Complexation selective

Fig. 11) form very strong and selective complexes with Fe or actinide and lanthanide ions (63,64) while a similar receptor with hard endocarboxyhc acid groups is efficient for hard and ions showing again responsibility of a charge density effect in the receptor—substrate recognition (65). Thus,... 

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

This system has characteristic in ingeneous combination of a redox pump and the selective complexation of cation by the macrocyclic ligand. It must be noted that this new system is very promising from the point of view of extending the scope of the selection of the cation carriers, since any carrier can be employed so long as it has selectivity for a special cation and has enough stability toward redox system. 

In this review, recent development of active transport of ions accross the liquid membranes using the synthetic ionophores such as crown ethers and other acyclic ligands, which selectively complex with cations based on the ion-dipole interaction, was surveyed,... 

The conditional association constant for [18]aneN4 ( cyclic spermine ) with ATP - at pH 7.5 is calculated from the (3L value (Table 5) and protonation constants (Table 1) to be 2.4x 105 M-1, which is larger than the association constants for the linear spermidine (9 xi 02 M ) and spermine (9.5 x 103 M-1)23). It is also of interest that cyclic spermine is selective for ATP over AMP (ratio association constants is 700), while linear spermine prefers ATP to AMP only by a ratio of 26 to 1 43). The selective complexation of biologically important anions is of particular interest, especially if the ligands are converted into selective anion carriers by attachment of lipophilic hydrocarbon chains. 

Puzin et al.h] reported that the tacticity of PMMA prepared in bulk is influenced (slight increase in syndiotacticity) by very small amounts of titanoecnc diehloride (1 O 3 M). Selective complexation of the propagating radical was postulated. 

Table III. Selected complex formation constants for plutonium (at 25°C and 1=0) (41).

A new class of host molecules for the selective complexation of salts [237], alcohols [238], amines [239], and catecholamines [240] has been designed by combining crown ethers of different sizes with a boronic acid or boronate (Figs. 39 and 40). 

Bidentate binding of two Lewis acidic boron centers to one methoxide anion was first reported in 1967 [241]. Further examples did not appear until 1985 [242]. Today, other bis(boronates) like 152 and 154-158 (Fig. 41) are known that can be applied to the selective complexation of amines and diamines [243-247]. 

Table 17. Bond distances [pm], C-NMR chemical shifts [ppm] and Ai vibration numbers [cm ] of pure Ni(CO)4 and selected complexes ...

Table 2.1 Bond distances (pm) in selected complexes with monodentate ligands.

Selective Complexations of Polar Guests by Hosts Containing Functional Sensors ... 

Each product system consists of a variable number of processes involved in the product life cycle. However, the product under consideration is often related to other processes that may no longer be important for the LCA study. The system boundary serves to the separation of essential and non-essential processes of the product life cycle. Since the choice of system boundaries significantly affects LCA study outcomes and in addition, its intensity and complexity, system boundaries should always be well considered and clearly defined. The choice of system boundaries is carried out with regard to the studied processes, studied environmental impacts and selected complexity of the study. Not-including any life cycle stages, processes or data must be logically reasoned and clearly explained [32]. 

A general strategy developed for the synthesis of supramolecular block copolymers involves the preparation of macromolecular chains end-capped with a 2,2 6/,2//-terpyridine ligand which can be selectively complexed with RUCI3. Under these conditions only the mono-complex between the ter-pyridine group and Ru(III) is formed. Subsequent reaction with another 2,2 6/,2"-terpyridine terminated polymer under reductive conditions for the transformation of Ru(III) to Ru(II) leads to the formation of supramolecular block copolymers. Using this methodology the copolymer with PEO and PS blocks was prepared (Scheme 42) [ 107]. 

The choice of new complexes was guided by some simple considerations. The overall eel efficiency of any compound is the product of the photoluminescence quantum yield and the efficiency of excited state formation. This latter parameter is difficult to evaluate. It may be very small depending on many factors. An irreversible decomposition of the primary redox pair can compete with back electron transfer. This back electron transfer could favor the formation of ground state products even if excited state formation is energy sufficient (13,14,38,39). Taking into account these possibilities we selected complexes which show an intense photoluminescence (0 > 0.01) in order to increase the probability for detection of eel. In addition, the choice of suitable complexes was also based on the expectation that reduction and oxidation would occur in an appropriate potential range. 

Schuster, M. Selective complexing agents for the trace enrichment of platinum metals. Fresenius J. Anal. Chem. 1992, 342, 791-794. 

Solvent polymeric membranes, conventionally prepared from a polymer that is highly plasticized with lipophilic organic esters or ethers, are the scope of the present chapter. Such membranes commonly contain various constituents such as an ionophore (or ion carrier), a highly selective complexing agent, and ionic additives (ion exchangers and lipophilic salts). The variety and chemical versatility of the available membrane components allow one to tune the membrane properties, ensuring the desired analytical characteristics. 

Similar complex data has been reported by Haowen et al. [109] for Ni-Sn-P films, again using citrate as a complexant, and by Aoki and Takano [110] for the influence of citrate concentration on the composition W in Ni-W-P alloys. In a study of the deposition of films containing up to 30 at% Sn, Osaka and coworkers [111] observed simpler behavior, evidently due to the more selective complexation of Ni2+ by citrate as a function of citrate concentration, they reported a rapid decrease in alloy deposition rate, an increase in Sn content in the deposit, and a slow decline in P content of the deposits. 

Electroless Ni-Ge-P was studied as a model system for ternary alloy deposition [112], A chloride-free solution with GeC>2 as a source of Ge, hypophosphite as reducing agent, aspartic acid as a selective complexant for Ni2+ ions, which was operated at 80 °C in the pH range of 5-5.8, was developed for depositing Ni-Ge-P films with a tunable Ge content from 0 to 25+ at%. The use of a complexant such as citric acid, which complexed Ge(IY) ions as well as Ni2+ ions, resulted in a much lower Ge content in the electroless deposit, and a more complicated solution to study for the reasons discussed above. The aspartate-containing electroless solution, with its non-complexing pH buffer (succinic acid), approximated a modular system, and, with the exception of the aspartic acid - Ni2+ complexation reaction, exhibited a minimum level of interactions in solution. 

As the aspartate concentration was increased in solution (Fig. 11(a)), the deposition rate decreased rapidly, while the Ge content of the films underwent a minor increase. This behavior appears to be consistent with selective complexation of Ni2+... 

The most important structural parameters of the transition metal complexes are summarized in Table XXV and Figs. 35-37 display the solid state structures of three selected complexes. 

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