Anisotropy of the Complex Permittivity of the Kagome-Staircase Compounds Co<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> and Ni<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript>: Experiment and Ab Initio Calculations

The anisotropy of the components of the complex permittivity of vanadate Co₃V₂O₈ and Co₃V₂O₈ single crystals in the paramagnetic phase are studied by optical ellipsometry in the spectral region 0.5–5.0 eV. Our experimental results support the weak anisotropy of the optical response detected earlier for axes a and c. The optical properties are also investigated along axis b. The properties of both compounds are compared. The optical spectra of both compounds along axis b are shifted toward low energies as compared to axes a and c. The maximum of the main interband absorption band of Co₃V₂O₈ is shifted toward low energies by 0.25–0.3 eV as compared to Co₃V₂O₈. The electronic structure parameters of both compounds are determined. Optical function spectra are analyzed using the results of ab initio band calculations.     

Emergent Quantum Euler Equation and Bose–Einstein Condensates

In this paper, proceeding from the recently developed way of deriving the quantum-mechanical equations from the classical ones, the complete system of hydrodynamical equations, including the quantum Euler equation, is derived for a perfect fluid and an imperfect fluid with pairwise interaction between the particles. For the Bose–Einstein condensate of the latter one the Bogolyubov spectrum of elementary excitations is easily reproduced in the acoustic approximation.     

Phase separation in semidilute aqueous poly(N-isopropylacrylamide) solutions

The phase separation mechanism in semidilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is investigated with small-angle neutron scattering (SANS). The nature of the phase transition is probed in static SANS measurements and with time-dependent SANS measurements after a temperature jump. The observed critical exponents of the phase transition describing the temperature dependence of the Ornstein-Zernike amplitude and correlation length are smaller than values from mean-field theory. Time-dependent SANS measurements show that the specific surface decreases with increasing time after a temperature jump above the phase transition. Thus, the formation of additional hydrogen bonds in the collapsed state is a kinetic effect: A certain fraction of water remains as bound water in the system. Moreover, H-D exchange reactions observed in PNIPAM have to be taken into account.     

Hydrogen-bonding-driven self-assembly of PEGylated organosilica nanoparticles with poly(acrylic acid) in aqueous solutions and in layer-by-layer deposition at solid surfaces

PEGylated organosilica nanoparticles have been synthesized through self-condensation of (3-mercaptopropyl)trimethoxysilane in dimethyl sulfoxide into thiolated nanoparticles with their subsequent reaction with methoxypoly(ethylene glycol) maleimide. The PEGylated nanoparticles showed excellent colloidal stability over a wide range of pH in contrast to the parent thiolated nanoparticles, which have a tendency to aggregate irreversibly under acidic conditions (pH < 3.0). Due to the presence of a poly(ethylene glycol)-based corona, the PEGylated nanoparticles are capable of forming hydrogen-bonded interpolymer complexes with poly(acrylic acid) in aqueous solutions under acidic conditions, resulting in larger aggregates. The use of hydrogen-bonding interactions allows more efficient attachment of the nanoparticles to surfaces. The alternating deposition of PEGylated nanoparticles and poly(acrylic acid) on silicon wafer surfaces in a layer-by-layer fashion leads to multilayered coatings. The self-assembly of PEGylated nanoparticles with poly(acrylic acid) in aqueous solutions and at solid surfaces was compared to the behavior of linear poly(ethylene glycol). The nanoparticle system creates thicker layers than the poly(ethylene glycol), and a thicker layer is obtained on a poly(acrylic acid) surface than on a silica surface, because of the effects of hydrogen bonding. Some implications of these hydrogen-bonding-driven interactions between PEGylated nanoparticles and poly(acrylic acid) for pharmaceutical formulations are discussed.     

Synthesis of a novel Boc-protected cyclopropane-modified proline analogue

The synthesis of the Boc derivative of a novel member of the cyclopropane-modified proline library, Boc-protected 5-azaspiro[2.4]heptane-6-carboxylic acid, is reported. The synthesis was performed in six steps starting from (2S,4R)-4-hydroxyproline using a modified Simmons-Smith reaction as the key step. The reaction conditions for all the steps were carefully selected to avoid racemization at the chiral centers in the intermediates and the final product.     

