CASING Crosslinking by Activated

CASING crosslinking by activated species of inert gases... 

Surfaces may be treated in inert gas plasmas. In the early studies of plasma treatment with inert plasmas (CASING - crosslinking by activated species of inert gas), plasma contamination probably resulted in oxidation. The activation that does occur in an inert gas plasma is probably from UV radiation from the plasma, causing bond scission in polymers or the generation of electronic charge sites in ceramics. 

In the presence of an inert gas, such as He or Ar, crosslinking can be introduced into the surface layer of material by plasma treatment. Hansen and Schon-horn [60] named this Crosslinking by Activated Species of Inert Gases (CASING). As a result, bond strength is enhanced because crosslinking strengthens the surface layer. 

Although mononitrenes do not act as crosslinking agents themselves, they can generate unpaired electrons in the polymer chains by the abstraction of hydrogen molecules from the polymer. As the result, the polymer chains are crosslinked by the recombinations of these unpaired electrons. Crosslinking by mononitrene in such a way, depends on the activity of the nitrene and may be not necessarily less efficient in some combination of monoazide with the polymer than that by dinitrene as is seen in the case for... 

Although lantibiotics are not enzymes and do not contain cofactors they are included here and briefly discussed because they are proteins whose biosynthesis requires extensive and unusual posttranslational modifications. These modifications endow the gene product with a new function, in this case an antimicrobial activity, which would not exist in the absence of these covalent modifications to the protein. They are found in peptides of microbial origin. Their name derives from lanthionine, which is a nonproteinogenic amino acid composed of two alanine residues that are crosslinked on their /3-carbon atoms by a thioether linkage (Figure 15). The wide array of fascinating posttranslational modifications which are present in this class of peptide antibiotics is reminiscent of those seen in some protein-derived cofactors. 

Coumarin side-chain polymers can be also crosslinked by the (2 - - 2) cycloaddition reaction, and it is clear that cis-trans isomerization cannot occur [8], The fraction of dimerized product is much greater in this case and LC alignment is parallel to the polarization of the activating UV light [8, 48] (Figure 2.14). 

Use of sulfo-NHS-LC-SPDP or other heterobifunctional crosslinkers to modify PAMAM dendrimers may be done along with the use of a secondary conjugation reaction to couple a detectable label or another protein to the dendrimer surface. Patri et al. (2004) used the SPDP activation method along with amine-reactive fluorescent labels (FITC or 6-carboxytetramethylrhodamine succinimidyl ester) to create an antibody conjugate, which also was detectable by fluorescent imaging. Thomas et al. (2004) used a similar procedure and the same crosslinker to thiolate dendrimers for conjugation with sulfo-SMCC-activated antibodies. In this case, the dendrimers were labeled with FITC at a level of 5 fluorescent molecules per G-5 PAMAM molecule. 

Thioureas mainly find use for the vulcanisation of CR, epichlorohydrin (ECO) and some ethylene propylene diene terpolymer (EPDM) compounds. They show high crosslinking activity, with usually adequate compound flow time before onset of the crosslinking. In EPDMs, the thioureas are used as activators for low activity third monomer types and, in the presence of calcium oxide desiccants, in free state vulcanisation of extrudates, etc. The use of thioureas can overcome the retardation caused by the desiccant. In this case some care must be taken otherwise overcompensation may occur. Thioureas are not used in food product applications and are a known health hazard, particularly for pregnant women. 

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