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Josef Michl

Yuki Kanazawa, Hayato Tsuji, Masahiro Ehara, Ryoichi Fukuda, Deborah L Casher, Kohei Tamao, Hiroshi Nakatsuji, Josef Michl
Photophysical properties of oligosilanes show unique conformational dependence due to σ-electron delocalization. Excited states of SAS, AAS, and AEA conformations of peralkylated n-hexasilanes, in which SiSiSiSi dihedral angles are controlled into either syn (S), anti (A), or eclipsed (E) conformation, have been investigated using UV absorption, magnetic circular dichroism (MCD), and linear dichroism (LD) spectroscopy. Simultaneous Gaussian fit of all three spectra identifies a minimal set of transitions and their wavenumbers v, oscillator strengths f, and MCD B terms in all three compounds...
June 21, 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
Joel N Schrauben, Akin Akdag, Jin Wen, Zdenek Havlas, Joseph L Ryerson, Millie B Smith, Josef Michl, Justin C Johnson
Two isomers of both the lowest excited singlet (S1) and triplet (T1) states of the directly para, para'-connected covalent dimer of the singlet-fission chromophore 1,3-diphenylisobenzofuran have been observed. In one isomer, excitation is delocalized over both halves of the dimer, and in the other, it is localized on one or the other half. For a covalent dimer in solution, such "excitation isomerism" is extremely rare. The vibrationally relaxed isomers do not interconvert, and their photophysical properties, including singlet fission, differ significantly...
May 26, 2016: Journal of Physical Chemistry. A
Peter R Craig, Zdeněk Havlas, Marianela Trujillo, Pawel Rempala, James P Kirby, John R Miller, Bruce C Noll, Josef Michl
Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF4(-) anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results...
May 26, 2016: Journal of Physical Chemistry. A
Cecile C Givelet, Paul I Dron, Jin Wen, Thomas F Magnera, Matibur Zamadar, Klára Čépe, Hiroki Fujiwara, Yue Shi, Michael R Tuchband, Noel Clark, Radek Zbořil, Josef Michl
Proving the structures of charged metallacages obtained by metal ion coordination-driven solution self-assembly is challenging, and the common use of routine NMR spectroscopy and mass spectrometry is unreliable. Carefully determined diffusion coefficients from diffusion-ordered proton magnetic resonance (DOSY NMR) for six cages of widely differing sizes lead us to propose a structural reassignment of two molecular cages from a previously favored trimer to a pentamer or hexamer, and another from a trimer to a much higher oligomer, possibly an intriguing tetradecamer...
May 25, 2016: Journal of the American Chemical Society
Filip Šembera, Jan Plutnar, Alexander Higelin, Zbyněk Janoušek, Ivana Císařová, Josef Michl
The anionic nitriles 1-R-12-NC-CB11H10(-) (R = H, CH3, I, COOH), 12-NC-1-H-CB11Me10(-), and 12-NC-1-H-CB11F10(-) were prepared, and three of them were examined for complex formation with (Et3P)2Pt(II) and (Et3P)2Pd(II). Several stable internally charge-compensated zwitterionic complexes were obtained and characterized. RI-BP86/SV(P) calculations suggest that their dipole moments exceed 20 D. An attempt to measure the dipole moments in solution failed due to insufficient solubility in solvents of low polarity...
April 18, 2016: Inorganic Chemistry
Veronika Urbanová, František Karlický, Adam Matěj, Filip Šembera, Zbyněk Janoušek, Jason A Perman, Václav Ranc, Klára Čépe, Josef Michl, Michal Otyepka, Radek Zbořil
Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecules and development of new biosensors owing to their improved electron transfer kinetics compared to pristine graphene. Here, we report complex electrochemical behavior and electrocatalytic performance of variously fluorinated graphene derivatives prepared by reaction of graphene with a nitrogen-fluorine mixture at 2 bars pressure. The fluorine content was simply controlled by varying the reaction time and temperature...
June 16, 2016: Nanoscale
Jan Merna, Petr Vlček, Victoria Volkis, Josef Michl
After a brief survey of conventional radical polymerization of alkenes, we review their Li(+) catalyzed radical polymerization and their controlled radical polymerization. Emphasis is on homopolymerization, but related copolymerization of less activated monomers is mentioned as well.
