Seawater usable for production and consumption of hydrogen peroxide as a solar fuel.

Hydrogen peroxide (H2O2) in water has been proposed as a promising solar fuel instead of gaseous hydrogen because of advantages on easy storage and high energy density, being used as a fuel of a one-compartment H2O2 fuel cell for producing electricity on demand with emitting only dioxygen (O2) and water. It is highly desired to utilize the most earth-abundant seawater instead of precious pure water for the practical use of H2O2 as a solar fuel. Here we have achieved efficient photocatalytic production of H2O2 from the most earth-abundant seawater instead of precious pure water and O2 in a two-compartment photoelectrochemical cell using WO3 as a photocatalyst for water oxidation and a cobalt complex supported on a glassy-carbon substrate for the selective two-electron reduction of O2. The concentration of H2O2 produced in seawater reached 48 mM, which was high enough to operate an H2O2 fuel cell.

Mechanism of a one-photon two-electron process in photocatalytic hydrogen evolution from ascorbic acid with a cobalt chlorin complex.

A one-photon two-electron process was made possible in photocatalytic H2 evolution from ascorbic acid with a cobalt(II) chlorin complex [Co(II)(Ch)] via electron transfer from ascorbate to the excited state of [Ru(bpy)3](2+) followed by electron transfer from [Ru(bpy)3](+) to Co(II)(Ch) with proton to give the hydride complex, which reacts with proton to produce H2. [Co(III)(Ch)](+) was reduced by ascorbate to reproduce Co(II)(Ch).

Selective electrochemical reduction of CO2 to CO with a cobalt chlorin complex adsorbed on multi-walled carbon nanotubes in water.

Electrocatalytic reduction of CO2 occurred efficiently using a glassy carbon electrode modified with a cobalt(II) chlorin complex adsorbed on multi-walled carbon nanotubes at an applied potential of -1.1 V vs. NHE to yield CO with a Faradaic efficiency of 89% with hydrogen production accounting for the remaining 11% at pH 4.6.

Much enhanced catalytic reactivity of cobalt chlorin derivatives on two-electron reduction of dioxygen to produce hydrogen peroxide.

Effects of changes in the redox potential or configuration of cobalt chlorin derivatives (Co(II)(Chn) (n = 1-3)) on the catalytic mechanism and the activity of two-electron reduction of dioxygen (O2) were investigated based on the detailed kinetic study by spectroscopic and electrochemical measurements. Nonsubstituted cobalt chlorin complex (Co(II)(Ch1)) efficiently and selectively catalyzed two-electron reduction of dioxygen (O2) by a one-electron reductant (1,1'-dimethylferrocene) to produce hydrogen peroxide (H2O2) in the presence of perchloric acid (HClO4) in benzonitrile (PhCN) at 298 K. The detailed kinetic studies have revealed that the rate-determining step in the catalytic cycle is the proton-coupled electron transfer reduction of O2 with the protonated Co(II)(Ch1) complex ([Co(II)(Ch1H)](+)), where one-electron reduction potential of [Co(III)(Ch1)](+) was changed from 0.37 V (vs SCE) to 0.48 V by the addition of HClO4 due to the protonation of [Co(III)(Ch1)](+). The introduction of electron-withdrawing aldehyde group (position C-3) (Co(II)(Ch3)) and both methoxycarbonyl group (position C-13(2)) and aldehyde group (position C-3) (Co(II)(Ch2)) on the chlorin ligand resulted in the positive shifts of redox potential for Co(III/II) from 0.37 V to 0.45 and 0.40 V, respectively, whereas, in the presence of HClO4, no positive shifts of those redox potentials for [Co(III)(Chn)](+)/Co(II)(Chn) (n = 2, 3) were observed due to lower acceptability of protonation. As a result, such a change in redox property resulted in the enhancement of the catalytic reactivity, where the observed rate constant (kobs) value of Co(II)(Ch3) was 36-fold larger than that of Co(II)(Ch1).

