Azines and Azoloazines,Part 1: Reactions of Triazolo[3,4‐a]phthalazine and Its Derivatives with Carbanions

Triazolo[3,4‐a]phthalazine as well as their chloro and nitro derivatives were subjected to the reactions with the carbanions typical for the vicarious nucleophilic substitution (VNS) of hydrogen. The reactions were strongly dependent on the substituents present on the triazolo[3,4‐a]phthalazine ring and resulted not only in the substitution of hydrogen but also in exchange of chlorine atom and pyridazine ring scission; the latter process dominated for the unsubstituted triazolophthalazine. Two of the products showed promising stimulating activity towards the central nervous system with no significant toxic effects.     

Physical and Bioengineering Properties of Polyvinyl Alcohol Lens-Shaped Particles Versus Spherical Polyelectrolyte Complex Microcapsules as Immobilisation Matrices for a Whole-Cell Baeyer–Villiger Monooxygenase

Direct comparison of key physical and chemical-engineering properties of two representative matrices for multipurpose immobilisations was performed for the first time. Polyvinyl alcohol lens-shaped particles LentiKats® and polyelectrolyte complex microcapsules were characterised by advanced techniques with respect to the size distribution of the particles, their inner morphology as revealed by fluorescent probe staining, mechanical resistance, size-exclusion properties, determination of effective diffusion coefficient and environmental scanning electron microscope imaging. While spherical polyelectrolyte complex microcapsules composed of a rigid semipermeable membrane and a liquid core are almost uniform in shape and size (diameter of 0.82 mm; RSD?=?5.6 %), lens-shaped LentiKats® are characterised by wider size distribution (diameter of 3.65 mm; RSD?=?10.3 % and height of 0.341 mm; RSD?=?32.3 %) and showed the same porous structure throughout their whole volume at the mesoscopic (micrometre) level. Despite differences in their inner structure and surface properties, the pore diameter of?～?2.75 nm for regular polyelectrolyte complex microcapsules and?～?1.89 nm for LentiKats® were similar. These results were used for mathematical modelling, which provided the estimates of the effective diffusion coefficient of sucrose. This value was 1.67?×?10^?10 m² s^?1 for polyelectrolyte complex microcapsules and 0.36?×?10^?10 m² s^?1 for LentiKats®. Recombinant cells Escherichia coli-overexpressing enzyme cyclopentanone monooxygenase were immobilised in polyelectrolyte complex microcapsules and LentiKats® for comparison of their operational stability using model Baeyer–Villiger oxidation of (±)-cis-bicyclo [3.2.0] hept-2-en-6-one to regioisomeric lactones as important chiral synthons for potential pharmaceuticals. Both immobilisation matrices rendered high operational stability for whole-cell biocatalyst with no reduction in the biooxidation rate over 18 repeated reaction cycles.     

Adsorption of La,Eu and Lu on raw and modified red clay

Adsorption of La, Eu, and Lu on red clay was studied in an initial concentration range of 10^?4–10^?3 mol/dm³ and a pH range of 2–10. Among the different forms of red clay: T-clay (thermally modified), R-clay (raw, unmodified), Na-clay (sodium form), H-clay (acid form), and HDTMA-clay (surfactant-modified form), T-clay was found to be the most effective adsorbent of the lanthanides studied. The adsorption/desorption isotherms, i.e. log K _d versus log c _eq dependencies, had a linear character. Among the investigated lanthanides, Eu was most strongly bound by the clay surface and, therefore, parameters a (slopes of the lines log K _d = alog c _eq + b) of Eu were the highest compared to those for La and Lu. Desorption isotherms were located above adsorption isotherms, which resulted from chemiadsorption of the investigated lanthanides. Changes in lanthanide adsorption with pH were successfully modelled based on the molar fractions of Ln³⁺, LnOH²⁺, LnCO₃ ⁺, and Ln(CO₃) ₂ ^? species in the aqueous phase [Ln—lanthanide(III)].     

