Oral Presentation AUS-oMicS 2025

The role of unsaturation in defining the 3-dimensional structure of ionised lipids in the gas phase (#20)

Therese M. Fulloon 1 , Venkateswara R. Narreddula 1 , Sam C. Brydon 1 , Berwyck L. J. Poad 2 , Tim Causon 3 , Stephen J. Blanksby 1 4
  1. School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD, Australia
  2. Thermo Fisher Scientific, Seventeen Mile Rocks, QLD, Australia
  3. Department Natural Sciences and Sustainable Resources, Institute of Analytical Chemistry, BOKU University, Vienna, Austria
  4. Central Analytical Research Facility, Queensland University of Technology, Brisbane, QLD, Australia

The complexity and structural diversity of the lipidome represents a frontier challenge for analytical technologies to separate and identify individual molecular components among many hundreds or thousands of similar structures. Ion mobility-mass spectrometry (IM-MS) is emerging as one means to address this challenge, with its the ability to rapidly resolve ionised lipids based on differences in shape, charge and mass. Further, IM-derived collision cross sections (CCS) are increasingly being utilised to identify lipids and differentiate isomers. Despite this, the influence of primary molecular structure on lipid ion CCS is poorly understood and thus less predictable when compared to other biomolecular classes. Herein we systematically explore the influence of unsaturation position in the acyl chain on the structure(s) of ionised lipids in the gas phase.

A test set was generated comprising eleven different monounsaturated fatty acids with carbon-carbon bond positions ranging from n-3 to n-15 (relative to the methyl terminus) and including a subset of cis- and trans-stereoisomers. These fatty acids were derivatized as 3-pyridylcarbinol amides (PA), 3-pyridylcarbinol esters (PE) and N-methyl-pyridinium-3-methanamines (N-MePA). Methanolic solutions of each compound were ionised by electrospray ionisation to form variously, [M-H]-, M+ and [M+H]+ ions.  Accurate DTCCSN2 measurements were made for each ion using an Agilent Drift Tube Ion Mobility-Q-TOF Mass Spectrometer (DTIM-QTOFMS) while high-resolution ion mobility measurements were used to study the same precursors using both Waters Cyclic Ion Mobility (cIM-MS) and MOBLIion Structures for Lossless Ion Manipulation (SLIM-MS) instrumentation.

A clear correlation is observed between the unsaturation position and mobility of the derivatives, whereby as the double bond shifts along the acyl chain from the methyl terminus to the head group, the respective CCS increases. In addition to showcasing the reproducibility of these trends, this dataset provides new fundamental insights into the difference in ion mobility between IM-MS technologies.