New Strong Fibrates with Piperidine Moiety KOMOTO, Teruo; HIROTA, Hiroyuki; OTSUKA, Mari ...
Chemical & pharmaceutical bulletin,
12/2000, Letnik:
48, Številka:
12
Journal Article
Recenzirano
Odprti dostop
New fibrates containing piperidine, 4-hydroxypiperidine, piperidin-3-ene, and piperazine moieties in the structures were synthesized and evaluated. Among the synthesized compounds, ...2-3-1-(4-fluorobenzoyl)-piperidin-4ylphenoxy-2-methylpropanoic acid (9aA : AHL-157) showed very superior activities in decreasing triglyceride, cholesterol, and blood sugar compared to bezafibrate in mice and rats.
Phase development during melt-drawing of ultra-high molecular weight polyethylene (UHMW-PE) was analyzed by in situ small-angle X-ray scattering measurements using synchrotron radiation at the ...SPring-8. Films with different entanglement characteristics were prepared by solution blending of higher and lower MW samples with a viscosity average MW of 1.07×107 (higher) and 1.73×106 (lower), followed by compression molding at 180°C. Independent of blend ratio, the strong streak attributed to extended-chain crystals (ECCs) appeared on the equator at the beginning point of the plateau stress region in the stress profile, which was one of the characteristic features of melt-drawing. A series of detailed analyses of these streaks suggested that two components with different dimensions were formed during melt-drawing: one was a precursory ECC, and the other was a mature ECC. These two ECC components grew synchronously at the beginning point of the plateau stress region for both films, independent of the entanglement characteristics of the film. However, the time of this synchronized growth was longer for the film with the lower MW component than for the film containing only the higher MW component. The resultant morphologies of the melt-drawn samples observed by transmission electron microscopy also reflected these characteristics. These results demonstrate that molecular entanglement characteristics dominate the unique crystallization mechanism that forms ECCs with different dimensions during melt-drawing of UHMW-PE.
Morphological effects on molecular mobility have been studied for solid ultrahigh molecular weight polyethylenes (UHMW-PE) crystallized from the melt and from solution or during polymerization. On ...the basis of transmission electron microscopic (TEM) observation, a crystalline domain structure was well identified for nascent UHMW-PE powders, which is quite different from regular lamellar stacking for solution-crystallized samples and the usual spherulites for melt-crystallized samples. Nuclear magnetic resonance (NMR) results showed that the amorphous chains between these crystalline domains in nascent powders were constrained, as well as those sandwiched between stacked crystalline lamellae for the solution-crystallized sample. Also, the existence of three regimes was recognized in the relaxation behavior of the crystalline phase, as revealed by 1H pulse NMR measurements. In process 1 (heating from room temperature), activation of molecular motion at the boundary between crystal/amorphous regions takes place. During process 2 (above the critical temperature of 60−90 °C), the crystallinity increases with the acceleration of the entire molecular motion caused by sliding of molecular chains in the crystalline region. Further raising the temperature (process 3) leads to the start of sample melting. These relaxation mechanisms suggest that the accelerated molecular motion in the crystal/amorphous boundaries initiates following lamellar thickening without passing the melt state.
The macrotribological behavior observed when a Si3N4 ball of a friction tester slid on polystyrene (PS) surface was compared with the nanotribological behavior observed when a Si3N4 tip of a scanning ...force microscope (SFM) slid on the same surface. The macro- and nanofriction forces were measured by a conventional ball-on-disk type friction tester and a SFM, respectively, as a function of the applied load. The morphological changes of the rubbed PS surfaces were also characterized by optical microscopy or SFM observations. Surface plastic deformation of PS always occurred under both tribological conditions examined in this study. The morphology formations of the macrocrack and the nanoperiodic pattern that might be attributed to the crack opening were observed at the rubbed PS surfaces under the macro- and nanotribological conditions. It should be noted that these formations occurred at the same level of apparent average contact pressure estimated based on the Johnson−Kendall−Roberts contact theory. Furthermore, under a comparable contact pressure, these surface plastic deformations yielded similar values of the macro- and nanofriction coefficients. The friction coefficient was considerably influenced by surface plastic deformation regardless of measurement scales. These results demonstrated that the macro- and nanotribological mechanisms of PS were similar.
