Boronic acid fluorophore/beta-cyclodextrin complex sensors for selective sugar recognition in water.

A novel boronic acid fluorophore 1/beta-cyclodextrin (beta-CyD) complex sensor for sugar recognition in water has been designed. The probe 1 bearing pyrene moiety as a fluorescent signal transducer exhibits no fluorescence emission, due to its aggregation in water containing 2% DMSO; however, the addition of beta-CyD to this solution largely changes UV-vis and fluorescence spectra of 1 by forming an inclusion complex with beta-CyD, and an efficient fluorescence emission response of 1/beta-CyD complex upon sugar binding is found to be obtained at pH 7.5. The pH-fluorescence profile of the 1/beta-CyD complex reveals that the boronate ester formation with fructose induces the apparent pKa shift from 7.95+/-0.03 in the absence of fructose to 6.06+/-0.03 in the presence of 30 mM fructose, resulting in the fluorescence emission response under the neutral condition. The spectral properties of 1 in 95% methanol:5% water (v/v), as well as the fluorescence quenching study of 1-methylpyrene with 4-methoxycarbonylphenyl-boronic acid 2, demonstrate that the response mechanism is based on the photoinduced electron transfer (PET) from the pyrene donor to the acid form of phenylboronic acid acceptor in 1, and thus, the proton dissociation of phenylboronic acid induced by sugar binding inhibits the PET system while increasing the fluorescence intensity of the pyrene moiety. To evaluate the binding ability and selectivity of the 1/beta-CyD complex for monosaccharides in water, the response equilibria have been derived. The 1:1 binding constants of the 1/beta-CyD complex obtained from the equilibrium analysis are in the order: D-fructose (2515+/-134 M(-1)) >> L-arabinose (269 +/- 28 M(-1)) > D-galactose (197+/-28 M(-1)) > D-glucose (79+/-33 M(-1)), which is consistent with the binding selectivity of phenylboronic acid.

Selective potassium ion recognition by benzo-15-crown-5 fluoroionophore/gamma-cyclodextrin complex sensors in water.

Three fluoroionophores Cn (n = 1, 3, 5), in which the crown ether unit and pyrenyl moiety are connected by a -(CH2)n- spacer, have been used to construct supramolecular Cn/gamma-cyclodextrin (gamma-CyD) complexes for alkali metal ion sensing in water. The Cn (n = 3, 5) are found to selectively form 2:1 complexes with K+ in the presence of gamma-CyD and exhibit the pyrene dimer emission in water. Equilibrium analysis of the C3/gamma-CyD complex reveals that the observed dimer emission arises from a 2:1:1 complex of C3 with K+ and gamma-CyD. In the absence of K+, the fluorescence lifetimes for the dimer species ((C3)2CyD and (C3)2(CyD)2) and the monomer species (C3CyD and C3(CyD)2) are 13-18 and 130-180 ns, respectively. Upon addition of 0.10 M KCI, a rising component corresponding to pyrene excimer formation is observed at the dimer emission region. For the C3/gamma-CyD complex, the apparent association constant for K+ of (3.8 +/- 1.3) x 10(9) M(-2) is only slightly affected by the presence of Na+. Although the C5/gamma-CyD complex shows high sensitivity for K+, the selectivity for K+ over Na+ is lower than that of the C3/gamma-CyD complex. In contrast, fluoroionophore C1 with the shortest methylene spacer exhibits no response for alkali metal cations in the presence of gamma-CyD. These results demonstrate that the response function of supramolecular Cn/gamma-CyD complexes is strongly affected by the methylene spacer length of Cn. The highest K+ selectivity is obtained for the C3/gamma-CyD complexes in water.

Molecular design of lipophilic disalicylic acid compounds with varying spacers for selective lead(II) extraction.

Lipophilic disalicylic acids 5,5'-decyl-2,2'-[1,2-ethanediylbis(oxy)]bisbenzoic acid (1), 5,5'-decyl-2,2'-[1,3-propanediylbis(oxy)]bisbenzoic acid (2), 5,5'-decyl-2,2'-[oxybis(1,2-ethanediyl-oxy)]bisbenzoic acid (3), 3,5-bis[2'-(2''-carboxyphenoxy)ethyl]-4-oxahexacyclo-[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane (4), and 1,3-bis[2'-(2''-carboxyphenoxy)ethyl]adamantane (5) are evaluated as selective Pb(II) extractants. The solvent extraction of Pb(II) and of Cu(II) from buffered aqueous solutions of varying pH into chloroform by ligands 1-5 is examined in relation to the molecular structure of the dicarboxylic acid extractant. Ligand 1, with an ethylene spacer between two lipophilic salicylic acid units, exhibits excellent extraction selectivity for Pb(II) over Cu(II). Lengthening the spacer in ligands 2 and 3 diminishes both the extraction efficiency and selectivity. Ligands 4 and 5, with rigid spacer units, show significant reductions in both Pb(II) and Cu(II) extraction. Slope analysis reveals that ligand 1 reacts in a 2:1 stoichiometry with Pb(II) in extraction, which differs from the 1:1 stoichiometries for 2 and 3. The differences in the half extraction pH (DeltapH(1/2)) values for Pb(II) and Cu(II) extraction are 1.29, 0.49, and 0.48 for 1-3, respectively.

