Reeves Savanah G, Somogyi Arpad, Zeller Wayne E, Ramelot Theresa A, Wrighton Kelly C, Hagerman Ann E
Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States.
Campus Chemical Instrument Center, Mass Spectrometry and Proteomics Facility, The Ohio State University, Columbus, Ohio 43210, United States.
J Agric Food Chem. 2020 Nov 25;68(47):14038-14048. doi: 10.1021/acs.jafc.0c04877. Epub 2020 Nov 10.
Proanthocyanidins (condensed tannins) are important in food chemistry, agriculture, and health, driving demand for improvements in structure determination. We used ultrahigh resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) methods to determine the exact composition of individual species in heterogeneous mixtures of proanthocyanidin polymers from grain and leaves. Fragmentation patterns obtained with FT-ICR ESI MS-MS (electrospray ionization) confirmed structural details from thiolysis-high-performance liquid chromatography (HPLC)-diode array detection (DAD) and H-C heteronuclear single quantum coherence (HSQC) NMR. We found that A-type linkages were characteristic of shorter polymers in predominantly B-linked proanthocyanidin. We suggest that supramolecular complex formation between proanthocyanidins and matrix components such as 2,5-dihydroxybenzoic acid was responsible for anomalous 152 dalton peaks, incorrectly assigned as 3--galloylation, when using FT-ICR matrix-assisted laser desorption ionization (MALDI-MS). Our data illustrate the power of the ultrahigh resolution FT-ICR methods but include the caveat that MALDI-MS must be paired with complementary analytical tools to avoid artifacts.
原花青素（缩合单宁）在食品化学、农业和健康领域具有重要意义，这推动了对改进结构测定方法的需求。我们使用超高分辨率傅里叶变换离子回旋共振质谱（FT-ICR MS）方法来确定来自谷物和叶子的原花青素聚合物异质混合物中各个物种的确切组成。通过FT-ICR ESI MS-MS（电喷雾电离）获得的裂解模式证实了硫解-高效液相色谱（HPLC）-二极管阵列检测（DAD）和H-C异核单量子相干（HSQC）核磁共振的结构细节。我们发现，在主要为B型连接的原花青素中，A型连接是较短聚合物的特征。我们认为，当使用FT-ICR基质辅助激光解吸电离（MALDI-MS）时，原花青素与基质成分（如2,5-二羟基苯甲酸）之间形成的超分子复合物是导致异常152道尔顿峰的原因，该峰被错误地指定为3-没食子酰化。我们的数据说明了超高分辨率FT-ICR方法的强大功能，但也提醒注意，MALDI-MS必须与互补的分析工具配合使用，以避免出现假象。
