Biologically active metabolites from fungi, 17. 8-alpha-acetoxyverrol,a new member of the trichothecene sesquiterpenes

8-alpha-Acetoxyverrol (4), the first open chain example of the trichothecenes with oxygenation at C-8, was isolated from cultures of Aphanocladium spectabile. The compound doses the biosynthetic gap to the macrocyclic verrucarins.     

Electron-impact dissociation and transient properties of a stored LiH2 - beam

The fragmentation of LiH₂ ^- anions after electron impact was investigated at the heavy-ion storage ring TSR. The main reaction channel was found to be electron detachment followed by a breakup into LiH + H. In the first ms after production of the molecular ions in a cesium sputtering ion source, additional contributions were observed in the Li + H₂ and Li^- + H₂ channels, hinting at an initial population of a short-lived state of the anion. To gain a better understanding of the mechanisms underlying the observed behavior of the system, ab initio calculations of relevant potential energy surfaces were performed at selected geometries. The experimental findings are discussed in the light of these calculations.     

Nondeterministic approach to tree-based jet substructure

Jet substructure is typically studied using clustering algorithms, such as k(T), which arrange the jets' constituents into trees. Instead of considering a single tree per jet, we propose that multiple trees should be considered, weighted by an appropriate metric. Then each jet in each event produces a distribution for an observable, rather than a single value. Advantages of this approach include (1) observables have significantly increased statistical stability, and (2) new observables, such as the variance of the distribution, provide new handles for signal and background discrimination. For example, we find that employing a set of trees substantially reduces the observed fluctuations in the pruned mass distribution, enhancing the likelihood of new particle discovery for a given integrated luminosity. Furthermore, the resulting pruned mass distributions for (background) QCD jets are found to be substantially wider than that for (signal) jets with intrinsic mass scales, e.g., boosted W jets. A cut on this width yields a substantial enhancement in significance relative to a cut on the standard pruned jet mass alone. In particular the luminosity needed for a given significance requirement decreases by a factor of 2 relative to standard pruning.     

Amino acid adsorption on zeolite beta

A thermodynamic equilibrium model has been developed to describe amino acid adsorption on microporous materials. The model addresses electrostatic, hydrophobic and steric interactions. A procedure for fitting the model's parameters is presented and should be applicable to the majority of the common 20 amino acids. The approach is demonstrated using experimental measurements of L-phenylalanine and L-arginine on zeolite beta. Between the adsorption mechanisms of ion exchange and physisorption, the first can contribute as much as two-thirds of the phenylalanine adsorbed at saturation. For the materials tested, ion exchange is maximized when the zeolite's silicon-to-aluminum ratio is 12. When this atom ratio is raised to 100, ion exchange no longer plays a significant role, but the amount physisorbed increases by 30%.     

The short range expansion

Let V_i be short range potential and λ_i(ε) analytic functions. We show that the Hamiltonians H_ε = −Δ + ε⁻²∑_{i = l}ⁿλ_i(ε)V_i((· − x_i)/ε converge in the strong resolvent sense to the point interactions as ε → 0, and if V_i have compact support then the eigenvalues and resonances of H_ε, which remains bounded as ε → 0, are analytic in ε in a complex neighborhood of zero. We compute in closed form the eigenvalues and resonances of H_ε to the first order in ε.     

Enantioselective synthesis of 3-demethoxyaranciamycinone via asymmetric epoxidation

The tetracyclic olefin 1 was enantioselectively epoxidized using a molybdenum(VI)- oxodiperoxo complex containing a chiral lactamide. Conversion to the glycosides 8 and 9 showed the epoxide 2 to be the predominant (3 : 1) enantiomer.     

The vibrational transition moment for the ν2 bands of 14ND3 and 15ND3

Intensities were measured at high pressure (200 Torr) for blended K-multiplets in the P and R branches of the s0 → aν₂ and a0 → sν₂ bands of ¹⁴ND₃. Intensities of 55 individual lines at 10 Torr of ¹⁵ND₃ were also measured by deconvolution of the true line shape from the observed vibration-rotation spectrum and the instrumental line shape. From these results we estimate a transition moment of 0.179 ± 0.010 D for both ¹⁴ND₃ and ¹⁵ND₃. These lead to a derivative of the dipole moment, $\text{|}\text{?μ}\text{?Q}{}_2\text{| = 93}\text{cm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{sec}{}^{\mathrm{?1}}$.