| Abstract
| - Negatively charged halide adducts of serine octamers, (Ser8+2Cl)2- and (Ser8+2Br)2-, appear as magic numberclusters in the negative ion electrospray mass spectra of solutions containing serine and the halide. Like thewell-known protonated serine octamer, these negatively charged adducts are formed with homochiral preferenceand also undergo chiroselective substitution reactions with other amino acids. Tandem mass spectra of negativelycharged halide adducts of serine octamers show that these ions also have a characteristic fragmentation signature.The fact that octamers of both polarities display analogous chemical properties suggests that these may becharacteristics of the so-far-unknown neutral octamer. If serine played a key role in the origin of homochiralityon the primitive earth, it was likely through both the neutral octamer and the ionic adducts. Unlike the octamers,the formation of halide-containing serine cluster ions of particular sizes is unfavorable under the conditionsof the experiment. Signals corresponding to the ions (Ser9+2Br)2- and (Ser15+2Br)2- are particularly low inintensity, giving rise to gaps in the distribution of serine/bromide clusters in the negative ion electrospraymass spectra. These cluster sizes are likely to correspond to unstable “anti-magic number” clusters recentlyreported by Clemmer.
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