Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates

An efficient direct one-pot glycosylation method with anomeric hydroxy sugars as glycosyl donors employing phthalic anhydride and triflic anhydride as activating agents has been developed. Thus, highly stereoselective beta-mannopyranosylations were achieved by the reaction of 2,3-di-O-benzyl-4,6-O-benzylidene-D-mannopyranose (2) with phthalic anhydride in the presence of DBU at room temperature followed by sequential addition of DTBMP and Tf2O and glycosyl acceptors to the reaction mixture at -78 degrees C in one-pot. Stereoselective alpha-glucopyranosylations with 2,3-di-O-benzyl-4,6-O-benzylidene-D-glucopyranose (25) and other glycosylations with glucopyranoses and mannopyranoses having tetra-O-benzyl- and tetra-O-benzoyl protecting groups were also possible by utilizing the present one-pot glycosylation protocol. The possible mechanism for the beta-mannosylation with 2 was proposed based on the NMR study, in which alpha-mannosyl phthalate 55alpha and alpha-mannosyl triflate 59 were detected as intermediates. The versatility and efficiency of the present glycosylation methodology, especially those of the beta-mannopyranosylation protocol, were readily demonstrated by the efficient synthesis of protected beta-(1-->4)-D-mannotriose 62 and beta-(1-->4)-D-mannotetraose 67 with perfect beta-stereoselectivity.     

Effect of electrode spacing on image flicker in fringe-field-switching liquid crystal display

Low-frequency driving of a liquid crystal display (LCD) panel to minimise power consumption has drawn much attention recently. In case an LCD panel is driven by a low-frequency fringe field, image flickering phenomenon is detected by the naked human eye when the sign of the applied electric field is reversed. We investigated the effect of electrode spacing on the image flickering phenomenon induced by the flexoelectric effect in a fringe-field-switching (FFS) liquid crystal cell. We found that the image flicker in an FFS cell under low-frequency driving can be eliminated in a simple manner by changing the electrode spacing.     

Hydrodynamic fabrication of polymeric barcoded strips as components for parallel bio-analysis and programmable microactuation

In this paper, we report a novel technique for the manufacture of polymeric barcoded strips having diverse characteristics such as biocatalyst-based sensing and pH-responsive actuation. The fabrication involves the use of both a microfluidic platform and in-situ photopolymerization. It is expected that this method, which is a very simple, cost-effective, and environment-friendly means for mass production, will facilitate the stable immobilization of diverse biological substances such as enzymes, DNA, and antigens. Therefore, we fabricated an enzyme-immobilized barcoded strip for multiple bio-analysis. On the basis of this technology, we adopted different materials and thereby fabricated programmable microactuation components that are responsive to pH variation.     

A new phenolic glycoside from the fruits of <Emphasis Type=Italic>Capsicum annuum</Emphasis>

A new compound, 4-O-(6'-O-p-hydroxybenzoyl-β-D-glucopyranosyl)-cis-p-coumaric acid, was isolated from the fruits of hot pepper (Capsicum annuum L.). The structure of the compound was established on the basis of NMR, FAB-MS, and IR spectroscopic data.     

Synthesis of 3-phenoxy-1,3-dihydro-1-isobenzofuranones by palladium-catalyzed carbonylative cyclization of 2-bromobenzaldehyde with phenols

2-Bromobenzaldehyde reacts with phenols in acetonitrile under carbon monoxide pressure in the presence of a catalytic amount of bis(triphenylphosphine)palladium(II) chloride to afford the corresponding 3-phenoxy-1,3-dihydro-1-isobenzofuranones in high yields.     

