Spontaneous chiral separation in noncovalent molecular clusters

A new method is introduced to determine the extent to which spontaneous chi ral separation occurs in small noncovalently bound clusters. Soft-sampling electrospray ionization was used to transfer noncovalent complexes from sol ution to the gas phase. Mixing D and L enantiomers with one of the pair iso topically labeled reveals the effect of chirality on cluster stability. The observed cluster distribution is compared to the predicted statistical dis tribution to determine any preference for homo- or heterochirality. Arginin e, for example, forms a stable trimer with no preference for the chirality of the individual amino acids. Serine, however, forms a protonated octamer with a pronounced preference for homochirality. The implications of these r esults for the structures of the complexes are discussed along with the bro ader implications for the origins of homochirality in living systems (homoc hirogenesis). (C) 2001 Wiley-Liss, Inc.