Differences in the complexation of sodium with methyl esterified carboxymethyl/methoxyacetyl-O-glucans in electrospray ionization-mass spectrometry
Differences in the complexation of sodium with methyl esterified carboxymethyl/methoxyacetyl-O-glucans in electrospray ionization-mass spectrometry
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DOI：
10.1016/j.ijms.2017.05.007
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发表时间：
2017-08-01
影响因子：
1.8
通讯作者：
Mischnick, Petra
中科院分区：
文献类型：
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作者：
Bol, Matthias;Sakellaris, Constantine N.;Mischnick, Petra
甲氧乙酸酯和醇的（甲氧羰基）甲基醚是只有C=0和CH2的位置互换的异构体。因此，在电喷雾质谱分析中，甲氧基乙酸甲酯化的葡聚糖羧甲基衍生物可以得到相同的反应，这是定量分析羧甲基纤维素（CMC）中取代模式的先决条件。为了找出原因，在ESI-MS中研究了1,2-乙二醇和反式-1,2-环己二醇的相应衍生物，类似于葡萄糖的2,3-二醇特征。在高浓度（10(-3)M）的纯乙腈中，模型化合物的甲氧乙酸酯被强烈分辨。随着稀释，同分异构体分析物的相对强度（RI）逐渐下降，在总浓度为10(-10)m时达到类似于2的水平。类似的色谱保留、表面活性和极性参数并不表明构成异构体的不同表面化学性质是这种强烈抑制的主要原因。量子化学计算（DFT）表明，两种二醇衍生物的Na+结合能相差约50 kJ/mol。cm -醚可以将碱性羰基加入到四配位的钠络合物中，而甲氧基乙酸酯在空间上是不可能的。添加10%的水后，RI急剧下降，这可能是由于竞争钠配合物的条件稳定常数发生了变化。将钠的摩尔浓度从10(-4)M调整到10(-2)M会产生典型的盐效应，但也会影响钠加合物的形成。在单-和二-和低聚糖的情况下，能配位Na+的构象数量更加复杂，各种取代基模式之间的差异减小，但并未完全消失。
Methoxyacetates and (methoxycarbonyl)methyl ethers of alcohols are isomers where only the positions of C=0 and CH2 are interchanged. Therefore, methoxyacetates of methyl esterified carboxymethyl derivatives of glucans were expected to give equal response in electrospray ionization mass spectrometry which is a prerequisite for the quantitative analysis of substitution patterns in carboxymethyl celluloses (CMC). In order to fad out why this is not the case, corresponding derivatives of 1,2-ethanediol and trans-1,2-cyclohexanediol, resembling the 2,3-diol feature of glucose, where studied in ESI-MS. At high total concentration (10(-3) M) in pure acetonitrile, the methoxyacetates of the model compounds were strongly discriminated. With dilution, the relative intensities (RI) of the isomeric analytes progressively dropped to achieve similar to 2 at a total concentration of 10(-10) M. Similar retention in chromatography and surface activity and polarity parameters do not indicate to different surface chemistry of the constitutional isomers as predominant reason for this strong suppression. Quantum-chemical calculations (DFT) showed a difference of binding energies for Na+ between the two diol derivatives of about 50 kJ/mol. While the CM-ethers can involve the more basic carbonyls into the tetra-coordinated sodium complex, this is sterically not possible for the methoxyacetates. At addition of 10% water RI drastically decreased' probably due to change of conditional stability constants of the competing sodium complexes. Adjusting sodium molarities to 10(-4) M up to 10(-2) M caused typical salt effects, but will also influence the formation of sodium adducts. In case of mono- and substantially in di- and oligosaccharides, the number of conformations that can coordinate Na+ are more complex, and the discrepancy between the various substituent patterns decreases, but does not fully disappear.