Metalloporphyrins metal incorporation

The metalloporphyrin formation reaction is one of the important ptrocesses from both analytical and bioinorganic points of view. The large molar absorption coefficient and the very high stability of p>orphyrins is valuable for the separation of various kinds of metal ions (Tabata et al.,1998). A variety of metalloporphyrin formation rates are also ap>phcable for the kinetic analysis of metal ions (Tabata Tanaka, 1991). Also, kinetic studies of metalloporphyrin formation are indispensable in order to imderstand in vivo metal incorporation processes leading to the natural metaUopwrphyiins. Generally pwrphyiins are synthesized in a metal-free form and metal ions are successively inserted. 

To select the metal to be incorporated into the substrate porphyrin unit, the following basic properties of metalloporphyrins should be considered. The stability constant of MgPor is too small to achieve the usual oligomeric reactions and purification by silica gel chromatography. The starting material (Ru3(CO)i2) for Ru (CO)Por is expensive and the yield of the corresponding metalation reaction is low. Furthermore, the removal of rutheniirm is difficult, and it is likewise difficult to remove the template from the obtained ruthenium CPOs. Therefore, ZnPor is frequently used as a substrate in this template reaction, because of the low prices of zinc sources (zinc acetate and/or zinc chloride), the high yield in the metalation reaction, the sufficient chemical stability of the ZnPor under con-... 

The qualitative stabihty constants of metalloporphyrins are summarized in Table 1. The metals classified in class I produce the most stable metalloporphyrins and the demetalation reaction does not proceed smoothly even under concentrated sulfuric acid condition. The incorporated metals classified in classes 11 and III are removed using mild acids such as hydrochloric acid. Calcium classified in class V is removed by (the pH of) water. The mixed cyclization reactions afford the heterometalated CPO, and the acid treatment of the CPO obtained produces the CPO containing 2HPor moiety. Further treatment of the metal salt classified in a class lower than that of the unremoved metal(s), which is classified in a class higher in Table 1, produces another heterometalated CPO. Representative examples are summarized in Fig. 5 [25]. The initial cyclization reaction is carried out by using Ru (CO)Por 6, the metal of which is classified in class 1, and ZnPor 5, clas-... 

Metal ions within organometallic dendrimers can be incorporated at the core, in the branches, or at branch points. Examples of dendrimers having metal-ion-containing cores included the dendritic metalloporphyrins [66,67] and related materials reported by Aida and Enomoto [68],Diederich et al. [69], Moore et al. [70], and Erechet et al. [71], dendritic terpyridine-ruthenium complexes report-... 

Metalloporphyrins are formed by the chelation of a metal ion into the porphyrin structure. This involves the incorporation of the metal ion into the center of the tetrapyrrole ring with the simultaneous displacement of two protons from the pyrrolic nitrogen atoms. Nickel is present in petroleum as Ni (II), and it sits in the plane of the four pyrrole rings comprising the porphyrin. The vanadium is present as V (IV), but exists in... 

Porphyrin and its derivatives are well-known model compounds for photosynthetic processes that involve charge separation [87], A zinc porphyrin, a copper porphyrin, and a zinc phthalocyanine (Pc) are chosen and incorporated into PPV backbones. Four polymers are synthesized via the Heck polycondensation [88], The incorporation of these metal complex moieties in polymers XI to XIII is manifested by the appearance of Q bands from metalloporphyrin and zinc Pc... 

Metalloporphyrins, similar to those shown in Fig. 3a, offer an excellent method for exploring anion selectivity due to the various types of metal ion that can be incorporated into the complex. A metal centre of Fe3+ has been shown to exhibit selectivity for SCN [64], whereas Sn4+ shows good selectivity for salicylate [65]. 

Metalloporphyrins are synthesized naturally and utilized biologically as redox catalysts, and as such are essential to life. These metal complexes have different chemical functions (see [1]) nature has discovered the ability to modulate the function by incorporating them into proteins which allow for a tremendous diversity of architecture and chemical environments surrounding the prosthetic group. Within the protein framework the prosthetic group becomes a versatile tool with varying, highly specialized capabilities. 

