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71.
Peter Hudák František Kardoš Tomáš Madaras Michaela Vrbjarová 《Czechoslovak Mathematical Journal》2016,66(4):1119-1128
We study improper interval edge colourings, defined by the requirement that the edge colours around each vertex form an integer interval. For the corresponding chromatic invariant (being the maximum number of colours in such a colouring), we present upper and lower bounds and discuss their qualities; also, we determine its values and estimates for graphs of various families, like wheels, prisms or complete graphs. The study of this parameter was inspired by the interval colouring, introduced by Asratian, Kamalian (1987). The difference is that we relax the requirement on the original colouring to be proper. 相似文献
72.
A method for determination of metabisulfite and hydrosulfite in poultice and decolorant by isotachophoresis was developed. Metabisulfite and hydrosulfite are ionizable oxoanions of sulfur of similar character that can easily be oxidized to sulfates. To protect the analytes from oxidation the solid samples were dissolved in a 1% (w/v) solution of formaldehyde. Hydrosulfite and metabisulfite present in the samples were transformed by the reaction with formaldehyde to stable compounds, hydroxymethanesulfinate and hydroxymethanesulfonate that were determined isotachophoretically without any pretreatment except for sample filtering and degassing. A capillary of 0.4 mm i.d. and 100 mm effective length made of fluorinated ethylene-propylene copolymer was filled with an electrolyte system consisting of 10 mmol L−1 HCl + 11 mmol L−1 imidazole, 0.15% (w/v) hydroxyethylcellulose, pH 6.0 (leading electrolyte) and 5 mmol L−1 benzoic acid + 6 mmol L−1 imidazole, pH 6.5 (terminating electrolyte). Separation was performed at a driving current of 80 μA and for detection current was decreased to 30 μA. Using contactless conductivity detection, the calibration curves in the tested concentration range up to 2.5 mmol L−1 were linear for both metabisulfite and hydrosulfite complexes. The concentration detection limits for metabisulfite and hydrosulfite were 2.9 and 3.4 μmol L−1, respectively. For 1 mmol L−1 concentration, values of R.S.D. (n = 6) were 2.6% for hydrosulfite and 0.8% for metabisulfite. Isotachophoretic determination took about 20 min. The elaborated isotachophoretic procedure is simple to perform, sufficiently sensitive and accurate. In addition to this, low cost of analyses makes the method an alternative procedure to methods used so far for the determination of oxoanions of sulfur. 相似文献
73.
Martín-Matute B Aberg JB Edin M Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(21):6063-6072
The racemization of sec-alcohols catalyzed by pentaphenylcyclopentadienyl-ruthenium complex 3a has been investigated. The mechanism involves ruthenium-alkoxide intermediates: reaction of tert-butoxide ruthenium complex 4 with a series of sec-alcohols with different electronic properties gave ruthenium complexes bearing a secondary alkoxide as a ligand. The characterization of these alkoxide complexes by NMR spectroscopy together with a study of the reaction using in situ IR spectroscopy is consistent with a mechanism in which the alkoxide substitution step and the beta-hydride elimination step occur without CO dissociation. The alkoxide substitution reaction is proposed to begin with hydrogen bonding of the incoming alcohol to the active ruthenium-alkoxide intermediate. Subsequent alkoxide exchange can occur via two pathways: i) an associative pathway involving a eta3-CpRu intermediate; or ii) a dissociative pathway within the solvent cage. Racemization at room temperature of a 1:1 mixture of (S)-1-phenylethanol and (S)-1-phenyl-[D4]-ethanol gave only rac-1-phenylethanol, and rac-1-phenyl-[D4]-ethanol, providing strong support for a mechanism in which the substrate stays coordinated to the metal center throughout the racemization, and does not leave the coordination sphere. Furthermore, racemization of a sec-alcohol bearing a ketone moiety within the same molecule does not result in any reduction of the original ketone, which rules out a mechanism where the intermediate ketone is trapped within the solvent cage. These results are consistent with a mechanism where eta3-Ph(5)C(5)-ruthenium intermediates are involved. Competitive racemization on nondeuterated and alpha-deuterated alpha-phenylethanols was used to determine the kinetic isotope effect kH/kD for the ruthenium-catalyzed racemization. The kinetic isotope effect kH/kD for p- X-C(6)H(4)CH(OH)CH(3) was 1.08, 1.27 and 1.45 for X=OMe, H, and CF3, respectively. 相似文献
74.
