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Shigeru Nagase

Publications and source records attributed to Shigeru Nagase.

At least 19 recordsLinked to original sources
PubMed2007

Theoretical study of the electronic spectra of oxidized and reduced states of lumiflavin and its derivative.

Time-dependent density functional theory has been applied to investigate the electronic absorption spectrum of oxidized and reduced lumiflavin and its derivative, 8-NH(2)-lumiflavin. The calculations allow the authors to explain the origin of the difference in spectral features between oxidized and reduced states of lumiflavin. For the reduced lumiflavin, a reasonable assignment of the experimental spectrum has been made for the first time. Furthermore, the results obtained reveal that the NH(2) group plays a critical role in shaping the spectral features of 8-NH(2)-lumiflavin, and offer a reasonable explanation for the spectral changes upon substituting the NH(2) group for the CH(3) group of lumiflavin.

Computational Biology↗
PubMed2006

Computed structures of two known Yb@C74 isomers.

Six isomers of Yb@C74 are considered, namely one cage with isolated pentagons, three isomers with a pentagon-pentagon junction, two structures with one pentagon-pentagon pair, and one heptagon. The computations based on the Gibbs energy point out the endohedral derived from the only C74 cage with the isolated pentagons and from a cage with one pentagon-pentagon junction as the major and minor observed isomer, respectively. Temperatures giving the best agreement with the experimental production ratio are evaluated.

Journal Article↗
PubMed2006

Selective extraction and purification of endohedral metallofullerene from carbon soot.

A preferential extraction of endohedral metallofullerenes (EMFs) from carbon soot through the use of reduction in the extraction process and a convenient isolation of endohedral metallofullerene anions (EMFs(-)) and empty fullerenes utilizing their difference in solubility are accomplished. EMFs are easily isolated by one-stage high-performance liquid chromatography after chemical oxidation of the extracted endohedral EMFs(-).

Journal Article↗
PubMed2006

La@C72 having a non-IPR carbon cage.

We show here that La@C72 has a non-IPR cage, unique electronic properties, and high reactivity by the spectroscopic and X-ray crystallographic analysis and the theoretical study. The isolation of La@C72 as a stable derivative might constitute an important stepping-stone on the way to isolation of these unknown metallofullerenes and open new material science of metallofullerenes.

Journal Article↗
PubMed2006

One-electron reduction of kinetically stabilized dipnictenes: synthesis of dipnictene anion radicals.

The redox behavior of kinetically stabilized dipnictenes, BbtE=EBbt [E = P, Sb, Bi; Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], was systematically disclosed using cyclic voltammetry and theoretical calculations. It was found that they showed reversible one-electron redox couples in the reduction region. The anion radical species of the Bbt-substituted diphosphene and distibene were successfully synthesized by the reduction of the corresponding neutral dipnictenes (BbtP=PBbt and BbtSb=SbBbt). Their structures were reasonably characterized by ESR, UV-vis, and Raman spectroscopy, and the distibene anion radical was structurally characterized by X-ray crystallographic analysis.

Journal Article↗
PubMed2006

Dispersion and separation of small-diameter single-walled carbon nanotubes.

The dispersion of small-diameter single-walled carbon nanotubes (SWNTs) produced by the CoMoCAT method in tetrahydrofuran (THF) with the use of amine was studied. The absorption, photoluminescence, and Raman spectroscopies showed that the dispersion and centrifugation process leads to an effective separation of metallic SWNTs from semiconducting SWNTs. Since this method is simple and convenient, it is highly applicable to an industrial utilization for widespread applications of SWNTs.

Journal Article↗
PubMed2006

Experimental determination of the nN --> sigma*P-O interaction energy of O-equatorial C-apical phosphoranes bearing a primary amino group.

The reaction of a chlorophosphorane (9-Cl) with primary amines produced anti-apicophilic spirophosphoranes (5, O-equatorial phosphoranes), which violate the apicophilicity concept, having an apical carbon-equatorial oxygen configuration, along with the ordinarily expected O-apical stereoisomers (6) with the apical oxygen-equatorial carbon configuration. Although the amino group is electronegative in nature, the O-equatorial phosphoranes were found to be stable at room temperature and could still be converted to their more stable O-apical pseudorotamers (6) when they were heated in solution. X-ray analysis implied that this remarkable stability of the O-equatorial isomers could be attributed to the orbital interaction between the lone-pair electrons of the nitrogen atom (n(N)) and the antibonding sigma(P-O) orbital in the equatorial plane. A kinetic study of the isomerization of 5 to 6 and that between diastereomeric O-apical phosphoranes 13b-exo and 13b-endo revealed that 5b bearing an n-propylamino substituent at the central phosphorus atom was found to be less stable than the corresponding isomeric 6b by ca. 7.5 kcal mol(-1). This value was smaller than the difference in energy (11.9 kcal mol(-1)) between the O-equatorial (1b) and the O-apical n-butylphosphorane (2b) by 4.4 kcal mol(-1). This value of 4.4 kcal mol(-1) can be regarded as the stabilization energy induced by the n(N) --> sigma(P-O) interaction. The experimentally determined value was in excellent agreement with that derived from density functional theory (DFT) calculations at the B3PW91 level (4.0 kcal mol(-1)) between the nonsubstituted aminophosphoranes (5g is less stable than 6g by 10.1 kcal mol(-1)) and their P-methyl-substituted counterparts (1a is less stable than 2a by 14.1 kcal mol(-1)).

