Song-Ling Jia

Nonplanar porphyrins and their significance in proteins

Nonplanar distortions of tetrapyrroles are prevalent in the hemes of hemoproteins, the pigments of photosynthetic proteins, and cofactor F430 of methylreductase. The nonplanarity of these porphyrin cofactors is currently believed to influence factors in the biological activity of the proteins, in part, because the porphyrin deformations are often conserved within functional classes of proteins. The occurrence, classification, and study of nonplanar porphyrins in proteins and synthetic nonplanar porphyrin analogs are reviewed.

Electron transfer photosensitized by a tin lipoporphyrin in solution, micelles, and at water—organic solvent interfaces

Abstract Electron transfer photosensitized by a tin lipoporphyrin [Sn(IV) octakis((methoxycarbonyl-methyl)-meso-tetrakis-(((eicosanyloxy)carbonyl) phenyl)-porphyrin (SnLipoP)] is investigated under various solution conditions using a donor—SnLipoP—methylviologen (MV2+) ternary system, where the donor is triethanolamine (TEA) or ethylenediaminetetraacetic acid (EDTA). The photoreaction of SnLipoP is compared with the photoreactions sensitized by common Sn porphyrins like tin protoporphyrin IX (SnPP) and octaethylporphyrin (SnOEP). A constant photoreaction rate is observed in a water/organic solvent (hexane, benzene) two-phase system in which the porphyrin (SnLipoP, SnOEP) is in the organic solvent and MV2+ is in the aqueous phase. The rate is monitored by the change in the UV—visible absorption spectra produced by aqueous methylviologen radical MV·+. In contrast with the two-phase system, macroscopically homogeneous solutions (aqueous SnPP and micellar solutions of SnLipoP, SnPP and SnOEP) give pseudo-logarithmic rates. These electron-transfer processes are completely consistent with reductive primary electron transfer to the tin porphyrin and optical shielding effects. Differences in the rates for SnLipoP and the other Sn porphyrins are explained by structural differences in the porphyrins. In particular, the structure of the porphyrin influences the phase in which the porphyrin resides, its location relative to interfacial regions, and the way it interacts with itself and other system components.

NMR STUDIES OF NONPLANAR PORPHYRINS. PART 1. AXIAL LIGAND ORIENTATIONS IN HIGHLY NONPLANAR PORPHYRINS

The ligand orientations in the nonplanar porphyrin complexes 1a–e and 2a–e have been investigated using molecular mechanics calculations and proton NMR spectroscopy. The minimum energy structures calculated for complexes 1a–e show that the planes of the axial pyridine or imidazole ligands are orientated approximately parallel to the CoIII–Nporphyrin bonds, with the ligand ring planes being perpendicular to each other. For complexes 2a–e, the planes of the axial ligands in the calculated minimum energy structures are orientated along the porphyrin meso carbon axis and the ligand ring planes are perpendicular to each other. Thus, for both series of complexes the planes of the axial ligands are orientated parallel to cavities formed by these very nonplanar porphyrins. Proton NMR studies suggest that structures similar to those obtained from the molecular mechanics calculations are retained in solution. In some complexes, hindered rotation of the axial ligands is also observed. Complexes 1a–e and 2a–e are unusual examples of the porphyrin conformation influencing the orientations of axial ligands and, as such, may be useful as models for studying ligand orientation effects in relation to biological systems.

Synthesis and unusual properties of the first 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraalkylporphyrin

The new perhalogenated porphyrin 2,3,7,8,12,13,17,18- octabromo-5,10,15,20-tetrakis(trifluoromethyl)porphinatonickel(II) exhibits several striking features, including an extremely ruffled macrocycle with a very short Ni–N distance, an unusually red-shifted optical spectrum, and, surprisingly, hindered rotation of the meso-trifluoromethyl substituents (ΔG‡278 = 47 kJ mol–1).

NMR studies of nonplanar porphyrins. Part 2. Effect of nonplanar conformational distortions on the porphyrin ring current

The ring currents in the sterically congested and highly nonplanar porphyrin complexes 1a and 2a have been investigated using a double-dipole model of the porphyrin ring current effect. The equivalent dipoles needed to simulate the ring current in the saddle-shaped complex 1a were indistinguishable from those previously determined for the planar or nearly planar complex 3a. A 5% decrease in the equivalent dipoles was required to reproduce the ring current shifts in the ruffled complex 2a. The extremely large nonplanar conformational distortions seen for the porphyrin macrocycles in complexes 1a and 2a thus seem to cause little decrease in the porphyrin ring currents measured by this empirical model.

Synthesis and characterization of a chiral nonplanar porphyrin

The chiral nonplanar porphyrin zinc(II) 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin has been synthesized and its properties investigated.