Solid-state 2-D double cross polarization magic angle spinning 15N 13C NMR spectroscopy on degraded algal residues

Solid-state 2-D 15N 13C NMR spectroscopy was applied for the first time to reveal the chemical nature of nitrogen in degraded algae. Cross peaks indicating coupling between 13C and 15N were detected only for carboxyl/amide-C and N-substituted-alkyl-C. Cross peaks correlating 15N intensity to sp2-C and supporting the presence of heteroaromatic-N were not observed. The Bloch decay 15N NMR spectrum demonstrated that the lack of pyridine-type-N and/or imine-N signals in the CPMAS 15N NMR spectrum is not caused by inefficient magnetization transfer. The results give further evidence that amide-N in peptide-like structures comprises the major form of nitrogen in degraded algal residues.