Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
J Am Soc Mass Spectrom. 2011 Jun;22(6):1040-51. doi: 10.1007/s13361-011-0099-7. Epub 2011 Apr 6.
Several lignin model compounds were examined to test whether gas-phase ion-molecule reactions of trimethylborate (TMB) in a FTICR can be used to differentiate the ortho-, meta-, and para-isomers of protonated aromatic compounds, such as those formed during degradation of lignin. All three regioisomers could be differentiated for methoxyphenols and hydroxyphenols. However, only the differentiation of the ortho-isomer from the meta- and para-isomers was possible for hydroxyacetophenones and hydroxybenzoic acids. Consideration of the previously reported proton affinities at all basic sites in the isomeric hydroxyphenols, and the calculated proton affinities at all basic sites in the three methoxyphenol isomers, revealed that the proton affinities of the analytes relative to that of TMB play an important role in determining whether and how they react with TMB. The loss of two methanol molecules (instead of one) from the adducts formed with TMB either during ion-molecule reactions, or during sustained-off resonance irradiated collision-activated dissociation of the ion-molecule reaction products, revealed the presence of two functionalities in almost all the isomers. This finding supports earlier results suggesting that TMB can be used to count the functionalities in unknown oxygen-containing analytes.
几种木质素模型化合物被检测，以检验在 FTICR 中三甲基硼酸（TMB）的气相离子-分子反应是否可用于区分质子化芳香族化合物（如木质素降解过程中形成的那些化合物）的邻位、间位和对位异构体。甲氧基苯酚和羟基苯酚的三种区域异构体都可以区分。然而，对于羟基苯乙酮和羟基苯甲酸，仅可以区分邻位异构体与间位和对位异构体。考虑到在所有异构羟基苯酚中的所有碱性位点处的先前报道的质子亲和力，以及在三个甲氧基苯酚异构体中的所有碱性位点处的计算质子亲和力，发现相对于 TMB，分析物的质子亲和力在确定它们是否以及如何与 TMB 反应方面起着重要作用。与 TMB 形成的加合物在离子-分子反应期间或在离子-分子反应产物的持续非共振辐照碰撞激活解离期间失去两个甲醇分子（而不是一个），揭示了几乎所有异构体中存在两种官能团。这一发现支持了早先的结果，表明 TMB 可用于计算未知含氧分析物中的官能团数量。
