Non-conventional Behavior of a 2,1-Benzazaphosphole: Heterodiene or Hidden Phosphinidene?

Invited for the cover of this issue are Zoltán Benkő, Libor Dostál and co-workers at the University of Pardubice and the Budapest University of Technology and Economics. The image depicts signs for the two different pathways representing the two differing reaction types which were clearly observed for 2,1-benzazaphosphole. Read the full text of the article at 10.1002/chem.202101686 .     

Estimation of acidity constants,ionic mobilities and charges of antimicrobial peptides by capillary electrophoresis

Capillary electrophoresis (CE) was employed for the determination of thermodynamic acidity constants (pK_a) and actual ionic mobilities of polycationic antimicrobial peptides (AMPs). The effective electrophoretic mobilities of AMPs were measured by CE in a series of the background electrolytes within a wide pH range (2.00–12.25), at constant ionic strength (25 mM) and ambient temperature, using polybrene coated fused silica capillaries to suppress sorption of cationic AMPs to the capillary wall. Eventually, Haarhoff–Van der Linde peak fitting function was used for the determination of correct migration times of some AMPs peaks that were distorted by electromigration dispersion. The measured effective mobilities were corrected to 25°C. Mixed acidity constants, , and actual ionic mobilities, m_i, of AMPs were determined by the nonlinear regression analysis of pH dependence of their effective mobilities. The values were recalculated to thermodynamic pK_as using the Debye–Hückel theory. Thermodynamic pK_a of imidazolium group of histidine residues was found to be in the range 3.72–4.98, pK_a of α‐NH₃⁺ group was in the range 6.14–6.93, and pK_a of ε‐NH₃⁺ group of lysine spanned the interval 7.26–9.84, depending on the particular amino acid sequence of the AMPs. Actual ionic mobilities of AMPs with positive charges from one to six elementary units achieved values (9.8 – 36.5) × 10^?9 m²V^?1s^?1.     

Short- and long-term stability of lyophilised melatonin-loaded lecithin/chitosan nanoparticles

The aim of this study was to establish a freeze-drying process for melatonin-loaded lecithin/chitosan nanoparticles (NPs) to preserve their chemical and physical stability for a longer time period that what is possible in an aqueous suspension. Glucose and trehalose were investigated as potential excipients during freeze-drying of NP suspensions. Lecithin/chitosan NPs were characterised by mean diameter and zeta potential, ranging between 117.4 and 328.5 nm and 6.7 and 30.2 mV, respectively, depending on the lecithin type and chitosan content in the preparation. Melatonin loadings were up to 7.1%. For all lecithin/chitosan NPs, no notable differences in the mean particle size, size distribution, zeta potential or melatonin content were observed before or immediately after the lyophilisation process or after 7 months of storage at 4 °C. The residual moisture contents of lyophilisates with glucose and trehalose immediately after the lyophilisation process varied between 4.0-4.8% and 2.4-3.0%, respectively. All lecithin/chitosan NPs had a fully amorphous nature after the freeze-drying process, as indicated by modulated differential scanning calorimetry. NP lyophilisates with glucose had a low glass transition temperature (ca. 5 °C), confirming that lyophilisation with glucose as a cryoprotectant was not appropriate. All lyophilisates with trehalose had a glass transition temperature above the room temperature, allowing formation of the cake without a collapse of the structure, which was capable of preserving its characteristics and appearance following 7 months of storage at 4 °C.     

Blue phase III widening in CE6-dispersed surface-functionalised CdSe nanoparticles

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature.     

Optimization Strategy for Isocratic Separation of α-Aspartame and Its Breakdown Products by Reversed Phase Liquid Chromatography

α-Aspartame (L-α-aspartyl-L-phenylalanine methyl ester) is increasingly being used in wide variety of commonly consumed food products. This structure contains ester and peptide bonds. The ester linkage may hydrolyze to produce L-α-aspartyl-L-phenylalanine or cyclohydrolyze to produce the corresponding diketopiperazine ring. This ring can open to form L-α-aspartyl-L-phenylalanine and ultimately this compound can hydrolyze to L-phenylalanine and L-aspartic acid. The pH, buffer type, concentration, the presence of water and temperature are other important factors affecting its stability. Because α-aspartame can lose its sweetness under these conditions determination of aspartame and its breakdown products is extremely important for diet foods quality. The optimum mobile phase for the chromatographic separation was found to be acetonitrile-water (20:80, ν/ν) with 5.10^?3 M hexanesulfonic acid and a pH of 2.6.     

Quantitative analysis of sea-bed sediments from Eastern Black Sea by EDXRF spectrometry

Sea-bed sediments from Eastern Black Sea have been analyzed for their Fe, Ba and Sr contents using the methods of standard addition and energy dispersive X-ray fluorescence (EDXRF). Samples were prepared from powder sifted by a 200 mesh sieve. An annular 100 mCi²⁴¹Am radioactive source emitting 59.543 keV photons was used for excitation and a Ge(Li) detector, which has a 190 eV FWHM for 5.9 keV photons was used for intensity measurements. 2048 channels of the MCA are employed for 20 or 30 min. Dried and ground sea-bed sediments are found to contain 2.95–7.50% Fe, 0.032–0.268% Ba and about 73–273 ppm Sr. These results agree with those obtained via atomic absorption methods.     

Adsorption of organics on activated carbon cloth at zero surface coverage

Summary Adsorption properties of activated carbon cloth were investigated by gas-solid chromatography. Retention of several organic compounds was measured in the temperature range from 200 to 250°C. The gas/solid distribution coefficients and the related thermodynamic function of adsorption at zero surface coverage were determined. The obtained experimental data were used to explain the adsorbent-adsorbate interaction.     

Measurement of absolute intensity of 1001 keV gamma-ray of 234mPa

The sorption behavior of ²³⁵U fission fission products ⁹⁹Mo and ¹³²Te was studied through batch and dynamic experiments when they were dissolved in 1 to 7M HNO₃ solutions. It was found that ⁹⁹Mo is always totally adsorbed on hydrated SnO₂, while ¹³²Te is rather weakly adsorbed, therefore they can be separated from each other although ¹³²Te in the solution still remains contaminated with other radionuclides as well as ⁹⁹Mo does in the solid.