute molecules confined in nonpolar domains of ionic liquids.

In this study, we address the following question about the dynamics of solute molecules in ionic liquids (ILs). Are the intermolecular vibrational motions of nonpolar molecules confined in the nonpolar domains formed by tail aggregation in ILs the same as those in an alkane solvent? To address this question, the optical Kerr effect (OKE) spectrum of CS(2) in the IL 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C(5)mim][NTf(2)]) was studied as a function of concentration at 295 K by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The OKE spectrum broadens and shifts to higher frequency as the CS(2) concentration is decreased from 20 to 10 mol %; at lower concentrations, no further change in the width of the OKE spectrum is observed. Multicomponent line shape analysis of the OKE spectrum of 5 mol % CS(2) in [C(5)mim][NTf(2)] reveals that the CS(2) and [C(5)mim][NTf(2)] contributions to the spectrum are separable and that the CS(2) contribution is similar to the OKE spectrum of 5 mol % CS(2) in n-pentane with the spectrum being lower in frequency and narrower than that of neat CS(2). These results suggest that, at this concentration, CS(2) molecules are isolated from each other and mainly localized in the nonpolar domains of the IL.

Effect of cation symmetry and alkyl chain length on the structure and intermolecular dynamics of 1,3-dialkylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids.

In this article, the structure and intermolecular dynamics of 1,3-alkylmethylimidazolium bis(trifluoromethanesulfonyl)amides [C(n)mim][NTf(2)] with n = 2-5 are compared to those of 1,3-dialkylimidazolium bis(trifluoromethanesulfonyl)amides [(C(n))(2)im][NTf(2)] with n = 2-5. The structures of these room-temperature ionic liquids (RTILs) were studied by small-wide-angle X-ray scattering (SWAXS), and their intermolecular dynamics were studied by optical Kerr effect (OKE) spectroscopy. The SWAXS measurements indicate that, on a microscopic scale, the liquid structure of RTILs with symmetric cations is similar to that of RTILs with asymmetric cations. The OKE measurements indicate that the intermolecular dynamics of RTILs with symmetric cations are higher in frequency than those of RTILs with asymmetric cations. These results suggest that the local structure of RTILs with symmetric cations is more solid-like than that of RTILs with asymmetric cations. Further evidence for this difference in local structure on a mesoscopic spatial scale is that the width of the low-Q peak in the SWAXS data is narrower for [(C(5))(2)im][NTf(2)] than for [C(5)mim][NTf(2)]. Moreover, the structure and intermolecular dynamics of the RTILs with ethyl-substituted cations appear to be quite different from those of other RTILs within a given series. This difference is evidenced by a clear change in the dependence of the spectral parameters of the intermolecular part of the OKE spectrum on the alkyl chain length in going from n = 2 to n = 3. The dependence of the SWAXS and OKE data on alkyl chain length is discussed within the context of the nanoscale heterogeneities of RTILs.

Effect of pendant group length upon metal ion complexation in acetonitrile by di-ionized calix[4]arenes bearing two dansyl fluorophores.

A series of three di-ionizable calix[4]arenes with two pendant dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims was synthesized. Structures of the three ligands were identical except for the length of the spacers which connected the two dansyl groups to the calix[4]arene scaffold. Following conversion of the ligands into their di-ionized di(tetramethylammonium) salts, absorption and emission spectrophotometry were utilized to probe the influence of metal cation (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Ag+, Cd2+, Co2+, Fe2+, Hg2+, Mn2+, Pb2+, Zn2+ and Fe3+) complexation in acetonitrile. Upon complexation with these metal cations, emission spectra underwent marked red shifts and quenching of the dansyl group fluorescence for the di-ionized ligand with the shortest spacer. A similar effect was noted for the di-ionized ligand with an intermediate spacer for all of the metal ions, except Ba2+. For the di-ionized ligand with the longest spacer, the metal cations showed different effects on the emission spectrum. Li+, Mg2+, Ca2+ and Ba2+ caused enhancement of emission intensity with a red shift. Other metal cations produce quenching with red shifts in the emission spectra. Transition metal cations interacted strongly with all three di-ionized ligands. In particular, Fe3+ and Hg2+ caused greater than 99% quenching of the dansyl fluorescence in the di-ionized ligands.

