The Voltammetric Study of the Reduction of Tetraalkylammonium Perchlorate by Fe(TPP)\u3csup\u3e2-\u3c/sup\u3e

Tetraalkylammonium ions react with Fe(TPP)2− to form Fe(TPP)(R)− and trialkylamine. The tetrabutylammonium cation was verified to be the source of the alkyl group in the product, Fe(TPP)(R)−, by using (1H5C2)3(2H5C2)N− as the cation and 2H NMR. The reaction of Fe(TPP)2− with Bu4N− was monitored by cyclic voltammetry and thin layer spectroelectrochemistry. The activation parameters were measured, and were most consistent with an electron transfer (ET) mechanism. The rate of the reaction of tetramethyl and tetraethylammonium ions with Fe(TPP)2− was also examined. The rate constant decreased significantly as the carbon chain length decreased, which was also consistent with an ET mechanism

Visible and Resonance Raman Spectra of Low Valent Iron Porphyrins

The resonance Raman spectrum of Fe(TPP)2− was obtained after the three-electron electrochemical reduction of Fe(TPP)(Cl). The coulometric reduction was carried out in the presence of bis(triphenylphosphoanylidine)ammonium chloride in DMF in order to avoid the formation of iron–σ-alkyl complexes. The resonance Raman spectrum of the intermediate oxidation states (Fe(TPP) and Fe(TPP)−) were consistent with previous work. The spectrum of the three-electron product, Fe(TPP)2−, obtained at 442 nm, was qualitatively similar to the two-electron reduced product, Fe(TPP)−, with an intense ν2 band at 1537 cm−1. The high frequency bands generally decreased in energy, contrary to the expectations based on the X-ray crystallographic core size. In particular, the ν2 and ν10 bands decreased by 18 and 22 cm−1. A small increase was observed for the ν4 band (+4 cm−1). While these changes were not consistent with the measured core size, they were in agreement with other porphyrin π-anion radicals such as Zn(TPP)− and VO(OEP)−. Based on the resonance Raman spectra, Fe(TPP)2− can be formulated as an iron(I) π-radical anion. Significant backbonding between the dπ-orbitals of the iron to the eg* orbital of the porphyrin, though, is probably occurring. As a result, the complex is probably not a pure π-anion radicals

The Stability of Low-Valent Iron Porphyrins in Electrochemical Solutions

The geosphere and atmosphere upon which plants and auxotrophic bacteria depend for growth and reproduction contain three key elements: carbon, nitrogen, and sulfur which are present in a relatively oxidized state. These species must be reduced for incorporation into biological material. Carbon dioxide must be reduced to the carbohydrate or fatty acid oxidation state, sulfate to the sulfide stage for incorporation into the sulfur-containing amino acids, and nitrogen must be reduced from elemental dinitrogen or nitrate to the ammonia oxidation state for incorporation into nitrogencontaining amino acids\u27. As such, electron transfer plays an important role in the function of natural systems. A large number of highly specific and diverse enzymatic systems have evolved to catalyze these electron transfer reactions in vivo. Among the many electron transfer reactions that are known, one of particular interest is the enzymatic reduction of inorganic nitrate which plays a major role in nitrogen cycle in the biosphere2 (Figure 1-1)..

The stability of low-valent iron porphyrins in electrochemical solutions

The substituent effect on Fe(P)NO complex was studied using Fe(X-TPP)NO, where X was a substituent at 3- or 4-position on the phenyl ring. The slope of the E\sb{1/2} value for the first wave was 0.045V indicative of metal centered reduction. A value of 0.072V was observed for the second wave suggesting a macrocyclic reduction. Two and three-electron reduced complexes of Fe(TPP) were electrochemically generated and characterized by electrochemical, visible and resonance Raman spectroscopic methods. The resonance Raman shifts that were observed upon the reduction of Fe(TPP)\sp{-} to Fe(TPP)\sp{2-} were quite similar to the shifts that were observed for other $\pi$-anion radicles such as Zn(TPP)\sp{-}. In particular the \nu\sb2 and \nu\sb{10} bands were quite sensitive to reduction with downshifts of 18 and 22 cm\sp{-1}, respectively. The \nu\sb4 band was relatively insensitive to the reduction of the complex. Several modes maintained the normal depolarization values upon reduction whereas significantly higher depolarization ratios were observed for the \nu\sb2 and \nu\sb3 bands. $\sigma$-alkyl iron porphyrin complexes were found to be formed from the reaction of Fe(TPP)\sp{2-} with tetraalkylammonium ions. At room temperature, this reaction was too slow to be observed with cyclic voltammetry. However, when electrolyzed at a potential that generate Fe(TPP)\sp{2-} and initiate the scan in the forward direction, waves for alkylated products were observed. Visible spectroelectrochemical characterization of electrolysis products at Fe(TPP)\sp{2-} potential with alkylated supporting electrolytes, showed the Fe(TPP)R\sp{-} visible spectrum. Further characterization by resonance Raman spectroscopy of chemically generated Fe(TPP)(CH\sb3)\sp{0/-} and Fe(TPP)(butyl)\sp{0/-} complexes, and compared the results with coulometrically reduced complexes. The ferrous alkyl porphyrins gave spectra that were consistent with low-spin five coordinate complexes, with \nu\sb2 and \nu\sb4 bands being observed at 1566 and 1363 cm\sp{-1}, respectively. The \nu\sb2 and \nu\sb4 bands for the electrochemically generated product were at 1562 and 1363 cm\sp{-1}, respectively. The source of alkylation in the electrochemically reduced samples was investigated using a deuterated supporting electrolyte. Deuterium NMR data are consistent with the Fe(II)alkyl complexes. These results ensured that the stability of the highly reduced iron porphyrin complexes is affected by the alkylated electrolyte present in the electrolytic solutions. The activation energies for the reaction of Fe(TPP)\sp{2-} with tetrabutyl ammonium perchlorate were more consistent with ET behavior than with S\sb{\rm N}2 behavior