Amines↗
PubMed2006

Characterization of the bis-silylated endofullerene Sc3N@C80.

The photochemical reaction of Sc(3)N@C(80) with 1,1,2,2-tetramesityl-1,2-disilirane affords the adduct as a bis-silylated product. The adduct was characterized by NMR spectroscopy and single-crystal X-ray structure analysis. The dynamic behavior of the disilirane moiety and the encapsulated Sc(3)N cluster were also investigated. The unique redox property of the adduct is reported by means of CV and DPV. Experimental results were confirmed by density functional calculations.

Journal Article↗
PubMed2006

Structural and electronic properties of fluorinated boron nitride nanotubes.

The effects of F doping on the structural and electronic properties of the (5, 5) single-walled boron nitride nanotube (BNNT) are investigated by using the density functional theory method. The chemiadsorption of F maintains the hexagonal BN network, increases the lattice constant, and introduces acceptor impurity states. On the other hand, substitutional doping of F destroys the hexagonal BN network, decreases the lattice constant, but does not alter the insulating feature of the BNNT. The observed insulator-to-semiconducting transition, a lattice contraction, and a highly disordered atom arrangement in the sidewall of BNNTs upon F doping appear to be most reasonably attributed to a codoping of dominating substitutional F over chemiabsorbed F, which can induce deep donor impurity states, a lattice contraction, and a destruction of the hexagonal BN network simultaneously.

Journal Article↗
PubMed2006

The Bingel monoadducts of La@C82: synthesis, characterization, and electrochemistry.

The reaction of La@C82 with diethyl bromomalonate in the presence of base (the Bingel reaction) generated five monoadducts which have been fully characterized. It was found that four of them (mono-A, -B, -C, and -D) are ESR-inactive, suggesting singly bonded regioisomers. In contrast, the fifth product (mono-E) is ESR-active, indicating that it possesses a cyclic moiety between the appended malonate group and the fullerene cage, analogous to conventional Bingel adducts. The differences in the molecular structures of mono-A, -B, -C, and -E result in varying thermal stabilities and electrochemical behavior. In particular, the singly bonded monoadducts undergo the retro-Bingel reaction either under thermal treatment or during electron transfer on the cyclic voltammetric timescale. However, mono-E shows remarkable thermal stability and perfect reversibility under the same experimental conditions.

Journal Article↗
PubMed2006

Host-guest complexation of endohedral metallofullerene with azacrown ether and its application.

Complexation of endohedral metallofullerene La@C(82)-A (1) with macrocyclic compounds, such as 1,4,7,10,13,16-hexaazacyclooctadecane (2), 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane (3), mono-aza-18-crown-6 ether (4), 18-crown-6 ether (5), and p-tert-butylcalix[n]arenes (n = 4-8, 6-10), for the first time is examined. Among them, 1 forms a complex with azacrown ethers 2-4 while accompanying the electron transfer between them. This is characteristic of endohedral metallofullerene and caused by its low reduction potential. Activation energies, DeltaG(et), for the electron transfer from 2-4 to 1 are 4.6, 2.8, and 11 kcal/mol, respectively. These small DeltaG(et) values indicate that the electron transfer from the azacrown ethers to 1 is facile in the ground state. Furthermore, the selective isolation of lanthanum endohedral metallofullerenes from the extracts of soot is accomplished by utilizing the complexation of 1 with 2.

Journal Article↗
PubMed2006

Synthesis and characterization of a bisadduct of La@C82.

A bisadduct of La@C82 has been synthesized in a good yield by a Bingel-Hirsch reaction. Its structure has been well-defined by X-ray crystallographic analysis. A pair of enantiomers of the adduct form a dimer in the single crystal.

Journal Article↗
PubMed2006

Reactivity of 1-hydro-5-carbaphosphatrane based on tautomerization between pentavalent phosphorane and trivalent cyclic phosphonite.

The reaction behavior of 1-hydro-5-carbaphosphatrane (1 a) was examined. Treatment of 1 a with oxidants such as 3-chloroperoxybenzoic acid (mCPBA) and tBuOCl gave cyclic phosphonate 2 and 1-chloro-5-carbaphosphatrane (4), respectively, via cyclic phosphonite 3, a tautomer of 1 a. Compound 4 was readily hydrolyzed to afford 2. Compound 1 a was also sulfurized via 3 by elemental sulfur to afford cyclic thioxophosphonate 5, which was also obtained by reactions in the presence of bases. Treatment of 1 a with bases also proceeded through 3 to give an equilibrium mixture of the corresponding phenoxide anion 10 and the phosphoranide anion 9, which was quenched with MeI to afford a mixture of 11 and 1-methyl-5-carbaphosphatrane (1 b). Such reactivities are typical for neutral phosphoranes. Theoretical investigations of these reactivities were also performed.

Journal Article↗
PubMed2006

Selective interaction of large or charge-transfer aromatic molecules with metallic single-wall carbon nanotubes: critical role of the molecular size and orientation.

Using first principles calculations, we report for the first time that large nearly neutral aromatic molecules, such as naphthalene and anthracene, and small charge-transfer aromatic molecules, such as TCNQ and DDQ, interact more strongly with metallic single-wall carbon nanotubes (SWNTs) versus their semiconducting counterparts as the molecular orientation of DDQ is taken into account. Hence two new mechanisms for separating metallic and semiconducting SWNTs via noncovalent pi-pi stacking or charge-transfer interaction are suggested.

Journal Article↗