Molecular dynamic heterogeneity of confined lipid films by 1H magnetization-exchange nuclear magnetic resonance

The molecular dynamic heterogeneity of monolayer to submonolayer thin lecithin films confined to submicron cylindrical pores were investigated by 1H magnetization exchange nuclear magnetic resonance. In this experiment a z-magnetization gradient was generated by a double-quantum dipolar filter. The magnetization-exchange decay and buildup curves were interpreted with the help of a theoretical model based on the approximation of a one-dimensional spin-diffusion process in a three-domain morphology. The dynamic heterogeneity of the fatty acid chains and the effects of the surface area per molecule, the diameter of the pores, and the temperature were characterized with the help of local spin-diffusion coefficients. The effect of various parameters on the molecular dynamics of the mobile region of the fatty acid chains was quantified by introducing an ad hoc Gaussian distribution function of the 1H residual dipolar couplings. For the lipid films investigated in this study, the surface induced order and the geometrical confinement affect the chain dynamics of the entire molecule. Therefore, each part of the chain independently reflects the effect of surface coverage, pore size, and temperature.     

Highly sensitive method for the determination of ropinirole with a lower limit of quantitation of 3.45 pg/mL in human plasma by LC‐ESI‐MS/MS: application to a clinical pharmacokinetic study

A highly sensitive, rapid assay method has been developed and validated for the estimation of ropinirole (RPR) in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. A solid‐phase process was used to extract RPR and citalopram (internal standard, IS) from human plasma. Chromatographic separation was operated with 0.2% ammonia solution:acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on a Hypurity C₁₈ column with a total run time of 3.2 min. The MS/MS ion transitions monitored were 261.2 → 114.2 for RPR and 325.1 → 209.0 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 3.45 pg/mL and the linearity was observed from 3.45 to 1200 pg/mL. The intra‐day and inter‐day precisions were in the range of 4.71–7.98 and 6.56–8.31%, respectively. This novel method has been applied to a pharmacokinetic study of RPR in humans. Copyright © 2008 John Wiley & Sons, Ltd.     

High-temperature ferromagnetism in Zn1−xMnxO semiconductor thin films

Clear evidence of ferromagnetic behavior at temperatures >400 K as well as spin polarization of the charge carriers have been observed in Zn_1−xMn_xO thin films grown on Al₂O₃ and MgO substrates. The magnetic properties depended on the exact Mn concentration and the growth parameters. In well-characterized single-phase films, the magnetic moment is 4.8 μ_B/Mn at 350 K, the highest moment yet reported for any Mn doped magnetic semiconductor. Anomalous Hall effect shows that the charge carriers (electrons) are spin-polarized and participate in the observed ferromagnetic behavior.     

Roe linearization for the Euler equations augmented by the convective terms from the k–ω turbulence model

This paper describes the method of calculation of the eigenvalues, eigenvectors of the Jacobian matrix of the Euler equations augmented by the convective part of k–ω turbulence model. The equations are 3D and values are expressed in terms of cell normals of a finite volume. The expressions for wave strengths are also found, which are also necessary to calculate the inter‐cell fluxes for Roe's scheme. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetics of oxidation of pantothenic acid by chloramine‐T in perchloric acid and in alkaline medium catalyzed by OsO4: A mechanistic approach

Kinetics of oxidation of pantothenic acid (PA) by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) in the presence of HClO₄ and NaOH (catalyzed by OsO₄) has been investigated at 313 K. The stoichiometry and oxidation products are same in both media; however, their kinetic patterns were found to be different. In acid medium, the rate shows first‐order dependence on [CAT]_o, fractional‐order dependence on [PA]_o, and inverse fractional‐order on [H⁺]. In alkaline medium, the rate shows first‐order dependence each on [CAT]_o and [PA]_o and fractional‐order dependence on each of [OH^?] and [OsO₄]. Effects of added p‐toluenesulfonamide and halide ions, varying ionic strength, and dielectric constant of medium as well as solvent isotope on the rate of reaction have been investigated. Activation parameters were evaluated, and the reaction constants involved in the mechanisms have been computed. The proposed mechanisms and the derived rate laws are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 201–210, 2005     

Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel

A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2) of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and pitching moment components.      

Band‐selective excited ultrahigh resolution PSYCHE‐TOCSY: fast screening of organic molecules and complex mixtures

Precise assignments of ¹H atomic sites and establishment of their through‐bond COSY or TOCSY connectivity are crucial for molecular structural characterization by using ¹H NMR spectroscopy. However, this exercise is often hampered by signal overlap, primarily because of ¹H–¹H scalar coupling multiplets, even at typical high magnetic fields. The recent developments in homodecoupling strategies for effectively suppressing the coupling multiplets into nice singlets (pure‐shift), particularly, Morris's advanced broadband pure‐shift yielded by chirp excitation (PSYCHE) decoupling and ultrahigh resolution PSYCHE‐TOCSY schemes, have shown new possibilities for unambiguous structural elucidation of complex organic molecules. The superior broadband PSYCHE‐TOCSY exhibits enhanced performance over the earlier TOCSY methods, which however warrants prolonged experimental times due to the requirement of large number of dwell increments along the indirect dimension. Herein, we present fast and band‐selective analog of the broadband PSYCHE‐TOCSY, which is useful for analyzing complex organic molecules that exhibit characteristic yet crowded spectral regions. The simple pulse scheme relies on band‐selective excitation (BSE) followed by PSYCHE homodecoupling in the indirect dimension. The BSE‐PSYCHE‐TOCSY has been exemplified for Estradiol and a complex carbohydrate mixture comprised of six constituents of closely comparable molecular weights. The experimental times are greatly reduced viz., ~20 fold for Estradiol and ~10 fold for carbohydrate mixture, with respect to the broadband PSYCHE‐TOCSY. Furthermore, unlike the earlier homonuclear band‐selective decoupling, the BSE‐PSYCHE‐decoupling provides fully decoupled pure‐shift spectra for all the individual chemical sites within the excited band. The BSE‐PSYCHE‐TOCSY is expected to have significant potential for quick screening of complex organic molecules and mixtures at ultrahigh resolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Lower Bounds on Scalar Dissipation in Bounded Rectilinear Flows

Lower bounds on the scalar dissipation rate in rectilinear flows are found for three sets of constraints. The bounding dissipation rates provide upper bound estimates of the scalar concentration variance. One of the lower bounds on the dissipation rate is close to the dissipation rate assessed from detailed numerical simulation. This proximity enables a simplified model of concentration variance. For a pulse input of solute, the predictions of concentration variance by the simplified model are in agreement with the results of detailed simulation. The large-time bimodality of the concentration variance and its rate of decay observed in the detailed numerical simulations is predicted by the simplified model.     

The Efficient Palladium-Catalyzed Selective t Synthesis of Benzenesulfonic Acids

α-Chloroalkyl aryl ethers has been obtained in good yields from phenols and aryl α-chloroalkyl sulfides.