Catalytic two-electron reduction of dioxygen catalysed by metal-free [14]triphyrin(2.1.1).

The catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) occurs with a metal-free triphyrin (HTrip) in the presence of perchloric acid (HClO4) in benzonitrile (PhCN) at 298 K to yield Me8Fc+ and H2O2. Detailed kinetic analysis has revealed that the catalytic two-electron reduction of O2 by Me8Fc with HTrip proceeds via proton-coupled electron transfer from Me8Fc to HTrip to produce H3Trip˙+, followed by a second electron transfer from Me8Fc to H3Trip˙+ to produce H3Trip, which is oxidized by O2via formation of the H3Trip/O2 complex to yield H2O2. The rate-determining step in the catalytic cycle is hydrogen atom transfer from H3Trip to O2 in the H3Trip/O2 complex to produce the radical pair (H3Trip˙+ HO2˙) as an intermediate, which was detected as a triplet EPR signal with fine-structure by the EPR measurements at low temperature. The distance between the two unpaired electrons in the radical pair was determined to be 4.9 Šfrom the zero-field splitting constant (D).

High-valent chromium-oxo complex acting as an efficient catalyst precursor for selective two-electron reduction of dioxygen by a ferrocene derivative.

Efficient catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) produced hydrogen peroxide (H2O2) using a high-valent chromium(V)-oxo corrole complex, [(tpfc)Cr(V)(O)] (tpfc = tris(pentafluorophenyl)corrole) as a catalyst precursor in the presence of trifluoroacetic acid (TFA) in acetonitrile (MeCN). The facile two-electron reduction of [(tpfc)Cr(V)(O)] by 2 equiv of Me8Fc in the presence of excess TFA produced the corresponding chromium(III) corrole [(tpfc)Cr(III)(OH2)] via fast electron transfer from Me8Fc to [(tpfc)Cr(V)(O)] followed by double protonation of [(tpfc)Cr(IV)(O)](-) and facile second-electron transfer from Me8Fc. The rate-determining step in the catalytic two-electron reduction of O2 by Me8Fc in the presence of excess TFA is inner-sphere electron transfer from [(tpfc)Cr(III)(OH2)] to O2 to produce the chromium(IV) superoxo species [(tpfc)Cr(IV)(O2(•-))], followed by fast proton-coupled electron transfer reduction of [(tpfc)Cr(IV)(O2(•-))] by Me8Fc to yield H2O2, accompanied by regeneration of [(tpfc)Cr(III)(OH2)]. Thus, although the catalytic two-electron reduction of O2 by Me8Fc was started by [(tpfc)Cr(V)(O)], no regeneration of [(tpfc)Cr(V)(O)] was observed in the presence of excess TFA, regardless of the tetragonal chromium complex being to the left of the oxo wall. In the presence of a stoichiometric amount of TFA, however, disproportionation of [(tfpc)Cr(IV)(O)](-) occurred via the protonated species [(tpfc)Cr(IV)(OH)] to produce [(tpfc)Cr(III)(OH2)] and [(tpfc)Cr(V)(O)].

Efficient two-electron reduction of dioxygen to hydrogen peroxide with one-electron reductants with a small overpotential catalyzed by a cobalt chlorin complex.

