Modulation of characteristics of a ruthenium-coordinated flavin analogue that shows an unusual coordination mode.
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Flavins↗
Biomedical subjects
Shunichi Fukuzumi
Publications and source records attributed to Shunichi Fukuzumi.
Organized assemblies of single wall carbon nanotubes and porphyrin for photochemical solar cells: charge injection from excited porphyrin into single-walled carbon nanotubes.
Photochemical solar cells have been constructed from organized assemblies of single-walled carbon nanotubes (SWCNT) and protonated porphyrin on nanostructured SnO2 electrodes. The protonated form of porphyrin (H4P2+) and SWCNT composites form 0.5-3.0 microm-sized rodlike structures and they can be assembled onto nanostructured SnO2 films [optically transparent electrode OTE/SnO2] by an electrophoretic deposition method. These organized assemblies are photoactive and absorb strongly in the entire visible region. The incident photon to photocurrent efficiency (IPCE) of OTE/SnO2/SWCNT-H4P2+ is approximately 13% at an applied potential of 0.2 V versus saturated calomel electrode. Femtosecond pump-probe spectroscopy experiments confirm the decay of the excited porphyrin in the SWCNT-H4P2+ assembly as it injects electrons into SWCNT. The dual role of SWCNT in promoting photoinduced charge separation and facilitating charge transport is presented.
Electrodes↗
Photocatalytic formation of dimethyllepidopterene from 9,10-dimethylanthracene via electron-transfer oxidation.
[Structure: see text] Photocatalytic carbon-carbon bond formation of 9,10-dimethylanthracene (DMA) in chloroform occurs efficiently via the electron-transfer oxidation of DMA with the photoinduced electron-transfer state of 9-mesityl-10-methylacridinium ion (Acr+-Mes), followed by deprotonation from the methyl group of DMA radical cation and the radical coupling reaction between anthracenylmethyl radicals to produce dimethyllepidopterene.
Journal Article↗
An OFF-OFF-ON fluorescence sensor for metal ions in stepwise complex formation of 2,3,5,6-tetrakis(2-pyridyl)pyrazine with metal ions.
The fluorescence intensity of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ) begins to increase at concentrations of metal ions (Mn+) above the 1:2 ratio of metal ion concentration to the initial concentration of TPPZ ([Mn+]/[TPPZ]0 > 0.5), when a 2:1 complex of TPPZ with Mn+ [(TPPZ)2-Mn+] is converted to a 1:1 complex of TPPZ with Mn+ (TPPZ-Mn+), which exhibits strong fluorescence.
Journal Article↗
Viologen-modified platinum clusters acting as an efficient catalyst in photocatalytic hydrogen evolution.
A highly efficient photocatalytic system for hydrogen evolution with dihydronicotinamide coenzyme (NADH) as a sacrificial agent in an aqueous solution has been constructed by using water-soluble platinum clusters functionalized with methyl viologen-alkanethiol (MVA2+) and a simple electron-donor dyad, 9-mesityl-10-methylacridinium ion (Acr+-Mes), which is capable of fast photoinduced electron transfer but extremely slow back electron transfer. The mean diameter of the platinum core was determined as R(CORE) = 1.9 nm with a standard deviation sigma = 0.5 nm by transmission electron microscopy (TEM). As a result, the hydrogen-evolution rate of the photocatalytic system with MVA2+-modified platinum clusters (MVA2+-PtC) is 10 times faster than the photocatalytic system with the mixture of the same amount of MVA2+ and platinum clusters as that of MVA2+-PtC under otherwise the same experimental conditions. The radical cation of NADH has been successfully detected by laser flash photolysis experiments. The decay of the absorbance due to NAD*, produced by the deprotonation from NADH*+, coincides with the appearance of the absorption band due to Acr*-Mes. This indicates electron transfer from NAD* to Acr+-Mes to give Acr*-Mes, which undergoes the electron-transfer reduction of MVA2+-PtC, leading to the efficient hydrogen evolution.
Journal Article↗
A mechanistic dichotomy in scandium ion-promoted hydride transfer of an NADH analogue: delicate balance between one-step hydride-transfer and electron-transfer pathways.
