Efficient Catalytic Interconversionbetween NADH andNAD⁺ Accompanied by Generation and Consumption of Hydrogenwith a Water-Soluble Iridium Complex at Ambient Pressure and Temperature

Maenaka, Yuta,Suenobu, Tomoyoshi,Fukuzumi, Shunichi American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.1

<P>Regioselective hydrogenation of the oxidized form ofβ-nicotinamideadenine dinucleotide (NAD<SUP>+</SUP>) to the reduced form (NADH)with hydrogen (H<SUB>2</SUB>) has successfully been achieved in thepresence of a catalytic amount of a [C,N] cyclometalated organoiridiumcomplex [Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)benzoic acid-κ<I>C</I><SUP>3</SUP>)(H<SUB>2</SUB>O)]<SUB>2</SUB> SO<SUB>4</SUB> [<B>1</B>]<SUB>2</SUB>·SO<SUB>4</SUB> under an atmospheric pressure ofH<SUB>2</SUB> at room temperature in weakly basic water. The structureof the corresponding benzoate complex Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)-benzoate-κ<I>C</I><SUP>3</SUP>)(H<SUB>2</SUB>O) <B>2</B> has been revealedby X-ray single-crystal structure analysis. The corresponding iridiumhydride complex formed under an atmospheric pressure of H<SUB>2</SUB> undergoes the 1,4-selective hydrogenation of NAD<SUP>+</SUP> toform 1,4-NADH. On the other hand, in weakly acidic water the complex <B>1</B> was found to catalyze the hydrogen evolution from NADH toproduce NAD<SUP>+</SUP> without photoirradiation at room temperature.NAD<SUP>+</SUP> exhibited an inhibitory behavior in both catalytichydrogenation of NAD<SUP>+</SUP> with H<SUB>2</SUB> and H<SUB>2</SUB> evolution from NADH due to the binding of NAD<SUP>+</SUP> to thecatalyst. The overall catalytic mechanism of interconversion betweenNADH and NAD<SUP>+</SUP> accompanied by generation and consumptionof H<SUB>2</SUB> was revealed on the basis of the kinetic analysisand detection of the catalytic intermediates.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-1/ja207785f/production/images/medium/ja-2011-07785f_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja207785f'>ACS Electronic Supporting Info</A></P>

Hydrogen storage and evolution catalysed by metal hydride complexes

Fukuzumi, Shunichi,Suenobu, Tomoyoshi The Royal Society of Chemistry 2013 Dalton transactions Vol.42 No.1

<P>The storage and evolution of hydrogen are catalysed by appropriate metal hydride complexes. Hydrogenation of carbon dioxide by hydrogen is catalysed by a [C,N] cyclometalated organoiridium complex, [Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)benzoic acid-κ<I>C</I><SUP>3</SUP>)(OH<SUB>2</SUB>)]<SUB>2</SUB>SO<SUB>4</SUB> [<B>Ir</B>–OH<SUB>2</SUB>]<SUB>2</SUB>SO<SUB>4</SUB>, under atmospheric pressure of H<SUB>2</SUB> and CO<SUB>2</SUB> in weakly basic water (pH 7.5) at room temperature. The reverse reaction, <I>i.e.</I>, hydrogen evolution from formate, is also catalysed by [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> in acidic water (pH 2.8) at room temperature. Thus, interconversion between hydrogen and formic acid in water at ambient temperature and pressure has been achieved by using [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> as an efficient catalyst in both directions depending on pH. The Ir complex [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> also catalyses regioselective hydrogenation of the oxidised form of β-nicotinamide adenine dinucleotide (NAD<SUP>+</SUP>) to produce the 1,4-reduced form (NADH) under atmospheric pressure of H<SUB>2</SUB> at room temperature in weakly basic water. In weakly acidic water, the complex [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> also catalyses the reverse reaction, <I>i.e.</I>, hydrogen evolution from NADH to produce NAD<SUP>+</SUP> at room temperature. Thus, interconversion between NADH (and H<SUP>+</SUP>) and NAD<SUP>+</SUP> (and H<SUB>2</SUB>) has also been achieved by using [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> as an efficient catalyst and by changing pH. The iridium hydride complex formed by the reduction of [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> by H<SUB>2</SUB> and NADH is responsible for the hydrogen evolution. Photoirradiation (<I>λ</I> > 330 nm) of an aqueous solution of the Ir–hydride complex produced by the reduction of [<B>Ir</B>–OH<SUB>2</SUB>]<SUP>+</SUP> with alcohols resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir–hydride complex, which can catalyse hydrogen evolution from alcohols in a basic aqueous solution (pH 11.9). The catalytic mechanisms of the hydrogen storage and evolution are discussed by focusing on the reactivity of Ir–hydride complexes.</P> <P>Graphic Abstract</P><P>Hydrogen storage and evolution were catalysed by [C,N] and [C,C] cyclometalated iridium hydride complexes in water at ambient temperature under atmospheric pressure. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2dt31823g'> </P>

