Molecular Insights into the Photochemical Transformation of Phytosterols: Formation of Carboxylic Acid Derivatives Characterized by FT-ICR Mass Spectrometry
ID：586
Oral Presentation
2025-01-15 09:30 （China Standard Time）
Session：Session 45-New Data and Technologies Driven Insights Into Marine Organic Matter Cycling
Abstract
The accumulation of dissolved organic matter (DOM) in the ocean has been associated with linear terpenoid structures, and carotenoid degradation products, which are considered potential precursors (Arakawa, et al., 2017; Semitsoglou-Tsiapou, et al., 2022). Steroidal compounds, particularly those resembling Carboxylic-rich Alicyclic Material (CRAM), are significant in marine biogeochemistry due to their role in DOM formation (Hertkorn et al., 2006; Liu et al., 2023). Phytosterols, such as fucosterol, β-sitosterol, campesterol, cholesterol, stigmasterol, ergosterol, and brassicasterol, are prevalent in brown macroalgae and marine environments (Hannan, et al., 2020). This study explores the photochemical degradation of stigmasterol (C29H50O) as a model for the formation of CRAM-like structures in marine DOM.
We conducted in vitro photooxidation of stigmasterol under UVA irradiation (365 nm, 5 μmole/m²/s) for three days and characterized the photodegraded products using Negative Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR MS). The goal was to identify water-soluble compounds with structural features similar to those observed in marine DOM samples isolated by the PPL resin-based solid-phase extraction (SPE) method.
Stigmasterol was dissolved in n-hexane and subjected to UVA irradiation. The photodegraded products were extracted with ultrapure water and purified using a Bond Elut-PPL resin cartridge. A dark control was included for comparative analysis. We identified thirty-one new CHO-class ions [C8-29H7-45O2-7, m/z 179-505; DBE = 2–8, average DBE 5.65; O/C ratio 0.15–0.57; H/C ratio 0.82–1.79]. Notably, eight molecular formulas met the criteria for CRAM structures, including C9H7O4, C11H11O4, C13H13O4, C13H13O5, C12H15O6, C15H19O5, C14H19O6, and C17H23O5. Intensity variations were observed among these ions, with significant intensities noted for C29H43O6 (DBE 8), C28H43O6 (DBE 7), C28H43O7 (DBE 7), C28H41O7 (DBE 8), C17H25O5 (DBE 5), and C17H23O5 (DBE 6).
Comparative analysis with PPL-DOM from Coastal Seawater (CSW) and Deep-Sea Water (DSW) at 2000 m depth in the Mariana Trench revealed the presence of eighteen and seven molecules, respectively, with six and three molecular formulas aligning with CRAM criteria. These findings suggest that photochemical oxidation of stigmasterol leads to carboxylation reactions, contributing to the pool of recalcitrant marine DOM. The FT-ICR MS data provide molecular evidence supporting the role of photodegraded sterols in the formation of CRAM-like structures in marine environments.
We conducted in vitro photooxidation of stigmasterol under UVA irradiation (365 nm, 5 μmole/m²/s) for three days and characterized the photodegraded products using Negative Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR MS). The goal was to identify water-soluble compounds with structural features similar to those observed in marine DOM samples isolated by the PPL resin-based solid-phase extraction (SPE) method.
Stigmasterol was dissolved in n-hexane and subjected to UVA irradiation. The photodegraded products were extracted with ultrapure water and purified using a Bond Elut-PPL resin cartridge. A dark control was included for comparative analysis. We identified thirty-one new CHO-class ions [C8-29H7-45O2-7, m/z 179-505; DBE = 2–8, average DBE 5.65; O/C ratio 0.15–0.57; H/C ratio 0.82–1.79]. Notably, eight molecular formulas met the criteria for CRAM structures, including C9H7O4, C11H11O4, C13H13O4, C13H13O5, C12H15O6, C15H19O5, C14H19O6, and C17H23O5. Intensity variations were observed among these ions, with significant intensities noted for C29H43O6 (DBE 8), C28H43O6 (DBE 7), C28H43O7 (DBE 7), C28H41O7 (DBE 8), C17H25O5 (DBE 5), and C17H23O5 (DBE 6).
Comparative analysis with PPL-DOM from Coastal Seawater (CSW) and Deep-Sea Water (DSW) at 2000 m depth in the Mariana Trench revealed the presence of eighteen and seven molecules, respectively, with six and three molecular formulas aligning with CRAM criteria. These findings suggest that photochemical oxidation of stigmasterol leads to carboxylation reactions, contributing to the pool of recalcitrant marine DOM. The FT-ICR MS data provide molecular evidence supporting the role of photodegraded sterols in the formation of CRAM-like structures in marine environments.
Keywords
Dissolved organic matter,CRAM,phytosterol,photochemical oxidation,precursor,recalcitrant organic matter,FT-ICR MS