• Explanation of efficient quenching of molecular ion vibrational motion by ultracold atoms

      Stoecklin, T; Halvick, P; Gannouni, MA; Hochlaf, M; Kotochigova, S; Hudson, ER (2016-04-18)
      Buffer gas cooling of molecules to cold and ultracold temperatures is a promising technique for realizing a host of scientific and technological opportunities. Unfortunately, experiments using cryogenic buffer gases have found that although the molecular motion and rotation are quickly cooled, the molecular vibration relaxes at impractically long timescales. Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl+ by a laser-cooled Ca buffer gas. We perform intense close-coupling calculations that agree with the experimental result, and use both quantum defect theory and a statistical capture model to provide an intuitive understanding of the system. This result establishes that, in contrast to the commonly held opinion, there exists a large class of systems that exhibit efficient vibrational cooling and therefore supports a new route to realize the long-sought opportunities offered by molecular structure.
    • Fluorescence Spectrometric Determination of Drugs Containing alpha-Methylene Sulfone/Sulfonamide Functional Groups Using N-1-Methylnicotinamide Chloride as a Fluorogenic Agent

      Elokely, Khaled M; Eldawy, Mohamed A; Elkersh, Mohamed A; El-Moselhy, Tarek F; Elokely, Khaled M.|0000-0002-2394-021X (2011)
      <jats:p>A simple spectrofluorometric method has been developed, adapted, and validated for the quantitative estimation of drugs containing -methylene sulfone/sulfonamide functional groups using<jats:italic>N</jats:italic><jats:sup>1</jats:sup>-methylnicotinamide chloride (NMNCl) as fluorogenic agent. The proposed method has been applied successfully to the determination of methyl sulfonyl methane (MSM)<jats:bold>(1)</jats:bold>, tinidazole<jats:bold>(2)</jats:bold>, rofecoxib<jats:bold>(3)</jats:bold>, and nimesulide<jats:bold>(4)</jats:bold>in pure forms, laboratory-prepared mixtures, pharmaceutical dosage forms, spiked human plasma samples, and in volunteer's blood. The method showed linearity over concentration ranging from 1 to 150 g/mL, 10 to 1000 ng/mL, 1 to 1800 ng/mL, and 30 to 2100 ng/mL for standard solutions of<jats:bold>1</jats:bold>,<jats:bold>2</jats:bold>,<jats:bold>3</jats:bold>, and<jats:bold>4</jats:bold>, respectively, and over concentration ranging from 5 to 150 g/mL, 10 to 1000 ng/mL, 10 to 1700 ng/mL, and 30 to 2350 ng/mL in spiked human plasma samples of<jats:bold>1</jats:bold>,<jats:bold>2</jats:bold>,<jats:bold>3</jats:bold>, and<jats:bold>4</jats:bold>, respectively. The method showed good accuracy, specificity, and precision in both laboratory-prepared mixtures and in spiked human plasma samples. The proposed method is simple, does not need sophisticated instruments, and is suitable for quality control application, bioavailability, and bioequivalency studies. Besides, its detection limits are comparable to other sophisticated chromatographic methods.</jats:p>
    • Nanoparticle-Infused UHMWPE Layer as Multifunctional Coating for High-Performance PPTA Single Fibers

      Zhang, Z; Zhao, Y; Li, H; Percec, S; Yin, J; Ren, F; Ren, Fei|0000-0002-8868-4536 (2019-12-01)
      © 2019, The Author(s). High-performance fibers made of poly-(p-phenylene terephthalamide) (PPTA) with high stiffness and high strength are widely used in body armor for protection due to their high degree of molecular chain alignment along the fiber direction. However, their poor mechanical properties in the transverse direction and low surface friction are undesirable for applications requiring resistance to ballistic impact. Here we provide a simple yet effective surface engineering strategy to improve both the transverse mechanical properties and the tribological property by coating PPTA fibers with ultra-high molecular weight polyethylene (UHMWPE) embedded with silica nanoparticles. The coated-PPTA fiber shows remarkable enhancement in transverse mechanical properties including ~127% increase of Young’s modulus, which is attributed to both the alignment of UHMWPE chains in the transverse direction and the embeded ceramic nanoparticles. Meanwhile, the surface friction of the coated fiber increases twofold as a result of the ceramic nanoparticles. In addition, the coated fibers exhibit an enhanced chemical resistance to external harsh environment. The improved transverse mechanical properties, surface frictional characteristics, and chemical resistance demonstrate that coating with UHMWPE and ceramic nanoparticles can be used as an effective approach to enhance the performance of PPTA and other high-performance polymer fibers for body armor applications.
    • Pyrite-induced hydroxyl radical formation and its effect on nucleic acids

