Photochemical Reactions of Microcystin-LR Following Irradiation with UV Light

Yoshihiro Mizukami

doi:10.4236/ojpc.2016.64008

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

Introduction

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

Methods

Results and Discussions

Conclusion