Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy.
J Phys Chem A. 2022 Apr 21;126(15):2373-2387. doi: 10.1021/acs.jpca.2c01419. Epub 2022 Apr 6.
The first step to shed light on the abiotic synthesis of biochemical building blocks, and their further evolution toward biological systems, is the detection of the relevant species in astronomical environments, including earthlike planets. To this end, the species of interest need to be accurately characterized from structural, energetic, and spectroscopic viewpoints. This task is particularly challenging when dealing with flexible systems, whose spectroscopic signature is ruled by the interplay of small- and large-amplitude motions (SAMs and LAMs, respectively) and is further tuned by the conformational equilibrium. In such instances, quantum chemical (QC) calculations represent an invaluable tool for assisting the interpretation of laboratory measurements or even observations. In the present work, the role of QC results is illustrated with reference to glycolic acid (CHOHCOOH), a molecule involved in photosynthesis and plant respiration and a precursor of oxalate in humans, which has been detected in the Murchison meteorite but not yet in the interstellar medium or in planetary atmospheres. In particular, the equilibrium structure of the lowest-energy conformer is derived by employing the so-called semiexperimental approach. Then, accurate yet cost-effective QC calculations relying on composite post-Hartree-Fock schemes and hybrid coupled-cluster/density functional theory approaches are used to predict the structural and ro-vibrational spectroscopic properties of the different conformers within the framework of the second-order vibrational perturbation theory. A purposely tailored discrete variable representation anharmonic approach is used to treat the LAMs related to internal rotations. The computed spectroscopic data, particularly those in the infrared region, complement the available experimental investigations, thus enhancing the possibility of an astronomical detection of this molecule.
阐明生化构建块的非生物合成及其进一步向生物系统进化的第一步是在天文环境中检测相关物种，包括类地行星。为此，需要从结构、能量和光谱观点准确地描述感兴趣的物种。当涉及到柔性系统时，这项任务特别具有挑战性，因为其光谱特征由小振幅运动（SAMs）和大振幅运动（LAMs）的相互作用以及构象平衡的进一步调节决定。在这种情况下，量子化学（QC）计算代表了辅助解释实验室测量甚至观测的宝贵工具。在目前的工作中，参考甘醇酸（CHOHCOOH）说明了 QC 结果的作用，该分子参与光合作用和植物呼吸作用，也是人体草酸盐的前体，已在默奇森陨石中检测到，但尚未在星际介质或行星大气中检测到。特别是，通过采用所谓的半实验方法，推导出最低能量构象的平衡结构。然后，使用基于复合后 Hartree-Fock 方案和混合耦合簇/密度泛函理论方法的精确且经济高效的 QC 计算，在二阶振动微扰理论的框架内预测不同构象的结构和 ro-振动光谱性质。专门定制的离散变量表示非谐方法用于处理与内部旋转相关的 LAMs。计算的光谱数据，特别是在红外区域，补充了可用的实验研究，从而增强了这种分子在天文探测中的可能性。
