FINE-STRUCTURE OF 5,10,15,20-TETRAKIS(M-HYDROXYPHENYL)CHLORIN (M-THPC) - A H-1, C-13 AND N-15 NMR-STUDY

The H-1, C-13 and natural abundance N-15 NMR spectra of tetrakis(m-hydroxyphenyl)chlorin (m-THPC) are assigned through the complementary analysis of the data from one-dimensional, and both homo- and hetero-nuclear two-dimensional NMR experiments. The analysis of the H-1 and C-13 spectra showed that the symmetry of the structure includes an effective mirror plane, sigma(v), and the H-1-N-15 coupling constant of 99 Hz (measured from the 'inverse-mode' H-1-N-15 2D experiment) showed that the central imino protons undergo slow intramolecular tautomeric exchange. The single N-15 chemical shift (delta 111.8 relative to (NH4+)-N-15) of the proton-bearing nitrogens is characteristic of a 'pyrrole' type, and the long range coupling H-1 chemical shift correlation (2D) spectrum showed that, on the NMR time scale, the imino hydrogens are localised on five-membered rings that are not in the sigma(v) plane. Taken together these data prove that the fine structure of m-THPC is correctly represented with the imino hydrogens placed on opposite rings which are not reduced, as shown in structure 4.