Silicone-acrylic hybrid aqueous dispersions of core–shell particle structure and corresponding silicone-acrylic nanopowders designed for modification of powder coatings and plastics. Part I – Effect of silicone resin composition on properties of dispersions and corresponding nanopowders

Aqueous silicone-acrylic dispersions with core–shell particle structure can be obtained in the process of emulsion polymerization of acrylic or methacrylic monomers in previously synthesized silicone resin dispersions. If the glass transition temperature (T_g) of the shell is around +120 °C or higher, drying of such dispersions leads to “nanopowders” which can be applied as impact modifiers for powder coatings and plastics due to the presence of low T_g silicone resin contained in the hybrid nanoparticles. The aim of our study was to investigate the effect of silicone resin composition on the properties of dispersions and the corresponding nanopowders what, in turn, was expected to influence the properties of powder coatings modified with such nanopowders. Silicone resin dispersions (DSI) were synthesized by emulsion polymerization of three silicone monomers: octamethylcyclotetrasiloxane (D4), methyltrimethoxysilane (METMS) and methacryloyltrimethoxysilane (MATMS) in the presence of dodecylbenzenesulphonic acid playing the role of both surfactant and polymerization catalyst. Silicone-acrylic hybrid dispersions (DASI) having core–shell particle structure confirmed by TEM were further obtained by emulsion polymerization of methyl methacrylate in DSI, and eventually nanopowders (NP-DASI) were produced by spray-drying of DASI. A designed experiment was conducted where the different proportions of D4, METMS and MATMS were used in DSI synthesis and a range of properties of DSI, DASI and NP-DASI were tested. A significant effect of starting silicone monomers composition (reflected in silicone resin structure) on dispersion particle size was observed what could be explained by differences in their hydrophobicity. SEM investigations revealed that NP-DASI were produced in the form of 1–10 μm agglomerates of round-shaped nanoparticles of ca. 120 nm in size. Two clear glass transition temperatures (T_g) of NP-DASI were identified by DSC: one attributed to silicone part – around −120 °C – and the other attributed to poly(methyl methacrylate) (PMM) part – around +120 °C. T_g attributed to silicone part decreased with increased share of D4 and MATMS in the silicone monomers composition while T_g of PMM part showed a minimum for specific composition of silicone monomers.     

Structural Characterization of EnpA D,L-Endopeptidase from Enterococcus faecalis Prophage Provides Insights into Substrate Specificity of M23 Peptidases

The best-characterized members of the M23 family are glycyl-glycine hydrolases, such as lysostaphin (Lss) from Staphylococcus simulans or LytM from Staphylococcus aureus. Recently, enzymes with broad specificities were reported, such as EnpA_CD from Enterococcus faecalis, that cleaves D,L peptide bond between the stem peptide and a cross-bridge. Previously, the activity of EnpA_CD was demonstrated only on isolated peptidoglycan fragments. Herein we report conditions in which EnpA_CD lyses bacterial cells live with very high efficiency demonstrating great bacteriolytic potential, though limited to a low ionic strength environment. We have solved the structure of the EnpA_CD H109A inactive variant and analyzed it in the context of related peptidoglycan hydrolases structures to reveal the bases for the specificity determination. All M23 structures share a very conserved β-sheet core which constitutes the rigid bottom of the substrate-binding groove and active site, while variable loops create the walls of the deep and narrow binding cleft. A detailed analysis of the binding groove architecture, specificity of M23 enzymes and D,L peptidases demonstrates that the substrate groove, which is particularly deep and narrow, is accessible preferably for peptides composed of amino acids with short side chains or subsequent L and D-isomers. As a result, the bottom of the groove is involved in interactions with the main chain of the substrate while the side chains are protruding in one plane towards the groove opening. We concluded that the selectivity of the substrates is based on their conformations allowed only for polyglycine chains and alternating chirality of the amino acids.     

