Novel methyl-branched alkenones with up to five double bonds in saline lakes
Long-chain alkenones, a class of highly specific and widely used lipid biomarkers found in ocean and lake sediments, have been so far found as straight-chain alkyl ketones with 2 to 4 double bonds. Jaraula et al. (2010) reported assignments of a series of tri- to penta-unsaturated alkenones as strai...
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Online Access: | https://doi.org/10.1016/j.orggeochem.2021.104243 |
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fteawag:oai:dora:eawag_22577 2023-06-18T03:38:13+02:00 Novel methyl-branched alkenones with up to five double bonds in saline lakes Liao, Sian Wang, Karen J. Xue, Yazhen Huo, Jingfeng Santos, Ewerton Wang, Jianbo Schubert, Carsten J. Huang, Yongsong 2021 https://doi.org/10.1016/j.orggeochem.2021.104243 eng eng Elsevier Organic Geochemistry--Org. Geochem.--journals:2271--0146-6380 eawag:22577 doi:10.1016/j.orggeochem.2021.104243 journal id: journals:2271 issn: 0146-6380 ut: 000656665200003 α-methyl-branched alkenones Lake Van isochrysidales mass spectrometry double bond position Journal Article Text 2021 fteawag https://doi.org/10.1016/j.orggeochem.2021.104243 2023-06-04T23:49:55Z Long-chain alkenones, a class of highly specific and widely used lipid biomarkers found in ocean and lake sediments, have been so far found as straight-chain alkyl ketones with 2 to 4 double bonds. Jaraula et al. (2010) reported assignments of a series of tri- to penta-unsaturated alkenones as straight-chain C 38 methyl (C 38 Me) and C 39 ethyl (C 39 Et) alkenones in Lake Fryxell, Antarctica. The same series of compounds were later found in sediments from Lake Van (Randlett et al., 2014). The structure assignments by Jaraula et al (2010) were primarily based on strong ions at [M-43] + for C 38 alkenones and [M-57] + for C 39 alkenones, which were interpreted as a loss of CH 3 CO and CH 3 CH 2 CO groups. However, such fragmentation is atypical for common straight-chain methyl and ethyl alkenones. In this study, we reanalyzed Lake Van sediment samples. We show these new C 38 and C 39 alkenones elute earlier than the common straight-chain C 38 Me and C 39 Et alkenones on a mid-polarity GC column. After hydrogenation, mass spectra of these new alkenones show distinct peaks at m / z 72 or 86 caused by McLafferty rearrangement, indicating a methyl substitution at the α position of the carbonyl group in these C 38 and C 39 alkenones (i.e., α-methyl-branched C 38 Me and C 39 Et). Our new assignments as methyl-branched alkenones are further confirmed by the synthesis of an analog α-methyl C 25 methyl ketone and comparison of mass spectra. Double bond positions for branched C 38:5 Me (brC 38:5 Me) are found to be Δ 4 , Δ 7 , Δ 14 , Δ 21 and Δ 28 based on the mass spectrum of corresponding dimethyl disulfide adducts. Analysis of Lake Van alkenone data reveals that based on brC 38 Me shows a trend similar to for the past 270 ka, suggesting that the degree of unsaturation of branched alkenones is also sensitive to temperature. Article in Journal/Newspaper Antarc* Antarctica DORA Eawag Fryxell ENVELOPE(163.183,163.183,-77.617,-77.617) Lake Fryxell ENVELOPE(163.183,163.183,-77.617,-77.617) Organic Geochemistry 156 104243 |
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Open Polar |
collection |
DORA Eawag |
op_collection_id |
fteawag |
language |
English |
topic |
α-methyl-branched alkenones Lake Van isochrysidales mass spectrometry double bond position |
spellingShingle |
α-methyl-branched alkenones Lake Van isochrysidales mass spectrometry double bond position Liao, Sian Wang, Karen J. Xue, Yazhen Huo, Jingfeng Santos, Ewerton Wang, Jianbo Schubert, Carsten J. Huang, Yongsong Novel methyl-branched alkenones with up to five double bonds in saline lakes |