Solution-grown single crystals of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P(3HB-co-4HB) were hydrolyzed by polyhydroxybutyrate (PHB) depolymerase from Ralstonia pickettii T1. Enzymatic ...degradation proceeded from the edges of lamellar crystals, yielding serrated contour and small crystal fragments. Gel permeation chromatography analysis revealed that the molecular weights of the crystals decreased during enzymatic degradation, suggesting that the enzymatic hydrolysis of chain-folding regions at the crystal surfaces occurred in addition to the enzymatic degradation at crystal laterals or edges. After P(3HB-co-4HB) single crystals were aminolysed in 20% aqueous methylamine solution to remove the folded-chain regions and enzymatic degradation by lipase from Rhizopus oryzae to remove 4HB components at crystal surfaces of single crystal aminolyzed, it was found that a small amount (up to ca. 2 mol%) of 4HB component can be incorporated into the P(3HB) mother crystal lattice irrespective of the 4HB content.
The purpose of this study is to clarify the superiority of five polyfunctional acrylates to composite filler and comonomer system, and the reasonable concentration of catalyst, Camphor ...quinone/Dimethylamino-ethylmethacrylate (CQ/DMAEMA), in the photocured resin for crown and bridge. The results are summarized as follows: 1. The influence of acrylate resin matrix of composite fillers was found in the elastic modulus (Em), Knoop hardness (Hk) and the wear resistance (Rw) of the photocured resin. Two photocured resins including Dipentaerythrytol hexaacrylate (DPHA) or DPHA-4(3-acryloxy propyl) tetramethylol methane (DPHA-APTM) composite fillers showed a higher Em, Hk and Rw but slightly lower tensile strength (Ts) and bending strength (Bs) than the one which included Bis-2-methacryloxyethyl 2, 2, 4-trymethyl hexamethylene diurethane (UDMA) or Trimethylolpropane trimethacrylate (TMPTMA) under a wet condition. And these two resins showed as a high water sorption value (Ws) as that of the photocured resin of UDMA. 2. The conversion of polymerization, cured depth and physical properties (Em, Hk and Rw) of the photocured resins were examined. They increased up to 0.5/1.0 or 1.0/1.0 in proportion to the increase of the concentration of the catalysts (CQ/DMAEMA). 3. When DPHA was added into the photocured resins consisted with UDMA monomer and DPHA or DPHA-APTM composite fillers, these resins showed a higher Em, Hk and Rw than the photocured resin with only UDMA as monomer. No significant difference of Ts and Bs between the photocured resins with and without DPHA was observed under a dry condition, but the values of Ts and Bs decreased in proportion to the increase of DPHA monomer under the wet condition. The residual monomer of the photocured resins was less than 1.2 per cent.
Measurements of the neutron and gamma-ray leakage spectra from 15 spherical target assemblies (carbon, nitrogen, H
2
O, C
2
F
4
, aluminum, silicon, titanium, iron, copper, tantalum, tungsten, gold, ...lead,
232
Th, and
238
U) pulsed with 14-MeV neutrons were made using time-of-flight techniques. The spheres were ∼30 g/cm
2
thick to maximize the gamma-ray leakage per central source neutron. Among all the materials studied, silicon shows the highest conversion factor (∼2 γMeV/n), and lead the lowest (0.31 γMeV/n). Monte Carlo neutron-photon transport calculations were done using the TART and SANDYL codes, with the ENDL and ENDF/B-V libraries. Comparisons with the neutron measurements confirm earlier results, where both libraries reproduced the leakage spectra for most of these materials reasonably well. The gamma spectra calculated with ENDL give a fair representation of the measurements, with the exception of the initial calculations for
16
O(H
2
O) and
19
F(C
2
F
4
), where serious discrepancies are found. Improvements were obtained for
16
O after a re-evaluation of the neutron-induced cross sections based on more recent microscopic experimental data. This was also the case for
19
F, where the calculations now overestimate the measurements by 30%. Calculations with the ENDF/B-V are lower than the experimental measurements for most of the materials.
Evidence-based CME Komoto, Timothy; Davis, Nancy
American family physician,
2002-Jul-15, 20020715, Letnik:
66, Številka:
2
Journal Article
Recenzirano
The American Academy of Family Physicians, through its Commission on Continuing Medical Education, is again taking a leadership role in the area of continuing medical education (CME). At the ...beginning of this year, a new process to grant credit for evidence-based CME was instituted.
PDF
