Mercury complexes porphyrins

Mercury(II) porphyrins seem to be rather irregular, since various types of Hg11 complexes have been reported (Scheme 25).174... 

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 ... 

Kinetic studies have proposed evidence for the formation of heterodinuclear intermediate. In order to study the structure of the intermediate in solution as related to the reaction mechanism, extended X-ray absorption fine structure (EXAFS) measurements have been undertaken for the metal-substitution reaction of mercury(ll) porphyrin complex with copper(II) in an acetate buffer (pH = 5.6). 

Neither of these metalloporphyrins has been found in crude oil, however. Mercury forms porphyrin complexes with mesoporphyrin but the complexes are decomposed by water. The extraction of crude oil C-1 with distilled water removed insignificant amounts of Hg, thus indicating that Hg is not present in the oil as a porphyrin complex. Arsenic also shows a higher concentration in the low-molecular-weight fraction than in the 1000-4000 fraction. This is consistent with the previous conclusion that part of the As in crude oil is present in low-molecular-weight compounds such as alkyl or aryl arsines. 

Stromberg D, Sandstrom M, Wahlgren U (1990) Theoretical calculations on the stracture of the hexahydrated divalent zinc, cadmium and mercury ions. Chem Phys Lett 172 49-54 Svegensky DA, Shock EL, Helgeson HC (1997) Prediction of thermodynamic properties of aqueorrs metal complexes to 1000°C and 5 kb. Geochim Cosmochim Acta 61 1359-1412 Tabata M, Ozutsumi K (1992) Eqirilibrium and EXAFS studies of mercury(II) porphyrin in aqueous solution. Brrll Chem Soc Jap 65 1438-1444... 

Heavy metal ions detection with porphyrin in sol-gel is possible, too56. The porphyrin, used for detection of heavy metal ions (Hg2+, Pb2+, Cd2+), was 5,10,15,20-tetra(4-N-methylpyridil)porphyrin (TMPyP) preferred to other porphyrins because it was not leaked out of the matrix. The study of metallation of the porphyrin immobilized in sol-gel emphasized the formation of 1 1 complex for each ion with a constant of complexation depending on the nature of the ions. The strongest effects were observed for mercury due to the specific interaction of this metal with the porphyrin. 

Porphyrins in which the metal is bound to fewer than four pyrrole nitrogen atoms have attracted attention as models for the early steps in the metallation of the macrocycle. The bis[chloromer-cury(II)] complex of N-tosylaminooctaethylporphyrin involves one mercury coordinated to three porphyrin N atoms and one Cl, and the other to Cl and the remaining pyrrole N atom.614... 

Sequestering in a cyclic environment imparts to the metal novel properties and favours redox activity. For instance, [Nin(cyclam)]2+ in 1 M HC1 is oxidised to the indefinitely stable [Nira(cyclam)]3+ complex, at a moderately positive potential (0.72 V vs. NHE) [9]. The acidic medium is required to prevent intramolecular electron transfer processes, leading to decomposition [10]. Moreover, [Nin(cyclam)]2+ can be electrochemically reduced to NiVcyclam) + at a mercury electrode, where it catalyses the reduction of CO2 to CO and HCOO (in an aqueous solution buffered to pH 5) [11]. This is nothing especially new encircling by tetra-aza macrocycles (e.g. porphyrins) is a trick known to Nature for billions of years to favour and control the redox activity of metal ions. 

Scheme 2. Reaction scheme of the metal-substitution reaction of Hg2(lpps)2- with copperfll) in an acetate buffer. 1. free base porphyrin 2, mercury(II) acetato complex 3, homodinuclear mcrcury(ll) porphyrin 4, copperfll) acetato complex 5, heterodinuclear intermediate 6, mercuryfll) acetato complex 7, coppetflll porphyrin.

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