Abstract-Biocompatibility of materials strongly depends on their surface properties. Therefore, surface derivatization in a controllable manner provides means for achieving interfaces essential for a broad range of chemical, biological, and medical applications. Bioactive interfaces, while manifesting the activity for which they are designed, should suppress all nonspecific interaction between the supporting substrates and the surrounding media. This article describes a procedure for chemical derivatization of glass and silicon surfaces with polyethylene glycol (PEG) layers covalently functionalized with proteins. While the proteins introduce the functionality to the surfaces, the PEGs provide resistance against nonspecific interactions. For formation of aldehyde-functionalized surfaces, we coated the substrates with acetals (i.e., protected aldehydes). To avoid deterioration of the surfaces, we did not use strong mineral acids for the deprotection of the aldehydes. Instead, we used a relatively weak Lewis acid for conversion of the acetals into aldehydes. Introduction of a,x-bifunctional polymers into the PEG layers, bound to the aldehydes, allowed us to covalently attach green fluorescent protein and bovine carbonic anhydrase to the surfaces. Spectroscopic studies indicated that the surface-bound proteins preserve their functionalities. The surface concentrations of the proteins, however, did not manifest linear proportionality to the molar fractions of the bifunctional PEGs used for the coatings. This finding suggests that surface-loading ratios cannot be directly predicted from the compositions of the solutions of competing reagents used for chemical derivatization.
Coordination polymers of poly(Schiff bases) derived from the condensation of methylene bis(salicyla1dehyde) or sulfone bis(salicyla1dehyde) with aromatic diamines have been known for some time.'S2 Marvel and Torkoy were among the first to explore the thermal stability of these polymers' while others evaluated their conducting properties?s4 More recently, a number of poly(Schiff base) complexes of transition metals have been synthesized! We have been interested in the syntheses of novel poly(Schiff base) chelates because of their conductive and metal-coordinating properties. In principle these polymers may incorporate catalytically-active redox functionalities which can be continually regenerated via electronic conduction through the polymer. Recent efforts of Elliot et al."7 to synthesize an electronicallyconducting bipyridyl polychelate prompted us to investigate poly(Schiff bases) of the type reported in this paper. EXPERIMENTAL MaterialsReagent grade chemicals were used. o-Dianisidine (Loba) and hexammine ruthenium (II1) chloride (Strem) were used as received. Tetrabutylammonium tetrafluoroborate (Aldrich) was recrystallized from ethyl acetate. Acetonitrile (Fisher) was of pesticide grade. 4,4'-Diamino-diphenylmethane (Aldrich) was purified by vacuum sublimation. 4,4'-dihydroxy-3,3'-diacetylbiphenyl, 4,4'-dihydroxy-3,3'-dibenzoylbiphenyl, and 4,4'-dihydroxy-3,3'-dipropionylbiphenyl were synthesized? MethodsThe poly(Schiff base) chelates were prepared by reacting the appropriate bis(o-ketophenol) with an equimolar amount of diamine. Typically, bis(o-ketophenol) in hot ethanol was added to an ethanolic solution of the diamine. The reaction was heated at reflux for 10 h, filtered, the precipitate washed with ethanol, and then dried.An attempt was made to synthesize the following polymers:Polymer 1 prepared from the reaction of 4,4'-dihydroxy-3,3'-diacetylbiphenyl with 4,4'-diaminodiphenylmethane, Polymer 2 prepared from the reaction of 4,4'-dihydroxy-3,3'-dibenzoylbiphenyl with 4,4'-diaminodiphenylmethane, and Polymer 3 prepared from the reaction of 4,4'-dihydroxy-3,3'-dipropionylbiphenyl with o-dianisidine. Polymer solutions needed for electrochemical analysis were prepared by adding 40 mg of polymer to 50 mL of hot acetonitrile. A 20-40 pL aliquot of the polymer solution was placed on 1 cm2 of Nesatron (ln203) conducting glass (PPC Industries, Pittsburgh PA). Assuming a polymer density of 1 g Ru(NH3)i+ waa dissolved in a (40:24:1) vol% solution of acetonitri1e:water:conc. NH,, and the complex impregnated into the polymer by soaking for 1 hour.UV-visible spectra were obtained on a Varian-DMS-100 dual-beam spectrophotometer. All solution spectra were obtained in 1 cm quartz cuvets. IR spectra of the poly(Schiff base) chelates were recorded in KBr on a Perkin-Elmer 683 spectrophotometer. Elemental analyses were done using a Perkin-Elmer 240 B elemental analyzer. All electrochemical experiments were performed in an undivided three-electrode cell with a 30 mL the film thickness was calculated as 0.2-0.4 pm.
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