Collisional broadening of Ba I line (553.5 nm) by He or Ar

The Doppler-free line shape of the 6s ^{2 1} S ₀ – 6s ¹6p ^{1 1} P ₁ transition at 553.5 nm in natural Ba in the presence of an argon or helium buffer gas has been measured at 744 K for gas pressures from 0.2 to 100 Torr. Using the measured data for pressures above 5 Torr, the broadening rate coefficients for the half width at half maximum (HWHM) are determined to be (4.9±0.5)10^–9 and (5.0±0.5)10^–9 s^–1 cm^–3 for helium and argon respectively.     

DEB-FAPy-dG Adducts of 1,3-Butadiene: Synthesis,Structural Characterization,and Formation in 1,2,3,4-Diepoxybutane Treated DNA**

Metabolic activation of the human carcinogen 1,3-butadiene (BD) by cytochrome 450 monooxygenases gives rise to a genotoxic diepoxide, 1,2,3,4-diepoxybutane (DEB). This reactive electrophile alkylates guanine bases in DNA to produce N7-(2-hydroxy-3,4-epoxy-1-yl)-dG (N7-DE-dG) adducts. Because of the positive charge at the N7 position of the purine heterocycle, N7-DEB-dG adducts are inherently unstable and can undergo spontaneous depurination or base-catalyzed imidazole ring opening to give N⁶-[2-deoxy-D-erythro-pentofuranosyl]-2,6-diamino-3,4-dihydro-4-oxo-5-N-1-(oxiran-2-yl)propan-1-ol-formamidopyrimidine (DEB-FAPy-dG) adducts. Here we report the first synthesis and structural characterization of DEB-FAPy-dG adducts. Authentic standards of DEB-FAPy-dG and its ¹⁵N₃-labeled analogue were used for the development of a quantitative nanoLC-ESI⁺-HRMS/MS method, allowing for adduct detection in DEB-treated calf thymus DNA. DEB-FAPy-dG formation in DNA was dependent on DEB concentration and pH, with higher numbers observed under alkaline conditions.     

Hole‐transporting host‐polymer series consisting of triphenylamine basic structures for phosphorescent polymer light‐emitting diodes

A series of novel styrene derived monomers with triphenylamine‐based units, and their polymers have been synthesized and compared with the well‐known structure of polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine with respect to their hole‐transporting behavior in phosphorescent polymer light‐emitting diodes (PLEDs). A vinyltriphenylamine structure was selected as a basic unit, functionalized at the para positions with the following side groups: diphenylamine, 3‐methylphenyl‐aniline, 1‐ and 2‐naphthylamine, carbazole, and phenothiazine. The polymers are used in PLEDs as host polymers for blend systems with the following device configuration: glass/indium–tin–oxide/PEDOT:PSS/polymer‐blend/CsF/Ca/Ag. In addition to the hole‐transporting host polymer, the polymer blend includes a phosphorescent dopant [Ir(Me‐ppy)₃] and an electron‐transporting molecule (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole). We demonstrate that two polymers are excellent hole‐transporting matrix materials for these blend systems because of their good overall electroluminescent performances and their comparatively high glass transition temperatures. For the carbazole‐substituted polymer (T_g = 246 °C), a luminous efficiency of 35 cd A^?1 and a brightness of 6700 cd m^?2 at 10 V is accessible. The phenothiazine‐functionalized polymer (T_g = 220 °C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well‐known polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A^?1 and a brightness of 2500 cd m^?2 (10 V). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3417–3430, 2010     

High resolution electrospray ionization ion mobility spectrometry

Current commercially available ion mobility spectrometers are intended for the analysis of chemicals in the gas phase. Sample introduction methods, such as direct air sampling, a GC injector or a thermal desorber, are commonly an integral part of these instruments. This paper describes an electrospray ionization ion mobility spectrometer system that allows direct introduction samples in solution phase. This allows direct analysis of non-volatile organic and biological samples, and avoids decomposition of thermally liable samples, providing reliable chemical identification. In addition, the new ion mobility spectrometer allows mobility analysis with high resolving power. Commonly used commercial IMS systems provide resolving powers between 10 and 30; this new ion mobility spectrometer has resolving power greater than 60 for routine analysis. A high resolution instrument is necessary for many applications where a complex mixture needs to be separated and quantified. This paper demonstrates the advantages of using a high resolution ion mobility spectrometer and an electrospray ionization source for the analysis of non-volatile pharmaceuticals as well as dissolved explosive in solution phase.     

