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Cyanobacterial Toxins and Cyanopeptide Transformation Kinetics by Singlet Oxygen and pH-Dependence in Sunlit Surface Waters
journal contributionposted on 2021-10-29, 19:43 authored by Regiane Natumi, Christoph Dieziger, Elisabeth M.-L. Janssen
To assess the risks associated with cyanobacterial blooms, the persistence and fate processes of cyanotoxins and other bioactive cyanobacterial metabolites need to be evaluated. Here, we investigated the reaction with photochemically produced singlet oxygen (1O2) for 30 cyanopeptides synthesized by Dolichospermum flos aquae, including 9 anabaenopeptins, 18 microcystins, 2 cyanopeptolins, and 1 cyclamide. All compounds were stable in UVA light alone but in the presence of a photosensitizer we observed compound-specific degradation. A strong pH effect on the decay was observed for 18 cyanopeptides that all contained tyrosine or structurally related moieties. We can attribute this effect to the reaction with 1O2 and triplet sensitizer that preferentially react with the deprotonated form of tyrosine moieties. The contribution of 1O2 to indirect phototransformation ranged from 12 to 39% and second-order rate constants for 9 tyrosine-containing cyanopeptides were assessed. Including the pH dependence of the reaction and system-independent second-order rate constants with 1O2 will improve the estimation of half-lives for multiclass cyanopeptide in surface waters. Our data further indicates that naturally occurring triplet sensitizers are likely to oxidize deprotonated tyrosine moieties of cyanopeptides and the specific reactivity and its pH dependence needs to be investigated in future studies.
uva light aloneorder rate constantsindirect phototransformation rangedstructurally related moietiescyanopeptide transformation kineticssunlit surface waters30 cyanopeptides synthesized2 sub1 supstrong ph effectph dependence needssurface waterstyrosine moietiesmulticlass cyanopeptide2 cyanopeptolins1 cyclamideph dependencetriplet sensitizerspecific reactivityspecific degradationsinglet oxygenrisks associatedpreferentially reactfuture studiesfate processesdeprotonated formcyanobacterial toxinscyanobacterial bloomscontaining cyanopeptidescontained tyrosine9 tyrosine18 microcystins18 cyanopeptides