Cobalt-porphyrin polymers

H. Nishide, H. Kawakami, T. Suzuki, Y. Azechi, E. Tsuchida, Enhanced stabihty and facilitation in oxygen transport through cobalt porphyrin polymer membranes, Macromolecules 23 (15) (1990) 3714-3716. 

Figure 9-10. Oxygen absorption into the cobalt porphyrin-polymer membranes at 25 °C.

Figure 9-14. Oxygen and nitrogen permeability coeffieients (/ 02 and Pn2) for the cobalt porphyrin-polymer complex menftrane. The cob

Measurement of Oxygen-Binding Rate Constants for Solid State Cobalt Porphyrin-Polymer Complexes (Section 9.2.4) [27]... 

Table 2 Diffusion Constants of Oxygen (D) in Fig. 10 and Oxygen-Binding and Oxygen-Releasing Rate Constants in the Cobalt-Porphyrin Polymer...

A freeze-dried powder of the cobalt-porphyrin (6) polymer possessed a fine porous structure, and it adsorbed and desorbed oxygen rapidly. The (6) powder containing 30% cobalt-porphyrin was charged in a chamber, and the air supply and evacuation with a simple pump was repeated at 30-sec intervals This pressure swing method with the cobalt-porphyrin polymer as an oxygen adsorbent provided oxygen-enriched air (oxygen concentration in the product flow 45%). 

The deoxy-oxy cycle was repeated at 1-min intervals and recorded 1.2 X 10 times (about 6 months) by changing the atmosphere of the cobalt-porphyrin polymer membrane from reduced pressure (about 2 cm Hg) to laboratory air pressure (76 cm Hg) at ambient temperature. Lifetime or half-life periods for the oxygen-binding ability were estimated to be 6 months for Structure (6) in the solid membrane state. The corresponding cobalt-porphyrin (6) in homogeneous toluene solution was able to repeat the oxy-deoxy cycle with a lifetime close to only 1 day. 

Figure 9 Oxygen (P02) and nitrogen (PN2) permeability coefficients for the cobalt-porphyrin polymer membrane p2, upstream gas pressure the cobalt-porphyrin concentration in the membrane 1.2 and 4.5% for closed and open symbols, respectively, at 30°C.

Cobalt porphyrin complexes are involved in the chain transfer catalysis of the free-radical polymerization of acrylates. Chain transfer catalysis occurs by abstraction of a hydrogen atom from a grow ing polymer radical, in this case by Co(Por) to form Co(Por)H. The hydrogen atom is then transferred to a new monomer, which then initiates a new propagating polymer chain. The reaction steps are shown in Eqs. 12 (where R is the polymer chain. X is CN), (13), and (14)." ... 

Buttry DA, Anson FC. 1984. New strategies for electrocatalysis at polymer-coated electrodes. Reduction of dioxygen by cobalt porphyrins immobilized in Nalion coatings on graphite electrodes. J Am Chem Soc 106 59. 

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

Despite some small spectral differences, the similarities have been sufficient to confirm the slow step in the electrochemistry of immobilized cobalt porphyrin mediators (113) and to identify the intermediates involved in a tetrathiafulvalene polymer coated electrode (7). A polyxylylviologen -polystyrenesulfonate co-polymer coated electrode, on the other hand, showed no changes in the position of the peaks in the absorption spectra upon immobilization (111). Presumably this indicated an absence of interactions between neighboring viologen moieties. Similar spectral results have been obtained using photoacoustic spectroscopy (PAS). Heptyl viologen adsorbed on Pt exhibited an unshifted spectrum which correlated with the electrochemical results (115). 

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

In this paper, we report the development of ISEs that have been designed by using molecular recognition principles. Specific examples include the development of polymer membrane anion-selective electrodes based on hydrophobic vitamin B12 derivatives and a cobalt porphyrin. The selectivity patterns observed with these electrodes can be related to differences in the structure of the various ionophores, and to properties of the polymer film. 

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

Chiral binaphthyl-bridged mevo-tetrakis(2-aminophenyl)porphyrin]cobalt or polymer-supported chiral (salen)Co complexes also catalyzed the cyclopropanation of styrenes albeit so far with lower diastereo- and enantioselectivities [363, 364],... 

Diffuse reflectance UV-vis spectroscopy was applied in electrocatalysis by El Mouahid et al. (1998), who followed the electropolymerization of a cobalt porphyrin complex on a vitreous carbon electrode. The thin polymer... 

In 1975, Boris Smirnov and Alexander Marchenko discovered a method in which they could control the molecular weight in a methacrylate polymerization by introducing catalysts that could greatly enhance the process of chain transfer to monomer.10 They found that substituted cobalt porphyrins, 1, or ben-zoporphyrins, 2, provided dramatic reductions in the molecular weight of the methacrylate polymers during radical polymerization with little to no reduction in overall yield of polymer.11 15... 

H. Nishide, M. Ohyanagi, O. Okada, E. Tsuchida, Dual mode transport of molecular oxygen in a membrane containing a cobalt porphyrin complex, Polym. J. 19 (7) (1987) 839-844. 

Another approach uses a cobalt tetrakis(o-aminophenyl)porphyrin polymer film, prepared by electrooxidative polymerization of the monomer on top of the electrode as conductive film-mediator-couple [19]. 

Fig. 17 Self-assembly of a multicyclic homo-polymer via coordination of a cobalt porphyrin symmetrically functionalized with two pyridine ligands...

A macromolecule provides a suitable fimctional group for either complexation with metal ions of metal salts or attaching metal complexes into the macromolecular matrix through a coordination bond typical examples of the former are silver-polymer complexes, while cobalt porphyrins incorporated on a polymer backbone through coordination bonding are examples of the latter. 

Casting the complex solution of a metalloporphyrin and a polymer ligand such as poly(vinylimidazole-co-alkylmethacrylate) (Olm in Fig. 9-8), for example, on a Teflon plate and drying, yielded both a homogenously dispersed metalloporphyrin in a solid state and a mechanically tough membrane [26]. The Tg of the membrane was increased, for example, from -1 °C for the Olm itself to 6 °C and the membrane became brittle after the incorporation of 40 wt.% cobalt porphyrin this was explained by the stiffening effect of the incorporated... 

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