Hydrogen Evolution from Aliphatic Alcohols and 1,4-Selective Hydrogenation of NAD⁺ Catalyzed by a [C,N] and a [C,C] Cyclometalated Organoiridium Complex at Room Temperature in Water

Maenaka, Yuta,Suenobu, Tomoyoshi,Fukuzumi, Shunichi American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.22

<P>A [C,N] cyclometalated Ir complex, [Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)benzoic acid-κ<I>C</I><SUP>3</SUP>)(H<SUB>2</SUB>O)]<SUB>2</SUB>SO<SUB>4</SUB> [<B>1</B>]<SUB>2</SUB>·SO<SUB>4</SUB>, was reduced by aliphatic alcohols to produce the corresponding hydride complex [Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)-benzoate-κ<I>C</I><SUP>3</SUP>)H]<SUP>−</SUP><B>4</B> at room temperature in a basic aqueous solution (pH 13.6). Formation of the hydride complex <B>4</B> was confirmed by <SUP>1</SUP>H and <SUP>13</SUP>C NMR, ESI MS, and UV–vis spectra. The [C,N] cyclometalated Ir-hydride complex <B>4</B> reacts with proton to generate a stoichiometric amount of hydrogen when the pH was decreased to pH 0.8 by the addition of diluted sulfuric acid. Photoirradiation (λ > 330 nm) of an aqueous solution of the [C,N] cyclometalated Ir-hydride complex <B>4</B> resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir-hydride complex <B>5</B> with no byproduct. The complex <B>5</B> catalyzed hydrogen evolution from ethanol in a basic aqueous solution (pH 11.9) under ambient conditions. The 1,4-selective catalytic hydrogenation of β-nicotinamide adenine dinucleotide (NAD<SUP>+</SUP>) by ethanol was also made possible by the complex <B>1</B> to produce 1,4-dihydro-β-nicotinamide adenine dinucleotide (1,4-NADH) at room temperature. The overall catalytic mechanism of hydrogenation of NAD<SUP>+</SUP>, accompanied by the oxidation of ethanol, was revealed on the basis of the kinetic analysis and detection of the reaction intermediates.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-22/ja302788c/production/images/medium/ja-2012-02788c_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja302788c'>ACS Electronic Supporting Info</A></P>

Catalytic interconversion between hydrogen and formic acid at ambient temperature and pressure

Maenaka, Yuta,Suenobu, Tomoyoshi,Fukuzumi, Shunichi The Royal Society of Chemistry 2012 ENERGY AND ENVIRONMENTAL SCIENCE Vol.5 No.6

