THE ENVIRONMENT OF THE 4 NITROGEN-ATOMS OF BACTERIOCHLOROPHYLL A IN SOLUTIONS AS REVEALED BY N-15 NMR-SPECTROSCOPY

The 50 MHz N-15 NMR spectra of N-15-enriched bacteriochlorophyll a were recorded in twelve different solvents. The N-15 signals of the four nitrogens in the tetrapyrrole rings I, II, III and IV (signals I, II, III and IV) were assigned by the use of correlations with those of the alpha, beta and delta methine H-1. Signals I and III appeared in the higher field, while signals II and IV appeared in the lower field; the difference in the chemical shifts within each pair of signals was small. The results indicate an approximate D2h symmetry of the nitrogen environment, with higher electronic density on the ring I and ring III nitrogens.