Biomedical subjects

Tohru Ikegami

Publications and source records attributed to Tohru Ikegami.

At least 19 recordsLinked to original sources

PubMed2007

Anion- and cation-exchange MicroHPLC utilizing poly(methacrylates)-coated monolithic silica capillary columns.

A novel method was developed for the preparation of highly efficient anion- and cation-exchange microHPLC columns using an on-column polymerization of methacrylates having amine or sulfonic acid functional groups onto monolithic silica capillary columns modified with 3-methacryloxypropyltriethoxysilane as the anchor groups. The chromatographic evaluation of the columns using nucleic acids, nucleotides, and inorganic anions as samples showed the characteristics of the ion-exchange-type stationary phases. These columns exhibited higher separation efficiency when compared with the conventional particle-packed columns. A capillary column for the simultaneous anion- and cation-exchange separation could be prepared by a step-by-step functionalization. The advantages of this column preparation will include: (1) no need of column packing; (2) no need of the preparation of silane reagents possessing anion- and cation-exchange functionalities; (3) the amount of immobilized polymer could be controlled by changing polymerization conditions. These columns should be suitable for the separation of biologically active compounds by the microHPLC modes.

Anion Exchange Resins↗

PubMed2006

Preparation of high efficiency and highly retentive monolithic silica capillary columns for reversed-phase chromatography by chemical modification by polymerization of octadecyl methacrylate.

High efficiency and highly retentive monolithic silica capillary columns were obtained by polymerization of octadecyl methacrylate using alpha,alpha'-azobis-isobutyronitrile (AIBN) as a free radical initiator. Hybrid type monolithic silica columns (25 cm total length x 200 microm I.D.) prepared from a mixture of tetramethoxysilane and methyltrimethoxysilane were used as a support. The effects of the monomer and the radical initiator concentrations in the reaction mixture were examined. The performance of the columns was tested in terms of column efficiency and retention behavior by using alkylbenzenes and a few other compounds as solutes and compared with that of hybrid monolithic silica columns modified with octadecylsilyl-(N,N-diethylamino)silane (ODS-DEA). Highly retentive monolithic silica columns were obtained by polymerization at high monomer concentrations. Although a decrease in column efficiency was observed with the increase in the monomer concentration in a feed mixture, an improvement in efficiency was achieved (a plate height value lower than 10 microm) by increasing an initiator concentration without significant variations in column retention properties. Results obtained by polymerization using other monomers are also presented to demonstrate the applicability of the preparation method.

Benzene Derivatives↗

PubMed2006

Performance of monolithic silica capillary columns with increased phase ratios and small-sized domains.

Monolithic silica capillary columns for HPLC were prepared from tetramethoxysilane to have smaller sized domains and increased phase ratios as compared to previous materials, and their performance was evaluated. The monolithic silica columns possessed an external porosity of 0.65-0.76 and a total porosity of 0.92-0.95 and showed considerably higher performance and greater retention factors in a reversed-phase mode after chemical modification than columns previously reported. An octadecylsilylated monolithic silica column with the smallest domain size (through-pores of approximately 1.3 microm and silica skeletons of approximately 0.9 microm) showed a plate height of less than 5 microm at optimum linear velocities (u) of 2-3 mm/s in 80% acetonitrile for a solute having retention factors of approximately 1, and approximately 7 microm at u = 8 mm/s. With a permeability similar to that of a column packed with 5-microm particles, the monolithic silica columns were able to attain column efficiencies comparable to that of particulate columns packed with 2-2.5-microm particles, and showed performance in the "forbidden region" for the previous columns. The performance of the monolithic column can be compared favorably with that of a particle-packed column when 15,000-30,000 or more theoretical plates are desired at a pressure drop of 20-40 MPa or lower. The increased homogeneity of the co-continuous structures, in addition to the small-sized domains, contributed to the higher performance as compared to previous monolithic silica columns.

Benzene Derivatives↗

PubMed2006

Preparation of highly efficient monolithic silica capillary columns for the separations in weak cation-exchange and HILIC modes.

