Porphyrin cadmium

Among the most stable cation radical salts are those of metallo-porphyrins. Most commonly the zinc, and magnesium metallo-porphyrins are used (M = Zn, Mg), but others, such as the cadmium porphyrin, are also used (Dolphin et al., 1973 Fajer et al., 1973 Dolphin and Felton, 1974). Tetraarylporphyrins [6, R = H Rj = aryl] or octaalkylporphyrins (R = alkyl, R = H) are the most common parent molecules. Recently, some zinc tetraalkylporphyrin cation radicals were also reported (Fajer et al., 1974). The metallo-porphyrins have low oxidation potentials (Fuhrhop and Mauzerall, 1969 Fuhrhop et al., 1973 Stanienda and Biebl, 1967), and their salts (e.g. perchlorates) can be made quite easily by anodic oxidation in the presence of an appropriate electrolyte. Chemical oxidation, by bromine or ferric ion for example, is also easily achieved, while... 

Properties and Reactions.—meso-Substituted zinc or cadmium porphyrins (43) undergo oxidation by thallium trifluoroacetate at the neighbouring position and after acidic work-up they form the corresponding -substituted oxophlorin (44) ... 

Porphyrin, octaethyl-, cadmium complex cyclic voltammetry, 4, 399 <73JA5I40)... 

Because of its ionic size, cadmium(II) does not fit well into the coordination site of the porphyrin nucleus (N-centre distance 200 pm), and the complexes are readily demetalated (stability group IV, Tables land 2). The complexes can be prepared, of course, but zinc(II) compounds have been overwhelmingly favored for PDT purposes. 

Unusual arene-cadmium 7r-complexes have been recently prepared and structurally characterized. For example, the /w /zz-bcn/i porphyrin complex 194, which can be obtained by reaction of the free base with CdCl2, possesses a cadmium atom that is bound to the Mfez-phcnylcnc unit of the ligand in an apparent /-fashion (Figure 32). The resulting Cd-C distance of 2.71 A is shorter than the sum of the van der Waals radii.252 Despite this relatively short contact, DFT calculations and AIM analysis point to the weakness of the interaction. Comparable weak arene-cadmium 7r-interactions are also observed in the /wra-benziporphyrin cadmium chloride complex 195.253... 

Adults given a single oral dose of either PCB 47 at 87.6 mg/kg body weight (BW), PCB 77 at 87.6 mg/kg BW, or Aroclor 1242 at 100-500 mg/kg BW. Quail were killed 48 h postdosing and liver and intestine analyzed for porphyrins and cytochrome P-450 monooxygenases Adults fed diets for 30 days containing 100 mg cadmium/kg diet, 100 mg Aroclor 1260/kg diet, or mixture of 100 mg cadmium plus 100 mg Aroclor 1260/kg Fed in diet for 25 days at 5, 50, or 500 mg Aroclor 1260/kg diet... 

A number of studies concerning zinc complexes of porphyrins or related ligands have also been reported 1193-1196 cadmium complexes of a number of porphyrins have also been investigated,1197-1199 a number of NMR studies of zinc porphyrin complexes have been made1200,1201 and a number of donor-acceptor complexes of zinc tetrapyrrole species with 1,3,5-trinitrobenzene have been described.1202 Recent developments in metallo-phthalocyamine chemistry, including aspects of zinc complexes, have been reviewed.9-15,12026,1468 11... 

The cadmium(II) complex corresponding to 9 (M = Cd n = 2) was the first texaphyrin made [6], This aromatic expanded porphyrin was found to differ substantially from various porphyrin complexes and it was noted that its spectral and photophysical properties were such that it might prove useful as a PDT agent. However, it was also appreciated that the poor aqueous solubility and inherent toxicity of this particular metal complex would likely preclude its use in vivo [29-31], Nonetheless, the coordination chemistry of texaphyrins such as 9 was soon generalized to allow for the coordination of late first row transition metal (Mn(II), Co(II), Ni(II), Zn (II), Fe(III)) and trivalent lanthanide cations [26], This, in turn, opened up several possibilities for rational drag development. For instance, the Mn(II) texaphyrin complex was found to act as a peroxynitrite decomposition catalyst [32] and is being studied currently for possible use in treating amyotrophic lateral sclerosis. This work, which is outside the scope of this review, has recently been summarized by Crow [33],... 

Cyanide is also an effective infrared probe (Yoshikawa et al., 1985). A drawback of this reagent as an infrared probe is its infrared intensity, which is much weaker than that of CO. However, as given in Fig. 10, the recent development in the infrared technique has solved this problem with the introduction of a mercury/cadmium/tellurium (MCT) detector (Fig. 10) (Yoshikawa et al., 1995). The C-N stretch vibrational band is sensitive to many factors, such as the oxidation state and species of the coordinating metal, the structures of porphyrin ring substituents, and the ligand trans to the cyanide and protein structure (Yoshikawa et al., 1985). This technique can be quite effectively applied for determination of the protonation state of the cyanide bound at a metal site. Possible binding modes of cyanide to a ferric iron are shown by Structures (1), (11), and (HI). Infrared spectroscopy is the best method for identihcation of these... 

In order to accelerate the slow metalation, several methods have been proposed (1) use of substitution reaction of cadmium(II) or mercuty(II) porphyrin, (2) use of N-substituted porphyrins at the pyrrole nitrogen, (3) addition of aromatic heterocyclic bases such as pyridine and imidazole, (4) introduction of functional groups to bind metal ions in the vicini of the porphyrin nucleus (e. g. tetracarboxylic add "picket-fence" porphyrins) and (5) use of reducing agents such as hydroxylamine and ascorbic add in copperfll) incorporation. 

Heterodinuclear metalloponhyrin, postulated in the metalloporphyrin fomiation catalyzed by mercury(II) or cadmium(Il)10 12 was detected kinetically in the reaction of zincfll) or copper(ll) with homodinuclear mercury(II) porphyrin complex of Hg2tpps2 - The following biphasic reaction was observed ... 

As alluded to above, metal complexes of a number of lanthanide and actinide texaphyrin complexes have also been prepared. In the case of Dy(III) texaphyrin 9.74, as in the case of the bis-pyridine cadmium complex 9.61b, the metal center sits directly within the mean plane of the macrocycle (Figure 9.1.12). This result stands in direct contrast to the highly labile, typically sandwich-type 2 1 or 3 2 complexes observed for porphyrin complexes with these larger metal cations. ... 

A mixed organic-inorganic 3D porphyrin network was obtained by cocrystallization of palladium mc n-tetrapyridylporphyrinate and cadmium nitrate. All four pyridyl units are bound to octahedral cadmium centres which are each coordinated by two nitrate, water and pyridyl ligands (Figure 7.27). One half of the py-Cd-py connections is linear, the other half bent (103°), having two cis pyridine ligands. As is common in mc o-tetraarylporphyrins,... 

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