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Josef Michl

Jan Tarabek, Jin Wen, Paul I Dron, Lubomir Pospisil, Josef Michl
We report the electron paramagnetic resonance spectra of the radical cation and radical anion of 1,2,2,3-tetramethyl-2,3-dihydro-1H-naphtho[2,3-d]imidazole-4,9-dione (1) and its doubly 13C labeled analog 2, of interest for singlet fission. The hyperfine coupling constants are in excellent agreement with density functional theory calculations and establish the structures beyond doubt. Unlike the radical cation 1∙+, the radical anion 1∙- and its parent 1 have pyramidalized nitrogen atoms and inequivalent methyl groups 15 and 16, in agreement with the calculations...
April 13, 2018: Journal of Organic Chemistry
Jiří Kaleta, Jin Wen, Thomas F Magnera, Paul I Dron, Chenhui Zhu, Josef Michl
In situ grazing-incidence X-ray scattering shows that a monolayer of artificial rod-shaped dipolar molecular rotors produced on the surface of an aqueous subphase in a Langmuir trough has a structure conducive to a 2D ferroelectric phase. The axes of the rotors stand an average of 0.83 nm apart in a triangular grid, perpendicular to the surface within experimental error. They carry 2,3-dichlorophenylene rotators near rod centers, between two decks of interlocked triptycenes installed axially on the rotor axle...
March 23, 2018: Proceedings of the National Academy of Sciences of the United States of America
Antonio Rodríguez-Fortea, Jiří Kaleta, Cécile Mézière, Magali Allain, Enric Canadell, Pawel Wzietek, Josef Michl, Patrick Batail
An asymmetric mechanism for correlated motion occurring in noninteracting pairs of adjacent orthogonal 1,4-bis(carboxyethynyl)bicyclo[1.1.1]pentane (BCP) rotators 1 in the solid state is unraveled and shown to play an important role in understanding the dynamics in the crystalline rotor, Bu4 N+ [ 1 - ]·H2 O. Single crystal X-ray diffraction and calculation of rotor-rotor interaction energies combined with variable-temperature, variable-field 1 H spin-lattice relaxation experiments led to the identification and microscopic rationalization of two distinct relaxation processes...
January 31, 2018: ACS Omega
Andrew R Cook, Michal Valášek, Alison M Funston, Pavel Poliakov, Josef Michl, John R Miller
Optical electron transfer (intervalence) transitions in radical anions of p-carborane oligomers attest to delocalization of electrons between two p-carboranes cages or a p-carborane and a phenyl ring. Oligomers of the 12 vertex p-carborane (C2 B10 H12 ) cage, [12], with up to 3 cages were synthesized, as well as p-carboranes with one or two trimethylsilylphenyl groups, [6], attached to the carbon termini. Pulse radiolysis in tetrahydrofuran produced radical anions, determined redox potentials by equilibria and measured their absorption spectra...
January 25, 2018: Journal of Physical Chemistry. A
Eric A Buchanan, Josef Michl
A simplified version of the frontier orbital model for a noncovalent dimer is used to derive guidelines for dimer geometries that maximize the square of the electronic matrix element for singlet fission. The use of the guidelines requires only the knowledge of the highest occupied and lowest unoccupied orbital of the monomer and the overlaps of the atomic orbitals on partner A with those on partner B.
October 30, 2017: Journal of the American Chemical Society
Paul I Dron, Josef Michl, Justin C Johnson
We describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (1) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of 1 while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions result in films that are largely amorphous as judged by the absence of strong X-ray diffraction peaks. The films of 1 carrying a methyl in the para position of one phenyl ring undergo SF relatively efficiently (≥75% triplet yield, ΦT ) but more slowly than thin films of 1...
November 16, 2017: Journal of Physical Chemistry. A
Justin C Johnson, Josef Michl
In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The highest quantum yield of triplet formation by singlet fission, 200% at 80 K, is found in one of the two known crystal modification of the parent. In the other modification and in many derivatives, excimer formation competes successfully and triplet yields are low...
September 11, 2017: Topics in Current Chemistry (Journal)
Robin Grotjahn, Toni M Maier, Josef Michl, Martin Kaupp
Chromophores suitable for singlet fission need to meet specific requirements regarding the relative energies of their S0 , S1 , and T1 (and T2 ) electronic states. Accurate quantum-chemical computations of the corresponding energy differences are thus highly desirable for materials design. Methods based on density functional theory (DFT) have the advantage of being applicable to larger, often more relevant systems compared to more sophisticated post-Hartree-Fock methods. However, most exchange-correlation functionals do not provide the needed accuracy, in particular, due to an insufficient description of the T1 state...
