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Biomedical subjects

Eiichi Nakamura

Publications and source records attributed to Eiichi Nakamura.

At least 55 records · Page 3Linked to original sources
PubMed2004

Mechanism and ligand-transfer selectivity of 1,2-addition of organozincate complexes to aldehyde.

Density functional theory (DFT) calculations have been performed to investigate the origin of the reactivity and ligand-transfer selectivity of organozincates in the 1,2-addition to carbonyl compounds. Examination of the addition of Me(3)ZnLi to formaldehyde as compared with that of Me(2)Zn showed that the addition reaction is facilitated by the push-pull synergy of the Lewis acidic Li atom and the negatively charged Me(3)Zn moiety. This analysis then provided an answer to the mechanistic question about the experimentally established ligand-transfer selectivity in the 1,2-addition of heteroleptic organozincate Me(2)Zn(X)Li (X = H-, R(2)N-, and R(3)Si-). The addition of these heteroleptic zincate compounds results in selective transfer of H, R(2)N, and R(3)Si groups owing to the favorable orbital interaction between these groups and the carbonyl pi-system. The addition reaction of the zincate compounds conforms to the mechanistic framework of the conventional nucleophilic reaction, such as the addition reaction of MeLi dimer, and is different from the reaction of organocuprates, where oxidation/reduction of the copper atom is involved.

Journal Article↗
PubMed2004

Creation of hoop- and bowl-shaped benzenoid systems by selective detraction of [60]fullerene conjugation. [10]cyclophenacene and fused corannulene derivatives.

Selective penta-addition of a methylcopper reagent followed by addition of a phenylcopper reagent to a suitably modified synthetic intermediate results in creation of 40pi-electron systems-hoop- and bowl-shaped cyclic benzenoid compounds, [10]cyclophenacene, and dibenzo-fused corannulene derivatives. The 40pi-electron cyclophenacene derivatives have been found to be chemically stable, yellow-colored, luminescent (560 nm), and EPR-silent. X-ray crystallographic analysis provided precision structural data sets. The dibenzo-fused corannulene derivatives exhibit blue-green (460 nm) to red (649 nm) fluorescence.

Journal Article↗
PubMed2004

Multilayer vesicles and vesicle clusters formed by the fullerene-based surfactant C60(CH3)5K.

The self-assembly behavior of a fullerene-based surfactant, C60(CH3)5K, in water was studied using a combination of static and dynamic light scattering, as well as transmission electron microscopy, and compared to that of the compound C60(C6H5)5K. Both fullerene surfactant systems spontaneously assemble into large vesicles consisting of closed spherical shells formed by bilayers, with critical aggregation concentrations (CAC) lower than 10(-6) g ml(-1). At low concentrations, the aggregate sizes of C60(CH3)5K (radius R approximately 26.8 nm) and C60(C6H5)5K (R approximately 17.0 nm) were found to be substantially different from each other, showing that the change of the substituents surrounding the polar cyclopentadienide head group makes it possible to control the size of the resulting aggregates. Furthermore, the C60(CH3)5K vesicles were found to exist in two qualitatively different types of aggregation with a critical reaggregation concentration (CRC) located at 3.30 x 10(-6) g ml(-1). Above the CRC, larger aggregates were observed (R approximately 37.6 nm), showing a more complex form of supramolecular aggregation, e.g., in terms of multi-bilayer vesicles and/or of clusters of bilayer vesicles.

Journal Article↗
PubMed2004

Reaction pathway and stereoselectivity of asymmetric synthesis of chrysanthemate with the aratani C1-symmetric salicylaldimine-copper catalyst.

The reaction pathway and the mechanism of asymmetric induction in the synthesis of (+)-trans-(1R,3R)-chrysanthemic acid methyl ester from methyl diazoacetate and 2,5-dimethyl-2,4-hexadiene in the presence of a C(1)-chiral salicylaldimine Cu(I) complex has been probed with the aid of hybrid density functional calculations. The key finding is that the alkoxycarbonyl carbene complex intermediate is intrinsically chiral and that the intramolecular hydrogen bonding in the carbene complex transmits the chirality information from the side chain to the carbene complex. Molecular orbital backgrounds of the structure of the carbene complex and the transition state of the cyclopropanation have been elucidated.

Journal Article↗
PubMed2004

Zn(II)/amine-catalyzed coupling reaction of alkylidenemalonates with propargyl alcohol: a one-pot synthesis of methylenetetrahydrofurans.