Weak cation-exchange (WCX) and HILIC modes columns were prepared by on-column polymerization of acrylic acid on monolithic silica capillary columns modified with N-(3-triethoxysilylpropyl)methacrylamide anchor groups. The polymer-coated columns could be used for HILIC mode separation of pyridylamino (PA)-sugars and peptides including a tryptic digest of BSA, while for weak cation-exchange mode for the separation of proteins and nucleosides even at high linear velocity. The poly(acrylic acid) coated monolithic silica capillary columns showed greater retention toward PA-sugars than a polyacrylamide coated monolithic silica capillary columns prepared in the same manner. Proteins and nucleosides were separated effectively at pH 6.9 using the same column. The column provided fair permeability after the polymer-coating step. High-speed separation of proteins at u=4.66 mm/s with high efficiency was shown to be possible, while high-speed separation of nucleosides has achieved within one minute using the column at u=8.67 mm/s, suggesting that the column will be suitable for the second dimension separation of multidimensional HPLC systems.

Acrylic Resins↗

PubMed2006

HILIC mode separation of polar compounds by monolithic silica capillary columns coated with polyacrylamide.

HILIC mode columns were prepared by an on-column polymerization of acrylamide on a monolithic silica capillary column modified with N-(3-trimethoxysilylpropyl)methacrylamide as the anchor group. The products showed HILIC mode retention characteristics with three times greater permeability and slightly higher column efficiency compared to a commercially available amide-type HILIC column packed with 5-mum particles. The selectivity of the monolithic silica-based column was similar to that of the particulate column for each group of solutes towards nucleosides, nucleic bases and carbohydrate derivatives, although a considerable difference was observed in the selectivity for the solute groups. Although the retention of solutes based on the polar functionality was much smaller with the monolithic silica columns, which had a smaller phase ratio, than with the particle-packed column, the former can achieve better separation utilizing the high permeability and higher column efficiencies of a longer column.

Journal Article↗

PubMed2006

Improved endcapping method of monolithic silica columns.

Following a bonding reaction with octadecyldimethyl-N,N-diethylaminosilane (ODS-DEA), a monolithic silica was subjected to consequential on-line endcapping reactions with hexamethyldisilazane (HMDS) or N-(trimethylsilyl)imidazole (TMSI) to compare the two reagents. Endcapping of monolithic silica C(18) columns prepared by a manufacturer was also studied. After endcapping with TMSI in acetonitrile (ACN), all columns provided better performance for hydrogen-bonding compounds and basic compounds than C(18) phases endcapped with HMDS. TMSI endcapping of commercial Chromolith Performance columns also gave improved performance. The results indicate that one can significantly improve the performance of monolithic silica C(18) columns for basic compounds by a simple on-column reaction with TMSI in ACN at a relative low temperature.

Amphetamine↗

PubMed2006

Preparation of glycerol dimethacrylate-based polymer monolith with unusual porous properties achieved via viscoelastic phase separation induced by monodisperse ultra high molecular weight poly(styrene) as a porogen.

The preparation of polymer-based monolith capillary was examined by the use of glycerol dimethacrylate (GDMA) as monomer and monodisperse standard polystyrene (PS) solution in chlorobenzene as porogen. Poly-GDMA monoliths were prepared in situ in test tubes with standard PS having the variety of molecular weight (defined as Mw hereafter) from 50,000 to 3,840,000, and their morphology was compared to that of poly-GDMA monolith prepared in situ with a poor porogenic solvent of GDMA. According to scanning electron micrograph (SEM) observation, the structure of poly-GDMA monolith prepared in situ with toluene as a poor porogenic solvent showed a typical agglomerated globular structure, whereas the morphology of poly-GDMA monolith prepared in situ with the polymer (PS) porogenic solution was transformed from the aggregated globule form to three dimensionally (3D) continuous skeletal structure with the increase of Mw of standard PS utilized. Along with this morphological transformation or change, in the case of poly-GDMA monolith prepared in situ with ultra high Mw standard PS porogenic solution, the pore size distribution showed a sharp bimodal distribution, with one peak being located around 4 nm in the mesopore range (2-50 nm) and the other peak located around 1-2 microm in the macropore range (>50 nm), respectively. The poly-GDMA capillaries were prepared in situ with toluene, low Mw (50,000, 600,000) PS solution in chlorobenzene and the above mentioned ultra high Mw PS solution in chlorobenzene as a porogen, respectively, and measured by mu-HPLC with benzene and n-alkyl phenyl ketone as solutes for the evaluation in aqueous methanol (MeOH/H(2)O = 50/50-80/20, v/v). The permeability of capillaries prepared in situ with ultra high Mw standard PS polymer porogenic solution was much larger, compared to those of the capillaries prepared in situ with low Mw standard PS polymer porogenic solution or with toluene as porogen. On the other hand, the column efficiency was better in the case of the capillary prepared in situ with the ultra high Mw PS solution than in the latter capillaries. Those observations indicated that the ultra high Mw standard PS polymer porogenic solution should delay dynamically the phase separation of polymerizing mixture because of its visco-elasticity and should contribute to the creation of three dimensionally continuous skeletal monolith structure better to afford high separation efficiency.

