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121.
Enhancing Temporal Control and Enabling Chain‐End Modification in Photoregulated Cationic Polymerizations by Using Iridium‐Based Catalysts 下载免费PDF全文
Veronika Kottisch Michael J. Supej Prof. Dr. Brett P. Fors 《Angewandte Chemie (International ed. in English)》2018,57(27):8260-8264
Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers. 相似文献
122.
Daria Nawrot Marek Kolenič Jiří Kuneš Filip Kostelansky Miroslav Miletin Veronika Novakova Petr Zimcik 《Tetrahedron》2018,74(5):594-599
The reaction of methyl iodide with tert-butylphenylsulfide in DMF leads to a transalkylation that produces methylphenylsulfide. This transalkylation reaction was further studied by 1H NMR spectroscopy. The polarity of the solvent, the electron density on the sulfur atom, and the strength of the alkylating agent (MeI, EtI, BuI, dimethyl sulfate, or dimethyl carbonate) played important roles in the reaction. The suggested mechanism of the reaction involves the formation of a dialkyl aryl sulfonium salt that subsequently eliminates the radical. This mechanism was supported by the observation of higher conversion rates for compounds with more branched alkyl groups on the sulfur atom, which may lead to the formation of more stable radicals. 相似文献
123.
Veronika Chrastinová 《Georgian Mathematical Journal》1995,2(3):237-240
Automorphisms of the family of all Sturm-Liouville equationsy=qy are investigated. The classical Darboux transformation arises as a particular case of a general results. 相似文献
124.
Arkosi Z Szabó-Plánka T Rockenbauer A Nagy NV Lázár L Fülöp F 《Inorganic chemistry》2003,42(16):4842-4848
We have studied the complex equilibria of copper(II) with a series of beta-substituted beta-amino acids (R: H, Me, Et, iBu, iPr, cHex, 1-EtPr, and tBu) in aqueous solution by pH potentiometry and electron paramagnetic resonace (EPR) spectroscopy in the range pH = 2-8 at various metal and ligand concentrations. The basicities of the corresponding donor groups differed only slightly in the series of ligands. A purely mathematical method, the matrix rank analysis carried out on the EPR spectrum package recorded in the presence of copper(II), indicated the formation of 6 independent paramagnetic species. Accordingly, Cu(2+) (aqua complex) and the complexes [CuLH](2+), [CuL](+), [CuL(2)H(2)](2+), [CuL(2)H](+), and [CuL(2)] were considered in the subsequent analysis of series of spectra, and also two isomers of [CuL(2)] were identified. The formation constants and the EPR parameters, e.g. the isotropic g-factors and the copper and nitrogen hyperfine couplings for the above species, were determined in the same optimization procedure by the simultaneous evaluation of spectra. The ligands "LH" are suggested to bind in equatorial positions through their carboxylate groups, while the amino acids in the L protonation state are likely to occupy two equatorial sites via the amino and carboxylate groups. For the isomers of [CuL(2)], the donors of the same kind are in the cis or trans position. As far as we know, this is the first reported case in which a strong correlation has been found between the steric effects of substituents characterized by Meyer's steric parameter V(a) and the protonation constants of metal complexes. The observed trend for the preference for nonprotonated complexes [CuL](+) and [CuL(2)] to increase with the steric demand of the substituent was explained by the increasing shielding effect of the substituent hindering protonation of the nonprotonated complex. 相似文献
125.
Mojmír Trefulka Veronika Ostatná Luděk Havran Miroslav Fojta Emil Paleček 《Electroanalysis》2007,19(12):1281-1287
Osmium tetroxide complexes with nitrogen ligands [Os(VIII)L] have been widely applied as probes of the DNA structure and as electroactive labels of DNA. Here we describe the electrochemical behavior of Os(VIII)2,2‐bipyridine (Os, bipy)‐base‐labeled nucleosides. We show that electroactive label can be introduced also in the nucleoside ribose residues using six‐valent osmium complex. Cyclic voltammograms of sugar‐Os(VI)‐modified ribosides are similar but not identical to those of the base‐modified ribosides. Our results showing the electroactivity of sugar modified ribosides pave the way to facile end‐labeling of RNA. 相似文献
126.
