Immobilization combined attachment methods

To characterize the properties of molecules and polymer films attached to an electrode surface, a wide variety of methods have been used to measure the electroactivity, chemical reactivity, and surface structure of the electrode-immobilized materials [9]. These methods have been primarily electrochemical and spectral as indicated in Table I. Suffice it to say that a multidisciplinary approach is needed to adequately characterize chemically modified electrodes combining electrochemical methods with surface analysis techniques and a variety of other chemical and physical approaches. 

The immobilization of any enzyme can be carried out using different methods. These are classified into (1) adsorption on hydrophobic and ionic exchange resins, (2) covalent attachment on highly activated supports, (3) entrapment, and (4) encapsulation in matrices, as shown in Figure 3.1. Combinations of two or more of these methods have also been developed (Katzbauer et al., 1995 Yadav and Jadhav, 2005 Zarcula et al., 2009). It has been demonstrated that such combinations can solve problems that cannot be solved using only one method. 

Procter and coworkers" have described a Sm(II)-mediated (106), asymmetric capture and release approach (Scheme 7.22) to y-butyrolactones (107) that involves intermolecular radical additions to a,[3-unsaturated esters (105) attached to resin through an ephedrine chiral linker (108). Resin capture-release is a hybrid technique that combines elements of traditional solid-phase synthesis and the use of supported reagents. Fukuzawa s Sm(II)-mediated, asymmetric method to y-butyrolactones was chosen to demonstrate the feasibility of such a process. y-Butyrolactones (107) were obtained by capture of a reactive intermediate from solution through an asymmetric transformation starting from a,p-unsaturated esters (105) immobilized on an ephedrine chiral resin. Lactone products were obtained in moderate yields with selectivities up to 96% ee. Nevertheless, the ephedrine resin can be efficiently reused for many cycles although in some cases lower yields were obtained on reuse of the chiral resin. 

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