Acetophenones↗

PubMed2006

Properties of monolithic silica columns for HPLC.

Monolithic silica columns and their use in high peak-capacity HPLC separations are reviewed. Monolithic silica columns can potentially provide higher overall performance than particle-packed columns based on the variable external porosity and variable through-pore size/skeleton size ratios. The high permeability of monolithic silica columns resulting from the high porosity is shown to be advantageous to generate large numbers of theoretical plates with long capillary columns. High permeability together with the high stability of the network structures of silica allows their use in high-speed separations required for a second-dimension column in two dimensional HPLC. Disadvantages of monolithic silica columns are also described.

Benzene Derivatives↗

PubMed2005

Faster axial band dispersion in a monolithic silica column than in a particle-packed column.

The contribution of molecular diffusion to peak broadening was studied in a reversed-phase HPLC system, consisting of a monolithic silica C18 column and methanol-water mobile phase. Study on the band broadening effect of holding a solute in a column or elution at very low linear velocity of mobile phase allowed facile determination of the contribution of the molecular diffusion term. Less obstruction against molecular diffusion, or the faster axial band dispersion in a monolithic silica column than in a particle-packed column, was found both in mobile phase and in stationary phase.

Benzene Derivatives↗

PubMed2005

Two-dimensional reversed-phase liquid chromatography using two monolithic silica C18 columns and different mobile phase modifiers in the two dimensions.

Comprehensive two-dimensional (2D) HPLC in the reversed-phase liquid chromatography (RPLC) mode using C18 silica monolith columns at first dimension (1st-D) (10 cm x 4.6mm I.D.) and second dimension (2nd-D) (5 cm x 4.6mm I.D.) was carried out successfully. A mixture of water and tetrahydrofuran (THF) was used as a mobile phase in the 1st-D separation, and a mixture of water and methanol (CH3OH) in the 2nd-D separation. Sample fractions from 1st-D column were directly loaded into an injection loop of the 2nd-D HPLC equipped with two injector valves for one column. The fractionation time at the 1st-D that was equal to the separation time at the 2nd-D was 45 or 60s. Total peak capacity up to 900 was obtained in about 60 min for the isocratic mode separation of aromatic compounds in this system. Gradient elution mode applied to both 1st-D and 2nd-D separations resulted in shorter separation time and better separation efficiencies than the isocratic mode. It was demonstrated that 2D-HPLC systems employing popular C18 stationary phases with different organic modifiers in mobile phases for each dimension could produce large peak capacity. The different selectivities were provided by the difference in polar interactions between a solute and the organic modifier existing in the stationary phase.

Chromatography, High Pressure Liquid↗

PubMed2005

Silica monolithic membrane as separation medium. Summable property of different membranes for high-performance liquid chromatographic separation.

We studied an applicability of a silica monolithic membrane as separation medium for high-performance liquid chromatography (HPLC). We prepared porous monolithic silica membranes having a three-dimensional network structure to cut and shape into a membrane separation medium. We evaluated chromatographic properties of a variety of solutes using a column containing the membranes with HPLC to elucidate summable property of the membrane separation media. In addition, we made brief study on separation of HbA1c in whole blood with the stacked" membranes having different surface characteristics in one column, which is a membrane column. We confirmed that the membrane column was able to separate HbA1c from other matrix in whole blood to some extent, and it also had an excellent ability for hydrophobic and ion exchange adsorption.

Chromatography, High Pressure Liquid↗

PubMed2005

Application of a radiophotoluminescent glass plate dosimeter for small field dosimetry.