Francesca Porta Concetta Bifulco Paola Fermo Claudia L. Bianchi Michaela Fadoni Laura Prati 《Colloids and surfaces. A, Physicochemical and engineering aspects》1999,160(3):1380-290
Nanoparticles of Cu2L2O5 (L=Ho, Er) (15–25 nm in size) were synthesised by the intermediate use of W/O microemulsions. In this process the aqueous cores of water/cetyltrimethylammonium bromide/n-octane/1-butanol microemulsions were used as microreactors for the precipitation of Cu2Ho2(CO3)4(OH)2 (25–30 nm) and Cu2Er2(CO3)4(OH)2 (10–40 nm) as precursors. These mixed salts were separated and further decomposed to the corresponding mixed oxides at 900°C for 16 h. All solids were characterised by scanning and transmission electron microscopy, IR, XRPD, ICP-OES, TGA, XPS measurements and elemental analyses. 相似文献
75.
Gabriela Kuzderov Michaela Rendoov Rbert Gyepes Simona Sovov Danica Sabolov Mria Vilkov Petra Olejníkov Ivana Ba
ov Simonida Stoki
Martin Kello Zuzana Vargov 《Molecules (Basel, Switzerland)》2021,26(21)
Three silver(I) dipeptide complexes [Ag(GlyGly)]n(NO3)n (AgGlyGly), [Ag2(GlyAla)(NO3)2]n (AgGlyAla) and [Ag2(HGlyAsp)(NO3)]n (AgGlyAsp) were prepared, investigated and characterized by vibrational spectroscopy (mid-IR), elemental and thermogravimetric analysis and mass spectrometry. For AgGlyGly, X-ray crystallography was also performed. Their stability in biological testing media was verified by time-dependent NMR measurements. Their in vitro antimicrobial activity was evaluated against selected pathogenic microorganisms. Moreover, the influence of silver(I) dipeptide complexes on microbial film formation was described. Further, the cytotoxicity of the complexes against selected cancer cells (BLM, MDA-MB-231, HeLa, HCT116, MCF-7 and Jurkat) and fibroblasts (BJ-5ta) using a colorimetric MTS assay was tested, and the selectivity index (SI) was identified. The mechanism of action of Ag(I) dipeptide complexes was elucidated and discussed by the study in terms of their binding affinity toward the CT DNA, the ability to cleave the DNA and the ability to influence numbers of cells within each cell cycle phase. The new silver(I) dipeptide complexes are able to bind into DNA by noncovalent interaction, and the topoisomerase I inhibition study showed that the studied complexes inhibit its activity at a concentration of 15 μM. 相似文献
76.