Optimization of the QuEChERS Method for Determination of Pesticide Residues in Chicken Liver Samples by Gas Chromatography-Mass Spectrometry

The goal of this research was to evaluate the application of Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method for the determination of organochlorine, organophosphate, and carbamate pesticides in fatty animal matrices such as liver of chicken obtained from National Research Institute of Animal Production in Balice (Poland). Pesticides extraction effectiveness was evaluated at two different spiking levels (0.010 and 0.020 mg kg^?1) and efficiency of the dispersive solid-phase extraction (d-SPE) clean-up step was evaluated by comparison adding different d-SPE sorbent combinations (PSA?+?GCB, PSA?+?C₁₈, PSA?+?SAX, and PSA?+?NH₂). The analysis of pesticide residues was performed by gas chromatography ion trap mass spectrometry (GC/IT-MS). The linear relation was observed from 0 to 400 ng mL^?1 and the determination coefficient R ²?>?0.997 in all instances for all target analytes. Better recoveries were obtained in samples at 0.020 mg kg^?1 spiking level. The recoveries were in the range 70–120 %, with relative standard deviation (RSD) values lower than 15 % at 0.020 mg kg^?1 spiking level for most pesticides. Similar recovery ratios were obtained with the four different combinations of sorbents tested in the clean-up step, with better precision when the (PSA?+?SAX) combination was tested. Limits of detection (LODs) ranged from 0.001 to 0.005 mg kg^?1 and limits of quantification (LOQs) ranged from 0.003 to 0.015 mg kg^?1. The proposed method was successfully applied analyzing pesticide residues in real chicken liver samples; detectable pesticide residues were observed, but in all of the cases, the contamination level was lower than the default maximum residue levels (MRLs) set by European Union (EU), Regulation (EC) N 396/2005.     

Evaluating tear clearance rate with optical coherence tomography

Purpose

To assess the early-phase of tear clearance rate (TCR) with anterior segment optical coherence tomography (OCT) and to determine the association between TCR and other clinical measures of the tear film in a group of young subjects with different levels of tear film quality.

Influence of flexible segment length on the phase structure and properties of poly(hexamethylene 2,5-furandicarboxylate)-block-biopolytetrahydrofuran copolymers

Two series of biobased poly(ether-ester)s comprised of poly(hexamethylene 2,5-furandicarboxylate) (PHF) as the rigid segments and biopolytetrahydrofuran (pTHF) with different molecular masses (1000 and 2000 g/mol) as the flexible segments were synthesized employing polycondensation in the molten state. The study mainly focuses on comparing these two series in terms of the length of the flexible segment. The content of pTHF segments in the copolymer chains varied from 25 to 75 wt.%. The molecular structure and composition, phase structure, and thermal and mechanical properties were characterized by nuclear magnetic resonance (¹H NMR) and Fourier-transformed infrared (FTIR) spectroscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and positron annihilation lifetime spectroscopy (PALS). In addition, mechanical performance and thermo-oxidative and thermal stability have been investigated. Moreover, cyclic tensile properties were studied to evaluate the elastic properties. ¹H NMR and FTIR spectroscopies demonstrate that the syntheses were correctly carried out, which made it possible to obtain the desired compositions of the block copolymers with high molecular masses. The decrease in T_m1, T_c1, and X_cPHF values was visible, along with the increase in the flexible segment content. Moreover, the characteristic properties measured by PALS and the values of temperatures designated from TGA (inert and oxidizing atmosphere) did not vary between copolymer series PHF-b-F-pTHF1000 and PHF-b-F-pTHF2000. In turn, along with an increase in flexible segment content and the length of the pTHF, the values of tensile modulus, stress at break, and hardness decrease, while the value of elongation at break increases.     

