Synthesis and NMR analysis of C-13 and N-15-labeled long-chain polyamines (LCPAs)

N-15, C-13, or both isotope labels were introduced in selected positions of several LCPAs containing 5, 11, or 13 nitrogens. The number of transformations during chemical synthesis wasminimized by coupling Fmoc-glycine-N-15, Fmoc-glycine-1-C-13, or Fmoc-beta-alanine simultaneously at both ends of the growing oligoamide chain on resin-linked norspermidine. LCPAs containing 10-20 nitrogens are the main organic constituent of diatom biosilica. Preliminary NMR studies of bioinspired silica nanocomposites obtained from double-labeled LCPA 14 and Si-29-enriched orthosilicic acid identified the close spatial arrangement of Si-29 and C-13 nuclei.