Conformational control of selectivity and stability in hybrid amide/urea macrocycles

The anion-binding properties of two similar hybrid amide/urea macrocycles containing either a 2,6-dicarboxamidophenyl or a 2,6-dicarboxamidopyridine group are compared. Significant differences in anion affinity and mode of interaction with anions are attributed to the presence of intramolecular hydrogen bonds in the pyridine system. In fact, remarkably, the phenyl macrocycle undergoes amide hydrolysis under neutral conditions in DMSO/water. The anion binding abilities of the receptors are compared to those of acyclic analogues of the macrocycles that show that the phenyl receptor behaves in a similar fashion to acyclic urea-containing receptors (i.e., showing little selectivity amongst oxo anions), whilst the pyridine-containing receptor shows a high affinity and selectivity for carboxylates.     

Reversible terbium luminescent polyelectrolyte hydrogels for detection of H2PO4(-) and HSO4(-) in water

Polyelectrolyte gels are promising soft networks that can accommodate various guest species and retain liquid nature. The incorporation of two novel silica based terbium complexes (Tb(a)(2) and Tb(b)(2)) in the poly(acrylamide) host can exhibit the characteristic green terbium emission in water. More interestingly, we noted that these target materials can selectively recognize H(2)PO(4)(-) (detection limit 10(-5) M) and HSO(4)(-) (detection limit 5 × 10(-5) M) compared with other anions, such as F(-), Cl(-), Br(-), and I(-). The fluorescence intensity ratios against both anions (H(2)PO(4)(-) and HSO(4)(-)) concentration all follow the simple linear equations by the least-squares fitting method.     

Anion and carboxylic acid binding to monotopic and ditopic amidopyridine macrocycles

Binding of inorganic anions, carboxylic acids, and tetraalkylammonium carboxylates by macrocyclic compounds of different size was studied by NMR in DMSO-d6. It has been shown that at least a 15-membered ring is necessary for successful recognition of fluoride. Larger macrocycles were shown to bind HSO4(-), H2PO4(-), Cl(-), and carboxylic acid salts. Effects of binding topicity are discussed. The 30-membered macrocycles 4 and 4m selectively bind substrates that are size- and shape-complementary: maximum binding is observed for dicarboxylic acids and dicarboxylates with four-carbon chains, and the binding constant for association of fumaric acid and 4 is ca. 5 orders of magnitude higher than that of maleic acid. The 30-membered macrocycle 4m showed selectivity toward alpha-ketocarboxylic acids. Secondary amino groups were not crucial for binding of fluoride to the macrocycles; however, they proved to be very important for selectivity and strength of carboxylic acid binding. The X-ray structure of the adduct of 4 and nitrobenzoic acid confirmed the guest H-bonding with both the amide and the secondary amino groups of the 30-membered macrocyclic host.     

Mercapto thiadiazole-based sensor with colorimetric specific selectivity for AcO- in aqueous solution

A novel acetate selective anion sensor 3 based on azophenol and mercapto thiadiazole had been designed and synthesized. Sensor 3 behaves a single selectivity and sensitivity in the recognition for AcO(-) anion over other anions such as F(-), Cl(-), Br(-), I(-), H(2)PO(4)(-), HSO(4)(-) and ClO(4)(-) by naked-eyes and UV-vis spectra changes in aqueous solution (H(2)O/DMSO, 5:5, v/v). The color of the solution containing sensor 3 had an obvious change from colorless to orange only after the addition of AcO(-) in aqueous solution while other anions did not cause obvious color change. (1)H NMR titration results revealed that the binding process includes two steps: (i) hydrogen bonding interactions (for small quantities of acetate) and (ii) proton transfer between the sensor 3 and the coordinated anion (for high quantities of acetate). The association constant K(a) was 7.35×10(3) M(-1). The detection limitation of AcO(-) with the sensor 3 was 1.0×10(-6) mol L(-1).     

