DNA circular dichroism in gas phase Circular dichroism spectroscopy is widely used to distinguish between nonidentical mirror-image molecules. The technique relies on differential absorption of left versus right circularly polarized light and therefore tends to require solution-phase samples for adequate sensitivity. Daly et al. now report gas-phase circular dichroism spectra of DNA oligonucleotides based on detection of photodetached electrons rather than transmitted light (see the Perspective by Barran). The salient spectral features matched those in solution. Pairing the technique with mass spectrometry enables prior mass selection of particular molecules for analysis. Science, this issue p. 1465; see also p. 1426 Electron ejection by left versus right circularly polarized light tracks configurations of gas-phase DNA oligonucleotides. DNA and proteins are chiral: Their three-dimensional structures cannot be superimposed with their mirror images. Circular dichroism spectroscopy is widely used to characterize chiral compounds, but data interpretation is difficult in the case of mixtures. We recorded the electronic circular dichroism spectra of DNA helices separated in a mass spectrometer. We studied guanine-rich strands having various secondary structures, electrosprayed them as negative ions, irradiated them with an ultraviolet nanosecond optical parametric oscillator laser, and measured the difference in electron photodetachment efficiency between left and right circularly polarized light. The reconstructed circular dichroism ion spectra resembled those of their solution-phase counterparts, thereby allowing us to assign the DNA helical topology. The ability to measure circular dichroism directly on biomolecular ions expands the capabilities of mass spectrometry for structural analysis.

中文翻译：

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质量分辨电子圆二色性离子光谱

气相中的 DNA 圆二色性圆二色性光谱广泛用于区分不同的镜像分子。该技术依赖于左圆偏振光与右圆偏振光的不同吸收，因此往往需要溶液相样品以获得足够的灵敏度。戴利等人。现在报告了基于检测光分离电子而不是透射光的 DNA 寡核苷酸的气相圆二色光谱（参见 Barran 的观点）。显着的光谱特征与溶液中的特征相匹配。将该技术与质谱法相结合，可以预先选择特定分子的质量以进行分析。科学，这个问题 p。1465; 另见第 1426 左圆偏振光与右圆偏振光的电子喷射跟踪气相 DNA 寡核苷酸的配置。DNA 和蛋白质是手性的：它们的三维结构不能与其镜像叠加。圆二色光谱广泛用于表征手性化合物，但在混合物的情况下难以解释数据。我们记录了在质谱仪中分离的 DNA 螺旋的电子圆二色光谱。我们研究了具有各种二级结构的富含鸟嘌呤的链，将它们作为负离子进行电喷雾，用紫外纳秒光学参量振荡器激光照射它们，并测量了左右圆偏振光之间电子光分离效率的差异。重建的圆二色性离子光谱类似于它们的溶液相对应物，从而使我们能够分配 DNA 螺旋拓扑。