An ion trap-ion mobility-time of flight mass spectrometer with three ion sources for ion/ion reactions

This instrument combines the capabilities of ion/ion reactions with ion mobility (IM) and time-of-flight (TOF) measurements for conformation studies and top-down analysis of large biomolecules. Ubiquitin ions from either of two electrospray ionization (ESI) sources are stored in a three dimensional (3D) ion trap (IT) and reacted with negative ions from atmospheric sampling glow discharge ionization (ASGDI). The proton transfer reaction products are then separated by IM and analyzed via a TOF mass analyzer. In this way, ubiquitin +7 ions are converted to lower charge states down to +1; the ions in lower charge states tend to be in compact conformations with cross sections down to ～880 Ų. The duration and magnitude of the ion ejection pulse on the IT exit and the entrance voltage on the IM drift tube can affect the measured distribution of conformers for ubiquitin +7 and +6. Alternatively, protein ions are fragmented by collision-induced dissociation (CID) in the IT, followed by ion/ion reactions to reduce the charge states of the CID product ions, thus simplifying assignment of charge states and fragments using the mobility-resolved tandem mass spectrum. Instrument characteristics and the use of a new ion trap controller and software modifications to control the entire instrument are described.     

On C *-Extreme Maps and *-Homomorphisms of a Commutative C *-Algebra

The generalized state space of a commutative C^*-algebra, denoted , is the set of positive unital maps from C(X) to the algebra of bounded linear operators on a Hilbert space . C^*-convexity is one of several non-commutative analogs of convexity which have been discussed in this context. In this paper we show that a C^*-extreme point of satisfies a certain spectral condition on the operators in the range of the associated positive operator-valued measure. This result enables us to show that C^*-extreme maps from C(X) into , the algebra generated by the compact and scalar operators, are multiplicative. This generalizes a result of D. Farenick and P. Morenz. We then determine the structure of these maps. This paper constitutes a part of the author’s Ph.D. thesis at the University of Nebraska-Lincoln.     

Structurally characterized hetero-oligopolyphenylenes: synthetic advances toward next-generation heterosuperbenzenes

The successful Diels-Alder [2+4] cycloaddition of dipyrimidyl acetylene and suitably substituted 2,3,4,5-tetraarylcyclopenta-2,4-dien-1-ones (3-7) generates a series of selectively functionalized hexaarylbenzenes. Each has two pairs of peripheral functional groups (R' and R=tert-butyl 8 and R=methyl 9, methoxy 10, bromo 11, triisopropylsilylethynyl 12) and four ortho-imine nitrogen atoms. The dibromo derivative 11 is a useful precursor for the formation of a mono ethynyl 13 and diethynyl 14 substituted polyphenylene. Changing the dienophile to di(2-thienyl)acetylene gives an S-heteroatom polyphenylene 15. The compounds were fully characterized by using (1)H, (13)C and a range of 2 D NMR spectroscopic techniques, elemental analysis, and mass spectrometry. Oxidative cyclodehydrogenation of dimethoxy hexaphenylbenzene 10 by using iron(III) chloride results in the formation of a spirocyclic dienone 16, which in a separate reaction undergoes dienone/phenol rearrangement to give the first 4-fused-ring, N-heterosuperbenzene (HSB) 17. Six single crystal molecular structures reveal the commonality of unidirectional twisting of the external aromatic rings in these heteroatom polyphenylenes. The twist angles and any H-bonding or interdigitation in these structures are discussed.     

On the mechanics of functional asymmetry in bipedal walking

This paper uses two symmetrical models, the passive compass-gait biped and a five-link 3-D biped, to computationally investigate the cause and function of gait asymmetry. We show that for a range of slope angles during passive 2-D walking and mass distributions during controlled 3-D walking, these models have asymmetric walking patterns between the left and right legs due to the phenomenon of spontaneous symmetry-breaking. In both cases a stable asymmetric family of gaits emerges from a symmetric family of gaits as the total energy increases (e.g., fast speeds). The ground reaction forces of each leg reflect different roles, roughly corresponding to support, propulsion, and motion control as proposed by the hypothesis of functional asymmetry in able-bodied human walking. These results suggest that body mechanics, independent of neurophysiological mechanisms such as leg dominance, may contribute to able-bodied gait asymmetry.     

Activation Energy Spectra: Insights into Transport Limitations of Organic Semiconductors and Photovoltaic Cells

Some mechanisms of charge transport in organic semiconductors and organic photovoltaic (OPV) cells can be distinguished by their predicted change in activation energy for the current, E_a, versus applied field, F. E_a versus F is measured first in pure films of commercially available regioregular poly(3‐hexylthiophene) (P3HT) and in the same P3HT treated to reduce its charged defect density. The former shows a Poole–Frenkel (PF)‐like decrease in E_a at low F, which then plateaus at higher F. The low defect material does not exhibit PF behavior and E_a remains approximately constant. Upon addition of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), however, both materials show a large increase in E_a and exhibit PF‐like behavior over the entire field range. These results are explained with a previously proposed model of transport that considers both the localized random disorder in the energy levels and the long‐range electrostatic fluctuations resulting from charged defects. Activation energy spectra in working OPV cells show that the current is injection‐limited over most of the voltage range but becomes transport‐limited, with a large peak in E_a, near the open circuit photovoltage. This causes a decrease in fill factor, which may be a general limitation in such solar cells.     