Photoelectron spectra and structures of three cyclic dipeptides: PhePhe, TyrPro, and HisGly

We have investigated the electronic structure of three cyclic dipeptides: cyclo(Histidyl-Glycyl) (cHisGly), cyclo(Tyrosyl-Prolyl) (cTyrPro), and cyclo(Phenylalanyl-Phenylalanyl) (cPhePhe) in the vapor phase, by means of photoemission spectroscopy and theoretical modeling. The last compound was evaporated from the solid linear dipeptide, but cyclised, losing water to form cPhePhe in the gas phase. The results are compared with our previous studies of three other cyclopeptides. Experimental valence and core level spectra have been interpreted in the light of calculations to identify the basic chemical properties associated with the central diketopiperazine ring, and with the additional functional groups. The valence spectra are generally characterized by a restricted set of outer valence orbitals separated by a gap from most other valence orbitals. The theoretically simulated core and valence spectra of all three cyclic dipeptides agree reasonably well with the experimental spectra. The central ring and the side chains act as independent chromophores whose spectra do not influence one another, except for prolyl dipeptides, where the pyrrole ring is fused with the central ring. In this case, significant changes in the valence and core level spectra were observed, and explained by stronger hybridization of the valence orbitals.     

1-Alkyl-5-((di)alkylamino) tetrazoles: building blocks for peptide surrogates

An approach to the synthesis of 1-alkyl-5-((di)alkylamino)tetrazoles by nucleophilic substitution in 1-alkyl-5-sulfonyltetrazoles with anions generated from the primary or secondary amines was developed. Tolerance of the method to the presence of some functional groups (i.e., protected amine) in both components of the reaction was demonstrated. Obtained tetrazoles are promising building blocks for the design of peptide surrogates, in particular, for replacement approaches of alkyl urea derivatives.     

Microwave‐Assisted Hydrogel Synthesis: A New Method for Crosslinking Polymers in Aqueous Solutions

It has been found that hydrogels may be formed by microwave irradiation of aqueous solutions containing appropriate combinations of polymers. This new method of hydrogel synthesis yields sterile hydrogels without the use of monomers, eliminating the need for the removal of unreacted species from the final product. Results for two particularly successful combinations, poly(vinyl alcohol) with either poly(acrylic acid) or poly(methylvinylether‐alt‐maleic anhydride), are presented. Irradiation using temperatures of 100–150 °C was found to yield hydrogels with large equilibrium swelling degrees of 500–1000 g g⁻¹. Material leached from both types of hydrogel shows little cytotoxicity towards HT29 cells.     

Photoelectron spectra of some antibiotic building blocks: 2-azetidinone and thiazolidine-carboxylic Acid

X-ray photoelectron spectra of the core and valence levels of the fundamental building blocks of β-lactam antibiotics have been investigated and compared with theoretical calculations. The spectra of the compounds 2-azetidinone and the 2- and 4-isomers of thiazolidine-carboxylic acid are interpreted in the light of theoretical calculations. The spectra of the two isomers of thiazolidine-carboxylic acid are rather similar, as expected, but show clear effects due to isomerization. Both isomers are analogues of proline, which is well-known to populate several low energy conformers in the gas phase. We have investigated the low energy conformers of thiazolidine-4-carboxylic acid theoretically in more detail and find some spectroscopic evidence that multiple conformers may be present. The measured valence levels are assigned for all three compounds, and the character of the frontier orbitals is identified and analyzed.     

Study of the mobility of lattice oxygen in complex oxide catalysts for partial oxidation of propylene to acrolein

The amount of oxygen in the lattice of solids that participates in the elementary stages of partial propylene oxidation is determined for two types of Co-Mo-Bi-Fe-Sb-K-O catalysts (I, II) differing in the method of introduction of antimony and potassium. Two independent methods are used: (1) on the basis of the yield of the oxygen-containing products of propylene oxidation by oxygen of the catalyst in a pulse regime and (2) with the use of Möessbauer spectroscopy. Coincidence of the results obtained by both methods indicates that the active oxygen of the catalyst lattice is formed during redox transformations of iron(III) molybdate entering the composition of the catalysts. Data on the reduction of the catalysts in a pulse regime at various temperatures, which were processed in the framework of the diffusion model, allowed the estimation of the rate constants for diffusion of the lattice oxygen. An increase in the mobility of the lattice oxygen in catalyst I, which is modified with a small amount of antimony as compared to catalyst II, results in an increase in the overall productivity of the sample and in a decrease in the selectivity of propylene oxidation to acrolein. This correlates with the increase in the total amount of the lattice oxygen participating in the process.