A synthesis of the tetracyclic carboskeleton of isaindigotidione

An efficient synthesis of the unique indolizino[7,6-c]quinoline carboskeleton of isaindigotidione has been achieved. This strategy employed l-proline and isatin as the main building blocks in the construction of the framework. Four transformations occurred in a one-pot operation to furnish the tetracyclic nucleus.     

Determination of avilamycin as dichloroisoeverninic acid in poultry and porcine muscles by isotope dilution liquid chromatography–tandem mass spectrometry

Avilamycin residue in food is regulated as its marker residue dichloroisoeverninic acid (DIA). An isotope dilution liquid chromatography–tandem mass spectrometry method is established for the accurate determination of DIA in animal muscles without any pre-extraction and preconcentration prior to alkaline hydrolysis. Optimization of the sample cleanup procedures such as liquid–liquid extraction and solid phase extraction was performed by fine-tuning several critical parameters to reduce the matrix effects. Quantification of DIA in edible muscle was accomplished by using matrix-matched calibration with dichloroisoeverninic acid-d₆ as internal standard. The method was validated with DIA and avilamycin-fortified poultry and porcine muscles at three different levels (25, 50, and 100 μg/kg). Conversion of avilamycin to DIA by alkaline hydrolysis was ≥92 %. The recoveries of DIA in both muscles at three fortification levels ranged from 94 to 106 % and RSDs were ≤11 % in all cases. The estimated limit of detection values in poultry and porcine muscles were 2.7 and 0.7 μg/kg, respectively. The estimated limit of quantitation values in poultry and porcine muscles were 8.3 and 2.4 μg/kg, respectively. This method is suitable for routine monitoring of avilamycin residue in food safety surveillance programs.     

Stereochemical features of the physical and chemical interactions of singlet oxygen with enecarbamates

Oxazolidinone-substituted enecarbamates represent a mechanistically rich system for the study of stereoelectronic, steric, and conformational effects on stereoselectivity and mode selectivity in (1)O(2) [2 + 2] and ene reactions. Photooxygenation of these enecarbamates with (1)O(2) leads to diastereomerically pure dioxetanes that decompose to yield an oxazolidinone carbaldehyde and one of the two enantiomers of methyldesoxybenzoin in enantiomeric excess. Stereoselectivity originates at the allylic stereocenter, a result supported by quenching studies, computational analysis, and deuterium solvent isotope effects. [reaction: see text]     

Objective measurement of minimal erythema and melanogenic doses using natural and solar-simulated light

Very little information exists on the amount of natural and artificial UV light required to cause sunburn and tanning in individuals with very pale skin who are at the greatest risk of developing skin cancer. We have investigated minimal erythema dose (MED) and minimal melanogenic dose (MMD) in a group of 31 volunteers with Fitzpatrick skin types I and II using an Oriel 1000 W xenon arc solar simulator and natural sunlight in Sydney, Australia. We measured the erythemal and melanogenic responses using conventional visual scoring, a chromameter and an erythema meter. We found that the average MED measured visually using the artificial UV source was 68.7 +/- 3.3 mJ/cm2 (3.4 +/- 0.2 standard erythema doses [SED]), which was significantly different from the MED of sunlight, which was 93.6 +/- 5.6 mJ/cm2 (P < 0.001) (11.7 +/- 0.7 SED). We also found significant correlations between the solar-simulated MED values, the melanin index (erythema meter) and the L* function (chromameter). The average MMD (obtained in 16 volunteers only) using solar-simulated light was 85.6 +/- 4.9 mJ/cm2, which was significantly less than that measured with natural sunlight (118.3 +/- 8.6 mJ/cm2; P < 0.05). We mathematically modeled the data for both the chromameter and the erythema meter to see if we were able to obtain a more objective measure of MED and differentiation between skin types. Using this model, we were able to detect erythemal responses using the erythema index function of the erythema meter and the a* function of the chromameter at lower UV doses than either the standard visual or COLIPA methods.     

Algebraic dimension of twistor spaces

The author is partially supported by a grant of the National Science Foundation     

Equivariant connected sums of compact self-dual manifolds

Partially supported by NSF grant #DMS-9306950 and UC Riverside grant #5-510000-07427-5     

Oligo(fluorenyleneethynylenegermylene)s and their metallopolymers

Oligo(fluorenyleneethynylenegermylene)s and their polyplatinynes are synthesized and photophysically characterized; inclusion of heavy germylene bridges greatly boosts the phosphorescence decay rate in metallopolymers.