Conformers of guanosines and their vibrations in the electronic ground and excited states, as revealed by double-resonance spectroscopy and ab initio calculations.
Conformers of guanosines and their vibrations in the electronic ground and excited states, as revealed by double-resonance spectroscopy and ab initio calculations.
复制标题
双共振光谱和从头算计算揭示了鸟苷的构象异构体及其在电子基态和激发态下的振动。
作者：
Eyal Nir;Isabel Huenig;K. Kleinermanns;M. de Vries
双光子电离结果表明，在没有溶剂相互作用和DNA集体模式的外部影响的情况下，可以非常详细地研究核碱基和由成对碱基组成的复合物。在这里，我们通过双共振激光光谱和从头计算表明，在290 nm附近的研究波长范围内，鸟苷（Gs），2-脱氧鸟苷（2-deoxyGs），和3-脱氧鸟苷（3-deoxyGs）都只显示一个稳定的异构体的光谱，这是由一个强大的分子内糖（5-OH）烯醇鸟嘌呤（3-N）氢键稳定。图1显示了鸟苷（Gs）与其烯醇形式的鸟嘌呤的可能结构;对以下讨论重要的原子被编号。激光解吸的Gs、2-deoxyGs、3 ± deoxyGs的R_2PI谱已经发表。[5，21]在早期的论文中，我们推测两种构象可能有助于Gs和3deoxyGs的振动光谱。为了验证这一假设，我们进行了UV ± UV光谱烧孔（SHB）测量。图2显示，三个光谱中的每一个都只来自一个构象异构体，因为R2 PI光谱中的每个单峰都反映在相应的SHB光谱中。为了比较，还显示了2，3-二异丙基鸟苷的R2 PI光谱。图3显示了通过IR ± UV测量获得的IR光谱，其中UV激光器固定在相应鸟苷的最强电子振动跃迁处，在图2中由λ sks表示。为了比较，还示出了2，3-二异丙基G和一种烯醇和一种酮基鸟嘌呤（G）互变异构体的IR光谱。在2，3-二异丙基G中，2-和3-位糖部分的OH基团被封闭。因此，其IR光谱不显示相应的OH振动，但与
two-photon ionization. The results showed that nucleobases and complexes composed of paired bases can be studied in great detail in the absence of the external effects of solvent interactions and the collective modes of DNA. Here we show by means of double-resonance laser spectroscopy and ab initio calculations that, in the investigated wavelength range around 290 nm, guanosine (Gs), 2-deoxyguanosine (2-deoxyGs), and 3-deoxyguanosine (3-deoxyGs) each exhibit only the spectrum of one stable isomer, which is stabilized by a strong intramolecular sugar(5-OH) ¥¥¥ enolguanine(3-N) hydrogen bond. Figure 1 shows a possible structure of guanosine (Gs) with guanine in its enol form; atoms which are important for the following discussion are numbered. The R2PI spectra of laser-desorbed Gs, 2-deoxyGs, 3 ± deoxyGs have already been published. [5, 21] In the earlier paper we speculated that two conformers might contribute to the vibronic spectra of Gs and 3deoxyGs. To test this hypothesis we performed UV ± UV spectral hole burning (SHB) measurements. Figure 2 shows that each of the three spectra originates from only one conformer, because every single peak in the R2PI spectrum is reflected in the corresponding SHB spectrum. For comparison the R2PI spectrum of 2,3-diisopropylguanosine is shown as well. Figure 3 shows the IR spectra obtained from IR ± UV measurements with the UV laser fixed to the most intense vibronic transition of the respective guanosine, indicated by asterisks in Figure 2. For comparison the IR spectra of 2,3-diisopropylGs and one enol and one keto guanine (G) tautomer are also shown. In 2,3-diisopropylGs, the OH groups of the sugar moiety in the 2and 3-positions are blocked. Therefore, its IR spectrum does not exhibit the corresponding OH vibrations but agrees well with