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Josef Michl

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https://www.readbyqxmd.com/read/28531349/low-temperature-pm-irras-of-a-monolayer-on-au-spectra-of-c18d37sh
#1
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
https://www.readbyqxmd.com/read/28497963/ir-spectra-of-n-bu4m-m-si-ge-sn-pb-n-buaupph3-d15-and-n-bu-on-a-gold-surface
#2
Jiří Kaleta, Lucie Bednárová, Martina Čížková, Jin Wen, Eva Kaletová, Josef Michl
Observed and DFT-calculated IR spectra of n-Bu4M (M = Si, Ge, Sn, Pb), (CH3CH2CH2(13)CD2)4Sn, 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 8, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28460170/mechanism-of-surface-alkylation-of-a-gold-aerogel-with-tetra-n-butylstannane-d36-identification-of-byproducts
#3
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 11, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28346750/intuitive-understanding-of-%C3%AF-delocalization-in-loose-and-%C3%AF-localization-in-tight-helical-conformations-of-an-oligosilane-chain
#4
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
https://www.readbyqxmd.com/read/27993876/emerging-role-of-mdm2-as-target-for-anti-cancer-therapy-a-review
#5
REVIEW
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
https://www.readbyqxmd.com/read/27989211/electrochemical-oxidation-of-1-x-12-i-cb11me10-anions-formation-of-borenium-ylides-12-dehydro-1-x-cb11me10-and-iodonium-ylide-anions-12-1-x-cb11me10-2i
#6
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-CB11Me10(-)] (X = H, CH3, C2H5, C3H7, C4H9, C6H13, 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-CB11Me11(-)], identical with the anionic product of its reaction with [Et3Si-H-SiEt3](+) and/or Et3Si(+), allows it to be identified as the iodonium ylide anion [{12-(1-H-CB11Me10(-))}2I(+)]...
December 19, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27936641/anodic-oxidation-of-18-halogenated-and-or-methylated-derivatives-of-cb11h12
#7
Abdul Wahab, Christos Douvris, Jiří Klíma, Filip Šembera, Juri Ugolotti, Jiří Kaleta, Jiří Ludvík, Josef Michl
Anodic oxidation of [CB11H12](-) 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 [CB11Me12](-)) 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
https://www.readbyqxmd.com/read/27324741/electronic-transitions-in-conformationally-controlled-peralkylated-hexasilanes
#8
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
https://www.readbyqxmd.com/read/27181994/correction-to-pyridine-ligand-rotation-in-self-assembled-trigonal-prisms-evidence-for-intracage-solvent-vapor-bubbles
#9
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
https://www.readbyqxmd.com/read/27158903/excitation-localization-delocalization-isomerism-in-a-strongly-coupled-covalent-dimer-of-1-3-diphenylisobenzofuran
#10
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
https://www.readbyqxmd.com/read/27136127/electronic-spectra-of-the-tetraphenylcyclobutadienecyclopentadienylnickel-ii-cation-and-radical
#11
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
https://www.readbyqxmd.com/read/27035214/challenges-in-the-structure-determination-of-self-assembled-metallacages-what-do-cage-cavities-contain-internal-vapor-bubbles-or-solvent-and-or-counterions
#12
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
https://www.readbyqxmd.com/read/27018918/metal-complexes-with-very-large-dipole-moments-the-anionic-carborane-nitriles-12-nc-cb11x11-x-h-f-ch3-as-ligands-on-pt-ii-and-pd-ii
#13
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
https://www.readbyqxmd.com/read/26879645/fluorinated-graphenes-as-advanced-biosensors-effect-of-fluorine-coverage-on-electron-transfer-properties-and-adsorption-of-biomolecules
#14
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
https://www.readbyqxmd.com/read/26761074/li-catalysis-and-other-new-methodologies-for-the-radical-polymerization-of-less-activated-olefins
#15
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
https://www.readbyqxmd.com/read/26663795/ex-vivo-efficacy-of-anti-cancer-drug-pnc-27-in-the-treatment-of-patient-derived-epithelial-ovarian-cancer
#16
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
https://www.readbyqxmd.com/read/26382886/synthesis-of-triptycene-based-molecular-rotors-for-langmuir-blodgett-monolayers
#17
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
https://www.readbyqxmd.com/read/26327466/the-scope-of-direct-alkylation-of-gold-surface-with-solutions-of-c1-c4-n-alkylstannanes
#18
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
https://www.readbyqxmd.com/read/25946511/arrays-of-molecular-rotors-with-triptycene-stoppers-surface-inclusion-in-hexagonal-tris-o-phenylenedioxy-cyclotriphosphazene
#19
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
https://www.readbyqxmd.com/read/25937858/time-resolved-fluorescence-anisotropy-of-bicyclo-1-1-1-pentane-tolane-based-molecular-rods-included-in-tris-o-phenylenedioxy-cyclotriphosphazene-tpp
#20
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
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