[reaction: see text] A metal-catalyzed tandem 1,4-addition/cyclization between propargyl alcohol and a Michael acceptor, such as alkylidene malonate, has been developed. In the presence of catalytic amounts of zinc triflate [Zn(OTf)(2)] and triethylamine (Et(3)N), various 2-alkylidene-1,3-dicarbonyl compounds reacted with propargyl alcohol to give 3- or 4-methylene tetrahydrofurans in excellent yields.

Alkynes↗
PubMed2004

Mechanism and regioselectivity of reductive elimination of pi-allylcopper (III) intermediates.

Reductive elimination of a pi-allylcopper(III) compound leading to the formation of a C-C bond on an allylic terminal has been considered to occur via the corresponding sigma-allylcopper(III) species. The present B3LYP density functional study has shown however that the C-C bond formation occurs directly from the pi-allyl complex via an enyl[sigma+pi]-type transition state, which has structural features different from a simple sigma-allylcopper(III) intermediate. In the case of unsymmetrically substituted pi-allylcopper(III) compound that has a partial sigma-allylcopper(III) structure, the reductive elimination occurs preferentially at the sigma-bonded allylic terminal since, in this way, the copper atom can recover most effectively its d-electrons shared with the allyl system. The regioselectivity of the reductive elimination of a substituted pi-allylcopper(III) intermediate is mainly controlled by the electronic effect, and correlated well to the Hammett sigma(p)(+) constant. The analyses revealed mechanistic kinship between the allylic substitution and the conjugate addition reaction of organocopper reagents.

Journal Article↗
PubMed2004

Selective deposition of a gadolinium(III) cluster in a hole opening of single-wall carbon nanohorn.

Selective synthesis of particles of angstrom to nanometer size consisting of one to many metal atoms is instrumental in various applications, but it has been hampered by the tendency of the metal atom to form large clusters. We found, as studied by the state-of-the-art electron microscopic technique, a strategy to produce metal-containing nanoparticles isolated from each other by depositing metal atoms in a hydrophilic hole on or in the interior of a carbon nanotube as demonstrated by the reaction of Gd(OAc)(3) with oxidized single-wall nanohorns. Besides the potential utilities of the deposited metal clusters, the metal deposition protocol provides a method to control permeation of molecules through such openings.

Journal Article↗
PubMed2004

Stacking of molecules possessing a fullerene apex and a cup-shaped cavity connected by a silicon connection.

Hexagonal or tetragonal packing of columnar stacks in crystals and liquid crystals has been observed for a series of molecules possessing a fullerene apex and an aromatic cone that are connected with a Si-C connection. The columnar stacking of the new shuttlecock molecules is constitutionally stable but conformationally flexible due to the large cavity created on the top of the fullerene molecule.

Journal Article↗
PubMed2004

Three-dimensional computed tomography evaluation of semitendinosus harvest after anterior cruciate ligament reconstruction.

PURPOSE: Recent studies have shown the regeneration potential of hamstring tendons harvested for anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to evaluate the morphology of the regenerated semitendinosus tendon using 3-dimensional (3-D) images of volume-rendered multidetector helical computed tomography (MD-CT). TYPE OF STUDY: Retrospective study on a convenient sample of patients. METHODS: Eight patients were selected from those with a minimum 2-year follow-up evaluation after ACL reconstruction with hamstring tendons. The harvest site of the semitendinosus tendon was evaluated using 3-D CT, in addition to magnetic resonance imaging (MRI) analysis, at an average of 37 months (range, 27 to 47 months) after surgery. RESULTS: In 5 of 8 patients, MRI evaluation indicated recurrence of the region with the same signal intensity as the native at the harvest site of the semitendinosus tendon. In these patients, the 3-D image of MD-CT visualized the stringy tendinous tissue regenerated at the harvest site originating from the semitendinosus muscle belly and running in the same pathway as the native tendon. However, the distal part attached into the medial surface of the popliteal fascia. By contrast, in the involved sides of the remaining 3 patients with no detection on MRI, the 3-D CT image showed no tendinous tissue at the harvest site. The remnants of the semitendinosus had reduced or fused into the muscle belly of the semimembranous. CONCLUSIONS: Using the 3-D CT technique, we could first depict the distinct morphology of the regenerate at the harvest site of the semitendinosus tendon. LEVEL OF EVIDENCE: Level IV, therapeutic study.

