Walter S. Trahanovsky

Use of a 13C tracer to quantify the plasma appearance of a physiological dose of lutein in humans.

Increased intake of lutein from vegetables promotes increased density of the macular pigment and therefore may protect against age-related macular degeneration. Our objective was to use a 13C tracer and high-precision gas chromatography-combustion interfaced-isotope ratio mass spectrometry (GC-C-IRMS) to investigate metabolism of a lutein dose equivalent to that absorbed from vegetables. Biosynthetic per-labeled (>99% 13C) lutein was purified from a commercially available extract of algal biomass. Subjects (n=4) ingested 3 mg of [13C]lutein with a standardized low-carotenoid breakfast. Blood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. To produce perhydro-β-carotene suitable for analysis by GC-C-IRMS, the plasma lutein fraction was hydrogenated on palladium-on-carbon catalyst with acid-catalyzed hydrogenolysis. The stable carbon isotope (13C/12C) ratio measured by GC-C-IRMS was used to calculate the plasma concentration of [13C]lutein. There was a rapid increase in [13C]lutein in plasma until peak enrichment at 16 h followed by a decline to the next measurement at 24 h. At 528 h, small changes in 13C enrichment from baseline could still be measured in plasma lutein. High-precision GC-C-IRMS enables complete definition of the appearance and disappearance of [13C]lutein in plasma after ingestion of a dose similar to that absorbed from foods.

Synthesis and characterization of a catechol-terminated alkanethiolate monolayer adsorbed on gold

Structural, redox, and metal ion binding characterizations of the monolayer formed by the chemisorption of 3,4-dihydroxyphenethyl mercaptan (DHPM) on gold are described. This system was explored as a model for investigations of surface-immobilized molecules that contain redox-transformable coordination sites for binding metal ions from solution. The characterizations were carried out using infrared reflection spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and long optical pathlength thin-layer spectroscopy. The XPS data show that this monolayer adsorbs as a thiolate, and the IRS results indicate that the average orientation of the aromatic ring plane is close to the surface normal. Cyclic voltammetry reveals that the pendant catechol/quinone undergoes the expected two-electron, two-proton redox transformation; however, the oxidized form of the couple is unstable, particularly in alkaline aqueous solutions. A determination of Cu(II) binding ability to the surface-immobilized catechol moieties, using a long optical pathlength thin-layer cell to follow the depletion of Cu(II) from solution, indicated that the complexation of the metal was not substantially different from that for the solution form of catechol. The instability of the oxidized form of the ligand, nevertheless, precluded an assessment of its metal ion binding ability. An approach using these data for estimating the conditional formation constant for the surface complexation reaction is also developed.

1H-nuclear magnetic resonance spectroscopy of reducing-residue anomeric protons of pertrifluoroacetylated carbohydrates.

Eight monosaccharides (L-arabinoside, L-fucose, D-galactose, D-glucose, D-lyxose, D-mannose, L-rhamnose, and D-xylose), eight disaccharides (cellobiose, gentiobiose, isomaltose, lactose, maltose, nigerose, sophorose, and xylobiose), and three trisaccharides (isomaltotriose, maltotriose, and xylotriose) were derivatized with N-methylbis-(trifluoroacetamide) in pyridine solution to form trifluoroacetylated derivatives. These were analyzed by 1H-n.m.r. spectroscopy to determine the characteristics of the spectra and distributions of the reaction products. Peaks corresponding to reducing-residue anomeric protons were located significantly downfield of all others, and were in general 0.4 p.p.m. or more downfield of equivalent signals from the same carbohydrates when they were free or derivatized with other groups. Neither the location of anomeric proton peaks relative to each other nor the degree of spin-spin coupling between H-1 and H-2 varied greatly with type of derivatization. Spin-spin coupling, however, decreased for some beta-pyranose forms of xylobiose and the three trisaccharides. In all examples except some where H-2 was oriented equatorially to a pyranose ring, the proportion of the alpha-pyranose was either enhanced or not changed in concentration by trifluoroacetylation.

On the mechanism of the formation of benzocyclobutene by flash vacuum pyrolysis of ortho-methylbenzyl chloride

Abstract Flash vacuum pyrolysis of o -methylbenzyl chloride- ∝ , ∝ - d 2 gives benzocyclobutene- ∝ , ∝ - d 2. This finding indicates that the reaction involves net δ-elimination of hydrochloric acid.

Organic oxalates. Cyclizations of the ortho-methyl- and ortho-trifluoromethyl-cinnamyl radicals to the corresponding indenes

Summary ortho-Methyl- and ortho-trifluoromethyl-cinnamyl radicals, generated by gas-phase pyrolysis of the appropriate oxalate, undergo cyclization reaction to form indene or substituted indenes.