A cobalt chlorin complex (Co(II)(Ch)) efficiently and selectively catalyzed two-electron reduction of dioxygen (O(2)) by one-electron reductants (ferrocene derivatives) to produce hydrogen peroxide (H(2)O(2)) in the presence of perchloric acid (HClO(4)) in benzonitrile (PhCN) at 298 K. The catalytic reactivity of Co(II)(Ch) was much higher than that of a cobalt porphyrin complex (Co(II)(OEP), OEP(2-) = octaethylporphyrin dianion), which is a typical porphyrinoid complex. The two-electron reduction of O(2) by 1,1'-dibromoferrocene (Br(2)Fc) was catalyzed by Co(II)(Ch), whereas virtually no reduction of O(2) occurred with Co(II)(OEP). In addition, Co(II)(Ch) is more stable than Co(II)(OEP), where the catalytic turnover number (TON) of the two-electron reduction of O(2) catalyzed by Co(II)(Ch) exceeded 30000. The detailed kinetic studies have revealed that the rate-determining step in the catalytic cycle is the proton-coupled electron transfer reduction of O(2) with the protonated Co(II)(Ch) ([Co(II)(ChH)](+)) that is produced by facile electron-transfer reduction of [Co(III)(ChH)](2+) by ferrocene derivative in the presence of HClO(4). The one-electron-reduction potential of [Co(III)(Ch)](+) was positively shifted from 0.37 V (vs SCE) to 0.48 V by the addition of HClO(4) due to the protonation of [Co(III)(Ch)](+). Such a positive shift of [Co(III)(Ch)](+) by protonation resulted in enhancement of the catalytic reactivity of [Co(III)(ChH)](2+) for the two-electron reduction of O(2) with a lower overpotential as compared with that of [Co(III)(OEP)](+).

Electroreduction and acid-base properties of dipyrrolylquinoxalines.

The electroreduction and acid-base properties of dipyrrolylquinoxalines of the form H(2)DPQ, H(2)DPQ(NO(2)), and H(2)DPQ(NO(2))(2) were investigated in benzonitrile (PhCN) containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). This study focuses on elucidating the complete electrochemistry, spectroelectrochemistry, and acid-base properties of H(2)DPQ(NO(2))(n) (n = 0, 1, or 2) in PhCN before and after the addition of trifluoroacetic acid (TFA), tetra-n-butylammonium hydroxide (TBAOH), tetra-n-butylammonium fluoride (TBAF), or tetra-n-butylammonium acetate (TBAOAc) to solution. Electrochemical and spectroelectrochemical data provide support for the formation of a monodeprotonated anion after disproportionation of a dipyrrolylquinoxaline radical anion produced initially. The generated monoanion is then further reduced in two reversible one-electron-transfer steps at more negative potentials in the case of H(2)DPQ(NO(2)) and H(2)DPQ(NO(2))(2). Electrochemically monitored titrations of H(2)DPQ(NO(2))(n) with OH(-), F(-), or OAc(-) (in the form of TBA(+)X(-) salts) give rise to the same monodeprotonated H(2)DPQ(NO(2))(n) produced during electroreduction in PhCN. This latter anion can then be reduced in two additional one-electron-transfer steps in the case of H(2)DPQ(NO(2)) and H(2)DPQ(NO(2))(2). Spectroscopically monitored titrations of H(2)DPQ(NO(2))(n) with X(-) show a 1:2 stoichiometry and provide evidence for the production of both [H(2)DPQ(NO(2))(n)](-) and XHX(-). The spectroscopically measured equilibrium constants range from log ß(2) = 5.3 for the reaction of H(2)DPQ with TBAOAc to log ß(2) = 8.8 for the reaction of H(2)DPQ(NO(2))(2) with TBAOH. These results are consistent with a combined deprotonation and anion binding process. Equilibrium constants for the addition of one H(+) to each quinoxaline nitrogen of H(2)DPQ, H(2)DPQ(NO(2)), and H(2)DPQ(NO(2))(2) in PhCN containing 0.1 M TBAP were also determined via electrochemical and spectroscopic means; this gave rise to log ß(2) values ranging from 0.7 to 4.6, depending upon the number of nitro substituents present on the H(2)DPQ core. The redox behavior of the H(2)DPQ(NO(2))(n) compounds of the present study were further analyzed through comparisons with simple quinoxalines that lack the two linked pyrrole groups, i.e., Q(NO(2))(n) where n = 0, 1, or 2. It is concluded that the pyrrolic substituents play a critical role in regulating the electrochemical and spectroscopic features of DPQs.

Catalytic four-electron reduction of O2 via rate-determining proton-coupled electron transfer to a dinuclear cobalt-µ-1,2-peroxo complex.

