Hopping crosslinking

Schuster GB, Landman U (2004) The mechanism of long-distance radical cation transport in duplex DNA Ion-gated hopping of polaron-like distortions. Top Curr Chem 236 139-161 Schussler H, Jung E (1989) Protein-DNA crosslinks induced by primary and secondary radicals. Int J Radiat Biol 56 423-435... 

In summary, it is shown that the 3-arm star PIB ionomer is useful in the study of ion-hopping kinetics. The polymer chains are crosslinked by covalent trifunctional linkages and ionic aggregate exist mostly as multiplets in the middle of the chains. The kinetic constants for ion-hopping in this system are given by k = 7.11 x 10 exp(-94,100/RT). 

The soliton model was first proposed for degenerated CPs (polyacetylene [PA] in particular] and it was noted for its extremely one-dimensional character, each soliton being confined to one polymer chain. Thus, there was no conduction via interchain hopping. Furthermore, solitons are very susceptible to disorder and any defect such as impurities, twists, chain ends, or crosslinks will localize them. 

Arsenic pentafluoride effects a Friedel-Crafts chain extension and crosslinking in PPV [93]. The electrical conductivity takes place by a variable-range hopping mechaiusm. 

The reduced enzyme is reoxidized by osmium redox couples on the polymer chain close to the active site on the enzyme The electrons from the reaction then propagates to the electrode surface by means of electron hopping between the redox sites in the polymer The polymer is crosslinked by PEGDGE to the electrode surface, where the osmium complex oxidizes and the electrons are transferred to the electrode The electron transfer procedure is shown in figure 1 The current produced is proportional to the rate of glucose conversion, and provides a measure of the substrate concentration... 

Another approach is based on the application of redox polders, e.g. osmium complex-modified poly(vinyl pyridine) (9-11) or ferrocene-modified poly(siloxanes) (12,13X crosslinked together with an enzyme on the top of the electrode. The electron transfer fi-om the active site of the polymer-entrapped enzyme to the electrode surfece occurs to a first polymer-bound mediator which has suflSdently approached the prosthetic group to attain a fast rate constant for the electron-tranrfer reaction. From this first mediator the redox equivalents are transported along the polymer chains by means of electron hopping between adjacent polymer-linked mediator molecules (Fig. 2). Extremely fast amperometric enzyme electrodes have been obtained with si ificantly decreased dependence fi-om the oxygen partial pressure. However, die redox polymer/enzyme/crosslinker mbcture has to applied either manually or by dipcoating procedures onto the electrode surface. 

The crosslinks formed in irradiated polymers are usually attributed to combination of radicals on different molecules in close proximity to each other. This proximity may result from C-H scission, followed by H abstraction from the adjacent molecule, or by migration of radical sites along the polymer backbone, e.g. by a hydrogen-hopping mechanism. This conventional and widely accepted mechanism of crosslinking produces a H-type crosslink. The reactive species may also be ions or radical-ions. 

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