Imidazolium-based macrocycles as multisignaling chemosensors for anions

A series of structurally novel anion receptors , , and in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1'-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF(6)(-) and Br(-). Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and (1)H NMR spectroscopy. All the receptors showed a special electrochemical response to the F(-) anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F(-) and AcO(-) anions with fluorescence enhancement over various other anions of present interest (Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-)). In addition, for receptor , obvious absorption changes were observed when the H(2)PO(4)(-) anion was added while other anions (F(-), Cl(-), Br(-), I(-), AcO(-), HSO(4)(-)) showed only a minor influence on the UV-vis spectra. (1)H NMR titrations demonstrated that receptors and can bind anions through (C-H)(+)X(-) hydrogen bonds and showed strong affinity and high selectivity for the AcO(-) anion in acetonitrile.     

Nanoscopic assemblies between supramolecular redox active metallodendrons and gold nanoparticles: synthesis,characterization, and selective recognition of H2PO4-, HSO4-, and adenosine-5'-triphosphate (ATP2-) anions

Tri- and nonaferrocenyl thiol dendrons have been synthesized and used to assemble dendronized gold nanoparticles either by the ligand-substitution method from dodecanethiolate-gold nanoparticles (AB(3) units) or Brust-type direct synthesis from a 1:1 mixture of dodecanethiol and dendronized thiol (AB(9) units). The dendronized colloids are a new type of dendrimers with a gold colloidal core. Two colloids containing a nonasilylferrocenyl dendron have been made; they bear respectively 180 and 360 ferrocenyl units at the periphery. These colloids selectively recognize the anions H(2)PO(4)(-) and adenosine-5'-triphosphate (ATP(2)(-)) with a positive dendritic effect and can be used to titrate these anions because of the shift of the CV wave even in the presence of other anions such as Cl(-) and HSO(4)(-). Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). The anion HSO(4)(-) is also recognized and titrated by the dendronized colloid containing the tris-amidoferrocenyl units, because of the progressive shift of the CV wave until the equivalence point. These dendronized colloids can form robust modified electrodes by dipping the naked Pt electrode into a CH(2)Cl(2) solution containing the colloids. The robustness is all the better as the dendron is larger. These modified electrodes can recognize H(2)PO(4)(-), ATP(2)(-) and HSO(4)(-), be washed with minimal loss of adsorbed colloid, and be reused.     

A novel thiourea-based dual fluorescent anion receptor with a rigid hydrazine spacer

[structure: see text] A neutral receptor with a rigid hydrazine spacer, N-p-(dimethylamino)benzamido-N'-phenylthiourea, was prepared, and its dual fluorescence in acetonitrile was found to show response toward the presence of anions such as AcO(-), H(2)PO(4)(-), HSO(4)(-), Br(-), Cl(-), F(-), and ClO(4)(-) with high sensitivity and selectivity toward AcO(-).     

Fluorescent acridine-based receptors for H2PO4(-)

Two new pseudopeptidic molecules (one macrocyclic and one open chain) containing an acridine unit have been prepared. The fluorescence response of these receptors to a series of acids was measured in CHCl(3). Receptors are selective to H(2)PO(4)(-) versus HSO(4)(-), and an even higher selectivity is found over other anions such as Cl(-), Br(-), CH(3)COO(-), and CF(3)COO(-). We show that the macrocyclic receptor is more selective for H(2)PO(4)(-) than the related open chain receptor. The supramolecular interactions of triprotonated receptors with different anions have been modeled in silico and have been studied by different experimental techniques. Optimized geometries obtained by computational calculations agree well with experimental data, in particular fluorescence experiments, suggesting that the selective supramolecular interaction takes places through coordination of the anions to the triprotonated form of the receptor.     

Fluoride-selective colorimetric sensor based on thiourea binding site and anthraquinone reporter

A structurally simple colorimetric sensor, N-4-nitrobenzene-N'-1'-anthraquinone-thiourea (1), for anions was synthesized and characterized by (1)H NMR, ESI mass and IR methods. In acetonitrile, the addition of F(-) changed 1 solution from colorless to yellow. In the presence of other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-), however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F(-)>CH(3)CO(2)(-)>H(2)PO(4)(-)>HSO(4)(-)>Cl(-)>Br(-), which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z-E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH(3)CO(2)(-) and H(2)PO(4)(-), thus leading to a high selectivity and sensitivity for the detection of F(-).     

