Mamoru Kamiya

Photochemical effects of humic substances on the degradation of organophosphorus pesticides

Abstract Photochemical effects of humic substances on the aquatic degradation of organophosphorus pesticides were studied on the basis of photo-induced radical generation abilities of humic substances and the increase percentage of the humin-sensitized photodegradation rate constants relative to those measured in the humin-less system.The increase percentages above stated were enhanced depending on the radical generation abilities of humic substances.Also, the degree of the sensitization effects of humic acids to be expressed by the increase percentages of the rate constants tended to enhance with the decrease in the inherent photodegradation reactivities of pesticides in the humin-less system. This suggests that the sensitization action of humic acids depends on binding affinities of pesticides to the radical generation source of humic acids, as the affinities may hinder the pesticide photodegradation in huminless aquatic systems possibly initiated by any route other than the radical mechanism.

Effects of selected metal ions on photodegradation of organophosphorus pesticides sensitized by humic acids.

Selected metal ions having paramagnetic property were found to exert inhibition effects on aquatic photodegradation of organophosphorus pesticides sensitized by humic acids, according to the increasing order of Cr(III) < Co(II) < Mn(II) < Cu(II). Basic factors dominating the metal-ion effects were clarified on the basis of the fluorescence quenching as well as radical scavenging abilities of metal ions complexed with humic acids.

Effects of cyclodextrins on photodegradation of organophosphorus pesticides in humic water

Cyclodextrin (CyD) effects on photodegradations of organophosphorus pesticides in humic water were monitored on the basis of the increase percentage of the photodegradation rate constant for CyD-containing humic water. Remarkable promotion effects of CyDs were observed in humic water for photo-induced radical generation. The promotion effects could be mainly assigned to the inclusion effects of CyDs to catalyze interactions of pesticides with reactive radicals generated by the humin photosensitizer and inclusion-trapped in CyDs.

Inclusion effects of cyclodextrins on photodegradation rates of parathion and paraoxon in aquatic medium

Abstract Inclusion effects of α-, β- and γ -cyclodextrins on photodegradation rates of parathion and paraoxon were investigated in aquatic medium. The effects were in a characteristic relationship with the inclusion-depth parameters of the pesticides determined by use of the rotational-strength analysis of the circular dichroism induced to the pesticides by inclusion. The inclusion effect of β- cyclodextrin was found to inhibit the photodegradation rate of parathion but to promote that of paraoxon.

Cyclodextrin inclusion effects on photodegradation rates of organophosphorus pesticides

Abstract The inclusion effects of α-, β-, γ-, hexa-2,6-dimethyl α-, and hepta-2,6-dimethyl β-cyclodextrins (CyDs) on the photodegradation of parathion and paraoxon were investigated in methanolic aqueous solution. The above effects of CyDs were in a characteristic relationship with the inclusion depth parameters of the pesticides determined by the rotational-strength analysis of the induced circular dichroism of the inclusion complexes. The inclusion effect of β-CyD was found to inhibit the photodegradation of parathion but to promote that of paraoxon. Basic properties of the CyD inclusion effects were explained in terms of the difference in the degree of proximity between the catalytic sites of the CyD host cavities and the reaction centers of the includes pesticide guests.

Cyclodextrin inclusion: catalytic effects on the degradation of organophosphorus pesticides in neutral aqueous solution.

alpha-, beta and gamma-Cyclodextrins were found to have promotive inclusion-catalytic effects on the degradation of organophosphorus pesticides solubilized in neutral aqueous media. Pesticide degradations were especially accelerated in such systems as alpha-cyclodextrin plus diazinon and beta-cyclodextrin plus chloropyrifos. The above findings are in contrast with the inhibitive catalytic effects of cyclodextrins on pesticide degradations in alkaline media. Cyclodextrin catalytic effects found here were considerably affected by differences in the substitutional and hetero-cyclic properties of the aromatic rings of pesticides and also by the sizes of cyclodextrin cavities.

Effects of humic acids on the inclusion complexation of cyclodextrins with organophosphorus pesticides

Abstract Concentration effects of humic acids on the inclusion of cyclodextrins with organophosphorus pesticides were investigated by monitoring the circular dichroism intensities induced by the pesticide inclusion.It was revealed that humic acids exert characteristic inhibition effects on the pesticide inclusion to cyclodextrins.The limiting inhibition indexes for the above effects were in correlation with the inclusion-depth parameters of the cyclodextrin-pesticide complexes.These findings were explained in terms of the complexation functions of humic materials to be effectual for solubilizing environmental chemicals such as pesticides.

Inclusion effects of β-cyclodextrins on the hydrolysis of organophosphorus pesticides

Abstract Inclusion effects of β-cyclodextrin ( β-CyD ) and its methyl derivatives on the hydrolysis of organothiophosphate pesticides, such as parathion, methyl parathion and fenitrothion, were investigated in humin-rich alkaline medium.The inclusion effects of β-CyDs were characterized by the multiple linear regression analysis using as descriptors the inclusion depth and orientation of the pesticides, the dissociation constant of CyD-pesticide inclusion complexes and degree of the methylation of the catalytically active secondary hydroxyl groups of the CyDs host cavity. The inclusion-geometrical parameters were estimated by the rotational-strength analysis of the circular dichroiss spectra induced in the included pesticides.

Cyclodextrin inclusion effects on fluorescence and fluorimetric properties of the pesticide warfarin

Fluorescence of the pesticide warfarin in aqueous solution was investigated in the presence of α-, β-, γ-cyclodextrins (CyDs) and their methyl derivatives.The fluorescence intensity of warfarin was found to be enhanced in the order of α < γ < β for CyD species, and the methylation of the CyD cavity was found to decrease the fluorescence intensity. Based on the linear regression analysis of the fluorescence increments depending on CyD concentrations, binding constants of warfarin with CyDs were estimated as follow: 552 M1 (β -CyD),285 M1 (dimethyl (β-CyD), 190 M−1 (γ-CyD), 38 M1 (α -CyD). The f luorimetric determination of recovery data of warfarin spiked in irrigation water was improved by using the fluorescence enhancing effects of β-CyD and its methyl derivative.

Catalytic properties of cyclodextrins on the hydrolysis of parathion and paraoxon in aquatic medium containing humic acids

Abstract The inclusion catalysis effects of α-,β- and γ-cyclodextrins(CyDs) on the hydrolysis rate of parathion, methyl parathion and paraoxon were investigated at 25°C in alkaline buffer solution(pH=8.5) containing humic acids. The hydrolysis rate of these pesticides was increased by the presence of humic acids. The inclusion catalysis of β-CyD inhibited parathion hydrolysis but promoted paraoxon hydrolysis. The CyD inclusion catalysis showed characteristic correlation with relative magnitudes of the inclusion-depth parameters of the pesticides which could be determined by the rotational-strength analysis of the induced circular dichroism. The essential properties of the CyD inclusion catalysis were explained in terms of the geometries of the CyD-pesticide inclusion complexes which determine degree of the proximity between the pesticide reaction site and the CyD catalytic site.