Constituents of the Vietnamese medicinal plant Orthosiphon stamineus

From the MeOH extract of the aerial part of Vietnamese Orthosiphon stamineus, five new isopimarane-type diterpenes [orthosiphols F-J (1-5)] and two new diterpenes [staminols A (6) and B (7)] with a novel carbon-framework, to which we proposed the name "staminane", and three new highly-oxygenated staminane-type diterpenes [staminolactones A (8) and B (9) and norstaminol A (10)1 were isolated. Moreover, staminolactone A (8) is 8,14-secostaminane-type and staminolactone B (9) is 13,14-secostaminane-type, while norstaminol A (10) is 14-norstaminen-type. Together with these new diterpenes, sixteen known compounds were also isolated and identified to be: 7,3',4'-tri-O-methylluteolin (11), eupatorin (12), sinensetin (13), 5-hydroxy-6,7,3',4'-tetramethoxyflavone (14), salvigenin (15), ladanein (16), tetramethylscutellarein (17), 6-hydroxy-5,7,4'-trimethoxyflavone (18), vomifoliol (19), aurantiamide acetate (20), rosmarinic acid (21), caffeic acid (22), oleanolic acid (23), ursolic acid (24), betulinic acid (25), and beta-sitosterol (26). All the isolated compounds were tested for their cytotoxicity towards highly liver metastatic murine colon 26-L5 carcinoma cells, and the new diterpenes, except for 4, and flavonoids (11, 12, 16, 18) showed cytotoxicity with an ED50 value between 10 and 90 microg/ml.     

Prototype reflectivity analyses of hydrogen storage levels in single-walled carbon nanotubes

A prototype case study is presented that examines the level of hydrogen content in H-SWNTs using the Surface Plasmon Resonance technique. The damping effect and the angular shift in the resonance minimum of an SWNT-gold interface due to the presence of hydrogen is analyzed using a parametric model, which is based on the concept of an effective permittivity. The new approach provides for a non-invasive analysis of the level of hydrogen content in H-SWNTs and is potentially extendable to other carbon-based hydrogen storage materials.     

Rearrangements of transient neutral molecules in the gas phase. Does the conversion of CCCHO to HCCCO involve oxygen or hydrogen migration?

Stable (CC13CHO)- may be formed in the chemical ionisation ion source of a VG ZAB 2HF mass spectrometer by the SN2(Si) reaction between Me3SiC[triple bond]C13CHO and F-. Vertical (Franck-Condon) one-electron oxidation of (CC13CHO)- in the first of the tandem collision cells of a VG ZAB 2HF mass spectrometer gives CC13CHO. Some of these neutrals have sufficient excess energy to effect rearrangement to HCC13CO, some of which are energised and to decompose to HCC. and 13CO. Thus the neutral rearrangement exclusively involves H migration: no products from O migration are detected. The corresponding two-electron oxidation of (CC13CHO)- gives mainly unrearranged (CC13CHO)+. A minority of these cations are energised and rearrange by H and O migration to yield (HCC13CHO)+ and (OCC13CHO)+ respectively. All experimental observations are backed up by molecular modelling at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory.     

Studies on pyridazine azide cyclisation reactions

Reaction of sodium azide with 4-methyl-3,5,6-tribromopyridazine results in the formation of 3,5,6-triazide intermediate which could cyclise to give two possible bicyclic products while ab initio calculations show that the formation of a tricyclic compound is extremely energetically unfavourable. However, experimentally, only one major product is isolated. The structure of this unstable product has been conclusively established by X-ray crystallography as 3,5-diazido-4-methyl[1,5-b]tetrazolopyridazine confirming theoretical predictions.     

Anechoic chamber qualification: traverse method,inverse square law analysis method,and nature of test signal

Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance.