Calorimetric study of the copolymers on basis perfluorinated germanium hydrides with different structures

The temperature dependences of heat capacity of copolymers on the basis of perfluorinated germanium hydrides have been measured using an adiabatic vacuum calorimeter over the temperature range from 6 K to the final temperature of their stability for the first time. Thus, the physical transformations were detected and their thermodynamic characteristics were estimated. The experimental results were used to calculate the standard thermodynamic functions, namely heat capacity, enthalpy, entropy and Gibbs function over the range from T → 0 to the final temperature stability of copolymers. The standard entropy of formation of the under study copolymers at T = 298.15 K was calculated. The obtained results were compared with corresponding data for hyperbranching perfluor polyphenylenegermaniums with other structures. Some conclusions about dependences of the thermodynamic polymers properties versus their structures were made.     

Molecular structure and relative stability of trans and cis isomers of formanilide: gas-phase electron diffraction and quantum chemical studies

Molecular structure of formanilide is determined by gas-phase electron diffraction (GED) augmented by quantum chemical calculations (B3LYP/cc-pVTZ and MP2/cc-pVTZ) and literature microwave (MW) data. The combined GED and MW data are well reproduced for the mixture of trans and cis isomers with the relative abundance of 59 ± 5 and 41 ± 5 %, respectively, at T = 410 K. The trans isomer (C _s symmetry) is planar, while the cis isomer (C ₁ symmetry) has the twisted structure with the amide group rotated by 36.7 ± 2.7° with respect to the phenyl ring. In accord with theoretical calculations, the amide bond –NH–C(O)– is planar in trans formanilide and a somewhat nonplanar in cis isomer. Accurate structural parameters were obtained by a simultaneous fit of the rotational constants reported in the literature and GED intensities obtained in this study. The N–C(O) and N–C_Ph bond dissociation energies in formanilide are calculated using Gaussian-4 method. It is revealed that the strength of N–C(O) bond in formanilide is 50 kJ/mol less than that in benzamide. On the contrary, the strength of adjacent bond (N–C_Ph) increases by 35 kJ/mol compared to aniline. It is rather unexpectedly that the bond strength weakening does not result in the bond elongating, and vice versa.     

Structure and energetic properties of 1,5-dinitrobiuret

The two-dimensional potential energy scan shows that the pseudo-trans conformer of 1,5-dinitrobiuret (DNB) is the most stable form of isolated molecule, while the pseudo-cis conformer is about 7.5 kJ/mol higher in energy. Thus, the structure of gaseous DNB is different from that in crystal state, where the molecules have pseudo-cis conformation. The value of enthalpy of formation of gaseous DNB (?257 ± 5 kJ/mol) is calculated from isodesmic reactions using G4 energies. Combining this value with empirically estimated enthalpy of sublimation, the enthalpy of formation of crystal DNB is predicted to be ?415 ± 15 kJ/mol. The bond dissociation enthalpies are calculated for all bonds. The energy of the weakest N–NO₂ bonds is equal to 190–200 kJ/mol. Similar calculations were carried out for biuret. The gaseous biuret exists predominantly in the pseudo-trans form. The calculated enthalpy of formation of gaseous biuret agrees well with the experimental one. The correlation of calculated bond energies with corresponding bond distances and electron density is discussed for biuret and DNB.     

Synthesis of cyclic carbonates from epoxides or olefins and CO2 catalyzed by metal-organic frameworks and quaternary ammonium salts

Catalytic properties of the metal-organic framework Cr-MIL-101 in solvent-free cycloaddition of CO₂ to epoxides to produce cyclic carbonates using tetrabutylammonium bromide as co-catalyst have been explored under mild reaction conditions (8 bar CO₂, 25 ⁰C). Styrene and propylene carbonates were formed with high yields (95% and 82%, respectively). Catalytic performance of Cr-MIL-101 was compared with other MOFs: Fe-MIL-101, Zn-MOF-5 and HKUST-1. The catalytic properties of different quaternary ammonium bromides, Cr-MIL-101 as well as PW₁₂/Cr-MIL-101 composite material have been assessed in oxidative carboxylation of styrene in the presence of both tert-butyl hydroperoxide and H₂O₂ as oxidants at 8–100 bar CO₂ and 25–80 ⁰C with selectivity to styrene carbonate up to 44% at 57% substrate conversion.     