The Protective Function and Modification of Secondary Metabolite Accumulation in Response to Light Stress in Dracocephalum forrestii Shoots

The aim of this work was to determine the effect of stress conditions caused by different light sources, i.e., blue LED (λ = 430 nm), red LED (λ = 670 nm), blue and red LED (70%:30%) and white LED (430–670 nm) on the growth and morphology of cultivated in vitro Dracocephalum forrestii shoot culture. It also examines the effects on bioactive phenolic compound production and photosynthetic pigment content, as well as on antioxidant enzyme activity (CAT, SOD, POD) and antioxidant properties. The most beneficial proliferation effect was observed under white LEDs (7.1 ± 2.1 shoots per explant). The white and blue lights stimulated the highest fresh weight gain, while red light induced the highest dry weight gain. The total phenolic acid content ranged from 13.824 ± 1.181 to 20.018 ± 801 mg g DW⁻¹ depending on light conditions. The highest content of rosmarinic acid was found in the control shoots (cultivated under fluorescent lamps), followed by culture grown under red light. All LED treatments, especially red and blue, increased salvianolic acid B content, and blue increased apigenin p-coumarylrhamnoside biosynthesis. The greatest ferric reduction activity was observed in shoots cultivated under red light, followed by blue; this is associated with the presence of the highest total phenol content, especially phenolic acids. Similarly, the highest DPPH radical scavenging potential was observed under red light followed by blue. This study proves that LEDs have emerged as significant support for directed in vitro propagation, taking advantage of specific stress responses on various light spectra. This study also showed how stress induced by different LED light spectra increases in Dracocephalum forrestii the synthesis of pharmacologically-active compounds. Hence, light stress may turn out to be a simpler alternative to metabolic engineering for improving the production of secondary metabolites of therapeutic value.     

Novel Antibacterial Copolymers Based on Quaternary Ammonium Urethane-Dimethacrylate Analogues and Triethylene Glycol Dimethacrylate

The growing scale of secondary caries and occurrence of antibiotic-resistant bacterial strains require the development of antibacterial dental composites. It can be achieved by the chemical introduction of quaternary ammonium dimethacrylates into dental composites. In this study, physicochemical and antibacterial properties of six novel copolymers consisting of 60 wt. % quaternary ammonium urethane-dimethacrylate analogues (QAUDMA) and 40 wt. % triethylene glycol dimethacrylate (TEGDMA) were investigated. Uncured compositions had suitable refractive index (RI), density (d_m), and glass transition temperature (Tg_m). Copolymers had low polymerization shrinkage (S), high degree of conversion (DC) and high glass transition temperature (Tg_p). They also showed high antibacterial effectiveness against S. aureus and E. coli bacterial strains. It was manifested by the reduction in cell proliferation, decrease in the number of bacteria adhered on their surfaces, and presence of growth inhibition zones. It can be concluded that the copolymerization of bioactive QAUDMAs with TEGDMA provided copolymers with high antibacterial activity and rewarding physicochemical properties.     

Zinc Coordination Compounds with Benzimidazole Derivatives: Synthesis,Structure, Antimicrobial Activity and Potential Anticancer Application

Developing new, smart drugs with the anticancer activity is crucial, especially for cancers, which cause the highest mortality in humans. In this paper we describe a series of coordination compounds with the element of health, zinc, and bioactive ligands, benzimidazole derivatives. By way of synthesis we have obtained four compounds named C1, C2, C4 and C4. Analytical analyses (elemental analysis (EA), flame atomic absorption spectrometry (FAAS)), spectroscopic (Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS)) and thermogravimetric (TG) methods and the definition of crystal structures were used to explore the nature of bonding and to elucidate the chemical structures. The collected analytical data allowed the determination of the stoichiometry in coordination compounds, thermal stability, crystal structure and way of bonding. The cytotoxicity effect of the new compounds as a potential antitumor agent on the glioblastoma (T98G), neuroblastoma (SK-N-AS) and lung adenocarcinoma (A549) cell lines and human normal skin fibroblasts (CCD-1059Sk) was also determined. Cell viability was determined by the MTT assay. The results obtained confirmed that conversion of ligands into the respective metal complexes significantly improved their anticancer properties. The complexes were screened for antibacterial and antifungal activities. The ADME technique was used to determine the physicochemical and biological properties.     

