In this article, a new method for modification of silica surfaces is presented that is based on a photochemical reaction of terminal alkenes with the surface. The functionalization of optically transparent substrates is of importance, for example, in the field of biosensing. No hydrolysis was observed for the zwitterionic polymer after 1 week exposure to PBS solution, and the surfaces still repelled 98% FIB as compared to C(16)-Si(x)N(4) surfaces, demonstrating the long-term efficiency of these easily prepared surface coatings. After exposure to PBS solution, the zwitterionic polymer coating remained intact, and its thickness was unchanged within experimental error. The zwitterionic polymer-coated Si(x)N(4) surfaces before and after exposure to PBS solution were characterized by XPS, AFM, and water contact angle measurements, and their protein-repelling properties were evaluated by reflectometry.
Furthermore, the stability of these zwitterionic polymer-coated Si(x)N(4) surfaces was surveyed by exposing the surfaces for 1 week to phosphate buffered saline (PBS) solution at room temperature. Excellent protein repellence (>99%) was observed for these zwitterionic polymer-coated Si(x)N(4) surfaces during exposure to FIB solution as compared to C(16)-Si(x)N(4) surfaces. L(-1), and compared to hexadecyl-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)), uncoated air-based plasma oxidized Si(x)N(4) surfaces (SiO(y)-Si(x)N(4)), and hexa(ethylene oxide)-coated Si(x)N(4) surfaces (EO(6)-Si(x)N(4)).The adsorption of proteins onto zwitterionic polymer coated surfaces was evaluated by in situ reflectometry, using a fibrinogen (FIB) solution of 0.1 g Zwitterionic polymer brushes of SBMAA were grown from these initiator-coated surfaces (thickness ∼30 nm), and the polymer-coated surfaces were characterized in detail by static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and an atomic force microscope (AFM). A reaction with 2-bromoisobutyryl bromide led to ATRP initiator-covered surfaces. A UV-induced reaction of 1,2-epoxy-9-decene with hydrogen-terminated Si(x)N(4) surfaces was followed by conversion of the epoxide with 1,2-ethylenediamine resulting in primary and secondary amine-terminated surfaces. To this aim ATRP initiators were immobilized onto Si(x)N(4) through stable Si-C linkages via three consecutive reactions. Zwitterionic poly(sulfobetaine acrylamide) (SBMAA) brushes were grafted from silicon-rich silicon nitride (Si(x)N(4), x > 3) surfaces by atom transfer radical polymerization (ATRP) and studied in protein adsorption experiments. These results are compared with the previously reported effects of CDs on trifluoroacetanilide and phenyl ester hydrolysis and proposals of CD as a model of chymotrypsin. The CD cavity may provide an environment complementary to the transition state for expulsion of the anilide leaving group. The data are most simply interpreted by a mechanism in which CD accelerates formation of a tetrahedral intermediate 5 in the case of 1, the rate of breakdown of this intermediate is greater than the rate of buffer-catalyzed breakdown of the hydrolysis intermediate. The nature of the buffer catalysis in the absence of CD, exhibited in the hydrolysis of 1, also shows marked differences with that exhibited by 2-4. Moreover, CD catalyzes the hydrolysis of 1 but inhibits the hydrolysis of 2-4 across the pH range studied. The behavior of CD with 4 is more complex. For 1-3, cyclodextrin (CD) exhibits simple Michaelis-Menten saturation kinetics, with no evidence for reaction via other than 1:1 CD-substrate complexes.
The hydrolysis of p-nitro-N-methyltrifluoroacetanilide (1), p-chloro-N-methyltrifluoroacetanilide (2), N-methyltrifluoroacetanilide (3), and p-methoxy-N-methyltrifluoroacetanilide (4) in the presence and absence of α- and β-cyclodextrin has been studied at 7.5 < pH < 10.6.
0 kommentar(er)
