Complex Formation between Metallic

The most direct evidence for surface precursor complex formation prior to electron transfer comes from a study of photoreduc-tive dissolution of iron oxide particles by citrate (37). Citrate adsorbs to iron oxide surface sites under dark conditions, but reduces surface sites at an appreciable rate only under illumination. Thus, citrate surface coverage can be measured in the dark, then correlated with rates of reductive dissolution under illumination. Results show that initial dissolution rates are directly related to the amount of surface bound citrate (37). Adsorption of calcium and phosphate has been found to inhibit reductive dissolution of manganese oxide by hydroquinone (33). The most likely explanation is that adsorbed calcium or phosphate molecules block inner-sphere complex formation between metal oxide surface sites and hydroquinone. 

Complex Formation between Metallic Cations and Proteins, Peptides, and Amino Acids... 

Ion pairing is due to electrostatic forces between ions of opposite charges in a medium of moderate to low relative permittivities. It should be distinguished from complex formation between metal cations and anionic ligands, in which coordinative bonds (donation of an electron pair) takes place. One distingnishing feature is that, contrary to complex formation, the association is nondirectional in space. The association of a cation and an anion to form an ion pair can, however, be represented as an equilibrium reaction by analogy to complex formation with an equilibrium constant A)ass [3,5]. If a is the fraction of the electrolyte that is dissociating into ions and therefore (1 - a) is the fraction that is associated, then... 

Gurd, F. R. N., and Wilcox, P. E. (1956). Complex formation between metallic cations and proteins, peptides, and amino acids. Adv. Protein Chem. 11,311-418. 

Gurd, F. R. N. Wilcox, P. E. Complex Formation Between Metallic Cations and Proteins, Peptides and Amino Acids Anson, M. C. Bailey, K. Edsall, J. T., Eds. Advances in Protein Chemistry No. 11 Academic New York, 1956 pp. 312-62. 

Kojima Y., Isobe T., Senna M. Shinohara T., Ono S., Sumiyama K., Suzuki K. Mechanism of complex formation between metallic Al and titania hydrogel via a mechanical route. J. Mater. Res. 1996 11 1305-9. 

Complex formation between metals and l,2-dithiole-3-thiones has long been known. The mercury(II) complex is often used for purification of 1,2-dithiole-3-thiones.1... 

Complex formation between metal ions and ligands in aqueous solution has always been of great interest. This interest is enhanced by the role of metal ions in biology. The first use of the concept of chemical hardness was to explain complex ion formation in water. However, it turns out that this is not so easy as one might expect. 

A cross-reactive sensor array based on luminescence changes has been reported by Severin and coworkers [74]. In this case no synthetic modifications were operated, but the sensing elements were created by mixing some metal complexes with fluorescent dyes. The complex formation between metal ions, such as Rh, Ru or Pd, quenches the dye fluorescence the peptide competes with the dye for metal ion complexation, removing it from the complex. The fluorescence turn on is the signal of the peptide interaction. The activation of fluorescence is also an indication of the equilibrium reported in Fig. 24 and it is the basis of the peptides discrimination. The sensor array was able to differentiate between several dipeptides at 20-50 X 10 M concentration higher oligopeptides, such as bradykinin and kallidin were also discriminated and the system was also able to differentiate between two dipeptides, carnosine and homocamosine, in a more complex environment such as human serum. 

In aqueous solutions at pH 7, there is little evidence of complex formation between [MesSnflV)] and Gly. Potentiometric determination of the formation constants for L-Cys, DL-Ala, and L-His with the same cation indicates that L-Cys binds more strongly than other two amino acids (pKi ca. 10,6, or 5, respectively). Equilibrium and spectroscopic studies on L-Cys and its derivatives (S-methyl-cystein (S-Me-Cys), N-Ac-Cys) and the [Et2Sn(IV)] system showed that these ligands coordinate the metal ion via carboxylic O and the thiolic 5 donor atoms in acidic media. In the case of S-Me-Cys, the formation of a protonated complex MLH was also detected, due to the stabilizing effect of additional thioether coordination. ... 

