Surface polyvinylpyridine

Figure 4 shows the relatively even adsorption on polyvinylpyridine surfaces spread by knife coating and dipped into radioactive heparin solution (500 fig./ml.) for 6 minutes. Six discs each 1 inch in diameter were die cut from each of two duplicate preparations which were similar in visual evenness to the ones shown. Planchet counts gave the results shown below ... 

Figure 3. Autoradiograph showing uneven adsorption on an initially dry polyvinylpyridine surface. Rotated with bubble 48 hours at 37°C. Heparin concentration 638 fxg./ml., average heparin adsorption 7.6 fjig./cm.2. Autoradiograph exposure 72 hours (comparable with Figure 2). In the lower third there is a fold or crack line in the filmy probably introduced before the sack was made...

Protective Colloids. Another approach in preparing and stabilizing metal colloids is by adsorption of macromolecules on their surfaces. A wide variety of materials have been used including gummy gelatinous liquids,(J 0) albumin,(27) Icelandic moss,(28) latex,(22) polyvinylpyrrolidone, (29) antibodies, ( 30 ) carbowax 20M, ( 31 ) polyvinylpyridine, (31 ) and various polymer-water/oil-water mixtures.( 2) These studies clearly indicate that "steric stabilization of metal colloids is also important (along with electronic stabilization).(33)... 

Cordes and co-workers 191 found that the alkaline hydrolysis of p-nitrophenyl hexanoate is subject to catalysis by polyvinylpyridine-based polysoaps. For example, k bs is increased from 0.1 mm to 1.4 mm in the presence of 5 x 10 7 M 38% polysoap (23) (the same material used in the Strauss work). With 5 x 10-7 M polymer having a 15 % dodecyl content, the rate is increased only 3 times above background. The simplest rationale for the kinetics invokes both hydrophobic and electrostatic forces. Thus, dodecyl chains on the polymer hydrophobically bind p-nitrophenyl hexanoate to the polymer surface. Since the polymer possesses a high density of cationic nitrogens, hydroxide ions also accumulate at the polymer surface where they catalyze the hydrolysis of bound ester. Addition of nitrate ion to the aqueous reaction... 

Figure 4. Relatively even autoradiograph of two portions of polyvinylpyridine filmy A and B. There is some gradation from top to bottom, but the uniformity is high compared with Figure 1 through 3. This was dipped into heparin solution, held immersed 6 minutes, then withdrawn and rinsed. Planchet counts of die cut one inch circles taken from a pair of surfaces similar in visual evenness are given in the text, showing coefficients of variation of 12 and 6% for duplicates...

For ftirther refinement of the Pt catalyst we made use of Tiirkevich s method to prepare ultrafine and monodisperse Pt sols ho,). Employing polymer surfactants as protective agents a first successful attenpt was made to render the intervention of these particles specific. Th is polyvinylpyridine absorbs well to the 30 X platinum particles rendering their surface anphiphilic. Hydrophobic relays such as long chain siibstituted viologen radicals are readily trapped by these particles and subsequently affect water reduction. In contrast the oxidized sensitizer is rejected from the Pt surface by l drophobic and electrostatic interactions. Thus, short-circuitiy of the back reaction is avoided. 

Polysoaps belong to a class of compounds which incorporate both of the features of polyelectrolytes and micelles into a single structure, and forms intramolecular micelles having a structural organization related to micelles formed from simple surfactants. Because of the high charge density at the surface and a compact hydrophobic core, they provide interesting microenvironments. A typical polysoap 22 can be formed throu treatment of polyvinylpyridine with linear alkyl halides (33). 

Another way to functionalize the surface of microlatex particles is to incorporate amphiphilic block copolymers (for example, polystyrene/polyvinylpyridine) as cosurfactants together with the classical surfactants used in the formulation [86,87]. The protruding polyvinylpyridinium chains are anchored to the glassy core through the polystyrene blocks. These blocks copolymers were shown to stabilize the oil/water interface and to effectively bind ions of transition and heavy metals via complexation. 

The redox polymers, both of organic and inorganic origin (such as polyvinylpyridine modified by redox-active complexes of metals Prussian blue and related materials), can be considered as a version of electrodes of the second kind however, the equilibrium is usually estabhshed with respect to cations. Electron conducting polymers (polyanyline, polypyrrol, and so forth) also pertain, in the first approximation, to the electrodes of the second kind, which maintain equilibrium with respect to anion. Ion exchange polymer films on electrode surfaces form a subgroup of membrane electrodes. 

Numerous examples of these systems have been studied experimentally. Tirrell et ah measured the adsorption of AB copolymers of polystyrene and polyvinylpyridine on mica. A wide range of molecular weights was tested, and it was found that, for most samples, about 200 ng/cm of polymer adsorbed to the surface, and that the buoy segments easily formed polymer combs , unless the size of the anchoring segment was too large. The maximum surface density was found with small... 

Big. 4. Coordination of Ru(III)EDTA to graphite electrodes coated with increasing quantities of polyvinylpyridine. Ru(III)-EDTA dissolved in aqueous solution containing 0.2 M CFjCOONa at pH 7.1. Surface concentration of pyridine groups in polyvinylpyridine A, 1.2x10 B, 3.3 X 10 C, 7.6x 10 molcm ... 

FIGURE 2.29. Typical RDE profiles recorded for the reduction of 1 mM Fe (aq) in 0.1 M HCl at (a) a glassy carbon electrode coated with a polyhydroxyphenazine film (F = 6 X 10" mol cm ) and at (b) a bilayer electrode consisting of an inner polyhydroxyphenazine layer [same surface coverage as in (a)] and an outer electroactive ruthenium-loaded polyvinylpyridine polymer (F = 1 X 10 mol cm ). Rotation speed in each case is 1000 rpm (Ref. 80). 

Conducting polymer-based immobilization or wired enzymes is a global enzyme immobilization method that differs in many respects from those just described. In one example, a redox polymer is formed on the surface by the oxidation of pyrrole molecules to pyrrole radical cations, which then polymerize on the surface to form conductive polypyrrole [60,68]. Other conducting polymers include polyvinylpyridine, polythiophene, polyaniline, and polyindole. If enzymes are present in the solution as polymerization takes place, they are entrapped within the polymer. When these polymers are cross-linked with redox mediators such as [Os(bpy)2Cl]+ 2 the resulting amperometric (or potentiomet-ric) biosensors are referred to as wired enzyme electrodes [5-7]. The distance between the redox centers of the polymer and the FADH2 centers of the reduced enzyme is reduced sufficiently for electrons to be transferred and, therefore, for the mediated electro-oxidation of glucose on conventional electrodes. These electrodes do not require diffusing redox mediators or membranes to contain the enzyme and the redox polymer. 

In most electrochemical systems used for glucose determination, a common element is the use of an electron transfer "shuttle" for transport of electrons between glucose oxidase and the electrode surface. This species can be a monomeric, freely diffusing mediator that is soluble in the analyte sample, or polymeric in nature, and immobilized on the electrode surface along with the enzyme in the form of a thin film or hydrogel. An example of the latter type has been pioneered by Gregg and Heller whereby a polymeric electron-transfer relay based on an osmium-substituted polyvinylpyridine polymer is co-immobilized with glucose oxidase on an electrode... 

The fabrication of a polyvinylpyridine (PVP) brush inside a single PET nanopore by surface-initiated free radical polymerization [8]... 

Fig. 3. Surface density of the grafted macromolecules dependent on chain length ( O polystyrene 20°C, polyvinylpyridine 20°C, p ] polyvinylpyridine 45 C).

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