Principles of Intercalation

Intercalation compounds of weU-defined stoichiometry are formed by reacting a host matrix (H) with so-called intercalate atoms or molecules (A). The product of the heterogeneous reactimi. 

A lamellar compound implies atomic layers in which the atoms are strongly bonded by covalent or ionic forces, while the link between the layers is insured by much weaker forces frequently referred as the vdW interactirais [12], Accordingly, one says intercalation for introduction of ions or molecules into a lamellar compound—the host—while the term insertion is devoted to other frameworks with one-dimensional (ID) and three-dimensional (3D) structure. Two major aspects must be considered for an insertion process taking place (Fig. 3.1)  

Consequently, most of the intercalation compounds are mixed-conductors, i.e., electronic and ionic to some extent, in which the charge transfer occurs between the intercalant species and the host structure. The tendency for this charge transfer process is the main driving force for the intercalation reaction and it is one of the basic properties that make the host framework a suitable cathode material. Intercalation is crucial in the working cycle of modem batteries and supercapacitors it involves complex diffusion processes along and across the layers. 

The stmctural modification with respect to the pristine compound results in changes of the unit cell parameters of the pristine material that are related to the radii of the guest ions, the size of the empty sites of the host lattice and the nature of these sites, i.e., octahedron or tetrahedron. It has been shown that intercalation of alkali ions can induce staging phenomenon due to the minimization of repulsive forces between intercalated cations and a special ordering that results in superstrac-tures [13, 14]. 

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Raman spectra have also been reported on ropes of SWCNTs doped with the alkali metals K and Rb and with the halogen Br2 [30]. It is found that the doping of CNTs with alkali metals and halogens yield Raman spectra that show spectral shifts of the modes near 1580 cm" associated with charge transfer. Upshifts in the mode frequencies are observed and are associated with the donation of electrons from the CNTs to the halogens in the case of acceptors, and downshifts are observed for electron charge transfer to the CNT from the alkali metal donors. These frequency shifts of the CNT Raman-active modes can in principle be u.sed to characterise the CNT-based intercalation compound for the amount of intercalate uptake that has occurred on the CNT wall. 

Intensive research on the electrocatalytic properties of polymer-modified electrodes has been going on for many years Until recently, most known coatings were redox polymers. Combining redox polymers with conducting polymers should, in principle, further improve the electrocatalytic activity of such systems, as the conducting polymers are, in addition, electron carriers and reservoirs. One possibility of intercalating electroactive redox centres in the conducting polymer is to incorporate redoxactive anions — which act as dopants — into the polymer. Most research has been done on PPy, doped with inter alia Co 96) RyQ- 297) (--q. and Fe-phthalocyanines 298,299) Co-porphyrines Evidently, in these... 

Armin Weiss (1981) presented some results of experimental work using mont-morillonite, he was able to show that the complete information present in a matrix is passed on to the daughter layers. In principle, the intercalating synthesis of a new layer of montmorillonite from the nutrient solution can be compared to the replication of a DNA chain. The distance between the layers is of great importance in these experiments and acts as a performance-limiting factor. 

In principle, all the kinetic concepts of intercalation introduced for layer-structured silicates hold for zeolites as well. Swelling, of course, is not found because of the rigidity of the three dimensional frame. The practical importance of zeolites as molecular sieves, cation exchangers, and catalysts (cracking and hydrocracking in petroleum industry) is enormous. Molecular shape-selective transport (large differences in diffusivities) and micro-environmental catalysis (in cages and channels)... 

It may be relevant to mention here the commonplace within the discipline of genetics—that only 2 to 5 percent of the genome is active at any one time, that these inactive areas can be activated by external (i.e., extracellular) factors such as hormones, and that large populations of similar nucleotide sequences exist in the DNA complements of higher organisms. It is possible to speculate on a memory mechanism, based on an interaction of intercalating amines and neural DNA, that would function on principles similar to the intercalator/RNA interaction that may be involved in neural transmission. The remainder of this chapter is concerned with a discussion of such a speculation. 

Fig. 7.3. Principle of acridinium-ester probe hybridization in solution and detection. Acridiniura-NHS is linked to allyl nucleotides (Section 7.3.1.2) in the probe. When the probe hybridizes with its target in solution, the acridinium moiety intercalates in the duplex. Unhybridized acridinium ester probes can be hydrolyzed selectively (Table 7.7, step 2), whereas protected acridinium ester remains intact (ID. After nonspecific chemiluminescence is sufficiently eliminated, specific chemiluminescence is measured (in). The whole procedure takes less than 30 min.

In order to consider the contribution of electrons to the chemical potential of intercalation compounds, several groups have applied an ah initio or first principles calculation method to analyze the thermodynamics of lithium intercalation [37—44]. 

The principle of the mechanism is a selective protonation of sites according to their basicity. This basicity depends on the geometry of the position and on the nature of the associated cation. This trend is shown by the intercalation of an interesting illustration of that point of view can be found in bases such as amines in the starting layered oxides. This intercalation is favored by a more acidic framework. Substitution in the slabs also changes the chemical and thermal stabilites of the materials. 

Toyota. S. Woods. C.R. Benaglia, M. Haldimann. R. Warnmark. K. Hardcastle. K. Siegel, J.S. Tetranuclear copper(i)-biphenanthroline gridwork Violation of the principle of maximal donor coordination caused by intercalation and CH-to-N forces. Angew. Chem. Int. Ed. 2001. 40. 751-754. 

Fig. 14 Schematic diagram for the principle of the developed ECL aptasensor for detecting thrombin. (A) The adsorption of thiolated antithrombin aptamer on and the 2-mercapto-ethanol block to the electrode. (B) The formation of the dsDNA between aptamer and its complementary ssDNA. (C) The intercalation of Ru(phen)3 into the dsDNA sequence. (D) Dissociation of dsDNA and release of Ru(phen)3 due to the interaction between thrombin and its aptamer. Reprinted with permission from Ref 97. Copyright (2009) American Chemical Society.

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