Competition Between Radial Expansion and Thickening in the Enlargement of an Intracranial Saccular Aneurysm

Rupture of intracranial saccular aneurysms is the leading cause of spontaneous subarachnoid hemorrhage, which results in significant morbidity and mortality. Although many have suggested that saccular aneurysms enlarge and rupture due to mechanical instabilities, our recent nonlinear analyses suggest that at least certain classes of aneurysms do not exhibit a quasi-static limit point instability or dynamic instabilities in response to periodic loading. Based on an increased understanding of the ubiquitous role of growth and remodeling within the vasculature and recent histopathological data on saccular aneurysms, it is hypothesized that a stress-mediated regulation of collagen turnover causes their enlargement. There is a need, however, for a theoretical framework to explore this and competing hypotheses. In this paper, we present a 2-D constrained mixture model for growth and remodeling of an ellipsoidally shaped saccular aneurysm and numerically simulate enlargement and changes in material symmetry in the aneurysmal wall. Results suggest that ellipsoidal aneurysms tend toward spherical shapes, and a competition between radial expansion and wall thickening plays a critical role in determining the stability of an enlarging lesion.     

A study on the correlation between the thermal contact conductance and effective factors in fin–tube heat exchangers with 9.52 mm tube

The thermal contact resistance is a principal parameter interfering with heat transfer in a fin–tube heat exchanger. However, the thermal contact resistance in the interface between tubes and fins has not been clearly investigated. The objective of the present study is to examine the thermal contact conductance for various fin–tube heat exchangers with tube diameter of 9.52 mm and to find a correlation between the thermal contact conductance and effective factors such as expansion ratio, fin type, fin spacing and hydrophilic coating. In this study, experiments have been conducted only to measure heat transfer rate between hot and cold water. To minimize heat loss to the ambient air by the natural convection fin–tube heat exchangers have been placed in an insulated vacuum chamber. Also, a numerical scheme has been employed to calculate the thermal contact conductance with the experimental data. As a result, a new correlation including the influences of expansion ratio, slit of fin and fin coating has been introduced, and the portion of each thermal resistance has been estimated in the fin–tube heat exchangers with 9.52 mm tube.     

Testing a priority-based queue model with Linux command histories

We study human dynamics by analyzing Linux history files. The goodness-of-fit test shows that most of the collected datasets belong to the universality class suggested in the literature by a variable-length queuing process based on priority. In order to check the validity of this model, we design two tests based on mutual information between time intervals and a mathematical relationship known as the arcsine law. Since the previously suggested queuing process fails to pass these tests, the result suggests that the modelling of human dynamics should properly consider the statistical dependency in the temporal dimension.     

Limiting mixture distributions for AR(1) model indexed by a branching process

First order autoregressive model indexed by a supercritical Galton–Watson branching process is discussed. Limiting distributions of the least squares estimates are derived both for the stationary and explosive cases. It is shown that a certain random variable inherent in the branching process is acting as a mixing variable in limiting mixture distributions. In particular, with explosive Gaussian case, we obtain a mixture of Cauchy distributions rather than Cauchy.     

Epoxy/amine‐functionalized short‐length vapor‐grown carbon nanofiber composites

Short length vapor‐grown carbon nanofibers (VGCNFs) were functionalized with 4‐aminobenzoic acid in polyphosphoric acid/phosphorous phentoxide medium via “direct” Friedel‐Crafts acylation reaction to afford aminobenzoyl‐functionalized VGCNFs (AF‐VGCNFs). The AF‐VGCNFs as a cocuring agent were mixed with epoxy resin by simple mechanical stirring in methanol which was added to help efficient mixing. After evaporation of methanol, 4,4′‐methylenedianiline as a curing agent was added to the mixture, which was then cured at elevated temperatures. The resultant composites displayed uniform dispersion of AF‐VGCNFs into cured epoxy matrix. During curing process, the amine functionalities on AF‐VGCNF together with 4,4′‐methylenedianiline were expected to be involved in covalent attachment to the epoxy resin. As a result, both tensile modulus and strength of the composites were improved when compared with those of pure epoxy resin. Thus, the AF‐VGCNFs play a role as an outstanding functional additive, which could resolve both dispersion and interfacial adhesion issues at the same time by functionalization of VGCNFs and covalent bonding between the additive and matrix, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7473–7482, 2008