February 10, 2016: Chemical Reviews
Ehsan Sarafraz-Yazdi, Constantine Gorelick, Allison R Wagreich, Ghadir Salame, Mallorie Angert, Charles H Gartman, Vinita Gupta, Wilbur B Bowne, Yi-Chun Lee, Ovadia Abulafia, Matthew R Pincus, Josef Michl
OBJECTIVE: Despite an 80% response rate to chemotherapy, epithelial ovarian cancer has the highest case fatality rate of all gynecologic malignancies. Several studies have shown the efficiency of anticancer peptides PNC-27 and PNC-28 in killing a variety of cancer cells selectively in vitro and in vivo. The purpose of this study was to evaluate the efficacy of PNC-27 against human primary epithelial ovarian cancer. METHODS: We established primary cultures of freshly isolated epithelial ovarian cancer cells from patients with newly diagnosed ovarian cystadenocarcinomas...
2015: Annals of Clinical and Laboratory Science
Jiří Kaleta, Eva Kaletová, Ivana Císařová, Simon J Teat, Josef Michl
We describe syntheses of six triptycene-containing molecular rotors with several single-crystal X-ray diffraction analyses. These rod-shaped molecules carrying an axial rotator are designed to interleave on an aqueous surface into Langmuir-Blodgett (LB) monolayers containing a two-dimensional trigonal array of dipoles rotatable about an axis normal to the surface. Monolayer formation was verified with the simplest of the rotor structures. On an aqueous subphase containing divalent cations (Mg(2+), Ca(2+), Zn(2+), Sr(2+), or Cd(2+)), the LB isotherm yielded an area of 53 ± 3 Å(2)/molecule (monolayer of type A), compatible with the anticipated triangular packing of axes normal to the surface...
October 16, 2015: Journal of Organic Chemistry
Eva Kaletová, Anna Kohutová, Jan Hajduch, Jiří Kaleta, Zdeněk Bastl, Lubomír Pospíšil, Ivan Stibor, Thomas F Magnera, Josef Michl
Treatment of cleaned gold surfaces with dilute tetrahydrofuran or chloroform solutions of tetraalkylstannanes (alkyl = methyl, ethyl, n-propyl, n-butyl) or di-n-butylmethylstannyl tosylate under ambient conditions causes a self-limited growth of disordered monolayers consisting of alkyls and tin oxide. Extensive use of deuterium labeling showed that the alkyls originate from the stannane and not from ambient impurities, and that trialkylstannyl groups are absent in the monolayers, contrary to previous proposals...
September 23, 2015: Journal of the American Chemical Society
Jiří Kaleta, Paul I Dron, Ke Zhao, Yongqiang Shen, Ivana Císařová, Charles T Rogers, Josef Michl
A new generation of rod-shaped dipolar molecular rotors designed for controlled insertion into channel arrays in the surface of hexagonal tris(o-phenylenedioxy)cyclotriphosphazene (TPP) has been designed and synthesized. Triptycene is used as a stopper intended to prevent complete insertion, forcing the formation of a surface inclusion. Two widely separated (13)C NMR markers are present in the shaft for monitoring the degree of insertion. The structure of the two-dimensional rotor arrays contained in these surface inclusions was examined by solid-state NMR and X-ray powder diffraction...
June 19, 2015: Journal of Organic Chemistry
Marco Cipolloni, Jiří Kaleta, Milan Mašát, Paul I Dron, Yongqiang Shen, Ke Zhao, Charles T Rogers, Richard K Shoemaker, Josef Michl
We examine the fluorescence anisotropy of rod-shaped guests held inside the channels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) host nanocrystals, characterized by powder X-ray diffraction and solid state NMR spectroscopy. We address two issues: (i) are light polarization measurements on an aqueous colloidal solution of TPP nanocrystals meaningful, or is depolarization by scattering excessive? (ii) Can measurements of the rotational mobility of the included guests be performed at low enough loading levels to suppress depolarization by intercrystallite energy transfer? We find that meaningful measurements are possible and demonstrate that the long axis of molecular rods included in TPP channels performs negligible vibrational motion...
