Intercalation Complexes

Alexander, Inorg. Nuclear Chem. Letters, 1971, 7, 1053 L. E. Alexander, I. R. Beattie, and 

Geetsma, C. Haas, R. Huisman, and F. Jellinek, Solid State Comm., 1972, 10, 75. 

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M. Makha, A. Purich, C. L. Raston, A. N. Sbolev, Strucutral diversity of host-guest and intercalation complexes of fullerene C60. Eur. J. Inorg. Chem. 2006, 507. 

The catalyst effectiveness decreased upon increasing the concentration of the intercalated complexes via aggregation of the closely associated complexes.164 Sulfides were also oxidized by heterogeneous Co(II) complexes.163 Catalytic oxidation of thiols was mediated by Mo complex intercalated in a layered double hydroxide.166... 

When supported complexes are the catalysts, two types of ionic solid were used zeolites and clays. The structures of these solids (microporous and lamellar respectively) help to improve the stability of the complex catalyst under the reaction conditions by preventing the catalytic species from undergoing dimerization or aggregation, both phenomena which are known to be deactivating. In some cases, the pore walls can tune the selectivity of the reaction by steric effects. The strong similarities of zeolites with the protein portion of natural enzymes was emphasized by Herron.20 The protein protects the active site from side reactions, sieves the substrate molecules, and provides a stereochemically demanding void. Metal complexes have been encapsulated in zeolites, successfully mimicking metalloenzymes for oxidation reactions. Two methods of synthesis of such encapsulated/intercalated complexes have been tested, as follows. 

Site I is characterized by a relatively large red shift of 10 nm in the absorption maxima (relative to the aqueous solution spectra), exhibiting maxima at 337 and 354 nm, and a negative AA spectrum all of these properties are consistent with an intercalation-complex geometry in which the planar pyrene ring-system is nearly parallel to the planes of the DNA bases. 

Equation (4) demonstrates that the relationship between the association constant K, which is sensitive to the ionic strength (16,17,21,25), and the level of covalent binding, f v, is a complex one. It is known that fcov decreases upon the addition of NaCl or MgCl2, and this effect has been taken as evidence that physical intercalation complexes play a role in the covalent binding reaction (17,22,26). While this conclusion may still be correct, such evidence is insufficient since it has been shown that not only K, but also k3 (21,25), and the branching ratio kc/k (21) in Equation (4) depend on the salt concentration. 

Physical Intercalation Complexes, Covalent Binding and Hydrolysis... 

Intercalation of BPDE. Several groups have studied the reversible intercalative binding of BPDE to DNA. The fluorescence quantum yield of BPDE is much lower than that of BP derivatives which do not contain an epoxide group and fluorescence techniques have not been widely used to study BPDE physical binding to DNA (4). Association constants for the DNA intercalation of BPDE have been obtained by measuring red shifts in the UV absorption spectra of BPDE which occur upon the formation of intercalated complexes and from fluorescence studies (8) of the kinetics of DNA catalyzed hydrolysis of BPDE. The hydrolysis reaction is conveniently monitored by following the fluorescence of the hydrolysis product, BPT, which has a quantum yield many times greater than BPDE. 

The derivation of an intercalation association constant from kinetic studies of BPDE hydrolysis presumes that the reaction proceeds via an intercalated complex This mechanism is supported by the observations that the catalytic activity of denatured DNA is lower than that of native DNA (8), that catalysis is inhibited at high ionic strengths ( 3, 8, 17), and that mononucleotides such as GMP exhibit much greater catalytic activity than does free phosphate (80). 

The non-covalently bound BPDEs to DNA formed initially appear to be intercalation complexes (1 6,52-55) Meehan et al. (1 6) report that the BPDE intercalates into DNA on a millisecond time scale while the BPDE alkylates DNA on a time scale of minutes. Most of the BPDE is hydrolyzed to tetrols (53-56). Geacintov et al. (5l ) have shown with linear dichroism spectral measurements that the disappearance of intercalated BPDE l(+) is directly proportional to the rate of appearance of covalent adducts. These results suggest that either there may be a competition between the physically non-covalently bound BPDE l(+) and an externally bound adduct or as suggested by the mechanism in the present paper, an intercalative covalent step followed by a relaxation of the DNA to yield an externally bound adduct. Their results for the BPDE i(-) exhibit both intercalative and externally bound adducts. The linear dichroism measurements do not distinguish between physically bound and covalent bound forms which are intercalative in nature. Hence the assumption that a superposition of internal and external sites occurs for this isomer. 

