A comparative relativistic DFT and ab initio study on the structure and thermodynamics of the oxofluorides of uranium(IV), (V) and (VI)

All the possible uranium(VI, V, IV) oxides, fluorides and oxofluorides were studied theoretically by using density functional theory (DFT) in the generalised gradient approximation (GGA), and three different relativistic methods (all-electron scalar four component Dyall RESC method (AE), relativistic small-core ECPs, and zeroth order regular approximation ZORA). In order to test different correlation methods, for the two former relativistic methods hybrid DFT, and, for the AE method, MP2 molecular orbital calculations were performed as well. Single-point AE-CCSD(T) energies were calculated on MP2 geometries as well. Energies of the uranium(VI) and (V) oxofluorides dissociation, uranium(VI) fluoride hydrolysis and oxofluoride disproportionation were calculated and compared against the available experimental thermochemical data. AE-CCSD(T) energies were the closest to the experiment. For GGA DFT methods, all the relativistic methods used yield similar results. For thermochemistry, the best quantitative agreement with the experimental and CCSD(T) values for both U=O and U-F bond strengths was obtained with hybrid DFT methods, provided that a reliable basis set was used. Both the GGA DFT and MP2 MO methods show overbinding of these bonds; moreover, this overbinding was found to be not uniform but strongly dependent on the coordination environment of the uranium atom in each case. U=O vibrational frequencies given by hybrid DFT, however, are systematically overestimated, and are better reproduced by GGA DFT; MP2 values usually fall in-between. Reaction enthalpies, U=O frequencies and complex geometries given by the PBE, MPBE, BPBE, BLYP and OLYP GGA functionals are quite similar, with OLYP performing slightly better than the others but still not as good as hybrid DFT. The geometries of the molecules are found to be influenced by the following factors: the inverse transinfluence (ITI) of the oxygen ligand and, for U(V), and U(IV), the Jahn-Teller distortion.     

Mechanochemical formation of a 1:1 C60: tert-butylcalix[4]azulene supramolecular complex: solid-state NMR and DFT computational studies

Abstract

Solid-state NMR data are presented to clearly support the formation of a 1:1 supramolecular complex between C₆₀ and the tetra-tert-butylated analogue of calix[4]azulene by a simple mechanochemical hand-grinding of host and guest in a mortar and pestle. The experimental results are supported by a DFT study.     

Phase synchronization of chaotic oscillations in terms of periodic orbits

We consider phase synchronization of chaotic continuous-time oscillator by periodic external force. Phase-locking regions are defined for unstable periodic cycles embedded in chaos, and synchronization is described in terms of these regions. A special flow construction is used to derive a simple discrete-time model of the phenomenon. It allows to describe quantitatively the intermittency at the transition to phase synchronization. (c) 1997 American Institute of Physics.     

New TEMPO–Appended 2,2′-Bipyridine-Based Eu(III), Tb(III), Gd(III) and Sm(III) Complexes: Synthesis,Photophysical Studies and Testing Photoluminescence-Based Bioimaging Abilities

Linked to Alzheimer’s disease (AD), amyloids and tau-protein are known to contain a large number of cysteine (Cys) residues. In addition, certain levels of some common biogenic thiols (cysteine (Cys), homocysteine (Hcy), glutathione (GSH), etc.) in biological fluids are closely related to AD as well as other diseases. Therefore, probes with a selective interaction with the above-mentioned thiols can be used for the monitoring and visualizing changes of (bio)thiols in the biological fluids as well as in the brain of animal models of Alzheimer’s disease. In this study, new Eu(III), Tb(III), Gd(III) and Sm(III) complexes of 2,2′-bipyridine ligands containing TEMPO fragments as receptor units for (bio)thiols are reported. The presence of free radical fragments of the ligand in the complexes was proved by using the electronic paramagnetic resonance (EPR) method. Among all the complexes, the Eu(III) complex turned out to be the most promising one as luminescence- and spin-probe for the detection of biogenic thiols. The EPR and fluorescent titration methods showed the interaction of the resulting complex with free Cys and GSH in solution. To study the practical applicability of the probes for the monitoring of AD in-vivo, by using the above-mentioned Eu(III)-based probe, the staining of the brain of mice with amyloidosis and Vero cell cultures supplemented with the cysteine-enriched medium was studied as well as the fluorescence titration of Bovine Serum Albumin, BSA (as the model for the thiol moieties containing protein), was carried out. Based on the results of fluorescence titration, the formation of a non-covalent inclusion complex between the above-mentioned Eu(III) complex and BSA was suggested.     

Hydroxyquinolines with extended fluorophores: arrays for turn-on and ratiometric sensing of cations

8-Hydroxyquinoline-based ligands with extended conjugated fluorophores were designed to provide turn-on and ratiometric signal output optimized for use in fluorescence-based sensor arrays, where the changes in blue and green channels of the RGB signal are used to distinguish between cationic analytes.     

A PASE-based approach towards 12-(1H-1,2,3-triazol-1-yl)-indolo[2,1-a]isoquinolines via the reaction of 3-(isoquinolin-1-yl)-1,2,4-triazines with benzyne

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Synthesis and Photophysical Properties of α-(N-Biphenyl)-Substituted 2,2′-Bipyridine-Based Push–Pull Fluorophores

A series of new α-(N-biphenyl)-substituted 2,2′-bipyridines were obtained through the combination of the ipso-nucleophilic aromatic substitution of the C5-cyano group, aza-Diels–Alder and Suzuki cross-coupling reactions, starting from 5-cyano-1,2,4-triazines. For the obtained compounds, photophysical and fluorosolvatochromic properties were studied. Fluorophores 3l and 3b demonstrated unexpected AIEE activity, while 3a and 3h showed promising nitroexplosive detection abilities.     

Fluorescent Pyranoindole Congeners: Synthesis and Photophysical Properties of Pyrano[3,2-f], [2,3-g], [2,3-f], and [2,3-e]Indoles

This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2-f]indole, pyrano[2,3-g]indole, pyrano[2,3-f]indole, and pyrano[2,3-e]indole and photophysical studies in this series. The synthesis of pyrano[3,2-f], [2,3-g], and [2,3-e]indoles involve a tandem of Bischler–Möhlau reaction of 3-aminophenol with benzoin to form 6-hydroxy- or 4-hydroxyindole followed by Pechmann condensation of these hydroxyindoles with β-ketoesters. Pyrano[2,3-f]indoles were synthesized through the Nenitzescu reaction of p-benzoquinone and ethyl aminocrotonates and subsequent Pechmann condensation of the obtained 5-hydroxyindole derivatives. Among the pyranoindoles studied, the most promising were pyrano[3,2-f] and [2,3-g]indoles. These compounds were characterized by moderate to high quantum yields (30–89%) and a large (9000–15,000 cm⁻¹) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2-f] and [2,3-g]indoles to demonstrate their positive solvatochromism, and the data collected was analyzed using Lippert-Mataga equation. Quantum chemical calculations were performed to deepen the knowledge of the absorption and emission properties of pyrano[3,2-f] and [2,3-g]indoles as well as to explain their unusual geometries and electronic structures.