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SynopsisMonodispersed, N-and C-protected homo-oligopeptides [number ( n ) of residues from 2 to 51 of L-valine, L-isoleucine, and L-phenylalanine were studied by ir absorption spectroscopy between 1200 and 3500 cm-' a t various concentrations in various solvents. The solvents and chain-length effects were examined for non-hydrogen-bonded peptide groups. The frequencies of the self-associated species are consistent with a model derived from the amide data. Self-association is favored by higher values of n and by the cooperative hydrogen bonding of successive peptide groups between the chains. For n = 2, the peptide is insoluble when more than two chains are bonded. For n = 3,4, several chains may be associated by sliding along one another and remain soluble. For n = 5, the effect of n is to favor a model in which two chains exactly face each other so that the peptide precipitates a t relatively low concentration.

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