The rate constant (kH) of hydride transfer from an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2), to 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) increases with increasing Sc(3+) concentration ([Sc(3+)]) to reach a constant value, when all TolSQ molecules form the TolSQ-Sc(3+) complex. When AcrH2 is replaced by the dideuterated compound (AcrD2), however, the rate constant (kD) increases linearly with an increase in ([Sc(3+)]) without exhibiting a saturation behavior. In such a case, the primary kinetic deuterium isotope effect (kH/kD) decreases with increasing ([Sc(3+)]). On the other hand, the rate constant of Sc(3+)-promoted electron transfer from tris(2-phenylpyridine)iridium [Ir(ppy)3]to TolSQ also increases linearly with increasing ([Sc(3+)]) at high concentrations of Sc(3+) due to formation of a 1:2 complex between TolSQ*- and Sc(3+), [TolSQ*--(Sc(3+)2], which was detected by ESR. The significant difference with regard to dependence of the rate constant of hydride transfer on ([Sc(3+)]) between AcrH2 and AcrD2 in comparison with that of Sc3+-promoted electron transfer indicates that the reaction pathway is changed from one-step hydride transfer from AcrH2 to the TolSQ-Sc3+ complex to Sc3+-promoted electron transfer from AcrD2 to the TolSQ-Sc3+ complex, followed by proton and electron transfer. Such a change between two reaction pathways, which are employed simultaneously, is also observed by simple changes of temperature and concentration of Sc3+.
Electron Spin Resonance Spectroscopy↗
Spin-site exchange system constructed from endohedral metallofullerenes and organic donors.
Complexation behavior of the paramagnetic La@C82 metallofullerene with organic donor molecules (D) in solution is investigated. It is revealed that La@C82 and D form a 1:1 complex as a result of electron transfer. La@C82 and D are in equilibrium with [La@C82]-/[D]*+ in solution, which is readily controllable by changing the temperature and solvent.
Journal Article↗
Persistent electron-transfer state of a pi-complex of acridinium ion inserted between porphyrin rings of cofacial bisporphyrins.
A free-base cofacial bisporphyrin, H(4)DPOx, forms a pi-complex with acridinium ion (AcH(+)) by pi-pi interaction in benzonitrile (PhCN). Formation of the H(4)DPOx-AcH(+) pi-complex was probed by UV-vis and NMR spectroscopy. The binding constant between AcH(+) and H(4)DPOx is determined as 9.7 x 10(4) M(-)(1). Photoinduced electron transfer (ET) from the H(4)DPOx to the AcH(+) moiety occurred efficiently in the pi-complex to form the ET state (H(4)DPOx(*)(+)-AcH(*)). The ET state is successfully detected by laser flash photolysis. The lifetime of the ET state is 18 mus in PhCN at 298 K, and the quantum yield of the ET state is 90%. The temperature dependence of the ET state lifetime has been examined in the range from 273 to 353 K. The ET state lifetime exhibited a large temperature dependence, and the linear plot of ln(k(BET)T(1/2)) vs T(-)()(1), in accordance with the Marcus equation, affords the ET reorganization energy (0.54 eV). As a result, a remarkably long-lived ET state has been attained at low temperature, and virtually no decay of the ET state was observed at 77 K. Such an extremely long-lived ET state is indeed detected by steady-state UV-vis absorption spectroscopy.
Journal Article↗
Mechanistic borderline between one-step hydrogen transfer and sequential transfers of electron and proton in reactions of NADH analogues with triplet excited states of tetrazines and Ru(bpy)(3)2+.
Efficient energy transfer from Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine, denotes the excited state) to 3,6-disubstituted tetrazines [R(2)Tz: R = Ph (Ph(2)Tz), 2-chlorophenyl [(ClPh)(2)Tz], 2-pyridyl (Py(2)Tz)] occurs to yield the triplet excited states of tetrazines ((3)R(2)Tz(*)), which have longer lifetimes and higher oxidizing ability as compared with those of Ru(bpy)(3)(2+). The dynamics of hydrogen-transfer reactions from NADH (dihydronicotinamide adenine dinucleotide) analogues has been examined in detail using (3)R(2)Tz(*) by laser flash photolysis measurements. Whether formal hydrogen transfer from NADH analogues to (3)R(2)Tz(*) proceeds via a one-step process or sequential electron and proton transfer processes is changed by a subtle difference in the electron donor ability and the deprotonation reactivity of the radical cations of NADH analogues as well as the electron-acceptor ability of (3)R(2)Tz(*) and the protonation reactivity of R(2)Tz(*)(-). In the case of (3)Ph(2)Tz(*), which is a weaker electron acceptor than the other tetrazine derivatives [(ClPh)(2)Tz; Py(2)Tz], direct one-step hydrogen transfer occurs from 10-methyl-9,10-dihydroacridine (AcrH(2)) to (3)Ph(2)Tz(*) without formation of the radical cation (AcrH(2)(*)(+)). The rate constant of the direct hydrogen transfer from AcrH(2) to (3)Ph(2)Tz(*) is larger than that expected from the Gibbs energy relation for the rate constants of electron transfer from various electron donors to (3)Ph(2)Tz(*), exhibiting the primary deuterium kinetic isotope effect. On the other hand, hydrogen transfer from 9-isopropyl-10-methyl-9,10-dihydroacridine (AcrHPr(i)) and 1-benzyl-1,4-dihydronicotinamide (BNAH) to (3)R(2)Tz(*) occurs via sequential electron and proton transfer processes, when both the radical cations and deprotonated radicals of NADH analogues are detected by the laser flash photolysis measurements.
