Intramolecular cross-linking

Bis-Pyndoxal Tetraphosphate. A second class of bifunctional reagents, described in 1988, involves two pyridoxal groups linked by phosphates of different lengths (89). As shown in Table 4, the yield of intramolecularly cross-linked hemoglobin increases dramatically with increasing length of the phosphate backbone. It is beheved that the site of reaction of (bis-PL) is between the amino-terminal amino group of one P-chain and the... 

Aminopropionitrile (present in sweet peas) covalently inactivates lysyl oxidase, preventing intramolecular cross-linking of collagen and causing abnormalities in joints, bones, and blood vessels. 

The core of reversed micelles can be transformed to a highly viscous domain (nanogel) by entrapping appropriate species, such as viscous solvents and hydrophilic macromolecules, or by performing in situ appropriate polymerization reactions or intramolecular cross-linking of water-soluble polymer chains [232-234]. 

Nanogels made up of various intramolecularly cross-linked macromolecules have been prepared simply by performing the polymerization of hydrophilic monomers solubilized in the micellar core of reversed micelles, and they represent distinct macromolecular species from those obtained in bulk [191,240]. 

The total number of molecules in the sol fraction, neglecting intramolecular cross-linking, will equal the number of primary molecules minus the number of cross-linkages in the sol. Expressing these as numbers of moles per equivalent of structural units, we have N = 1/% primary molecules and p /2 cross-linkages in the sol. The number average degree of polymerization in the sol is then... 

Murthy, S.N.P., Wilson, J., Guy, S.L. and Lorand, L. (1991) Intramolecular cross-linking of monomeric fibrinogen by tissue transglutaminase. Proceedings of the National Academy of Sciences USA 88, 10601-10604. 

Benesch, R.E., and Kwong, S. (1988) B/s-pyndoxal polyphosphates A new class of specific intramolecular cross-linking agents for hemoglobin. Biochem. Biophys. Res. Comm. 156, 9. 

Pearson, K.M. et al. (2002) Intramolecular cross-linking experiments on cytochrome C and ribonuclease A using an isotope multiplet method. Rapid Comm. Mass Spectrom. 16, 149-159. 

Kinetics of Intramolecular Cross-Linking and Conformational Properties of Cross-Linked Chains... 

The reactions of intramolecular cross-linking is a rather poorly investigated area in the field of macro-molecular reactions. However, the problems of regularities of such processes are related to such important problems of polymer chemistry as chemical modification of polymers, networks formation, sorption of low molecular reagents by polymers, intramolecular catalysis, conformational transitions and so on. In spite of the great importance of the study of regularities of cross-linking reactions, the experimental and theoretical analysis of such processes is complicated by many difficulties. ... 

The first problem of the theory of the intramolecular reactions is a calculation of dimensions of the intramolecularly cross-linked coils as a function of the degree of cross-linking. For the analytical calculation of such dependence one needs to know all possible topological structures for any number of cross-linkages and to have the calculation algorithm for each of... 

The second important problem is a kinetical description of intramolecular cross-linking. Kinetic characteristics can vary in wide range depending on the nature of cross-linking agents, properties of the polymeric chain and experimental conditions. ... 

The kinetic problem for the intramolecular cross-linking reactions in general form was not yet solved. Only some particular cases, i.e. the cvclization of macromolecules, the intramolecular catalysis and diffusion-controlled collision of two reactive groups were studied theoretically bv Xorawetz, Sisido and Fixman... 

Thus this model study permitted to elucidate the main regularities of the process of intramolecular cross-linking. The most interesting of them are, firstly, the existence of a uniform relationship between the kinetics of the reaction and the equilibrium properties of partially cross-linked chains and secondly, the independence of the kinetics of cross-linking on the character of reactive groups distribution on the initial stage of the reaction. 

The hypothesis can be checked by the mathematical experiment, if one takes into consideration the probability of the intemolecular cross-linking. Let s assume that sol fraction contains only intramolecularly cross-linked chains while the formation of even one intermole-cular cross-linkage leads to the sol-gel transition. Because only the properties of sol fraction are of our interest we don t need to follow the intermolecularly cross-linked chains. It is rather natural to assume that the probability of the transition into the gel is proportional to the dimensions of the macromolecular coil. 

Thus the approach described can be apolied to the description of the kinetics of intramolecular cross-linking and the conformational properties of cross-linked products. 

The gel fraction increased with the consumption of the unsaturated groups. The efficiency of gel formation by the total consumption of the unsaturated groups, that is, the slope of the curves decreased with the increase in the initial total concentration of the unsaturated groups. The lower efficiency in the polyethylene with higher concentration of the unsaturated groups may be caused by the more frequent intramolecular cross-linking reaction in the dienes-grafted polyethylenes. 

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