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Biomedical subjects

S Fukuzumi

Publications and source records attributed to S Fukuzumi.

At least 37 records · Page 2Linked to original sources
PubMed2001

Effects of metal ions on physicochemical properties and redox reactivity of phenolates and phenoxyl radicals: mechanistic insight into hydrogen atom abstraction by phenoxyl radical-metal complexes.

Phenolate and phenoxyl radical complexes of a series of alkaline earth metal ions as well as monovalent cations such as Na+ and K+ have been prepared by using 2,4-di-tert-butyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)phenol (L1H) and 2,4-di-tert-butyl-6-(1,4,7,10,13-pentaoxa-16-aza-cyclooctadec-16-ylmethyl)phenol (L2H) to examine the effects of the cations on the structure, physicochemical properties and redox reactivity of the phenolate and phenoxyl radical complexes. Crystal structures of the Mg2+- and Ca2+-complexes of L1- as well as the Ca2+- and Sr2+-complexes of L2- were determined by X-ray crystallographic analysis, showing that the crown ether rings in the Ca2+-complexes are significantly distorted from planarity, whereas those in the Mg2+- and Sr2+-complexes are fairly flat. The spectral features (UV-vis) as well as the redox potentials of the phenolate complexes are also influenced by the metal ions, depending on the Lewis acidity of the metal ions. The phenoxyl radical complexes are successfully generated in situ by the oxidation of the phenolate complexes with (NH4)(2)[Ce4+(NO3)6] (CAN). They exhibited strong absorption bands around 400 nm together with a broad one around 600-900 nm, the latter of which is also affected by the metal ions. The phenoxyl radical-metal complexes are characterized by resonance Raman, ESI-MS, and ESR spectra, and the metal ion effects on those spectroscopic features are also discussed. Stability and reactivity of the phenoxyl radical-metal complexes are significantly different, depending on the type of metal ions. The disproportionation of the phenoxyl radicals is significantly retarded by the electronic repulsion between the metal cation and a generated organic cation (Ln+), leading to stabilization of the radicals. On the other hand, divalent cations decelerate the rate of hydrogen atom abstraction from 10-methyl-9,10-dihydroacridine (AcrH2) and its 9-substituted derivatives (AcrHR) by the phenoxyl radicals. On the basis of primary kinetic deuterium isotope effects and energetic consideration of the electron-transfer step from AcrH2 to the phenoxyl radical-metal complexes, we propose that the hydrogen atom abstraction by the phenoxyl radical-alkaline earth metal complexes proceeds via electron transfer followed by proton transfer.

Free Radicals↗
PubMed2001

Photochemical generation of cyclopentadienyliron dicarbonyl anion by a nicotinamide adenine dinucleotide dimer analogue.

Irradiation of the absorption band of an NAD (nicotinamide adenine dinucleotide) dimer analogue, 1-benzyl-1,4-dihydronicotinamide dimer, (BNA)(2), in acetonitrile containing a cyclopentadienyliron dicarbonyl dimer, [CpFe(CO)(2)](2), results in generation of 2 equiv of the cyclopentadienyliron dicarbonyl anion, [CpFe(CO)(2)](-), accompanied by the oxidation of (BNA)(2) to yield 2 equiv of BNA(+). The studies on the quantum yields, the electrochemistry, and the transient absorption spectra have revealed that the photochemical generation of [CpFe(CO)(2)](-) by (BNA)(2) proceeds via photoinduced electron transfer from the triplet excited state of (BNA)(2) to [CpFe(CO)(2)](2).

Electrochemistry↗
PubMed2001

Comparison between electron transfer and nucleophilic reactivities of ketene silyl acetals with cationic electrophiles.

The products and kinetics for the reactions of ketone silyl acetals with a series of p-methoxy-substituted trityl cations have been examined, and they are compared with those of outer-sphere electron transfer reactions from 10,10'-dimethyl-9,9', 10, 10'- tetrahydro-9,9'-biacridine [(AcrH)2] to the same series of trityl cations as well as other electron acceptors. The C-C bond formation in the reaction of beta,beta-dimethyl-substituted ketene silyl acetal (1: (Me2C=C(OMe)OSiMe3) with trityl cation salt (Ph3C+ClO4-) takes place between 1 and the carbon of para-positon of phenyl group of Ph3C+, whereas a much less sterically hindered ketene silyl acetal (3: H2C=C(OEt)OSiEt3) reacts with Ph3C+ at the central carbon of Ph3C+. The kinetic comparison indicates that the nucleophilic reactivities of ketene silyl acetals are well correlated with the electron transfer reactivities provided that the steric demand at the reaction center for the C-C bond formation remains constant.