Superfluorescent Squaraine with Efficient Two‐Photon Absorption and High Photostability

The synthesis, linear photophysical, two‐photon absorption (2PA), femtosecond transient absorption, and superfluorescence properties of a new symmetrical squaraine derivative ( 1 ) are reported. Steady‐state linear spectral and photochemical properties, fluorescence lifetimes, and excitation anisotropy of 1 were investigated in various organic solvents. High fluorescence quantum yields (≈0.7) and very high photostability (photodecomposition quantum yields ≈10^?6–10^?8) were observed. An open‐aperture Z‐scan method was used to obtain 2PA spectra of 1 over a broad spectral range (maximum 2PA cross section ≈1000 GM). Excited‐state absorption (ESA) and gain was observed by femtosecond transient absorption spectroscopy, in which both reached a maximum at approximately 500 fs. Squaraine 1 exhibits efficient superfluorescence. The quantum chemical study of 1 revealed the simulated vibronic nature of the 1PA and 2PA spectra were in good agreement with experimental data; this may provide the ability to predict potential advanced photonic materials.     

Aqueous photocatalytic oxidation of prednisolone

The research into the aqueous photocatalytic oxidation of the anti-inflammatory drug prednisolone was undertaken with P25 titanium dioxide (Evonik) and visible light-sensitive sol-gel synthesized titania-based photocatalysts containing carbon, sulphur, and iron. Possible prednisolone photocatalytic oxidation reaction pathways were proposed based on a number of oxidation by-products determined in the present study. The prednisolone adsorption properties, effects of initial prednisolone concentration, pH, usual wastewater matrix admixtures, like carbamide and sucrose, were studied. The nontoxicity of doped catalysts towards Tetrahymena thermophila, a ciliate protozoa present in the activated sludge, indicated their lower oxidative ability compared to P25, but also implied their potential application in pre-treatment of toxic hazardous materials under VIS or solar radiation before the biological degradation stage.      

A facile direct nucleophilic synthesis of O-(2-[18F]fluoroethyl)-l-tyrosine ([18F]FET) without HPLC purification

Due to favourable in vivo characteristics, its high specificity and the longer half-life of ¹⁸F (109.8 min) allowing for remote-site delivery, O-(2-[¹⁸F]fluoroethyl)-l-tyrosine ([¹⁸F]FET) has gained increased importance for molecular imaging of cerebral tumors. Consequently, the development of simple and efficient production strategies for [¹⁸F]FET could be an important step to further improve the cost-effective availability of [¹⁸F]FET in the clinical environment. In the present study [¹⁸F]FET was synthesized via direct nucleophilic synthesis using an earlier developed chiral precursor, the Ni^II complex of an alkylated (S)-tyrosine Schiff base, Ni-(S)-BPB-(S)-Tyr-OCH₂CH₂OTs. The purification method has been developed via solid phase extraction thereby omitting cumbersome HPLC purification. The suggested SPE purification using combination of reverse phase and strong cation exchange cartridges provided [¹⁸F]FET in high chemical, radiochemical and enantiomeric purity and 35 % radiochemical yield (decay-corrected, 45 min synthesis time). The method was successfully automated using a commercially available synthesis module, Scintomics Hotbox^one. Based on the current results, the proposed production route appears to be well suited for transfer into an automated cassette-type radiosynthesizers without using HPLC.     

Peculiarities and mechanism of surface topography changes in photochromic cholesteric oligomer-based films

Detailed investigations of surface topography peculiarities for two cholesteric mixtures with photovariable helix pitch are presented. The mixtures were prepared by doping cholesteric cyclosiloxane with two chiral-photochromic substances possessing different handedness. Both chiral-photochromic dopants are susceptible to UV light-induced E-Z isomerization and changing of their helical twisting power. UV irradiation allows one to change the helix pitch values of the mixtures in a wide spectral range (~350–740 nm). AFM investigation reveals the specific peculiarities of the surface topography of the mixtures’ films (formation of “fingerprint like” topography or circular, spiralized domains depending on helix pitch). Quantitative analysis of the geometry of the domains (size and cross sections) allows one to find the correlations between photo- and thermally induced helix pitch values and surface features of the films. The handedness of the dopants does not affect surface relief topography. A mechanism has been suggested to explain the topographical changes under helix untwisting, which occurs upon slow cooling of mixtures films.     

Novel 1,2,3-Triazole Derivatives as Mimics of Steroidal System—Synthesis,Crystal Structures Determination,Hirshfeld Surfaces Analysis and Molecular Docking

Herein, we present the synthesis and crystal structures determination of five 4-(1-phenyl-1H-1,2,3-triazol-4-yl)phenol derivatives containing halogen atoms, 6a–e, which may be used as an excellent mimic of steroids in the drug development process. Good quality crystals obtained for all of the synthesized compounds allowed the analysis of their molecular structures. Subsequently, the determined crystal structures were used to calculate the Hirshfeld surfaces for each of the synthesized compounds. Furthermore, results of our docking studies indicated that synthesized derivatives are able to bind effectively to the active sites of selected enzymes and receptors involved in the hormone biosynthesis and signaling pathways, analogously to the native steroids.     

Limit varieties of J-trivial monoids

Semigroup Forum - We show that limit varieties of monoids recently discovered by Gusev, Zhang and Luo and their subvarieties are generated by monoids of the form $$M_\tau (W)$$ for certain...