Missing-link macrocycles: hybrid heterocalixarene analogues formed from several different building blocks

The synthesis and structural characterization of hybrid heterocalix[4]arene analogues containing pyrrole, benzene, methoxy-substituted benzene, and pyridine subunits is described. Macrocycles 1 and 2, examples of calix[2]benzene[2]pyrrole and calix[1]benzene[3]pyrrole systems, respectively, are synthesized by the condensation of pyrrole and an appropriate phenylbis(carbinol). Macrocycles 3 and 7, examples of calix[2]benzene[1]pyridine[1]pyrrole and calix[1]pyridine[3]pyrrole, respectively, are synthesized by the use of a carbene-based pyrrole-to-pyridine ring-expansion procedure. Single-crystal X-ray analysis reveals that compounds 1a, 1b, and 2b adopt 1,3-alternate conformations in the solid state, whereas compounds 3 and 7 display structures that are best described as "flattened partial cones" in terms of their conformation. (Series a refers to pure benzene-derived systems, whereas series b indicates macrocycles containing 5-methoxyphenyl subunits). In the solid state, the methoxy-functionalized macrocycles 1b and 2b, and the chloropyridine-containing macrocycle 7 exist as dimers. In the case of 1a and 7, these compounds interact with neutral solvent in the solid state. The conformations of the macrocycles in solution were explored by temperature-dependent proton NMR and NOESY spectral analysis. At 188 K, macrocycles 1a and 2a adopt flattened 1,3-alternate conformations, whereas macrocycles 3 and 7 exist in the form of flattened partial-cone conformations. Standard proton NMR titration analyses were carried out in the case of macrocycles 1a and 2a, and reveal that at least the second of these systems is capable of binding fluoride and chloride anions in CD(2)Cl(2) solution at room temperature (K(a)=571 and 17M(-1) in the case of 2a and F(-) and Cl(-), respectively).     

Displacement method to develop highly sensitive and selective dual chemosensor towards sulfide anion

By utilizing a displacement method, a macrocyclic compound 1, could report the presence of sulfide anion, with the detection limit of 7.0 × 10(-7) mol/L; moreover, no interference was observed from other anions, including SO(3)(2-), HSO(3)(-), SO(4)(2-), ClO(4)(-), I(-), Br(-), Cl(-), F(-), IO(3)(-), HPO(4)(2-), PO(4)(3-), C(2)O(4)(2-), S(2)O(3)(2-), CO(3)(2-), AcO(-), CN(-) and P(2)O(7)(4-), making compound 1 a new, highly sensitive and selective sulfide anion chemosensor.     

Synthesis,crystal structures,and third-order nonlinear optical properties of a series of ferrocenyl organometallics

Three novel ferrocenyl complexes [Zn(4-PFA)(2)(NO(3))(2)](H(2)O) (1), [Hg(2)(OAc)(4)(4-BPFA)(2)](CH(3)OH) (2), and [Cd(2)(OAc)(4)(4-BPFA)(2)] (3) (4-PFA = [(4-pyridylamino)carbonyl]ferrocene, 4-BPFA = 1,1'-bis[(4-pyridylamino)carbonyl]ferrocene) were prepared, and complexes 1 and 2 were structurally characterized by means of X-ray single-crystal diffraction. In complex 1, the zinc(II) atom is coordinated at a distorted tetrahedral environment by two nitrogen atoms from two 4-PFA moieties and two oxygen atoms from two nitrate anions; [Zn(4-PFA)(2)(NO(3))(2)] units are linked by hydrogen bonds N-H.O and O-H.O forming one-dimensional chains. Complex 2 is a tetranuclear macrocycle compound consisting of two 4-BPFA moieties and two Hg atoms; [Hg(2)(OAc)(4)(4-BPFA)(2)] units form 1-D chains by hydrogen bonds N-H.O as complex 1. Some complexes with 1,1'-bisubstituted pyridine-containing ferrocene ligands have been described, but their crystal data are limited. Compound 2 is the first example of a macrocyclic pyridine-containing ferrocenyl complex. The third-order nonlinear optical (NLO) properties of 4-PFA, 4-BPFA, and complexes 1-3 were determined by Z-scan techniques. The results indicate that all the compounds exhibit strong self-focusing effect. The hyperpolarizability gamma values are calculated to be in the range 1.51 x 10(-)(28) to 3.12 x 10(-)(28) esu. The gamma values are nearly twice as large for complexes 1-3 as for their individual ligands, showing that the optical nonlinearity of the complexes is dominated by the ligands.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 1. Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: a new macrocycle with remarkable electron-deficient properties

