Volatile compounds composition and antioxidant activity of bee pollen collected in Lithuania

Characterization of volatile compounds composition and evaluation of antioxidant properties of bee pollen collected in Lithuania is presented in the paper, which is the first study on pollen of Lithuanian origin to our knowledge. Three polyfloral pollen samples collected by honey bees were analyzed. Characterization of volatile compounds was performed using solid phase microextraction (SPME) and GC-MS. Styrene was predominant in all samples contributing 19.6–27.0 mass %. Sample A distinguished by a high amount of limonene, 9.0 mass %, sample B differed from the rest by a high content of hexanal, 9.3 mass %, and nonanal, 12.3 mass %, while sample C showed the highest content of 1-tridecene, 43.3 mass %. Screening of antioxidant properties was carried out by spectrophotometric methods and liquid chromatography coupled with a post-column 1,1-diphenyl-2-picrylhydrazyl (DPPH) reaction detector and electrochemical detector. Total phenolic and flavonoid contents together with radical scavenging activity in the free radical (DPPH) model system were evaluated in the tested samples. Total phenolic content varied from 24.4 mg g^?1 to 38.9 mg g^?1, total flavonoid content was in the range of 7.3–10.0 mg g^?1 and radical scavenging activity was found between 30.7 mg g^?1 and 34.9 mg g^?1, all data are expressed in rutin equivalents. To process the collected data statistically and classify the bee pollen samples to clusters according to their volatile composition and antioxidant activity, principal component analysis, hierarchical cluster analysis and non-linear discriminant analysis were applied.     

The Normal-Mode Entropy in the MM/GBSA Method: Effect of System Truncation, Buffer Region, and Dielectric Constant

We have performed a systematic study of the entropy term in the MM/GBSA (molecular mechanics combined with generalized Born and surface-area solvation) approach to calculate ligand-binding affinities. The entropies are calculated by a normal-mode analysis of harmonic frequencies from minimized snapshots of molecular dynamics simulations. For computational reasons, these calculations have normally been performed on truncated systems. We have studied the binding of eight inhibitors of blood clotting factor Xa, nine ligands of ferritin, and two ligands of HIV-1 protease and show that removing protein residues with distances larger than 8-16 ? to the ligand, including a 4 ? shell of fixed protein residues and water molecules, change the absolute entropies by 1-5 kJ/mol on average. However, the change is systematic, so relative entropies for different ligands change by only 0.7-1.6 kJ/mol on average. Consequently, entropies from truncated systems give relative binding affinities that are identical to those obtained for the whole protein within statistical uncertainty (1-2 kJ/mol). We have also tested to use a distance-dependent dielectric constant in the minimization and frequency calculation (ε = 4r), but it typically gives slightly different entropies and poorer binding affinities. Therefore, we recommend entropies calculated with the smallest truncation radius (8 ?) and ε =1. Such an approach also gives an improved precision for the calculated binding free energies.     

Sumsets of sparse sets

Let ?? be a constant in the interval (0, 1), and let A be an infinite set of positive integers which contains at least c ₁ x ^?? and at most c ₂ x ^?? elements in the interval [1, x] for some constants c ₂ > c ₁ > 0 independent of x and each x ?? x ₀. We prove that then the sumset A + A has more elements than A (counted up to x) by a factor ${{c\left( \sigma \right)\sqrt {\log x} } \mathord{\left/ {\vphantom {{c\left( \sigma \right)\sqrt {\log x} } {\log }}} \right. \kern-0em} {\log }}$ log x for x large enough. An example showing that this function cannot be greater than ? log x is also given. Another example shows that there is a set of positive integers A which contains at least x ^?? and at most x ^??+? elements in [1, x] such that A + A is greater than A only by a constant factor. The proof of the main result is based on an effective version of Freiman??s theorem due to Mei-Chu Chang.     

Phenoxyhydroxypropylhydroxyethylcellulose—new amphiphilic cellulose derivative

A new amphiphilic cellulose derivative phenoxyhydroxypropylhydroxyethylcellulose of substitution degree up to 0.67 was synthesized by reaction of water-soluble hydroxyethylcellulose with 2,3-epoxypropylphenylether in the presence of sodium hydroxide as a catalyst. The chemical composition of the derivative was confirmed by means of UV, IR- and ¹³C-NMR-spectroscopy. The derivatives with substitution degree up to 0.12 are soluble in water and water–alcohol mixtures. With increasing substitution degree, the polymers lose their water solubility, but still dissolve in water–alcohol mixtures. All products are soluble in aprotic solvents. The effect of the reaction conditions, such as temperature and molar ratios of reaction components, on both the reaction rate and degree of substitution was investigated.     

Modelling linear reactions in inhomogeneous catalytic systems

The kinetics of linear chemical reactions in an inhomogeneous medium is modeled as an evolutionary system characterized by a fractional derivative. The corresponding mathematical model depending on one nonlocal parameter $0< \alpha <1$ is proposed. Reactions with one degree of freedom are analyzed. Solutions of the corresponding kinetic equations are shown to depend on the nonlocality parameter $\alpha $ . The concept of the critical moment of time is introduced, and the dependence of its value on the value of the relaxation coefficient is determined.     

The Evidence of the Bystander Effect after Bleomycin Electrotransfer and Irreversible Electroporation

One of current applications of electroporation is electrochemotherapy and electroablation for local cancer treatment. Both of these electroporation modalities share some similarities with radiation therapy, one of which could be the bystander effect. In this study, we aimed to investigate the role of the bystander effect following these electroporation-based treatments. During direct CHO-K1 cell treatment, cells were electroporated using one 100 µs duration square wave electric pulse at 1400 V/cm (for bleomycin electrotransfer) or 2800 V/cm (for irreversible electroporation). To evaluate the bystander effect, the medium was taken from directly treated cells after 24 h incubation and applied on unaffected cells. Six days after the treatment, cell viability and colony sizes were evaluated using the cell colony formation assay. The results showed that the bystander effect after bleomycin electrotransfer had a strong negative impact on cell viability and cell colony size, which decreased to 2.8% and 23.1%, respectively. On the contrary, irreversible electroporation induced a strong positive bystander effect on cell viability, which increased to 149.3%. In conclusion, the results presented may serve as a platform for further analysis of the bystander effect after electroporation-based therapies and may ultimately lead to refined application of these therapies in clinics.