“Surface-photografting”: new applications to synthetic fibers

“Surface-photografting” with UV-irradiation of polypropylene (PP) fiber and film and high-strength polyethylene (HSPE) yarn has been made with acrylic acid (AA) and acrylamide (AM) as monomers and benzophenone (BP), 4-chlorobenzophenone (4-BCP) and hydroxylcyclohexylacetophenone (HHA) as photoinitiators using a new continuous method. The grafting reaction occurs in a thin liquid layer on the fiber or film substrate, which is presoaked in a solution containing initiator and monomer. After irradiation with a highpressure mercury lamp, HPM 15 (2 kW) from Philips, for 5–20 sec at about 50°C the fiber and film surface is completely covered with a 2–8 nm thick layer of grafted polymer, analyzed by electron spectroscopy for chemical analysis. The grafting efficiency is 70–80%, i.e. only 20–30% of the polymer is homopolymer which can be removed by extraction. The grafted layers are so thin that they cannot be analyzed as weight increase (<0.1% of fiber weight). Absolute values for the amount of grafted AA polymer is analyzed by microtitration of the COOH groups at the fiber surface. The results agree well with the relative ESCA values. Grafting of commercial PP yarn with AA increases the adsorption of Crystal Violet dye with a factor of about 6. Grafting the same yarn with AM increases the adhesion to epoxy resin by a factor of 3–4 without affecting the mechanical properties of the fiber more than a few percent. For comparison, strips of blown PP film (5 mm wide) are modified by “surface-photografting” with AM. With increasing grafting, the contact angle for drops of distilled water decreases from 90° to 20°, indicating extensive wetting. The adhesion to epoxy resin increases from about 0.35 to 1.7 N/mm², i.e. with a factor of about 5 when the film surface is completely covered. Other comparisons are made with grafting of commercial HSPE yarn. Grafting with AA increases the adsorption of Crystal Violet dye by a factor of about 6. Grafting with AM increases the adhesion to epoxy resin from 0.25 to 1.3 N/nm², i.e. with a factor of 5. The bulk mechanical properties of the HSPE filaments are not affected by the grafting measured as tensile strength 2.7±0.1 GPa, elongation at break 4.8±0.3%, and Young's modulus 55±3 GPa, both before and after “surface-photografting”.     

Amphiphilic segmented polyurethanes as surface modifying additives

Amphiphilic segmented polyetherurethanes were prepared from methylene diphenylene diisocyanate (MDI), poly(ethylene glycol) 1500 (PEG), and a fatty acid monoglyceride as a chain extender. The polymers were not soluble in water or methanol, but dissolved readily in organic solvents. The amphiphilic properties were demonstrated as a large hysteresis in the water contact angles, exceeding 110°. The amphiphilic polymers were shown to modify the surface properties of a poly(ether urethane) (PEU) and a poly(ether urethane urea) (PEUU) when added in 1–10 wt %, presumably due to migration of the additive to the surface. The surfaces of particularly the PEU blends became highly amphiphilic, exhibiting contact angles hystereses up to 90–100°. A surface saturation effect was observed at 5% added amphiphilic polymer. A difference in the behavior of PEU and PEUU was ascribed to differences in solubility of the additive in the matrix. On long-term exposure to water the PEUU blends increased their amphiphilic behavior.     

Linear‐dendritic polymeric amphiphiles as carriers of doxorubicin—In vitro evaluation of biocompatibility and drug delivery

In our recent work, we have explored the formation of chemotherapeutic delivery vehicles constructed from four different amphiphilic linear‐dendritic hybrid block copolymers. These micelles were found to form about 100‐nm‐sized structures that were capable of sequestering doxorubicin at loading efficiencies up to 22%. Here, the cellular toxicity of these biocompatible and biodegradable linear‐dendritic hybrid materials was evaluated on two breast cancer cell lines and primary human macrophages. The micelles were found not to affect the cellular viability at concentrations below 35 μg mL^?1. After drug loading, these constructs could deliver an efficient dose of drugs, resulting in significant decreases in cell viability. Kinetic studies indicated that the drug formulation in the polymer micelles slowed down the cell uptake compared with the nonformulated drug, but similar efficacy in viability reduction and cell apoptosis were found. Taken together, these linear‐dendritic hybrid materials represent an interesting novel architecture for the construction of drug delivery systems. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The intrinsic GTPase activity of the Gtr1 protein from Saccharomyces cerevisiae

ABSTRACT: BACKGROUND: The Gtr1protein of Saccharomyces cerevisiae is a member of the RagA subfamily of the Ras-like small GTPase superfamily. Gtr1 has been implicated in various cellular processes. The Switch regions in Gtr1 mediate activation of the TORC1 complex [R. Gong, L. Li, Y. Liu, P. Wang, H. Yang, L. Wang, J. Cheng, K.L. Guan, Y. Xu, Genes Dev. 25 (2011) 1668-1673]. Therefore, knowledge about the biochemical activity is required to understand its mode of action and regulation. RESULTS: Here we employ tryptophan fluorescence analysis and radioactive GTPase assays to demonstrate that Gtr1 can adopt two distinct GDP- and GTP-bound conformations, and that it hydrolyses GTP much slower than Ras proteins. Using cysteine mutagenesis of Arginine-37 and Valine-67, residues at the Switch I and II regions, respectively, we show altered GTPase activity and associated conformational changes as compared to the wild type protein and the cysteine-less mutant. CONCLUSIONS: The extremely low intrinsic GTPase activity and distinct conformations upon nucleotide binding imply a strict regulation of Gtr1. These findings as well as the altered properties obtained by mutagenesis in the Switch regions provide insights into the function of Gtr1 and its homologues in yeast and mammals.     

A potential tool for high-resolution monitoring of ocean acidification

Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acidification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and low oceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck for research on ocean acidification is long-term monitoring and the collection of consistent high-resolution pH measurements. This study presents a low-power (<1 W) small sample volume (25 μL) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatial resolution (approximately 15 s and 100 m between samples). A 405 nm light emitting diode and the blue and green channels from a digital camera was used for swift detection of fluorescence from the pH sensitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated by automated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegat region with a large range in salinity (∼3–30) and temperature (∼0–25 °C). Ship-board precision of salinity and temperature adjusted pH measurements were estimated as low as 0.0001 pH units.     

ESR applications to photochemical polymer reactions

ESR spectroscopy combined with spin-trapping technique is a selective and powerful method for studies of reaction mechanisms and intermediates in free radical reactions of polymer systems. The method has been applied to several problems in our research program of which three are presented in this paper. - The mechanism of photo-initiation with aromatic ketone/tert. amine and subsequent photocuring of acrylic coatings has been largely resolved. - The mechanism of photocrosslinking of ethylene-propylenediene copolymers (EPDM elastomers) studied by model compounds has been shown to involve formation of allyl radicals in the diene groups and crosslinking by allyl radical combination. - The photoinitiated crosslinking of polyethylenes (LD, LLD and HD) has been studied using model compounds. It involves formation of primary alkyl and allyl radicals which crosslink the polymer by radical combination. - The mechanism of photocrosslinking indicates a second order reaction, i.e. rate of crosslinking depends of the square of irradiation intensity which has been verified experimentally. This result is the basis for development of rapid crosslinking processes of technical and industrial interest.