A new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py(8)TPyzPzH(2)].2H(2)O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)(2)Py(2)Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV-vis spectra of [Py(8)TPyzPzH(2)] were measured in two nondonor solvents (CHCl(3), CH(2)Cl(2)), a slightly basic solvent (pyridine), and an acidic solvent (CH(3)COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py(8)TPyzPzH(2)] (in CHCl(3), CH(2)Cl(2), and CH(3)COOH) or dianionic [Py(8)TPyzPz](2)(-) (in pyridine). A spectrally monitored titration of [Py(8)TPyzPzH(2)] in CH(2)Cl(2) with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py(8)TPyzPzH(2)] to [Py(8)TPyzPz](2)(-). Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py(8)TPyzPzH(2)] is present in CH(2)Cl(2) while [Py(8)TPyzPz](2)(-) is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py(8)TPyzPzH(2)] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle.     

Anion-free bambus[6]uril and its supramolecular properties

Methods for the preparation of anion-free bambus[6]uril (BU6) are presented. They are based on the oxidation of iodide anion, which is bound inside the macrocycle, utilizing dark oxidation by hydrogen peroxide or photooxidation in the presence of titanium dioxide. Anion-free BU6 was found to be insoluble in any of the investigated solvents; however, it dissolves in methanol/chloroform (1:1) or acetonitrile/water (1:1) mixtures in the presence of the tetrabutylammonium salt of a suitable anion. The association constants with halide ions, BF(4)(-), NO(3)(-), and CN(-), were measured by (1)H NMR spectroscopy. The highest association constant (8.9×10(5) M(-1)) was found for the 1:1 complex of BU6 with I(-) in acetonitrile/water mixture. A number of crystal structures of BU6 complexes with various anions were obtained. The influence of the anion size on the macrocycle diameter is discussed together with an unusual arrangement of the macrocycles into separate layers.     

Anion binding to a ferric porphyrin complexed with per-O-methylated beta-cyclodextrin in aqueous solution

5,10,15,20-Tetrakis(4-sulfonatophenyl)porphinato iron(III) (Fe(III)TPPS) forms a very stable 1:2 complex with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD), whose iron(III) center is located at a hydrophobic cleft formed by two face-to-face TMe-beta-CD molecules. Various inorganic anions (X(-)) such as F(-), Cl(-), Br(-), I(-), N(3)(-), and SCN(-) coordinate to Fe(III)TPPS(TMe-beta-CD)(2) to form five-coordinate high-spin Fe(III)TPPS(X)(TMe-beta-CD)(2), while no coordination occurs with ClO(4)(-), H(2)PO(4)(-), NO(3)(-), and HSO(4)(-). Except for F(-), none of the anions investigated coordinate to Fe(III)TPPS in the absence of TMe-beta-CD due to extensive hydration to the anions as well as to Fe(III)TPPS. The present system shows a high selectivity toward the N(3)(-) anion. The thermodynamics suggests that Lewis basicity, hydrophilicity, and shape of an X(-) anion are the main factors to determine the stability of the Fe(III)TPPS(X)(TMe-beta-CD)(2) complex.     

Radiotracer Study of the Specific Adsorption of Anions on Metal Oxides in Acid Media: An Experimental Approach

The specific adsorption of anions (HSO(4)(-), H(2)PO(4)(-), and Cl(-)) was studied at Fe(2)O(3), ZnO, and CuO surfaces by the radiotracer technique in strongly acidic medium (1 M HClO(4)). A significant specific adsorption of HSO(4)(-) and H(2)PO(4)(-) ions was found in all cases studied while no measurable adsorption of Cl(-) ions was observed. In the cases of ZnO and CuO, the specific adsorption takes place over the course of continuous dissolution of the oxide. Copyright 2000 Academic Press.     