Nanostructural organization and anion effects in the optical Kerr effect spectra of binary ionic liquid mixtures.

This article reports a study of the effect of anions on the optical Kerr effect (OKE) spectra of binary ionic liquid mixtures with one mixture comprising the 3-methyl-1-pentylimidazolium ([C 5mim] (+)) cation and the anions PF 6 (-) and CF 3CO 2 (-) (TFA (-)), and another mixture comprising the [C 5mim] (+) cation and the anions Br (-) and bis(trifluomethanesulfonyl)imide (NTf 2 (-)). The spectra were obtained by the use of optical heterodyne-detected Raman-induced Kerr Effect Spectroscopy at 295 K. The OKE spectra of the mixtures are compared with the calculated mole-fraction weighted sum of the normalized OKE spectra of the neat liquids. The OKE spectra are nearly additive for [C 5mim]Br/[C 5mim][NTf 2] mixtures, but nonadditive for [C 5mim][PF 6]/[C 5mim][TFA] mixtures. In the case of the equimolar [C 5mim][PF 6]/[C 5mim][TFA] mixture, the nonadditivity is such that the experimental OKE spectrum is narrower than the calculated OKE spectrum. The additivity or nonadditivity of OKE spectra for IL mixtures can be explained by assuming ionic liquids are nanostructurally organized into nonpolar regions and ionic networks. The ionic networks in mixtures will be characterized by "random co-networks" for anions that are nearly the same in size (PF 6 (-) and TFA (-)) and by "block co-networks" for anions that differ greatly in size (Br (-) and NTf 2 (-)).

Nanostructural organization and anion effects on the temperature dependence of the optical Kerr effect spectra of ionic liquids.

The intermolecular spectra of three imidazolium ionic liquids were studied as a function of temperature by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids comprise the 1,3-pentylmethylimidazolium cation ([C(5)mim]+), and the anions, bromide (Br-), hexafluorophosphate (PF(6)-), and bis(trifluoromethanesulfonyl)imide (NTf(2)-). Whereas the optical Kerr effect (OKE) spectrum of [C(5)mim][NTf(2)] is temperature-dependent, the OKE spectra of [C(5)mim]Br and [C(5)mim][PF6] are temperature-independent. These results are surprising in light of the fact that the bulk densities of these room temperature ionic liquids (RTILs) are temperature-dependent. The temperature independence of the OKE spectra and the temperature dependence of the bulk density in [C(5)mim]Br and [C(5)mim][PF(6)] suggest that there are inhomogeneities in the densities of these liquids. The existence of density inhomogeneities is consistent with recent molecular dynamics simulations that show RTILs to be nanostructurally organized with nonpolar regions arising from clustering of the alkyl chains and ionic networks arising from charge ordering of the anions and imidazolium rings of the cations. Differences in the temperature dependences of the OKE spectra are rationalized on the basis of the degree of charge ordering in the polar regions of the RTILs.

Additivity in the optical kerr effect spectra of binary ionic liquid mixtures: implications for nanostructural organization.

Low-frequency spectra of binary room-temperature ionic liquid (RTIL) mixtures of 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-pentyl-3-methylimidazolium bromide in the 0-250 cm(-1) region were studied as a function of mole fraction at 295 K. The spectra were obtained by use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The spectra of these binary mixtures are well described by the weighted sums of the spectra for the neat RTILs. This surprising result implies that the intermolecular modes giving rise to the spectra of the neat liquids must also produce the spectra of the mixtures. Additivity of the OKE spectra can be explained by a model in which locally ordered domains are assumed to exist in the neat liquid with the structures of these locally ordered domains preserved upon mixing. Recently published molecular dynamics simulations show that RTILs are nanostructurally organized with ionic networks and nonpolar regions. If ionic networks also exist in the mixture, the additivity of the OKE spectra implies that there are "blocks" along the network of the mixture that are ordered in the same way as in the neat liquids. These "block co-networks" would have a nanostructural organization resembling that of a block copolymer.

