William E. Hull

15N-NMR Spectroscopy. V. Investigation of Peptides and Sequence Polyamides Containing ω-Aminosulfonic Acids

Abstract Natural abundance 15N-NMR spectra of ten different sequence polymers containing taurine, γ-aminopropanesulfonic acid, or sulfanilic acid as well as various aminocarboxylic acids were measured in trifluoroacetic acid. Strong neighboring residue effects and a relationship between chemical shift and chain length of the ω-amino acyl residues are observed and discussed. Isomeric sequences of first and second order like (Tau-γ-Abu)n, and (γ-Aps-β-Ala)n or (Tau-Gly-β-Ala)n, and (Tau-β-Ala-Gly)n, show different spectra. The deprotonation of the sulfonamide groups in alkaline solution results in a downfield shift as well as a substantial decrease in signal intensity.

13C-NMR Sequence Analysis. XVIII. Tacticity of Poly(D,L-β-amino Acids)

Abstract D, L-Cis-2-aminocyclobutane-1-carboxylic acid NCA, D, L-cis-and trans-2-aminocyclohexane-1-carboxylic acid N-carboxyanhydride (NCA) and D, L-cis-2-aminocyclohexane-1-carboxylic acid NCA were polymerized under various conditions. The 13C-NMR spectra of the resulting β-polyamides measured in trifluoro-acetic acid show splittings of all signals reflecting diads and triads. Poly-D, L-3-aminobutyric acid obtained by anionic polymerization of D, L-4-methyl acetidinone does not display tacticity effects in its 13C-NMR spectrum. Hence it is concluded that tacticity effects are observable only if both α- and β-carbons have a substituent. Furthermore, it was found that the reaction conditions do not have a strong influence on the stereospecificity of the NCA-polymerization. In all cases nearly random sequences of D and L-units were obtained.