Self‐assembled polyurea macromer nanodispersion and resulting hybrid polyurea‐acrylic emulsions and films

A polyurea macromer (PUM) was synthesized and dispersed in basic conditions to form self‐assembled nanoparticles (<20 nm dispersions, up to 30 wt % aq. soln.). These nanoparticles enabled surfactant‐free emulsion polymerization to form hybrid polyurea‐acrylic particles despite the absence of a measureable water‐soluble fraction. The T_g of the starting PUM material was a strong function of the PUM's extent of neutralization and hydration (varying between 100 °C and >175 °C) due to changes in hydrogen and ionic bonding. Two separate hybrid polyurea‐acrylic emulsion systems were prepared: one by direct polymerization of (meth)acrylic monomers in the presence of the nanodispersion and a second by a physical blend of PUM nanodispersion with an acrylic latex control. The direct polymerization method resulted in a hybrid emulsion particle size that developed by a mechanism resembling conventional emulsion polymerization and was unlike that described for seeded polyurethane dispersion systems. Film hardness was shown to increase with increasing coating thickness for the hybrid film prepared by direct polymerization. The resulting mechanical properties could be explained by applying mechanical models for a composite foam structure. These results were unprecedented for normal elastomer films. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1373–1388     

Crystal structure of K[PtCl3(caffeine)] and its interactions with important nitrogen-donor ligands

The crystal structure of K[PtCl₃(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl^? ions. The bond lengths and angles of K[PtCl₃(caffeine)] were compared with those reported for [PtCl₃(caffeine)]^? and K[PtCl₃(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K⁺ and Cl^? are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl₃(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by ¹H NMR spectroscopy at 295 K in D₂O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl₃(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine.     

Catalytic activity of glucose oxidase after dielectrophoretic immobilization on nanoelectrodes

Dielectrophoresis (DEP) is an AC electrokinetic effect that is proven to be effective for the immobilization of not only cells, but also of macromolecules, for example, antibodies and enzyme molecules. In our previous work, we have already demonstrated the high catalytic activity of immobilized horseradish peroxidase after DEP. To evaluate the suitability of the immobilization method for sensing or research in general, we want to test it for other enzymes, too. In this study, glucose oxidase (GOX) from Aspergillus niger was immobilized on TiN nanoelectrode arrays by DEP. Fluorescence microscopy showed the intrinsic fluorescence of the immobilized enzymes flavin cofactor on the electrodes. The catalytic activity of immobilized GOX was detectable, but a fraction of less than 1.3% of the maximum activity that was expected for a full monolayer of immobilized enzymes on all electrodes was stable for multiple measurement cycles. Therefore, the effect of DEP immobilization on the catalytic activity strongly depends on the used enzyme.     

Improved Dermal and Transdermal Delivery of Curcumin with SmartFilms and Nanocrystals

Poor aqueous solubility of active compounds is a major issue in today’s drug delivery. In this study the smartFilm-technology was exploited to improve the dermal penetration efficacy of a poorly soluble active compound (curcumin). Results were compared to the dermal penetration efficacy of curcumin from curcumin bulk suspensions and nanocrystals, respectively. The smartFilms enabled an effective dermal and transdermal penetration of curcumin, whereas curcumin bulk- and nanosuspensions were less efficient when the curcumin content was similar to the curcumin content in the smartFilms. Interestingly, it was found that increasing numbers of curcumin particles within the suspensions increased the passive dermal penetration of curcumin. The effect is caused by an aqueous meniscus that is created between particle and skin if the dispersion medium evaporates. The connecting liquid meniscus causes a local swelling of the stratum corneum and maintains a high local concentration gradient between drug particles and skin. Thus, leading to a high local passive dermal penetration of curcumin. The findings suggest a new dermal penetration mechanism for active compounds from nano-particulate drug delivery systems, which can be the base for the development of topical drug products with improved penetration efficacy in the future.     

Fluorescence Polarization Based Nucleic Acid Testing for Rapid and Cost‐Effective Diagnosis of Infectious Disease

A new nucleic acid detection method was developed for a rapid and cost‐effective diagnosis of infectious disease. This approach relies on the three unique elements: 1) detection probes that regulate DNA polymerase activity in response to the complementary target DNA; 2) universal reporters conjugated with a single fluorophore; and 3) fluorescence polarization (FP) detection. As a proof‐of‐concept, the assay was used to detect and sub‐type Salmonella bacteria with sensitivities down to a single bacterium in less than three hours.     

Nannocystin A: an Elongation Factor 1 Inhibitor from Myxobacteria with Differential Anti‐Cancer Properties

Cultivation of myxobacteria of the Nannocystis genus led to the isolation and structure elucidation of a class of novel cyclic lactone inhibitors of elongation factor 1. Whole genome sequence analysis and annotation enabled identification of the putative biosynthetic cluster and synthesis process. In biological assays the compounds displayed anti‐fungal and cytotoxic activity. Combined genetic and proteomic approaches identified the eukaryotic translation elongation factor 1α (EF‐1α) as the primary target for this compound class. Nannocystin A ( 1 ) displayed differential activity across various cancer cell lines and EEF1A1 expression levels appear to be the main differentiating factor. Biochemical and genetic evidence support an overlapping binding site of 1 with the anti‐cancer compound didemnin B on EF‐1α. This myxobacterial chemotype thus offers an interesting starting point for further investigations of the potential of therapeutics targeting elongation factor 1.     

Plastic stress-strain history at notch roots in tensile strips under monotonic loading

Various authors have proposed analytic relations for predicting the plastic behavior at the root of a notch. Among these are relations by Neuber and by Hardrath and Ohman, the latter having generalized on earlier work by Stowell. These methods have had limited experimental confirmation and it was the objective of the investigation reported herein to assess the predictive value of each of the two theories by comparison with test data on externally notched tensile specimens, monotonically loaded to large strains. Since maximum notch-root strain and net-section stress are the only parameters which can be directly measured in a test, theoretical predictions of these same parameters were developed. This was done using a piece-wise analytical representation of the stress-strain curve. Computer programs were developed for analyzing the stress-strain data and for computing the theoretical results. A comparison of theory with tests on flat, notched specimens of AISI 4340 steel, heat treated, with initial elastic concentration factors of 1.5 to 2.0 showed a systematic discrepancy which is attributed in part to notch strengthening due to triaxial stress. The discrepancy is of the order of 5 percent for the Neuber theory and larger for the Hardrath-Ohman theory for notch strains less than of 0.015 in./in. and becomes progressively larger for both theories at notch strains in excess of 0.015 in./in. For the mild notches studied here, the Neuber theory has better predictive value.