April 23, 2015: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Joel N Schrauben, Yixin Zhao, Candy Mercado, Paul I Dron, Joseph L Ryerson, Josef Michl, Kai Zhu, Justin C Johnson
Investigations of singlet fission have accelerated recently because of its potential utility in solar photoconversion, although only a few reports definitively identify the role of singlet fission in a complete solar cell. Evidence of the influence of singlet fission in a dye-sensitized solar cell using 1,3-diphenylisobenzofuran (DPIBF, 1) as the sensitizer is reported here. Self-assembly of the blue-absorbing 1 with co-adsorbed oxidation products on mesoporous TiO2 yields a cell with a peak internal quantum efficiency of ∼70% and a power conversion efficiency of ∼1...
February 4, 2015: ACS Applied Materials & Interfaces
Josef Michl
No abstract text is available yet for this article.
January 14, 2015: Chemical Reviews
Jin Wen, Zdenĕk Havlas, Josef Michl
Singlet fission offers an opportunity to improve solar cell efficiency, but its practical use is hindered by the limited number of known efficient materials. We look for chromophores that satisfy the desirable but rarely encountered adiabatic energy conditions, E(T2) - E(S0) > E(S1) - E(S0) ≈ 2[E(T1) - E(S0)], and are small enough to permit highly accurate calculations. We provide a rationale for the use of captodative biradicaloids, i.e., biradicals stabilized by direct interaction between their radical centers, which carry both an acceptor and a donor group...
January 14, 2015: Journal of the American Chemical Society
Akin Akdag, Abdul Wahab, Pavel Beran, Lubomír Rulíšek, Paul I Dron, Jiří Ludvík, Josef Michl
The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory...
January 2, 2015: Journal of Organic Chemistry
Katlin Davitt, Blake D Babcock, Maly Fenelus, Chi Kong Poon, Abhishek Sarkar, Vincent Trivigno, Paul A Zolkind, Sheena M Matthew, Natalia Grin'kina, Zulfiya Orynbayeva, Mohammad F Shaikh, Victor Adler, Josef Michl, Ehsan Sarafraz-Yazdi, Matthew R Pincus, Wilbur B Bowne
GOALS: We have developed the anti-cancer peptide, PNC-27, which is a membrane-active peptide that binds to the HDM-2 protein expressed in the cancer cell membranes of solid tissue tumor cells and induces transmembrane pore formation in cancer, but not in normal cells, resulting in tumor cell necrosis that is independent of p53 activity in these cells. We now extend our study to non-solid tissue tumor cells, in this case, a primitive, possible stem cell human leukemia cell line (K562) that is also p53-homozygously deleted...
2014: Annals of Clinical and Laboratory Science
Hayato Tsuji, Heather A Fogarty, Masahiro Ehara, Ryoichi Fukuda, Deborah L Casher, Kohei Tamao, Hiroshi Nakatsuji, Josef Michl
Unlike π-electron chromophores, the peralkylated n-tetrasilane σ-electron chromophore resembles a chameleon in that its electronic spectrum changes dramatically as its silicon backbone is twisted almost effortlessly from the syn to the anti conformation (changing the SiSiSiSi dihedral angle ω from 0 to 180°). A combination of UV absorption, magnetic circular dichroism (MCD), and linear dichroism (LD) spectroscopy on conformationally controlled tetrasilanes 1-9, which cover fairly evenly the full range of angles ω, permitted a construction of an experimental correlation diagram for three to four lowest valence electronic states...
July 21, 2014: Chemistry: a European Journal
Matthew K MacLeod, Josef Michl
Excited singlet state structures believed to be responsible for the Franck-Condon-allowed and the strongly Stokes-shifted (blue) emissions in linear permethylated oligosilanes (Si(n)Me(2n+2)) have been found and characterized with time-dependent density functional (TD-DFT) methods for chain lengths 4 ≤ n ≤ 16. For chain lengths with n > 7, the S1 relaxed structures closely resemble the S0 equilibrium structures where all valence angles are tetrahedral and all backbone dihedral angles are transoid. At chain lengths with n < 8 more strongly distorted structures with one long Si-Si bond built from silicon 3p orbitals are encountered...
November 13, 2014: Journal of Physical Chemistry. A
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