Abstract
Photochemical reactions of microcystin-LR, a toxic compound produced by some blue green algae, were investigated. Ultraviolet absorption of microcystin-LR was assessed. Time-dependent density functional theory (TDDFT) calculations indicated that absorption peak at 238 nm was mainly due to excitation of electrons from the linear chain structure Adda of microcystin-LR. Irradiation of microcystin-LR with UV light resulted in the reduction of the 238 nm absorption peak and the appearance of a new peak at 300 nm. Density functional theory (DFT) and TDDFT calculations with a model molecule suggested that this 300 nm peak was due to tricyclo-Adda microcystin-LR, an intermediate in photochemical reactions of microcystin-LR. Analysis of the rate of this photochemical reaction showed that it was a first order reaction.
Highlights
Eutrophication of fresh water resources often causes algae blooms of blue-green algae
Density functional theory (DFT) and Time-dependent density functional theory (TDDFT) calculations with a model molecule suggested that this 300 nm peak was due to tricyclo-Adda microcystin-LR, an intermediate in photochemical reactions of microcystin-LR
In the absence of UV irradiation (0 sec), microcystin-LR showed a peak around 238 nm, which may be due to electron excitation at conjugated diene in Adda [9]
Summary
Eutrophication of fresh water resources often causes algae blooms of blue-green algae. Some species of blue-green algae produce toxic compounds called microcystins [1], which are cyclic polypeptides containing seven amide acids. Microcystins are characterized by a linear chain structure called Adda (3-amino-9methoxy-2,6,8-trimethyl-10-phenyl-4E,6E-decadienoic acid). UV Irradiation to microcystin formed non-toxic geometrical isomer [4(Z)-Adda] and [6(Z)-Adda] microcystins and toxin was completely decomposed by 10 minutes irradiations [3]. Kaya and Sano reported a photochemical product. Y. Mizukami of microcystin-LR by UV irradiation. They identified its structure as tricyclo-Adda microcystin-LR by NMR [2]. Character of UV spectra for tricycle-Adda microcystin-LR is not reported yet. To further characterize microcystin-LR and its photochemical product, we measured its UV spectrum and the effects of UV irradiation on its spectra over time. We evaluated the kinetic rate process of this photochemical reaction
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