Resurfacing of facial acne scars with a new variable-pulsed Er:YAG laser in Fitzpatrick skin types IV and V

Introduction: The Er:YAG laser, considered to be less effective than CO2 laser in its traditional form, in its new modulated version has variable pulse technology that is claimed to be superior to the earlier versions of the laser.Aim: The aim of the study was to check efficacy and safety of the new variable square pulse (VSP) Er:YAG laser in the management of acne scar in patients with Fitzpatrick skin types IV and V.Materials and Methods: This retrospective study consisted of 80 patients (Fitzpatrick skin types IV and V) with atrophic and hypertrophic facial acne scars. Records of the patients who had undergone four treatment sessions with VSP technology equipped with Er:YAG laser were extracted. Each patient had undergone a minimum of four sessions. Fractional mode at medium laser pulse (SP) and long pulse (LP) was employed for the depressed center of the scars to stimulate neocollagenogenesis. Short laser pulse (MSP) in nonfractionated mode was used for ablating the raised scar border and hypertrophic scars. Goodman and Baron global scarring grading system was used for qualitative and quantitative assessments. Patient’s satisfaction to the treatment and observer’s assessment of improvement (based on photographs) was graded as poor (75% improvement).Results: At the end of the four sessions, the number of patients in grade IV postacne scarring reduced from 16 to 2 and that in grade III from 47 to 29. The mean score significantly dropped from 36.94 to 27.5. Subjective assessment revealed that 78 of 80 patients had noticed more than 25% improvement, with 50 of them showing more than 50% improvement at the end of four sessions. Eight patients perceived an excellent response and 42 reported a good response. This is notably higher than the observer’s grading, which showed an excellent response in only 2 patients and a good response in 35. Adverse effects were limited to prolonged erythema (two patients), prolonged crusting (one patient), and postinflammatory hyperpigmentation (one patient).Conclusion: Ninety-seven percent of the subjects in our study perceived at least a fair improvement. We also saw a significant change in the objective score with a fall of the mean quantitative score from 36.94 to 27.15. This underscores the new variable-pulsed Er:YAG laser’s effectiveness in the treatment of acne scars. It also has the added advantage of lesser adverse events and faster healing

Analyzing how users utilize 'riff' for collaborative searching and sharing contents for social learning in So.cl

Microsoft So.cl combines the collaborative features of a social network and the capabilities of a search engine to create a unique social search environment. The activity of riffing provides a unique twist on a typical search results page since users can actually contribute to the results of another persons’ search string, and/or annotate their own searches, also providing multimodal content such as image, video, and text within one results display; as well as user generated metadata via comments and tags. These collaborative and search features give so.cl the potential to promote discovery through interaction with search result content. Unfortunately not many so.cl users exhibit riffing behavior. For this reason, we explored behaviors of users who had riffed in order to further examine their behaviors, focusing also on some of the top riff posters, to determine both what behaviors and post activity might be popular among these users. Results from this analysis indicate that overwhelmingly users who riff on others’ posts also tend to create their own riff postings, as well as the fact that as users tend to become more acclimated to the so.cl service, they also tend to riff more. These findings can be used to determine implications for pushing certain behaviors within so.cl to promote riffing behavior.published or submitted for publicationis peer reviewe

Reaction of Low-Valent Iron Porphyrins with Alkyl Containing Supporting Electrolytes