October 10, 2017: Journal of Chemical Theory and Computation
Jonas Rosendahl, Holger Kirsten, Eszter Hegyi, Peter Kovacs, Frank Ulrich Weiss, Helmut Laumen, Peter Lichtner, Claudia Ruffert, Jian-Min Chen, Emmanuelle Masson, Sebastian Beer, Constantin Zimmer, Katharina Seltsam, Hana Algül, Florence Bühler, Marco J Bruno, Peter Bugert, Ralph Burkhardt, Giulia Martina Cavestro, Halina Cichoz-Lach, Antoni Farré, Josef Frank, Giovanni Gambaro, Sebastian Gimpfl, Harald Grallert, Heidi Griesmann, Robert Grützmann, Claus Hellerbrand, Péter Hegyi, Marcus Hollenbach, Sevastitia Iordache, Grazyna Jurkowska, Volker Keim, Falk Kiefer, Sebastian Krug, Olfert Landt, Milena Di Leo, Markus M Lerch, Philippe Lévy, Markus Löffler, Matthias Löhr, Maren Ludwig, Milan Macek, Nuria Malats, Ewa Malecka-Panas, Giovanni Malerba, Karl Mann, Julia Mayerle, Sonja Mohr, Rene H M Te Morsche, Marie Motyka, Sebastian Mueller, Thomas Müller, Markus M Nöthen, Sergio Pedrazzoli, Stephen P Pereira, Annette Peters, Roland Pfützer, Francisco X Real, Vinciane Rebours, Monika Ridinger, Marcella Rietschel, Eva Rösmann, Adrian Saftoiu, Alexander Schneider, Hans-Ulrich Schulz, Nicole Soranzo, Michael Soyka, Peter Simon, James Skipworth, Felix Stickel, Konstantin Strauch, Michael Stumvoll, Pier Alberto Testoni, Anke Tönjes, Lena Werner, Jens Werner, Norbert Wodarz, Martin Ziegler, Atsushi Masamune, Joachim Mössner, Claude Férec, Patrick Michl, Joost P H Drenth, Heiko Witt, Markus Scholz, Miklós Sahin-Tóth
OBJECTIVE: Alcohol-related pancreatitis is associated with a disproportionately large number of hospitalisations among GI disorders. Despite its clinical importance, genetic susceptibility to alcoholic chronic pancreatitis (CP) is poorly characterised. To identify risk genes for alcoholic CP and to evaluate their relevance in non-alcoholic CP, we performed a genome-wide association study and functional characterisation of a new pancreatitis locus. DESIGN: 1959 European alcoholic CP patients and population-based controls from the KORA, LIFE and INCIPE studies (n=4708) as well as chronic alcoholics from the GESGA consortium (n=1332) were screened with Illumina technology...
July 28, 2017: Gut
Ioannis Alagkiozidis, Constantine Gorelick, Tana Shah, Yi-Ju Amy Chen, Vinita Gupta, Dimitre Stefanov, Abhi Amarnani, Yi-Chun Lee, Ovadia Abulafia, Ehsan Sarafraz-Yazdi, Josef Michl
OBJECTIVES: Paclitaxel is widely used in the treatment of gynecologic malignancies. It targets tumor cells in the M phase of the cell cycle. Cells in other phases survive the insult and repopulate the tumor. PNC-27 is a peptide synthesized of amino acids of the p53-MDM-2 binding domain. It kills various cancer cell lines in a dose-dependent manner. The goal of this study is to assess ovarian cancer cells' sensitivity to PNC-27 after surviving exposure to paclitaxel and to investigate the potential for synergy between PNC-27 and paclitaxel in the treatment of ovarian cancer...
May 2017: Annals of Clinical and Laboratory Science
Jiří Kaleta, Jiawen Chen, Guillaume Bastien, Martin Dračínský, Milan Mašát, Charles T Rogers, Ben L Feringa, Josef Michl
A new unidirectional light-driven molecular motor suitable for host-guest surface inclusion complexes with tris(o-phenylene)cyclotriphosphazene (TPP) was synthesized. The motor molecules formed regular two-dimensional trigonal arrays covering the large facets of disc-shaped TPP nanocrystals. Photochemical and thermal isomerization studies demonstrated that the light-driven rotation of the anchored motors is similar to that observed in solution and is not compromised neither by either the surface confinement or the density of surface coverage (50 vs 100%)...
July 20, 2017: Journal of the American Chemical Society
Milan Mašát, Jin Wen, Zdeněk Sofer, Josef Michl
We describe an experimental setup suitable for the measurement of photomodulated IR reflection/absorption spectra of monolayers on a flat gold substrate at temperatures from room to 14 K. Results obtained for a monolayer of C18D37SH on gold are shown and compared with IR spectra of C18D37SH in a KBr pellet at these temperatures. Band widths are reduced by only ∼10%. Upon cooling below 100-150 K, the frequencies and intensities of vas(CD3) and vas(CD2) bands in the C-D stretching region in both types of spectra undergo reversible changes attributed to disappearance of gauche defects by analogy to the behavior of previously studied chains...
