Crosslinking procedures

The greatest degree of control in crosslinking procedures is afforded using heterobifunctional reagents (Chapter 5). Since a heterobifunctional crosslinker has different reactive groups on either end of the molecule, each side can be directed specifically toward different functional... 

There are several methods available for the detection or measurement of amine groups in proteins and other molecules. Accurate determination of target amine groups in molecules before or after modification may be important for assessing reaction yield or suitability for subsequent crosslinking procedures. The following methods use commercially available reagents and are easily employed to detect primary amines with simple spectrophotometric measurement. 

Figure 20.7 Glutaraldehyde antibody-enzyme crosslinking procedures usually produce a wide range of high-molecular-weight complexes, some of which may precipitate from solution.

Bz s-imidoesters like DMS may be used to couple proteins to PE-containing liposomes by crosslinking with the amines on both molecules (Figure 22.24). However, single-step crosslinking procedures using homobifunctional reagents are particularly subject to uncontrollable polymerization of protein in solution. Polymerization is possible because the procedure is done with the liposomes, protein, and crosslinker all in solution at the same time. 

Using the step 3 product and the step 5 crosslinking procedure at 5°C and stirring for 20 hours generated a gelated material. 

Grabarek, Z. and Gergely, J. (1990). Zero-length crosslinking procedure with the use of active esters. Anal. Biochem. 185 131-135. 

Samples containing more than 2% of sulfur did not pick up any iodine even after a 72-hour period. The completely saturated EPDM portions of the blend seem to prevent any iodine molecules from permeating into the polyacetylene moieties. In order to circumvent this problem, we have doped the blend with iodine prior to the crosslinking procedure. Subsequently, the doped material having a conductivity of 60 ft-1 cm-1 was reacted with sulfur monochloride in a toluene solution for 10 minutes. The color of the solution turned from pale yellow to dark red while the polymer film remained insoluble in the toluene solution. 

Quinone methides are formed as reactive intermediates (equation 30) [111-114] and these species can be understood as mesomeric structures to quinones and quinone methanes (equations 31 - 32) [115], These quinone methides are highly reactive intermediates. They cannot be isolated during the crosslinking procedure [116,117] but the presence of quinone methides is confirmed by C-NMR experiments [117], Generally, 4-quinone methides are more stable in comparison to then-ortho compounds. 

In the field of chemical analysis, biosensors have undergone rapid development over the last few years. This is due to the combination of new bioreceptors with the ever-growing number of transducers [1]. The characteristics of these biosensors have been improved, and their increased reliability has yielded new applications. Recently, a new technique of enzyme immobilization has been developed to obtain biosensors for the determination of enzyme substrates [2]. It is based on the enzyme adsorption followed by a crosslinking procedure. Therefore, a penicillin biosensor can be obtained and associated with a flow injection analysis (FIA) system for the on-line monitoring of penicillin during its production by fermentation [3-4]. This real-time monitoring of bioprocess would lead to optimization of the procedure, the yield of which could then be increased and the material cost decreased. 

Although general features of the crosslinking procedure are the same for all polyolefins, substantial differences exist regarding the efficiency and mechanism of the process depending on the chemical structure and physical state of the material. Since basically all common procedures leading to polyolefin crosslinking are based on a free radical formation and subsequent recombination of macroradicals, it is important to be... 

In the following, a detailed description of the two-step crosslinking procedure, including many practical details that proved to be useful in order to obtain high quality samples will be presented. Readers not interested in experimental details can proceed below. 

Fig. 11 Photograph of the LSCE preparation according to the two-step crosslinking procedure under mechanical load after Kiipfer. The elastomer strip is fixed using Kapton adhesive tape...

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