Journal Article↗
Electron-transfer reduction of cup-stacked carbon nanotubes affording cup-shaped carbons with controlled diameter and size.
The electron-transfer reduction of cup-stacked carbon nanotubes (CSCNTs) with sodium naphthalenide and the subsequent treatment with 1-iodododecane results in electrostatically destacking of CSCNTs to afford cup-shaped carbons with controlled diameter and size. The dodecylated cup-shaped carbons were highly dispersed and stable in nonpolar solvents, such as THF, tetrachloroethylene, and chloroform, as compared with the pristine CSCNTs.
Journal Article↗
Activation of electron-transfer reduction of oxygen by hydrogen bond formation of superoxide anion with ammonium ion.
A hydrogen bond formed between the superoxide anion and the ammonium ion (NH4+) accelerates electron transfer from the C60 radical anion to oxygen significantly, whereas the tetra-n-butylammonium ion has no ability to form a hydrogen bond with the superoxidie anion, exhibiting no acceleration of the electron-transfer reduction of oxygen. The second-order rate constant of electron transfer from C60*- to O2 increases linearly with increasing concentration of NH4+. This indicates that O2*- produced in the electron transfer from C60 to O2 is stabilized by 1:1 complex formation between O2*- and NH4+. The 1:1 complex formed between O2*- and NH4+ was detected by ESR. The binding of O2*- with NH4+ results in a positive shift of the reduction potential of O2 with increasing concentration of NH4+, leading to the acceleration of electron transfer from C60*- to O2.
Electron Spin Resonance Spectroscopy↗
DNA cleavage by UVA irradiation of NADH with dioxygen via radical chain processes.
Efficient DNA cleaving-activity is observed by UVA irradiation of an O(2)-saturated aqueous solution of NADH (beta-nicotinamide adenine dinucleotide, reduced form). No DNA cleavage has been observed without NADH under otherwise the same experimental conditions. In the presence of NADH, energy transfer from the triplet excited state of NADH ((3)NADH*) to O(2) occurs to produce singlet oxygen ((1)O(2)) that is detected by the phosphorescence emission at 1270 nm. No quenching of (1)O(2) by NADH was observed as indicated by no change in the intensity of phosphorescence emission of (1)O(2) at 1270 nm in the presence of various concentrations of NADH. In addition to the energy transfer, photoinduced electron transfer from (3)NADH* to O(2) occurs to produce NADH(*+) and O(2)(*-), both of which was observed by ESR. The quantum yield of the photochemical oxidation of NADH with O(2) increases linearly with increasing concentration of NADH but decreases with increasing the light intensity absorbed by NADH. Such unusual dependence of the quantum yield on concentration of NADH and the light intensity absorbed by NADH indicates that the photochemical oxidation of NADH with O(2) proceeds via radical chain processes. The O(2)(*-) produced in the photoinduced electron transfer is in the protonation equilibrium with HO(2)(*), which acts as a chain carrier for the radical chain oxidation of NADH with O(2) to produce NAD(+) and H(2)O(2), leading to the DNA cleavage.
DNA↗
Reductive DNA cleavage induced by UVA photoirradiation of NADH without oxygen.
UVA irradiation of dihydronicotinamide coenzyme (NADH), which plays a key role in a number of biological redox processes, results in effective DNA cleavage without oxygen via photoionization of NADH and the subsequent reaction of hydrated electron with DNA as well as photoinduced electron transfer from NADH to DNA.
DNA↗
Mechanistic investigation of CO2 hydrogenation by Ru(II) and Ir(III) aqua complexes under acidic conditions: two catalytic systems differing in the nature of the rate determining step.
Ruthenium aqua complexes [(eta(6)-C(6)Me(6))Ru(II)(L)(OH(2))](2+) {L = bpy (1) and 4,4'-OMe-bpy (2), bpy = 2,2'-bipyridine, 4,4'-OMe-bpy = 4,4'-dimethoxy-2,2'-bipyridine} and iridium aqua complexes [Cp*Ir(III)(L)(OH(2))](2+) {Cp* = eta(5)-C(5)Me(5), L = bpy (5) and 4,4'-OMe-bpy (6)} act as catalysts for hydrogenation of CO(2) into HCOOH at pH 3.0 in H(2)O. The active hydride catalysts cannot be observed in the hydrogenation of CO(2) with the ruthenium complexes, whereas the active hydride catalysts, [Cp*Ir(III)(L)(H)](+) {L = bpy (7) and 4,4'-OMe-bpy (8)}, have successfully been isolated after the hydrogenation of CO(2) with the iridium complexes. The key to the success of the isolation of the active hydride catalysts is the change in the rate-determining step in the catalytic hydrogenation of CO(2) from the formation of the active hydride catalysts, [(eta(6)-C(6)Me(6))Ru(II)(L)(H)](+), to the reactions of [Cp*Ir(III)(L)(H)](+) with CO(2), as indicated by the kinetic studies.
