Studies on pyrazines. 12 . N-oxidation of aminopyrazines with m-chloroperbenzoic acid

N-Oxidation reactions of 2-aminopyrazines, substituted by methyl or phenyl groups at C-3 or C-5, with m-chloroperbenzoic acid were undertaken to obtain the 2-aminopyrazine 1-oxides.     

Lesions involving the fourth ventricle evaluated by CT and MR: A comparative study

A retrospective review of 21 patients with lesions involving the fourth ventricle was performed to determine the relative capability of computed tomography (CT) and MR for detection, characterization, localization, and diagnosis. Lesions involving the fourth ventricle included ependymoma (three), subependymoma (one), glioma (five), cysticercosis cyst (three), medulloblastoma (three), bleeding into the fourth ventricle (two), epidermoid cyst (two), “trapped” fourth ventricle (one), and lymphomatoid granuloma (one). Posterior fossa lesions that displaced but did not invade the fourth ventricle were excluded. Lesion detectability on CT was judged excellent in ten, good in 8, and fair or poor in 3. Detectability of lesions by MR was judged excellent in 16 and good in 5. There was complete agreement on lesion extension between CT and MR in 6 lesions, mild disagreement in 4, and moderate to significant disagreement in 11. Preoperatively, MR alone correctly diagnosed seven lesions, and CT alone correctly diagnosed three lesions. A review of the combined scans (after the correct diagnosis was given) showed both CT and MR were equal in the diagnosis of 14 lesions, MR better than CT in six, and CT better in one. There was complete agreement on both CT and MR with the surgical/pathologic findings in three lesions. Both studies proved disappointing in their ability to make the correct histologic diagnosis, probably because CT and MR characteristics may not always offer a definitive diagnosis and because of the wide spectrum of pathologic processes that may involve the fourth ventricle.     

Formation of hydrogen bonding in ionized poly(N‐isopropylacrylamide) gels by continuous water exchange

The effects of continuous water exchange on the swelling behavior of poly(N‐isopropylacrylamide‐co‐sodium acrylate) gel were studied. The diameter of gels and the Na⁺ concentration in the solvent were measured at several constant intervals after the solvent (the distilled deionized water) was exchanged. The diameter decreased at room temperature as the solvent was exchanged with water, and it continued to decrease even after more than about 97% of the initial Na⁺ diffused into the water. Thus, the final swelling ratio of the gel was only slightly larger than that of the neutral poly(N‐isopropylacrylamide) gel. To reveal the structural change in molecular level, solid‐state ¹³C cross‐polarization/magic‐angle spinning, solid‐state ¹H combined rotation and multiple‐pulse spectroscopy, and swollen‐state ¹³C dipolar decoupled/magic‐angle spinning NMR experiments were carried out for several dried and swollen samples by varying the times of water exchange. As a result, the intensity and position of the carboxyl peak changed, and the relative intensity of the nonionized carboxyl groups of gels increased with an increasing number of water exchanges. These results indicated that hydrogen bonding was formed between the two, nonionized carboxyl groups (? COOH) and/or between the ? COOH and ? CONH? groups. The macroscopic polymer network shrinkage is discussed in terms of the replacement of counterions Na⁺ by H⁺ and of the formation of intermolecular hydrogen bonding. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1090–1098, 2004     

Initiator‐fragment incorporation radical copolymerization of divinylbenzene and N‐isopropylacrylamide with dimethyl 2,2′‐azobisisobutyrate: Formation of soluble hyperbranched polymer nanoparticle