Arthur Reichmuth Samuel Wunderli Michael Weber Veronika R. Meyer 《Mikrochimica acta》2004,148(3-4):133-141
Weighing is a common task in any chemical laboratory and weighing data are associated with some uncertainty, as this is common with all other working procedures and their data. This paper presents the influence factors which are part of the combined measurement uncertainty of a mass determination and their interplay, namely the technical specifications of the balance (repeatability, nonlinearity, sensitivity tolerance, and temperature coefficient of the sensitivity) and the effect of air buoyancy. Depending on the net and gross weight, the densities involved (density of air and of the weighing object in relation to the density of the reference weights) and the uncertainties of these densities the relative uncertainty of weighing data is often in the 10–5 to 10–4 range (10 to 100ppm). It must be kept in mind that such low values can only be obtained with simple weighing goods, i.e. in the absence of disturbances such as electrostatic charges, air drafts, evaporation, or water adsorption phenomena. 相似文献
127.
Syntheses of poly(γ‐benzyl L ‐glutamate)s (PBLGs) labeled with various fluorophores (tryptophan, dansyl, and anthracene) having different molecular weights are reported. Association of PBLG chains was studied by time‐resolved emission anisotropy in the solvents supporting the aggregation process (1,4‐dioxane and tetrahydrofuran) and in N,N‐dimethylformamide, where the aggregates were not formed. The influence of molecular weight and polymer concentration on PBLG association was studied as well. The limiting emission anisotropy (r∞) and rotational correlation times (ϕ) were determined. The chain relaxation dynamics were compared with the fluorescence lifetimes of the fluorophores and spectroscopically suitable labels were selected. Tryptophan was found to be an inconvenient fluorophore for the association study of PBLGs because of its short excited‐state lifetime. Dansyl and anthracene fluorophores, however, proved to be suitable labels for the chain dynamics study of PBLGs in solution. The mobilities of PBLG chains in 1,4‐dioxane were slower than those in tetrahydrofuran and N,N‐dimethylformamide because of PBLG association in this solvent. 相似文献
128.
Lukas Zell Constanze Lainer Jakub Kollr Veronika Temml Daniela Schuster 《Molecules (Basel, Switzerland)》2022,27(14)
Diseases of the central nervous system are an alarming global problem showing an increasing prevalence. Dopamine receptor D2 (D2R) has been shown to be involved in central nervous system diseases. While different D2R-targeting drugs have been approved by the FDA, they all suffer from major drawbacks due to promiscuous receptor activity leading to adverse effects. Increasing the number of potential D2R-targeting drug candidates bears the possibility of discovering molecules with less severe side-effect profiles. In dire need of novel D2R ligands for drug development, combined in silico/in vitro approaches have been shown to be efficient strategies. In this study, in silico pharmacophore models were generated utilizing both ligand- and structure-based approaches. Subsequently, different databases were screened for novel D2R ligands. Selected virtual hits were investigated in vitro, quantifying their binding affinity towards D2R. This workflow successfully identified six novel D2R ligands exerting micro- to nanomolar (most active compound KI = 4.1 nM) activities. Thus, the four pharmacophore models showed prospective true-positive hit rates in between 4.5% and 12%. The developed workflow and identified ligands could aid in developing novel drug candidates for D2R-associated pathologies. 相似文献
129.
Gordana Pavlovi Lidija Barii Vladimir Rapi Veronika Kova
《Acta Crystallographica. Section C, Structural Chemistry》2003,59(2):m55-m57
Heteroannularly substituted ferrocene derivatives can act as model systems for various hydrogen‐bonded assemblies of biomolecules formed, for instance, by means of O—H⋯O and N—H⋯O hydrogen bonding. The crystal structure analysis of 1′‐(tert‐butoxycarbonylamino)ferrocene‐1‐carboxylic acid, [Fe(C10H14NO2)(C6H5O2)] or (C5H4COOH)Fe(C5H4NHCOOC(CH3)3, reveals two independent molecules within the asymmetric unit, and these are joined into discrete dimers by two types of intermolecular hydrogen bonds, viz. O—H⋯O and N—H⋯O. The –COOH and –NHCOOR groups are archetypes for dimer formation via two eight‐membered rings. The O—H⋯O hydrogen bonds [2.656 (3) and 2.663 (3) Å] form a cyclic carboxylic acid dimer motif. Another eight‐membered ring is formed by N—H⋯O hydrogen bonds [2.827 (3) and 2.854 (3) Å] between the N—H group and an O atom of another carbamoyl moiety. The dimers are assembled in a herring‐bone fashion in the bc plane. 相似文献