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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Structures of Alkali Metal Ion-Adenine Complexes and Hydrated Complexes by IRMPD Spectroscopy and Electronic Structure Calculations
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Structures of Alkali Metal Ion-Adenine Complexes and Hydrated Complexes by IRMPD Spectroscopy and Electronic Structure Calculations

机译：碱金属离子-腺嘌呤配合物和水合配合物的结构通过IRMPD光谱和电子结构计算

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Complexes between adenine and the alkali metal ions Li+, Na+, K+, and Cs+ have been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy between 2800 and 3900 cm-1, as have some singly hydrated complexes. The IRMPD spectra clearly show the N-H stretching and the NH2 symmetric and asymmetric stretching vibrations of adenine; and for the solvated ions, the O-H stretching vibrations are observed. These experimental spectra were compared with those for a variety of possible structures, including both A9 (A9 refers to the tautomer where hydrogen is on the nitrogen in position 9 of adenine, see Scheme 1) and A7 adenine tautomers, computed using B3-LYP/6-31+G(d,p). By comparing the experimental and the simulated spectra it is possible to rule out various structures and to further assign structures to the species probed in these experiments. Single-point calculations on the B3-LYP/6-31+G(d,p) geometries have been performed at MP2/6-311++G(2d, p) to obtain good estimates of the relative thermochemistries for the different structures. In all cases the computed IR spectrum for the lowest energy structure is consistent with the experimental IRMPD spectrum, but in some cases structural assignment cannot be confirmed based solely upon comparison with the experimental spectra so computed thermochemistries can be used to rule out highenergy structures. On the basis of the IRMPD spectra and the energy calculations, all adenine-M+ and adenine-M+-H2O are concluded to be composed of the A7 tautomer of adenine, which is bound to the cations in a bidentate fashion through N3 and N9 (see Scheme 1 for numbering convention). For the hydrated ions water binds directly to the metal ion through oxygen, as would be expected since the metal contains most positive charge density. For the hydrated lithium cation-bound adenine dimer, the water molecule is concluded to be hydrogen bonded to a free basic site of one of the adenine monomers, which is also bound to the lithium cation. Experimental and theoretical results on adenine-Li+-H2O suggest that the electrosprayed adenine-Li+ resembles the lowest-energy solution phase ion rather than the lowest-energy gas-phase ion, which is the imine form.
机译：腺嘌呤与碱金属离子Li +，Na +，K +和Cs +之间的络合物已通过2800至3900 cm-1之间的红外多光子离解（IRMPD）光谱进行了研究，其中包括一些水合的络合物。 IRMPD光谱清楚地显示了腺嘌呤的N-H拉伸以及NH2对称和不对称的拉伸振动。对于溶剂化离子，观察到O-H拉伸振动。将这些实验光谱与各种可能结构的光谱进行比较，包括A9（A9指互变异构体，其中氢位于腺嘌呤9位的氮上，参见方案1）和A7腺嘌呤互变异构体（使用B3-LYP / 6-31 + G（d，p）。通过比较实验光谱和模拟光谱，可以排除各种结构，并将结构进一步分配给在这些实验中探测到的物种。已在MP2 / 6-311 ++ G（2d，p）上对B3-LYP / 6-31 + G（d，p）几何结构进行了单点计算，从而获得了不同结构的相对热化学的良好估计。在所有情况下，计算得到的最低能级结构的IR光谱与实验IRMPD光谱一致，但是在某些情况下，不能仅根据与实验光谱的比较来确定结构分配，因此可以使用计算出的热化学方法排除高能结构。根据IRMPD光谱和能量计算，得出所有腺嘌呤-M +和腺嘌呤-M + -H2O均由腺嘌呤的A7互变异构体组成，该互变异构体通过N3和N9以双齿形式与阳离子结合（请参见编号惯例的方案1）。对于水合离子，水会通过氧气直接与金属离子结合，这是可以预料的，因为金属含有最多的正电荷密度。对于水合的锂阳离子结合的腺嘌呤二聚体，结论是水分子氢键合到也与锂阳离子结合的腺嘌呤单体之一的游离碱性位点上。关于腺嘌呤-Li + -H2O的实验和理论结果表明，电喷雾的腺嘌呤-Li +类似于最低能量的溶液相离子，而不是最低能量的气相离子（亚胺形式）。

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