A discrete conglomerate of a distorted Mo(v)-porphyrin with a directly coordinated Keggin-type polyoxometalate.

The reaction of a saddle-distorted Mo(v)-dodecaphenylporphyrin complex and a Keggin-type polyoxometalate gives a discrete and nanosized molecule, [{Mo(DPP)(O)}(2)(H(2)SiW(12)O(40))], which involves direct coordination between the Mo(v) centers and terminal oxo groups of the polyoxometalate and exhibits excellent stability in solution to show reversible multi-redox processes.

Contrasting photodynamics between C60-dithiapyrene and C60-pyrene dyads.

The photodynamics of a C60-dithiapyrene donor-acceptor conjugate were compared with the corresponding C60-pyrene conjugate. The photoinduced charge separation and subsequent charge recombination processes were examined by time-resolved fluorescence measurements on the picosecond timescale and transient absorption measurements on the picosecond and microsecond timescales with detection in the visible and near-infrared regions. We have observed quite long lifetimes (i.

A long-lived o-semiquinone radical anion is formed from N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), an insect-derived antibacterial substance.

N-beta-Alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), an insect-derived antibacterial peptide, generates hydrogen peroxide (H(2)O(2)) that exerts antitumour activity. We have investigated the precise mechanism of H(2)O(2) production from 5-S-GAD by autoxidation aiming to understand its action toward tumour cells. Using the electron spin resonance (ESR) technique, we detected a strong signal due to radical formation from 5-S-GAD.

Selective inclusion of electron-donating molecules into porphyrin nanochannels derived from the self-assembly of saddle-distorted, protonated porphyrins and photoinduced electron transfer from guest molecules to porphyrin dications.

A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated.

Enhanced photoinduced oligomerization of fullerene via radical coupling between fullerene radical cation and radical anion using 9-mesityl-10-methylacridinium ion.

Photocatalytic oligomerization of fullerene in toluene-acetonitrile solution occurs efficiently via electron-transfer reactions with the photogenerated electron-transfer state of 9-mesityl-10-methylacridinium ion, followed by the radical coupling reaction between fullerene radical cation and radical anion.

Synthesis and photophysical studies of a new nonaggregated C60-silicon phthalocyanine-C60 triad.

A C60-SiPc-C60 triad showing no aggregation is synthesized and characterized. Photoexcitation of the triad results in formation of the charge-separated state by photoinduced electron transfer from the singlet excited state of the SiPc moiety to the C60 moiety. The charge-separated state has a lifetime of 5 ns in benzonitrile at 298 K.

Synthesis and characterization of mononuclear ruthenium(III) pyridylamine complexes and mechanistic insights into their catalytic alkane functionalization with m-chloroperbenzoic acid.

A series of mononuclear RuIII complexes [RuCl2(L)]+, where L is tris(2-pyridylmethyl)amine (TPA) or one of four TPA derivatives as tetradentate ligand, were prepared and characterized by spectroscopic methods, X-ray crystallography, and electrochemical measurements. The geometry of a RuIII complex having a non-threefold-symmetric TPA ligand bearing one dimethylnicotinamide moiety was determined to show that the nicotine moiety resides trans to a pyridine group, but not to the chlorido ligand. The substituents of the TPA ligands were shown to regulate the redox potential of the ruthenium center, as indicated by a linear Hammett plot in the range of 200 mV for RuIII/RuIV couples with a relatively large rho value (+0.

Quinoxalino[2,3-b']porphyrins behave as pi-expanded porphyrins upon one-electron reduction: broad control of the degree of delocalization through substitution at the macrocycle periphery.

The synthesis and redox properties of a series of free-base and metal(II) quinoxalino[2,3-b']porphyrins and their use in an investigation of the substituent effects on the degree of communication between the porphyrin and its beta,beta'-fused quinoxalino component are reported. ESR, thin-layer spectroelectrochemistry, and quantum chemical calculations of the resultant radical anions from one-electron reduction indicate that localization of the unpaired electron across both the porphyrin and the fused quinoxalino group can be controlled, the system as a whole behaving as a highly polarizable pi-expanded porphyrin radical anion. ESR studies on the radical anions of zinc(II) quinoxalino[2,3-b']porphyrin derivatives indicate that nitrogen-atom spin distribution changes as a function of chemical substitution: 27% quinoxaline character when the porphyrin ring bears a 7-nitro substituent, 34% quinoxaline character in the unsubstituted parent, and 51-61% nitroquinoxaline character when the quinoxalino unit has one or more nitro groups.

A tightly coupled bis(zinc(II) phthalocyanine)-perylenediimide ensemble to yield long-lived radical ion pair states.

A conjugated donor-acceptor array composed of two phthalocyanines connected to the bay region of a perylenediimide is assembled by using palladium chemistry. Excitation of the phthalocyanine produces a nanosecond lived charge-separated state.