We have recently developed a prototypical radiophotoluminescent glass plate dosimeter (GPD) system as a device for small field dosimetry. The purpose of this study is to examine the usefulness of the GPD system for small field dosimetry. The profiles measured with the GPD were evaluated by comparing them to those from Kodak X-Omat V and GAFCROMIC XR type R film dosimeters for 2, 5, 9, and 15 mm circular collimators created by a linear accelerator-based radiosurgery system. The GPD output factors were compared with those of various detectors including an ion chamber, a p-type silicon diode detector, a glass rod dosimeter (GRD), and a diamond detector. The results measured with the GPD were also confirmed by comparing them to those from Monte Carlo simulations. The accuracy of a simulated beam is validated by the excellent agreement between Monte Carlo calculated and measured central axis depth-dose curves for 9- and 15 mm circular collimators using 4- and 10 MV photon beams. The GPD profiles show almost the same full width at half maximum as those of film dosimeters and Monte Carlo simulations at 4- and 10 MV photon beams, but a little narrower penumbrae than the film dosimeters and Monte Carlo simulations. The output factors measured with the GPD are in good agreement with those from a diode detector, a diamond detector, and the GRD with a small active volume and Monte Carlo simulations, except for a very small 2 mm circular collimator. It was found that the GPD is a very useful detector for small field dosimetry.

Computer Simulation↗

PubMed2005

[A comparison of the helmet output factors for five Gamma-Knife units.].

A radiophotoluminescent (RPL) glass rod dosimeter (GRD) and a small active volume p-type silicon diode detector are used for the measurement of the helmet output factors from five Gamma-Knife units, which include four Model B units and a Model C unit. The output factors for the five units measured with the GRD from 14, 8 and 4 mm helmets relative to the 18 mm helmet are 0.984 +/- 0.003, 0.951 +/- 0.003 and 0.884 +/- 0.006, respectively. Similarly, the corresponding output factors measured with the p-type silicon diode detector are 0.983 +/- 0.002, 0.952 +/- 0.003 and 0.867 +/- 0.015, respectively. The output factors are corrected with the end effect for each helmet of the five units. The end effect time for the four Model B units ranges from 4 sec for the 18 mm helmet to 2 sec for the 4 mm helmet. The results for the Model C unit are within 1 sec for all the helmets. The output factors for the five units obtained from both detectors are in good agreement with the values in a recent publication and the values recommended by Elekta, the device manufacturer, except for that of the 4 mm helmet measured with the GRD. The average GRD output factor for the 4 mm helmet is 1.6% higher than Elekta's value, 0.870, but is in good agreement with the published value which was measured using small active volume detectors. The helmet output factors for the five Gamma-Knife units measured with the GRD agree within measurement deviation.

Glass↗

PubMed2004

A molecular recognition strategy towards tetra-chlorinated dibenzo-p-dioxins, TCDDs.

Uniformly sized polymeric separation media were prepared using o- or p-xylene as porogenic template to investigate chromatographic selectivity towards tetra-chlorinated dibenzo-p-dioxins (TCDDs). TCDDs having chlorine atoms at ortho positions of phenyl rings were selectively retained on stationary phase prepared with o-xylene as porogenic template, while TCDDs having chlorine atoms at para positions of phenyl ring were found to be retained selectively on the stationary phase imprinted by the porogenic template, p-xylene. Slightly longer cross-linking agent afforded chromatographically selective retention for larger TCDD isomers. It was also found that positional relationship between substituted chlorine atoms was also important for chromatographic recognition.

Chromatography, High Pressure Liquid↗

PubMed2004

Photophysical properties of a carbazolyl mesogen of 8PCzC as revealed by absorption, fluorescence, and transient absorption measurements.

Fluorescence spectra in three phases [crystalline, smectic A liquid crystal (SmA), and isotropic] of a mesogen including one carbazolyl (Cz) chromophore, 4'-n-octylphenyl carbazole-2-carboxylate (8PCzC), were measured at various temperatures and compared with fluorescence spectra in solvents with various dielectric constants. Further, for the first time, picosecond transient absorption spectroscopy was applied to elucidating photoinduced electron-transfer dynamics (charge separation, charge recombination, and hole transfer reactions) in the three phases of 8PCzC doped with a small amount of an electron acceptor. The fluorescence spectra showed clearly the presence of two crystalline phases, which was supported by DSC measurement. On the basis of a comparison of the fluorescence spectra and those in solution, the 8PCzC molecule in the first crystal structure was suggested to be in polar environment compared to that in the second one. The fluorescence yields of 8PCzC in both SmA and isotropic phases were remarkably small compared to that in crystalline one. This was ascribed to the formation of hydrogen bonds between 8PCzC molecules in both SmA and isotropic phases. As a first approximation, the picosecond transient absorption spectra in the three phases of 8PCzC doped with 2,4,7-trinitrofluorenone were analyzed by the simple model of one-dimensional hole migration. The rate constants obtained for the hole transfer from the cation state of Cz chromophore to neighboring Czs decreased in the order of SmA (approximately 10(9) s(-1)) > isotropic (approximately 10(8) s(-1)) > crystalline (approximately 10(7) s(-1)) phases, although these measurement temperatures were different.

