Formation of poly(ethylene phosphates) in polycondensation of H3PO4 with ethylene glycol. Kinetic and mechanistic study

Conditions of synthesis of poly(ethylene phosphates) in reaction of H₃PO₄ with HOCH₂CH₂OH (EG), the actual path of polycondensation, and structure of the obtained polymers (mostly oligomers) and kinetics of reaction are described. Preliminary kinetic information, based on the comparison of the MALDI‐TOF‐ms and ³¹P{¹H} NMR spectra as a function of conversion is given as well. Because of the dealkylation process fragments derived from di‐ and triethylene glycols are also present in the repeating units. Structures of the end groups (? CH₂CH₂OH or ? OP(O)(OH)₂) depend on the starting ratio of [EG]₀/[H₃PO₄]₀, although even at the excess of EG the acidic end groups prevail because of the dealkylation process. In MALDI‐TOF‐ms products with P_n equal up to 21 have been observed. The average polymerization degrees (P_n) are lower and have been calculated from the proportion of the end groups. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 830–843, 2008     

Crystal growth, structure and electrical properties of thorium phosphorosulfide

Single crystals of thorium phosphorosulfide have been grown by the chemical vapour transport method. The X-ray diffraction examination showed that the unit cell of the crystals belongs to a tetragonal system of the PbFCl-type structure. The basal plane resistivity ρ(300 K)=64 μΩ cm and thermoelectric power S(300 K)=−7.7 μV/K, examined between 0.4 and 315 K, show metallic behaviour.     

Topological solitons and zero modes in high-T c superconductivity

The realization of topological solitons, zero modes, and supersymmetry in theCP ₁ nonlinear sigma model, a theory of high-T _c superconductivity, is presented.     

Modeling study of non-line-narrowed hole-burned spectra in weakly coupled dimers and multi-chromophoric molecular assemblies

Several different models have been proposed to explain the origin of the complex anti-hole features observed in hole-burned (HB) spectra of excitonically coupled systems such as photosynthetic complexes. This lack of consensus presents a serious constraint on the interpretation of HB spectra and the underlying electronic structures of these systems. To resolve this problem we present results of modeling studies of non-resonant HB spectra taking uncorrelated excitation energy transfer and excitonic interactions into account. Simplified analytical results are compared with Monte Carlo simulations in which excitonic interactions are explicitly taken into account in order to disentangle a number of distinct effects. It is shown that these effects can accurately account for both hole shapes and the broad anti-hole structure observed in excitonically coupled systems. We argue that these models will provide a necessary framework for probing the electronic structure of these systems via HB spectroscopy.     

Characterization of metal glycinate complexes by electrospray Q-TOF-MS/MS and their determination by capillary electrophoresis–ICP-MS: application to premix samples

A method was developed for the determination of metal complexes with glycine (glycinates, [M(Gly)_x(H₂O)_y(SO₄)_z]_n, where M denotes Zn, Cu, Mn and Fe) in premix samples used for the preparation of animal feeds enriched in essential trace elements. The method was based on the extraction of the glycinates with 10 mM ammonium acetate (pH 7.4) followed by their determination using capillary electrophoresis with ICP MS detection. The stability of the glycinates in solution was verified by electrospray TOF-MS. Each supplement was shown to be a mixture of complexes, with polymerization degrees ranging from n = 1 to n = 4 (depending on the metal), that were fully or partially dehydrated. The metal glycine complex moiety was found to be preserved during capillary electrophoresis. The detection limits, calculated as three times the standard deviation of the blank plus the blank, were between 0.05 and 0.2 μg mL⁻¹ (as the metal), and the calibration curves were linear, allowing the analysis of premix samples. Repeatability for glycinate standards was below 12%, and analytical precision was typically within 15%.     

DFT studies on tautomeric preferences of 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione in the gas phase and in solution

Density functional theory (DFT) calculations show that in vacuum such α-diketone as 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione is much less stable than its enolimine–enaminone ((1Z,3Z)-3-hydroxy-4-(pyridin-2-yl)-1-(quinolin-2(1H)-ylidene)but-3-en-2-one) and dienaminone tautomers ((1Z,3Z)-1-(pyridin-2-yl)-4-(quinolin-2-yl)buta-1,3-diene-2,3-diol). Other its tautomers (multiple basic and acidic centers in their molecules enable multiple proton transfer to take place) are even more labile. Strength of the intramolecular hydrogen bonds and aromatic character of the (quasi)rings [proved by the Harmonic Oscillator Model of Aromaticity (HOMA) index] in their molecules were found to be responsible for the observed tautomeric preferences. Polar and basic solvent disfavors and favors the enolimine and enaminone tautomers, respectively.     

DFT studies on tautomeric preferences. Part 3: Proton transfer in 2-(8-acylquinolin-2-yl)-1,3-diones

8-Acetyl- and 8-benzoyl-2-(quinolin-2-yl) derivatives of 1,3-diketones were studied from point of view of their tautomeric preferences. Effective electron delocalization and strong hydrogen bonds were found to be responsible for high stability of the enaminone form (the most stable tautomer). Density functional theory (DFT) calculations prove that enolimine and ketimine species are less favored. Contribution of the zwitterionic resonance structures to the enaminone form is most significant in 2-(quinolin-2(1H)-ylidene)-2H-indene-1,3-dione derivatives. Formation of the bifurcated hydrogen bonds was found to take place only in 8-acetyl derivatives. One of these bonds is of the RAHB (Resonance Assisted Hydrogen Bond) type. There is a steric interaction of the pyridine β-hydrogen and carbonyl oxygen atoms in the enaminone tautomers.     

Preparation, characterization and photocatalytic activity of metal-loaded NaNbO3

Fe-, Ni-, Co- and Ag- loaded NaNbO₃ catalysts were prepared and their activities have been investigated in the reaction of photocatalytic hydrogen generation. Me/NaNbO₃ were synthesized by impregnation of NaNbO₃ in an aqueous solution of metal nitrates and then by calcination at the temperature of 400 °C. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-Ray spectrometer (EDX) as its mode. The detailed analysis has revealed that all the investigated catalysts exhibit high crystallinity and the presence of Fe₂O₃, NiO, Co₃O₄ and Ag₂O oxides on Me/NaNbO₃ was confirmed. Finally, the influence of different metal loadings (Fe, Ni, Co and Ag) on the photocatalytic activity of NaNbO₃ for photocatalytic hydrogen generation has been investigated. Here we report that among all the Me/NaNbO₃ photocatalysts Ag-loaded NaNbO₃ exhibited higher photocatalytic efficiency for photocatalytic hydrogen generation than NaNbO₃.