Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, Osaka 599-8531, Japan.
Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, Osaka 599-8531, Japan.
J Pharm Biomed Anal. 2023 Sep 20;234:115567. doi: 10.1016/j.jpba.2023.115567. Epub 2023 Jul 10.
Free d-amino acids and amino acid isomers were differentiated using tandem mass spectrometry without chromatographic separation. Ultraviolet photodissociation and water adsorption of leucine (Leu) and isoleucine (Ile) enantiomers hydrogen-bonded with tryptophan (Trp) were investigated at 8 K in the gas phase. The enantiomer-selective C-C bond cleavage of Trp was observed in the product ion spectra obtained by 285 nm photoexcitation, where the abundance of NHCHCOOH-eliminated ion of heterochiral H(d-Trp)(l-Leu) was higher than that of homochiral H(l-Trp)(l-Leu). When comparing water adsorption on the surfaces of the heterochiral and homochiral clusters in a cold ion trap, the number of water molecules adsorbed on the heterochiral cluster was greater than that adsorbed on the homochiral cluster. These results indicate that the stronger intermolecular interactions within the homochiral H(l-Trp)(l-Leu) compared to the heterochiral cluster inhibit enantiomer-selective photodissociation. Leu and Ile were differentiated by the isomer-selective C-C bond cleavage of Trp in the clusters. Calibration curves for the differentiation of isomeric amino acids and their enantiomers were developed using monitoring isomer- and enantiomer-selective photodissociation, indicating that the molar fractions in solution could be determined from a single product ion spectrum.
游离的 d-氨基酸和氨基酸异构体无需色谱分离即可通过串联质谱进行区分。在气相中，于 8 K 下研究了与色氨酸（Trp）氢键结合的亮氨酸（Leu）和异亮氨酸（Ile）对映体的紫外线光解和水吸附。在通过 285nm 光激发获得的产物离子谱中观察到 Trp 的对映体选择性 C-C 键断裂，其中杂互变异构体 H(d-Trp)(l-Leu)的 NHCHCOOH 消除离子的丰度高于同型 H(l-Trp)(l-Leu)。当在冷离子阱中比较异质和同质簇表面上的水吸附时，吸附在异质簇上的水分子数量大于吸附在同质簇上的水分子数量。这些结果表明，与异质簇相比，同型 H(l-Trp)(l-Leu) 内更强的分子间相互作用抑制了对映体选择性光解。亮氨酸和异亮氨酸通过在簇中 Trp 的异构体选择性 C-C 键断裂来区分。通过监测异构体和对映体选择性光解，为区分异构体氨基酸及其对映体开发了校准曲线，表明可以从单个产物离子谱确定溶液中的摩尔分数。
