Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Osaka 599-8531, Japan.
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Osaka 599-8531, Japan.
Anal Chim Acta. 2017 Aug 1;979:31-35. doi: 10.1016/j.aca.2017.04.027. Epub 2017 Apr 26.
To explore the origin of biomolecule homochirality in interstellar molecular clouds, enantiomer-selective photodissociation via chiral recognition between amino acids in the gas phase was examined using a tandem mass spectrometer containing an electrospray ionization source and a cold ion trap. Ultraviolet photodissociation mass spectra of cold gas-phase noncovalent complexes of sodiated l-tryptophan ion, Na(l-Trp), with an amino acid such as serine (Ser), threonine (Thr), or alanine (Ala) were obtained by the photo-excitation of l-Trp in the noncovalent complexes. Dissociation of l-Trp via CO loss occurred when it was noncovalently complexed with d-Ser or d-Thr in the presence of Na. For the l-enantiomers, the energy absorbed by l-Trp was released through evaporation of l-Ser or l-Thr, and dissociation of the amino acids was suppressed. In contrast, the enantiomer-selective phenomenon was not observed in the noncovalent complex with Ala, suggesting that a side-chain OH group plays an important role in chiral recognition and enantiomer-selective photodissociation. The enantiomer-selective photodissociation was applied to the quantitative chiral analysis of amino acids. The enantiomeric excess of Ser and Thr in solution could be determined by measuring the relative abundance ratio of the enantiomer-selective photodissociation of Trp to amino acid evaporation in a single photodissociation mass spectrum obtained by photo-excitation of l-Trp used as a chiral probe in cold gas-phase noncovalent complexes with the analyte amino acids, and by referring to the linear relationships established in this work.
为了探索星际分子云中生物分子手性的起源，我们使用串联质谱仪（包含电喷雾电离源和冷离子阱）研究了气相中氨基酸之间手性识别的对映体选择性光解。通过对非共价复合物中 l-色氨酸（l-Trp）的光激发，获得了与丝氨酸（Ser）、苏氨酸（Thr）或丙氨酸（Ala）等氨基酸形成的加钠 l-色氨酸离子（Na(l-Trp)）的冷气相非共价复合物的紫外光解质谱。当 l-Trp 与 d-Ser 或 d-Thr 在 Na 存在下形成非共价复合物时，通过 CO 损失发生 l-Trp 的解离。对于 l-对映体，l-Trp 吸收的能量通过蒸发 l-Ser 或 l-Thr 释放，并且抑制了氨基酸的解离。相比之下，在与 Ala 形成的非共价复合物中未观察到对映体选择性现象，这表明侧链 OH 基团在手性识别和对映体选择性光解中起着重要作用。将对映体选择性光解应用于氨基酸的定量手性分析。通过测量在单个光解质谱中，由 l-Trp 作为手性探针与分析物氨基酸形成的冷气相非共价复合物中光激发所产生的 Trp 对映体选择性光解与氨基酸蒸发的相对丰度比，并参考本文中建立的线性关系，可以确定 Ser 和 Thr 在溶液中的对映体过量。
