Low-temperature complexes of europium atoms and dimers with cyanophenylpyridines and alkylcyanophenylpyridines

It is shown by IR-Fourier and UV-visible spectroscopy that two biligand complexes of different stoichiometric composition Ln·2L and 2Ln·2L (Ln = Eu; L = 4-pentyl-4′-cyanophenylpyridine) are formed in the course of low-temperature co-condensation of metal and ligand vapors on the surfaces cooled with liquid nitrogen. Quantum-chemical modeling of the equilibrium structures of the mono-and binuclear complexes of europium with unsubstituted cyanophenylpyridyl and para-ethylcyanophenylpyridyl ligands was carried out. The main geometrical parameters of these compounds were determined. For mononuclear complexes, there is a competition between two mechanisms of coordination of the metal atom: formation of sandwich π complexes by interactions with the π orbitals of the aromatic ligand system and σ coordination at the nitrogen atoms of the pyridine ring. The sandwich structures of the binuclear complexes with 4-ethylcyanophenylpyridine are stabilized by N…H intermolecular contacts between the N atom of the cyano group and the terminal H atom of the ethyl group. The spectral shifts and the relative thermal stability of complexes with varying nuclearity are discussed.     

Annulated dinuclear metal-free and Zn(II) phthalocyanines: photophysical studies and quantum mechanical calculations

The results of steady-state and time-resolved absorption and fluorescence experiments as well as quantum mechanical density functional theory (DFT) calculations of metal-free and Zn(II) mononuclear and dinuclear (sharing a common benzene ring) phthalocyanines are presented. A detailed comparison between measured and calculated absorption spectra of all compounds is done, showing a good agreement between theory and experiment. The NH tautomerization for phthalocyanines with an extended pi-electron system was shown for the first time at room temperature. The photophysical properties of all possible NH tautomers of metal-free dinuclear Pc have been fully characterized. In the first tautomer, Pc(parallel), both pairs of hydrogen atoms are parallel to the connection line of two Pc units. The maximum of the lowest-energy Q absorption band, lambda abs, in Pc(parallel) is located at 832 nm, whereas the spectral position of the fluorescence maximum lies at lambdafl=837 nm. The second NH tautomer, Pc(perpendicular) (lambdaabs=853 nm, lambdafl=860 nm), presents the two pairs of hydrogen atoms perpendicularly orientated to the covalent axis, and the third one, Pc(mix) (lambdaabs=864 nm, lambdafl=872 nm), contributing in a minor extend to the absorption and fluorescence spectra of the metal-free dinuclear phthalocyanine, has one perpendicular and one parallel pair of hydrogen atoms. Obviously, only one configuration exists in the case of the Zn(II)-containing dinuclear phthalocyanine (lambdaabs=845 nm, lambdafl=852 nm).     

Anionic biopolyelectrolytes of the syndecan/perlecan superfamily: Physicochemical properties and medical significance

In the review article presented here, we demonstrate that the connective tissue is more than just a matrix for cells and a passive scaffold to provide physical support. The extracellular matrix can be subdivided into proteins (collagen, elastin), glycoconjugates (structural glycoproteins, proteoglycans) and glycosaminoglycans (hyaluronan). Our main focus rests on the anionic biopolyelectrolytes of the perlecan/syndecan superfamily which belongs to extracellular matrix and cell membrane integral proteoglycans. Though the extracellular domain of the syndecans may well be performing a structural role within the extracellular matrix, a key function of this class of membrane intercalated proteoglycans may be to act as signal transducers across the plasma membrane and thus be more appropriately included in the group of cell surface receptors. Nevertheless, there is a continuum in functions of syndecans and perlecans, especially with respect to their structural role and biomedical significance.     

A Frost-Resistant Structural Material Based on a High-Molecular-Mass Divinyl–Isoprene Copolymer

A new three-dimensionally cross-linked plasticized elastomer filled with polyfractional silicon dioxide was developed on the basis of a frost-resistant high-molecular-mass divinyl–isoprene copolymer. A quinol ether was suggested as an effective cross-linking agent. The envelopes of the experimental and calculated energies of mechanical failure at different temperatures as applied to uniaxial extension were constructed. The composite was recommended as a structural material for the development of wear-resistant parts and units of automobile and aviation transport intended for operation in a wide temperature range, including the Russian Extreme North and Arctic.     

Representation of the quantum Fourier transform on multilevel basic elements by a sequence of selective rotation operators

To experimentally realize quantum computations on d-level basic elements (qudits) at d > 2, it is necessary to develop schemes for the technical realization of elementary logical operators. We have found sequences of selective rotation operators that represent the operators of the quantum Fourier transform (Walsh-Hadamard matrices) for d = 3–10. For the prime numbers 3, 5, and 7, the well-known method of linear algebra is applied, whereas, for the factorable numbers 6, 9, and 10, the representation of virtual spins is used (which we previously applied for d = 4, 8). Selective rotations can be realized, for example, by means of pulses of an RF magnetic field for systems of quadrupole nuclei or laser pulses for atoms and ions in traps.     

Photoinduced energy and electron transfer processes in hexapyropheophorbide a- fullerene [C(60)] molecular systems

The photophysical properties of the novel hexapyropheophorbide a (P6), and hexakis (pyropheophorbide a)-C60 (FP6) were studied and compared with those of hexakis (pyropheophorbide a)-fullerene [5:1] hexaadduct (FHP6). It was found that after light absorption the pyropheophorbide a molecules in all three compounds undergo very efficient energy transfer as well as partly excitonic interactions. The last process results in the formation of energy traps, which could be resolved experimentally. For P6, due to shorter distances between neighboring dye molecules, stronger interactions between pyropheophorbide a units than for FHP6 were observed. As a consequence, the excitation energy is delivered rapidly to traps formed by stacked pyropheophorbide a molecules resulting in the reduction of fluorescence, intersystem crossing, and singlet oxygen quantum yields compared to the values of FHP6. For FP6 the reduction of these values is much stronger due to an additional fast and efficient deactivation process, namely photoinduced electron transfer from pyropheophorbide a to the fullerene moiety. Consequently, FP6 can be considered as a combination of a light-harvesting system consisting of several separate pyropheophorbide a molecules and a charge-separating center.     

Ab initio study of the comparative stability of ruthenium(VI) and osmium(VI) oxo hydroxo complexes with different coordination numbers

The comparative stability of oxohydroxoruthenium(VI) and oxohydroxoosmium(VI) anions with different coordination numbers has been calculated by the relativistic density functional theory method with inclusion of spin-orbit coupling. In line with experimental data, the computations point to the stability of the ruthenium complex RuO₃(OH) ₂ ^2? ? with CN = 5, whereas osmium is stabilized in a six-coordinate environment (OsO₂(OH) ₄ ^2? ). The spin state of the stable Ru complex is close to triplet and that of the Os complex, to singlet.     

Systems AIPUO6-H2O (AI = Na,K): Phase Diagrams and Thermochemistry

The ranges of existence of crystal hydrates in the systems NaPUO₆-H₂O and KPUO₆-H₂O were studied by isopiestic and static tensimetric methods. All the compounds formed in these systems were isolated and studied by reactive calorimetry. The enthalpies of their formation and dehydration were determined.