Fig. 1. Visible-light activated [2 + 2] cycloaddition (VACA) reaction of anthraquinone (AQ) to unsaturated lipids. (a) Schematic illustration of the reaction between AQ and unsaturated lipids, and the dissociation pathways of reaction products; (b and c) MS spectra of the VACA reaction solution of AQ and FA 20:1 (11E) in (b) negative and (c) positive ion modes. Insets show the retention times of the VACA reaction products in LC-MS in (b) negative and (c) positive modes, respectively; (d and e) MS/MS spectra of the VACA reaction products in (d) negative (m/z 517.1, [M − H]⁻) and (e) positive (m/z 541.4 , [M + Na]⁺) ion modes; (f) proposed dissociation pathways and fragments of the VACA reaction product isomers.