New terphenyl based mercury ensemble for detection of acetate ions in a plasma like system

A new terphenyl based chemosensor 3 has been designed and synthesized. The binding behavior of 3 and its chemosensing ensemble 3-Hg toward various anions (F(-), Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-), CH(3)COO(-), NO(3)(-), N(3)(-), SO(4)(2-), SO(3)(2-), and Cr(2)O(7)(2-)) has been investigated by UV-Vis, fluorescence and NMR spectroscopy. Compound 3 shows a sensitivity for both F(-) and CH(3)COO(-) ions among various anions tested, whereas the ensemble 3-Hg shows a better selectivity for CH(3)COO(-) ions. The ensemble is utilized for CH(3)COO(-) recognition in a blood plasma like system.     

A novel colorimetric sensor of dihydrogen-phosphate based on metal complex between 8-hydroxy quinoline-5-azo-4'-nitrobenzene and cobalt

A novel colorimetric sensor based on 8-hydroxy quinoline-5-azo-4'-nitrobenzene (1) was prepared and used for recognizing anions. 1 and its metal complex (1.Co) were found to show response to anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-), F(-) and dramatic color changes were observed. The selectivity and sensitivity of 1 and 1.Co for sensing anions were different, which was in the order of CH(3)CO(2)(-)>F(-)>H(2)PO(4)(-)>HSO(4)(-) for 1 and H(2)PO(4)(-)>HSO(4)(-)>CH(3)CO(2)(-) approximately F(-) for 1.Co, respectively. In CH(3)CN, sensor 1.Co exhibited excellent specificity toward H(2)PO(4)(-), and the color variety was dependent on the concentration of H(2)PO(4)(-) which was attributed to anion structure and stability of anionic complex (1-anion), metal complex (1-Co) and inorganic complex (Co-anion).     

A bis-guanidine-based multisignaling sensor molecule that displays redox-ratiometric behavior or fluorescence enhancement in the presence of anions and cations

[structure: see text]The guanidine bridge in the new structural motif [3,3]ferrocenophane acts as a dual binding site for anions and metal ions. Sensing of anions (Cl(-), F(-), NO(3)(-), HSO(4)(-), and H(2)PO(4)(-)) takes place by redox-ratiometric measurements, whereas metal ion (Zn(2+), Ni(2+), and Cd(2+)) recognition is achieved by fluorescence measurements.     

Alkyl- and aryl-substituted corroles. 4. Solvent effects on the electrochemical and spectral properties of cobalt corroles

Solvent effects on the electrochemistry and spectroscopic properties of alkyl- and aryl-substituted corroles in nonaqueous media are reported. The oxidation and reduction of six compounds containing zero to seven phenyl or substituted phenyl groups on the macrocycle were studied in four different nonaqueous solvents (CH(2)Cl(2), PhCN, THF, and pyridine) containing 0.1 M tetra-n-butylammonium perchlorate. Dimers were formed upon oxidation of all corroles in CH(2)Cl(2), but this was not the case in the other three solvents, where either monomers or dimers were formed upon oxidation depending upon the solvent Gutmann donor number and the number or location of aryl substituents on the macrocycle. The half-wave potentials were analyzed as a function of the number of aryl substituents on the macrocycle as well as the concentration of added pyridine to PhCN solutions of the compound, and these data were combined with data from the spectroelectrochemistry experiments to determine the stoichiometry of the species actually in solution after the first oxidation or first reduction of each compound. The results of these experiments indicate that reduction of the bispyridine adduct (Cor)Co(III)(py)(2) proceeds via the monopyridine complex (Cor)Co(III)(py) to give in each case the unligated cobalt(II) corrole [(Cor)Co(II)](-). In contrast, pyridine remains coordinated after electrooxidation, and the final product was characterized as [(Cor)Co(III)(py)(2)](+).