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Biomedical subjects

Toshiki Tajima

Publications and source records attributed to Toshiki Tajima.

10 recordsLinked to original sources
PubMed2006

Selective increase in high molecular weight adiponectin concentration in serum of women with preeclampsia.

Total adiponectin concentrations have been shown to increase in serum of preeclamptic women. However, variance of concentrations of different isoforms has not been studied, despite the emerging notion that high, medium and low molecular weight adiponectin exert different functions. We have determined serum concentrations of each adiponectin isoform using a newly developed enzyme immunosorbent assay. High molecular weight (HMW) adiponectin concentrations were significantly higher in women with preeclampsia (n=14; median, 11.2 microg/ml; interquartile range, 9.2-15.8) compared to normal pregnant women (n=14; 6.8 microg/ml, 5.4-10.7; P=0.04). In contrast, medium molecular weight and low molecular weight adiponectin concentrations were substantially equal between the groups. The ratio of HMW adiponectin to total adiponectin was also markedly higher in preeclamptic women (52.3%, 49.5-58.7) than control women (43.0%; 39.8-48.0; P=0.004). Taken together with other reports our findings imply a physiological feedback response to minimize endothelial damage in preeclamptic women.

Adiponectin↗
PubMed2006

Electrolytic partial fluorination of organic compounds. 83. Anodic fluorination of N-substituted pyrroles and its synthetic applications to gem-difluorinated heterocyclic compounds.

Anodic fluorination of N-substituted pyrroles was carried out in MeCN containing supporting fluoride salts such as Et3N-nHF (n = 2-5) and Et4NF-4HF with use of platinum electrodes under constant current conditions. Anodic fluorination of N-methyl- and N-p-tosylpyrroles having an electron-withdrawing cyano group proceeded smoothly to provide the corresponding fluorinated products in moderate to excellent yields, while anodic fluorination of N-methylpyrrole devoid of an electron-withdrawing cyano group did not take place and a polymeric product was formed at the anode surface. In sharp contrast to the cases of N-methylpyrroles, even N-p-tosylpyrrole devoid of an electron-withdrawing cyano group underwent anodic fluorination efficiently. Diels-Alder reaction of 5,5-difluoro-1-methyl-3-pyrrolin-2-one (2e) derived from anodic fluorination of 2-cyano-1-methylpyrrole (2a) with various dienes was carried out to provide the cycloaddition products in excellent yields. Furthermore, Michael reaction of 2e with various nucleophiles was also successfully carried out to provide the Michael addition products in good to excellent yields.

Acetonitriles↗
PubMed2005

Electrochemical partial fluorination of organic compounds. 80. Synthesis of cyclic alpha-arylthio-alpha-monofluorophosphonate esters.

[Reaction: see text]. Seven-membered cyclic alpha-monofluorophosphonate esters such as 2-allyloxy-3-fluoro-3-phenylthio-4,7-dihydro-[1, 2]-oxaphosphinine-2-oxide were successfully synthesized in moderate total yield as 41% from open-chain allyl phosphonates having an alpha-arylthio group as an electroauxiliary using an alternative sequence of anodic fluorination and ring-closing olefin metathesis (RCM). On the other hand, in an attempt to synthesize an eight-membered analogue, a different type of seven-membered fluorinated cyclic product was formed predominantly by the RCM reaction between the allyloxy groups.

Cyclization↗
PubMed2005

Development of a novel environmentally friendly electrolytic system by using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent: application for anodic methoxylation of organic compounds.

We have successfully developed a novel environmentally friendly electrolytic system using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. It was found that solid-supported bases are electrochemically inactive at an electrode surface. It was also found that solid-supported bases dissociate methanol into methoxide anions and protons. Therefore, in the presence of solid-supported bases, it was clarified that methanol serves as both a solvent and a supporting electrolyte generated in situ. Anodic methoxylation of various compounds with solid-supported bases was carried out to provide the corresponding methoxylated products in good to excellent yields with a few exceptions. The methoxylated products and the solid-supported bases were easily separated by only filtration, and the desired pure methoxylated products were readily isolated simply by concentration of the filtrates. The separated and recovered solid-supported bases were recyclable for several times.

