Porphyrins zinc-containing

Organometallic porphyrin complexes containing the late transition elements (from the nickel, copper, or zinc triads) are exceedingly few. In all of the known examples, either the porphyrin has been modified in some way or the metal is coordinated to fewer than four of the pyrrole nitrogens. For nickel, copper, and zinc the 4-2 oxidation state predominates, and the simple M"(Por) complexes are stable and resist oxidation or modification, thus on valence grounds alone it is easy to understand why there are few organometallic examples. The exceptions, which exist for nickel, palladium, and possibly zinc, are outlined below. Little evidence has been reported for stable organometallic porphyrin complexes of the other late transision elements. 

Other supramolecular structures such as dendrimers have also been synthesized with zinc-containing porphyrins. Sixteen free base and sixteen zinc porphyrin units were added at the fifth generation of dendritic poly(L-lysine) and intramolecular fluorescence energy transfer was observed.823 Assembly of supramolecular arrays in the solid state has been achieved with the incorporation of an amide group for hydrogen bonding. Zinc meso-tetra(4-amidophenyl)porphyrin... 

Campidelli et al. have synthesized interesting linear and hyperbranched porphyrin polymers from CNTs via copper-catalyzed alkyne-azide cycloaddition (CuAAC) [122], Zinc porphyrin monomers containing an azide group and one or three alkyne groups were synthesized and chemically bound to alkyne functionalized SWCNTs via CuAAC. Depending upon the number of alkyne functionalities either linear (single alkyne) or dendrimer-like (triple alkyne) porphyrin polymers were produced (Fig. 5.9) [122],... 

The ionic separation may not be the only factor giving rise to the behavior of 19, as the photoinduced electron transfer rate constant does not change appreciably, even when the driving force is increased by 0.4 eV through introduction of zinc into the porphyrin macrocycle. In this connection, very rapid photoinduced electron transfer has been observed in other zinc-containing porphyrin-quinone systems [80, 86], and photoinduced electron transfer in zinc-containing porphyrin dyads has... 

If one examines the speed of reaction as measured by rate constants k and also the strength of the bonds formed, as reflected in the formation constants (A or P), one can find many instances where, for example, the zinc-containing metalloprotein carboxypeptidase would have been kinetically and thermodynamically better placed to undertake this role in vivo had the zinc have been replaced with cobalt(n). Similarly, there are kinetic and thermodynamic reasons for replacing the ferrous ion in porphyrins with cobalt(ii) or with copper ions. 

Bis(zinc porphyrin)-oxoporphyrinogen [(ZnTPP)2-OxP] is an example of a donor-acceptor-type triad. Excitation of the zinc porphyrin gronps leads to an efficient energy or electron transfer in the triad and this process depends on the polarity of the solvent used. Further elaboration of this system was accomplished by complexing this compound and other derivatives with fullerene-containing compounds capable of coordinating at the porphyrin zinc metal ions. The structures of the complexes are shown in Figure 14. 

I iguri 2.1 l.eft one of Gustave F-iffcl s blueprints for the framework of the Eiffel Tower in Paris, France [4] Right A 3D zinc-teirakis(4-pyridyl)porphyrine framework containing a four-connected diamond (dia) net [5. ... 

Several reports of carboranylated porphyrins have appeared for utilization in the BNCT of cancer.150 The examples include both nido- (126) (Fig. 73) and closo-carborane cluster-containing (124 and 125) (Fig. 73) materials. Metal-free nido-carboranylporphyrins were able to deliver a higher amount of boron to cells than the corresponding zinc complexes. 

---