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171.
Shaping a Porphyrinoid Frame by Heteroatoms Extrusion: Formation of an Expanded [22]Triphyrin(6.6.0)
Dr. Ewa Pacholska-Dudziak Prof. Dr. Lechosław Latos-Grażyński Dr. Agata Białońska 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10088-10097
An aromatic expanded triphyrin, [22]triphyrin(6.6.0) 2 , containing a pyrrole unit, a bipyrrole moiety, and annulene links, was obtained from a tellurium-containing precursor meso-tetraaryl-26,28-ditellurasapphyrin 1 . The reaction path proceeds through an acid-promoted tellurium extrusion from 1 yielding directly 2 , characterized in a dicationic form by X-ray crystallography. In solution the neutral macrocycle 2 reveals flexibility typical for annulenes and it exists as a mixture of conformers that differ by the configuration of the annulene fragments, as proven by 1H NMR studies and analyzed by DFT methods. The conformation is controlled by protonation state, the nature of an interacting anion, solvent identity, and by interaction with water. 相似文献
172.
The surface of quasi-hexagonal reconstructed Au(100) is used as the template for monolayer pentacene (PEN) self-assembly. The system is characterized by means of scanning tunneling microscopy at room temperature and under an ultra-high vacuum. A new modulated pattern of molecules with long molecular axes (MA) arranged along hex stripes is found. The characteristic features of the hex reconstruction are preserved herein. The assembly with MA across the hex rows leads to an unmodulated structure, where the molecular layer does not recreate the buckled hex phase. The presence of the molecules partly lifts the reconstruction—i.e., the gold hex phase is transformed into a phase. The arrangement of PEN on the gold structure is the same as that of the surrounding molecular domain on the reconstructed surface. The apparent height difference between phases allows for the distinction of the state of the underlying gold surface. 相似文献
173.
174.
P. Kowalczyk A. Katern F. Engelke 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,17(1):47-50
Laser excitation spectroscopy is performed on K2 molecules produced in a supersonic molecular beam. 83 vibrational levels of the 21 Σ u + state are observed under conditions permitting rotational resolution. The 21 Σ u + state is partially analysed and its preliminary potential curve is compared with theoretical calculations. 相似文献
175.
A new method based on the cascade reaction between β,γ-unsaturated-α-ketophosphonates and cyclic 1,3-dicarbonyls is reported for the synthesis of highly enantiomerically enriched δ-lactones bearing a fused cyclohexenone scaffold. The target products bearing a δ-lactone moiety and one stereogenic center were obtained in good to excellent yields (83–96%) and enantioselectivities (63:32–95:5 er). The best results were obtained in the presence of a chiral Brønsted base catalyst derived from the cinchona alkaloid quinine and modified by a squaramide moiety. 相似文献
176.
177.
Kowalczyk RM Schleicher E Bittl R Weber S 《Journal of the American Chemical Society》2004,126(36):11393-11399
The photogenerated triplet states of riboflavin and flavin mononucleotide (FMN) have been examined by time-resolved electron paramagnetic resonance (EPR) spectroscopy at low temperature (T = 80 K). Because of the high time resolution of the utilized EPR instrumentation, the triplets are for the first time observed in the nonequilibrated electron-spin polarized state and not in their equilibrated forms with the population of the triplet sublevels governed by Boltzmann distribution. The electron-spin polarization pattern directly reflects the anisotropy of the intersystem crossing from the excited singlet-state precursor. Spectral analysis of the resulting enhanced absorptive and emissive EPR signals yields the zero-field splitting parameters, |D| and |E|, and the zero-field populations of the triplet at high accuracy. These parameters are sensitive probes for the protonation state of the flavin's isoalloxazine ring, as becomes evident by a comparison of the spectra recorded at different pH values of the solvent. The three protonation states of the flavins can furthermore be distinguished by the kinetics of the transient EPR signals, which are dominated by spin-lattice relaxation. The fastest decays are observed for the protonated FMN and riboflavin triplets, followed by the deprotonated flavin triplets. Slow decays are measured for the triplet states of neutral FMN and riboflavin. Because proton transfer is found to be slow on the time scale of spin-polarized triplet detection by transient EPR, the pH-dependent spin-relaxation and zero-field splitting parameters offer a novel approach to probe the protonation state of flavins in their singlet ground state through the characterization of their triplet-state properties. 相似文献
178.
Urszula Kosikowska Monika Wujec Nazar Trotsko Wojciech Ponka Piotr Paneth Agata Paneth 《Molecules (Basel, Switzerland)》2021,26(1)
The development of drug-resistant bacteria is currently one of the major challenges in medicine. Therefore, the discovery of novel lead structures for the design of antibacterial drugs is urgently needed. In this structure–activity relationship study, a library of ortho-, meta-, and para-fluorobenzoylthiosemicarbazides, and their cyclic analogues with 1,2,4-triazole scaffold, was created and tested for antibacterial activity against Gram-positive bacteria strains. While all tested 1,2,4-triazoles were devoid of potent activity, the antibacterial response of the thiosemicarbazides was highly dependent on substitution pattern at the N4 aryl position. The optimum activity for these compounds was found for trifluoromethyl derivatives such as 15a, 15b, and 16b, which were active against both the reference strains panel, and pathogenic methicillin-sensitive and methicillin-resistant Staphylococcus aureus clinical isolates at minimal inhibitory concentrations (MICs) ranging from 7.82 to 31.25 μg/mL. Based on the binding affinities obtained from docking, the conclusion can be reached that fluorobenzoylthiosemicarbazides can be considered as potential allosteric d-alanyl-d-alanine ligase inhibitors. 相似文献
179.
Emel'yanenko VN Strutynska A Verevkin SP 《The journal of physical chemistry. A》2005,109(19):4375-4380
Molar enthalpies of sublimation of 2-chloro-, 3-chloro-, and 4-chlorobenzoic acids were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Thermochemical investigations of chlorobenzoic acids available in the literature were collected and combined with own experimental results to obtain their reliable standard molar enthalpies of formation at T = 298.15 K in the gaseous state. Ab initio calculations of chlorobenzoic acids have been performed using the G3(MP2) theory, and results from the homodesmic reactions are in excellent agreement with experiment. New results help us to resolve the uncertainty in the available thermochemical data on chlorobenzoic acids. The strain enthalpies of chlorobenzoic acids have been assessed using an isodesmic reaction procedure. 相似文献