Rearrangements of cyclopentadienyl cyanates,isocyanates and their thio-,seleno-, and telluro-analogs

Dynamic NMR spectroscopy revealed that pentaphenylcyclopentadienyl isoselenocyanate undergoes reversible hetero-Cope rearrangement (ΔG ^≠ _{408 K} ∼ 22 kcal mol⁻¹, C₆D₅CD₃) giving isomeric selenocyanate in which 1,5-sigmatropic shifts of the SeCN group along the perimeter of the cyclopentadiene ring occur (ΔG ^≠ _{298 K} = 16.7 kcal mol⁻¹, C₆D₅CD₃). On the contrary, pentaphenylcyclopentadienyl iso(thio)cyanates Ph₅C₅NCO and Ph₅C₅NCS are structurally rigid compounds on the NMR time scale. The energy barrier to the 3,3-shift of the isoselenocyanate group in pentaphenylcyclopentadienyl derivative Ph₅C₅NCSe (ΔG _{298 K} ^≠ = 17.9 kcal mol⁻¹) caclulated using the B3LYP/6-31G** method is 7.6 kcal mol⁻¹ lower than for the unsubstituted analog H₅C₅NCSe.     

CrxRe1−xO2 oxides with different rutile-like structures: changes in the electronic configuration and resulting physical properties

Mixed chromium-rhenium oxides, Cr_xRe_1−xO₂ with 0.31?x?0.66, have been synthesized for the first time by high-pressure high-temperature synthesis and in evacuated quartz tubes. The crystal structures of the compounds have been determined by single crystal and powder X-ray diffraction. Depending on synthesis conditions (pressure and temperature) these phases crystallize either in a tetragonal structure (P4₂/mnm) with statistical distribution of metal ions on one site (rutile-type), with cation ordering along c-axis (trirutile-type), or in a monoclinic rutile-like structure (C2/m) with ordering of Cr- and Re-cations and metallic Re-Re bonds. The “a” parameter of the tetragonal unit cell increases with increasing Re content whereas the “c” parameter decreases, indicating a strengthening of the Re-Re bond. The thermal stability of tetragonal Cr_xRe_1−xO₂ in Ar-atmosphere depends on the Re-content, decomposition is observed at 1241 K for x=0.34, but already at 966 K for x=0.5. The thermal expansion of Cr_xRe_1−xO₂ is anisotropic with a larger expansion coefficient in the “c” direction. Tetragonal Cr_xRe_1−xO₂ with 0.31?x<0.54 order antiferromagnetically at low temperatures with T_N depending on the Cr-content x.     

IN AQUA SYNTHESIS OF A HIGH MOLECULAR WEIGHT ARYLETHYNYLENE POLYMER EXHIBITING REVERSIBLE HYDROGEL PROPERTIES

ABSTRACT

A high molecular weight poly(aryleneethynylene) (M_w ～ 60,000) is prepared by the palladium catalyzed copolymerization of 3,5-diiodobenzoic acid and acetylene gas in a basic aqueous medium. The polymer has a “zig-zag”, fully conjugated backbone. The polymer has been characterized by a variety of methods and exhibits high thermal stability. Furthermore, the polymer is readily soluble in aqueous base and is reversibly switchable from the solution state to a hydrogel state, in water, by changing the pH of the solvent.     

Selectivity of vibronic coupling in complex molecules with benzene fragments

This paper deals with the mechanisms of localization of Franck-Condon vibronic coupling of πσ^*- or πlπ^*-orbital type in a few vibrational modes, (LVM) in excited electronic states of polyatomic molecules. The analysis of vibronic coupling uses highly symmetric basis sets (for representing MO structures and normal coordinates ξ_R) as well as simplified models that relate the shift Δ_R of the electron potential minima along the normal coordinates to the MO structure and to ξ_R in the form of analytical expressions. The modes that are active in LVM are determined from the experimental luminescence spectra. These ideas about approximately high local symmetry of vibronic coupling in benzene fragments as well as the estimates of Δ_R depending on variations in the MO structure explain the experimental results. L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 286–291, March–April, 1995. Translated by L. Smolina     

Proteomic Profiling of the Human Fetal Multipotent Mesenchymal Stromal Cells Secretome

