Chirally-modified metal surfaces: energetics of interaction with chiral molecules

Imparting chirality to non-chiral metal surfaces by adsorption of chiral modifiers is a highly promising route to create effective heterogeneously catalyzed processes for the production of enantiopure pharmaceuticals. One of the major current challenges in heterogeneous chiral catalysis is the fundamental-level understanding of how such chirally-modified surfaces interact with chiral and prochiral molecules to induce their enantioselective transformations. Herein we report the first direct calorimetric measurement of the adsorption energy of chiral molecules onto well-defined chirally-modified surfaces. Two model modifiers 1-(1-naphthyl)ethylamine and 2-methylbutanoic acid were used to impart chirality to Pt(111) and their interaction with propylene oxide was investigated by means of single-crystal adsorption calorimetry. Differential adsorption energies and absolute surface uptakes were obtained for the R- and S-enantiomers of propylene oxide under clean ultrahigh vacuum conditions. Two types of adsorption behavior were observed for different chiral modifiers, pointing to different mechanisms of imparting chirality to metal surfaces. The results are analyzed and discussed in view of previously reported stereoselectivity of adsorption processe

NMR Determination of 2D Electron Spin Polarization at ν=1/2\nu=1/2

Using a `standard' NMR spin-echo technique we determined the spin polarization of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature and magnetic field dependencies of spin polarization at Landau level filling factor $\nu =1/2$, we find that the results are described well by a simple model of non-interacting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.Comment: 4 pages (REVTEX) AND 4 figures (PS

The Intrinsic Origin of Spin Echoes in Dipolar Solids Generated by Strong Pi Pulses

In spectroscopy, it is conventional to treat pulses much stronger than the linewidth as delta-functions. In NMR, this assumption leads to the prediction that pi pulses do not refocus the dipolar coupling. However, NMR spin echo measurements in dipolar solids defy these conventional expectations when more than one pi pulse is used. Observed effects include a long tail in the CPMG echo train for short delays between pi pulses, an even-odd asymmetry in the echo amplitudes for long delays, an unusual fingerprint pattern for intermediate delays, and a strong sensitivity to pi-pulse phase. Experiments that set limits on possible extrinsic causes for the phenomena are reported. We find that the action of the system's internal Hamiltonian during any real pulse is sufficient to cause the effects. Exact numerical calculations, combined with average Hamiltonian theory, identify novel terms that are sensitive to parameters such as pulse phase, dipolar coupling, and system size. Visualization of the entire density matrix shows a unique flow of quantum coherence from non-observable to observable channels when applying repeated pi pulses.Comment: 24 pages, 27 figures. Revised from helpful referee comments. Added new Table IV, new paragraphs on pages 3 and 1

Measurement of direct photon emission in K+→π+π0γK^+ \to \pi^+ \pi^0 \gamma decay using stopped positive kaons

The radiative decay $K^+ \to \pi^+ \pi^0 \gamma$ ($K_{\pi 2 \gamma}$) has been measured with stopped positive kaons. A $K_{\pi 2 \gamma}$ sample containing 4k events was analyzed, and the $K_{\pi 2 \gamma}$ branching ratio of the direct photon emission process was determined to be $[6.1\pm2.5({\rm stat})\pm1.9({\rm syst})]\times 10^{-6}$. No interference pattern with internal bremsstrahlung was observed.Comment: 12 pages, 6 figures, 2 tables, to be published in Phys. Lett.

Dynamic nuclear polarization and spin-diffusion in non-conducting solids

There has been much renewed interest in dynamic nuclear polarization (DNP), particularly in the context of solid state biomolecular NMR and more recently dissolution DNP techniques for liquids. This paper reviews the role of spin diffusion in polarizing nuclear spins and discusses the role of the spin diffusion barrier, before going on to discuss some recent results.Comment: submitted to Applied Magnetic Resonance. The article should appear in a special issue that is being published in connection with the DNP Symposium help in Nottingham in August 200

Spectroscopic Evidence for the Localization of Skyrmions near Nu=1 as T->0

Optically pumped nuclear magnetic resonance measurements of Ga-71 spectra were carried out in an n-doped GaAs/Al0.1Ga0.9As multiple quantum well sample near the integer quantum Hall ground state Nu=1. As the temperature is lowered (down to T~0.3 K), a ``tilted plateau'' emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and Nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional skyrmions.Comment: 4 pages (REVTEX), 5 eps figures embedded in text, published versio

Test of exotic scalar and tensor interactions in K_e3 decay using stopped positive kaons

The form factors of the decay K+ --> pi0 e+ nu (K_e3) have been determined from the comparison of the experimental and Monte Carlo Dalitz distributions containing about 10^5 K_e3 events. The following values of the parameters were obtained: lambda_+ = 0.0278 +- 0.0017(stat) +- 0.0015(syst), f_S/f_+(0) = 0.0040 +- 0.0160(stat) +- 0.0067(syst) and f_T/f_+(0) = 0.019 +- 0.080(stat) +- 0.038(syst). Both scalar f_S and tensor f_T form factors are consistent with the Standard Model predictions of zero values.Comment: 10 pages, 5 figures, contributed to the proceedings of NANP Conference, Dubna, June 19-23, 200

Comparative study of perindopril and perindopril metabolite pharmacokinetics using the HPLC/MS method

