Highly effective contact antimicrobial surfaces via polymer surface modifiers

Contact antimicrobial coatings with poly(alkylammonium) compositions have been a subject of increasing interest in part because of the contribution of biocide release coatings to antibiotic resistance. Herein, a concept for antimicrobial coatings is developed on the basis of the thermodynamically driven surface concentration of soft block side chains. The concept incorporates structural and compositional guidance from naturally occurring antimicrobial proteins and achieves compositional economy via a polymer-surface modifier (PSM). To implement this concept, polyurethanes were prepared having random copolymer 1,3-propylene oxide soft blocks with alkylammonium and either trifluoroethoxy or PEGlyted side chains. Six carbon (C6) and twelve carbon (C12) alkylammonium chain lengths were used. The PSMs were first tested as 100% coatings and were highly effective against aerosol challenges of Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli). To evaluate the surface concentration, solutions containing 2 wt % PSM with a conventional polyurethane were evaporatively coated onto glass slides. These 2% PSM coatings were tested against aerosol challenges of Gram-negative (Pseudomonas aeruginosa and Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria (107 CFU/mL/30 min). A copolymer soft block containing trifluorethoxy (89 mol %) and C-12 alkylammonium (11 mol %) side chains gave the highest biocidal effectiveness in 30 min: 2 wt %, Gram(+/-) bacteria, 100% kill, and 3.6-4.4 log reduction. A zone of inhibition test showed no biocide release for PSMs and PSM-modified compositions. Characteristics that contribute to concept validation include good hard block/soft block phase separation, a cation/co-repeat group ratio mimicking natural biocidal proteins, a semifluorinated "chaperone" aiding in alkylammonium surface concentration, and a low Tg for the alkylammonium soft block.     

The role of growth temperature in the adhesion and mechanics of pathogenic L. monocytogenes: an AFM study

The adhesion strengths of pathogenic L. monocytogenes EGDe to a model surface of silicon nitride were quantified using atomic force microscopy (AFM) in water for cells grown under five different temperatures (10, 20, 30, 37, and 40 °C). The temperature range investigated was chosen to bracket the thermal conditions in which L. monocytogenes survive in the environment. Our results indicated that adhesion force and energy quantified were at their maximum when the bacteria were grown at 30 °C. The higher adhesion observed at 30 °C compared to the adhesion quantified for bacterial cells grown at 37, 40, 20, and 10 °C was associated with longer and denser bacterial surface biopolymer brushes as predicted from fitting a model of steric repulsion to the approach distance-force data as well from the results of protein colorimetric assays. Theoretically predicted adhesion energies based on soft-particle DLVO theory agreed well with the adhesion energies computed from AFM force-distance retraction data (r(2) = 0.94); showing a minimum energy barrier to adhesion at 30 °C.     

Credible intervals for nanoparticle characteristics

Solving the inverse problem of nanoparticle characterization has the potential to advance science and benefit society. While considerable progress has been made within a framework based on the scattering of surface plasmon-polaritons, an aspect not heretofore considered is the quantification of uncertainty in the estimation of a nanoparticle characteristic. Therefore, the present article offers a technique by which an investigator may augment an estimate of a nanoparticle characteristic with a companion “credible interval”. Analogous to the familiar confidence interval but arising from within the Bayesian statistical paradigm, a credible interval allows the investigator to make a statement such as “the nanoparticle diameter lies between 36 and 48 nm with 95% probability” instead of merely “the nanoparticle diameter is estimated to be 42 nm”. Our technique may even be applied outside of the surface plasmon-polariton scattering framework, as long as the investigator specifies his/her prior beliefs about the nanoparticle characteristic and indicates which potential outcomes are likely or unlikely in whatever experiment he/she designs to estimate the nanoparticle characteristic. Two numerical studies illustrate the implementation and performance of our technique in constructing ranges of likely values for nanoparticle diameters and agglomeration levels, respectively.     

Electrochemical DNA biosensor for the determination of benzo[a]pyrene–DNA adducts

The metabolites of the environmental pollutant, benzo[a]pyrene (BaP) are carcinogenic and mutagenic agents. Thus, the determination of additional products (adducts) of the interaction between DNA and BaP, attracts great interest in cancer research.

