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August 13, 2001
Volume 79, Number 33
CENEAR 79 33 p. 13
ISSN 0009-2347
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Amino Acid Assembles In Eight-Member Clusters


Magic numbers, noncovalent assemblies, and the homochirality of life play leading roles in a multipart chemistry drama unfolding now at Purdue University. Chemistry professor R. Graham Cooks, graduate student Kim J. Koch, and postdoctoral associate Duxi Zhang find that the amino acid serine is overwhelmingly predisposed to forming clusters of eight molecules over other-sized clusters [Anal. Chem., 73, 3646 (2001)].

CLUSTERS Serine molecules readily form octamers that are stabilized by noncovalent interactions.
The octamers, which are readily formed in a mass spectrometer via electrospray ionization, are noncovalent complexes that provide an accessible route to studying noncovalent interactions between drugs and receptors, enzymes and substrates, and related systems.

A key finding of the study is that serine's propensity to assemble in units of eight is chiroselective--that is, clusters form from enantiopure samples but not from racemic mixtures. Furthermore, the researchers discovered that they could incorporate more than one type of amino acid into the clusters, provided that all of the amino acids have the same chirality. For example, they prepared octamers composed of six D-serine molecules and two D-homoserine molecules. Computational studies by colleagues at the State University of Campinas in Brazil indicate that the octamers can accommodate up to two homoserine molecules and still maintain their structure and stability.

The group proposes that the study may have implications for the century-old question about the origin of homochirality of life--the puzzling observation that living organisms are almost always made up of left-handed amino acids and right-handed sugars.

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