Lerner N R, Peterson E, Chang S
Planetary Biology Branch, NASA-Ames Research Center, Moffett Field, CA 94035, USA.
Geochim Cosmochim Acta. 1993 Oct;57(19):4713-23. doi: 10.1016/0016-7037(93)90195-3.
Deuterium-enriched amino acids occur in the Murchison carbonaceous chondrite. Synthesis from D-enriched interstellar precursors by Strecker reactions during aqueous alteration of the parent body has been proposed. To test this hypothesis, we have measured the retention of deuterium in amino acids produced from HCN, NH3, and formaldehyde-D2, acetaldehyde-D4, and acetone-D6 in H2O. The isotopic label is 50% to 98% retained, with variations in retentivity depending on the amino acid and the reaction conditions. If amino acids, once formed on the parent body by the Strecker synthesis, lose no deuterium by subsequent exchange with water or H-bearing minerals, then the observed deuterium isotopic composition of Murchison amino acids represents as much as 50% or more of the enrichments inherited from their interstellar precursors. Imino diacids are prominent side products of the Strecker synthesis which have not been reported in carbonaceous chondrites. Under the conditions of the Strecker reaction using deuterium labeled aldehydes and ketones, unlabeled amino acids are also formed by an HCN polymerization route indicating multiple pathways for the synthesis of amino acids in meteorites.
富含氘的氨基酸存在于默奇森碳质球粒陨石中。有人提出，在母体水蚀变过程中，通过斯特雷克反应由富含氘的星际前体合成氨基酸。为了验证这一假设，我们测量了由HCN、NH₃以及水中的甲醛-D₂、乙醛-D₄和丙酮-D₆生成的氨基酸中氘的保留情况。同位素标记的保留率为50%至98%，保留率因氨基酸和反应条件而异。如果氨基酸一旦在母体上通过斯特雷克合成形成，随后不会因与水或含氢矿物交换而失去氘，那么默奇森氨基酸中观察到的氘同位素组成代表了从其星际前体继承的富集量的50%或更多。亚氨基二酸是斯特雷克合成的主要副产物，在碳质球粒陨石中尚未见报道。在使用氘标记醛和酮的斯特雷克反应条件下，未标记的氨基酸也通过HCN聚合途径形成，这表明陨石中氨基酸的合成有多种途径。