      Cohn, CA; Mueller, S; Wimmer, E; Leifer, ND; Greenbaum, S; Strongin, DR; Schoonen, MAA; Strongin, Daniel R.|0000-0002-1776-5574 (2006-04-04)
      Background: Pyrite, the most abundant metal sulphide on Earth, is known to spontaneously form hydrogen peroxide when exposed to water. In this study the hypothesis that pyrite-induced hydrogen peroxide is transformed to hydroxyl radicals is tested. Results: Using a combination of electron spin resonance (ESR) spin-trapping techniques and scavenging reactions involving nucleic acids, the formation of hydroxyl radicals in pyrite/aqueous suspensions is demonstrated. The addition of EDTA to pyrite slurries inhibits the hydrogen peroxide-to-hydroxyl radical conversion, but does not inhibit the formation of hydrogen peroxide. Given the stability of EDTA chelation with both ferrous and ferric iron, this suggests that the addition of the EDTA prevents the transformation by chelation of dissolved iron species. Conclusion: While the exact mechanism or mechanisms of the hydrogen peroxide-to-hydroxyl radical conversion cannot be resolved on the basis of the experiments reported in this study, it is clear that the pyrite surface promotes the reaction. The formation of hydroxyl radicals is significant because they react nearly instantaneously with most organic molecules. This suggests that the presence of pyrite in natural, engineered, or physiological aqueous systems may induce the transformation of a wide range of organic molecules. This finding has implications for the role pyrite may play in aquatic environments and raises the question whether inhalation of pyrite dust contributes to the development of lung diseases. © 2006 Cohn et al; licensee BioMed Central Ltd.
    • Robust singlet fission in pentacene thin films with tuned charge transfer interactions

      Broch, K; Dieterle, J; Branchi, F; Hestand, NJ; Olivier, Y; Tamura, H; Cruz, C; Nichols, VM; Hinderhofer, A; Beljonne, D; Spano, FC; Cerullo, G; Bardeen, CJ; Schreiber, F (2018-12-01)
      © 2018 The Author(s). Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.
    • The effect of adsorbed lipid on pyrite oxidation under biotic conditions

      Hao, J; Cleveland, C; Lim, E; Strongin, DR; Schoonen, MAA; Strongin, Daniel R.|0000-0002-1776-5574 (2006-07-25)
      The chemolithoautotrophic bacterium, Acidithiobacillus ferrooxidans, commonly occurs in acid mine drainage (AMD) environments where it is responsible for catalyzing the oxidation of pyrite and concomitant development of acidic conditions. This investigation reports on the growth of this bacterial species on the pyrite surface and in the aqueous phase at a pH close to 2 as well as the role of adsorbed lipid in preventing pyrite dissolution. Both acid washed pyrite and acid-washed pyrite coated with lipids were used as substrates in the studies. The choice of lipid, 1,2-bis(10, 12-tricosadiynoyl)-sn-Glycero-3-Phosphocholine lipid (23:2 Diyne PC), a phosphocholine lipid, was based on earlier work that showed that this lipid inhibits the abiotic oxidation rate of pyrite. Atomic force microscopy showed that under the experimental conditions used in this study, the lipid formed ∼4-20 nm layers on the mineral surface. Surface-bound lipid greatly suppresses the oxidation process catalyzed by A. ferrooxidans. This suppression continued for the duration of the experiments (25 days maximum). Analysis of the bacterial population on the pyrite surface and in solution over the course of the experiments suggested that the pyrite oxidation was dependent in large part on the fraction of bacteria bound to the pyrite surface. © 2006 Hao et al; licensee BioMed Central Ltd.
    • Tunable two-dimensional interfacial coupling in molecular heterostructures

