'Ancestral Eve' Crystal May Explain Origin of Life's Left-Handedness
ScienceDaily (Apr. 21, 2010) — Scientists are reporting discovery of what may be the "ancestral Eve" crystal that billions of years ago gave life on Earth its curious and exclusive preference for so-called left-handed amino acids. Those building blocks of proteins come in two forms -- left- and right-handed -- that mirror each other like a pair of hands.
Molecules of aspartic acid with a left-handed orientation, shown in crystal form, could be the "ancestral Eve" of all amino acids -- the building blocks of proteins -- in life on Earth. (Credit: American Chemical Society)
Their study, which may help resolve one of the most perplexing mysteries about the origin of life, is in ACS'Crystal Growth & Design, a bi-monthly journal.
Tu Lee and Yu Kun Lin point out that conditions on the primordial Earth held an equal chance of forming the same amounts of left-handed and right-handed amino acids.
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The Origin of Life and the Crystallization of Aspartic Acid in Water
Tu Lee* and Yu Kun Lin
Department of Chemical and Materials Engineering, National Central University, 300 Jhong-Da Road, Jhong-Li City 320, Taiwan, R.O.C.
Cryst. Growth Des., 2010, 10 (4), pp 1652–1660
DOI: 10.1021/cg901219f
Publication Date (Web): February 27, 2010
Copyright © 2010 American Chemical Society
*Corresponding author. Telephone: +886-3-422-7151 ext. 34204. Fax: +886-3-425-2296. E-mail:tulee@cc.ncu.edu.tw.
Abstract
The unusual molecular complexation of the enantiomers of aspartic acid in water was discovered and proven by a solubility test, solution freezing point, crystallization kinetics, and the incubation time change. The transformation of a “conglomerate solution” (CS) to a “racemic compound solution” (RCS) was dependent on both temperature and time. The CS was the solution phase which produced conglomerate crystals, and the RCS was the solution phase which gave a racemic compound. Fourier transformed infrared spectroscopy and powder X-ray diffraction were used to characterize aspartic acid solids crystallized from those complex solution phases and to distinguish conglomerate crystals from a racemic compound. We found that it took more than 36 h at 25 °C and 5 h at 45 °C just to complete the solution phase transformation of the CS of aspartic acid to the RCS of aspartic acid. However, the presence of an equimolar of succinic acid could hinder the solution phase transformation of the CS of aspartic acid to the RCS of aspartic acid for up to at least 8 h at 60 °C. This leeway of hours had provided an opportunity for the thermodynamically stable racemic aspartic acid to convert into the metastable conglomerate in water first by either a rapid acid−base reaction or the addition of an antisolvent with the temperature drop, without being concerned by its back conversion later to a racemic compound thermodynamically for quite some time. As a result, enantioseparation of aspartic acid by preferential crystallization in a large scale would have been very common and easy to occur on the primitive earth.
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