Serine octamer cluster 3938313 220306818 2008-06-19T06:06:04Z Cyfal 4637213 resolved disambig The '''Serine octamer cluster''' in [[physical chemistry]] is an unusually stable cluster consisting of eight [[serine]] [[molecule]]s (Ser) implicated in the origin of [[homochirality]].<ref>{{cite journal | title = Chiroselective Self-Directed Octamerization of Serine: Implications for Homochirogenesis | author = Cooks, R. G., Zhang, D., Koch, K. J. | journal = [[Anal. Chem.]] | volume'''2001''' | volume = 73 | issue = 15) | pages = 3646–3655 | doi = 10.1021/ac010284l}}</ref><ref>{{cite journal | title = Serine Octamers: Cluster Formation, Reactions, and Implications for Biomolecule Homochirality | author = Nanita, S., Cooks, R. G. | journal = [[Angew. Chem. Int. Ed.]] | year = 2006 | volume = 45 | issue = 4 | pages = 554–569 | doi = 10.1002/anie.200501328}}</ref> This cluster was first discovered in [[mass spectroscopy]] experiments. [[Electrospray ionization]] of an [[aerosol]] of serine in [[methanol]] results in an MS spectrum with a prominent ion peak of 841 corresponding to the Ser<sub>8</sub>+H<sup>+</sup> [[cation]]. The smaller and larger clusters are virtually absent in the spectrum and therefore the number 8 is called a [[magic number (chemistry)|magic number]]. The same octamer ions are also produced by rapid [[evaporation]] of a serine solution on a hot (200-250°C) metal surface or by [[Sublimation (physics)|sublimation]] of solid serine. After production, detection again is by mass-spectroscopic means. For the discussion of homochirality it is important to note that these laboratory production methods are designed to mimic [[prebiotic]] conditions. The cluster is not only unusually stable but also unusual because the clusters have a strong homochiral preference. A [[racemic]] serine solution produces a minimum amount of cluster and with solutions of both [[enantiomer]]s a maximum amount is formed of both homochiral D-Ser<sub>8</sub> and L-Ser<sub>8</sub>. In another experiment cluster formation of a racemic mixture with [[deuterium]] enriched L-serine results in a product distribution with hardly any 50/50 D/L clusters but a preference for either D or L enantioenriched clusters. A model for [[chiral amplification]] is proposed whereby enantioenriched clusters are formed from a non-racemic mixture already enriched by L-serine as a result of a [[mirror-symmetry breaking]] process. Cluster formation is followed by isolation and on subsequent dissociation of the cluster a serene solution forms with a higher concentration of L-serine than in the original mixture. A cycle can be maintained in which each turn results in an incremental enrichment in L-serine. Many such cycles eventually result in [[enantiopure]] L-serine. This model has been experimentally verified. [[Chiral transmission]] is assumed to take place through so-called substitution reactions of serine clusters. In these reactions, a serine monomer in a cluster can be replaced by another small biologically relevant molecule. For instance Ser<sub>8</sub> reacts with [[glucose]] (Glc) to the Ser<sub>6</sub> + Glc<sub>3</sub> + Na<sup>+</sup> cluster. Moreover the cluster of synthetic L-glucose with Ser<sub>8</sub> is less abundant than that with the biological D-glucose. == See also == * Other magic numbers in chemistry: [[methane clathrate]], [[Magic angle spinning]] * Other stable clusters in: aluminium [[superatom]]s == References == {{reflist}} [[Category:physical chemistry]] [[Category:stereochemistry]]