<P>Interconversion between hydrogen and formic acid in water at ambient temperature and pressure has been made possible by using a [C,N] cyclometalated organoiridium complex, [Ir<SUP>III</SUP>(Cp*)(4-(1<I>H</I>-pyrazol-1-yl-κ<I>N</I><SUP>2</SUP>)benzoic acid-κ<I>C</I><SUP>3</SUP>)(H<SUB>2</SUB>O)]<SUB>2</SUB>SO<SUB>4</SUB> [<B>1</B>]<SUB>2</SUB>·SO<SUB>4</SUB>, as an efficient catalyst for both directions depending on pH. Hydrogenation of carbon dioxide by hydrogen occurs in the presence of a catalytic amount of <B>1</B> under an atmospheric pressure of H<SUB>2</SUB> and CO<SUB>2</SUB> in weakly basic water (pH 7.5) at room temperature, whereas formic acid efficiently decomposes to afford H<SUB>2</SUB> and CO<SUB>2</SUB> in the presence of <B>1</B> in acidic water (pH 2.8).</P> <P>Graphic Abstract</P><P>A [C,N] cyclometalated water-soluble iridium aqua complex acts as an efficient catalyst for interconversion between H<SUB>2</SUB> and HCOOH at ambient temperature and pressure in water by controlling pH. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee03315a'> </P>

A Vanadium Porphyrin with Temperature-Dependent Phase Transformation: Synthesis, Crystal Structures, Supramolecular Motifs and Properties

Chen, W.,Suenobu, T.,Fukuzumi, S. WILEY 2011 Chemistry - An Asian Journal Vol.6 No.6

Unusually Large Tunneling Effect on Highly Efficient Generation of Hydrogen and Hydrogen Isotopes in pH-Selective Decomposition of Formic Acid Catalyzed by a Heterodinuclear Iridium−Ruthenium Complex in Water

Fukuzumi, Shunichi,Kobayashi, Takeshi,Suenobu, Tomoyoshi American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.5

<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-5/ja910349w/production/images/medium/ja-2009-10349w_0005.gif'> <P>A heterodinuclear iridium−ruthenium complex [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB> {<B>1</B>(SO<SUB>4</SUB>)<SUB>2</SUB>, Cp* = η<SUP>5</SUP>-pentamethylcyclopentadienyl, bpm = 2,2′-bipyrimidine, bpy = 2,2′-bipyridine} acts as the most effective catalyst for selective production of hydrogen from formic acid in an aqueous solution at ambient temperature among catalysts reported so far. An unusually large tunneling effect was observed for the first time for the catalytic hydrogen production in H<SUB>2</SUB>O vs D<SUB>2</SUB>O.</P></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja910349w'>ACS Electronic Supporting Info</A></P>

Catalytic mechanisms of hydrogen evolution with homogeneous and heterogeneous catalysts

Fukuzumi, Shunichi,Yamada, Yusuke,Suenobu, Tomoyoshi,Ohkubo, Kei,Kotani, Hiroaki Royal Society of Chemistry 2011 Energy & environmental science Vol.4 No.8

<P>This perspective focuses on reaction mechanisms of hydrogen (H<SUB>2</SUB>) evolution with homogeneous and heterogeneous catalysts. First, photocatalytic H<SUB>2</SUB> evolution systems with homogeneous catalysts are discussed from the viewpoint of how to increase the efficiency of the two-electron process for the H<SUB>2</SUB> evolution <I>via</I> photoinduced electron-transfer reactions of metal complexes. Two molecules of the one-electron reduced species of [Rh<SUP>III</SUP>(Cp*)(bpy)(H<SUB>2</SUB>O)](SO<SUB>4</SUB>) (bpy = 2,2′-bipyridine) and [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB> (bpm = 2,2′-bipyrimidine) produced by photoinduced electron-transfer reactions are converted to the two-electron reduced complexes suitable for H<SUB>2</SUB> generation by disproportionation. The photocatalytic mechanism of H<SUB>2</SUB> evolution using Pt nanoparticles as a catalyst is also discussed based on the kinetic analysis of the electron-transfer rates from a photogenerated electron donor to Pt nanoparticles, which are comparable to the overall H<SUB>2</SUB> evolution rates. The electron-transfer rates become faster with increasing proton concentrations with an inverse kinetic isotope effect, when H<SUP>+</SUP> is replaced by D<SUP>+</SUP>. The size and shape effects of Pt nanoparticles on the rates of hydrogen evolution and the electron-transfer reaction are examined to optimize the catalytic efficiency. Finally, catalytic H<SUB>2</SUB> evolution systems from H<SUB>2</SUB> storage molecules are described including shape dependent catalytic activity of Co<SUB>3</SUB>O<SUB>4</SUB> particles for ammonia borane hydrolysis and a large tunneling effect observed in decomposition of formic acid with [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB>.</P> <P>Graphic Abstract</P><P>Recent progress in understanding catalytic mechanisms for hydrogen evolution with homogeneous and heterogeneous catalysts is overviewed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1ee01551f'> </P>

