Determination of enantiomeric purity of the new D-2 dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) by reversed-phase high-performance liquid chromatography after pre-column derivatization with D(+)-glucuronic acid

This paper describes an enzymic derivatization procedure that allows accurate determination of very small amounts of enantiomeric impurities in the D-2 dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437). After pre-column glucuronidation of the individual enantiomers, two diastereoisomers were formed which were separated by reversed-phase high-performance liquid chromatography. An enantiomeric purity of 99.84% was calculated for the (-)-enantiomer, against 99.89% for the (+)-enantiomer. The assay was validated by spiking 1% of the (-)-enantiomer in the (+)-enantiomer. A high accuracy (error 4.5%) and precision (coefficient of variation 2.9%, n = 5) of the method were established.     

Pulse rise-time characterization of a high pressure xenon gamma detector for use in resolution enhancement

High pressure xenon ionization chamber detectors are possible alternatives to traditional thallium doped sodium iodide [NaI(Tl)] and hyperpure germanium as gamma-spectrometers in certain applications. Xenon detectors incorporating a Frisch grid exhibit energy resolutions comparable to cadmium/zinc/telluride (CZT) (e.g., 2% @ 662 keV) but with far greater sensitive volumes. The Frisch grid reduces the position dependence of the anode pulse rise-times, but it also increases the detector vibration sensitivity, anode capacitance, voltage requirements and mechanical complexity. We have been investigating the possibility of eliminating the grid electrode in high-pressure xenon detectors and preserving the high energy resolution using electronic rise-time compensation methods. A two-electrode cylindrical high pressure xenon gamma-detector coupled to time-to-amplitude conversion electronics was used to characterize the pulse rise-time of deposited gamma-photons. Time discrimination was used to characterize the pulse rise-time versus photo peak position and resolution. These data were collected to investigate the effect of pulse rise-time compensation on resolution and efficiency.     

Moisture Stability of Perovskite Solar Cells Processed in Supercritical Carbon Dioxide

Performance degradation under environmental conditions currently limits the practical utility of perovskite-based solar cells. The moisture stability of CH₃NH₃PbI₃ perovskite films and solar cells was measured during exposure to three different levels of relative humidity. The films were crystallized at two different temperatures with and without simultaneous exposure to supercritical carbon dioxide. The film crystallinity, optical absorption, and device photoconversion efficiency was measured over time for three relative humidity levels and both crystallization methods. It was determined that film crystallization in supercritical CO₂ resulted in significant improvement in moisture stability for films processed at 50 °C, but negligible improvement in stability for films processed at 100 °C.     

Halogen Bonding in Solution: Anion Recognition,Templated Self‐Assembly,and Organocatalysis

The halogen bond is a supramolecular interaction between a Lewis‐acidic region of a covalently bound halogen and a Lewis base. It has been studied widely in silico and experimentally in the solid state; however, solution‐phase applications have attracted enormous interest in the last few years. This Minireview highlights selected recent developments in halogen bond interactions in solution, with a focus on the use of receptors based on halogen bonds in anion recognition and sensing, anion‐templated self‐assembly, as well as in organocatalysis.     

Development of a high-pressure xenon ionization chamber gamma-ray spectrometer for field deployment in cone penetrometers

It is sometimes necessary to measure gamma-ray spectra under difficult circumstances such as those encountered during in situ characterization of radioactive soils. For some classes of soil, various measurement instruments can be inserted to depths of 100 feet or more using the cone penetrometer technique. The problems for gamma-ray spectroscopy in this application include size limitations, elevated and/or variable temperature environment, vibration and shock, and remote operation. Measurement of gamma-ray spectra under these conditions has been done using scintillation detectors such as NaI(Tl) or BGO. However, these instruments suffer from poor energy resolution (ca. 8-10%), temperature sensitivity and, in the case of NaI(Tl), activation by neutrons. Sentor Technologies, Inc., working under Department of Energy sponsorship and in conjunction with Virginia Commonwealth University and the University of California, San Diego, has developed a high-pressure xenon ionization chamber spectrometer that is specifically designed for use in cone penetrometers. Key features of the detector design include a 29 mm O.D. cylindrical geometry with concentric cathode, Frisch grid, and anode, and ultra-purified (ca. ppb) xenon pressurized to a density of 0.6 g·cm^-3. The results demonstrate the utility of high-pressure xenon ionization spectrometers for field use in cone penetrometers or similar applications including borehole logging.     

Biased AC Electrospinning of Aligned Polymer Nanofibers

A new method is reported for minimizing the inherent fiber instability in the electrospinning process. The method, dubbed “biased AC electrospinning”, employs a combination of DC and AC potentials and results in highly‐aligned mats of polymer or composite polymer fibers. The relationship between specific processing variables such as the AC frequency and the magnitude of the DC offset was investigated and related to the resulting fiber stability and uniformity. For optimum fiber stability, the AC frequency must fall within a relatively narrow range. The upper and lower frequency limits were measured for a small group of polymers and polymer composites and were qualitatively related to solution properties and processing variables. Potential applications of well‐ordered nanofiber materials include tissue engineering, filtration, drug delivery, and microelectronics.

     

Adjoint for operators in Banach spaces

In this paper we show that a result of Gross and Kuelbs, used to study Gaussian measures on Banach spaces, makes it possible to construct an adjoint for operators on separable Banach spaces. This result is used to extend well-known theorems of von Neumann and Lax. We also partially solve an open problem on the existence of a Markushevich basis with unit norm and prove that all closed densely defined linear operators on a separable Banach space can be approximated by bounded operators. This last result extends a theorem of Kaufman for Hilbert spaces and allows us to define a new metric for closed densely defined linear operators on Banach spaces. As an application, we obtain a generalization of the Yosida approximator for semigroups of operators.