Four-electron reduction of O(2) by octamethylferrocene (Me(8)Fc) occurs efficiently with a dinuclear cobalt-µ-1,2-peroxo complex, 1, in the presence of trifluoroacetic acid in acetonitrile. Kinetic investigations of the overall catalytic reaction and each step in the catalytic cycle showed that proton-coupled electron transfer from Me(8)Fc to 1 is the rate-determining step in the catalytic cycle.

Disproportionation of dipyrrolylquinoxaline radical anions via the internal protons of the pyrrole moieties.

Disproportionation of dipyrrolylquinoxaline radical anions occurs via hydrogen atom transfer from the pyrrole moiety to the quinoxaline moiety to produce monodeprotonated dipyrrolylquinoxaline anions and monohydrodipyrrolylquinoxaline anions. In contrast, simple quinoxaline radical anions without pyrrole moieties are stable, and disproportionation occurs only in the presence of external protons.

Phenotypic differences of proliferating fibroblasts in the stroma of lung adenocarcinoma and normal bronchus tissue.

Fibroblasts in tumor tissue are thought to interact with tumor cells directly and/or indirectly and to have important roles in tumor invasion and metastasis. To characterize the phenotype of proliferating fibroblasts in pulmonary adenocarcinoma, we established short-term fibroblast cell lines from both normal bronchus and adenocarcinoma tissues obtained from the same patients and compared the gene expression profiles. Four sets of fibroblast cell lines (eight cell lines in total) were used in the analysis. Total RNA was extracted from each cell line and hybridized with 550 cancer-related RNAs blotted on a cDNA filter array. Five up-regulated genes and 12 down-regulated genes (total of 17 genes) were detected in the fibroblast cell lines from the tumor tissues compared with those from normal bronchus. Using real-time quantitative RT-PCR methods, the expression profile of each gene was examined; five genes, one up-regulated (MLH1) and four down-regulated (Cox1, FGFR4, p120, and Smad3), were confirmed. Furthermore, the protein expression levels of the five genes in the cancerous and normal tissues were examined immunohistochemically, and the up-regulation of MLH1 and the down-regulation of Cox1 in cancerous tissue were confirmed in vivo. These results indicate that the proliferating fibroblasts in pulmonary adenocarcinomas are phenotypically different from fibroblasts in normal bronchus tissues.

Intrabronchial orthotopic propagation of human lung adenocarcinoma--characterizations of tumorigenicity, invasion and metastasis.

Using the intrabronchial orthotopic propagation method, we evaluated the biological characteristics of human adenocarcinoma cell lines in vivo and examined the expressions of matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9) and their related proteins. Nine human lung adenocarcinoma cell lines, including A549, NCI-H23, NCI-H322, NCI-H358, Calu-3, PC-14, LC-2/ad, RERF-LC-KJ and PL16T, were injected into the peripheral bronchi of mice using this method. The mice were sacrificed at 4 and 8 weeks after tumor cell propagation and the lungs and other organs were observed macroscopically and histologically. We classified the adenocarcinoma cell lines, according to their intrapulmonary tumorigenicity, into the following three groups: (A) those that showed a high incidence of intrapulmonary implantation (>50%) (A549 and NCI-H358). A549 showed mediastinal lymph node metastasis and pleural dissemination; (B) those that showed a low incidence of intrapulmonary implantation (PC-14, NCI-H322, NCI-H23, Calu-3, and LC-2/ad); (C) those that showed no tumorigenicity in the lung (RERF-LC-KJ and PL16T). In order to characterize the biological differences between each cell line, we investigated the expressions of MMP-2 and MMP-9 and their related molecules by northern blot analysis. The expressions of MMP-2 and MMP-9 and their activators (membrane-type 1-MMP and urokinase-type plasminogen activator) were thought to be associated with the growth, invasion and metastasis of the human lung adenocarcinoma cell lines examined.