Synthesis of the Core Oligosaccharides of Lipooligosaccharides from Campylobacter jejuni: A Putative Cause of Guillain-Barré Syndrome.

The chemical synthesis of the highly branched core oligosaccharides of lipooligosaccharides (LOSs) found in Campylobacter jejuni, which causes Guillain-Barré syndrome by a preceding infection, is described. The target LOS mimics, consisting of eight or nine monosaccharides, were classified into three groups as key building blocks: ganglioside-core tetra-/pentasaccharides (GM1-/GD1a-like), l-glycero-d-manno-heptose-containing trisaccharides, and 3-deoxy-d-manno-2-octulosonic acid (KDO) residues. These synthetic fragments were obtained from commercially available monosaccharides. Less obtainable l-glycero-d-manno-heptose and KDO residues, as key components of the LOSs, were synthesized from p-methoxyphenyl d-mannoside and di-O-isopropylidene-protected d-mannose, respectively. The synthesis of α-KDO glycoside, as one of the most difficult stereocontrolled glycosidic constructions, was achieved by treating a 2,3-ene derivative of KDO with phenylselenyl trifluoromethanesulfonate as a suitable α-directing reagent. All synthetic blocks were constructed through a convergent synthetic route, which resulted in the first synthesis of structurally challenging LOS core glycans containing ganglioside GM1 and GD1a-core sequences.

Influence of surface treatment of contaminated lithium disilicate and leucite glass ceramics on surface free energy and bond strength of universal adhesives.

This study investigates the influence of surface treatment of contaminated lithium disilicate and leucite glass ceramic restorations on the bonding efficacy of universal adhesives. Lithium disilicate and leucite glass ceramics were contaminated with saliva, and then cleaned using distilled water (SC), or 37% phosphoric acid (TE), or hydrofluoric acid (CE). Specimens without contamination served as controls. The surface free energy was determined by measuring the contact angles formed when the three test liquids were placed on the specimens. Bond strengths of the universal adhesives were also measured. Saliva contamination and surface treatment of ceramic surfaces significantly influenced the surface free energy. The bond strengths of universal adhesives were also affected by surface treatment and the choice of adhesive materials. Our data suggest that saliva contamination of lithum disilicate and leucite glass ceramics significantly impaired the bonding of the universal adhesives, and reduced the surface free energy of the ceramics.

Evaluation of a calcium phosphate desensitizer using an ultrasonic device.

This study evaluated the effect of a calcium phosphate desensitizer on the demineralization of bovine dentin by measuring changes in transmitted ultrasonic velocity. Bovine dentin specimens with and without application of desensitizer were immersed in 0.1 M lactic-acid buffer solution (pH 4.75) 10 min twice daily throughout the test period, and stored in artificial saliva solution (pH 7.0) between treatments. The propagation time of longitudinal ultrasonic waves was measured by a pulser-receiver. Data were evaluated using one-way ANOVA followed by Tukey HSD test (α=0.05). The ultrasonic velocity decreased over time in specimens stored in demineralizing solution (3,785-3,462 m/s); however, desensitizer-applied specimens had a significantly higher sonic velocity (3,945-3,990 m/s) than those without application. The calcium phosphate desensitizer appeared to reduce the demineralization of dentin and occluded dentinal tubules.

The origin of planetary impactors in the inner solar system.

Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old craters from a unique period of heavy bombardment that ended approximately 3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past approximately 3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.