Introduction. The interactions between polymers at interfaces and the environment is of the utmost importance for numerous processes in biomedical applications, but also in the food industry and in paint applications. 1,2 The past two decades polymers end-grafted to interfaces at high densities, so-called polymer brushes, have been recognized as interesting objects from an academic point of view. [2][3][4][5][6] Recently, numerous studies have examined brushes as promising candidates to modify the adsorption properties of surfaces in contact with heterogeneous solutions. [7][8][9][10] For instance, the adsorption of proteins and bacteria on surfaces, also known as biofouling, may be suppressed via grafting of hydrophilic polymers. 11 However, advancement in the field of brushes in contact with heterogeneous media seems to be slow due to two reasons: (a) the difficulty of experimentally preparing well-characterized polymer brushes and (b) the current lack of model systems to study brush-particle interactions. In recent papers we reported a novel method of preparing polymer brushes on solid substrates, based on the Langmuir-Blodgett (LB) technique. [12][13][14] Also, in the past the interaction between silica surfaces and PEO-homopolymers has been examined in detail. 15 Using reflectometry to measure the adsorption of nanocolloidal SiO 2 particles onto brushes prepared via the LB-technique, we believe to have the first brushparticle system in which the polymer-polymer, polymerparticle, and particle-particle interactions can be varied independently via the pH, grafting density, and ionic strength, respectively. In this communication, we report the first results for this model system and compare the results with predictions of theoretical models.Materials and Methods. Diblock copolymers consisting of PS(38)-PEO(700) were received from Dr. G. Riess, Mulhouse, France (the numbers denote the number of monomers in the blocks). 16 The PS-PEO was dissolved in chloroform (1 g L -1 ) and deposited on the air/water interface of a Langmuir trough via a micropipet. The PS-PEO monolayer was compressed to the desired density, characterized by the surface pressure. 17,18 Silicon wafers were hydrophobised using styrene as described in refs 19 and 20. On top of the styrene monolayer a PS layer of thickness 60 to 70 nm was spincoated at 3000 min -1 from a 14 g L -1 solution in toluene. Subsequently, the PS-PEO monolayer was transferred onto the coated wafer via the well-known LB-technique. 21 The interaction between the PS-groups on the block copolymer and the spin-coated PS layer is strong enough to provide stable PEO-brushes, irrespective of the solution conditions.
Adsorption (binding) isotherms of three cationic surfactants (hexadecyl trimethylammonium bromide,
dodecyl trimethylammonium bromide, and decyl trimethylammonium bromide) bound to poly(acrylic acid)
brushes were determined by means of optical reflectometry. The adsorption occurs reversibly. The shape
of the isotherms and the maximum degree of binding depends strongly on the grafting density of the brush.
Dense brushes exchanged at most about 40% of their counterions for surfactant ions and had isotherms
that could be fitted to the Langmuir equation. For more dilute brushes the isotherms had a quite different
shape: the quantity of surfactant could increase up to complete exchange in a second step occurring at
higher concentrations. It is shown that these differences are due to the bulkiness of the surfactant ions;
the volume required for full loading is so large that it forces the polymer chains to stretch too much. A
lamellar structure of the complex occurring in the fully loaded brush is proposed.
Pseudomonas fuscovaginae produces the lipodepsipeptides syringotoxin, fuscopeptin A and fuscopeptin B concurrently. These phytotoxins inhibit acidification of the external medium by fusicoccin-treated rice leaf sheath discs. When tested in vitro on H+-ATPase of rice shoot plasma membranes, syringotoxin and its structural analogue syringomycin, produced by P. syringae pv. syringae, displayed a double effect. At low concentrations they stimulated the ATPase activity of native right-side-out membrane vesicles in a detergent-like manner. At higher concentrations, however, this stimulation was reversed. With membranes treated with the detergent Brij 58, inhibition of ATPase activity was observed at low concentrations of the nonapeptides. The latter effect required the presence of an intact lactone ring formed by the nonapeptide head of these molecules. In contrast, fuscopeptins A and B inhibited enzyme activity regardless of the orientation of the vesicles. These observations were confirmed using plasma membranes from a yeast strain whose own H+-ATPase had been replaced by a single plant H+-ATPase isoform, PMA2, from Nicotiana plumbaginifolia. The kinetics of inhibition induced by the most active compound fuscopeptin B, showed a non-competitive pattern, with a Ki of about 1 microM. The combination of syringotoxin (or syringomycin) with the more hydrophobic fuscopeptins, in amounts with little or no effect, resulted in strong inhibition of the enzyme activity of rice membranes, suggesting a synergistic effect for the two types of toxins.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.