Bianco Mariachiara, Losito Ilario, Ventura Giovanni, Leoni Beniamino, Palmitessa Onofrio Davide, Renna Massimiliano, Santamaria Pietro, Calvano Cosima Damiana, Cataldi Tommaso R I
Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Via G. Amendola 165/a, 70126 Bari, Italy.
J Am Soc Mass Spectrom. 2025 Feb 5;36(2):318-328. doi: 10.1021/jasms.4c00399. Epub 2025 Jan 20.
Coenzyme Q (CoQ) and closely related compounds with varying isoprenoid tail lengths (CoQ, = 6-9) are biochemical cofactors involved in many physiological processes, playing important roles in cellular respiration and energy production. Liquid chromatography (LC) coupled with single or tandem mass spectrometry (MS) using electrospray (ESI) or atmospheric pressure chemical ionization (APCI) is considered the gold standard for the identification and quantification of CoQ in food and biological samples. However, the characteristic fragmentation exhibited by the CoQ radical anion ([M], / 862.684), the prevailing ion generated by APCI in negative polarity, has not been studied in detail. In this work, a systematic study was carried out to clarify this issue, using higher collisional energy dissociation (HCD) with high-resolution tandem FTMS and collision-induced dissociation-low-resolution sequential mass spectrometry (CID-MS, = 2-4). Various fragmentation pathways were successfully interpreted, with some structures proposed for product ions checked using density functional theory (DFT) calculations. Besides the already-known detachments of methyl radicals occurring directly from the CoQ radical anion and leading to ions like [M - CH] and [M - 2CH], the homolytic cleavage of C-C bonds along the oligo-isoprenoid side chain was tentatively proposed to explain some of the observed fragmentations. As a result, the generation of uncommon yet potentially stable distonic biradical anions was hypothesized, with some of them likely undergoing intramolecular cyclization to generate ions without unpaired electrons. Diagnostic product ions emerged from the fragmentation processes of CoQ and were found to be common also to the radical anions of other CoQ derivatives ( = 7-9), facilitating their identification in extracts of edible plant microgreens by reversed-phase liquid chromatography (RPLC)-APCI-FTMS.
辅酶Q（CoQ）以及具有不同异戊二烯尾巴长度（CoQ，n = 6 - 9）的密切相关化合物是参与许多生理过程的生化辅因子，在细胞呼吸和能量产生中发挥着重要作用。使用电喷雾（ESI）或大气压化学电离（APCI）的液相色谱（LC）与单级或串联质谱（MS）联用被认为是鉴定和定量食品和生物样品中CoQ的金标准。然而，CoQ自由基阴离子（[M] - ，m/z 862.684）所表现出的特征性碎裂，即APCI在负极性下产生的主要离子，尚未得到详细研究。在这项工作中，我们进行了一项系统研究以阐明这个问题，采用了具有高分辨率串联傅里叶变换质谱的更高碰撞能量解离（HCD）以及碰撞诱导解离 - 低分辨率串联质谱（CID - MS，n = 2 - 4）。成功解释了各种碎裂途径，并使用密度泛函理论（DFT）计算对一些提出的产物离子结构进行了检验。除了已经知道的直接从CoQ自由基阴离子上脱离甲基自由基并产生诸如[M - CH3] - 和[M - 2CH3] - 等离子外，还初步提出了沿着低聚异戊二烯侧链的C - C键的均裂来解释一些观察到的碎裂。结果，假设生成了不常见但可能稳定的双自由基阴离子，其中一些可能会进行分子内环化以产生没有未成对电子的离子。从CoQ的碎裂过程中出现了诊断性产物离子，并且发现它们对于其他CoQ衍生物（n = 7 - 9）的自由基阴离子也是常见的，这有助于通过反相液相色谱（RPLC） - APCI - FTMS在可食用植物嫩苗提取物中对它们进行鉴定。
