Abrosimov Roman, Moosmann Bernd
Evolutionary Biochemistry and Redox Medicine, Institute for Pathobiochemistry, University Medical Center of the Johannes Gutenberg University, 55128 Mainz, Germany.
Institute for Quantitative and Computational Biosciences, Johannes Gutenberg University, 55128 Mainz, Germany.
Life (Basel). 2024 Oct 18;14(10):1330. doi: 10.3390/life14101330.
Low-molecular-mass organic chemicals are widely discussed as potential indicators of life in extraterrestrial habitats. However, demarcation lines between biotic chemicals and abiotic chemicals have been difficult to define. Here, we have analyzed the potential utility of the quantum chemical property, HOMO-LUMO gap (HLG), as a novel proxy variable of life, since a significant trend towards incrementally smaller HLGs has been described in the genetically encoded amino acids. The HLG is a zeroth-order predictor of chemical reactivity. Comparing a set of 134 abiotic organic molecules recovered from meteorites, with 570 microbial and plant secondary metabolites thought to be exclusively biotic, we found that the average HLG of biotic molecules was significantly narrower (-10.4 ± 0.9 eV versus -12.4 ± 1.6 eV), with an effect size of g = 1.87. Limitation to hydrophilic molecules (XlogP < 2) improved the separation of biotic from abiotic compounds (g = 2.52). The "hydrophilic reactivity" quadrant defined by |HLG| < 11.25 eV and XlogP < 2 was populated exclusively by 183 biotic compounds and 6 abiotic compounds, 5 of which were nucleobases. We conclude that hydrophilic molecules with small HLGs represent valuable indicators of biotic activity, and we discuss the evolutionary plausibility of this inference.
低分子量有机化学物质作为外星栖息地生命的潜在指标受到广泛讨论。然而，生物化学物质和非生物化学物质之间的分界线一直难以界定。在此，我们分析了量子化学性质——最高占据分子轨道与最低未占据分子轨道能隙（HLG）作为一种新的生命替代变量的潜在效用，因为在遗传编码的氨基酸中已描述了HLG逐渐减小的显著趋势。HLG是化学反应性的零阶预测指标。将从陨石中回收的134种非生物有机分子与570种被认为完全是生物来源的微生物和植物次生代谢产物进行比较，我们发现生物分子的平均HLG显著更窄（-10.4±0.9电子伏特对-12.4±1.6电子伏特），效应大小g = 1.87。将范围限制在亲水性分子（XlogP < 2）可改善生物化合物与非生物化合物的分离效果（g = 2.52）。由|HLG| < 11.25电子伏特和XlogP < 2定义的“亲水性反应性”象限仅包含183种生物化合物和6种非生物化合物，其中5种是非生物碱基。我们得出结论，具有小HLG的亲水性分子代表了生物活性的有价值指标，并讨论了这一推断在进化上的合理性。