Journal Article↗
PubMed2005

Development of an electrolytic system using solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent.

We have successfully developed a novel electrolytic system using solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. Anodic methoxylation of phenyl 2,2,2-trifluoroethyl sulfide using solid-supported bases was carried out to provide the alpha-methoxylated product in good to excellent yields. The alpha-methoxylated product and solid-supported bases were easily separated by only filtration, and the separated solid-supported bases were recyclable. Anodic methoxylation of phenyl 2,2,2-trifluoroethyl sulfide was successfully carried out 10 times by the recycling of silica gel-supported piperidine in good yields.

Journal Article↗
PubMed2004

Soliton synchrotron afterglow in a laser plasma.

Coherent synchrotron radiation can be emitted by relativistic electromagnetic subcycle solitons dwelling in a low-temperature collisionless plasma. Using three-dimensional particle-in-cell simulations we show that solitons, left in a wake of a relativistically intense short circularly polarized laser pulse in the plasma, emit spiral electromagnetic wave, as a result of charge density oscillations in the wall of the soliton cavity. This high-frequency afterglow persists for tens of Langmuir periods.

Journal Article↗
PubMed2004

Laser electron accelerators for radiation medicine: a feasibility study.

Table-top laser wakefield accelerators (LWFAs), proposed theoretically in 1979, have now generated individual electron bunches in the laboratory with a significant number of electrons having energies up to 10 MeV and beyond with the maximum energy reaching tens of MeV and charge per laser pulse of > 1 nC. The attained electron beam properties have stimulated a discussion about the possible applications of LWFAs to medical radiation treatment, either directly or via conversion to x-rays. Our purpose in this paper is to analyze whether or not such applications are feasible, or can be made feasible with existing laser technology. Clinical electron beam applications require the selection of specific electron energies in the range of 6-25 MeV with a narrow energy bin (deltaE <5 MeV) for depth control, and a beam expansion to as much as 25 cm x 25 cm for various tumor radiation treatments. As a result, we show that present LWFA sources provide a dose rate that falls short of the requirements for clinical application by at least an order of magnitude. We then use particle simulations to evaluate the feasibility of developing an improved LWFA-based medical accelerator. Current LWFA sources require such high peak intensity that laser repetition rate is restricted to < or = 10 Hz. A scheme to lower the threshold and increase the repetition rate of efficient LWFA thus appears essential. We analyze one such scheme. We show that by "seeding" the primary laser pulse with a second, hundred-fold less intense pulse that is shifted downward in frequency by approximately the plasma frequency omegap, LWFA produces a yield of clinically useful electrons per pulse comparable to that provided by an unseeded source, except that the primary pulse energy is now more than one order of magnitude lower than that in current LWFAs. This enables a repetition rate of approximately 100 Hz or more using existing laser technology, and thus dose rates (several Gy/min) in the range required for medical radiation applications.

Computer Simulation↗
PubMed2003

Light intensification towards the Schwinger limit.

A method to generate ultrahigh intense electromagnetic fields is suggested, based on the laser pulse compression, carrier frequency upshift, and focusing by a counterpropagating breaking plasma wave, relativistic flying parabolic mirror. This method allows us to achieve the quantum electrodynamics critical field (Schwinger limit) with present-day laser systems.

Journal Article↗
PubMed2002

Plasma wakefield acceleration for ultrahigh-energy cosmic rays.

A cosmic acceleration mechanism is introduced which is based on the wakefields excited by the Alfvén shocks in a relativistically flowing plasma. We show that there exists a threshold condition for transparency below which the accelerating particle is collision-free and suffers little energy loss in the plasma medium. The stochastic encounters of the random accelerating-decelerating phases results in a power-law energy spectrum: f(epsilon) proportional, variant 1/epsilon(2). As an example, we discuss the possible production in the atmosphere of gamma ray bursts of ultrahigh-energy cosmic rays (UHECR) exceeding the Greisen-Zatsepin-Kuzmin cutoff. The estimated event rate in our model agrees with that from UHECR observations.

Journal Article↗