Estimating lean mass over a wide range of body composition: a calibration of deuterium dilution in the arctic ground squirrel

Calculating body water through isotope dilution has become a useful way to nondestructively estimate body composition in many species. The most accurate estimates using this method require calibration against proximate chemical analysis of body composition for individual species, but no studies to our knowledge have calibrated this method on a hibernating mammal that seasonally undergoes dramatic changes in body composition. We use deuterium oxide to estimate total body water in captive arctic ground squirrels, Urocitellus parryii, and compare two approaches of calculating lean mass from total body water, both calibrated against lean mass based on proximate analysis. The first method uses a single tissue hydration constant to calculate lean mass from total body water; the second method uses a predictive equation to calculate lean mass from total body water and body mass. We found that the predictive equation performs better over the large range of body composition common to this species. Distillation of blood samples did not affect lean mass estimates from either calculation method. These findings indicate that isotope dilution using a predictive equation should work well as an alternative to destructive methods in other small mammals that undergo radical changes in body composition across their annual cycle.     

On <Emphasis Type="Italic">g</Emphasis>-functions for Laguerre function expansions of Hermite type

We examine weighted L ^p boundedness of g-functions based on semigroups related to multi-dimensional Laguerre function expansions of Hermite type. A technique of vector-valued Calderón–Zygmund operators is used.     

Effect of strain on stripe phases in the quantum Hall regime

Preferential orientation of the stripe phases in the quantum Hall (QH) regime has remained a puzzle since its discovery. We show experimentally and theoretically that the direction of high and low resistance of the two-dimensional (2D) hole gas in the QH regime can be controlled by an external strain. Depending on the sign of the in-plane shear strain, the Hartree-Fock energy of holes or electrons is minimized when the charge density wave (CDW) is oriented along the [110] or [110] directions. We suggest that shear strains due to internal electric fields in the growth direction are responsible for the observed orientation of CDW in pristine electron and hole samples.     

Catalytic protein modification with dirhodium metallopeptides: specificity in designed and natural systems

In this study, we present advances in the use of rhodium(II) metallopeptides for protein modification. Site-specific, proximity-driven modification is enabled by the unique combination of peptide-based molecular recognition and a rhodium catalyst capable of modifying a wide range of amino-acid side chains. We explore catalysis based on coiled-coil recognition in detail, providing an understanding of the determinants of specificity and culminating in the demonstration of orthogonal modification of separate proteins in cell lysate. In addition, the concepts of proximity-driven catalysis are extended to include modification of the natural Fyn SH3 domain with metallopeptides based on a known proline-rich peptide ligand. The development of orthogonal catalyst-substrate pairs for modification in lysate, and the extension of these methods to new natural protein domains, highlight the capabilities for new reaction design possible in chemical approaches to site-specific protein modification.     

Magic-angle-spinning NMR of the drug resistant S31N M2 proton transporter from influenza A

We report chemical shift assignments of the drug-resistant S31N mutant of M2(18-60) determined using 3D magic-angle-spinning (MAS) NMR spectra acquired with a (15)N-(13)C ZF-TEDOR transfer followed by (13)C-(13)C mixing by RFDR. The MAS spectra reveal two sets of resonances, indicating that the tetramer assembles as a dimer of dimers, similar to the wild-type channel. Helicies from the two sets of chemical shifts are shown to be in close proximity at residue H37, and the assignments reveal a difference in the helix torsion angles, as predicted by TALOS+, for the key resistance residue N31. In contrast to wild-type M2(18-60), chemical shift changes are minimal upon addition of the inhibitor rimantadine, suggesting that the drug does not bind to S31N M2.     

Coherence control of Hall charge and spin currents

Using two-color optical coherence control techniques in intrinsic GaAs at 80 K with orthogonally polarized 70 fs, 1430 and 715 nm pulses, we generate a pure spin source current that yields a transverse Hall pure charge current; or alternatively, with parallel polarized pulses, we generate a pure charge source current that yields a pure spin current. By varying the relative phase or polarization of the incident pulses, one can effectively tune the type, magnitude and direction of both the source and transverse currents without application of electric or magnetic fields.     

Measurement of tobramycin by reversed-phase high-performance liquid chromatography with mass spectrometry detection

Analysis of tobramycin faces challenges owing to its significant basicity, hydrophilicity and lack of a UV absorbing chromophore. Chromatographic methods, coupled with derivatization to introduce chromophores for tobramycin analysis, were extensively studied. A direct reversed-phase HPLC method for tobramycin analysis has not been reported. Here, we would like to report a simple LC/MS method for quantitative analysis of tobramycin in pharmaceutical formulations. Reversed-phase HPLC analysis of tobramycin was achieved using a pH stable C18 column with basic (pH 11) aqueous mobile phase (ammonium hydroxide buffer), while direct detection was carried out employing a single quadruple mass detector in negative mode via electrospray ionization. This unique separation-detection combination provided simple and specific determination of tobramycin. This method was found to be linear at a tobramycin concentration range of 0.2-0.8 mg/mL with a correlation coefficient value of 0.999. The quantitation limit and detection limit were calculated as 0.210 and 0.063 μg/mL, respectively, with 99.994% confidence. This method was successfully applied to measure tobramycin content in matrices containing tobramycin and other pharmaceutical formulation ingredients. Recoveries of 101.8, 97.8 and 106.7% were obtained for tobramycin spiked in the pharmaceutical formulation at concentrations of 1.68, 1.0 and 0.35 mg/mL, respectively. The relative standard deviations for six injections of spiked samples ranged from 0.2 to 3.2%, indicating good method repeatability.