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer.

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.

Highly selective Ba2+ separations with acyclic, lipophilic di-[N-(X)sulfonyl carbamoyl] polyethers.

New lipophilic acyclic polyethers with two N-(X)sulfonyl carbamoyl groups of "tunable" acidity exhibit remarkable selectivity for Ba2+ over other alkaline earth metal ions in competitive solvent extraction and transport across polymer inclusion membranes.

Novel fluorogenic calix[4]arene-bis(crown-6-ether) for selective recognition of thallium(I).

A new fluorogenic, dansyl group-containing derivative of 1,3-alternate calix[4]arene-bis(crown-6-ether) provides optical recognition of Tl+ with selectivity over many other metal cations, including Na+, K+, Ca2+, Ag+, Hg2+ and Pb2+, and embodies the first example of a calixarene-based fluorescent Tl+-chemosensor.

Structural toxicity relationship of 4-alkoxyphenols' cytotoxicity towards murine B16-F0 melanoma cell line.

PURPOSE: The aim of this study was to identify phenolic agents that could form quinone reactive intermediate metabolites in melanocytes in order to be effective as anti-melanoma agents; but were not metabolized by liver P450 metabolizing enzymes in order to have minimal toxicity towards the liver. METHODS: Tyrosinase, an enzyme present abundantly in melanocytes was selected as a molecular target for the treatment of malignant melanoma. Ten alkoxyphenols were investigated for their metabolism by tyrosinase/O2, rat liver P450 microsomal/NADPH/O2 metabolizing systems and for their toxicity towards B16-F0 melanoma cells. RESULTS: All the alkoxyphenols showed a dose- and time-dependent toxicity towards B16-F0 cells except 2-iso-propoxyphenol. 4-n-hexyloxyphenol demonstrated the greatest toxicity towards B16-F0 cells while minimally depleting glutathione in microsomal preparations at its calculated LC10 and LC50 lethal concentrations for B16-F0. At 100 microM concentrations, 4-t-butoxyphenol showed the lowest amount of glutathione depletion by microsomal P450 system. Alkoxyphenols with at least two alkyl groups derivatized at alpha carbon of alkoxy group showed minimal rates of metabolism by tyrosinase/O2 metabolizing system. A quantitative structural toxicity relationship equation was also derived, LogLC50(mM)= -0.265(+/-0.064)LogP + 2.482(+/-0.179). CONCLUSIONS: 4-n-hexyloxy-phenol was identified as a potential lead anti-melanoma agent against B16-F0 melanoma cells with minimal metabolism by rat liver P450 microsomal preparation.

Evaluation of alkali and alkaline earth metal cation selectivities of lariat ether amides by electrospray ionization mass spectrometry.

Lariat ethers with pendant amide groups have shown promise as new ion sensors because of their selectivity towards particular metal ions. In this study we report alkali and alkaline earth metal binding selectivities of dibenzo-16-crown-5 and fifteen dibenzo-16-crown-5 lariat ether amides (LEAs) as determined by electrospray ionization mass spectrometry (ESI-MS). Additionally, the influence of the acid/base nature of the solution on metal cation selectivity is investigated. The validity of using ESI-MS for determination of selectivities is established by analogous experiments using hosts with known binding constants for the same metal cations and solvent systems. Collisionally activated dissociation (CAD) is used to evaluate the influence of the alkali metal cation binding on the fragmentation of the LEAs.

New Proton-Ionizable Lariat Ethers with Picrylamino-Type Side Arms and Their Alkali Metal Salts. Synthesis and Structural Studies(1).

