Solution Complexes with Cations

It has been reported that a complex between the hexa-(methoxyethyl) ether of p- m-butylcalix[6]arene and guanidinium tetraphenyl borate can be detected by H NMR measurements which show large shifts in the resonances of the hydrogens in the methoxyethyl groups and a reduced conformational inversion rate 121 . The 

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These can be prepared by electrolytic oxidation of chlorates(V) or by neutralisation of the acid with metals. Many chlorates(VII) are very soluble in water and indeed barium and magnesium chlorates-(VII) form hydrates of such low vapour pressure that they can be used as desiccants. The chlorate(VII) ion shows the least tendency of any negative ion to behave as a ligand, i.e. to form complexes with cations, and hence solutions of chlorates (VII) are used when it is desired to avoid complex formation in solution. 

It is expected, therefore, that the cyclic hexamer also exhibits a characteristic tendency to complex with cations. In fact, the addition of an acetonitrile solution of metal thiocyanates to a solution of the cyclic hexamer in the same solvent shifted the carbonyl absorption to a lower wave number46,52 The shift values depended upon the kind of metal ions present, and the largest shift value of 40 cm-1 was observed for barium thiocyanate (molar ratio of Ba2+/hexamer = 10). In addition to the shift of the carbonyl absorption, the intensities of the C—O-C stretching vibrations around 1200 cm-1 varied appreciably. 

Ring systems intermediate between phthalocyanines and naphthalocyanines are known 263,264 (51) is such a compound. They are most simply called benzonaphthoporphyrazines, and various zinc(II) complexes with cationic (A--m e t hy 1 pyridini um-3-oxy) substituents have Amax in the range 680-750 nm in solution or in Cremophor micelles, and show promise in bioassays in vivo.264... 

We have purified natural double-strand DNA from salmon testes, in which anionic DNA complexes with cationic proteins of protamine. After mincing salmon testes, the homogenized solution was treated with protease in order... 

We discovered that CB[10] was also capable of forming a complex with cationic calix [4]arene 27, which itself usually functions as a host molecule in aqueous solution (Scheme 4.10) [18], Interestingly, when 27 is incorporated inside CB[10], two sets of resonances are observed which were in slow exchange on the NMR... 

Chromoionophores of crown 4 and spherand cyclophane-type 5 with 2,4-dinitrophenylazophenol groups as a chromophore were also designed [7 a]. They show marked color changes from yellow into blue on complexation with cations in ethanol and chloroform solutions. This chapter describes selective complexation and coloration of azophenol hosts or fluorescent emission of benzothiazolyl crowns with alkaline metal ions and alkyl amines. 

Table IV also includes some values determined in methanol as the solvent these are very much higher (and, hence, also more accurate) than those in water, because the polyol competes with methanol, rather than with water, for outer-sphere positions on the cation. These figures explain why carbohydrates are soluble in methanol or ethanol containing high concentrations of calcium chloride, or even potassium acetate, and in such systems as lithium chloride in 2-methoxyethanol. ° Sugar derivatives that are soluble in non-hydroxylic solvents form complexes with cations in those solvents even more readily for example, methyl 2,3-0-isopropylidene-4-0-methyl-) -L-rhamnopyranoside (24) (but not its a anomer) will form a complex with sodium iodide in acetone, the Na" " ion coordinating to 0-1,0-2, and 0-3. In aqueous solution, the concentration of this complex would be negligible.

A naphthalene based oligomer, (Fig. 45.6) is the precursor for the formation of such a supramolecular tower. Ortho-linked azaheterocycles, in their transoid conformation, preorganize the oligomer into a helix. The inside of this helix is suited for complexation with cationic guests, which interact via van der Waal interactions and ion-dipole interactirais, leading to the formation of polymolecular assemblies of the oligomer. These assemblies compare well with the pH-based and salt-induced assemblies of TMV in aqueous solutions. 

Anionic polysaccharides respond in similar fashion to surfactants. They are relatively unaffected by anionic surfactants like sodium or ammonium lauryl sulfate. On the other hand, they form strong ionic complexes with cationic surfactants like dodecyltrimethylam-monium chloride, even at cationic surfactant concentrations below the critical micelle concentration (cmc), or concentration at which the surfactant molecules form micelles in solution (92,93). The behavior of polyelectrolytes in the presence of surfactants is summarized in Chapter 5 and has been reviewed (94). 

Angyal s group has extended its investigations on the association of polyhydroxy-compounds with cations in solution. N.m.r. spectroscopic studies showed that those cyclitols containing an ax., eg., ax. sequence of three hydroxy-groups (e.g. e/)/-inositol) form complexes with cations (e.g. Ca +, Sr +, and Ba +) addition of these divalent cations produced a downfield shift of all the proton resonances. 1 1-Complexes of c/ Z-inositol and calcium or strontium chloride... 

A useful property of the tetrahydroxyborate ion in solution is its ability to form soluble ion-pair complexes with cations, notably the hardness ions, calcium and magnesium (M +) [18] ... 

There are fewer reports of linear, acyclic, ion-binding polymers. It has been reported that poly(oxyethylene) improves the solubility of alkali metals in ethers such as tetrahydrofuran, dime thoxy ethane, and diglyme, stabilizes fluorenyl alkali metal compounds, accelerates Williamson reactions and accelerates several other nucleophilic reactions.All of these effects were attributed to the ability of poly(oxyethylene) to complex with cations in solution. Yanagida and coworkers studied the alkali metal cation complexation of poly(oxyethylene), using a picrate salt extraction technique similar to the one used by Pedersen and Frensdorff. Polymers with more than 23 oxyethylene units were effective iono-phores for potassium, with degrees of extraction (percent extracted) comparable to crown ethers. The extractability per oxyethylene unit was nearly constant, and the complex stability increased linearly with increasing numbers of repeating oxyethylene units. Seven oxyethylenes were the minimum number of repeat units necessary to bind potassium ion effectively in the aqueous phase. The less efficient extraction of short-chain poly(oxyethylene) is apparently caused by its hydrophilic character. 

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