A σ-alkyl iron porphyrin complex was found to be formed from the reaction of Fe(TPP)2− with tetraalkylammonium ions (TPP=tetraphenylporphyrin). At room temperature, this reaction was too slow to be observed with cyclic voltammetry. But, if one electrolyzes at a potential that generated Fe(TPP)2−, and then initiates the scan in the forward direction, waves for Fe(TPP)(R)−/Fe(TPP)(R) and Fe(TPP)(R)/Fe(TPP)(R)+, where R=alkyl group, were observed. Both tetramethyl- and tetrabutylammonium ions were found to react with Fe(TPP)2−. No alkylated products were observed if alkali salts were used as the supporting electrolyte. Visible spectroelectrochemistry with a thin layer cell showed that electrolysis at the first and second waves of Fe(TpP)(Cl) in DMF yielded the expected Fe(TPP) and Fe(TPP)− complexes, but Fe(TPP)2− was not observed at the third wave. Instead, the spectrum of Fe(TPP)(R)− was obtained. Oxidation of this species led to the formation of Fe(TPP)(R), and further oxidation regenerated Fe(TPP)(Cl) because of the poor stability of Fe(TPP)(R)+. Further characterization was carried out by obtaining the resonance Raman spectra of chemically generated Fe(TPP)(CH3)O/− and Fe(TPP)(butyl)O/− complexes, and comparing the results with the electrochemically generated complexes. The σ-alkyl iron porphyrins were not very stable under laser irradiation, and the best spectra were obtained in THF with frozen samples. The σ-alkyl ferric porphyrins were considerably less stable than the corresponding ferrous complexes, and the photoproduct, Fe(TPP), could be observed in all spectra. The ferrous alkyl porphyrins gave spectra that were consistent with low-spin five-coordinate complexes, with v2 and v4 bands being observed at 1566 and 1363 cm−1, respectively. The v2 and v4 bands for the ferric alkyl porphyrin were at 1565 and 1359 cm−1, respectively. The product, obtained by electrolyzing Fe(TPP)(Cl) at the potential for the generation of Fe(TPP)2−, gave a spectrum in THF that was consistent with an iron alkyl complex. The photoproduct appeared to be Fe(TPP)(OH)− rather than Fe(TPP), as was observed in the chemically generated product due to trace amounts of water in the supporting electrolyte. The visible spectrum of the resonance Raman was identical to the authentic Fe(TPP)(R)− sample. There was no evidence for Fe(TPP)(OH)−, which would have been quite apparent in the visible spectrum. The generation of Fe(TPP)(R)− from Fe(TPP)2− and tetrabutylammonium ion could occur by at least two pathways: nucleophilic attack or electron transfer between iron(`O\u27) on the tetrabutylammonium ion. Steric effects would favor an electron transfer mechanism over the nucleophilic process, but the data at this time are not conclusive

Electrochemistry of Nitrite Reductase Model Compounds 6. Voltammetric and Spectroelectrochemical Studies of Iron(II) Nitrosyl Complexes with Porphyrins, Hydroprophyrins and Porphinones

The effect of hydroporphine and porphinone macrocycles on the voltammetry and spectroscopy of Fe(P)(NO) was examined. Two oxidation and two reduction waves were observed for all the complexes examined. The variation in the half-wave potentials fell into two categories: those where the E12 of the complex varied linearly with the E12 of the free-based, and those where the relationship was non-linear. Linear relationships were observed where the electron transfer was primarily macrocycle-centered, while non-linear relationships were observed for metal-centered processes. Of the four waves observed, the first reduction and second oxidation of Fe(P)(NO) was non-linear, while the second reduction and first oxidation waves were linear. Comparison with the voltammetry of Fe(P)(Cl) showed the same relationships. The first reduction and second oxidation waves were non-linear while the second and third reductions and the first oxidation waves were linear. For the linear relationships, where the E12 of the complex was proportional to the E12 of the free-based, the energy of the LUMO or HOMO controlled the redox potential so that the porphyrin molecular orbital was involved substantially in the redox product, if not itself oxidized or reduced. This would indicate that the first reduction of Fe(P)(NO) was centered on the Fe(NO) moiety, while the second reduction led to the formation of a porphyrin radical anion. The variation in oxidation redox potentials was consistent with previous formulations of Fe(P)(NO)+ as a π-cation radical (except for Fe(OEP)(NO)+). The variations in the E12 of the second oxidation wave would indicate that the oxidation was centered on the Fe(NO) moiety. The variation in the half-wave potentials of Fe(X-TPP)(NO), where X was a substituent at the three- or four-position on the phenyl ring, also confirmed this interpretation. The slope of the E12 values for the first wave was 0.045 V, while a value of 0.072 V was observed for the second wave. It has been previously shown that slopes of about 0.068 V were indicative of porphyrin reduction, while lower values were generally observed for metal reduction. The formation constants for pyridine with Fe(P)(NO) were also determined. For the porphyrins and hydroporphyrins, the values were small (about 0.3 to 1.1), which were consistent with other iron nitrosyl porphyrins and chlorins. The porphinone and porphinedione complexes, though, showed a much greater affinity for pyridine, with formation constants of 4.8±0.2 and 88±3. These values are one to two orders of magnitude larger than the values observed for other iron-porphyrins nitrosyl complexes, and indicate a chemical advantage for the porphinedione (heme d1) in dissimilatory nitrite reductases, where the heme is coordinated by an imidazole in the fifth position. A weak complex (K = 9) was observed between Fe(2,4-OEiBC)(NO)+ and pyridine