Metalloporphyrin formation. Our earlier study of metal ion incorporation by TPP was carried out in a benzene in water micro-emulsion (ME) stabilized by cyclohexanol and a few different surfactants (.8). The Influence of Lewis bases, quinoline in particular, was studied in the ME system containing (anionic) sodium cetyl sulfate (SCS). For reasons to be discussed below, it was... 

Metalloporphyrin receptors (e.g., 73) based solely on a single metal ion-anion coordinative interaction have seen considerable application as receptor species for incorporation in electrode systems (176-180). The main goal in... 

Within the large number of multiredox arrays containing metalloporphyrins/covalently bound (conjugate) fullerene-metalloporphyrin dyads have gained enormous interest in the last ten years, mainly due to their potential application as artificial antennae Due to the multiredox behaviour of the fullerenes (up to six reversible one-electron reductions and at least one reversible one-electron oxidation), the porphyrin ligands and the incorporated metals, the assignment of electron-transfer steps in such systems is difficult. Recently, spectroelectrochemical characterisation has been carried out on a number of fullerene-[(TPP)Co] dyads shown in Scheme 4.3, which exhibit rather complex redox behaviour (Figure 4.19). 

In 10-2 M HC1, [In(tmpyp)]5+ has bands at 424 nm (e = 390,000), 518 nm (e = 3690), 558 nm (c = 23,200), and 597 nm (e = 4660). The spectrum is similar to that of indium(III)-tetraphenylporphyrin.16 The [In(tmpyp)]5+ is fully water soluble, and rapid acid solvolysis occurs only above 3 M HC1 levels. Refluxing a divalent metal chloride with H2tmpyp in water, and keeping the pH between 3 and 5, is the general method used to prepare the Cu2+, Zn2+, Ni2+, Mn3+, Fe3+, and Co3+ compounds.6 The 642-nm free-base porphyrin band disappears when the incorporation reaction is complete. The high-pH conditions (a) reduce the concentration of unreactive centrally protonated15 porphyrins, (b) minimize the extent of acid catalyzed metalloporphyrin solvolysis reactions,17 and (c) increase the concentration of the often more reactive hydrolyzed metal ion forms.18... 

The most important by-product of the analytic and synthetic work accomplished so far is knowledge about the stereochemistry and reactivity of natural compounds. There is an enormous potential for the chemists of the twenty-first century lying in the mastery and application of this knowledge in order to produce organized and finally functional materials. Typical contemporary examples include surface monolayers on metals and colloids made of fatty acid and steroid derivatives, the regio- and stereoselective assembly reactions between steroids and carbohydrates, coupled redox chains of metalloporphyrins and vitamins, noncovalent fibers made of amino acids, nucleotides, and saccharides, and the functionalization of proteins by incorporation of reactive molecules. The field of supramolecular or noncovalent natural compound chemistry has been scientifically fruitful for several decades and is presently exploited for the development of useful molecular devices and machines as well as for medical applications. 

Receptor 33 also incorporates a secondary Lewis acid anion binding site. This molecule is the zinc metallated ansdogue of 17 with the cobal-tocenium reporter groups replaced with ferrocenes [27]. The freebase precursor to 33 in dichloromethane solution shows no significant anion induced shifts in the H NMR signals of the amide protons, whereas the metalloporphyrin binds bromide (JC = 6200M ), nitrate (K = 2300M i)... 

Rollman (4 3) synthesized a series of polymer-bonded metalloporphyrins. Functionalized tetraphenyIporphyrines were attached to porous polystyrene resins via amine, carbonyl and ester linkages and metal ions (Co,Ni,Cu,Zn) were then incorporated into the structures. The porphyrin polymers that contained both oxidation (Co) and proton-acceptor sites (amine and carboxylate groups) were effective catalysts for the oxidation of thiols to disulfides. When the catalyst was exposed to a refinery stream containing only 180 ppm mercaptan sulfur, deactivation occurred. Deactivation was thought to occur via oxidation of the porphyrins by free radicals known to be present in such catalytic systems. 

Studies on water soluble and insoluble porphyrins have elucidated aspects of the mechanisms of metal ion incorporation into porphyrins to form metalloporphyrins (Bailey Hambright, 2003 Hambright et al, 2001 Lavallee, 1987 Funahashi et al., 2001). 

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