Perhaps of interest to Chase and others (re:chirality, other stuff):
This is from a post by Tim Thompson on a board that is now defunct:
Racemic amino acids from the ultraviolet photolysis of interstellar
ice analogues
Nature 416: 401-403, March 28, 2000
Max P. Bernstein, et al.
Abstract: The delivery of extraterrestrial organic molecules to Earth
by meteorites may have been important for the origin and early
evolution of life. Indigenous amino acids have been found in
meteorites - over 70 in the Murchison meteorite alone. Although it has been generally accepted that the meteoritic amino acids formed in
liquid water on a parent body, the water in the Murchison meteorite is depleted in deuterium relative to the indigenous organic acids.
Moreover, the meteoritical evidence for an excess of laevo-rotatory
amino acids is hard to understand in the context of liquid-water
reactions on meteorite parent bodies. Here we report a laboratory
demonstration that glycine, alanine and serine naturally form from
ultraviolet photolysis of the analogues of icy interstellar grains.
Such amino acids would naturally have a deuterium excess similar to
that seen in interstellar molecular clouds, and the formation process
could also result in enantiomeric excesses if the incident radiation
is circularly polarized. These results suggest that at least some
meteoritic amino acids are the result of interstellar photochemistry,
rather than formation in liquid water on an early Solar System body.
Amino acids from ultraviolet irradiation of interstellar ice analogues
Nature 416: 403-406, March 28, 2000
G.M. Muoz Caro, et al.
Abstract: Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth's early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.
Just to make the story complete, earlier studies on the stability of
amino acid molecules in space are encouraging. Once formed, they are
subject to fairly rapid destruction by the same UV that made it
possible, unless they are protected in ice mantles on interstellar
grains, or in a dense cloud protected from UV (The photostability of
Amino Acids in Space, P. Ehrenfreund et al., Astrophysical Journal
Letters 550: L95-L99, March 20, 2001). There is also evidence, as
suggested in both papers, that if the UV impacting the ice is
circularly polarized, the result could be a non-racemic product. There is some experimental evidence to support this view (Mechanism of pH-dependent photolysis of aliphatic amino acids and enantiomeric
enrichment of racemic leucine by circularly polarized light, H.
Nishino et al., Organic Letters 3(6): 921-924, March 22, 2001), and it is also evident that the necessary environment can be found in space (Astronomical sources of circularly polarized light and the origin of homochirality, J. Bailey, Origins of Life and Evolution of the Biosphere 31(1-2): 167-183, Feb-Apr, 2001).
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