The role of the coenzyme flavin adenine dinucleotide (FAD) in the catalytic oxidation of glucose was elucidated by MS using a new extraction and ionization method. By a multiphase flow of liquid–gas, extractive electrospray ionization was achieved, and this technique (MF-EESI) decreased the salt-matrix interference effectively, avoided salt crystallizations at the capillary tip and increased ionization efficiency by a concentric-sprayed solvent. Notably, two intermediate complexes of FAD–glucose have been observed and differentiated for the first time using this MF-EESI technique. These intermediate complexes were demonstrated to be responsible for the hydride abstraction from glucose, as well as the cyclic coenzyme conversion of FAD during glucose oxidation. Online monitoring was also employed in MF-EESI, thereby providing a potential and informative tool to scrutinize enzymatic catalytic reactions.

中文翻译：

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萃取电喷雾电离（MF-EESI）质谱多相流研究FAD在葡萄糖催化氧化中的作用

使用一种新的萃取和电离方法，通过质谱法阐明了辅酶黄素腺嘌呤二核苷酸（FAD）在葡萄糖催化氧化中的作用。通过液-气的多相流，实现了萃取式电喷雾电离，该技术（MF-EESI）有效地减少了盐基干扰，避免了盐在毛细管尖端结晶，并通过同心喷涂的溶剂提高了电离效率。值得注意的是，使用这种MF-EESI技术首次观察到了两种FAD-葡萄糖中间体复合物并对其进行了区分。这些中间体配合物被证明负责葡萄糖中氢化物的提取，以及葡萄糖氧化过程中FAD的循环辅酶转化。MF-EESI还采用了在线监控，