Aqueous conditions immobilized ligands

In this section, the potential application for amyloid fibrils and other selfassembling fibrous protein structures are outlined. These include potential uses in electronics and photonics presented in Section 4.1, uses as platforms for the immobilization of enzymes and biosensors presented in Section 4.2, and uses as biocompatible materials presented in Section 4.3. Each of these applications makes use of the ability of polypeptides to self-assemble and form nanostructured materials, a process that can occur under aqueous conditions. These applications also seek to exploit the favorable properties of fibrils such as strength and durability, the ability to arrange ligands on a nanoscale, and their potential biocompatibility arising from the natural materials used for assembly. 

Fig. 10. A SPR Detection realized in a BIAcore system. A fan of polarized light passes a prism and is focused at the interface to an aqueous phase under conditions of total reflection. An evanescent wave enters the solvent phase. If the prism is coated with a thin gold layer at the interface the free electrons in the metal absorb energy from the evanescent wave for a distinct angle, depending on the refractive index of the solvent near the interface. B The gold layer can be modified with, e.g., a carboxydextrane matrix, where catcher molecules can be immobilized by standard chemistry. If a ligand is applied with the aqueous phase it may interact with the catcher and accumulate in the matrix, causing a shift in the resonance angle. If no specific binding occurs the refractive index in proximity of the sensor is less affected...

However, the relatively high enzyme costs form an obstacle to commercialization. Inefficient laccase use is a result of its instability towards the oxidizing reaction conditions. We have recently shown that the stability of the laccase under reaction conditions can be improved by immobilization as a cross-linked enzyme aggregate (see Chapter 9). It has also been shown that a water-soluble iron complex of a sulfonated phthalocyanine ligand is an extremely effective catalyst for starch oxidation with hydrogen peroxide in an aqueous medium [11]. 

In a similar manner, a modified Rh(PPh3) catalyst was able to convert camphene under neat conditions at 200 bar into the aldehydes [77, 78]. This protocol was carried out in a >400 g scale. When the syngas pressure and temperature were lowered (90 bar, 100 °C), the linear aldehydes were formed in nearly quantitative yields [7 6]. In the presence of phosphorus ligands, the formation of the endo isomer was favored (exo/endo 1 1.5), whereas in immodified systems both exo and endo compounds were formed in nearly equal amounts. Neither steric nor electronic parameters of the Ugands were found to influence significantly the diastereose-lectivity of the rhodium-catalyzed hydroformylation. The reaction was likewise performed in a toluene/water biphasic system employing TPPTS to immobilize the rhodium catalyst in the aqueous phase [84]. A mixture of exo and endo isomers of the linear aldehyde (exo/endo 1/1.5) was obtained in nearly 100% chemoselectivity and 71% yield [Rh(COD)(OAc)]2, TPPTS, CO/Hj (1 1, 8 MPa), 80 C, toluene/water (2.5 1 v/v), 48 h. ... 

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