Fouling of nanofiltration membranes used for separation of fermented glycerol solutions

In this study, the glycerol solutions were fermented using Lactobacillus casei bacteria. The broths were pre-treated by microfiltration, followed by a further separation with nanofiltration. The latter process was carried out in two stages, using the NF270 and NF90 membranes, respectively. The concentrates thus obtained were enriched with citric acid (first stage) and then with lactic acid and glycerol (second stage). By means of SEM and AFM microscopy, as well as ATR-FTIR analysis, the intensity of membrane-fouling was studied. The colloidal fouling and bio-fouling caused a more than two-fold decrease in the permeate flux during microfiltration of the broth. This pre-treatment stage was effective, and a permeate turbidity of less than 0.2 NTU was obtained. However, the nanofiltration membranes exhibited a 30 % flux decline over the course of the process, mainly due to the organic fouling.     

Poly(vinyl methyl ether) hydrogels at temperatures below the freezing point of water—molecular interactions and states of water

Water interacting with a polymer reveals a number of properties very different to bulk water. These interactions lead to the redistribution of hydrogen bonds in water. It results in modification of thermodynamic properties of water and the molecular dynamics of water. That kind of water is particularly well observable at temperatures below the freezing point of water, when the bulk water crystallizes. In this work, we determine the amount of water bound to the polymer and of the so-called pre-melting water in poly(vinyl methyl ether) hydrogels with the use of Raman spectroscopy, dielectric spectroscopy, and calorimetry. This analysis allows us to compare various physical properties of the bulk and the pre-melting water. We also postulate the molecular mechanism responsible for the pre-melting of part of water in poly(vinyl methyl ether) hydrogels. We suggest that above ?60 °C, the first segmental motions of the polymer chain are activated, which trigger the process of the pre-melting.     

Excitation-wavelength Dependent Fluorescence of Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

The excitation wavelength dependence of the steady-state and time-resolved emission spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) in tetrahydrofuran (THF) at room temperature has been examined. It is found that the ratio of the fluorescence intensity of the long-wavelength and short-wavelength fluorescence bands strongly depends on the excitation wavelength, whereas the wavelengths of the fluorescence excitation and fluorescence bands maxima are independent on the observation/excitation wavelengths. The dynamic Stokes shift of fluorophore in locally excited (LE) and intramolecular charge transfer (ICT) states has been studied with a time resolution about 30 ps. The difference between Stokes shift in the LE and ICT states was attributed to the solvent response to the large photoinduced dipole moment of EAADCy in the fluorescent charge transfer state. On this base we can state that, the relaxation of the polar solvent molecules around the fluorophore was observed.     

The controlled separable projection property for Banach spaces

Let X, Y be two Banach spaces. We say that Y is a quasi-quotient of X if there is a continuous operator R: X → Y such that its range, R(X), is dense in Y.     

Atomic-scale friction on stepped surfaces of ionic crystals

We report on high-resolution friction force microscopy on a stepped NaCl(001) surface in ultrahigh vacuum. The measurements were performed on single cleavage step edges. When blunt tips are used, friction is found to increase while scanning both up and down a step edge. With atomically sharp tips, friction still increases upwards, but it decreases and even changes sign downwards. Our observations extend previous results obtained without resolving atomic features and are associated with the competition between the Schw?bel barrier and the asymmetric potential well accompanying the step edges.     

Crystal structure of novel R3Fe(Co,Ni)0.5SnS7 (R = Y,La, Ce,Pr, Nd,Sm, Gd,Tb, Dy and Ho) compounds

Structural Chemistry - The crystal structures of quaternary R3Fe0.5SnS7, R3Co0.5SnS7 and R3Ni0.5SnS7 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Ho) compounds of La3Mn0.5SiS7 structure type (space...     

Collision-Induced Dissociation of Diazirine-Labeled Peptide Ions. Evidence for Brønsted-Acid Assisted Elimination of Nitrogen

Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N₂ elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N₂ elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N₂ from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N₂ loss is proposed as a thermometer dissociation for peptide ion dissociations.