Selective oxidation of a keramaphidin B model.

A crucial step in the Baldwin and Whitehead proposal for explaining the biogenesis of the marine alkaloid manzamine A is the selective oxidation of natural keramaphidin B to an iminium salt 3, which is then hydrolyzed to give the aldehyde 4. Conditions are now presented in which this selective oxidation can be performed on model compound 8, leading to the iminium salt 16. Although this salt can be considered as a model equivalent of the proposed aldehyde intermediate 4, it was found to be very resistant to hydrolysis as was the corresponding amide 20. From a synthetic point of view, the reported results illustrate the usefulness of the temporary protection of tertiary amines as aminoborane derivatives and constitute a good method for the oxidation of a sterically hindered tertiary nitrogen atom in the presence of a second nitrogen.     

Two polycyclic compounds derived from a Diels–Alder reaction

In both 9,10‐di­methoxy‐11‐oxatri­cyclo­[6.2.1.0^2,7]­undeca‐4,9‐diene‐3,6‐diol, C₁₂H₁₆O₅, (I), and 5,6‐di­methoxy‐3,7‐dioxa­tetra­cyclo­[6.4.0.0^2,6.0^4,12]­dodec‐9‐en‐11‐ol, C₁₂H₁₆O₅, (II), the hetero‐oxygen‐containing five‐membered rings have an envelope conformation. The six‐membered rings are in a boat conformation in compound (I), and in (II), one is in a half‐boat and the other is in a slightly distorted boat conformation. The mol­ecules in both compounds interact through classical hydrogen bonds and C—H?O contacts.     

Modelling U.S. monthly inflation in terms of a jointly seasonal and non‐seasonal long memory process

This article examines monthly U.S. inflation rates by means of fractionally integrated time series techniques. We use a procedure of Robinson (J Am Statist Assoc 1994; 89 :1420) that permits us to simultaneously test the degrees of integration at both the zero and the seasonal frequencies. The results show that long memory takes place at both frequencies, the orders of integration being in both cases higher than 0 but smaller than 0.5, implying stationarity but long memory behaviour. In addition, the root at the long run or zero frequency seems to play a much more important role than the seasonal one, with shocks affecting the latter component decaying faster than in the former case. Copyright © 2005 John Wiley & Sons, Ltd.     

Growth of InN layers by MOVPE using different substrates

This study presents the MOVPE growth of InN films onto different substrate materials, including sapphire, nitrided or not, GaN and AlN buffer layers deposited onto sapphire, and Si(111).For InN growth onto nitrided sapphire, different growth parameters were investigated in order to determine the best growth conditions. We found that a low V/III molar ratio has to be used in order to increase the growth rate. A light nitridation treatment gives the best electrical properties: mirror like layers with a mobility of 800 cm²/V  s were obtained. At room temperature, reflectivity experiments show the existence of a transition at 1.2 eV, while photoluminescence appears around 0.8 eV.Using the same growth conditions onto GaN buffers (with thicknesses ranging from 15 to 1000 Å), we found that the best mobilities are obtained above a given buffer thickness.By comparing also with AlN buffer layers and silicon substrates, we found that our previous conclusion still holds; lightly nitrided sapphire substrate leads to the best electrical properties and morphology.     

N.m.r. studies of complexes of molybdenum(VI) with tartaric acid in aqueous solution

Summary Complex formation between molybdate ions and R,R-(+)-tartaric acid has been studied in aqueous solution, and to a limited extent in DMSO, over a range of concentrations and pH at 298K, using¹H and¹³C n.m.r. techniques. Only four main species are evident; two, which have Mo: L ratios of 11 and 12, are bondedvia a carboxylic oxygen atom and an adjacent hydroxyl oxygen atom. The 12 species forms stereospecifically. The other two main species contain bridging tartaric acid molecules, and a 22 species, also formed stereo-specifically in solution, have been isolated and characterised in the solid state. A limited number of experiments with racemic acid and meso-tartaric acid indicate that only a few species are formed in these systems and with a good deal of stereospecificity also.     

Incoherent bremsstrahlung in nuclei

We have studied the processes A(e, e′γ)X in nuclei, or incoherent bremsstrahlung, and determined expressions for the cross section in terms of the same nuclear response functions R_L, R_T, which appear in inclusive electron scattering (e, e′) in nuclei. Calculations of the cross sections are carried out using a Fermi gas model, complemented by the local-density approximation, to evaluate the response functions. We have carried out a study which shows that the reaction can be used to determine reliably the response functions from experimental data. On the other hand we have compared the incoherent bremsstrahlung with the coherent one in order to see the limits to the tagging technique, which produces monochromatic photons based on the assumption of the dominance of the coherent process. We observe that at energies E_γ < 1 GeV the dominance of the coherent process extends to relatively large scattering angles, making the present technique completely safe. However, as the energy of the electron increases, the region of dominance of the coherent process is reduced to smaller scattering angles. These results should be of use when extending the tagging technique to planned or future electron facilities.     

On the assignment of the carbon-13 NMR spectrum of bilirubin

An individual assignment of certain peaks in the proton and ¹³C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off-resonance decoupled ¹³C spectra of bilirubin dimethyl ester. The signals due to the endo and exo vinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin-lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation time.     

Nuclide distributions for Fe-like fragments in the 136Xe + 56Fe reaction

The nuclide distributions of Fe-like reaction products from the reaction 5.9 MeV/u ¹³⁶Xe on. ⁵⁶Fe were measured as a function of total kinetic energy loss at a laboratory angle of 55°. The first and second moments of N, Z and A were obtained in addition to the correlation coefficients and the isobaric variances. We compare these results for the Fe-like fragment to those implied by previous measurements of the secondary distribution of the Xe-like fragment. We incorporate the effects of particle evaporation on both the light and heavy complementary primary distributions. There is overall qualitative agreement, but the variances are somewhat smaller than those obtained previously even after correction for particle evaporation. Evaporation calculations are also performed on the primary distributions predicted by a nucleon exchange model, and yield distributions in good agreement with the present experimental data.