Spectroelectrochemistry and voltammetry of metalloporphinones

Metalloporphinones have been found in a number of enzymes involved in nitrogen metabolism. The emphasis of this research project has been to develop spectroscopic markers in order to identify metal versus porphinone reduction. The carbonyl group in the porphinone has a very strong signal which is quite sensitive to the extent of reduction of the porphinone macrocycle. The spectral change makes IR an important tool in the process of structure determination of metalloporphyrins because the carbonyl group shift can be correlated with the metal oxidation state. It was observed from previously published studies that a higher metal oxidation state moves the carbonyl group at a higher frequency while a lower oxidation state will shift the carbonyl vibration to a lower frequency. Previous work in our laboratory has focused on iron porphinones, but the lack of empirical relationships for the spectroscopic data has made it difficult to clearly interpret the results. Consequently, previous students\u27 work was extended to include zinc, cobalt and manganese complexes. It has been postulated that zinc and manganese complexes would lead to primarily macrocycle reduction while cobalt complexes would be more similar to iron. By using a combination of spectroscopic techniques (visible and infrared spectroscopy), it has been possible to separate metal from macrocycle reduction. Additional information was gathered using oxygen isotopic substitution. This information can be quite useful in understanding both the enzymatic process and the use of these compounds for catalysis. Based on this information, our studies will be focused on the mentioned correlation and bring supplementary evidence for the problem addressed by researchers in the last 25 years concerning the oxidation state of iron(II) upon reduction

Visible and Infrared Spectroelectrochemistry of Cobalt Porphinones and Porphinediones

The visible and infrared spectroelectrochemistry of the redox chemistry of CoII–porphinone complexes were examined and compared with similar studies of the respective iron complexes. Cobalt(II) porphinone complexes undergo a one-electron reduction and two one-electron oxidations within the potential region that was studied in this work. The one electron spectroelectrochemical reduction of CoII(P) (P = octaethylporphyrin (OEP), octaethylporphinone (OEPone), and octaethylporphinedione (OEPdione)) were studied using visible spectroscopy, and their cobalt(I) complexes were characterized. The same reduction was examined by FTIR spectroscopy for P = OEPone and OEPdione. The infrared spectra showed downshifts of the νCO band that were consistent with a cobalt(I) complex and were similar to the iron(I) complex. The two one-electron oxidations of CoII(OEPone) and CoII(OEPdione) were also carried out using visible and infrared spectroelectrochemistry. The νCO band for cobalt was less sensitive to the metal oxidation state (III vs. II) than was observed in the iron complexes. Additional upshifts in the νCO band were observed for the π-cation radical. Isotopic 18O substitution on the carbonyl group of the H2OEPone was done in order to determine the degree of mixing up the porphinone modes with the carbonyl vibrations

Visible and Infrared Spectroelectrochemistry of Zinc and Manganese Porphinones: Metal vs. Porphyrin Reduction

The visible and infrared spectroelectrochemistry of zinc and manganese porphinones and porphinediones was carried out in THF solutions. The aim of this work was to use FTIR spectroelectrochemistry and DFT calculation to determine whether the reduction was centered predominantly on the metal or the macrocycle. For zinc(II), the first one-electron reduction must occur on the macrocyclic ring because the metal’s d-orbitals are filled (d10). The carbonyl bands on the macrocyclic ring were used to probe the electronic structure because they can be readily observed in the infrared spectra. The results of this study are complementary to previous spectroelectrochemical studies that have been reported for the iron and cobalt complexes of the same macrocycles. As expected for the formation of a π-radical anion species, significant downshifts in the carbonyl bands were observed. DFT calculations showed that the behavior of the porphinedione complexes were most sensitive to the electronic structure of the M(OEPdione)− species. If a MI species is formed, the two carbonyl groups will be downshifted by similar energies. For MII-radical anions, one carbonyl will be downshifted significantly, and the second one will be downshifted by a small amount. On the basis of this criterion, it was determined that cobalt(I) and iron(I) complexes were formed, while zinc and manganese formed π-radical anion species. The visible spectroelectrochemistry was also consistent with these electronic structures

Combination of Carbon Nanotubes with Fire Retardants : the Thermal and Fire Properties of Polystyrene Nanocomposites

Polystyrene combined with fire retardants and nanomaterials have been used to study the thermal stability and fire properties. The nanomaterials used are a montmorillonite clay and carbon nanotubes. The amounts of fire retardants and nanomaterials were varied in order to study the effect of their loading on the properties. The samples were prepared by melt blending and analyzed by thermogravimetric analysis and cone calorimetry. In this study, representatives ofthree classes of fire retardants were used: bromine, decabromodiphenyl oxide; phosphorus, resorcinol diphosphate; and minerals, alumina trihydrate