Experimental and Theoretical Investigations of Infrared Multiple Photon Dissociation Spectra of Aspartic Acid Complexes with Zn2+ and Cd2.
Experimental and Theoretical Investigations of Infrared Multiple Photon Dissociation Spectra of Aspartic Acid Complexes with Zn2+ and Cd2.
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DOI：
10.1021/acs.jpcb.8b00801
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
G. C. Boles;Randy L. Hightower;R. A. Coates;Christopher P. McNary;G. Berden;J. Oomens;P. Armentrout
中科院分区：
文献类型：
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作者：
G. C. Boles;Randy L. Hightower;R. A. Coates;Christopher P. McNary;G. Berden;J. Oomens;P. Armentrout
利用自由电子激光产生的光，利用红外多光子解离(IRMPD)作用光谱研究了天冬氨酸(Asp)与锌离子(Asp-H)+、锌(Asp-H)+(Acn)(Acn=乙腈)和锌(Asp-H)+(Asp)的络合物以及与Cd~(2+)、Cd~(2+)(Asp)的络合物。通过量子化学计算发现了每个络合物的一系列低能构象，以确定实验形成的结构。观察到的重金属络合物CdCl+(Asp)[N，CO，Cos]的主要结合基序是电荷溶剂化的三齿结构，其中金属中心与主链和侧链羧酸的主链氨基和羰基结合。同样地，去质子化的锌(Asp-H)+(Acn)和Zn(Asp-H)+(Asp)配合物分别具有相似的[N，CO-，Cos](ACN)和[N，CO-，Cos][N，CO，Cos]配位。有趣的是，只有少量的光谱证据表明类似的锌(Asp-H)+[N，CO-，Cos]结合基序，尽管这种物种被预测为最低能量的构象。相反，观察到氨基酸的重排和部分解离，因为与实验光谱最一致的光谱特征是四配位的锌(Asp-NH4)+[Co2-，CoS](NH3)络合物。从理论上分析了从预测的最低能量构象到等压脱胺络合物的机理。此外，将目前的工作与天冬酰胺(ASN)的锌和镉配合物(ASN)进行比较，可以得出关于填充构象和羧胺与羧酸结合的影响的额外结论。
Complexes of aspartic acid (Asp) cationized with Zn2+: Zn(Asp-H)+, Zn(Asp-H)+(ACN) where ACN = acetonitrile, and Zn(Asp-H)+(Asp); as well as with Cd2+, CdCl+(Asp), were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy using light generated from a free electron laser. A series of low-energy conformers for each complex was found using quantum chemical calculations to identify the structures formed experimentally. The main binding motif observed for the heavy-metal complex, CdCl+(Asp)[N,CO,COs], is a charge-solvated, tridentate structure, where the metal center binds to the backbone amino group and carbonyl oxygens of the backbone and side-chain carboxylic acids. Likewise, the deprotonated Zn(Asp-H)+(ACN) and Zn(Asp-H)+(Asp) complexes show comparable [N,CO-,COs](ACN) and [N,CO-,COs][N,CO,COs] coordinations, respectively. Interestingly, there was only minor spectral evidence for the analogous Zn(Asp-H)+[N,CO-,COs] binding motif, even though this species is predicted to be the lowest-energy conformer. Instead, rearrangement and partial dissociation of the amino acid are observed, as spectral features most consistent with the experimental spectrum are exhibited by a four-coordinate Zn(Asp-NH4)+[CO2-,COs](NH3) complex. Analysis of the mechanistic pathway leading from the predicted lowest-energy conformer to the isobaric deaminated complex is explored theoretically. Further, comparison of the current work to that of Zn2+ and Cd2+ complexes of asparagine (Asn) allows additional conclusions regarding populated conformers and effects of carboxamide versus carboxylic acid binding to be drawn.