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New experimental techniques and protocols are needed to study microbiologically influenced corrosion (MIC). In this work, we studied the capacity of microorganisms to modify their environment in vitro. The methodology involved cyclic voltammetry measurements using carbon electrodes modified with cobalt phthalocyanine, which is a known catalyst for the two-electron reduction of O2 to give peroxide. Mueller-Hinton (21 g/L) was used as an electrolyte in a sterilized aqueous medium. The open circuit potential (OCP) and oxygen concentration behaved similarly over time, with generally similar growth curves. However, there were peculiarities that indicated the presence of peroxide and catalase. Catalase activity was demonstrated by comparing the voltammetric responses of the culture medium in the absence and presence of bacterial strains of Escherichia coli (Gram +) and Staphylococcus aureus (Gram-), both facultative and catalase positive. With this system, which is capable of discriminating O2 and hydrogen peroxide, catalase activity is highly evident, and at its maximum at the end of the exponential stage of the growth curve.

The Mn +/M(n − 1)+ redox potential of MN4 macrocyclic molecular catalysts is a very good reactivity descriptor for several electrochemical reactions. One important feature about this reactivity descriptor is that it can be determined experimentally under the same conditions of the kinetic measurements in contrast to other descriptors like intermediate binding energies that are estimated from DFT calculations. However a linear correlation between both descriptors seems to exist. Plots of activity as (logj)E at constant E versus the Mn +/M(n − 1)+ redox potential gives volcano correlations. Another important aspect about this parameter is that it is possible to tune the Mn +/M(n − 1)+ redox potential of the MN4 catalyst by manipulating the structure of the macrocyclic complex and tailoring the electron-withdrawing power of the ligands to obtain the maximum activity. In this work we have probed the redox potential as a reactivity descriptor for the oxidation of cysteamine studying a series of substituted Fe phthalocyanines and Fe porphyrins adsorbed on glassy carbon and pyrolytic graphite in alkaline media. As expected the catalytic activity of these FeN4 species varies strongly with the Fe (II)/(I) redox potential of the different Fe phthalocyanines and a plot of activity as (logj)E versus E°Fe(II/I) gives a volcano-shaped correlation so a formal potential value exists for which the highest activity can be achieved demonstrating that the formal potential of the complexes seems to be an universal reactivity descriptor for electrochemical reactions.

We have examined the electrocatalytic activity for the oxidation of glutathione of a wide variety of molecular catalysts: FeN4 complexes (MN4 = metal porphyrins and metal phthalocyanines) confined on the surface of graphite electrodes in order to establish reactivity descriptors for these catalysts for this reaction. We have conducted these studies mainly in alkaline media (pH = 13). The reaction order in OH− is 1 for pH values lower than 8. For higher pH values, the reaction becomes pH independent. The reaction order in glutathione is close to 1 in the concentration range examined (10−3–10−2 M). The activity of the surface-confined MN4 complexes is related to the Fe(II)/(I) and the Fe(III)/(II) redox transitions of the immobilized FeN4 complexes. The catalysts are active only in the potential range where the Fe(II) state predominates. The activity as (log j) E versus the Fe(II)/(I) formal potential varies in a non-linear fashion giving a volcano correlation as previously observed for the oxidation of L-cysteine and many other reactions catalyzed by MN4 complexes. A plot of (E)logj versus the Fe(II)/(I) formal potential gives also an asymmetrical volcano, with one of the branches with a slope close to unity. These volcano correlations clearly shows that the Fe(II)/(I) redox potential needs to be tuned to a certain potential to obtain a maximum activity for the oxidation of glutathione. Most Fe porphyrins show low activity because the metal center Fe(III) is in the wrong oxidation state in the potential range studied.

Nitrogen doped carbon nanotubes (N-CNTs) were synthesized by the chemical vapor deposition technique (CVD) using ferrocene and iron (II) phthalocyanine as carbon precursors and ethylendiamine as the carbon and nitrogen source. Fe2O3 nanoparticles, Co nanoparticles and MoO3 were supported on a sol–gel polymer and were used as catalyst and seed growth of the N-CNTs. The influence of the metal transition used as catalyst and the amount of ethylendiamine were studied in N-CNTs for oxygen reduction reaction (ORR) in alkaline media. The morphology of the N-CNTs was studied using scanning electron microscopy (SEM) revealing that de N-CNTs were multiwalled with averages of diameters ranging between 40 and 70 nm. The presence and type of nitrogen in the graphene grid was analyzed by means of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The obtained results indicated that N-CNTs catalyzed by MoO3 presented the highest content of pyridinic-type nitrogen (around 39%). The electrocatalytic activity of N-CNTs for the ORR was evaluated by rotating disk electrode (RDE) technique in 0.2 M NaOH. The electrochemical results showed that N-CNTs catalyzed with 0.2 wt.% MoO3 and synthesized with 19.5 wt.% of ethylendiamine exhibited higher activity for ORR than N-CNTs catalyzed with Co nanoparticles or Fe2O3 nanoparticles.

