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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Infrared multiple photon dissociation spectroscopy of cationized methionine: effects of alkali-metal cation size on gas-phase confofmation
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Infrared multiple photon dissociation spectroscopy of cationized methionine: effects of alkali-metal cation size on gas-phase confofmation

机译：阳离子化蛋氨酸的红外多光子解离光谱：碱金属阳离子大小对气相富集的影响

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摘要

The gas-phase structures of alkali-metal cation complexes of the amino acid methionine (Met) as well as protonated methionine are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser. Spectra of Li~+(Met) and Na~+(Met) are similar and relatively simple, whereas the spectra of K~+(Met), Rb~+ (Met), and Cs~+(Met) include distinctive new bands. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory to identify the conformations present in the experimental studies. For Li~+ and Na~+ complexes, the only conformation present is a charge-solvated, tridentate structure that binds the metal cation to the amine and carbonyl groups of the amino acid backbone and the sulfur atom of the side chain, [N,CO,S]. In addition to the [N,CO,S] conformer, bands corresponding to alkali-metal cation binding to a bidentate zwitterionic structure, [CO_2~-], are clearly present for the K~+, Rb~+, and Cs~+ complexes. Theoretical calculations of the lowest energy conformations of Rb~+ and Cs~+ complexes suggest that the experimental spectra could also include contributions from two additional charge-solvated structures, tridentate [COOH,S] and bidentate [COOH]. For H~ + (Met), the IRMPD action spectrum is reproduced by multiple low-energy [N,CO,S] conformers, in which the protonated amine group hydrogen bonds to the carbonyl oxygen atom and the sulfur atom of the amino acid side chain. These [N,CO,S] conformers only differ in their side-chain orientations.
机译：利用红外多光子离解（IRMPD）光谱，利用自由电子激光产生的光，研究了氨基酸蛋氨酸（Met）以及质子化蛋氨酸的碱金属阳离子配合物的气相结构。 Li〜+（Met）和Na〜+（Met）的光谱相似且相对简单，而K〜+（Met），Rb〜+（Met）和Cs〜+（Met）的光谱包含独特的新谱带。将测得的IRMPD光谱与在B3LYP / 6-311 + G（d，p）理论水平计算的光谱进行比较，以鉴定实验研究中存在的构象。对于Li〜+和Na〜+配合物，唯一存在的构象是电荷溶解的三齿结构，该结构将金属阳离子与氨基酸主链的胺和羰基以及侧链的硫原子[N， CO，S]。除了[N，CO，S]构象异构体外，K〜+，Rb〜+和Cs〜+上还明显存在与碱金属阳离子结合到双齿两性离子结构[CO_2〜-]的条带。复合体。 Rb〜+和Cs〜+配合物的最低能级构象的理论计算表明，实验光谱还可能包括两个附加的电荷溶剂化结构，三齿[COOH，S]和双齿[COOH]的贡献。对于H〜+（Met），IRMPD作用谱是由多个低能[N，CO，S]构象异构体复制的，其中质子化的胺基氢键合到氨基酸侧的羰基氧原子和硫原子上链。这些[N，CO，S]构象异构体仅在侧链方向上有所不同。

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