Journal Article↗
PubMed2001

Light-harvesting and photocurrent generation by gold electrodes modified with mixed self-assembled monolayers of boron-dipyrrin and ferrocene-porphyrin-fullerene triad.

Three different kinds of mixed self-assembled monolayers have been prepared to mimic photosynthetic energy and electron transfer on a gold surface. Pyrene and boron-dipyrrin were chosen as a light-harvesting model. The mixed self-assembled monolayers of pyrene (or boron-dipyrrin) and porphyrin (energy acceptor model) reveal photoinduced singlet-singlet energy transfer from the pyrene (or boron-dipyrrin) to the porphyrin on the gold surface. The boron-dipyrrin has also been combined with a reaction center model, ferrocene-porphyrin-fullerene triad, to construct integrated artificial photosynthetic assemblies on a gold electrode using mixed monolayers of the respective self-assembled unit. The mixed self-assembled monolayers on the gold electrode have established a cascade of photoinduced energy transfer and multistep electron transfer, leading to the production of photocurrent output with the highest quantum yield (50 +/- 8%, based on the adsorbed photons) ever reported for photocurrent generation at monolayer-modified metal electrodes and across artificial membranes using donor-acceptor linked molecules. The incident photon-to-current efficiency (IPCE) of the photoelectrochemical cell at 510 and 430 nm was determined as 0.6% and 1.6%, respectively. Thus, the present system provides the first example of an artificial photosynthetic system, which not only mimics light-harvesting and charge separation processes in photosynthesis but also acts as an efficient light-to-current converter in molecular devices.

Journal Article↗
PubMed2001

Catalytic control of redox reactivities of coenzyme analogs by metal ions.

Redox coenzymes and analogs have their own redox reactivities for both thermal and photochemical redox reactions. The redox activities of coenzymes can be tuned by using metal ions that can bind the redox coenzymes and analogs. Quantitative measure to determine the Lewis acidity of a variety of metal ions is given in relation to the catalytic reactivities. The mechanistic viability of metal ion catalysis in redox reactions of coenzyme analogs is described by showing a number of examples of both thermal and photochemical reactions that are made possible to proceed by controlling the redox reactivities of coenzymes with metal ions.

Catalysis↗
PubMed2000

Quantitative evaluation of Lewis acidity of metal ions derived from the g values of ESR spectra of superoxide: metal ion complexes in relation to the promoting effects in electron transfer reactions.

The g values of ESR spectra of superoxide-metal ion complexes (O2(*-)-Mn+, n = 1, 2, 3) are determined in acetonitrile at 143 K. The binding energies (deltaE) of metal ions with O2*- have been evaluated from deviation of the gzz values from the free spin value. The deltaE values are well correlated with the catalytic reactivities of metal ions in electron transfer from cobalt(II) tetraphenylporphyrin to O2 and p-benzoquinone, which does not occur in the absence of metal ions under otherwise the same experimental conditions. The deltaE values can thereby be used as the first quantitative measure for Lewis acidity of metal ions in relation with the catalytic reactivities in electron transfer reactions.

Journal Article↗
PubMed2000

100 selective oxygenation of p-xylene to p-tolualdehyde via photoinduced electron transfer

The 100% selective oxygenation of p-xylene to p-tolualdehyde is initiated by photoinduced electron transfer from p-xylene to the singlet excited state of 10-methyl-9-phenylacridinium ion under visible light irradiation, yielding p-tolualdehyde exclusively as the final oxygenated product. The reason for the high selectivity in the photocatalytic oxygenation of p-xylene is discussed on the basis of the photoinduced electron transfer mechanism.

Journal Article↗
PubMed2000

Hydrogen atom abstraction by Cu(II)- and Zn(II)-phenoxyl radical complexes, models for the active form of galactose oxidase.

The Cu(II) and Zn(II) complexes of phenoxyl radical species [M(II)(L1*)(NO3)]+ (M=Cu or Zn, L1H: 2-methylthio-4-tert-butyl-6-[[bis[2-(2-pyridyl)ethyl]amino]methyl]phenol ) and [M(II)(L2*)(NO3)]+ (M=Cu or Zn, L2H: 2,4-di-tert-butyl-6-[[bis[2-(2-pyridyl)ethyl]amino]methyl]phenol) are prepared as model complexes of the active form of galactose oxidase (GAO). Hydrogen atom abstraction of 1,4-cyclohexadiene and tert-butyl substituted phenols by the GAO model complexes proceeds very efficiently to give benzene and the corresponding phenoxyl radical or its C-C coupling dimer as the oxidation products, respectively. Kinetic analyses on the oxidation reactions have shown that the hydrogen atom abstraction of the phenol substrates is significantly enhanced by the coordinative interaction of the OH group to the metal ion center of the complex, providing valuable insight into the enzymatic mechanism of the alcohol oxidation. Details of the substrate-activation process have been discussed based on the activation parameters (deltaH* and deltaS*) of the reactions.