The donor properties of N3P3CI6 appear to be too weak to allow complex formation with metal halides, but it has been reported that complex formation between N3P3Cl5 NHBu" and Cu" or Co" chlorides in acetonitrile solutions can be detected by u.v. spectroscopy. Attempts to isolate the complexes were unsuccessful. 

Genge, J. A. R. Salmon, J. E. (1959). Aluminium phosphates. Part III. Complex formation between tervalent metals and orthophosphoric acid. Journal of the Chemical Society, 1459-63. 

Complex formation between a metal ion and a macrocyclic ligand involves interaction between the ion, freed of its solvation shell, and dipoles inside the ligand cavity. The standard Gibbs energy for the formation of the complex, AGjv, is given by the difference between the standard Gibbs... 

The formation of a coordinate bond is the result of the donation and acceptance of a pair of electrons. This in itself suggests that if a specific electron donor interacts with a series of metal ions (electron acceptors) there will be some variation in the stability of the coordinate bonds depending on the acidity of the metal ion. Conversely, if a specific metal ion is considered, there will be a difference in stability of the complexes formed with a series of electron pair donors (ligands). In fact, there are several factors that affect the stability of complexes formed between metal ions and ligands, and some of them will now be described. 

Romeo et al. (1978) clearly indicate that complexes of divalent metal ions with 1,2-diaminoethane are more stable than those with 1,3-diaminopro-pane. Moreover, in a thorough discussion of the relations between the chelate effect and the ring size, Anderegg (1980) has listed thermodynamic data of complex formation between divalent metal ions and ligand [45], showing that almost invariably the stability of chelate rings decreases with increasing n in the order 5 > 6 > 7. 

Metal ion catalyzed autoxidation reactions of glutathione were found to be very similar to that of cysteine (76,77). In a systematic study, catalytic activity was found with Cu(II), Fe(II) and to a much lesser extent with Cu(I) and Ni(I). The reaction produces hydrogen peroxide, the amount of which strongly depends on the presence of various chelating molecules. It was noted that the catalysis requires some sort of complex formation between the catalyst and substrate. The formation of a radical intermediate was not ruled out, but a radical initiated chain mechanism was not necessary for the interpretation of the results (76). 

Having commented briefly on the first two parts of my new theory (the self-ionisation and the initiation by AlX+2), it is appropriate to consider the complex formation between monomer and metal halide, expressed by Equation (ii), which we have mentioned in the previous section. This complex formation actually provides an easy and plausible explanation for some of the hitherto rather obscure phenomenological differences which are observable when monomer and aluminium halide solutions are brought together in different ways we can distinguish three such techniques which give very different results. 

These experiments provide the most direct evidence so far for the formation of complexes between A1X3 and isobutylene. The formation of such complexes was of course to be expected on the basis of the complex formation between aluminium halides and other olefins [29-33] and between titanium tetrachloride and isobutylene [34], and numerous other examples of complexes formed by an olefin and a metal halide it can be objected... 

Rates of reductive dissolution of transition metal oxide/hydroxide minerals are controlled by rates of surface chemical reactions under most conditions of environmental and geochemical interest. This paper examines the mechanisms of reductive dissolution through a discussion of relevant elementary reaction processes. Reductive dissolution occurs via (i) surface precursor complex formation between reductant molecules and oxide surface sites, (ii) electron transfer within this surface complex, and (iii) breakdown of the successor complex and release of dissolved metal ions. Surface speciation is an important determinant of rates of individual surface chemical reactions and overall rates of reductive dissolution. 

These observations have been interpreted in terms of complex formation between polymer and salt in the solid state. The change in Tg was shown to be an unusual function of metal ion concentration (i.e. Tg increases with increasing metal concentration up to... 

Separation is based on the reversible chelate-complex formation between the chiral selector covalently bonded to the chromatographic support, and the chiral solute with transition metal cations. Chelation properties of both the chiral selector and the chiral solute are required. Compounds therefore need to have two polar functional groups in a favorable arrangement to each other, like a )3-amino acids, amino alcohols and a-hydroxy acids, which can form rings membered with central chelating metal ions, like Cu(II), Zn(II), Cyclic... 

Fig. 5.8 Complex formation between PEO and various metal salts + complex formed — no evidence of complex. From Armand and Gauthier (1989).

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