Non-fouling surfaces that resist non-specific adsorption of proteins, bacteria, and higher organisms are of particular interest in diverse applications ranging from marine coatings to diagnostic devices and biomedical implants. Poly(ethylene glycol) (PEG) is the most frequently used polymer to impart surfaces with such non-fouling properties. Nevertheless, limitations in PEG stability have stimulated research on alternative polymers that are potentially more stable than PEG. Among them, we previously investigated poly(2-methyl-2-oxazoline) (PMOXA), a peptidomimetic polymer, and found that PMOXA shows excellent anti-fouling properties. Here, we compare the stability of films self-assembled from graft copolymers exposing a dense brush layer of PEG and PMOXA side chains, respectively, in physiological and oxidative media. Before media exposure both film types prevented the adsorption of full serum proteins to below the detection limit of optical waveguide in situ measurements. Before and after media exposure for up to 2 weeks, the total film thickness, chemical composition, and total adsorbed mass of the films were quantified using variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and optical waveguide lightmode spectroscopy (OWLS), respectively. We found (i) that PMOXA graft copolymer films were significantly more stable than PEG graft copolymer films and kept their protein-repellent properties under all investigated conditions and (ii) that film degradation was due to side chain degradation rather than due to copolymer desorption.
To enhance our understanding of liquids in contact with rough surfaces, a systematic study has been carried out in which water contact angle measurements were performed on a wide variety of rough surfaces with precisely controlled surface chemistry. Surface morphologies consisted of sandblasted glass slides as well as replicas of acid-etched, sandblasted titanium, lotus leaves, and photolithographically manufactured golf-tee shaped micropillars (GTMs). The GTMs display an extraordinarily stable, Cassie-type hydrophobicity, even in the presence of hydrophilic surface chemistry. Due to pinning effects, contact angles on hydrophilic rough surfaces are shifted to more hydrophobic values, unless roughness or surface energy are such that capillary forces become significant, leading to complete wetting. The observed hydrophobicity is thus not consistent with the well-known Wenzel equation. We have shown that the pinning strength of a surface is independent of the surface chemistry, provided that neither capillary forces nor air enclosure are involved. In addition, pinning strength can be described by the axis intercept of the cosine-cosine plot of contact angles for rough versus flat surfaces with the same surface chemistries.
The controlled/“living” radical polymerization of n-butyl acrylate (n-BA) and 2-trimethylsilyloxyethyl acrylate (TMS − HEA) by atom transfer radical polymerization (ATRP) is reported. Di- and triblock copolymers with predefined block lengths and low polydispersities were obtained, using methyl 2-bromopropionate as the initiator, CuIBr as catalyst and N,N,N‘,N‘‘,N‘‘-pentamethyldiethylenetriamine as the ligand. Hydrolysis of the trimethylsilyl groups led to block copolymers with n-BA and 2-hydroxyethyl acrylate (HEA) units which were characterized by SEC, 1H NMR, and DSC. Diblock copolymers of n-BA and HEA could also be obtained by successive addition of the two monomers, in that order. The amphiphilic di- and triblock copolymers formed dispersions in water.
COMMUNICATIONSa single diastereorner by chromatography. The sense of asymmetric induction in this cycloaddition is consistent with a Lewis acid catalyzed Diels-Alder reaction on the s-cis ZnBr, complex 8a.In analogy to previous experiments, Diels-Alder adduct 9 was transformed to the corresponding P-ketothioester in 90% yield and smoothly decarboxylated (70 "C, 24 h) to afford ketone 10 in 86% yield without epimerization at the ring fusion. The synthesis was completed by treatment of 10 with Tebbe reagent"81 to afford synthetic a-himachalene (11) (92% yield), whose spectroscopic and analytical data are identical in all respects to literature values ('HNMR, IR, TLC, [a]D).[151The removable auxiliary X = COX, described here should prove useful in enantioselective ketone-based bond constructions. Although the methodology has been highlighted with al-do1 and Diels-Alder reactions, absolute stereochemical control of other transformations such as the Michael reaction should also be possible. Studies extending the scope of these concepts are currently underway. Experimental SectionGeneral one-flask procedure for the decarboxylation of b-ketoimides: A stirred suspension of KH (1.2 mmol) in THF (10 mL) under argon was charged with EtSH (1 3 mmol) and gas evolved. The white suspension was stirred for 1 h before a solution of /I-oxoimide (1 mmol) in THF (10 mL) was added by cannula. The reaction mixture was stirred until the starting material had been consumed. To the reaction mixture was added water (4 mL) and 2,6-lutidine (10 mmol), followed by AgNO, (2.5 mmol). The reaction mixture was protected from light and stirred for two days. The pale yellow suspension was filtered through Celite with ether, and the organic solution was extracted between ether (50 mL) and aqueous CuSO, solution (50 mL). The ether layer was separated, dried over MgSO,, and concentrated in vacuo. Chromatography on silica gel using an appropriate solvent mixture provided pure ketone.
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