Copper↗
PubMed2000

Aliphatic Hydroxylation by a Bis(µ-oxo)dicopper(III) Complex.

By using molecular oxygen bis(µ-oxo)dicopper(III) complexes can be produced from Cu(I) complexes with ligand L(X) (L(X)=p-substituted N-ethyl-N-[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=OMe, Me, H, Cl, NO(2)) in which the benzylic position of the ligand is activated and hydroxylated by the Cu(2)O(2) core (see reaction scheme). Detailed characterization of this new C-H bond activation reaction by the bis(µ-oxo)dicopper(III) core reveals important information on the fundamental chemistry underlying copper monooxygenase reactivity.

Journal Article↗
PubMed2000

Multiple equivalent current dipole source localization of visual event-related potentials during oddball paradigm with motor response.

Event-related potentials (ERPs) during a visual oddball paradigm with button-pressing responses were recorded in 12 right-handed subjects from 32 scalp electrodes. The single equivalent current dipole (ECD) of the target C1 (weak occipito-parietal negativity from 30-80 ms) was consistently located at the primary visual cortex. From the 4-ECD localization of the target P1/N1 (temporally coincident frontal positivity and occipito-temporal negativity), it was suggested that this complex reflected activities from distributed sources along both dorsal occipito-parietal and ventral occipito-temporal areas. The stable multiple ECD solutions for the target P3b were chosen as those including the left primary motor and/or sensorimotor dipole and satisfying goodness-of-fit (GOF) of more than 98% and confidence limit (CL) of less than 1 mm. The obtained frontal dipoles were discussed in terms of visual working memory and sustained attention in reference to the previous PET, fMRI and MEG studies. The distributed multiple ECDs may suggest that P3 should be interpreted as being the embodiment of the cortico-limbic-thalamic network which involves Halgren and Marinkovic's emotional and behavioral model and Mesulam's attentional circuit.

Adult↗
PubMed1999

Oxidation of Benzyl Alcohol with Cu(II) and Zn(II) Complexes of the Phenoxyl Radical as a Model of the Reaction of Galactose Oxidase.

Profound insights into the catalytic mechanism of galactose oxidase (GO) are offered by new models of the active form of the metalloenzyme. The important role of the Cu(II) center in the oxidation of benzyl alcohol to benzaldehyde by the Cu(II)-phenoxyl radical complex of ligand 1 has been revealed by comparison with the reactivity of the corresponding Zn(II)-phenoxyl radical complex; py=2-pyridyl.

Journal Article↗
PubMed1999

Vaginal reconstruction with the femoral veno-neuroaccompanying artery fasciocutaneous flap.

The arterial anatomy of the anteromedial thigh was investigated in ten fresh cadavers that had been systemically injected with a lead oxide-gelatin mixture. The arteries accompanying the great saphenous vein and the anterior cutaneous branches of the femoral nerve were found to have branches not only to the cutaneous vein and nerve, but also to the skin. On the basis of the anatomy of these accompanying arteries, a pedicled fasciocutaneous flap containing them was developed consisting of an adipofascial pedicle and a skin island. This flap has been named the femoral veno-neuroaccompanying artery fasciocutaneous flap (the femoral V-NAF flap, the great saphenous-femoral V-NAF flap) and has been applied in three cases of vaginal reconstruction.

Adult↗
PubMed1999

Accompanying arteries of the lesser saphenous vein and sural nerve: anatomic study and its clinical applications.

The arteries adjacent to the lesser saphenous vein and sural nerve were investigated in 10 fresh cadavers that had been systemically injected with a lead oxide-gelatin mixture. The accompanying arteries were found to lie along the lesser saphenous vein and sural nerve and to nourish the skin through venocutaneous and neurocutaneous perforators. On the basis of the anatomy of these accompanying arteries, the lesser saphenous venoadipofascial (VAF) pedicled fasciocutaneous flap and the lesser saphenous-sural veno-neuro adipofascial (V-NAF) pedicled fasciocutaneous flap have been developed and applied to 23 cases of various reconstructions of the lower extremity with proximal and distal bases. Survival of the flaps has been extremely good, and the flaps have been clinically useful.

