Pacharin: a new dibenzo(2,3-6,7)oxepin derivative from bauhinia racemosa lamk

The isolation of resveratrol and a new dibenzoxepin derivative, pacharin, from the heartwood of $\text{Bauhinia}$$\text{racemosa}$ Lank is reported. The structure of pacharin has been established as l,7-dlhydroxy-3-methoxy-2-methyl-dibenzo(2,3-6,7) oxepin (Va) by a study of its chemical and spectroscopic properties, including X-ray analysis.     

Optical and magnetic properties of Er3+ in LiYF4

High-resolution, polarized fluorescence spectroscopy has been used to study magnetically split energy levels of triply ionized erbium in the scheelite host lithium yttrium fluoride. Primary attention focused upon characterizing the Stark components of JLS manifolds involved in the material's several lasing transitions. Measurements at 2K yield energies and signed g factors which differ considerably from previously published zero-field studies and corresponding theoretical predictions of magnetic splittings. Polarization data allow definitive assignment of S₄ irreducible representations similar to those reported for erbium levels in the isomorphic host CaWO₄. Summation of g∥'s for the three Γ_7,8 levels of the ${}^4\text{I}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ multiplet yields a value of 3.16 ± 0.23, whereas the recently developed partial g-sum rule predicts 3.32.     

Chains in the Bruhat order

We study a family of polynomials whose values express degrees of Schubert varieties in the generalized complex flag manifold G/B. The polynomials are given by weighted sums over saturated chains in the Bruhat order. We derive several explicit formulas for these polynomials, and investigate their relations with Schubert polynomials, harmonic polynomials, Demazure characters, and generalized Littlewood-Richardson coefficients. In the second half of the paper, we study the classical flag manifold and discuss related combinatorial objects: flagged Schur polynomials, 312-avoiding permutations, generalized Gelfand-Tsetlin polytopes, the inverse Schubert-Kostka matrix, parking functions, and binary trees. A.P. was supported in part by National Science Foundation grant DMS-0201494 and by Alfred P. Sloan Foundation research fellowship. R.S. was supported in part by National Science Foundation grant DMS-9988459.     

A Convenient Photocatalytic Fluorination of Unactivated C?H Bonds

Fluorination reactions are essential to modern medicinal chemistry, thus providing a means to block site‐selective metabolic degradation of drugs and access radiotracers for positron emission tomography imaging. Despite current sophistication in fluorination reagents and processes, the fluorination of unactivated C H bonds remains a significant challenge. Reported herein is a convenient and economic process for direct fluorination of unactivated C H bonds that exploits the hydrogen abstracting ability of a decatungstate photocatalyst in combination with the mild fluorine atom transfer reagent N‐fluorobenzenesulfonimide. This operationally straightforward reaction provides direct access to a wide range of fluorinated organic molecules, including structurally complex natural products, acyl fluorides, and fluorinated amino acid derivatives.     

Alpha spectrometric evaluation of SRM-995 as a potential uranium/thorium double tracer system for age-dating uranium materials

Uranium-233 (t _1/2 ~ 1.59E5 years) is an artificial, fissile isotope of uranium that has significant importance in nuclear forensics. The isotope provides a unique signature in determining the origin and provenance of uranium-bearing materials and is valuable as a mass spectrometric tracer. Alpha spectrometry was employed in the critical evaluation of a ²³³U standard reference material (SRM-995) as a dual tracer system based on the in-growth of ²²⁹Th (t _1/2 ~ 7.34E3 years) for ~35 years following radiochemical purification. Preliminary investigations focused on the isotopic analysis of standards and unmodified fractions of SRM-995; all samples were separated and purified using a multi-column anion-exchange scheme. The ²²⁹Th/²³³U atom ratio for SRM-995 was found to be 1.598E?4 (±4.50 %) using recovery-corrected radiochemical methods. Using the Bateman equations and relevant half-lives, this ratio reflects a material that was purified ~36.8 years prior to this analysis. The calculated age is discussed in contrast with both the date of certification and the recorded date of last purification.     

A brief introduction to analytical methods in nuclear forensics

Nuclear forensic (NF) techniques are critical in responding to both environmental releases of nuclear materials and illicit trafficking activities involving both nuclear and counterfeit materials. Despite rising need, however, significant barriers exist to the future success of such research. This subset of analytical chemistry contains unique concerns (e.g. chronometry and impurity signatures), a wide variety of preparatory/instrumental approaches, and is in need of innovative solutions to current problems both in and out of the lab. The present work introduces existing NF research, development challenges and notes potential areas for advancement by highlighting several key analytical approaches. Examples of concerns and techniques discussed in this review include: chronometry, reference materials, separations, counting spectrometry, mass spectrometry and more.     

Migration of Silicon from Oxygen to Carbon in O-Trialkylsilyl Ketene Acetals

The migration of silicon from oxygen to carbon for 1 and 3 is intramolecular. The half—life of migration is not influenced by the presence of t-BuMe₂SiCI or triethyIbenzylammonium chloride.