topic_facet |
α-methyl-branched alkenones Lake Van isochrysidales mass spectrometry double bond position |
description |
Long-chain alkenones, a class of highly specific and widely used lipid biomarkers found in ocean and lake sediments, have been so far found as straight-chain alkyl ketones with 2 to 4 double bonds. Jaraula et al. (2010) reported assignments of a series of tri- to penta-unsaturated alkenones as straight-chain C 38 methyl (C 38 Me) and C 39 ethyl (C 39 Et) alkenones in Lake Fryxell, Antarctica. The same series of compounds were later found in sediments from Lake Van (Randlett et al., 2014). The structure assignments by Jaraula et al (2010) were primarily based on strong ions at [M-43] + for C 38 alkenones and [M-57] + for C 39 alkenones, which were interpreted as a loss of CH 3 CO and CH 3 CH 2 CO groups. However, such fragmentation is atypical for common straight-chain methyl and ethyl alkenones. In this study, we reanalyzed Lake Van sediment samples. We show these new C 38 and C 39 alkenones elute earlier than the common straight-chain C 38 Me and C 39 Et alkenones on a mid-polarity GC column. After hydrogenation, mass spectra of these new alkenones show distinct peaks at m / z 72 or 86 caused by McLafferty rearrangement, indicating a methyl substitution at the α position of the carbonyl group in these C 38 and C 39 alkenones (i.e., α-methyl-branched C 38 Me and C 39 Et). Our new assignments as methyl-branched alkenones are further confirmed by the synthesis of an analog α-methyl C 25 methyl ketone and comparison of mass spectra. Double bond positions for branched C 38:5 Me (brC 38:5 Me) are found to be Δ 4 , Δ 7 , Δ 14 , Δ 21 and Δ 28 based on the mass spectrum of corresponding dimethyl disulfide adducts. Analysis of Lake Van alkenone data reveals that based on brC 38 Me shows a trend similar to for the past 270 ka, suggesting that the degree of unsaturation of branched alkenones is also sensitive to temperature. |
format |
Article in Journal/Newspaper |
author |
Liao, Sian Wang, Karen J. Xue, Yazhen Huo, Jingfeng Santos, Ewerton Wang, Jianbo Schubert, Carsten J. Huang, Yongsong |
author_facet |
Liao, Sian Wang, Karen J. Xue, Yazhen Huo, Jingfeng Santos, Ewerton Wang, Jianbo Schubert, Carsten J. Huang, Yongsong |
author_sort |
Liao, Sian |
title |
Novel methyl-branched alkenones with up to five double bonds in saline lakes |
title_short |
Novel methyl-branched alkenones with up to five double bonds in saline lakes |
title_full |
Novel methyl-branched alkenones with up to five double bonds in saline lakes |
title_fullStr |
Novel methyl-branched alkenones with up to five double bonds in saline lakes |
title_full_unstemmed |
Novel methyl-branched alkenones with up to five double bonds in saline lakes |
title_sort |
novel methyl-branched alkenones with up to five double bonds in saline lakes |
publisher |
Elsevier |
publishDate |
2021 |
url |
https://doi.org/10.1016/j.orggeochem.2021.104243 |
long_lat |
ENVELOPE(163.183,163.183,-77.617,-77.617) ENVELOPE(163.183,163.183,-77.617,-77.617) |
geographic |
Fryxell Lake Fryxell |
geographic_facet |
Fryxell Lake Fryxell |
genre |
Antarc* Antarctica |
genre_facet |
Antarc* Antarctica |
op_relation |
Organic Geochemistry--Org. Geochem.--journals:2271--0146-6380 eawag:22577 doi:10.1016/j.orggeochem.2021.104243 journal id: journals:2271 issn: 0146-6380 ut: 000656665200003 |
op_doi |
https://doi.org/10.1016/j.orggeochem.2021.104243 |
container_title |
Organic Geochemistry |
container_volume |
156 |
container_start_page |
104243 |
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1769003128409030656 |