Shunichi Aikawa

Colorimetric detection of oxalate in aqueous solution by a pyrogallol red‐based Cu2+ complex

The pyrogallol red (PR)-based Cu2+ complex was proven to be an effective and selective colorimetric chemosensing ensemble for recognition of oxalate over other anions in a perfect aqueous solution. The addition of oxalate to the PR-Cu2+ complex resulted in a colour change from purple to orange colour due to the regeneration of PR by the chelation of oxalate with Cu2+ , while other anions did not induce any significant colour change. Moreover, it was revealed that no obvious interference was observed during the titrations with oxalate into each other anion. Therefore, the PR-Cu2+ complex can be used as a simple and practical colorimetric chemosensor for detecting oxalate.

Colorimetric chemosensor based on a carminic acid and Pb 2+ complex for selective detection of cysteine over homocysteine and glutathione in aqueous solution

We have developed a colorimetric chemosensor for the selective and sensitive detection of Cys based on the complex (CA-2Pb2+) between a commercially available natural organic dye, carminic acid (CA) and Pb2+ in pure aqueous solution at physiological pH. The addition of Cys to the CA-2Pb2+ solution resulted in a distinct color change from purple to red together with a remarkable absorption spectral change by the restoration of CA through a displacement mechanism with formation of the Cys-Pb2+ complex, whereas other amino acids and glutathione induce no or minimal spectral and color changes. Moreover, the other amino acids and GSH do not affect the detection ability of CA-2Pb2+ for Cys. The reversibility even through several cycles was established for practical applications. The results indicate that CA-2Pb2+ may be useful as a potential colorimetric and naked-eye chemosensor for Cys over Hcy and GSH in aqueous solution.

Colorimetric chemosensor for Fe2+ and Fe3+ based on a ternary mixture of an anionic dye, a cationic polyelectrolyte, and a metal chelator in aqueous solution

A new colorimetric chemosensor based on a simple ternary mixture of an anionic dye, pyrogallol red (PR), a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), and a metal chelator, N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) for the colorimetric detection of Fe2+ and Fe3+ has been developed in an aqueous solution buffered at pH 5. Upon addition of Fe2+ or Fe3+ to the mixture, the absorption spectra showed a bathochromic shift; correspondingly, the solution color changed from red to blue, whereas other metal ions basically resulted in insignificant spectral and color changes. From the competitive experiments, no obvious interferences for the colorimetric detection of Fe2+ and Fe3+ were observed in the presence other metal ions. The results indicated that the mixture could be used as a potential Fe2+ and Fe3+ colorimetric and naked eye chemosensor in aqueous media. This research demonstrates that the ternary ensemble consisted of an organic dye, an oppositely charged polyelectrolyte, and a metal chelator is a versatile and convenient tool for the facile preparation of a novel chemosensor system.

Colorimetric Determination of Pb 2+ in Perfect Aqueous Solution Using Carminic Acid as a Selective Chemosensor

The commercially available natural organic dye, carminic acid (CA), an anthraquinone derivative bearing hydroxyl and carboxyl groups as recognition sites was found to be a colorimetric probe for Pb2+ in perfect aqueous solution under neutral conditions with specific selectivity and high sensitivity. Upon addition of Pb2+, the absorption maximum of CA showed a large red shift, and the resulted color change from red to purple could be easily identified even by the naked eye. The chemical stoichiometric ratio between CA and Pb2+ was determined to be 1:2 through Job plot, Pb2+ titration, and kinetic experiments. Moreover, other environmental relevant metal ions induced no or minimal spectral and color changes. The reversibility of Pb2+ to CA with EDTA even through several cycles was established for practical applications. The results indicated that CA can be a good candidate for simple, convenient and reversible colorimetric detection of Pb2+ in aqueous solution even though it was hard to be applied to determine Pb2+ on the water testing by US EPA.

Exploring an Artificial Metabolic Route in Fusarium sporotrichioides: Production and Characterization of 7-Hydroxy T-2 Toxin

An artificial metabolic route to an unnatural trichothecene was designed by taking advantage of the broad substrate specificities of the T-2 toxin biosynthetic enzymes of Fusarium sporotrichioides. By feeding 7-hydroxyisotrichodermin, a shunt pathway metabolite of F. graminearum, to a trichodiene synthase-deficient mutant of F. sporotrichioides, 7-hydroxy T-2 toxin (1) was obtained as the final metabolite. Such an approach may have future applications in the metabolic engineering of a variety of fungal secondary metabolites. The toxicity of 7-hydroxy T-2 toxin was 10 times lower than that of T-2 toxin in HL-60 cells.