Absorption↗

PubMed2004

An RNA-interacting protein, SYNCRIP (heterogeneous nuclear ribonuclear protein Q1/NSAP1) is a component of mRNA granule transported with inositol 1,4,5-trisphosphate receptor type 1 mRNA in neuronal dendrites.

mRNA transport and local translation in the neuronal dendrite is implicated in the induction of synaptic plasticity. Recently, we cloned an RNA-interacting protein, SYNCRIP (heterogeneous nuclear ribonuclear protein Q1/NSAP1), that is suggested to be important for the stabilization of mRNA. We report here that SYNCRIP is a component of mRNA granules in rat hippocampal neurons. SYNCRIP was mainly found at cell bodies, but punctate expression patterns in the proximal dendrite were also seen. Time-lapse analysis in living neurons revealed that the granules labeled with fluorescent protein-tagged SYNCRIP were transported bi-directionally within the dendrite at approximately 0.05 microm/s. Treatment of neurons with nocodazole significantly inhibited the movement of green fluorescent protein-SYNCRIP-positive granules, indicating that the transport of SYNCRIP-containing granules is dependent on microtubules. The distribution of SYNCRIP-containing granules overlapped with that of dendritic RNAs and elongation factor 1alpha. SYNCRIP was also found to be co-transported with green fluorescent protein-tagged human staufen1 and the 3'-untranslated region of inositol 1,4,5-trisphosphate receptor type 1 mRNA. These results suggest that SYNCRIP is transported within the dendrite as a component of mRNA granules and raise the possibility that mRNA turnover in mRNA granules and the regulation of local protein synthesis in neuronal dendrites may involve SYNCRIP.

3' Untranslated Regions↗

PubMed2004

Polymer-based adsorption medium prepared using a fragment imprinting technique for homologues of chlorinated bisphenol A produced in the environment.

A polymer-based adsorption medium having molecular recognition ability for homologues of chlorinated bisphenol A produced in environment was prepared using a fragment imprinting technique. 2,6-Dimethyl phenol was utilized as a pseudo-template molecule and the adsorption media prepared was evaluated by high performance liquid chromatography (HPLC) and solid-phase extraction (SPE). As results, the adsorption medium showed preferable chromatographic retention and specific adsorption ability for the chlorinated bisphenol As having chlorine substituents at 3,5-positions through fragment imprinting effect.

Adsorption↗

PubMed2004

Simple and comprehensive two-dimensional reversed-phase HPLC using monolithic silica columns.

Simple and comprehensive two-dimensional (2D)-HPLC was studied in a reversed-phase mode using monolithic silica columns for second-dimension (2nd-D) separation. Every fraction from the first column, 15 cm long (4.6-mm i.d.), packed with fluoroalkylsilyl-bonded (FR) silica particles, was subjected to the separation in the 2nd-D using one or two octadecylsilylated (C(18)) monolithic silica columns (4.6-mm i.d., 3 cm). Monolithic silica columns in the 2nd-D were eluted at a flow rate of up to 10 mL/min with separation time of 30 s that meets the fractionation every 15-30 s at the first dimension (1st-D) operated at a flow rate of 0.4-0.8 mL/min. Three cases were studied. (1) In the simplest scheme of 2D-HPLC, effluent of the 1st-D was directly loaded into an injector loop of 2nd-D HPLC for 28 s, and 2 s was allowed for injection. (2) Two six-port valves each having a sample loop were used to hold the effluent of the 1st-D alternately for 30 s for one 2nd-D column to effect comprehensive 2D-HPLC without the loss of 1st-D effluent. (3) Two monolithic silica columns were used for 2nd-D by using a switching valve and two sets of 2nd-D chromatographs separating each fraction of the 1st-D effluent with the two 2nd-D columns alternately. In this case, two columns of the same stationary phase (C(18)) or different phases, C(18) and (pentabromobenzyloxy)propylsilyl-bonded (PBB), could be employed at the 2nd-D, although the latter needed two complementary runs. The systems produced peak capacity of approximately 1000 in approximately 60 min in cases 1 and 2 and in approximately 30 min in case 3. The three stationary phases, FR, C(18), and PBB, showed widely different selectivity from each other, making 2D separations possible. The simple and comprehensive 2D-HPLC utilizes the stability and high efficiency at high linear velocities of monolithic silica columns.

Journal Article↗