Structural fluctuations and excitation transfer between adenine and 2-aminopurine in single-stranded deoxytrinucleotides

Steady-state fluorescence measurements on the deoxytrinucleotides (5')dTp2APpA(3') and (5')dAp2APpA(3') show a temperature-dependence and a viscosity-dependence for energy transfer that qualitatively differ from those seen in our previous study of charge transfer (CT) in these systems. Time-resolved anisotropy studies and molecular dynamics simulations are presented that provide a detailed characterization of the structural dynamics of these systems and how these fluctuations modulate the electronic interaction between 2AP and its neighbors. To gain quantitative insight into the interplay of conformational fluctuations and stacking-induced energy transfer, we present results from a new hybrid quantum-classical simulation method for computing the A --> 2AP energy transfer rate that makes use of the full three-dimensional nature of the donor and acceptor transition densities. Analysis of the results shows that the standard transition dipole-transition dipole approximation for the Coulombic coupling substantially overestimates the transfer rate and that the nearest neighbor energy transfer from adenine to 2AP occurs on a much faster time scale than that for CT. This suggests that, unlike the CT dynamics where conformational "gating" plays a critical role, the large amplitude fluctuations that modulate the process are largely "frozen" out on the energy transfer time scale.     

Club isomorphisms on higher Aronszajn trees

We prove the consistency, assuming an ineffable cardinal, of the statement that CH holds and any two normal countably closed ${\omega }_2$-Aronszajn trees are club isomorphic. This work generalizes to higher cardinals the property of Abraham–Shelah [1] that any two normal ${\omega }_1$-Aronszajn trees are club isomorphic, which follows from PFA. The statement that any two normal countably closed ${\omega }_2$-Aronszajn trees are club isomorphic implies that there are no ${\omega }_2$-Suslin trees, so our proof also expands on the method of Laver–Shelah [5] for obtaining the ${\omega }_2$-Suslin hypothesis.     

Obituary: Professor Valery Privalko

Gold decoration was applied to elucidate the morphology of annealed and unannealed oriented structures produced by shearing of polyethylene single crystals of known thicknesses, and the morphology of drawn and undrawn “shish kebabs” obtained by stirrer-induced crystallization. Distinct Au periodicities were observed perpendicular and parallel to the unannealed oriented structure, revealing distinctly the presence of microfibrils and an alternation of crystalline and noncrystalline regions within a given microfibril of which the periodicity is, however, found to be much larger than the corresponding original crystal thickness. Annealing resulted in fibrils being completely replaced by lamellae standing edgewise with the Au particles decorating directly on top of the edge but concentrated mainly on the folds leaving the crystalline region almost entirely void of gold. Deformation studies revealed an unusual ductility associated with the shish kebab structure, with the kebab splitting first, then disappearing with increasing elongation, and finally, resulting in a uniform fiber. The kebab disappearance implies that it is molecularly integrated with the interkebab material and not a completely separate chain-folded lamella attached to it. Distinct Au periodicities were observed perpendicular and parallel to the drawn shish-kebab fibers similar to the sheared single crystals. Annealing experiments and the high ductility suggest that the interkebab material is not of a fully extended-chain morphology.     

Phase transitions in calcium nitrate thin films

Calcium carbonate is a ubiquitous mineral and its reactivity with indoor and outdoor air pollutants will contribute to the deterioration of these materials through the formation of salts that deliquesce at low relative humidity (RH). As shown here for calcium nitrate thin films, deliquescence occurs at even lower relative humidity than expected from bulk thermodynamics and lower than the recommended humidity for the preservation of artifacts and antiques.     

A Theoretical Model of Pulmonary Surfactant Multilayer Collapse under Oscillating Area Conditions

Monolayers of adsorbed pulmonary surfactant collapse under compression and respread to the interface when the area expands. These mechanisms contribute to the large area hysteresis seen experimentally in a pulsating bubble surfactometer. This paper presents an analytical model which adds monolayer collapse and respreading to the more standard transport processes (diffusion, adsorption, and desorption). The model is robust and can mimic a large range of responses, from that of an insoluble monolayer to the large area hysteresis indicative of collapse and respreading. Our model suggests that multilayer dynamics are necessary to mimic the ultralow surface tensions of pulmonary surfactant. Copyright 2000 Academic Press.