Contrasting Effects of Axial Ligands on Electron-Transfer Versus Proton-Coupled Electron-Transfer Reactions of Nonheme Oxoiron(IV) Complexes

Fukuzumi, Shunichi,Kotani, Hiroaki,Suenobu, Tomoyoshi,Hong, Seungwoo,Lee, Yong-Min,Nam, Wonwoo WILEY-VCH Verlag 2010 Chemistry Vol.16 No.1

<P>The effects of axial ligands on electron-transfer and proton-coupled electron-transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe<SUP>IV</SUP>(O)(tmc)(X)]<SUP>n+</SUP> (1-X) with various axial ligands, in which tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is CH<SUB>3</SUB>CN (1-NCCH<SUB>3</SUB>), CF<SUB>3</SUB>COO<SUP>−</SUP> (1-OOCCF<SUB>3</SUB>), or N<SUB>3</SUB><SUP>−</SUP> (1-N<SUB>3</SUB>), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one-electron reduction potentials of 1-X (E<SUB>red</SUB>, V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron-donating axial ligands in the order of 1-NCCH<SUB>3</SUB> (0.39) > 1-OOCCF<SUB>3</SUB> (0.13) > 1-N<SUB>3</SUB> (−0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1-X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (λ) of electron transfer. The λ values decrease in the order of 1-NCCH<SUB>3</SUB> (2.37) > 1-OOCCF<SUB>3</SUB> (2.12) > 1-N<SUB>3</SUB> (1.97 eV). Thus, the electron-transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron-transfer rate in the order of 1-NCCH<SUB>3</SUB> > 1-OOCCF<SUB>3</SUB> > 1-N<SUB>3</SUB>. In sharp contrast to this, the rates of the proton-coupled electron-transfer reactions of 1-X are markedly accelerated in the presence of an acid in the opposite order: 1-NCCH<SUB>3</SUB> < 1-OOCCF<SUB>3</SUB> < 1-N<SUB>3</SUB>. Such contrasting effects of the axial ligands on the electron-transfer and proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen-atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 19 181–19 186).</P> <B>Graphic Abstract</B> <P>Counterintuitive reactivities: The rates of electron transfer (ET) and proton-coupled electron-transfer (PCET) in the reactions of with ferrocene derivatives are markedly affected by the electron-donating ability of the axial ligands (X) in opposite directions (see figure); the electron-donating axial ligand decelerates the ET rate in the reactions, but enhances the PCET reactivity of 1-X in the presence of acid. <img src='wiley_img/09476539-2010-16-1-CHEM200901163-content.gif' alt='wiley_img/09476539-2010-16-1-CHEM200901163-content'> </P>

Mechanistic Borderline of One-Step Hydrogen Atom Transfer versus Stepwise Sc³⁺-Coupled Electron Transfer from Benzyl Alcohol Derivatives to a Non-Heme Iron(IV)-Oxo Complex

Morimoto, Yuma,Park, Jiyun,Suenobu, Tomoyoshi,Lee, Yong-Min,Nam, Wonwoo,Fukuzumi, Shunichi American Chemical Society 2012 Inorganic Chemistry Vol.51 No.18

