Macroligand effectiveness

This is caused by the cooperative effect arising from the change in the macromolecular form during complex formation. The cooperative interactions in the system macroligand-MX in solution also produce a change in the charge of the chain. 

The above-mentioned factors essentially influence the thermodynamic parameters of MMC formation. One of the neigbor effects apparent in metal-polymer systems is that thermodynamic parameters do not depend on the length of the chain (i.e. the molecular weight of the macroligand). Using the temperature dependence of the constant of formation K, the changes in the free... 

The essential role of the polymer consists of the stabilization of catalytically active intermediates which are formed both at the binding of MX, with a macroligand (for example, monomerization of dimer complexes) and in the course of a catalytic reaction (in particular, establishing isolated low-valence metal ions, prevention of their aggregation, formation of coordinated unsaturated complexes, etc.). The factors determining these effects have been already mentioned and can be summarized as follows ... 

Two aspects of nanoparticles immobilization on biopolymers should be mentioned. First, most of the heavy metals bind simultaneously to several protein macroligands with a specific spatial environment and conformation. Triple complexes may also form composed of protein/metal/nucleic acid (metal = Au, Pt, Pd). Perhaps the presence of these structures provides the anticarcinogenic effect achieved on introduction of these metals into organisms. Second, heavy metals, such as Au(T), react with native Zn-, Cd-, and Co-thioneins by replacing selectively Zn and even Cd when added in excess. This process is characterized by only minimal changes in the protein conformation. 

The oxidative coupling of benzene with styrene and some paraderivatives catalyzed by palladium (II) acetate was also investigated in the presence of MIP-CD [41]. Under this condition, the approach of the reacting molecules was also required for a sufficient reaction rate, and the product itself could be a model of the transition state. Trans-stilbene was used as a template for molecular imprinting. Pd-complexes with the synthesized macroligands turned out to be effective catalysts for the oxidative coupling process (Fig. 2.13). 

If MX reacts with porous polymers, accessible pores are filled first. Such overgrown pores, which are associated with filling and shielding of the crosslinked macromolecule, is evidence for the MX contribution to a supramolecular buildup of macroligands. Thus it is impossible to predict the effect of a macrohgand pore size on complex formation for macroreticular glycidyl methacrylate-ethylene glycol dimethacrylate copolymer (Fig. 2) since the material has a bimodal and even polymodal pore distribution in radius. Nevertheless, it was shown that insertion of [RhCl(CO)2]2 in a polyamide is accompanied by a shift of the pore size to lower values some... 

Consistent with the chain effect, which can be added to the neighboring group effect, the Avc=o V tie is strongly affected by the molecular weight of a macroligand. For example, for C0CI2 complexes with poly(vinylpyrrolidone) with polymerization degrees of n = 100, 200, 360, and 6300 and Avc=o values of 54, 49, 48, and 43 cm , respectively, were found. ... 

The nature of functional groups of a polymer changes as a result of protonation, ionization, quartemization, and alkylation. There are numerous examples of this effect however, only a few will be described here. Particularly, PVA reaction with is accompanied by a partial conversion of hydroxyl to carboxyl groups (scheme 5). In an acidic medium, complex A decomposes, 1,2-glycol units are oxidized, and reduces to V. In addition, complex B is formed from and 1,2-ketol as a result of oxidation, which is accompanied by chain decomposition to reduce vanadium. The reaction is, to a certain extent, similar for Ce +. Furthermore, free-radical steps are observed in these reactions. It should be noted that this occurs only for PVA, which forms with 1,2-glycol units as a result of abnormal head-to-head addition. This illustrates the importance of both functional and structural uniformity of macroligands. 

There is still no resolution on the effect of macroligand stereochemistry on complex formation. A particular case is the formation of a complex between P2ViPy and MCI2 (M = Co, Ni, Cu, Zn). In that case, the order of reactivity is as follows atactic > isotactic > crosslinked. However, the rate of complex formation for isotactic poly(acrylic acid) (PAAc) with Cu is 1.5 times greater than for the syndiotactic form, and the E for these reactions is 6.0 and T.Okcal moP, respectively. 

Figure 3.2. Schematic presentation of a secondary effect affinity precipitation using a heterobifunctional affinity macroligand to precipitate the target molecule (reproduced with permission from reference 25).

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