Structural and Biofunctional Insights into the Cyclo(Pro-Pro-Phe-Phe-) Scaffold from Experimental and In Silico Studies: Melanoma and Beyond

Short peptides have great potential as safe and effective anticancer drug leads. Herein, the influence of short cyclic peptides containing the Pro-Pro-Phe-Phe sequence on patient-derived melanoma cells was investigated. Cyclic peptides such as cyclo(Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe-), called CLA, and cyclo(Pro-homoPro-β³homoPhe-Phe-), called P11, exert the cytotoxic and the cytostatic effects in melanoma cells, respectively. CLA was the most active peptide as it reduced the viability of melanoma cells to 50% of control at about 10 µM, whereas P11 at about 40 µM after 48 h incubation. Interestingly, a linear derivative of P11 did not induce any effect in melanoma cells confirming previous studies showing that cyclic peptides exert better biological activity compared to their linear counterparts. According to in silico predictions, cyclic tetrapeptides show a better pharmacokinetic and toxic profile to humans than CLA. Notably, the spatial structure of those peptides containing synthetic amino acids has not been explored yet. In the Cambridge Structural Database, there is only one such cyclic tetrapeptide, cyclo((R)-β²homoPhe-D-Pro-Lys-Phe-), while in the Protein Data Bank—none. Therefore, we report the first crystal structure of cyclo(Pro-Pro-β³homoPhe-Phe-), denoted as 4B8M, a close analog of P11, which is crucial for drug discovery. Comparative molecular and supramolecular analysis of both structures was performed. The DFT findings revealed that 4B8M is well interpreted in the water solution. The results of complex Hirshfeld surface investigations on the cooperativity of interatomic contacts in terms of electrostatic and energetic features are provided. In short, the enrichment ratio revealed O^…H/H^…O and C^…H/H^…C as privileged intercontacts in the crystals in relation to basic and large supramolecular H-bonding synthon patterns. Furthermore, the ability of self-assemble 4B8M leading to a nanotubular structure is also discussed.     

Aspalathin and Other Rooibos Flavonoids Trapped α-Dicarbonyls and Inhibited Formation of Advanced Glycation End Products In Vitro

The excessive dietary intake of simple sugars and abnormal metabolism in certain diseases contribute to the increased production of α-dicarbonyls (α-DCs), such as methylglyoxal (MGO) and glyoxal (GO), the main precursors of the formation of advanced glycation end products (AGEs). AGEs play a vital role, for example, in the development of cardiovascular diseases and diabetes. Aspalathus linearis (Burman f.) R. Dahlgren (known as rooibos tea) exhibits a wide range of activities beneficial for cardio-metabolic health. Thus, the present study aims to investigate unfermented and fermented rooibos extracts and their constituents for the ability to trap MGO and GO. The individual compounds identified in extracts were tested for the capability to inhibit AGEs (with MGO or GO as a glycation agent). Ultra-high-performance liquid chromatography coupled with an electrospray ionization mass spectrometer (UHPLC–ESI–MS) was used to investigate α-DCs’ trapping capacities. To evaluate the antiglycation activity, fluorescence measurement was used. The extract from the unfermented rooibos showed a higher ability to capture MGO/GO and inhibit AGE formation than did the extract from fermented rooibos, and this effect was attributed to a higher content of dihydrochalcones. The compounds detected in the extracts, such as aspalathin, nothofagin, vitexin, isovitexin, and eriodictyol, as well as structurally related phloretin and phloroglucinol (formed by the biotransformation of certain flavonoids), trapped MGO, and some also trapped GO. AGE formation was inhibited the most by isovitexin. However, it was the high content of aspalathin and its higher efficiency than that of metformin that determined the antiglycation and trapping properties of green rooibos. Therefore, A. linearis, in addition to other health benefits, could potentially be used as an α-DC trapping agent and AGE inhibitor.