Homochirality and life.
Homochirality and life.
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同手性与生命。
DOI：
10.1007/978-3-0348-8837-0_10
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Bonner Wa
中科院分区：
文献类型：
--
作者：
Bonner Wa
在澄清了经常被误用的术语“同手性”之后，讨论了同手性和手性纯度在生命的基本生物聚合物（蛋白质和核酸）的发展和维持中的关键重要性。描述了大约4.5 Gyr前地球形成后彗星撞击时代的严酷和险恶的生命前环境，然后列举了历史上提出的原始地球上手性分子起源的最重要的非生物机制。根据撞击时期施加的环境限制，分别对随机和确定的陆地机制进行了评估，并得出结论，所有这些机制在现实的益生元环境中都不适用和不可信。为了规避这些限制，提出了一个扩展的假设，描述了同手性陆地分子的外星来源。如图2所示，这种情况涉及到星际尘埃颗粒上有机地幔的外消旋成分被来自超新星中子星残余物的同步辐射的圆偏振紫外线成分部分不对称光解。在有机地幔中产生的具有低对映异构体过量（ees）的同手性成分随后通过直接积累或更有可能合并成彗星或小行星，然后在撞击时代重复撞击，随后传递到地球。最后，这样引入的外星同手性分子的低纯度被地球上的自催化或聚合机制放大到手性纯度状态，然后最终被浓缩并被隔离在自发形成的原细胞囊泡内部——在那里等待进一步的化学进化，以形成生命的生物分子。最近对默奇森陨石中过量的l -超过d -氨基酸的观察被引用为对所提出的假设的早期阶段的验证。
After clarifying the frequently misused term homochirality, the crucial importance of homochirality and chiral purity in the development and maintenance of the essential biopolymers of life--proteins and nucleic acids--is discussed. The harsh and forbidding prebiotic environment during the era of cometary impact after formation of the Earth approximately 4.5 Gyr ago is described, after which the most important abiotic mechanisms proposed historically for the genesis of chiral molecules on the primitive Earth are enumerated. Random and determinate terrestrial mechanisms are each evaluated with regard to the environmental restraints imposed during the impact era, and it is concluded that all such mechanisms would be inapplicable and implausible in the realistic prebiotic environment. To circumvent these limitations, an extended hypothesis is presented describing an extraterrestrial source of homochiral terrestrial molecules. Illustrated in Figure 2, this scenario involves the partial asymmetric photolysis of the racemic constituents of organic mantles on interstellar dust grains by the circularly polarized ultraviolet components of the synchrotron radiation emanating from the neutron star remnants of super-novae. The resulting homochiral constituents with low enanantiomeric excesses (ees) so produced in the organic mantles are subsequently conveyed to Earth either by direct accumulation or, more likely, after coalescence into comets or asteroids, followed by repetitive impingement during the impact era. Finally, the low ees of the extraterrestrial homochiral molecules so introduced are amplified by terrestrial autocatalytic or polymerization mechanisms into a state of chiral purity, then are ultimately concentrated and protected by sequestration in the interiors of spontaneously formed protocellular vesicles--there to await further chemical evolution toward the biomolecules of life. Recent observations of the excess of L-over D-amino acids in the Murchison meteorite are cited as validation for the early stages of the proposed hypothesis.