In this study, the determination of interaction between BaP and calf thymus double-stranded DNA (dsDNA) was performed by using differential pulse voltammetry (DPV) and constant current chronopotentiometric stripping analysis (PSA) in connection with carbon paste electrode (CPE) or glassy carbon electrode (GCE). As a result of interaction of BaP with dsDNA, the signal obtained from the oxidation of guanine decreased and a new adduct signal at a more positive potential appeared. This new peak is attributed to the formation of an adduct from the interaction of guanine with BaP. The chemically prepared anti-7,8,9,10-tetrahydrobenzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) adduct by using iodine oxidation was analyzed and the electrochemical signal of the adduct was observed. When the dsDNA modified GCE was immersed into various concentrations of BaP solution, the oxidation peak of guanine decreased and the adduct peak increased with the increasing BaP concentration. The partition coefficient was also obtained from the peak of BaP with dsDNA. The results revealed that the formation of adducts could be determined by using electrochemical DNA biosensors, which are fast, simple and cost-effective devices. Furthermore, this study promises that the analysis of other important adducts would benefit from the introduction of electrochemical methods.     

Minimal triangulations of graphs: A survey

Any given graph can be embedded in a chordal graph by adding edges, and the resulting chordal graph is called a triangulation of the input graph. In this paper we study minimal triangulations, which are the result of adding an inclusion minimal set of edges to produce a triangulation. This topic was first studied from the standpoint of sparse matrices and vertex elimination in graphs. Today we know that minimal triangulations are closely related to minimal separators of the input graph. Since the first papers presenting minimal triangulation algorithms appeared in 1976, several characterizations of minimal triangulations have been proved, and a variety of algorithms exist for computing minimal triangulations of both general and restricted graph classes. This survey presents and ties together these results in a unified modern notation, keeping an emphasis on the algorithms.     

Accelerated brush growth on nanoparticle surfaces by reversible addition‐fragmentation chain transfer polymerization

It is now well established that controlling the grafted chain lengths and densities on nanoparticle surfaces determines the effective interactions between particles, and their assembly. Here, we present unusual kinetic results for achieving grafted chain lengths longer than the free chains using reversible addition‐fragmentation chain transfer (RAFT) polymerization and discuss the limitations to obtaining polymer grafting density higher than ～0.06 chains/nm². We observe that surface initiated polymerization grows faster than the free chains in solution with high RAFT agent coverage (1.95 agents/nm²) on nanoparticles. The time‐dependence of graft density suggests that activation of the anchored chain transfer agent (CTA) is limited by the diffusion of macro‐radicals within growing grafts. Thus, radical transfer and exchange reactions become inefficient between grafts and free polymer, and convert the surface‐initiated RAFT mechanism to a free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1700–1705     

Die Isolierung weiterer Alkaloide aus Pleiocarba talbotii WERNHAM. 150. Mitteilung über Alkaloide

From the leaves of the Apocynaceae Pleiocarpa talbotii WERNHAM three new indole alkaloids were isolated and identified as 3,4,5,6-tetradehydrotalbotine ( 2 ), 5,6-dehydrotalbotine ( 3 ) and deformyl talbotinic acid methylester ( 4 ). From the stem bark of the same plant normacusine B (tombozine) was isolated.     

A Highly Efficient Chelating Polymer for the Adsorption of Uranyl and Vanadyl Ions at Low Concentrations

A new polymer containing double amidoxime groups per repeating unit was synthesized to enhance the metal ion uptake capacity. The adsorption properties of this new polymeric adsorbent, amidoximated poly(N,N-dipropionitrile acrylamide), for U(VI), V(V), Cu(II), Co(II) and Ni(II) ions were investigated by batch and flow-through processes at very low concentration levels (ppb). The chelating polymer showed high adsorption capacity for uranyl as well as vanadyl ions. In selectivity studies from a mixture of metal ions in aqueous solutions, the adsorbent showed high selectivity for uranyl and vanadyl ions in the following order: U(VI) > V(V) Co(II) = Cu(II) Ni(II) as determined by calculating the distribution coefficients D, of corresponding ions. The adsorption of uranyl and vanadyl ions from natural seawater by the new adsorbent was also examined in flow through mode.