Hidekazu Miyaji

Highly cooperative ion-pair recognition of potassium cyanide using a heteroditopic ferrocene-based crown ether–trifluoroacetylcarboxanilide receptor

A heteroditopic receptor having crown ether and trifluoroacetylcarboxanilide groups selectively recognizes both potassium and cyanide ions in acetonitrile with an association constant of as high as Ka = 1.9 x 10(7) M(-1) through a highly cooperative ion-pair interaction, resulting in two orders of magnitude enhancement in the binding affinity.

A ditopic ferrocene receptor for anions and cations that functions as a chromogenic molecular switch

A ferrocene-based ditopic receptor containing a urea and a benzocrown ether unit shows a remarkable colour switching (ON-and-OFF) function induced by anion and cation recognition.

Functionalized calix[4]pyrroles

The synthesis and properties of a number of functionalized calix(4)pyrroles are described. To date, two generalized preparative approaches have been pursued. The first involves modifying the basic pyrrole-plus-ketone synthesis of calix(4)pyrrole by using modified precursors or by co-condensing more than one ketone with pyrrole. The second approach relies on the reaction of a pre-formed calix(4)pyrrole with an electrophile. In both cases, the resulting species can be subject to further manipulation. In this way a range of structures, including ones bearing ancillary recognition subunits, electro- or photochemical reporter groups, and/or water solubilizing substituents may be obtained. Solid supports bearing calix(4)pyrroles may also be produced in this way.

A ‘building block’ approach to functionalized calix[4]pyrroles

Abstract Iodocalix[4]pyrrole 2 and trimethylsilylethynylcalix[4]pyrrole 3 are key intermediates en route to the preparation of the alkynyl-substituted calix[4]pyrrole system 4 . This latter species, in turn, provides a versatile precursor that can be used to prepare a range of arylalkynyl-functionalized calix[4]pyrroles (viz . , 5 – 9 ) by reacting with an appropriate aryl iodide under Sonogashira conditions (i.e., in the presence of tetrakis(triphenylphosphine)palladium(0)). Significant red-shifts in the λ max values and broadenings of the absorption peaks are seen in the UV–vis spectra of systems 6 and 7 upon addition of anions ( e.g ., F − , Cl − , H 2 PO 4 − ) in CH 2 Cl 2 , a finding that leads to the suggestion that these or other analogous systems could find application as anion sensors.

Calix[4]pyrrole dimers bearing rigid spacers: towards the synthesis of cooperative anion binding agents

Abstract Calix[4]pyrrole dimers ( 2 , 5 , and 6 ), potential hosts for anionic guests, were synthesized by a procedure involving a palladium(0) catalyzed C–C bond formation process. In the case of 2 , a dimer linked via a rigid di-ethynyl spacer, a detailed study of carboxylate anion binding was carried out using 1 H NMR spectroscopy. For isophthalate anion, a 1:1 binding stoichometry was observed with this receptor and a much higher association constant was found than for the control monomer, octamethylcalix[4]pyrrole. These findings are ascribed to cooperative binding. Consistent with this conclusion was the finding that, for phthalate and benzoate anions, 1:2 (host:guest) binding stoichometries and lower association constants were recorded than with isophthalate anion. The control compound, octamethylcalix[4]pyrrole, showed a 1:1 binding stoichometry and a much lower association constant than dimer 2 , not just with isophthalate but also phthalate and benzoate anions.

Anthracene-linked calix[4]pyrroles: fluorescent chemosensors for anions

Fluorescent anthracene–calix[4]pyrrole conjugates 2, 4 and 5 have been synthesized; these receptors can detect the presence of anions (e.g. F–, Cl–, H2PO4–) by a significant quenching of their fluorescence.

Bis(amidopyridine)-linked calix 4 arenes: a novel type of receptor for dicarboxylic acids

Calix[4]arenes 1 and 2, functionalised on their upper rim with amidopyridine groups, have been synthesised. In the case of 1, a detailed binding study with a range of aliphatic and aromatic dicarboxylic acids has been carried out using H-1 NMR spectroscopy. The binding affinities are largely dependent upon the length of the alkyl spacer group, with the highest binding constant observed for dodecanedioic acid. The X-ray crystal structures of 1 and 2 reveal chain structures formed through intermolecular hydrogen bonds between amidopyridine moieties.

ENERGY TRANSFER IN A PORPHYRIN CHELATE ASSEMBLY

Abstract Energy transfer among isoenergetic pigments, three oxinyl-substituted free-base porphyrins in an octahedral chelate Ga(III) complex, has been studied by the femtosecond fluorescence up-conversion technique. The anisotropy decay of the complex has a fast component of ∼10 ps which is assigned to the energy transfer between the nearest porphyrin units in the complex. The anisotropy decay of the monomer (oxinyl-substituted porphyrin) is much slower and reflects monomer rotational dynamics in solution with decay times of 50 and ∼200 ps in dichloromethane.

Mono Halogen Substituted Calix[4]pyrroles: Fine-tuning the Anion Binding Properties of Calix[4]pyrrole

Abstract Single halogen atom (i. e. I, Br, Cl and F) substituted calix[4]pyrroles, compounds 2, 3, 4 and 5, were synthesized. Studies of these systems reveal that replacement of a single β-pyrrolic hydrogen atom can increase the anion binding ability of calix[4]pyrroles for a variety of anions (e. g. Cl−, Br−, H2PO4 − and HSO− 4) relative to normal non-halogen substituted calix[4]pyrrole 1. In the case of chloride anion, the expected relative affinity sequence of 5 > 4 > 3 > 2 was observed. This was not found to be true for Br−, H2PO− 4, and HSO− 4. Here, the chlorine substituted calix[4]pyrrole 4 was found to display a slightly higher affinity in the case of each anion than the fluorine-bearing derivative 5. This was rationalized in terms of intermolecular NH … F hydrogen bonding interactions being present in CD2Cl2 solutions of 5. Support for this latter conclusion came from concentration and temperature-dependent NMR spectroscopic studies. A matched set of mono halogen substituted calix[4]pyrroles was used to study in detail, the extent to which halogen substituents may be used to fine-tune the anion binding properties of calix[4]pyrroles.

Selective electrochemical sensing of acidic organic molecules via a novel guest-to-host proton transfer reaction

Ferrocene-containing amidopyridine receptors bind carboxylic acids and the amino acid phenylalanine in acetonitrile via a novel proton transfer process that enables guests to be electrochemically sensed by positive shifts in the ferrocene-centred redox potentials.