Itaru Hamachi

Sugar sensing utilizing aggregation properties of a boronic-acid-appended porphyrin

Abstract It was shown that monosaccharides can be sensitively detected utilizing aggregation properties of a boronic-acid-appended porphyrin. Since the magnitude of the spectral change is correlated with the association tendency between sugars and boronic acids, the origin of the spectral change is related to the increase in the hydrophilicity in the sugar-binding site.

Synthesis, metal-binding properties and polypeptide solubilization of ‘crowned’ arborols

The first dendritic crown ether polymers (‘crowned’ arborols: G1, G2 and G3) have been synthesized and characterized. The convergent synthetic method was found to be more convenient than the divergent synthetic method. The building block in the branch was prepared from N-benzyloxycarbonyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane and 3,5-bis(ethoxycarbonylmethoxy)benzoyl chloride. Since the basic repeating unit is the amino dicarboxylic acid, one can utilize the methods developed for peptide synthesis. Final products were obtained in moderate yields by coupling of each generational fragment with a core (benzene-1,3,5-tricarbonyl trichloride) followed by reduction of all amide linkages to tertiary amine linkages by borane–dimethyl sulfide. The complexation ability of these ‘crowned’ arborols was estimated by two-phase solvent extraction of alkali picrate salts. We found that some of these arborols can solubilize proteins in organic solvents.

SINGLE- OR DUAL-MODE SWITCHING OF SEMISYNTHETIC RIBONUCLEASE S' WITH AN IMINODIACETIC ACID MOIETY IN RESPONSE TO THE COPPER(II) CONCENTRATION

Ribonuclease S′ bearing iminodiacetic acid as a metal-bindingsite was designed and semisynthesized by self-assembly of native S-protein with chemically modified S-peptide. Rationally designed incorporation of unnatural iminodiacetic acid groups as transition metal receptors can confer the dual mode of response to a metal cation (stabilization/destabilization, and thus activation/deactivation) with regard to the structure and activity of an enzyme (see diagram).

Ru(bpy)3-based artificial receptors toward a protein surface: selective binding and efficient photoreduction of cytochrome c

The binding properties of a series of Ru(bpy)3 complexes to cytochrome c are described; these compounds act as selective cytochrome c receptors and one derivatie is shown to be a photodriven modulator of the cytochrome c redox state.

Sugar sensing utilizing aggregation properties of boronic-acid-appended porphyrins and metalloporphyrins

It has been shown that saccharides in water can be sensitively detected by a boronic-acid-appended porphyrin (1) and its metal complexes (2M2+). The idea is based on the phenomenon that absorption and fluorescence spectra of porphyrins change sensitively in response to a shift in the aggregation–deaggregation equilibrium and that the self-association of saccharides with boronic acids in water affects this equilibrium. Among four monosaccharides tested in detail, the spectral change occurs in the order D-fructose > D-arabinose > D-mannose > D-glucose. In 2M2+ the saccharide-binding process is detectable visually through the colour change. The saccharide-induced fluorescence changes are very large because 1 and 2M2+ aggregates are almost non-fluorescent whereas monomeric 1 and 2M2+ generated by saccharide-binding are strongly fluorescent. This is a novel method for sugar sensing, useful in an aqueous system.

Metal-induced conformational changes in calix[n]arenes can control the electron-transfer efficiency between porphyrin and [60]fullerene in an on-off manner

Calix[n]aryl esters (1n:n=4 and 6) bearing a Zn(II)·porphyrin group as a fluorophore and a [60]fullerene group as a quencher on the lower rim were synthesized. In 16 a metal-induced 1,2,3-alternate-to-cone conformational change shortened the distance between these two groups and the electron-transfer efficiency was sharply increased. In 14 the electron-transfer efficiency was slightly increased in spite of a metal-induced rotation of the carbonyl groups which enlarges the distance between these two groups. These are novel responsive systems to control the electron-transfer efficiency between porphyrin and [60]fullerene.

Design and semisynthesis of spermine-sensitive ribonuclease S'

Spermine-sensitive stabilization of semisynthetic Ribonuclease S was successfully carried out by sequence specific incorporation of a poly-anion domain into alpha-helix region of S-peptide.

X-ray crystallographic studies of a Mn(II)-bridged biscalix[4]arene with a large inner cavity

Abstract A complex isolated from a mixture of tetrasodium 5,11,17,23-tetra-sulfonatocalix[4]arene-25,26,27,28-tetrol and Mn(II) has been analyzed by X-ray crystallography. The crystal packing diagram featured a clay-like bilayer structure as reported previously for the analogous crystals. Interestingly, Mn(II) ions present in the hydrophilic layer cross-link two hydrophobic layers through coordination to the sulfonato groups. Because of this complex formation the repeat unit of the layer (12.1 A) is shorter than those for analogous systems (13.7 –15.0 A). The structure features a Mn(II)-bridged biscalix[4]arene with a large inner cavity. X-Ray crystallographic and ESR spectral data show that Mn(II) ions adopt a distorted octahedral coordination geometry with two sulfonato groups occupying the cis coordination. This is a novel coordination mode for a metal-bridged biscalix[4]arene in the solid state.

Pyrenylboronic acids as a novel entry for photochemical DNA cleavage: diradical-forming pyrene-1,6-diyldiboronic acid mimics the cleavage mechanism of enediyne antitumor antibiotics

Pyren-1-ylboronic acid 4 and pyrene-1,6-diyldiboronic acid 5 are bound to supercoiled double-strand circular DNA plasmid ColE1 (colDNA) and effect its efficient photocleavage under visible light irradiation. Mechanistic studies show that the cleavage occurs according to the radical mechanism. The cleavage activity of monoacid 4 could be suppressed by the addition of D-fructose because of boronic acid–saccharide complexation. Diacid 5 is bound to colDNA more strongly than is monoacid 4 and effects its efficient photocleavage to yield Form III. The results show that diradical-forming diacid 5 is able to cleave DNA at two reaction sites, mimicking the cleavage mechanism of enediyne antitumor antibiotics.

PYRENYLBORONIC ACID AS A NOVEL ENTRY FOR PHOTOCHEMICAL DNA CLEAVAGE

Abstract 1-Pyrenylboronic acid is bound to supercoiled double strand circular DNA plasmid ColE1 and effects its efficient photocleavage under visible light irradiation: the cleavage reaction, which occurs according to the radical mechanism, can be suppressed by the addition of D-fructose because of boronic acid-saccharide complexation.