Cobalt(II) Hematoporphyrin IX immobilized in a cellulose acetate niobium(V) oxide composite membrane: preparation and oxygen reduction study

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Abstract

Hematoporphyrin IX [8,13,-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H-porphyrin-2,18-dipropionic acid] was adsorbed on the organic-inorganic composite membrane Cel/Nb2O5 surface. The porphyrin is strongly adhered on the Nb2O5 surface by reaction of the porphyrin CO2H groups with Nb2O5 forming the -COO-Nb chemical bond. Metallation of the porphyrine ring was made very easily by immersing the membrane in Co(II) solution and allowing to rest for a few hours. The electronic absorption bands due to the Q bands indicated the symmetry change from D2h to D4h upon metallation of the porphyrin ring. The chemical analyses of the material confirmed that the metallation yield was practically 100%. Oxygen was reduced on a electrode surface made with the material under a cathodic peak potential of -390 mV, in 1 M KCl solution at pH 1, temperature of 298 K and at ambient pressure. The oxygen reduction was proposed to occur by a two electron transfer mechanism. A linear cathodic peak current response was obtained for dissolved oxygen concentrations between 1.5 and 15 ppm.

Translated abstract

A Hematoporfirina IX [ácido (8,13,-bis(1-hidroxietil)-3,7,12,17-tetrametil-21-H-porfirina-2,18-dipropionico)] foi absorvida na superfície da membrana composta orgânica/inorgânica Cel/Nb2O5. A porfirina é fortemente aderida à superfície do Nb2O5 pela interação com o grupo carboxílico -COOH da porfirina e formação da ligação -COO-Nb. A metalação do anel porfirínico é feita mergulhando-se a membrana na solução de Co(II) por algumas horas. As bandas de absorção eletrônica Q indicaram a mudança de simetria de D2h para D4h pela metalação do anel porfirínico. A análise química demonstrou que a metalação ocorreu com rendimento de práticamente 100%. O oxigênio foi reduzido na superfície do eletrodo feito com o material a um potential de pico de -390 mV em solução de KCl 1 M a pH 1, a uma temperatura de 298 K à pressão ambiente. Supõe-se que o processo de redução ocorre segundo o mecanismo de transferência de dois elétrons. Foi obtida uma resposta linear da corrente de pico catódico para concentrações do oxigenio dissolvido entre 1,5 e 15 ppm.

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Long distance electron-transfer mechanism in peptidylglycine alpha-hydroxylating monooxygenase: a perfect fitting for a water bridge.

Aurélien de la Lande, Sergio Martí, Olivier Parisel … (2007)

The active sites of copper enzymes have been the subject of many theoretical and experimental investigations from a number of years. Such studies have embraced topics devoted to the modeling of the first coordination sphere at the metallic cations up to the development of biomimetic, or bioinspired, catalytic systems. At least from the theoretical viewpoint, fewer efforts have been dedicated to elucidate how the two copper cations act concertedly in noncoupled dicopper enzymes such as peptidylglycine alpha-hydroxylating monooxygenase (PHM) and dopamine beta-monooxygenase (DbetaM). In these metalloenzymes, an electronic transfer is assumed between the two distant copper cations (11 A). Recent experimental results suggest that this transfer occurs through water molecules, a phenomenon which has been theoretically evidenced to be of high efficiency in the case of cytochrome b5 (Science, 2005, 310, 1311). In the present contribution dedicated to PHM, we overpass the common theoretical approaches dedicated to the electronic and geometrical structures of sites CuM or CuH restricted to their first coordination spheres and aim at directly comparing theoretical results to the experimentally measured activity of the PHM enzyme. To achieve this goal, molecular dynamics simulations were performed on wild-type and various mutants of PHM. More precisely, we provide an estimate of the electron-transfer efficiency between the CuM and CuH sites by means of such molecular dynamics simulations coupled to Marcus theory joined to the Beratan model to approximate the required coupling matrix elements. The theoretical results are compared to the kinetics measurements performed on wild and mutated PHM. The present work, the dynamic aspects of which are essential, accounts for the experimental results issued from mutagenesis. It supports the conclusion that an electronic transfer can occur between two copper(I) sites along a bridge involving a set of hydrogen and chemical bonds. Residue Gln170 is evidenced to be the keystone of this water-mediated pathway.