PPV Polymerization through the Gilch Route: Diradical Character of Monomers

Despite various studies on the polymerization of poly(p‐phenylene vinylene) (PPV) through different precursor routes, detailed mechanistic knowledge on the individual reaction steps and intermediates is still incomplete. The present study aims to gain more insight into the radical polymerization of PPV through the Gilch route. The initial steps of the polymerization involve the formation of a p‐quinodimethane intermediate, which spontaneously self‐initiates through a dimerization process leading to the formation of diradical species; chain propagation ensues on both sides of the diradical or chain termination occurs by the formation of side products, such as [2.2]paracyclophanes. Furthermore, different p‐quinodimethane systems were assessed with respect to the size of their aromatic core as well as the presence of heteroatoms in/on the conjugated system. The nature of the aromatic core and the specific substituents alter the electronic structure of the p‐quinodimethane monomers, affecting the mechanism of polymerization. The diradical character of the monomers has been investigated with several advanced methodologies, such as spin‐projected UHF, CASSCF, CASPT2, and DMRG calculations. It was shown that larger aromatic cores led to a higher diradical character in the monomers, which in turn is proposed to cause rapid initiation.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

Principal component analysis of the main factors of line intensity enhancements observed in oscillating direct current plasma

Enhancement of emission line intensities by induced oscillations of direct current (DC) arc plasma with continuous aerosol sample supply was investigated using multivariate statistics. Principal component analysis (PCA) was employed to evaluate enhancements of 34 atomic spectral lines belonging to 33 elements and 35 ionic spectral lines belonging to 23 elements. Correlation and classification of the elements were done not only by a single property such as the first ionization energy, but also by considering other relevant parameters. Special attention was paid to the influence of the oxide bond strength in an attempt to clarify/predict the enhancement effect. Energies of vaporization, atomization, and excitation were also considered in the analysis. In the case of atomic lines, the best correlation between the enhancements and first ionization energies was obtained as a negative correlation, with weak consistency in grouping of elements in score plots. Conversely, in the case of ionic lines, the best correlation of the enhancements with the sum of the first ionization energies and oxide bond energies was obtained as a positive correlation, with four distinctive groups of elements. The role of the gas-phase atom-oxide bond energy in the entire enhancement effect is underlined.     

Microwave-assisted synthesis of allylic amines: considerable rate acceleration in the hydrozirconation-transmetalation-aldimine addition sequence

The hydrozirconation of alkynes with zirconocene hydrochloride and the dimethylzinc-mediated addition of alkenylzirconocenes to diphenylphosphinoyl imines can be greatly accelerated with microwave irradiation, resulting in a convenient and rapid one-pot process for the preparation of synthetically useful allylic amines.     

New tin templates for the synthesis of macrocyclic polythiaether-polythiaester ligands

The preparation of new tin templates, stannathianes 1-3 is described. New templates have been successfully applied to the synthesis of macrocyclic polythialactones 4-9 by cyclization of corresponding stannathianes 1-3 with pimeloyl dichloride.     

Novel polycarbonate-based polyurethane elastomers: Composition–property relationship

Novel all-aliphatic polycarbonate-based polyurethane (PC-PU) elastomers, as well as PC-PU nanocomposites filled with organic-modified clays were synthesized, characterized and studied. It was found that they have very attractive mechanical properties (e.g., elongation at break between 600% and 800%). The prepared PC-PUs possess a distinctly segmented structure, which is the key prerequisite for their behavior as strong physical rubbery networks. All synthesized materials melt at elevated temperatures (between 110 and 200 °C) and hence can be processed like normal thermoplastics. The dispersion of the clay nanofiller was achieved by its one day swelling in the alcohol and a brief successive stirring. This procedure is very successful and leads to a partial exfoliation of the clay (documented by X-ray diffraction and TEM). The best nanocomposites with very good tensile properties, particularly with significantly increased moduli were obtained using the bentonite nanofiller. The study shows that the nanofiller interacts strongly with the hard domains and influences their melting temperature (DMTA and DSC), but it does not affect the glass transition temperature of soft domains. While Cloisite 15A was found to interact preferentially with the hard domains, the organic modified bentonite shows a strong interaction with both soft and hard segments, behaving as a blending agent. Hard domains in neat matrices, formed by hydrogen bonding of hard segments, were practically invisible by X-ray or TEM, but were successfully detected by AFM. Besides excellent mechanical properties, the prepared elastomers and their nanocomposites showed an interesting phase behavior (which was studied by combining DMTA and modulated DSC).     

Application of the fractional factorial design in multiple W/O/W emulsions

In presented research, multiple W/O/W emulsions were developed by using experimental design method. A 24-1 fractional factorial design was performed by varying the following input parameters: primary polymeric emulsifier (PEG 30-dipolyhydroxystearate) concentration (0.8% and 2.4%), secondary polymeric emulsifier (Poloxamer 407) concentration (0.8% and 1.2%), electrolyte magnesium sulfate heptahydrate (0.08% and 0.4%) and electrolyte sodium chloride (0.08% and 0.4%). Multiple emulsions were prepared by a two-step emulsification process. Obtained emulsions were characterized with rheological measurements, conductivity and centrifugation tests. Factorial analysis revealed that the concentration of the primary emulsifier was the predominant factor influencing the phase separation, conductivity and maximal apparent viscosity. Additionally, electrolyte magnesium sulfate heptahydrate was more efficient in stabilizing these systems, compared to sodium chloride. The applied fractional factorial design method enabled determination of the optimal concentrations of the primary and secondary emulsifier, as well as the concentration of electrolytes, in order to obtain W/O/W emulsions with desired maximal apparent viscosities, low values of conductivity and without phase separation after centrifugation.     

Comparative analysis of CE‐SSCP to standard RFLP‐CE‐FLA method in quantification of known viral variants within an RNA virus quasispecies

RNA viruses display the highest replication error rate in our biosphere, leading to highly diverse viral populations termed quasispecies. The gold standard method for detection and quantification of variants in a quasispecies is cloning and sequencing, but it is expensive, laborious and time consuming. Therefore, other mutation detection approaches, including SSCP, are often used. In this study, we demonstrate development and the usage of a CE‐SSCP method for quantification of two nearly identical viral variants in heterogenic population of a mumps virus strain and its comparison to RFLP‐CE‐fragment length analysis (RFLP‐CE‐FLA). Analyzed PCR fragments were of the same size (245 bp) with one difference in their nucleotide sequence. The limit of detection of both methods was at 5% of the minor variant. When PCR amplicons of the two variants were pooled, methods' results were very similar. On the contrary, the quantification results of samples in which variants were mixed prior to PCR showed substantial difference between the two methods. Our results indicate that although both methods can be used for detection and monitoring of a specific mutation within a viral population, caution should be taken when quantitative analysis of complex samples is based solely on results of one method.     

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.