Magnetic Circular Dichroism in Archean Stratospheric Oxygen: Enantiomeric Excess of Amino Acids Produced in Volcanic Plumes.

IF 1.9 4区物理与天体物理 Q2 BIOLOGY

Origins of Life and Evolution of Biospheres Pub Date : 2023-06-01 Epub Date: 2023-06-06 DOI:10.1007/s11084-023-09637-y

A Sharma

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引用次数: 1

Abstract

While there is consensus that Archean atmosphere was anoxic with O₂ pressure, p(O₂) <10^-6 PAL (present atmospheric level) at sea-level, evidence suggests that p(O₂) at stratospheric altitudes of 10-50 km was orders of magnitude higher, a result of photodissociation of CO₂ by UVC sunlight and incomplete mixing of O₂ with other gases. Molecular O₂ is paramagnetic due to triplet ground state. Magnetic circular dichroism (MCD) by stratospheric O₂ is examined in earth's magnetic field and shows maximum circular polarization │(I₊ - I_-)│ at altitude of 15-30 km (I₊/I_- is intensity of left/right circularly polarized light). While (I₊ - I_-)/(I₊ + I_-) is small (~10^-10), it is an unexplored source of enantiomeric excess (EE) by asymmetric photolysis of amino acid precursors produced in volcanic eruptions. The precursors reside in stratosphere for periods of over a year due to relative absence of vertical transport. Due to negligible thermal gradient across equator, they are trapped in the hemisphere where they are produced, with interhemispheric exchange time of over a year. The precursors diffuse through altitudes of maximum circular polarization before getting hydrolyzed on ground to amino acids. Enantiomeric excess of ~10^-12 is calculated for precursors and amino acids. While small, this EE is orders of magnitude higher than predicted (~10^-18) by parity violating energy differences (PVED) and could be the seed for growth of biological homochirality. Preferential crystallization (PC) is described as a plausible mechanism for amplification of solution EE of some amino acids from 10^-12 to 10^-2, for period of several days.

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太古宙平流层氧的磁圆二色性：火山羽中产生的对映体过量氨基酸。

虽然人们一致认为太古宙大气缺氧，O2压力为海平面的p（O2）-6 PAL（当前大气水平），但有证据表明，平流层10-50公里高度的p（CO2）高出几个数量级，这是紫外线阳光对CO2的光解以及O2与其他气体不完全混合的结果。分子O2由于三重态基态而具有顺磁性。平流层O2的磁圆二色性（MCD）在地球磁场中被检测到，并显示出最大圆偏振│（I+-I-）│ 在15-30km的高度（I+/I-是左/右圆偏振光的强度）。虽然（I+-I-）/（I++I-）很小（~10-10），但它是火山喷发中产生的氨基酸前体的不对称光解导致对映体过量（EE）的一个未经探索的来源。由于相对缺乏垂直传输，这些前体在平流层中停留了一年多。由于横跨赤道的热梯度可以忽略不计，它们被困在产生它们的半球，半球间的交换时间超过一年。前体在最大圆极化的高度扩散，然后在地面上水解为氨基酸。前体和氨基酸的对映体过量为~10-12。尽管EE很小，但它比宇称破坏能量差（PVED）预测的（~10-18）高出几个数量级，可能是生物同手性生长的种子。优先结晶（PC）被描述为扩增某些氨基酸的溶液EE的一种可能的机制，从10-12到10-2，持续几天。

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来源期刊

Origins of Life and Evolution of Biospheres 生物-生物学

CiteScore

3.20

自引率

15.00%

发文量

审稿时长

>12 weeks

期刊介绍： The subject of the origin and early evolution of life is an inseparable part of the general discipline of Astrobiology. The journal Origins of Life and Evolution of Biospheres places special importance on the interconnection as well as the interdisciplinary nature of these fields, as is reflected in its subject coverage. While any scientific study which contributes to our understanding of the origins, evolution and distribution of life in the Universe is suitable for inclusion in the journal, some examples of important areas of interest are: prebiotic chemistry and the nature of Earth''s early environment, self-replicating and self-organizing systems, the theory of the RNA world and of other possible precursor systems, and the problem of the origin of the genetic code. Early evolution of life - as revealed by such techniques as the elucidation of biochemical pathways, molecular phylogeny, the study of Precambrian sediments and fossils and of major innovations in microbial evolution - forms a second focus. As a larger and more general context for these areas, Astrobiology refers to the origin and evolution of life in a cosmic setting, and includes interstellar chemistry, planetary atmospheres and habitable zones, the organic chemistry of comets, meteorites, asteroids and other small bodies, biological adaptation to extreme environments, life detection and related areas. Experimental papers, theoretical articles and authorative literature reviews are all appropriate forms for submission to the journal. In the coming years, Astrobiology will play an even greater role in defining the journal''s coverage and keeping Origins of Life and Evolution of Biospheres well-placed in this growing interdisciplinary field.