Twelve novel proton-ionizable dibenzo lariat ethers with picrylamino-type sidearms attached to the central carbon of a three-carbon bridge have been prepared in high yields by a three-step synthesis from the lariat ether alcohols via the corresponding lariat ether mesylates and amines. Structural studies conducted in solution by (1)H NMR spectroscopy and in the solid state by X-ray diffraction show that the picrylamino-type lariat ethers are preorganized for metal ion complexation with the sidearms oriented toward the macrocyclic polyether cavities due to intramolecular NH.O bonding. Structural investigations of the alkali metal salts of representative ionized picrylamino-lariat ethers in solution demonstrate cooperative coordination of the metal cation by the macrocyclic polyether unit and the ionized sidearm that serves as the counterion with the negative charge localized on the one of o-nitro groups. In the Li(+) salt of ionized sym-(picrylamino)dibenzo-14-crown-4, this places the aromatic ring of the sidearm perpendicular to the plane of the four ring oxygens.

Rationally designed fluorescence 'turn-on' sensor for Cu2+.

A rationally designed, coumarin-based fluorescent sensor imino-coumarin (IC) displays high selectivity for Cu(2+) over a variety of competing metal ions in aqueous solution with a significant fluorescence increase. DFT/TDDFT calculations support that the fluorescence 'turn-on' of IC originates from blocking the electron transfer of the nitrogen lone pair upon complexation with Cu(2+). IC was successfully applied to microscopic imaging for detection of Cu(2+) in LLC-MK2 cells (in vitro) and several living organs (in vivo).

Effect of cation symmetry on the morphology and physicochemical properties of imidazolium ionic liquids.

In this paper, the morphology and bulk physical properties of 1,3-dialkylimidazolium bis{(trifluoromethane)sulfonyl}amide ([(C(N/2))(2)im][NTf(2)]) are compared to that of 1-alkyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(N-1)C(1)im][NTf(2)]) for N = 4, 6, 8, and 10. For a given pair of ionic liquids (ILs) with the same N, the ILs differ only in the symmetry of the alkyl substitution on the imidazolium ring of the cation. Small-wide-angle X-ray scattering measurements indicate that, for a given symmetric/asymmetric IL pair, the structural heterogeneities are larger in the asymmetric IL than in the symmetric IL. The correlation length of structural heterogeneities for the symmetric and asymmetric salts, however, is described by the same linear equation when plotted versus the single alkyl chain length. Symmetric ILs with N = 4 and 6 easily crystallize, whereas longer alkyl chains and asymmetry hinder crystallization. Interestingly, the glass transition temperature is found to vary inversely with the correlation length of structural heterogeneities and with the length of the longest alkyl chain. Whereas the densities for a symmetric/asymmetric IL pair with a given N are nearly the same, the viscosity of the asymmetric IL is greater than that of the symmetric IL. Also, an even-odd effect previously observed in molecular dynamics simulations is confirmed by viscosity measurements. We discuss in this paper how the structural heterogeneities and physical properties of these ILs are consistent with alkyl tail segregation.

Sorption of heavy metal ions by silica gel-immobilized, proton-ionizable calix[4]arenes.

Silica gel-immobilized, di-ionizable calix[4]arenes are employed as stationary phases in ion-exchange chromatography for selected heavy metal ions. Sorption efficiencies for Pb(2+) are dependent on the structure of the calix[4]arene ligand and the linker that joins the ligand to the silica gel, as well as the acidity of the sample solution. Although the resins exhibit only poor sorption of Cd(2+), they are found to be scavengers for Hg(2+). Competitive sorption studies are conducted with selected resins.

Chromofluorescent indicator for intracellular Zn2+/Hg2+ dynamic exchange.

The fluorescence of NABQ increases remarkably in the presence of Zn(2+) and is quenched by Hg(2+). As shown by confocal imaging, NABQ-Zn(2+) can penetrate cells, where the bound Zn(2+) is exchanged for Hg(2+). This results in the concomitant export of Hg(2+) from the cells, showing that NABQ can act as a Zn(2+) carrier and as a Hg(2+) extracting agent in living cells.