Determination of Entropy Production for a Quantum System in the Presence of an Auxiliary System

International Journal of Theoretical Physics - A thorough understanding of entropy production, which can be used as a natural quantifier of the degree of irreversibility of a process, is both...     

Temperature and solvent dependent NMR studies on mangiferin and complete NMR spectral assignments of its acyl and methyl derivatives

By employing concerted 1 and 2D NMR techniques, exact NMR spectral assignments have been made of the acyl (2-7) and methyl (8 and 9) derivatives of mangiferin (1) isolated from the leaves of Bombax ceiba. Derivatives 2, 8 and 9 have been reported in literature, while 3-7 represent new compounds. The acetates 2 and 3 were found to be unstable and were converted into the same penta-acetate 4 at room temperature. Extensive NMR studies on mangiferin (1) and its derivatives showed that H-4 exchanges with deuterium of the solvent molecule more easily. This exchange under acidic conditions occurred at that position (C-4) where electrophilic substitution reactions can easily take place. This is the first report describing the exchange of C-4 proton of mangiferin (1), or any other xanthone, with deuterium of solvent molecules.     

Comprehensive survey of radionuclides in contemporary smokeless tobacco products

There is considerable interest in the chemical composition of smokeless tobacco products (STPs), owing to health concerns associated with their use. Previous studies have documented levels of ²¹⁰Po, ²¹⁰Pb and uranium in STP samples. Here, the levels of 13 α-particle and 15 β-radiation emitting radionuclides have been measured in a broad and representative range of contemporary STPs commercially available in the United States and Sweden. For each radionuclide, the level of radioactivity and calculated mass per gram of STP are reported. The results indicate that, among 34 Swedish snus and 44 US STPs, a more complex radionuclide content exists than previously reported for these products. Of the 28 radionuclides examined, 13 were detected and quantified in one or more STPs. The most frequently identified radionuclides in these STPs were ⁴⁰K, ¹⁴C, ²¹⁰Po and ²²⁶Ra. Over half the STPs also contained ²²⁸Th, and an additional 8 radionuclides were identified in a small number of STPs. The presence of ¹⁴C, ³H and ²³⁰Th are reported in tobacco for the first time. The activity of β-emitters was much greater than those of α-emitters, and the β-emitter ⁴⁰K was present in the STPs with both the greatest radioactivity and mass concentrations. Since the three radionuclides included in the FDA’s HPHC list were either not detected (²³⁵U), identified in only three of 78 samples (²³⁸U), and/or had activity levels over fifty times lower than that of ⁴⁰K (²¹⁰Po, ²³⁸U), there may be a rationale for reconsidering the radionuclides currently included in the FDA HPHC list, particularly with respect to ⁴⁰K. Using a model of the physical and biological compartments which must be considered to estimate the exposure of STP users to radionuclides, we conclude that exposure from α-emitters may be minimal to STP users, but ⁴⁰K in particular may expose the oral cavities of STP users to β-radiation. Although a more comprehensive picture of the radioisotope content of STPs has emerged from this study, epidemiological evidence suggests that the levels of radionuclides measured in this study appear unlikely to present significant risks to STP users.     

Two New Degraded Triterpenoids and a Novel seco‐Norabietane Diterpene from the Root Bark of Azadirachta indica

Three new compounds, the degraded ring C‐seco‐tetranortriterpenoid nimbolicidin ( 1 ), the degraded hexanortriterpenoid nimbocin ( 2 ), and the seco‐norabietane diterpene nimbocinin ( 3 ), were isolated from the root bark of Azadirachta indica A.Juss . Compound 1 is O‐bearing both at C(28) and C(29), which has been hitherto unreported in tetranortriterpenoids; 2 represents the first hexanortriterpenoid with a truncated apotirucallane (or apoeuphane) skeleton; 3 is an unprecedented seco‐norabietane. Spectroscopic data and chemical transformations of these compounds provided their complete structures.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Stability and efficiency of supported liquid membranes in electromembrane extraction—a link to solvent properties

The current work presents a large systematic screening of 61 possible organic solvents used as supported liquid membranes (SLM) in electromembrane extraction (EME). For each organic solvent, recovery, current across the SLM, and stability considerations have been investigated and correlated to relevant solvent properties through partial least square regression analysis. The five unpolar basic drugs pethidine, haloperidol, methadone, nortriptyline, and loperamide were used as model analytes. Efficient EME solvents were found to have a low water solubility (<0.5 g L^?1) and belonged to cluster 2 of a Kamlet–and–Taft-based solvent classification system (high dipole moments and proton acceptor properties). These parameters were especially found in nitroaromatic compounds and ketones. Small molecules with low log P value and high water solubility were unsuitable, as they tended to give unstable extractions, caused by a high current across the SLM. This was often combined with substantial solvent-related interferences and the generation of an electroosmotic flow across the SLM, with resulting acceptor solution expansion. Large molecules with a high log P value were classified as inefficient. For these solvents, no current was measured across the SLM and no analytes were extracted. This is the first time systematic knowledge on the SLM in EME has been gathered and investigated, and the presented results could be highly beneficial for future development and optimization of EME.