Silver nanofibers (Ag-Nfbs) ~ 80 nm in diameter were synthesized by hydrothermal treatment. The nanofibers (3 and 5 wt%) were added in the initial feed together with the catalytic system. Polymerizations in an ethylene atmosphere were performed, yielding PE nanocomposites in situ with 3 and 5 wt% content of Ag-Nfbs. The antibacterial effect of the silver-nanofiber composites was evaluated after incubation of Escherichia coli ATCC 25923 for 8 h on their surface. Bacterial viability tests showed that the silver-nanofiber composites inhibited the growth of Escherichia coli ATCC 25923 by 88 and 56%. This behavior is attributed to increased silver ions release from the nanocomposite. TEM analysis showed that the antibacterial effect is associated with membrane disruption but not with changes in shape.

We have revisited correlations between catalytic activity and formal potentials of MN4 catalysts for the reduction of O2 (ORR). When comparing the activities of Cr, Mn, Co and Fe MN4 complexes for ORR as a plot of (log i/n)E versus the M(III)/(II) formal potential of the catalyst (n = number of electrons involved in the ORR), two linear correlations are obtained: one for Cr, Mn and Fe complexes and another for Co complexes. Mn and Fe are 4-electron reduction catalysts and Cr and Co are 2-electron reduction catalysts for ORR in alkaline media. We show that instead of plotting the formal potential E°′ of the catalyst but the difference between this parameter and the reversible potential Erev of the corresponding catalytic reaction (O2/OH−) or (O2/HO2−), as (E°′ − Erev) and using the Co(II)/(I) formal potential for cobalt macrocyclics, instead of the Co(III)/(II) redox couple, all data points merge into one single linear correlation of slope +0.170 V/decade. It is possible that when (E°′ − Erev) approaches zero, the maximum activity could be achieved and this is especially important for 4-electron catalysts and the linear correlation might be part of an incomplete volcano correlation. Keywords: Linear correlations, Phthalocyanines, Fe porphine, O2 reduction catalyst, Redox potentials

We have investigated the electrocatalytic activity of tetraphenyl porphyrin, of substituted tetraphenyl porphyrins and of vitamin B 12 for the electro-oxidation of 2-aminoethanethiol, with the catalysts confined on graphite electrodes. Several N4-macrocyclic were used in order to have a great variety of formal potentials of the catalysts and compare this parameter with the catalytic activity. The electrocatalytic activity, measured as current at constant potential, increases with the formal potential of the catalysts as follows: Co-pentafluorotetraphenylporphyrin 12 . Vitamin B 12 exhibits the maximum activity. A correlation of log I (at constant potential) vs. the formal potential E ′ of the catalysts gives a volcano correlation when data of Co-phthalocyanines studied in previous work is included in the comparison. This clearly shows that the search for better catalysts for this reaction point to those N 4 -macrocyclic complexes with Co(II)/(I) formal potentials close to −1.0 V vs. SCE which corresponds to an optimum situation for the interaction of the thiol with the active site. When comparing reactivity trends of similar catalysts for the oxidation of other thiols ( l -cysteine, mercaptoacetate and 2-mercaptoethanol) E ′ max correlates linearly with the p K a of the thiol.

We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.

This study shows that cobalt macrocyclics, namely Co-phthalocyanine (CoPc), Co-hexadecafluorophthalocyanine (CoF16Pc), Co-octaethylhexyloxyphthalocyanine (CoOEHPc), Co-tetraaminophthalocyanine (CoTAPc) and Co-tetrasulfophthalocyanine (CoTSPc), strongly adsorbed on a graphite electrode surface, exhibit true electrocatalytic activity for the oxidation of glucose in alkaline solution. The Tafel analysis of the electrochemical process occurring at these chemically modified electrodes, that become “molecular phthalocyanine electrodes”, suggests that a first-one electron step is rate controlling with the symmetry of the energy barrier depending on the type of substituents grafted on the macrocycle. The effect of substituents on the phthalocyanine ring on the catalytic activity was analyzed and a non-linear correlation is found. The volcano-shaped plot obtained when comparing catalytic activities versus the Co(II)/(I) formal potential indicates that a narrow window of Co(II)/(I) formal potentials exists for achieving maximum activity. In the particular case of the present work, we find that the most active phthalocyanine is the unsubstituted CoPc.