Lead-selective poly(vinyl chloride) membrane electrodes based on acyclic dibenzopolyether diamides.

Lipophilic acyclic dibenzopolyether diamides, 12 kinds, have been designed to prepare solvent polymeric membrane ion-selective electrodes (ISEs) for Pb(2+). The ionophores include 1,5-bis[2-(N,N-dialkylcarbamoylmethoxy)phenoxy]-3-oxapentanes1-4, 1,5-bis[2-(N,N-dialkylcarbamoylpentadecyloxy)phenoxy]-3-oxapentanes 5-8, and 1,2-bis[2-(2'-N,N-dialkylcarbamoylpentadecyloxy)phenoxy]ethanes 9-12. Linear response concentration range of the ISE based on 9 is 3 x 10(-2) - 1 x 10(-6) M of Pb(2+) (average slope = 28.5 mV decade(-1)). Potentiometric selectivities of the ISEs based on 1-12 for Pb(2+) over other heavy metal cations, alkali metal cations, and alkaline earth metal cations have been assessed. These ISEs exhibit remarkably high selectivities for Pb(2+) relative to heavy metal cations, such as Cu(2+), Fe(2+), and Ni(2+), the selectivity coefficients (K(Pot)(Pb,Cu)) being 5 x 10(-5) - 6 x 10(-5) for 1-4 and ca. 6 x 10(-4) for 9. For the Pb(2+) selectivities over alkali metal cations, such as Na(+) and K(+), 9 which has an ethylene glycol spacer and a N,N-diethyl group is superior to other dibenzopolyether diamide ionophores 1-8 and 10-12.

Selective Liquid Membrane Transport of Lead(II) by an Acyclic Polyether Dicarboxylic Acid Ionophore.

The effects of the chain structure and substitutents in six acyclic polyether dicarboxylic acids and one acyclic polyether carboxylic acid upon the efficiency and selectivity of pH-driven Pb(2+) transport in a bulk chloroform membrane system have been assessed. Among the carriers, 1,2-bis[2-(o-carboxyphenoxy)ethoxy]-4-tert-butylbenzene (1) is found to exhibit high selectivity for transport of Pb(2+) compared with alkali metal cations and a variety of other divalent metal ion species. Ionophore 1 also extracts Pb(2+) from aqueous solution into chloroform with the loss of two protons. A 1:1 complex of Pb(2+) with di-ionized 1 was isolated.

Immobilization of crown ether carboxylic acids on silica gel and their use in column concentration of alkali metal cations from dilute aqueous solutions.

Eight crown ethers with pendent carboxylic acid groups are immobilized on silica gel and utilized for column concentration of alkali metal cations from dilute aqueous solutions. The column concentration selectivity and efficiency are found to be strongly influenced by (1) the cavity size of the crown ether unit, (2) conformational positioning of the proton-ionizable side arm with respect to the crown ether cavity, and (3) capping of residual silanol surface groups with trimethylsilyl functions. By use of a chromatographic stripping technique, selective column concentration of Na(+), K(+), (Rb(+) and Cs(+)), and Cs(+) by different functionalized silica gels has been achieved.

Influence of medium polarity upon selectivity and efficiency of alkali metal cation sorption by polyether carboxylic acid resins.

The influence of medium polarity upon competitive sorption of alkali-metal cations from aqueous and aqueous methanolic solutions by the polymethacrylic acid resin Amberlite CG-50, two acyclic polyether carboxylic acid resins, and six sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid resins has been investigated. Addition of methanol was found to strongly depress the selective Li(+) sorption of CG-50 and one of the acyclic polyether carboxylic acid resins. Enhancement of metal ion-crown ether interactions as the percentage of methanol in the medium was increased accentuates the Na(+) sorption selectivity for the lariat ether carboxylic acid resins. The highest Na(+) sorption selectivity was obtained for sym-(alkyl)-dibenzo-16-crown-5-oxyacetic acid resins with ethyl and propyl groups in 80% methanol-20% water.

Sorption and permeation behaviour of metal thiocyanate complexes on cellulose acetate polymers.

Various metal thiocyanate complexes in aqueous solution were sorbed on solid cellulose acetate polymers. The sorption selectivity increased in the order Zn(2+) >> Fe(3+) >> Cu(2+) >> Co(2+) >> Ni(2+). The sorption behaviour followed a Langmuir-type adsorption isotherm, and the maximum adsorption capacity was 6.1 x 10(-5) mole of complex per g of polymer under optimum conditions. The zinc species sorbed appear to be NH(4)Zn(H(2)O)(SCN)(3) or (NH(4))(2)Zn(SCN)(4) according to analysis of the sorption equilibrium. The ion-association species formed by the complex zinc anion and the ammonium ion was supposed to be sorbed (or "extracted") onto the polymer matrix. As an application of sorption of metal complexes, a new hyperfiltration process was proposed for selective separation of metal ions. Thus, a mixture of metal thiocyanate complexes was hyperfiltered through cellulose acetate membranes. Permeation of certain metal complexes was preferred, and the selectivity was found to be similar to the sorption selectivity. These findings lead to a generalized idea that hyperfiltration separation of ionic species, particularly anionic metal complexes, can be attained by using polymer membranes which selectively adsorb or extract such ionic species as ion-association complexes onto the polymer matrix.