Metal salt binding

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

In other sections in this chapter, we have referred to a variety of macropolycyclic structures which are more elaborate than the simple three-stranded bicyclic cryptands. This includes bridged double-macrocycles " , in-out bicyclic amines and the macrotricyclic quaternary ammonium salts of Schmidtchen. In addition to these, there are two other types of compounds which deserve special note. The first of these is a stacked twin-ring cryptand, but it is a hybrid molecule rather than a double-cryptand . The species shown below as 20 is a crowned porphyrin, and was designed to provide a pair of metal cation binding sites similar to those which might be available in natural biological systems . 

Apart from the hardness and softness, two reactivity-related features need to be pointed out. First, iron salts (like most transition metal salts) can operate as bifunctional Lewis acids activating either (or both) carbon-carbon multiple bonds via 71-binding or (and) heteroatoms via a-complexes. However, a lower oxidation state of the catalyst increases the relative strength of coordination to the carbon-carbon multiple bonds (Scheme 1). 

The complexing of chitosan and its basic derivatives with anionic substances is paralleled by compatibility with cationic and nonionic compounds. Similarly, the anionic derivatives of chitosan show complex formation with cationic agents and are compatible with anionic and nonionic compounds. The capability of these chitosan derivatives to complex with certain metal ions, notably those of the transition series, is also important, having possibilities for the removal of metal salts from effluent. The hierarchy in terms of binding capacity is Cr(III) < Cr(II) < Pb(II) < Mn(II) < Cd(II) < Ni(II) < Fe(II) < Co(II). 

In contrast to Bosman et al., who only found metal complexation in the periphery of polypropylene imine) dendrimers, Tomalia and co-workers reported on the incorporation of copper ions into the interior of PAMAM dendrimers judging from EPR and UV/Vis studies [220, 221]. Metal binding in the dendrimer interior has also been observed for dendrimers carrying multiple ligands for metal complexation within their framework such as crown-ethers [222, 223] (Cs(I)-complexes), piperazine [224] (Pd(II)- and Cu(II)-complexes) or triazocyclononane [225] (Cu(II)- and Ni(II)-complexes). In most cases addition of the metal-salt to the dendrimer led to the formation of 1 1 complexes. 

Metallodendrimers can be constructed via binding of groups with suitable donor atoms (e.g., polydentate ligands) on either the periphery or the core of the dendrimer and the subsequent complexation/coordination of these ligands to an appropriate metal salt. Ultimately, this binding can involve the formation of a direct a bond linkage (i.e., a M-C bond). This chapter describes various... 

One of the first results on the use of phosphine dendrimers in catalysis was reported by Dubois and co-workers [16]. They prepared dendritic architectures containing phosphorus branching points which can also serve as binding sites for metal salts. These terdentate phosphine-based dendrimers were used to incorporate cationic Pd centers in the presence of PPh3. Such cationic metalloden-dritic compounds were successfully applied as catalysts for the electrochemical reduction of C02 to CO (e.g. 9, Scheme 9) with reaction rates and selectivities comparable to those found for analogous monomeric palladium-phosphine model complexes suggesting that this catalysis did not involve cooperative effects of the different metal sites. 

Fortunately, the deposition potentials of these metals can be brought together by adjustment of their ionic concentrations. Thus, if KCN is added to the solution of the salts of these metals, it binds the Cu and Zn ions as rather stable Cu(CN)4 and Zn(CN)4 complexes, respectively. In solution, the copper complex dissociates to cuprous and cyanide ions according to... 

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