Amphiphilic polymers with applications

Oheme and co-workers investigated335 in an aqueous micellar system the asymmetric hydrogenation of a-amino acid precursors using optically active rhodium-phosphine complexes. Surfactants of different types significantly enhance both activity and enantioselectivity provided that the concentration of the surfactants is above the critical micelle concentration. The application of amphiphilized polymers and polymerized micelles as surfactants facilitates the phase separation after the reaction. Table 2 shows selected hydrogenation results with and without amphiphiles and with amphiphilized polymers for the reaction in Scheme 61.335... 

C. Tribet, R. Audebert, J.-L. Popot (1997) Stabilisation of hydrophobic colloidal dispersions in water with amphiphilic polymers application to integral membrane proteins. Langmuir, 13 5570-5576... 

Columns filled with polymer solutions are extremely simple to prepare, and the packing can easily be replaced as often as desired. These characteristics make the pseudostationary phases excellent candidates for use in routine CEC separations such as quality control applications where analysis and sample profiles do not change much. However, several limitations constrain their widespread use. For example, the sample capacity is typically very low, pushing typical detection methods close to their sensitivity limits. Additionally, the migration of the pseudostationary phase itself may represent a serious problem, e. g., for separations utilizing mass spectrometric detection. The resolution improves with the concentration of the pseudostationary phase. However, the relatively low solubility of current amphiphilic polymers does not enable finding the ultimate resolution limits of these separation media [88]. 

Many micellar catalytic applications using low molecular weight amphiphiles have already been discussed in reviews and books and will not be the subject of this chapter [1]. We will rather focus on the use of different polymeric amphiphiles, that form micelles or micellar analogous structures and will summarize recent advances and new trends of using such systems for the catalytic synthesis of low molecular weight compounds and polymers, particularly in aqueous solution. The polymeric amphiphiles discussed herein are block copolymers, star-like polymers with a hyperbranched core, and polysoaps (Fig. 6.3). 

A second interesting class of amphiphilic polymers is the polysoaps or miceUar polymers as they are often referred to. Such polymers are composed of hydrophilic and hydrophobic fragments leading to various molecular architectures that have been discussed in detail by A. Laschewsky [78]. The precise structure of the resulting micelles, that is, whether they are intra- or intermolecular assembhes, is still subject to discussion because the polymer structure is so versatile. Possible micellar structures are depicted in Fig. 6.8. The most interesting feature of such polymers with respect to their application in catalysis is (i) their remarkable abil-... 

Zhu C, Hard C, Lin C, Gitsov I. Novel materials for bioanalytical and biomedical applications environmental response and binding/telease capabilities of amphiphilic hydrogels with shape-persistent dendritic junctions. J Polym Sci Part A Polym Chem 2005 43 4017-4029. 

In addition to their traditional applications as surfactants, dispersants, etc., amphiphilic polymers have recently been attracting active interest in terms of their behavior at liquid-liquid, solid-liquid, and other interfaces (micellization, segmental conformation, etc.), along with their biocompatibility. In this section, amphiphilic block copolymers alone are briefly discussed. Graft and multiarmed polymers with amphiphilic arms will be treated later in this chapter (Section VI). 

The amphiphilic polymers and copolymers offer broad aspects for applications similar to low molar mass surfactants. Modifications of solutions, e.g. with respect to their viscosity, can be performed by the variation of the degree of polymerization of the polysurfactants easily. The liquid crystalline phase... 

Peptides are also amphiphilic polymers, i.e., mostly positively charged molecules with short amino acid chains, and are a key component of the innate immune system. The focus on amphiphilic polymers is due to some reports suggesting that the current global drug pipeline is woefully inadequate due to bacterial resistance to antibiotics [3]. The application of amphiphilic polymers and their block polymers to stop the microbial growth of infected tissue has been reported in the literature [4]. 

Peptides exhibit the highest antimicrobial activities of amphiphilic polymers and also possess antibacterial, antiviral, antifungi and anticancer activities [30-32]. In view of the potential applications of peptides, we will now discuss the synthesis of some important antibacterial peptides. Gad-1 and Gad-2 are peptides with amino acid chains and are prepared using O-fluorenylmethyloxycarbonyl (Fmoc) chemistry. 

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