This study reports on the role of both electron donor and electron acceptor substituents on the periphery of phthalocyanine cycle on the electrocatalytic activity of cobalt phthalocyanines for the oxidation of 2-aminoethanethiol (2-AET). By using these groups it is possible to modulate the Co(II)/(I) formal potential of the catalysts. The reported results show that the electrocatalytic activity of the adsorbed phthalocyanines containing electron-withdrawing groups decreases as the Co(II)/(I) formal potential of the catalyst becomes more positive, while electron-donating groups on the periphery of the ligand increase the catalytic activity.

The activity of the different iron phthalocyanines was examined using the complexes adsorbed on graphite electrodes. The effect of the Fe(II)/(I) formal potential of iron phthalocyanines on the their catalytic activity for the electro-oxidation of hydrazine was investigated. A plot of log k (rate constant at constant potential) versus the Fe(II)/(I) formal potential gives a volcano curve. The rate of the reaction increases with the driving force of the catalyst (measured as its formal potential) and then decreases for higher driving forces. A similar graph is obtained with a plot of log k versus the sum of the Hammett parameters of the substituents on the periphery of the phthalocyanine ligand. A maximum activity is obtained for a complexes having an M(II)/(I) redox potential close to −0.6 V which agrees with previous studies conducted with phthalocyanines of different metals and with cobalt phthalocyanines bearing different substituents.

We have carried out a systematic study of the electrocatalytic activity of metallophthalocyanines (M(II)-Pcs) adsorbed on graphite electrodes for the electro-oxidation of thiols (R-SH) and for the electroreduction of molecular oxygen. We have found for both reactions that when comparing the activity of substituted phthalocyanines of the same metal, plots of log k at constant potential versus the redox potential of the metallophthalocyanine, the rate of the reaction decreases with increasing driving force of the catalyst. In this work we present evidence that this behavior can be rationalized in terms of the donor–acceptor intermolecular chemical hardness ( η DA ). The energies of frontier orbitals involved in the estimation of η DA were calculated using the PM3 semi-empirical theoretical method. For the donor–acceptor pairs the lower is the hardness, the higher is the reactivity.

Vitamin B12 (acquo-cobalamine) adsorbs irreversibly on ordinary pyrolytic graphite (OPG) electrodes from aqueous solutions. The adsorbed vitamin exhibits cyclic voltammetric reversible waves corresponding to Co(II)/Co(I) and Co(III)/(II) couples and its redox chemistry is similar to that found in solution. The OPG/vitamin B12(ads) electrodes show substantial activity for the reduction of oxygen. In alkaline pH, a Tafel slope of −60 mV/decade and a chemical order in protons of −1 suggest a redox catalysis type of kinetics, governed by the Co(III)/Co(II) couple in the cobalamine. AtpH

We have found that CoPc and 16(F)CoPc when adsorbed on graphite electrode exhibit voltammograms in alkaline solution (0.2M NaOH) that show the typical redox peaks attributed to the Co(II)/(I) reversible. The peak potential for CoPc is independent of surface concentration of the catalyst. In contrast, for 16(F)CoPc the Co(II)/(I) redox process shifts to more negative potentials when the surface concentration of the catalyst increases. In a volcano correlation of log (i/G)E (activity per active site) versus Co (II)/(I) formal potential of catalyst (using several CoN4 chelates) CoPc appears in the ascending portion (activity increases with the Co (II)/(I) redox potential) whereas 16(F)CoPc appears in the region where activity decreases with the redox potential. In a plot of log (i/G)E versus the Co(II)/(I) formal potential of 16(F)CoPc the declining portion of the volcano is reproduced for one single complex. So 16(F)CoPc at different surface concentrations behaves as Co complexes having different redox potential in the declining portion of the volcano plot, when the activity is normalized for the surface concentration. This is not observed for CoPc.

In this paper we compare the catalytic activitites of untouched metal macrocyclic and pyrolyzed catalysts for ORR in acid versusthe formal potential of the catalyst and find in general that the catalysts reported in the literature exhibiting more positive formalpotentials are more active for ORR. These trends observed could serve as a hint for the development more active non-precious metalcatalysts for fuel cells.©2012 The Electrochemical Society. [DOI: 10.1149/2.032206esl] All rights reserved.Manuscript submitted January 16, 2012; revised manuscript received April 13, 2012. Published April 27, 2012.

We have prepared self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and 1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized with iron phthalocyanine (FePc) and copper phthalocyanine (CuPc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/MPc was examined for the reduction of O2 in aqueous solutions and compared to that of bare gold and with gold coated directly with preadsorbed MPc molecules. Scanning tunneling microscopy (STM) studies confirm the functionalization of the 4-ATP by MPc. STM images reveal that iron phthalocyanine molecules are chemically anchored to 4-aminothiophenol organic monolayers, probably having an “umbrella” type orientation with regards to the surface. The electrocatalytic studies carried out with Au/4-ATP/FePc and Au/MDPP/FePc electrodes show that the O2 reduction takes place by the transfer of 4-electron to give water in contrast to a 2-electron transfer process observed for the bare gold. The modifie...

