Substituted fatty acids in the leaves of some higher plants

Insights into the organic matter composition of soda lakes in the Pantanal, Brazil, through fatty acids analysis in sediments

We conducted a geochemical analysis on three sediment cores collected from soda and freshwater lakes in the Pantanal region, in Brazil. Our objective was to identify the primary sources of organic matter associated with the Pleistocene-Holocene transition, as previously documented in that area. The Nhecolandia region, located in the Pantanal, encompasses over 10,000 lakes, with approximately 10% of them exhibiting alkaline characteristics. Soda lakes became highly saline and alkaline after ~ 910 cal yr BP, which influences biogeochemistry and aquatic ecology. They have high electrical conductivity and pH can reach 10.5. In contrast to freshwater, soda lakes are absent of surrounding vegetation. Literature suggests a strong influence by the Last Glacial Maximum on the region. We hypothesized that periods of aridity and increased precipitation influenced the composition of organic matter present in sediments and preserved within these cores. Our analysis focused on examining the presence and distribution of fatty acids, organic carbon content, and total nitrogen. In general, the cores exhibited two distinct parts in terms of organic matter sources: the upper sections of the cores were primarily composed by terrestrial sources, identified by the presence of long-chain fatty acids, while the deeper sections were dominated by aquatic sources, therefore short-chain fatty acids. We did not find significant difference among fatty acid profile that could distinguish freshwater from soda lakes, the only remarkable difference was the occurrence of saturated fatty acids, which is lower in freshwater lake. These findings suggest the occurrence of humid and arid periods in the region. The C/N ratio displayed a similar trend to the fatty acid's profiles, exhibiting an abrupt change that was likely induced by climate variations. Although diagenesis can alter the composition of organic matter and, subsequently, the C/N values, it is noteworthy that the abrupt change observed in the Salina da Ponta (soda lake) core corresponds to 3,200 years BP. This coincides with documented climate changes that occurred during the Holocene. Our study revealed the influence of past climatic conditions on the sources and variations of organic matter in sediment cores from the Pantanal's soda and freshwater lakes. Consideration of diagenesis and climate variations is crucial for interpreting sedimentary records.

Identification of metabolites in Withania sominfera fruits by liquid chromatography and high-resolution mass spectrometry

RATIONALE

Withania somnifera is a rich source of biologically active secondary metabolites. Our earlier investigations on the fruits of this plant have yielded novel compounds, withanamides, with potent antioxidant activity and protective effect on β-amyloid-induced cytotoxicity in vitro. However, several minor compounds present in the fruits have not been characterized previously which may contribute to the observed biological activities.

METHODS

Liquid chromatography (LC) coupled with high-resolution mass spectrometry (HRMS) with data-dependent and targeted MS/MS experiments were conducted to elucidate the structure of observed metabolites.

RESULTS

A total of 62 metabolites identified included 32 withanamides, 22 withanolides, 3 steroidal saponins, 2 lignanamides, feruloyl tyramine, methoxy feruloyl tyramine and a diglucoside of hydroxyl palmitic acid. The structures of these compounds were proposed based on accurate masses of the molecular and fragment ions. Several of these new compounds identified from the profile were derived from withanamides with variations in aliphatic and/or glycosyl moieties. In addition, six new withanolides, a new hydroxy fatty acid diglucoside and several known compounds in the extract were identified.

CONCLUSIONS

The current study revealed the presence of several new and known compounds in Withania somnifera fruits. High-resolution MS and MS/MS experiments provide an extremely effective approach to derive the structures of plant secondary metabolites including isomeric compounds.

Sensitive and accurate quantitation of monoepoxy fatty acids in thermoxidized oils by gas-liquid chromatography

A sensitive and accurate methodology for quantitation of monoepoxy fatty acid methyl esters (FAME) by gas-liquid chromatography is proposed. Analytical problems of interfering compounds, ie, methyl monoester of azelaic acid and methyl docosanoate, were solved by a second methylation step with diazomethane and by elimination of nonpolar FAME by adsorption chromatography, respectively. Six monoepoxy FAME were identified and quantitated in olive and sunflower oils heated at 180 degrees C for 15 h: trans-9,10- and cis-9,10-epoxystearate coming from oleate and trans-12,13-, trans-9,10-, cis-12,13- and cis-9,10-epoxyoleate coming from linoleate. Results demonstrated total recovery of monoepoxy compounds after nonpolar FAME elimination with the additional advantage of sample concentration, which allowed quantitation of monoepoxy FAME in the initial oils. Also, repeatability was excellent as relative standard deviations ranged from 2.2 to 5.1% for on-column injection and from 0.1 to 2.0% for automatic split injection.

Capillary gas chromatography mass spectrometry and identification of substituted carboxylic acids in lipids extracted from a 4000-year-old Nubian burial

Polar carboxylic acid fractions of lipids extracted from samples from a 4000-year-old Nubian mummy were investigated by capillary gas chromatography mass spectrometry. They contain series of alpha,omega-dicarboxy, monohydroxy, dihydroxy and keto fatty acids, some of which were found for the first time outside the synthetic laboratory. Their chromatographic and mass spectrometric characteristic properties are reported.