Bifunctional spacers

Here we will focus on the biochemical aspects. The techniques of isolating enzymes, the process of enzyme immobilisation and the behaviour of immobilised enzyme reactors are discussed in detail in the BIOTOL text Technological Applications of Biocatalysts", so will not deal with these aspects in detail here. In outline, however, once the desired enzyme is isolated, it is attached to a carrier material. In order to ascertain sufficient accessibility of the enzyme, a bifunctional spacer molecule is attached to the carrier ... 

Bifunctional spacer molecules of different sizes have been used to construct nanoparticle networks formed via self-assembly of arrays of metal colloid particles prepared via reductive stabilization [88,309,310]. A combination of physical methods such as TEM, XAS, ASAXS, metastable impact electron spectroscopy (MIES), and ultraviolet photoelectron spectroscopy (UPS) has revealed that the particles are interlinked through rigid spacer molecules with proton-active functional groups to bind at the active aluminium-carbon sites in the metal-organic protecting shells [88]. 

A second strategy is to attach a linker (also referred to as a handle or anchor) to the resin followed by assembly of the molecule. A linker is bifunctional spacer that serves to link the initial synthetic unit to the support in two discrete steps (Fig. 3). To attach a linker to a chloromethyl-PS resin, a phenol functionality such as handle 4 is used to form an ether bond (Fig. 4). To attach the same handle to an amino-functionalized support, acetoxy function 5 or a longer methylene spacer of the corresponding phenol is applied to form an amide bond. Both of these resins perform similarly and only differ in their initial starting resin [4], An alternative approach is to prepare a preformed handle in which the first building block is prederivatized to the linker and this moiety is attached to the resin. For peptide synthesis, this practice is common for the preparation of C-terminal peptide acids in order to reduce the amount of racemization of the a-carbon at the anchoring position [5],... 

Simon, U. et al., Chemical tailoring of charging energy in metal cluster arrangements by use of bifunctional spacer molecules,./. Mater. Chem., 8, 517,1998. 

Activation of Aminopropyiated Silica with Bifunctional Spacers... 

Schematic representation of the motifs generated from the connection of transition metals by bifunctional spacer ligands. One-dimensional ...

Stepwise SPPS normally proceeds in the C N direction. (SPPS in the N —> C direction has been carried out in a few cases but suffers from inherent problems that limit its generality.) A general scheme of stepwise SPPS synthesis is shown in Fig. 1, and specific implementations are described in later chapters. The insoluble solid support must intrinsically bear an appropriate functional group or be capable of functionalization. The next step is to attach a handle (also called a linker), which is defined as a bifunctional spacer to connect the first amino acid to the solid support. The handle must be de-... 

Figure 9. Schematic representation of the insertion of bifunctional spacer molecules into a dense packing of ligand-stabilized Pdsei clusters. The stretching of the packing results in a 3-D network.

Fig. 2.14 Formation of particle networks via protolytic cross-linking with bifunctional spacers.

Multilayer assemblies of nanocrystals of CdSe are generally fragile and are not suited for use in functional devices. Assemblies involving alternate layers of nanocrystals and linkers are relatively robust. The method of layer-by-layer deposition has received a good deal of attention over the last few years, since it provides a convenient low-cost means to prepare ultrathin films of controlled thickness, suited for device applications. In a typical experiment, one end of a monolayer forming a bifunctional spacer, is tethered to a flat substrate such... 

Table 3. Bifunctional spacers for activation of polymer surfaces...

FIGURE 1 A schematic representation of the motifs that can be generated by linking transition metals by linear bifunctional spacer ligands. In each example the metal is the node of the resulting network. 

Covalent attachment provides usually the most stable biocomponent immobilization from all attachment procedures. A functional group of the biomolecule is covalently attached to a functional group of the support, either directly or with the aid of a bifunctional spacer in case of enzymes the active center should not be affected. °° ° Covalent attachment is possible not only for the biocomponent, but also for cofactors and coenzymes or mediators. The support can be the functionalized electrode surface itself, or nanostiuctured materials which will be integrated in immobilization layers, or precipitated or electropolymerized layers on the sensor surface. 

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