      Xu, B; Chakraborty, H; Yadav, VK; Zhang, Z; Klein, ML; Ren, S (2017-12-01)
      © 2017 The Author(s). Two-dimensional van der Waals heterostructures are of considerable interest for the next generation nanoelectronics because of their unique interlayer coupling and optoelectronic properties. Here, we report a modified Langmuir-Blodgett method to organize two-dimensional molecular charge transfer crystals into arbitrarily and vertically stacked heterostructures, consisting of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)/C60 and poly(3-dodecylthiophene-2,5-diyl) (P3DDT)/C60 nanosheets. A strong and anisotropic interfacial coupling between the charge transfer pairs is demonstrated. The van der Waals heterostructures exhibit pressure dependent sensitivity with a high piezoresistance coefficient of -4.4 × 10-6 Pa-1, and conductance and capacitance tunable by external stimuli (ferroelectric field and magnetic field). Density functional theory calculations confirm charge transfer between the n-orbitals of the S atoms in BEDT-TTF of the BEDT-TTF/C60 layer and the πorbitals of C atoms in C60 of the P3DDT/C60 layer contribute to the inter-complex CT. The two-dimensional molecular van der Waals heterostructures with tunable optical-electronic-magnetic coupling properties are promising for flexible electronic applications.
    • Universality and chaoticity in ultracold K+KRb chemical reactions

      Croft, JFE; Makrides, C; Li, M; Petrov, A; Kendrick, BK; Balakrishnan, N; Kotochigova, S; Li, Ming|0000-0003-0827-5976 (2017-07-19)
      © The Author(s) 2017. A fundamental question in the study of chemical reactions is how reactions proceed at a collision energy close to absolute zero. This question is no longer hypothetical: quantum degenerate gases of atoms and molecules can now be created at temperatures lower than a few tens of nanokelvin. Here we consider the benchmark ultracold reaction between, the most-celebrated ultracold molecule, KRb and K. We map out an accurate ab initio ground-state potential energy surface of the K2Rb complex in full dimensionality and report numerically-exact quantum-mechanical reaction dynamics. The distribution of rotationally resolved rates is shown to be Poissonian. An analysis of the hyperspherical adiabatic potential curves explains this statistical character revealing a chaotic distribution for the short-range collision complex that plays a key role in governing the reaction outcome.
    • Visualizing the structural evolution of LSM/xYSZ composite cathodes for SOFC by in-situ neutron diffraction

      Chen, Y; Yang, L; Ren, F; An, K; Ren, Fei|0000-0002-8868-4536 (2014-06-05)
      Thermal stability of composite cathodes for solid oxide fuel cells, the mixtures of (La0.8Sr0.2)0.95MnO 32-δ (LSM) and (Y2O3) x(ZrO2)1-x (xYSZ, x = 3, 6, 8 and 10), is determined using in-situ neutron diffraction. Thanks to the most advanced high flux neutron source, our work highlights the visualization of the phase evolutions in heterogeneous material systems at high temperatures, along with the analysis of the diffusion activities of transition metal ions that reveal the reaction mechanism and kinetics. It is found that the tetragonal-to-cubic phase transition in YSZ at T &gt'C leads to a heterogeneous redistribution of Mnions. The subsequent reaction of LSM and YSZ occurring at T > 1100°C is revealed as a three-stage kinetic process, yielding La2Zr 2O7, SrZrO3 and MnO. The diffusion activities of Y, Mn and La ions in the heterogeneous systems at elevated temperatures are derived by the structural analysis, and the three-stage reaction of YSZ and LSM is found strongly correlated to ions' behaviors as functions of temperature.