On the Identification of the Parts of Compound Quantum Objects

A view of the constitution of quantum objects as reducible, in the sense of being decomposable to elementary particles, is outlined. On this view, parts of composite quantum systems are considered to be identified according to a recently introduced, specifically quantum notion of individuation (Jaeger, Found Phys 40:1396 2010). These parts can typically also be considered particles according to Wigner’s symmetry-based notion. Particles are considered elementary when they satisfy a condition of elementarity, newly introduced here, that improves on that provided by Newton and Wigner. In any given instance, the compound character of a physical object can be verified in principle by decomposition, ultimately to a set of such elementary parts, through appropriate precise quantum measurements during experimentation consistently with this principle of individuation.     

Oscillatory energy exchange between waves coupled by a dynamic artificial crystal

We describe a general mechanism of controllable energy exchange between waves propagating in a dynamic artificial crystal. We show that if a spatial periodicity is temporarily imposed on the transmission properties of a wave-carrying medium while a wave is inside, this wave is coupled to a secondary counterpropagating wave and energy oscillates between the two. The oscillation frequency is determined by the width of the spectral band gap created by the periodicity and the frequency difference between the coupled waves. The effect is demonstrated with spin waves in a dynamic magnonic crystal.     

Total synthesis and structural elucidation of ent-micropyrone and (+)-ascosalipyrone

The total synthesis of 6-[(1S,3S)-1,3-dimethyl-2-oxopentyl]-4-hydroxy-3,5-dimethyl-2H-pyran-2-one (22), the enantiomer of the natural product micropyrone (1), was achieved in 9 linear steps (10% overall yield), from Evans auxiliary (R)-12 with key coupling of the dianion of dione 17 and aldehyde 11. Formation of the pyrone ring and subsequent oxidation at C7 was achieved without epimerization of the sensitive position α to both the pyrone ring and the carbonyl. The same sequence using the alternate dione 24 achieved the total synthesis of 6-[(1S,3S)-1,3-dimethyl-2-oxopentyl]-4-hydroxy-3-methyl-2H-pyran-2-one (28), the (+)-enantiomer of the natural product, ascosalipyrone (2). In both cases diastereomeric aldehydes 11 and 16 were taken through the synthetic sequence to give two possible diastereomers of the natural products. Comparison of the (1)H and (13)C NMR data for the synthetic isomers with that reported for the natural products determined their relative stereochemistry. Comparison of the optical rotation obtained for 22 established it to be the enantiomer of micropyrone.     

Affinity of An(VI) for N4-Tetradentate Donor Ligands: Complexation of the Actinyl(VI) Ions with N4-Tetradentate Ligands

In this report the affinity of four N₄-tetradentate ligands that incorporate the 2-methylpyridyl functionality with hexavalent actinides $(\mathrm{AnO}_{2}^{2+})$ has been investigated in methanol solution. The ligands studied include N,N??-bis(2-methylpyridyl)diaminoethane (BPMDAE), N,N??-bis(2-methylpyridyl)-1,3-diaminopropane (BPMDAP), N,N??-bis(2-pyridylmethyl)piperazine (BPMPIP), and trans-N,N-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (BPMDAC). Conditional stability constants describing the strength of the interaction were determined by UV?Cvisible spectrophotometry. The log₁₀ K ₁₀₁ values for both U(VI) and Pu(VI) are comparable and show the same trend of stability with ligand structure. Dinuclear complexes are also indicated as being important. The log₁₀ K ₂₀₁ values for Pu(VI) complexation with the N₄-ligands are identical for the four ligands (within experimental error), indicating that the structure of the ligand backbone has little effect on the stability of the (PuO₂)₂L²⁺ complex. The exception to this trend is the behavior of N,N??-bis(2-pyridylmethyl)piperazine (BPMPIP) with Pu(VI). This ligand displays a tendency to reduce Pu(VI) within the experimental time frame of 45 minutes. BPMPIP is the only ligand tested that contains tertiary amines in the ligand backbone. The decomposition of BPMPIP by Pu(VI) suggests a susceptibility of tertiary amines to oxidative degradation.     

PHOTOSTIMULATION OF AGGREGATION IN THE CELLULAR SLIME MOLD Polysphondylium violaceum

Abstract Aggregation in Polysphondylium violaceum is stimulated by light with an increase in the number of aggregates being one effect of light incubation. An aggregation-stimulating factor, D factor, has been shown previously to cause phenotypic reversal of the aggregation-defect in aggA mutants. The phenotypic reversal caused by D factor is stimulated by light. The initial time after starvation is the sensitive period for the light-stimulated increase in aggregate formation in wild type strains and also for light-stimulated sensitivity to D factor. At low light intensities both blue and green light have the greatest effect on the number of aggregates formed. However, the intensity dependence of the response is weak over the range tested (0.2 to 10 μW/cm²). Light also affects D factor causing as much as a 60-fold decrease in production and a change in the proportion of the three active components of D factor when compared to D factor produced in darkness. Light affects a decrease in D factor production when it is present during development but only significantly affects the proportions of the D factor components if present prior to aggregation.