Bifunctional Crosslinking Agents

The homobifunctional photoreactive BASED (Chapter 4, Section 5.1) has two photoreactive phenyl azide groups, each of which contains an activating hydroxyl. Radioiodination of this crosslinker can yield one or two iodine atoms on each ring, creating an intensely radioactive compound. Crosslinks formed between two interacting molecules are reversible by disulfide reduction, thus allowing traceability of both components of the conjugate. 

SASD (sulfosuccinimidyl-2-(p-azidosalicylamido)ethyl-l,3 -dithiopropionate) (Chapter 5, Section 3.2) behaves in a similar manner, except it contains an amine-reactive end that can be 

Finally, the small amine-reactive and photoreactive crosslinker, NHS-ASA (Chapter 5, Section 3.1), can be iodinated to provide a non-cleavable radioactive conjugate. 

There are many other compounds that have been investigated for their use in indirect radiolabeling of proteins. For an excellent overview of these chemical reactions (see Wilbur, 1992). 

Hydrogen bond formation with surface -OH groups 

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Modification Reagent that can create functional groups able to couple with reactive group 2 of the hetero bifunctional crosslinking agent... 

Another possible route to coupling ligands to amine particles is to use a bifunctional crosslinking agent to react with the amines and provide another reactive group at the other end to couple with the ligand. In this approach, virtually any reactive group desired can be formed on the... 

By Far the simplest bifunctional crosslinking agent is formaldehyde. Although structurally a mono-functional aldehyde compound, formaldehyde reacts with proteins via a two-step reaction... 

One can see that for a polymer obtained from BA2 at aB = 0.95, ( Af)2 =191 while (Af)n = 19. If this polymer is crosslinked with a bifunctional crosslinking agent C2 under stoichiometric conditions, the gel point conversion is about 0.07. However, the gel point conversion is expected to be somewhat higher not only because of the lower polydispersity of the hyperbranched polymer, but also because some cyclization can occur or multiple crosslinks can be formed during crosslinking. 

The monomer 1 was copolymerized by free radical initiation in the presence of an inert solvent with a large amount of a bifunctional crosslinking agent. Under these conditions, macroporous polymers were obtained which possessed a permanent pore structure, a high inner surface area, and good accessibility. Additionally, low polymer swellability would imply limited mobility of the polymer chains. From a polymer of this type, 40 to 90% of template molecules can be split off by treatment with water or alcohol (see Figure 3 ). If this polymer is... 

In order to reduce the molecular weight we routinely sonicate the mixture of cells and lysis solution. This also promotes efficient extraction of DNA. Many procedures employ ethanol to concentrate and desalt the DNA In order to fully remove the ethanol this DNA needs to be thoroughly dried. However, the resulting pellet may then be difficult to redissolve without extended incubation in buffer during which time labile adducts may be lost. Furthermore, in the case of DNA exposed to bifunctional crosslinking agents, there is the possibility of delayed reactions which can result in the formation of crosslinks between DNA fragments and this will impede the redissolution. 

When a linear polymer containing a number of active A groups is crosslinked with a bifunctional crosslinking agent containing B groups and A reacts with a network with trifunctional branch points is foimed as shown schematically in Fig. k. 

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