The copolymerization of divinylbenzene (DVB) and N‐isopropylacrylamide (NIPAm) with dimethyl 2,2′‐azobisisobutyrate of a concentration as high as 0.50 mol/L proceeded homogeneously without any gelation at 80 °C in N,N‐dimethylformamide, where the concentrations of DVB and NIPAm were 0.15 and 0.50 mol/L. The copolymer yield increased with time and leveled off over 50 min. Although DVB was consumed more rapidly than NIPAm, both comonomers were completely consumed in 50 min. The homogeneous polymerization system at 80 °C involved electron spin resonance‐observable propagating polymer radicals, the total concentration of which increased with time. The resulting copolymer was soluble in tetrahydrofuran, chloroform, acetone, ethyl acetate, acetonitrile, N,N‐dimethylformamide, dimethyl sulfoxide, and methanol, but insoluble in benzene, n‐hexane, and water. The copolymer showed an upper critical solution temperature (50 °C on cooling) in a methanol–water [11:3 (v/v)] mixture. Dimethyl 2,2′‐azobisisobutyrate fragments as high as 37–45 mol % were incorporated as terminal groups in the copolymers through initiation and primary radical termination. The contents of DVB and NIPAm were 10–30 mol % and 30–50 mol %, respectively. The intrinsic viscosity of the copolymer was very low (0.09 dL/g) at 30 °C in tetrahydrofuran despite high weight‐average molecular weight (1.2 × l0⁶ by multi‐angle laser light scattering). These results indicate that the copolymer was of hyperbranched structure. By transmission electron microscopy observation, the individual copolymer molecules were visualized as nanoparticle of 6–20 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1609–1617, 2004     

Single-electron transport through an individual InAs SAQD embedded in a graded-dope semiconductor nano-pillar

By using the semiconductor nano-pillar with a graded-dope configuration, we implemented the measurement for a single-electron transport through an individual InAs self-assembled quantum dot (SAQD). An atomic-force microscope observation showed that the SAQD had a disk-like shape with a diameter of 30 nm. We succeeded in observing a significant diamagnetic shift of the Coulomb oscillation peak under the magnetic field applied perpendicular to the disk plane. The measurement gave us a lateral confinement energy of 14 meV and an electron effective mass of 0.039, which provided us with quantitative evidence that the constituent material of the observed quantum dot originates from the InAs SAQD.     

Synthesis and silica coating of calcia-doped ceria/mica nanocomposite by seeded polymerization technique

Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of the excellent UV light absorption property and low catalytic ability for the oxidation of organic materials superior to undoped ceria. In order to reduce the oxidation catalytic activity further, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique. Generally, nanoparticles of inorganic materials do not provide a good coverage for human skin because of the agglomeration of the particles. The platy particles are required to enhance the covering ability of inorganic materials. This can be accomplished by synthesis of calcia-doped ceria/mica nanocomposite with subsequent silica coating to control catalytic activity of calcia-doped ceria. Calcia-doped ceria/mica nanocomposite was prepared by soft solution chemical method followed by silica coating via seeded polymerization technique. Silica coated calcia-doped ceria/mica nanocomposite was characterized by X-ray diffraction, SEM, TEM, XPS and FT-IR.     

The desalination of a mixed solution of an amino acid and an inorganic salt by means of electrodialysis with charge-mosaic membranes

A new electrodialysis with charge-mosaic membranes was proposed to achieve efficient desalination of a mixed solution of an amino acid and an inorganic salt. For such a mixed solution, the conventional electrodialytic desalination with both cation-and anion-exchange membranes had resulted in a considerable loss of the amino acid through the membranes. In this method, however, the amino acid in the desalination channel of the electrodialyzer migrates away from the membranes so that the permeation loss of the amino acid through the membrane can be prevented.

Batchwise desalination experiments by this method were carried out with a glutamic acid or arginine solution including NaCl under the condition of constant electric current density. Similar experiments by the conventional method were also carried out. As a result of comparing both methods, the amino acid loss in this method became much smaller than that in the conventional one. It was confirmed that this method was very useful for the desalination of an amino acid solution. The effects of operating conditions on the desalination process are also discussed.     

Stereoselective reduction of α-substituted β-keto esters by hydrostannane/organotin triflate

Stereoselective reduction of α-substituted β-keto esters is achieved by the combined use of hydrostannane/organotin triflate. syn-Aldols are obtained with more than 90% selectivities.