Type II photosensitized oxidation in senescent microalgal cells at different latitudes: Does low under-ice irradiance in polar regions enhance efficiency?

Use of Trifluoro-Acetate Derivatives for GC-MS and GC-MS/MS Quantification of Trace Amounts of Stera-3β,5α,6β-Triols (Tracers of Δ5-Sterol Autoxidation) in Environmental Samples

“…Detailed descriptions of the collection of samples of desert dusts, marine particulate matter and sediments used for validation of the proposed 3β,5α,6β-steratriol derivatization method can be found elsewhere [ 39 , 40 , 41 , 42 ]. Treatment of the whole material of the different samples involved reduction with excess NaBH 4 in MeOH (25 mL; 30 min) to convert labile hydroperoxides (resulting from oxidation) to their corresponding alcohols, which are more amenable to analysis using GC-EIMS, GC-EIMS/MS and GC-QTOF.…”

Cellular Damage of Bacteria Attached to Senescent Phytoplankton Cells as a Result of the Transfer of Photochemically Produced Singlet Oxygen: A Review

“…In fact, as we have seen previously, the attack of cis-vaccenic acid by 1 O 2 -mediated processes only produces trans allylic hydroperoxyacids ( Figure 1 ), whereas the irradiation of senescent AAPB results in the formation of high proportions of cis isomers, which are characteristic of radical oxidation processes [ 33 ]. Previous research shows that the 1 O 2 produced in senescent phytoplankton cells (for a review see [ 9 ]), but also in purple sulfur bacteria ( Thiohalocapsa halophila and Halochromatium salexigens ) [ 34 ] by type II chlorophyll or bacteriochlorophyll-photosensitized processes intensively attacks the phytyl side-chain of these pigments, affording a specific photoproduct (3-methylidene-7,11,15-trimethylhexadecan-1,2-diol) [ 8 ]. The fact that this compound is not found after irradiation of AAPB confirms that 1 O 2 is only very weakly produced during the senescence of these organisms.…”

“…It has been previously demonstrated that low solar irradiance favors slower production and diffusion of 1 O 2 across the cell membranes of phytoplankton and, thus, greater photo-oxidative damage to the unsaturated lipids in senescent phytoplankton rather than chlorophyll photodegradation (sensitizer photobleaching) [ 8 , 61 ]. A very recent study investigated the effect of solar irradiance intensity on the transfer of 1 O 2 from phytodetritus to their associated bacteria [ 41 ].…”

“…Hydroperoxides resulting from 1 O 2 -induced oxidation of unsaturated membrane components of bacteria (e.g., MUFAs) ( Figure 1 ) are relatively unstable (O–O bond dissociation energy = 34 kcal/mol) and can, thus, be readily cleaved by heat, light, some redox-active metal ions undergoing one-electron transfer (e.g., Fe 2+ , Co 2+ , Fe 3+ , Cu 2+ , Mn 2+ , Zn 2+ , Mg 2+ , V 2+ ), and certain enzymes (e.g., lipoxygenases) to hydroxyl, peroxyl, and alkoxyl radicals (for review, see [ 8 , 111 ]. In oxic environments, these radicals can then induce autoxidation (i.e., radical chain oxidation) of MUFAs.…”

“…Autoxidation of bacteria likely results from a transfer of 1 O 2 from senescent sympagic algae to their attached bacteria in ice and in the euphotic layer of the water column, followed by subsequent induction of radical chain oxidation by homolysis of the hydroperoxides formed in the underlying sediments [ 8 , 130 ]. This assumption is well-supported by the strong photooxidation state of bacteria observed in sinking particles that were also collected during the 2016 GreenEdge campaign [ 112 ].…”