Porphyrins ligand modification

Various chemical modifications of this compound have been carried out (the porphyrin ligand, solvent, acceptor molecule, and metal ion). " ... 

Several types of porphyrin and phthalocyanine ligand modification have been performed to create a new family of electrochemically polymerizable complexes. The most commonly used porphyrins are the amino " hydroxy methoxy ° ° , vinyl- and other " substituted macrocyclic complexes (see examples in Figure 8.13). In the case of phthalocyanine, tetra-amino-substituted macrocycle was exclusively and intensively developed. Studies of these complexes have focused on the electrochemical synthesis and characterization of conductive polymeric or copolymeric materials. 

The modification of the physical properties of some molecules as consequence of complexation with CDs is well known. Kongo et al.126 studied the TB-p-CD/porphyrine complex and observed a drastic change in the photochemical and photophysical properties of porphyrine. The conformational analysis by NMR revealed strong NOE interactions between the ligand and the internal part of the CD, in agreement with a deep insertion of the porphyrine analogue into the CD s cavity. The NOE data provided structural information to propose the 3D model of 1 2 inclusion complexes. 

Covalent modification of protohemin and deuterohemin complexes, by linkage of histidine residues to the propionate side chains of the porphyrins, is the standard approach followed to introduce the push effect exerted by the proximal ligand in peroxidases [205, 208-211], To combine the activation effect given by the axial imidazole and the substrate recognition given by an appended peptide chain, two model systems were studied by our group. These complexes contain an L-histidine... 

Modification of protoporphyrin IX at the propionate positions has been used by Traylor and coworkers and Casella eta/. to prepare porphyrin complexes with a covalently attached axial ligand or ligands. The latter workers... 

It has also been shown that with certain kinds of axial ligands (isocyanides, low-basicity pyridines ) or certain modifications of the porphyrin TT orbitals (such as occurs in the highly reduced hemes), the relative energies of the d y and d orbitals dxzAyz) can be reversed, leading to an electron configuration that is dxzAyzfi xy) This electron configuration results in axial (with > 2 > gy ) i74,i75,621,1217-1219,1280,1281... 

In order to increase the solubility of porphyrin and phthalocyanine complexes, several structural modifications have been made, a, jS, y, 6-Tetra-(4-pyridyl)-porphin complexes of copper(II), nickel(II), and zinc(II) have been synthesized (35) and their ultraviolet spectra determined in chloroform and in acid solution. By utilizing sulfonic acid groups to increase solubility, complexes of 4,4, 4",4" -tetrasulfophthalocyanine complexes of many metals were prepared (94j 95). This chelating agent was found to have a ligand field strength comparable to cyanide (94y 95). 

The metalloporphyrins as macrocyclic compounds have a few sites for specific and universal solvation and are able to axial coordination of some ligands. At the present time chemical modification of macrocycle is a main way of increasing of selectivity of molecular complex formation. The data obtained earlier [1,2] show that the selectivity may be increased due to specific %-% interactions of the metalloporphyrins with aromatic molecules. Aromatic molecules coplanar to the macrocycle will rise geometrical requirements to axial coordinating ligands. In particular, the results of the thermodynamic study of the axial coordination of n-propylamine by zinc(II) porphyrins in benzene have demonstrated the formation of the complexes of the metalloporphyrin containing both w-propylamine and benzene [2], The aim of this work is to study the molecular complexes of zinc (II) porphyrins prepared by slow crystallization from saturated solutions in benzene, w-propylamine and mixed solvent benzene - -propylamine. 

---