Z = 50 shell gap near 100Sn from intermediate-energy Coulomb excitations in even-mass 106-112Sn isotopes

Rare isotope beams of neutron-deficient 106,108,110Sn from the fragmentation of 124Xe were employed in an intermediate-energy Coulomb excitation experiment. The measured B(E2,0(1)(+)-->2(1)(+)) values for 108Sn and 110Sn and the results obtained for the 106Sn show that the transition strengths for these nuclei are larger than predicted by current state-of-the-art shell-model calculations. This discrepancy might be explained by contributions of the protons from within the Z = 50 shell to the structure of low-energy excited states in this region.     

Total Syntheses of 11-Acetoxy-4-deoxyasbestinin D, 4-Deoxyasbestinin C,Asbestinin-10, -20, -21 and -23

Six members of the asbestinin family of marine diterpene natural products have been synthesized in an efficient and stereoselective manner from a single oxa-bridged intermediate. Five of these natural products have not been synthesized previously and the structures of four of them have been confirmed as those proposed originally or following revisions to the original structures. The fifth natural product—asbestinin-21—has been shown to be a diastereomer of the compound that had been proposed previously.     

Selective Monofunctionalization Enabled by Reaction‐History‐Dependent Communication in Catalytic Rotaxanes

Selective monofunctionalization of substrates with distant, yet equally reactive functional groups is difficult to achieve, as it requires the second functional group to selectively modulate its reactivity once the first functional group has reacted. We now show that mechanically interlocked catalytic rings can effectively regulate the reactivity of stoppering groups in rotaxanes over a distance of about 2 nm. Our mechanism of communication is enabled by a unique interlocked design, which effectively removes the catalytic rings from the substrates by fast dethreading as soon as the first reaction has taken place. Our method not only led to a rare example of selective monofunctionalization, but also to a “molecular if function”. Overall, the study presents a way to get distant functional groups to communicate with each other in a reaction‐history‐dependent manner by creating linkers that can ultimately perform logical operations at the molecular level.     

Analysis of individual mitochondria via fluorescent immunolabeling with Anti-TOM22 antibodies

Mitochondria are responsible for maintaining a variety of cellular functions. One such function is the interaction and subsequent import of proteins into these organelles via the translocase of outer membrane (TOM) complex. Antibodies have been used to analyze the presence and function of proteins comprising this complex, but have not been used to investigate variations in the abundance of TOM complex in mitochondria. Here, we report on the feasibility of using capillary cytometry with laser-induced fluorescence to detect mitochondria labeled with antibodies targeting the TOM complex and to estimate the number of antibodies that bind to these organelles. Mitochondria were fluorescently labeled with DsRed2, while antibodies targeting the TOM22 protein, one of nine proteins comprising the TOM complex, were conjugated to the Atto-488 fluorophore. At typical labeling conditions, 94 % of DsRed2 mitochondria were also immunofluorescently labeled with Atto-488 Anti-TOM22 antibodies. The calculated median number of Atto-488 Anti-TOM22 antibodies bound to the surface of mitochondria was ～2,000 per mitochondrion. The combination of fluorescent immunolabeling and capillary cytometry could be further developed to include multicolor labeling experiments, which enable monitoring several molecular targets at the same time in the same or different organelle types.

Cooling overall spin temperature: protein NMR experiments optimized for longitudinal relaxation effects

In experiments performed on protonated proteins at high fields, 80% of the NMR spectrometer time is spent waiting for the ¹H atoms to recover their polarization after recording the free induction decay. Selective excitation of a fraction of the protons in a large molecule has previously been shown to lead to faster longitudinal relaxation for the selected protons [K. Pervushin, B. Vögeli, A. Eletsky, Longitudinal ¹H relaxation optimization in TROSY NMR spectroscopy, J. Am. Chem. Soc. 124 (2002) 12898–12902; P. Schanda, B. Brutscher, Very fast two-dimensional NMR spectroscopy for real-time investigation of dynamic events in proteins on the time scale of seconds, J. Am. Chem. Soc. 127 (2005) 8014–8015; H.S. Attreya, T. Szyperski, G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment, Proc. Natl. Acad. Sci. USA 101 (2004) 9642–9647]. The pool of non-selected protons acts as a “thermal bath” and spin-diffusion processes (“flip-flop” transitions) channel the excess energy from the excited pool to the non-selected protons in regions of the molecule where other relaxation processes can dissipate the excess energy. We present here a sensitivity enhanced HSQC sequence (COST-HSQC), based on one selective E-BURP pulse, which can be used on protonated ¹⁵N enriched proteins (with or without ¹³C isotopic enrichment). This experiment is compared to a gradient sensitivity enhanced HSQC with a water flip-back pulse (the water flip-back pulse quenches the spin diffusion between ¹H^N and ¹H^α spins). This experiment is shown to have significant advantages in some circumstances. Some observed limitations, namely sample overheating with short recovery delays and complex longitudinal relaxation behaviour are discussed and analysed.     

Measurement of charged-particle multiplicities in gluon and quark jets in pp collisions at square root of s = 1.8 TeV

We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations.     

Combined X‐ray diffraction and alpha particle X‐ray spectrometer analysis of geologic materials

The shallow interrogation depth of the lightest elements (Na, Mg, Al, and Si) detected by the particle‐induced X‐ray emission branch of the Curiosity Rover's alpha particle X‐ray spectrometer suggests that the X‐rays of these elements very likely emerge from a single mineral grain. This reality violates the assumption of atomic homogeneity at the micron scale made in both existing spectrum‐reduction approaches for the alpha particle X‐ray spectrometer. Consequently, analytical results for these elements in igneous geochemical reference materials exhibit deviations from certified concentrations in a manner that can be related to the total alkali‐silica diagram. A computer code is introduced here to provide quantitative prediction of these deviations using the mineral abundances determined from X‐ray diffraction. The latter are converted to area coverage fractions to represent the sample surface, and a fundamental parameters computation predicts the elemental X‐ray yields from each mineral and sums these. In this process, the chemistry of each individual mineral has to be varied by an iterative simplex approach; X‐ray yields are computed and compared with the peak areas from the fit of the bulk sample. When the difference between mineral yields and peak areas for each element are minimized, the mineral formulae are set and elemental X‐ray yields provided. The ratio between the summed mineral X‐ray yields and the corresponding yields based on the homogeneity assumption may then be compared directly with the concentration deviations measured in our earlier work. For several rock types, good agreement is found, thereby consolidating our understanding of the effects of sample mineralogy on alpha particle X‐ray spectrometer results. Copyright © 2017 John Wiley & Sons, Ltd.     

The transition from direct to delayed ionisation of C 60

The timescale for the coupling of electronic and vibrational excitation in isolated fullerenes is determined by recording positive ion time-of-flight mass spectra on excitation with ultrashort laser pulses at 790 nm of the same fluence but different pulse durations. The coupling leads to the onset of a delayed ionisation “tail” on the parent fullerene ion peak. This occurs for a pulse duration of 500-1000 fs, depending on laser fluence. Received 20 October 2000     

Experiments with a symbolic programming system for complex analysis

The paper reports the results of work on the construction of LISP programs for various symbolic operations in complex analysis, including the evaluation of integrals around closed contours by the use of Cauchy's Theorem. It is concluded that the only difficulty in the way of the preparation of programs for all of the important and useful textbook calculations in complex analysis is that large amounts of fast storage in the computer are needed.