Redox behavior of cyclo[6]pyrrole in the formation of a uranyl complex.

A uranyl complex, the first metal complex to be formed from the cyclo[n]pyrrole series of expanded porphyrins, is formed when cyclo[6]pyrrole is treated with the uranyl cation under aerobic conditions. Spectroscopic, spectroelectrochemical, and electron spin resonance data of this species are consistent with the ligand in the complex being oxidized to an antiaromatic form.

Intramolecular electron transfer within the substituted tetrathiafulvalene-quinone dyads: facilitated by metal ion and photomodulation in the presence of spiropyran.

Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)-quinone dyads 1 and 2 in the presence of metal ions. On the basis of the electrochemical studies of reference compound 5 and the comparative studies with dyad 3, it was proposed that the synergic coordination of the radical anion of quinone and the oligoethylene glycol chain with metal ions may be responsible for stabilizing the charge-separation state and thus facilitating the electron-transfer process. Most interestingly, the intramolecular electron-transfer processes within these two dyads can be modulated by UV-vis light irradiation in the presence of spiropyran, by taking advantage of its unique properties.

Porphyrin-diones and porphyrin-tetraones: reversible redox units being localized within the porphyrin macrocycle and their effect on tautomerism.

Porphyrin-2,3-diones and porphyrin-2,3,7,8- and porphyrin-2,3,12,13-tetraones were shown to have a redox-active unit that can function independently of the macrocycle at large. Electroreduction of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin-2,3-diones [(P-dione)M] and the corresponding -2,3,12,13-tetraones [L-(P-tetraone)M] and -2,3,7,8-tetraones [C-(P-tetraone)M], where M = 2H, CuII, ZnII, NiII, and PdII was investigated and the products were characterized by ESR and thin-layer UV-visible spectroelectrochemistry. Electrochemical and spectroelectrochemical data show that the first two reductions of the porphyrin-diones and the first three reductions of the porphyrin-tetraones occur at the dione units.

Electron-transfer oxidation properties of substituted bi-, ter-, and quaterpyrroles.

A set of open-chain fully substituted bi-, ter-, and quaterpyrroles bearing analogous substituents in the alpha- and beta-pyrrolic positions were studied as a function of their chain length, subunit number, and size of potential conjugation pathway by means of cyclic voltammetry, EPR, and UV-vis spectroelectrochemistry. A comparison of E1/2 values for the first one-electron abstraction of bipyrrole 1 (1.07 V), terpyrrole 2 (0.

Model studies of 6,7-indolequinone cofactors of quinoprotein amine dehydrogenases.

The electronic effects of the C-4 substituent on the physicochemical properties and reactivity of the 6,7-inodolequinone cofactors (CTQ and TTQ) have extensively been investigated with use of a series of C-4 substituted 6,7-inodolequinone derivatives (1-4). The one-electron reduction potentials of the 6,7-inodolequinone derivatives decrease with increasing the electron donating ability of the C-4 substituent (with the following order of E degrees': 4>1>2>3). The reaction of indolequinones 1-3 with benzylamine proceeds stepwise through the iminoquinone and the product-imine intermediates to give aminophenol as the final product as the case of TTQ model compound 4.

Efficient photocatalytic hydrogen evolution without an electron mediator using a simple electron donor-acceptor dyad.

A highly efficient photocatalytic hydrogen evolution system without an electron mediator such as methyl viologen (MV(2+)) has been constructed using 9-mesityl-10-methylacridinium ion (Acr(+)-Mes), poly(N-vinyl-2-pyrrolidone)-protected platinum nanoclusters (Pt-PVP) and NADH (beta-nicotinamide adenine dinucleotide, reduced form) as the photocatalyst, hydrogen evolution catalyst and electron donor, respectively. The photocatalyst (Acr(+)-Mes) undergoes photoinduced electron transfer (ET) from the Mes moiety to the singlet excited state of the Acr(+) moiety to produce an extremely long-lived ET state, which is capable of oxidizing NADH and reducing Pt-PVP, leading to efficient hydrogen evolution. The hydrogen evolution efficiency is 300 times higher than that in the presence of MV(2+) because of the much faster reduction rate of Pt-PVP by Acr(*)-Mes compared with that by MV(*+).

Fullerene acting as an electron donor in a donor-acceptor dyad to attain the long-lived charge-separated state by complexation with scandium ion.

A long-lived charge-separated (CS) state of fullerene-trinitrofluorenone linked dyad in which fullerene acts as an electron donor is formed by photoinduced electron transfer from C60 to TNF in the presence of Sc(OTf)3; the CS lifetime is determined as 23 ms in PhCN at 298 K.

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.

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.

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.

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.

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+.

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.

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.