Journal Article↗
Direct detection of nucleotide radical cations produced by electron-transfer oxidation of DNA bases with electron-transfer state of 9-mesityl-10-methylacridinium ion and resulting efficient DNA cleavage without oxygen.
Photoinduced electron transfer of DNA as well as DNA bases with 9-mesityl-10-methylacridinium ion results in formation of all types of DNA base radical cations, which have been detected as the transient absorption spectra measurements, leading to efficient DNA cleavage in the absence of O2.
Acridines↗
Solvent-free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen using 9-phenyl-10-methylacridinium.
9-Phenyl-10-methylacridium ion acts as an effective photocatalyst for solvent free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde under visible light irradiation via efficient photoinduced electron transfer from benzyl alcohol to the singlet excited state of the acridinium ion.
Journal Article↗
Binding modes in metal ion complexes of quinones and semiquinone radical anions: electron-transfer reactivity.
9,10-Phenanthrenequinone (PQ) and 1,10-phenanthroline-5,6-dione (PTQ) form 1:1 and 2:1 complexes with metal ions (M (n+)=Sc (3+), Y (3+), Mg (2+), and Ca (2+)) in acetonitrile (MeCN), respectively. The binding constants of PQ--M (n+) complexes vary depending on either the Lewis acidity or ion radius of metal ions. The one-electron reduced species (PTQ(-)) forms 1:1 complexes with M (n+), and PQ(-) also forms 1:1 complexes with Sc(3+), Mg(2+), and Ca(2+), whereas PQ(-) forms 1:2 complexes with Y(3+) and La(3+), as indicated by electron spin resonance (ESR) measurements. On the other hand, semiquinone radical anions (Q(-) and NQ(-)) derived from p-benzoquinone (Q) and 1,4-naphthoquinone (NQ) form Sc(3+)-bridged pi-dimer radical anion complexes, Q(-)--(Sc(3+))(n)--Q and NQ(-)--(Sc(3+))(n)-NQ (n=2 and 3), respectively. The one-electron reduction potentials of quinones (PQ, PTQ, and Q) are largely positively shifted in the presence of M (n+). The rate constant of electron transfer from CoTPP (TPP(2-)=dianion of tetraphenylporphyrin) to PQ increases with increasing the concentration of Sc(3+) to reach a constant value, when all PQ molecules form the 1:1 complex with Sc(3+). Rates of electron transfer from 10,10'-dimethyl-9,9'-biacridine [(AcrH)(2)] to PTQ are also accelerated significantly by the presence of Sc(3+), Y(3+), and Mg(2+), exhibiting a first-order dependence with respect to concentrations of metal ions. In contrast to the case of o-quinones, unusually high kinetic orders are observed for rates of Sc(3+)-promoted electron transfer from tris(2-phenylpyridine)iridium(III) [Ir(ppy)(3)] to p-quinones (Q): second-order dependence on concentration of Q, and second- and third-order dependence on concentration of Sc(3+) due to formation of highly ordered radical anion complexes, Q()--(Sc(3+))(n)--Q (n=2 and 3).
Benzoquinones↗
Photocatalytic oxygenation of pivalic acid with molecular oxygen via photoinduced electron transfer using 10-methylacridinium ions.
Photoirradiation of the absorption band of the 10-methylacridinium ion (AcrH+) with visible light in deaerated CH3CN/H2O (1:1 v/v) containing pivalic acid (Bu(t)COOH) and less than 1 equiv of NaOH results in the selective formation of 9-tert-butyl-9,10-dihydro-10-methylacridine (AcrHBu(t)). The same product is obtained in O2-saturated CH3CN/H2O under visible light irradiation. Photoirradiation of the absorption band of AcrHBu(t) with UV light in deaerated CH3CN/H2O (1:1 v/v) results in the formation of tert-butyl hydroperoxide (Bu(t)OOH), accompanied by regeneration of AcrH+. This cycle can be repeated several times. When AcrH+ is replaced by the 9-phenyl derivative (AcrPh+), AcrPh+ acts as an effective photocatalyst for the one-pot photooxygenation of Bu(t)COOH in the presence of less than 1 equiv of NaOH relative to Bu(t)COOH with O2 to yield Bu(t)OOH and Bu(t)H. The photocatalytic oxygenation mechanism is discussed based on the detection of radical intermediates by laser flash photolysis and ESR measurements as well as quantum yield determination.
Acridines↗