<P>The rate of oxidation of 2,5-dimethoxybenzyl alcohol (2,5-(MeO)<SUB>2</SUB>C<SUB>6</SUB>H<SUB>3</SUB>CH<SUB>2</SUB>OH) by [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> (N4Py = <I>N</I>,<I>N</I>-bis(2-pyridylmethyl)-<I>N</I>-bis(2-pyridyl)methylamine) was enhanced significantly in the presence of Sc(OTf)<SUB>3</SUB> (OTf<SUP>–</SUP> = trifluoromethanesulfonate) in acetonitrile (e.g., 120-fold acceleration in the presence of Sc<SUP>3+</SUP>). Such a remarkable enhancement of the reactivity of [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> in the presence of Sc<SUP>3+</SUP> was accompanied by the disappearance of a kinetic deuterium isotope effect. The radical cation of 2,5-(MeO)<SUB>2</SUB>C<SUB>6</SUB>H<SUB>3</SUB>CH<SUB>2</SUB>OH was detected in the course of the reaction in the presence of Sc<SUP>3+</SUP>. The dimerized alcohol and aldehyde were also produced in addition to the monomer aldehyde in the presence of Sc<SUP>3+</SUP>. These results indicate that the reaction mechanism is changed from one-step hydrogen atom transfer (HAT) from 2,5-(MeO)<SUB>2</SUB>C<SUB>6</SUB>H<SUB>3</SUB>CH<SUB>2</SUB>OH to [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> in the absence of Sc<SUP>3+</SUP> to stepwise Sc<SUP>3+</SUP>-coupled electron transfer, followed by proton transfer in the presence of Sc<SUP>3+</SUP>. In contrast, neither acceleration of the rate nor the disappearance of the kinetic deuterium isotope effect was observed in the oxidation of benzyl alcohol (C<SUB>6</SUB>H<SUB>5</SUB>CH<SUB>2</SUB>OH) by [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> in the presence of Sc(OTf)<SUB>3</SUB>. Moreover, the rate constants determined in the oxidation of various benzyl alcohol derivatives by [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> in the presence of Sc(OTf)<SUB>3</SUB> (10 mM) were compared with those of Sc<SUP>3+</SUP>-coupled electron transfer from one-electron reductants to [Fe<SUP>IV</SUP>(O)(N4Py)]<SUP>2+</SUP> at the same driving force of electron transfer. This comparison revealed that the borderline of the change in the mechanism from HAT to stepwise Sc<SUP>3+</SUP>-coupled electron transfer and proton transfer is dependent on the one-electron oxidation potential of benzyl alcohol derivatives (ca. 1.7 V vs SCE).</P><P>This Article scrutinizes the borderline of the reaction mechanism between one-step hydrogen atom transfer and electron transfer in the oxidation of benzyl alcohol derivatives by a nonheme iron(IV)-oxo complex in the presence of Sc<SUP>3+</SUP>. The borderline is found by examining the dependence of reaction rate constants on the driving force for electron transfer from substrate to the oxidant.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2012/inocaj.2012.51.issue-18/ic3016723/production/images/medium/ic-2012-016723_0015.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic3016723'>ACS Electronic Supporting Info</A></P>

Formic Acid Acting as an Efficient Oxygen Scavenger in Four-Electron Reduction of Oxygen Catalyzed by a Heterodinuclear Iridium−Ruthenium Complex in Water

Fukuzumi, Shunichi,Kobayashi, Takeshi,Suenobu, Tomoyoshi American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.34

<P>A heterodinuclear iridium−ruthenium complex [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB> (Cp* = η<SUP>5</SUP>-pentamethyl-cyclopentadienyl, bpm = 2,2′-bipyrimidine, bpy = 2,2′-bipyridine) acts as an effective catalyst for removal of dissolved O<SUB>2</SUB> by the four-electron reduction of O<SUB>2</SUB> with formic acid in water at an ambient temperature.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-34/ja104486h/production/images/medium/ja-2010-04486h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja104486h'>ACS Electronic Supporting Info</A></P>