Spacer molecule

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]. 

As long as the spacer molecules are not covalently bound to the cluster surface and the spacer molecules have no delocalized rc-electron system along their backbone between their termini, this relation is valid. The respective activation energy drops as soon as covalently linking species, equipped with delocalized n electrons... 

FIG. 5 Schematic representation of packing arrangements of natural amphipathic double-chain lipids with different headgroup size in crystalline bilayers. The small filled circles indicate the accommodation of spacer molecules, such as water or ions. (Reprinted by permission from Ref 14, copyright 1992, Elsevier Science.)... 

Bivalent inhibitors of thrombin have been synthesized to bind the anion-binding exosite and active (catalytic) site of thrombin simultaneously. By coupling the carboxy terminal fragment of hirudin to a tripeptide (D-Phe-Pro-Arg) by including a spacer molecule, both the anion exosite and the catalytic site are blocked. An example of such a molecule is Hirulog, which has 20 amino acids and has a Kj of 2 nM (61). Its ability to block the active site has been questioned, since thrombin has been shown to cleave the Arg-Pro bond of Hirulog slowly in vivo (58). In addition to hirudin and hirudin-like compounds, three other classes of site-directed thrombin inhibitors deserve mention. 

Halogenation of pyrimidine bases may be done with bromine or iodine. Bromination occurs at the C-5 of cytosine, yielding a reactive derivative, which can be used to couple diamine spacer molecules by nucleophilic substitution (Figure 1.48) (Traincard et al., 1983 Sakamoto et al., 1987 Keller et al., 1988). Other pyrimidine derivatives also are reactive to bromine compounds... 

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

This blend was obtained by polymers mixture extrusion and extraction with the azeotropic mixture of hexane/ethanol, and modifying the obtained polymer surface by coupling of 4-isocyanato butanoic acid methyl ester (as a spacer molecule) to PVA blend, saponification of methyl ester groups and coupling of 4-amino-TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) [229],... 

The lifetime of D+.C.A produced by the sequential electron transfer increases as the distance between D+ and A increases. Porphyrin-imide-fullerene triads have been synthesised (Figure 12.11), with the three components separated by nonreactive spacer molecules. 

Hapten Substance that can interact with antibody but cannot elicit an immune response unless it is conjugated to a carrier protein before its introduction into the tissues of an animal. Haptens are mostly small molecules of less than 1 kDa. For the generation of a catalytic antibody, a TSA (q.v.) is attached to a spacer molecule to give a hapten of which multiple copies can be linked to a carrier protein (q.v.). 

Spacers are sometimes attached on particles prior to immobilization of functional components in order to eliminate steric hindrance from the functional components and make them mobile. Spacer molecules have to have a proper chain length and affinity with the dispersant but not with the particle. The latter condition is necessary to prevent the train conformation of spacer on the particle surface. Ethyleneglycol diglycidyl ether satisfies the prerequisite in water and is attached to aminecarrying particles. 

---