Synthesis and Crystal Structure of U2Ta6O19, a New Compound with “Jahnberg‐Structure” and a Note to the First Oxide Chlorides in the Systems Th/Nb/O/Cl and Th/Zr(Hf)/Nb/O/Cl Black crystals of U2Ta6O19 with hexagonal shape were obtained (at T1) by chemical transport using HCl (p (HCl, 298 K) = 1 atm; silica tube) as transport agent in a temperature gradient (T2 → T1; 1000 °C → 950 °C) and using a mixture of UO2, Ta2O5, and HfO2 (or ZrO2) (1 : 2 : 2) as starting materials (at T2). For the structure determination the best result was achieved in space group P63/mcm (No. 193, a = 6.26(2) Å, c = 19.86(6) Å). U2Ta6O19 is isotypical to Th2Ta6O19. In the crystal structure each uranium atom is surrounded by oxygen atoms like a bi‐capped trigonal antiprism and tantalum atoms like a pentagonal bipyramid (CN = 7). Like the “Jahnberg Structures” both coordination polyhedra arrange themselves in separate layers (U–O‐polyhedra, in o‐, Ta–O‐polyhedra in p‐layers) so that in the direction of the c‐axis the sequence of layers is p‐p‐o. Using chemical transport it was possible to prepare the compounds Th12Nb16O63Cl2 and Th8M4Nb16O63Cl2 (M = Zr, Hf), which are the first quaternary and quinquinary examples in these systems. They crystallize isotypically. 相似文献
77.
Peter B. Karadakov Michaela Ellis Joseph Gerratt David L. Cooper Mario Raimondi 《International journal of quantum chemistry》1997,63(2):441-449
The electronic structure of borabenzene (C5H5B, known also as borinane, borinine, borine) is studied using modern valence bond theory in its spin-coupled (SC) form. Three different types of SC wave functions—with six active π orbitals and with four and eight active σ orbitals—are used to describe the π system of the molecule and the σ-bond framework around the boron atom. It is demonstrated that the SC picture of the π space in borabenzene is very similar to that in benzene: The spins of six distorted nonorthogonal 2pπ orbitals are combined in a spin-coupling pattern involving two dominating Kekulétype and three less important Dewar-type Rumer spin functions. This indicates that it is appropriate to consider the π-electron sextet in borabenzene as aromatic and that the reason for the reactivity of this molecule should lie with its σ framework. The two SC models of the σ bonding around B show that the boron-carbon σ bonds in borabenzene involve orbitals are “bent” to the outer side of the six-membered ring. This creates an orbital “hole” at the boron, which should represent the preferred attachment site for Lewis acids. © 1997 John Wiley & Sons, Inc. 相似文献
78.
Michaela Grg Uwe Dieckbreder Ralph-Matthias Schoth Gerd-Volker Rschenthaler Alexander A. Kadyrov 《Heteroatom Chemistry》1998,9(2):109-113
1,1,1,4,5,5,5-Heptafluoro-4-(trifluoromethyl)-2,3-pentanedione reacted with λ3σ3-phosphorus compounds, PR1R2R3 (R1 = CF3, R2 = R3 = Me, iPr, NEt2; R1 = NCO, R2 = R3 = OMe, OEt, R2−R3 = OCH2CH2O, OCMe2CMe2O; R1 = OSiMe3, R2 = R3 = OEt; R1 = NEt2, R2 = R3 = OCH2CF3; R1 = R2 = Et2N, R3 = OCH2CF3, OCH(CF3)2, OCH2Ph, OC6F5) to give new 1,3,2λ5σ5-dioxaphospholenes. The first λ5σ5 phosphoranes with an OCN group bonded to phosphorus were obtained. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:109–113, 1998 相似文献
79.
80.
X-Ray Single Crystal and Electron Microscopic Investigations on a New Uranium Niobate: γ-UNbO5 Black cuboid formed crystals of γ-UNbO5 were obtained (at T1) by chemical transport in a temperature gradient (T2 → T1; 1000 °C → 980 °C) using UNb2O7 as starting material (at T2) and a combination of NbCl5 and Cl2 as transport agent. They were examined by X-rays and electron microscopy. The new modification of γ-UNbO5 crystallizes orthorhombically (space group Pmma) with a = 7.492(3) Å, b = 4.124(4) Å and c = 6.434(4) Å. The compound is isostructural to UVO5 and UMoO5. The crystal structure shows parallel layers formed by edge sharing UO7 and NbO6 polyhedra. Polyhedra of neighbouring layers (distance = b) are mutually corner linked. 相似文献