Formation of replicating saponite from a gel in the presence of oxalate: implications for the formation of clay minerals in carbonaceous chondrites and the origin of life.
Formation of replicating saponite from a gel in the presence of oxalate: implications for the formation of clay minerals in carbonaceous chondrites and the origin of life.
复制标题
在草酸盐存在下从凝胶中形成复制皂石：对碳质球粒陨石中粘土矿物的形成和生命起源的影响。
作者：
D. Schumann;H. Hartman;D. Eberl;S. Sears;R. Hesse;H. Vali
粘土矿物在生命的非生物起源中的潜在作用一直是过去几十年来持续辩论的主题。争论的焦点是在一类被称为碳质陨石的陨石中发现的粘土矿物。这些粘土矿物是无水矿物相的水蚀变的产物，例如橄榄石和斜方辉石，它们通常存在于球粒中。此外，粘土矿物的出现和极性有机分子的存在有很强的相关性。在低温和常压下的实验室实验已经表明，极性有机分子，如陨石中发现的草酸盐，可以催化粘土矿物的结晶。在这项研究中，我们表明，草酸盐是一个强大的催化剂，在结晶皂石，铝和镁丰富，三八面体2：1层硅酸盐，从硅酸盐凝胶在60°C和环境压力。用十八烷基铵（n（C）=18）阳离子处理的皂石的高分辨率透射电子显微镜分析显示存在具有可变层间电荷的2：1层结构。这些不同电荷的2：1层状硅酸盐的结晶最可能独立地发生。在同一凝胶中形成的具有可变电荷的2：1层状硅酸盐这一事实对我们理解生命的起源具有重要意义，因为这些2：1粘土矿物很可能通过模板催化聚合的机制进行复制，并将电荷分布从一层传递到另一层。如果像草酸盐这样的极性有机分子可以催化粘土矿物晶体的形成，从而促进粘土微环境的形成，并为溶液中存在的其他有机分子提供丰富的吸附位点，那么这些吸附分子之间的相互作用可能导致更复杂的有机分子的聚合，如早期地球上核苷酸的RNA。
The potential role of clay minerals in the abiotic origin of life has been the subject of ongoing debate for the past several decades. At issue are the clay minerals found in a class of meteorites known as carbonaceous chondrites. These clay minerals are the product of aqueous alteration of anhydrous mineral phases, such as olivine and orthopyroxene, that are often present in the chondrules. Moreover, there is a strong correlation in the occurrence of clay minerals and the presence of polar organic molecules. It has been shown in laboratory experiments at low temperature and ambient pressure that polar organic molecules, such as the oxalate found in meteorites, can catalyze the crystallization of clay minerals. In this study, we show that oxalate is a robust catalyst in the crystallization of saponite, an Al- and Mg-rich, trioctahedral 2:1 layer silicate, from a silicate gel at 60°C and ambient pressure. High-resolution transmission electron microscopy analysis of the saponite treated with octadecylammonium (n(C)=18) cations revealed the presence of 2:1 layer structures that have variable interlayer charge. The crystallization of these differently charged 2:1 layer silicates most likely occurred independently. The fact that 2:1 layer silicates with variable charge formed in the same gel has implications for our understanding of the origin of life, as these 2:1 clay minerals most likely replicate by a mechanism of template-catalyzed polymerization and transmit the charge distribution from layer to layer. If polar organic molecules like oxalate can catalyze the formation of clay-mineral crystals, which in turn promote clay microenvironments and provide abundant adsorption sites for other organic molecules present in solution, the interaction among these adsorbed molecules could lead to the polymerization of more complex organic molecules like RNA from nucleotides on early Earth.