Modifications to a Paul-type quadrupole ion trap mass spectrometer providing optical access to the trapped ion cloud as well as hardware and software for coupling to a table-top IR optical parametric oscillator laser (OPO) are detailed. Critical experimental parameters for infrared multiple photon dissociation (IRMPD) on this instrument are characterized. IRMPD action spectra, collected in the hydrogen-stretching region with this instrument, complemented by spectra in the IR fingerprint region acquired at the FELIX facility, are employed to characterize the structures of the protonated forms of 2-thiouridine, [s²Urd+H]⁺, and 4-thiouridine, [s⁴Urd+H]⁺. The measured spectra are compared with predicted linear IR spectra calculated at the B3LYP/6-311+G(d,p) level of theory to determine the conformers populated in the experiments. This comparison indicates that thiation at the 2- or 4-positions shifts the protonation preference between the 2,4-H tautomer and 4-protonation in opposite directions versus canonical uridine, which displays a roughly equal preference for the 2,4-H tautomer and O4 protonation. As found for canonical uridine, protonation leads to a mixture of conformers exhibiting C2′-endo and C3′-endo sugar puckering with an anti nucleobase orientation being populated for both 2- and 4-thiated uridine.

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详细介绍了Paul型四极离子阱质谱仪的修改形式，该技术可提供对捕获离子云的光学访问以及用于耦合至台式IR光学参量振荡器激光器（OPO）的硬件和软件。表征了该仪器上红外多光子离解（IRMPD）的关键实验参数。用该仪器在氢气拉伸区收集的IRMPD作用谱与在FELIX设施获得的IR指纹区的光谱相补充，以表征2-硫尿苷的质子化形式的结构，[s ² Urd + H ] ⁺和4-硫尿苷，[s ⁴ Urd + H] ⁺。将测得的光谱与在理论上的B3LYP / 6-311 + G（d，p）水平计算的预测线性IR光谱进行比较，以确定在实验中填充的构象异构体。该比较表明，与经典尿苷相比，在2或4位上的硫杂在2,4-H互变异构体和4-质子化之间的质子化偏好在相反方向上发生了变化，这对于2,4-H互变异构体显示出大致相同的偏好。和O4质子化 如对于典型的尿苷所发现的，质子化导致呈现出C 2'-内切糖和C 3'-内切糖起皱的构象异构体的混合物，其中2-和4-硫代尿苷都具有抗核碱基方向。

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