Isolation and Monitoring of the Endohedral Metallofullerenes Y@C82 and Sc3@C82:On-Line Chromatographic Separation with EPR Detection

The direct coupling of high-performance liquid chromatography (HPLC) with on-line electron paramagnetic resonance (EPR) detection is demonstrated for monitoring separations of endohedral metallofullerenes (M@C2n). The HPLC-EPR approach readily permits detection of the paramagnetic species, such as Y@C82 and Sc3@C82, in the presence of the dominant empty-cage fullerenes (C60, C70) and diamagnetic metallofullerenes (e.g., M2@C2n). The results indicate that on-line EPR provides a noninvasive, selective detector for HPLC metallofullerene separations that is readily adaptable to air-sensitive and/or labile compounds. Specifically, the “EPR-active” metallofullerenes, Y@C82 and Sc3@C82, are selectively monitored on-line for an initial separation of the metallofullerene fraction from the dominant empty-cage fullerenes utilizing a combination of polystyrene columns. This preparative “cleanup” procedure is followed by HPLC-EPR separation and monitoring of Y@C82 and Sc3@C82 species using a selective tripodal π-acidic-phase column (Trident-Tri-DNP) for the final stages of isolation

Development and application of analytical techniques to chemistry of donor solvent liquefaction. Final report, August 31, 1977-December 31, 1979

The scope of this project was to develop and apply analytical techniques for the characterization of coal conversion products. Solvent-refined coal served as the coal-derived material for the duration of the study. The investigation has focused primarily in the areas of separations and nuclear magnetic resonance spectroscopy. Highlights of the twenty-eight month study are listed and followed by a brief synopsis of the major findings

KLauS – A charge readout and fast discrimination chip for silicon photomultipliers

KLauS is an application specific integrated circuit (ASIC) for the readout of silicon photomultipliers. The chip has been designed for the application in the analog hadronic calorimeter developed by the CALICE collaboration for the next linear collider experiment . To address the severe power constraints introduced by the highly granular design of the calorimeter, the chip has been designed for low power consumption while maintaining the high dynamic range and timing precision required by the experiment. In addition, a power gating scheme has been implemented to further decrease the average power consumption. For a duty cycle of 1% a value of 25µW per channel is achieved without affecting the readout capabilities of the chip. The chip has been designed in the 0.35µm SiGe technology and provides a low power readout channel for SiPMs with low gain for the input stage of the existing readout chip SPIROC. The analog channel of KLauS will be implemented in a future version of the SPIROC chip

KLauS: an ASIC for silicon photomultiplier readout and its application in a setup for production testing of scintillating tiles

KLauS is an ASIC produced in the AMS 0.35 mm SiGe process to read out the charge signals from silicon photomultipliers. Developed as an analog front-end for future calorimeters with high granularity as pursued by the AHCAL concept in the CALICE collaboration, the ASIC is designed to measure the charge signal of the sensors in a large dynamic range and with low electronic noise contributions. In order to tune the operation voltage of each sensor individually, an 8-bit DAC to tune the voltage at the input terminal within a range of 2V is implemented. Using an integrated fast comparator with low jitter, the time information can be measured with subnanosecond resolution. The low power consumption of the ASIC can be further decreased using power gating techniques. Future versions of KLauS are under development and will incorporate an ADC with a resolution of up to 12-bits and blocks for digital data transmission. The chip is used in a setup for mass testing and characterization of scintillator tiles for the AHCAL test beam program

Orientational Dynamics of the Sc3 Trimer in C82: An EPR Study

Electron paramagnetic resonance experiments on endohedral Sc3 in C82 show 22 hyperfine coupling split transitions with unusually large linewidths. Both the nuclear hyperfine coupling and the linewidths are found to be strongly temperature dependent. The data show that the three Sc ions are equivalent, and strongly suggest that they form a trimer which rapidly reorients within the C82 cage. A simple model is proposed which is in good agreement with the data.

La2@C72: Metal-Mediated Stabilization of a Carbon Cage

In this study, we report production, isolation, and characterization for the relatively small endohedral metallofullerene, La2@C72. As described, La2@C72 is readily isolated from conventional electric-arc-generated carbon/metal soot. This new species was purified by HPLC chromatography and characterized by laser desorption mass spectrometry and UV-vis spectroscopy. The mass spectrum also demonstrates the presence of the monometal species, La@C72, but the absence of empty-cage C72. Since empty-cage C72 has not been successfully isolated to date, the results of the present study are in agreement with the argument for metal-mediated stabilization of the C72 carbon cage by lanthanum ions. The chromatographic retention data suggest that the electronic structure of La2@C72 is consistent with a (La3+)2@C726- species and the prediction of a relatively small dipole moment.

High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb 2 @C 79 N with a Single-Electron Terbium–Terbium Bond

The azafullerene Tb 2 @C 79 N is found to be a single-molecule magnet with a high 100-s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy-axis single-ion magnetic anisotropy are strongly coupled by the unpaired spin of the single-electron Tb−Tb bond. Relaxation of magnetization in Tb 2 @C 79 N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τ QTM =16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA11sci