We have studied the trends in catalytic activity of several Co macrocyclics confined on the surface graphite electrodes for the oxidation of thiocyanate. A plot of log i (at constant E) versus the formal potential of the catalyst gives a volcano correlation, indicating that the Co(II/I) redox potential needs to be tuned, in order to achieve maximum reactivity. Graphite electrodes modified with Co phthalocyanine at pH 4 exhibit linear amperometric response for thiocyanate concentration in the range 10 � 7 and 10 � 3 M. Theoretical calculations show that electrocatalytic activity (as log i at constant E) plotted versus the energy of the LUMO of the Co complex also gives a volcano correlation.

Article history:Received 18 August 2011Received in revised form 25 August 2011Accepted 30 August 2011Available online 10 September 2011Keywords:O 2 reductionSAMsFe phthalocyaninesAu(111) We have obtained and characterized self assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized withiron phthalocyanine (FePc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/FePc wasexamined for the reduction of O 2 in aqueous media (pH=4) and compared with that of bare gold and of goldcoated directly with FePc molecules. Scanning tunneling microscopy (STM) studies confirm the functionali-zation of the 4-ATP by FePc. The electrocatalytic studies carried out with Au/FePc, Au/4-ATP/FePc and Au/MDPP/FePc electrodes show that the O 2 reduction takes place by a 4-electron transfer to give water in con-trast to a 2-electron-transfer processobserved on the bare gold. The activity of the electrodes increases as fol-lows: AubAu/FePcbAu/4-ATP/FePcbAu/MDPP/FePc.© 2011 Elsevier B.V. All rights reserved.

A comparative study of the electrocatalytic activity of metallophthalocyanines for O2 reduction in alkaline and acid media was conducted using H2Pc, VOTsPc, CrTsPc, MnTsPc, MnPc, FeTsPc, FePc, FeMeOPc, CoTsPc, CoPc, CoMeOPc, CoTnPc and ZnTsPc adsorbed on OPG electrodes. Different electron-transfer mechanisms for O2 reduction were found depending on the position of the M(III)/ M(II) redox couples on the potential scale and the onset potential for O2 reduction. Volcano-shaped correlations between the redox potential and the O2 catalytic activity were observed. This has been rationalized on the basis of the redox catalysis concept and in terms of molecular orbital theory considerations.

Graphite electrodes modified with four different cobalt N4 macrocyclics, namely Co tetrapentapyridinophthalocyanine, (CoTPenPyrPc), Co tetrapyridinoporphyrazine (CoTPyPz), Co octa(hydroxyethylthio)phthalocyanine (CoOEHTPc) and Co tetranitrophthalocyanine (CoTNPc) exhibit catalytic activity for the oxidation of glucose in alkaline media. The purpose of this work is to establish correlations between the catalytic activity of these complexes and their redox potential. The activity of the different modified electrodes was tested by linear voltammetry under hydrodynamic conditions using the rotating disk technique. Tafel plots constructed from mass-transport corrected currents give slopes ranging from 0.080 to 0.160 V/decade for the different catalysts which suggests that a first one-electron step is rate controlling with the symmetry of the energy barrier depending on the nature of the ligand of the Co complex. A plot of log I versus the Co(II)/(I) formal potential gives a volcano curve that also includes catalysts studied previously. This illustrates the concept that the formal potential of the catalyst needs to be tuned to a certain value for achieving maximum activity. A theoretical interpretation of these results is given in terms of Langmuir isotherms for the adsorption of glucose on the Co sites of the surface-confined metal complexes.

The authors of the above article regret to say that there is an error in the paper. It was stated that the catalytic activity of the different molecular assemblies containing Fe phthalocyanine for oxygen reduction was examined in aqueous media at pH=4.0, whereas it should have said at pH=13.0. This error appears three times: in the Abstract, in the Experimental Details and the caption of Fig. 1. The source of this error comes from the fact that the self-assembled monolayers with and without FePc were characterized using cyclic voltammetry in buffer solutions of pH=4.0, following protocols previously reported in the literature [2]. However, the kinetic measurements were conducted at pH 13 in order to compare them with data previously reported using phthalocyanines adsorbed on graphite [3]. The error in the pH does not invalidate the conclusions of the paper.

Etudes de comportement catalytique vis-a-vis de la reduction d'O 2 , de melanges de tetrasulfophtalocyanines de Fe et de Co coadsorbees sur du graphite, en vue de determiner si H 2 O 2 produit sur les sites de Co est decompose sur les sites de Fe sur les phtalocyanines adsorbees