基于量子化学探索土卫六生命有机分子的拉曼光谱特征

The origin and universality of life in the universe are fundamental questions of mankind’s awareness and cognition. As we know so far, the Earth is unique in our Solar System as being the only habitable planet and supports life and its evolution. However, considering the wide variety of physical and chemical conditions of the vast universal environment and the exponential increase of confirmed number of exoplanets, it is very likely that the Earth is not the only living world. Titan is the largest moon of Saturn that owns a dense atmosphere and hydrocarbon oceans. The presence of active and complex organic chemistries on Titan’s surface provides basic prebiotic planetary conditions that conducive to the origin of life. Titan is therefore considered as one of the most habitable environments in our solar system other than the earliest Earth. However, water-required terrestrial biochemistry cannot happen on the Titan's surface because of its extremely low temperature (~94K) and the absence of oxygen element. To answer the question of what kind of life can emerge on Titan, we previously hypothesized a water-absent & oxygen-free biochemistry, namely “CHN biochemistry” that could be adopted on Titan’s surface environment. Here, we aim to investigate the theoretical Raman spectroscopic signatures of the key prebiotic molecules involved in “CHN biochemistry”. Three kinds of prebiotic molecules are investigated, including polymers, phosphorus-containing biomolecules and RNA analogs. On the basis of quantum chemical calculations, their molecular configuration and thermodynamic parameters will then be obtained to evaluate the molecular stability, predict the reaction mechanism and investigate their potential biological functions. At last, the theoretical Raman spectroscopic features of those prebiotic molecules are predicted and summarized as a Raman databank. The implementation of this project will not only provide theoretical chemical bases for the future life detection by Raman spectroscopy on Titan as well as in the broader extraterrestrial environment.

宇宙中生命是否有普遍性和多种起源是人类认知的最根本的问题之一。土卫六是一个富碳、贫氧的天体，其表面积累了大量的非生物成因的有机化合物，并且其大气和烷烃海洋提供了有利于生命起源的物理条件。因此，土卫六被认为是太阳系内除行星地球之外最有可能的宜居卫星环境之一。在我们的前期研究中，以土卫六的表面环境为背景，构建了适合极低温的无水无氧生命化学基础，称之为“CHN生命化学”。本项目拟在前期研究基础上，进一步研究土卫六上合理存在的生命有机分子的拉曼光谱特征。具体而言，是从含磷分子、RNA分子和聚合反应等三个具有重要生物学意义的方面出发，构建相应的生命有机分子及相关的化学反应，利用量子化学计算方法得到这些分子的拉曼光谱特征。本项目的实施，不仅为将来用拉曼光谱探测土卫六上乃至其他地外环境中可能存在的生命提供理论基础，同时也有助于探索宇宙中生命化学的起源和演化。

宇宙中生命是否有普遍性和多种起源是人类认知的最根本的问题之一。土卫六是一个富碳、贫氧的天体，其表面积累了大量的非生物成因的有机化合物，并且其大气和烷烃海洋提供了有利于生命起源的物理条件。因此，土卫六被认为是太阳系内除行星地球之外最有可能的宜居卫星环境之一。在我们的前期研究中，以土卫六的表面环境为背景，构建了适合极低温的无水无氧生命化学基础，称之为“CHN生命化学”。本研究在前期研究基础上，进一步研究土卫六上合理存在的生命有机分子的存在形式及其拉曼光谱特征。具体地，是从聚合反应、含磷分子、RNA分子等三个具有重要生物学意义的方面出发，计算了相应的生命有机分子的稳定分子构型和热力学参数，以及对应的化学反应能量变化，进而讨论了其在能量转移和遗传信息传递中的功能和作用，并在最后预测了这些分子的拉曼光谱特征。本研究结果不仅为将来用拉曼光谱探测土卫六上乃至其他地外环境中可能存在的生命起源提供理论基础，同时也将有助于探索宇宙中生命化学的起源和演化。