Adolescent↗
PubMed2004

Active proliferation of mesenchymal cells prior to the chondrogenic repair response in rabbit full-thickness defects of articular cartilage.

OBJECTIVES: In full-thickness articular defects, fibroblast growth factor-2 (FGF-2) participates in the chondrogenic repair response which occurs in a defect-size dependent manner. Here we demonstrate that FGF-2 plays a critical role in the proliferation of pre-chondrogenic mesenchymal cells during chondrogenic induction. METHODS: Three-millimeter- or 5-mm-diameter cylindrical defects were created in the femoral trochlea of the rabbit knee. The defects received sterile saline or FGF-2 (50 pg/h) via an osmotic pump for the initial 2 weeks. We assessed the proliferative capacity of undifferentiated mesenchymal cells in the reparative tissue with the anti-proliferating cell nuclear antigen (PCNA) monoclonal antibody. Using a total of 180 rabbits, we performed three sets of experiments. RESULTS: In the 3-mm-diameter defects, undifferentiated mesenchymal cells spontaneously initiated chondrogenic differentiation within 2 weeks, resulting in the regeneration of surfacing articular cartilage concomitantly with the repair of subchondral bone. No evidence of chondrogenesis was seen in the 5-mm-diameter defects, whereas application of FGF-2 promoted successful regeneration of articular cartilage. In the 3-mm-diameter defects and in the FGF-2-treated 5-mm defects, PCNA immunoreactivity was widely detected in undifferentiated cells in the reparative tissue at 1 and 2 weeks after creation of the defects. In contrast, in the 5-mm-diameter defects without FGF-2 treatment, the PCNA-positive cells were found at a significantly lower incidence. CONCLUSIONS: Active expansion of undifferentiated cell population mediated by FGF-2 is required to initiate and support a chondrogenic repair response in full-thickness defects of articular cartilage. Endogenous FGF-2 could not meet the requirements of growth signaling in the center of larger sized defects.

Alkaline Phosphatase↗
PubMed2004

Greater frequency of distraction accelerates bone formation in open-wedge proximal tibial osteotomy with hemicallotasis.

BACKGROUND: In chickens, increased distraction frequency stimulates bone formation in distraction osteogenesis. PATIENTS AND METHODS: We investigated the effect of two different distraction frequencies on bone formation in the distracted portion, and on the time of removal of the fixator, in open-wedge osteotomies of the proximal tibia with hemicallotasis (HCO). The study included 20 consecutive patients (20 knees) who underwent HCO for medial osteoarthrosis of the knee. 10 knees were distracted at a rate of 0.25 mm four times a day (the 4-step group); and the other 10 knees were distracted at a rate of 0.125 mm eight times a day (the 8-step group). RESULTS: There were no significant differences in the preoperative FTAs or the correction angles between the two groups. At all intervals until 6 weeks after the completion of distraction, bone mineral density in the distraction gap was significantly higher in the 8-step group than in the 4-step group. The average time in external fixation was 78 (SD 5) days in the 8-step group as compared to 89 (SD 6) days in the 4-step group, a significantly shorter time. INTERPRETATION: Our findings indicate that an increase in the distraction frequency in HCO provides better bone formation, resulting in a shorter external fixation period.

Aged↗
PubMed2003

Synthesis of fullerene glycoconjugates through sulfide connection in aqueous media.

[reaction: see text] A thiolate/alkyl halide coupling reaction in aqueous media provides a one-step synthesis of fullerene glycoconjugates bearing five carbohydrate groups in good yield by using stoichiometric amounts of reactants, without recourse to hydroxy group protection. The sulfide-connection methodology is also useful for synthesis of simpler amphiphilic fullerene molecules, such as one bearing five carboxylic acid groups.

Fullerenes↗
PubMed2003

Theoretical studies on structures and aromaticity of finite-length armchair carbon nanotubes.

[structure: see text] Depending on the exact length of the tube, the chemical structure of finite-length armchair [n,n] single-wall carbon nanotube (n = 5 and 6) falls into three different classes that may be referred to as Kekulé, incomplete Clar, and complete Clar networks. The C-C bond lengths, nucleus-independent chemical shift analysis, and orbital energies suggest that the chemical reactivities of the finite-length tube change periodically as the tube length is elongated by one-by-one layering of cyclic carbon array.

Journal Article↗