June 1, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Jiří Kaleta, Lucie Bednárová, Martina Čížková, Jin Wen, Eva Kaletová, Josef Michl
Observed and DFT-calculated IR spectra of n-Bu4 M (M = Si, Ge, Sn, Pb), (CH3 CH2 CH2 13 CD2 )4 Sn, and n-BuAuPPh3 -d15 are reported and assigned. The asymmetric CH stretching vibration of the CH2 group adjacent to the metal atom appears as a distinct shoulder at ∼2934 cm-1 , whereas for other CH2 groups it is located at ∼2922 cm-1 . The characteristic peak at ∼2899 cm-1 is attributed to an overtone of a symmetric CH2 bend at ∼1445 cm-1 . In n-BuAuPPh3 -d15 , the CH stretching vibrations of the butyl group are shifted to lower frequencies by ∼10 cm-1 , and two possible rationalizations are offered...
June 22, 2017: Journal of Physical Chemistry. A
Monika Benkovičová, Dan Wen, Jan Plutnar, Martina Čížková, Alexander Eychmüller, Josef Michl
The formation of self-assembled monolayers on surfaces is often likely to be accompanied by the formation of byproducts, whose identification holds clues to the reaction mechanism but is difficult due to the minute amounts produced. We now report a successful identification of self-assembly byproducts using gold aerogel with a large specific surface area, a procedure likely to be applicable generally. Like a thin gold layer on a flat substrate, the aerogel surface is alkylated with n-butyl-d9 groups upon treatment with a solution of tetra-n-butylstannane-d36 under ambient conditions...
May 18, 2017: Journal of Physical Chemistry Letters
Milena Jovanovic, Dean Antic, David Rooklin, Annika Bande, Josef Michl
Conformational effects on the σ-electron delocalization in oligosilanes are addressed by Hartree-Fock and time-dependent density functional theory calculations (B3LYP, 6-311G**) at MP2 optimized geometries of permethylated uniformly helical linear oligosilanes (all-ω-Sin R2n+2 ) up to n=16 and for backbone dihedral angles ω=55-180°. The extent of σ delocalization is judged by the partition ratio of the highest occupied molecular orbital and is reflected in the dependence of its shape and energy and of UV absorption spectra on n...
June 1, 2017: Chemistry, An Asian Journal
Mohammad F Shaikh, William F Morano, John Lee, Elizabeth Gleeson, Blake D Babcock, Josef Michl, Ehsan Sarafraz-Yazdi, Matthew R Pincus, Wilbur B Bowne
The mouse/murine protein, MDM2, and its human homolog, HDM2, are important negative regulators of the p53 tumor suppressor protein. In normal, untransformed cells, MDM2 levels are tightly regulated to control expression of p53 and apoptosis. Conversely, MDM2 expression appears inherently higher in multiple types of cancer cells, thereby supporting its role as a suppressor of p53 pro-apoptotic activity. MDM2 amplification ranges between two- and ten-fold as reported in brain, breast, lung, and soft tissue tumors...
December 2016: Annals of Clinical and Laboratory Science
Abdul Wahab, Jiří Kaleta, Jin Wen, Michal Valášek, Miroslav Polášek, Josef Michl, Jiří Ludvík
Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB11 Me10 - ] (X = H, CH3 , C2 H5 , C3 H7 , C4 H9 , C6 H13 , and COOCH3 ) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO2 . Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB11 Me11 - ], identical with the anionic product of its reaction with [Et3 Si-H-SiEt3 ]+ and/or Et3 Si+ , allows it to be identified as the iodonium ylide anion [{12-(1-H-CB11 Me10 - )}2 I+ ]...
December 19, 2016: Inorganic Chemistry
Abdul Wahab, Christos Douvris, Jiří Klíma, Filip Šembera, Juri Ugolotti, Jiří Kaleta, Jiří Ludvík, Josef Michl
Anodic oxidation of [CB11 H12 ]- and 18 of its halogenated and/or methylated derivatives was examined. Reversible oxidation was found for four of the anions in liquid SO2 and for four more in 1,1,1,3,3,3-hexafluoroisopropyl alcohol. The oxidation occurred at ∼1 V (for [CB11 Me12 ]- ) up to more than 4 V (for [1-H-(2-6)-F5 -(7-12)-(CF3 )6 -CB11 ]- ) relative to ferrocene/ferricinium. The anodic peak potentials are reproduced by a set of additive position-sensitive substituent increments.
January 3, 2017: Inorganic Chemistry
Yuki Kanazawa, Hayato Tsuji, Masahiro Ehara, Ryoichi Fukuda, Deborah L Casher, Kohei Tamao, Hiroshi Nakatsuji, Josef Michl
The photophysical properties of oligosilanes show unique conformational dependence due to σ-electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n-hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds...
October 5, 2016: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Jaroslav Vacek, Douglas C Caskey, Dominik Horinek, Richard K Shoemaker, Peter J Stang, Josef Michl
No abstract text is available yet for this article.
May 25, 2016: Journal of the American Chemical Society
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