Theng BKG, Newman RH, Whitton JS (1998) Characterization of an alkylammonium-montmorillonite-phenanthrene intercalation complex by carbon-13 nuclear magnetic resonance spectroscopy. Clay Miner 33 221-229... 

In addition to stabilizing organic products by reaction with metal-exchanged clays, as indicated above, aluminosilicate minerals may enable the preparation of metal organic complexes that cannot be formed in solution. Thus a complex of Cu(II) with rubeanic acid (dithiooxamide) could be prepared by soaking Cu montmorillonite in an acetone solution of rubeanic acid (93). The intercalated complex was monomeric, aligned with Its molecular plane parallel to the interlamellar surfaces, and had a metal ligand ratio of 1 2 despite the tetradentate nature of the rubeanic acid. 

Brindley and Sempels (1), Vaughan et al. (2) and Shabtai (3) have shown that the experimental conditions of Al intercalation influences the physicochemical properties of the clay. The nature, amount and spacial distribution of the pillars change the thermal stability, texture and acidity of the pillared clays. For example, Rausch and Bale (4) have reported that the OH/Al ratio modifies the structure of the Al complex and that monomeric [Al(0H)x(H20)6-x] " or polymeric [A1i304(0H)24(H20)i2] species can be obtained. Clearfield (5) demonstrated that the polymerisation state of Zr species depends on the temperature, concentration and pH of the solutions. In any case, the height of pillars is largely controlled by the polymerisation state of the intercalated complexes. However, in order to maintain the accessibility of the inner surface, the density or spacial distribution of the pillars has to be controlled. This parameter has been studied by Flee et al (5), and Shabtai et al (7) for Al pillared clays and Farfan-Torres et al (8) for zirconium. 

A small increase of the (d 001) basal spacing is observed for the Li containing Zr pillared clays. However, the thermal stability of these solids drastically decrease. At high temperature, the collapse of the strucutre is also supported by the decrease of the surface area which is, at 700°C, almost identical to those measured for the montmorillonite. Different hypothesis may be proposed to explain the increase of the interlayer distance at low temperature (i) a better polymerization of the intercalated complex (ii) a modification of the distribution of the pillars (iii) a lower interaction between the pillar and the silica layer. The first hypothesis may easily be eliminated since the small variation of the height of the pillars (less than 1 A) cannot be explained by structural changes of the... 

Figure l i The structure of the CpG-acrldine orange intercalator complex. The C2 endo sugar conformation at the 3 end of the BNA chain surrounding the intercalator is indicated. 

Omloo and Jellinek7 have described the synthesis and characterization of intercalation compounds of alkali metals with the group V layered transition metal dichalcogenides. Typically, these types of intercalation complexes are sensitive to moisture and must be handled in dry argon or nitrogen atmospheres. The alkali metal atoms occupy either octahedral or trigonal prismatic holes between X-M—X slabs. There are two principal means by which these compounds may be prepared. 

DiSalvo et al.9 have carried out a systematic survey of intercalation compounds of 2H(a)-TaS2 with post-transition metals. In particular, the system SnxTaS2 was found to exist in two composition domains, 0 < x < /3 and x = 1. The following discussion briefly describes the techniques used by DiSalvo to synthesize the compound SnTaS2. Syntheses of other transition and post-transition metal intercalation complexes with the layered transition metal dichalcogenides are discussed in References 9 and 20-24. 

Heavier metal ions and metal complexes can find sites on nitrogen atoms of the nucleic acid bases. Examples are the platinum complex cisplatin and the DNA-cleaving antibiotic neocarzinostatin (Box 5-B). Can metals interact with the n electrons of stacked DNA bases A surprising result has been reported for intercalating complexes of ruthenium (Ru) and rhodium (Rh). Apparent transfer of electrons between Ru (II) and Rh (III) over distances in excess of 4.0 nm, presumably through the stacked bases, has been observed,181 as has electron transfer from other ions.181a Stacked bases are apparently semiconductors.182... 

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