Secretome of multipotent mesenchymal stromal cells (MSCs) is actively used in biomedical applications such as alveolar bone regeneration, treatment of cardiovascular disease, and neurodegenerative disorders. Nevertheless, hMSCs have low proliferative potential and production of the industrial quantity of their secretome might be challenging. Human fetal multipotent mesenchymal stromal cells (FetMSCs) isolated from early human embryo bone marrow are easy to expand and might be a potential source for pharmaceutical substances production based on their secretome. However, the secretome of FetMSCs was not previously analyzed. Here, we describe the secretome of FetMSCs using LC-MALDI shotgun proteomics. We identified 236 proteins. Functional annotation of the identified proteins revealed their involvement in angiogenesis, ossification, regulation of apoptosis, and immune response processes, which made it promising for biomedical applications. The proteins identified in the FetMSCs secretome are involved in the same biological processes as proteins from previously described adult hMSCs secretomes. Nevertheless, many of the common hMSCs secretome components (such as VEGF, FGF, Wnt and TGF-β) have not been identified in the FetMSCs secretome.     

Use of the mathematical apparatus of two-component spectrophotometry for the simultaneous catalymetric determination of two anions

Previously studied reactions of aluminum(III) with Xylenol Orange and of cobalt(III) with nitroso-R salt in weakly acidic solutions were proposed for the simultaneous catalymetric determination of carbonate and borate ions and carbonate and phosphate ions, respectively. It was demonstrated that the mathematical apparatus of two-component spectrophotometry is suitable for processing the results of analysis.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 7–10.Original Russian Text Copyright © 2005 by Mikhailova, Belikov, Blank.     

Mechanisms of the hydrogen atom and the phenyl group migration in the molecule of heptaphenylcycloheptatriene

In terms of the density functional theory using the B3LYP functional, 1,2,3,4,5,6,7-heptaphenylcycloheptatriene was shown to be the most stable in the boat conformation of the cycloheptatriene ring with the H atom in the equatorial position. 1,5-Sigmatropic shifts of the H atom along the seven-membered ring perimeter take place when it is in the axial position through the asymmetric transition state with the barrier ΔE ^≠ _ZPE = 28.7 kcal mol^?1. The H atom can attain the axial position upon inversion of the seven-membered ring, which is accompanied by the orthogonal turn of the phenyl group at the sp³-hybridized C atom (ΔE ^≠ _ZPE = 22.6 kcal mol^?1). The energy barrier to the circular rearrangement of the H atom (ΔE ^≠ _ZPE = 32.2 kcal mol^?1) explains formation of isomers during the high-temperature synthesis of di(p-tolyl)pentaphenylcycloheptatriene. The barrier to the 1,5-sigmatropic shifts of the phenyl group is 19.7 kcal mol^?1 higher than that for the competing shifts of the H atom.     

Phase formation along sections of the HfO(NO3)2-H3PO4-RbF-H2O system

The phase formation in the system HfO(NO₃)₂-H₃PO₄-RbF-H₂O was studied along the sections at the molar ratios PO ₄ ^3? /Hf = 0.5, 1.0, 1.5, 2.0, and 3.0 and RbF: Hf = 1?5. The initial solutions contained 2–10 wt % HfO₂. The synthesis was performed at room temperature. The following substances were obtained for the first time: crystalline fluorophosphatehafnate RbHfF₂PO₄ · 0.5H₂O, crystalline triple salt HfF₄ · Rb(PO₄)_0.33 · RbNO₃, crystalline solvate Rb₃Hf₃(PO₄)₅ · 3HF, and amorphous fluorophosphate Hf₃O₂F₂(PO₄)₂ · 8H₂O (formula is conditional). The compounds were studied by crystal-optical, elemental, X-ray diffraction, thermogravimetric, IR spectroscopic, and electron microscopic analyses.     

Immobilization of proteolytic enzymes trypsin and α-chymotrypsin to cellulose matrix

Trypsin and α-chymotrypsin were immobilized on a microcrystalline cellulose matrix by adsorption interaction with cellulose. The adsorption of enzymes was determined as a function of their concentration and the pH of solutions. Mechanisms of enzyme binding to functional groups of cellulose were suggested.     

Nucleation and Growth Synthesis of Siloxane Gels to Form Functional,Monodisperse, and Acoustically Programmable Particles

Nucleation and growth methods offer scalable means of synthesizing colloidal particles with precisely specified size for applications in chemical research, industry, and medicine. These methods have been used to prepare a class of silicone gel particles that display a range of programmable properties and narrow size distributions. The acoustic contrast factor of these particles in water is estimated and can be tuned such that the particles undergo acoustophoresis to either the pressure nodes or antinodes of acoustic standing waves. These particles can be synthesized to display surface functional groups that can be covalently modified for a range of bioanalytical and acoustophoretic sorting applications.