Adult↗
PubMed1999

Venous drainage of the distally based lesser saphenous-sural veno-neuroadipofascial pedicled fasciocutaneous flap: a radiographic perfusion study.

The drainage pathway of the distally based lesser saphenous-sural veno-neuroadipofascial pedicled fasciocutaneous flap using accompanying arteries of the lesser saphenous vein and sural nerve as nutrient vessels of the flap was radiographically investigated using five fresh cadavers. Small long veins existed along the lesser saphenous vein, and they were considered to be concomitant veins of the accompanying arteries of the lesser saphenous veins. They anastomosed with the lesser saphenous vein in some places and played a role in bypassing valves in the lesser saphenous vein.

Adipose Tissue↗
PubMed1998

Model studies on calcium-containing quinoprotein alcohol dehydrogenases. Catalytic role of Ca2+ for the oxidation of alcohols by coenzyme PQQ (4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2, 7,9-tricarboxylic acid).

Mechanistic studies on the action of calcium-containing quinoprotein alcohol dehydrogenases have been performed by using a series of PQQ model compounds in anhydrous organic media. The PQQ model compounds are shown to form 1:1 complexes with a series of alkaline earth metal ions by spectroscopic methods and theoretical calculations. The site of coordination of the PQQ molecule to the metal ions in solution is indicated to be the same as in the case of enzymatic systems. It has also been found that Ca2+ binds to the quinone most strongly among the alkaline earth metal ions. Formation of the C-5 hemiacetal derivatives with methanol, ethanol, and 2-propanol is also investigated spectrophotometrically to show that the alcohol addition to the quinone is enhanced in the presence of the metal ions. In this case as well, Ca2+ shows the highest efficiency for the enhancement of the C-5 hemiacetal formation. Addition of a strong base such as DBU into an MeCN solution containing the Ca2+ complex of the PQQ model compounds and the alcohols leads to the redox reactions to afford reduced PQQ derivatives and the corresponding aldehydes. On the basis of detailed kinetic studies on the redox reactions, including structural effects of PQQ analogues and metal ion effects, we propose the addition-oxidative elimination mechanism through the C-5 hemiacetal intermediate.

2-Propanol↗
PubMed1998

Physiological and psychological evaluation for visual display colour readability: a visual evoked potential study and a subjective evaluation study.

This study was conducted, by subjective and objective evaluation, to clarify the complex relationships among VDT (visual display terminal) display colour readability and the related physical and physiological factors. Readability was defined as participants being able to read sentences easily on a VDT screen irrespective of their meanings. In the subjective evaluation, paired comparison tests and a colour impression test using the semantic differential (SD) method with factor analysis were carried out for 30 colour stimuli with different dominant wavelengths and stimulus purity values. The former test yielded identification of the most readable stimulus purity, which was in the range of 0.2 to 0.55 for any dominant wavelength. From the latter test, a 'conspicuousness factor' and a 'comfort factor' were extracted for evaluating readability. In the objective evaluation, three kinds of dominant wavelengths and three levels of stimulus purity were used. This evaluation showed that P100 peak latencies of colour-VEPs (visual evoked potentials) evoked by the subjectively optimal stimulus purity colours fully displayed on the screen were significantly shorter than those evoked by any other stimulus purity colours. Moreover, VEP P100 peak latencies evoked by the text colours that had the most readable stimulus purities were also shorter than those evoked by any other stimulus purity colours. Consequently, it was concluded that the optimum VDT display colour was that which had the most readable stimulus purity for each dominant wavelength, and that colour-VEP peak latency could serve as an indicator for quantification of VDT display colour readability.

Adult↗
PubMed1998

Accompanying arteries of the cutaneous veins and cutaneous nerves in the extremities: anatomical study and a concept of the venoadipofascial and/or neuroadipofascial pedicled fasciocutaneous flap.

The arterial anatomy of the accompanying arteries of the cutaneous veins and cutaneous nerves in the extremities was investigated in 10 fresh cadavers that had been injected with a lead oxide-gelatin mixture throughout the entire body. It is well known that cutaneous nerves have neurocutaneous perforators, but it was found that cutaneous veins also have their own accompanying arteries as well. The accompanying arteries of the cutaneous veins had branches not only to the vein wall, but also to the skin, i.e., venocutaneous perforators. Based on these findings, the concept of the adipofascial pedicled fasciocutaneous flap using the accompanying arteries of the cutaneous veins, cutaneous nerves, or both was proposed.

Adipose Tissue↗