Lingpeng Zhan,Xi Huang,Jinjuan Xue,Huihui Liu,Caiqiao Xiong,Jiyun Wang,Zongxiu Nie
Mass spectrometry imaging (MSI) is a powerful technique for investigating the biomolecular locations within tissues. However, the isomeric compounds are rarely distinguished due to inability of MSI to differentiate isomers in the probing area. Coupling tandem mass spectrometry with MSI can facilitate differentiating isomeric compounds. Here MALDI-TOF/TOF tandem mass spectrometry imaging approach was applied to probing the spatial distributions of isomeric disaccharides in plant tissues. First, MS/MS imaging analysis of disaccharide-matrix droplet spots demonstrated the feasibility of distinguishing isomeric species in tissues, by measuring the relative intensity of specific fragments. Then, tandem MS imaging of disaccharides in onion bulb tissues indicated that sucrose and other unknown non-sucrose disaccharides exhibit heterogeneous locations throughout the tissues. This method enables us to image disaccharide isomers differentially in biological tissues, and to discover new saccharide species in plant. This work also emphasizes the necessity of considering isobaric compounds when interpreting MSI results.
Yingqiao He,Guodong Wei,Junhong Lin,Mingxu Sun,Ziheng Li
A novel non-enzymatic carbohydrates sensor which was an indium tin oxide (ITO) glass electrode modified by nickel and copper nanoparticles (Cu/Ni/ITO) was developed by an electrochemical method. The crystallinity, morphology, electrochemical measurements and amperometric response of the as-prepared ITO modified electrode were examined by the X-ray diffraction (XRD), scanning electron microscopic (SEM), cyclic voltammetry (CV) and chronoamperometry, respectively. The Cu/Ni/ITO electrode had better electroactivity for glucose oxidation than that obtained using Cu/ITO, Ni/ITO, and Ni/Cu/ITO. The logistic regression equation, I pa = ( A 1 – A 2 )/[1 + ( C glucose / x 0 ) p ] + A 2 , was used to fit the calibration curves of glucose aqueous solution concentrations and responsive current intensity. In research of other saccharides, such as fructose, lactose, sucrose, and maltose, which were detected by the Cu/Ni/ITO electrode, it was obvious that the Cu/Ni/ITO electrode was more sensitive to monosaccharides than disaccharides. Monosaccharides and disaccharides can be detected because the saccharides themselves had aldehyde group or be isomerized to an isomer having an aldehyde group in alkaline environment, and then aldehyde group produced carboxylic acid in the catalytic oxidation of the electrode, which lead to the change of electrode surface conductivity and the appearance of oxidation peak, and the alkaline environment further promotes the above reaction.
Nan Zhao,Mengchun Cheng,Shuai Huang,Dan Liu,Qiang Zhao,Yunpeng Bai,Xiaozhe Zhang
When characterizing components from ginseng, we found a vast number of multicharged anions presented in the liquid chromatography–mass spectrometry (LC-MS) chromatograms. The source of these anions is unclear yet, while ginsenosides, the major components of ginseng, are the main suspected type of molecules because of their sugar moiety. Our investigation using 14 pure ginsenosides affirmed that the multicharged anions were formed by ginsenosides rather than other types of ingredients in ginseng. Various anions could be observed for each ginsenoside. These anions contain ions ([M-2H]2−, [M+Adduct]2−), as well as those formed by polymerization of at least two ginsenosides, such as [nM-2H]2−, [nM-H+Adduct]2−, and [nM-3H]3−. The presence of so different types of ions from a ginsenoside explains the reason for the large number of anions in the LC-MS analysis of ginseng. We further found that formation of [nM-2H]2− ions was influenced by the number of sugar chains: ginsenosides containing two sugar chains produced all [nM-2H]2− ion types, whereas ginsenosides containing one sugar chain did not produce [2M-2H]2−. Thus, [2M-2H]2− and [3M-2H]2− can be utilized to rapidly identify monodesmosidic and/or bidesmosidic ginsenosides as joint diagnostic anions. The position of the glycosyl radical might be the key factor affecting the formation of multicharged multimer ions from monodesmosidic ginsenosides. Consequently, three groups of ginsenoside isomers were differentiated by characteristic [nM-2H]2− anions. Using concentration-dependent characteristics and collision-induced dissociation (CID), we confirmed that [nM-2H]2− ions are non-covalently bound multimers whose aggregation has marked distinction between monodesmosidic and bidesmosidic ginsenosides, accounting for the differentiated formation of [nM-2H]2− between them.
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