Perindopril is a prodrug which is converted to an active metabolite perindoprilat in the human organism. The present study led to the development of a fast and easily reproducible procedure for simultaneous detection of perinoprilat and its metabolite in plasma using HPLC with mass-spectrometric detector (LC-MS). Detection of the target substance was performed using atmospheric pressure electrospray ionization (API-ES) techniques in negative polarity in two modes: SIM1, ion, m/z=368,10 for perindopril and SIM2, ion, m/z=339,30 for perindoprilat. Retention time of perindopril was about 2,4 min, for perindoprilat - about 1,4 min. Sample processing was performed using solid-phase extraction. The method’s limit of quantification was equal to 1 ng/ml for perindopril and 1 ng/ml for perindoprilat. The developed procedure was used to analyse pharmacokinetics and bioequivalence of medicines containing 8 mg of perindopril. Values of all calculated pharmacokinetic parameters had no statistically meaningful differences. Confidence intervals obtained fall within bioequivalence criterion (80-125% for AUC and 75-133% for Сmax и Cmax/AUC). The medicines under analysis were found to be bioequivalent

Hyperpolarized Long-T1 Silicon Nanoparticles for Magnetic Resonance Imaging

Silicon nanoparticles are experimentally investigated as a potential hyperpolarized, targetable MRI imaging agent. Nuclear T_1 times at room temperature for a variety of Si nanoparticles are found to be remarkably long (10^2 to 10^4 s) - roughly consistent with predictions of a core-shell diffusion model - allowing them to be transported, administered and imaged on practical time scales without significant loss of polarization. We also report surface functionalization of Si nanoparticles, comparable to approaches used in other biologically targeted nanoparticle systems.Comment: supporting material here: http://marcuslab.harvard.edu/Aptekar_hyper1_sup.pd

СРАВНИТЕЛЬНОЕ ИССЛЕДОВАНИЕ IN VITRO ЭКВИВАЛЕНТНОСТИ ДВУХКОМПОНЕНТНЫХ ДОЗИРОВАННЫХ АЭРОЗОЛЬНЫХ ИНГАЛЯТОРОВ С ПОМОЩЬЮ ИМПАКТОРА НОВОГО ПОКОЛЕНИЯ

Aim. To compare in vitro the aerodynamic particle size distributions of original and generic inhalers, which contain both fluticasone (FP) and salmeterol (SM).Material and methods. The Next Generation Impactor (NGI; Copley Ltd., UK) was used to assess the particle size distribution and aerosol quality of two products to determine the equivalence in the aerosol released from the device. The first formulation was Seretide (SM/FP) 25/250 μg, an original SM/FP fixed combination developed by GlaxoSmithKline. The second formulation tested was Tevacomb 25/250 μg (SM/FP), the generic SM/FP fixed combination produced by Cipla. The mass of FP and SM recovered from each stage of impactor was quantified via high performance liquid chromatography (HPLC). The impactor results were statistically evaluated by log transformation of the single data NGI. Results. Statistically significant differences were seen between the deposition profile of Seretide and Tevacomb obtained using the NGI. Evaluating the single stages results in estimation of nonequivalence for all stages except stage 5 (FP) since their confidence intervals (CI) were out of the range of the tight conventional bioequivalence limits of Ѓ} 15 % (0,85–1,18). Also differences were observed by number of parameters, including the fine particle dose (FPD), emitted dose (ED), mass median aerodynamic diameter (MMAD), and geometric standard deviation (GSD) of SM and FP. Conclusion. These in vitro findings suggest that the particle size distributions of the generic formulation Tevacomb is not equivalent to that of the original product Seretide. Тест на аэродинамическое распределение частиц моделирует in vitro процессы, происходящие при вдыхании пациентом дозы аэрозольного препарата. Цель. Сравнить in vitro эквивалентность воспроизведенного (Тевакомб) и оригинального (Серетид) дозированных аэрозольных ингаляторов, содержащих флутиказона пропионат и салметерола ксинафоат по показателю «аэродинамическое распределение частиц». Материалы и методы. Исследуемые дозированные аэрозольные ингаляторы: Серетид, 25/250 (салметерола ксинафоат/флутиказона пропионат) мкг/доза, производство ГлаксоСмитКляйн Фармасьютикалсз, Польша, и Тевакомб, 25/250 (салметерола ксинафоат/флутиказона пропионат) мкг/доза, производство Ципла Лтд, Индия. В исследовании изучали по 6 образцов каждого из наименований ингалятора. Для моделирования in vitro вдоха пациента использовали 7-ступенчатый каскадный импактор нового поколения. Скорость потока воздуха через импактор составляла 30 Ѓ} 1 л/мин. Время ввода дозы аэрозоля — 8 с. К фракции мелкодисперсных частиц относили частицы с диаметром < 5 мкм. Количественный анализ частиц флутиказона пропионата и салметерола ксинафоата, собранных на ступенях импактора, проводили в соответствии с методами, описанными в Европейской фармакопее 6-го изд. Результаты. Результаты изучения аэродинамического распределения частиц на единичных ступенях показали статистически достоверное отличие между оригинальным и воспроизведенным дозированными аэрозольными ингаляторами. На всех ступенях, за исключением 5-й (для флутиказона пропионата), 90% доверительные интервалы не укладывались в нормируемый диапазон Ѓ} 15% (0,85–1,18). Различия подтвердились при определении таких статистически значимых параметров, как массмедианный аэродинамический диаметр частиц и геометрическое стандартное отклонение от массмедианного аэродинамического диаметра, а также значений фракции мелкодисперсных частиц (ФМЧ) и величины выпущенной дозы. Для салметерола ксинафоата величины ФМЧ составляли 42,06% (оригинальный ингалятор) и 35,53% (воспроизведенный ингалятор), для флутиказона пропионата — 42,94 и 35,44%, соответственно. Заключение. Результаты теста на аэродинамическое распределение частиц показали неэквивалентность обоих дозированных аэрозольных ингаляторов, что может обусловливать различия в фармакологических эффектах данных препаратов