Metalation of porphyrins

Fig. 3a,b. Template cyclization reactions of a crown ethers and b CPOs. The coordination bonds are illustrated by black arrows. In the crown ether synthesis, ethylene glycols coordinate toward the metal acting as the template (normal template reaction) however, the template coordinates to the incorporated metals of porphyrin In CPO synthesis (inverse-template reaction)... 

Finally, based on experimental studies many groups have reached a consensus that the mechanism of the direct metalation of porphyrins in solution consists of the following six steps ... 

Metallation of porphyrins with PdCl2 or PtCl2 in hot benzonitrile furnishes the square planar complexes, M(Por) (M = Pd11 or Pt11), which show no tendency for axial coordination.17 Pd11 and Ptn(Por) are oxidized in acidic media with H202 (or HOC1), presumably to MIV(Por)(OAc)2, which are converted to Mrv(Por)Cl2 with HC1 (Scheme 24).117... 

Cdn(Por) and HgII(Por), obtained by metallation of porphyrins with metal acetate in pyridine,17" resemble the Zn analogues in coordination behaviour. They are easily dissociated from the macro-cyclic ligand, and form five-coordinate complexes with N-donor ligands.18 In this group, the metal—ligand bonds, both cis and axial, become weaker as the metal becomes heavier (Zn > Cd > Hg) in contrast to other transition metal series but similar to other main group series (equation 23). 

General procedures for the metalation of porphyrins have been reviewed,1,2 but the most commonly employed method for the insertion of iron into the por-... 

The most general and convenient method for the metallation of porphyrins is the procedure employing iV,A-dimethylformamide (DMF) as the reaction medium. Previous methods employed either bases such as pyridine or organic acids such as acetic acid for the reaction medium. These methods are thermodynamically inefficient, as the base competes with the porphyrin for the metal in the former procedure and the protons of the solvent compete with the metal for the porphyrin in the latter. - The DMF method has been applied to the synthesis of a wide variety of materials with a considerable variation in both the chelating structure and the metal chelated. - - ... 

A number of studies on metalloporphyrin formation have been reported over 20 years, as a result of the important role of metalloporphyrins in biological systems. The general mechanism for the metalation of porphyrins was first proposed 1 Hambright emd Chock, and has been reviewed from time to time by Hambright, Lavallee. Schneider, and Tanaka. The rate of metalloporphyrin formation is several orders of magnitude slower than that of the... 

Finally, it is important to recognize that folded oligonucleotides can also be functional. For example, Sen s group has described a series of DNA oligonucleotide aptamers that are catalysts. Aptamers, selected with a transition state analog A-methylmesoporphyrin, catalyzed the Cu and Zn metallation of porphyrins. This catalytic DNA, which requires for its... 

On the other hand, for the first time, we have synthesized a nonnatural ribozyme using an indirect method (96. 97). A pool of RNAs consisting of random sequences was obtained in the presence of 2 -aminocytidine triphosphate instead of CTP. The pool was incubated with an A-methylmesoporphyrin-immobilized gel, and the bound nonnatural RNAs were then collected and amplified by RT-PCR. The selected nonnatural RNA catalyzed the metalation of porphyrin using the same mechanism. In addition, the selected RNA exhibited a peroxidase activity by complex formation with hemin. 

Ni (Por) complexes, obtained by metallation of porphyrin with Ni salts, form five- or six-coordinate complexes only in the presence of ligands in high concentration. The low ligand affinity of Ni(Por) is attributed to the stable diamagnetic configuration which converts to... 

Two classes of DNAzymes will be discussed in more detail here, namely the DNAzymes catalyzing the cleavage of RNA and the metallation of porphyrins. Other transformations catalyzed by DNAzymes include oxidative DNA cleavage... 

Another interesting example of metallosupramolecular dye polymers has been recently published by Groves and coworker [89]. They have constructed the polymer 36 by zinc complexation of two 9-carboxy-l,10-phenanthrolines that are connected to porphyrin. NMR and spectrophotometric monitoring of the complexation reaction revealed that upon addition of zinc ions the phenanthroline complex was formed in the first step prior to the metalation of porphyrin in the second step. In all experiments, an excess amount of zinc salt was used. 

Lindsay WT (1980) Estimation of concentration quotients for ionic equilibria in high temperature water the model substance approach. In Proc Int Water Conf, Engineering Society of Western Pennsylvania, vol 41, pp 284-294 Lipiner G, Willner I, Aizenshtat Z (1988) Correlation between geochemical environments and controlling factors in the metallation of porphyrins. Org Geochem 13 747-756 Lown DA, Thirsk HR, Wyane-Jones L (1970) Temperature and pressure dependence of the volume of ionization of acetic acid in water from 25 to 225 °C and 1 to 3000 bars. Trans Faraday Soc 66 51-73... 

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