Coordination with Metal Ion

It has not been determined which hydroxyl group contains the more acidic hydrogen atom corresponding to p Dyes of this type would behave as indicators and exhibit large color shifts with the pH range normally encountered in textile processing. Hence they are always stabUized by coordination with metal ions. 

Since enzymes are composed of amino acids they may be assumed to act as either acid or base catalysts through groups such as -COOH, -NH2 and -CONH2. The scope of activity, however, is enhanced considerably through coordination with metallic ions found in the body such as Mg, Fe, Fe ", Ca and Zn +. Enzymes have been classified into six functional types according to the reactions they catalyse ... 

In addition to line broadening due to accelerated relaxation, paramagnetic salts and chelates give rise to isotropic shifts when added to samples containing molecules with groups susceptible to coordination with metal ions, e.g. —OH, —NH2, — SH, — COOH, -C = 0. The isotropic shift A of a nucleus i in a sample S is the difference between chemical shifts measured before and after addition of the paramagnetic shift reagent SR [103] ... 

Within their scaffolds, POPAM dendrimers also possess amine groups which can undergo protonation or coordination with metal ions. The spectroscopic and photochemical properties of the first to the fourth POPAM generation with peripheral fluorescing naphthylsulfonamide groups were compared with those of reference compounds A (N-methylnaphthalenesulfonamide) and B (N-(3-di-methylaminopropyl)-2-naphthalene-l-sulfonamide) [22] (Fig. 5.19). 

This property of organic ligands (peptides, in particular) and their oligomers, coordinated with metal ions, opens up good possibilities for the development of highly active catalytic systems. Hence, such systems can be well soluble in water and operate at biologically suitable pH. 

Chelating agents can coordinate with metal ions at a minimum of two sites. Typically this bidentate coordination solubilizes or otherwise inactivates these metal ions. The effect is to counter any deleterious actions these metals might have on the system in which the chelates are used. The chelating agents form ring structures that incorporate the metal ion within the molecule250. 

Reactions of Schiff bases coordinated with metal ions have been examined from the standpoint of stability and reactivity. Eichhorn (23, 25) examined the complex formed between bis-(thiaphenal)ethylene-diimine and copper(II). It was found that, when complexed to copper(II), the ligand becomes unstable and hydrolysis occurs this leads to the aldehyde and the copper-ethylenediamine complex. 

Since the oxygen atoms as well as the alpha carbon on the /3-keto-enolate ring can function as bases to coordinate with metal ions (5, or to hydrogen bonding solvents (14)f it should be recognized that /3-keto-enolate complexes may have a stereochemistry quite different from that expected—based on the stoichiometry of the complex. However, by a suitable choice of a /3-ketoenol ligand, such as 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane), H-DPM, intermolecular effects can be reduced or eliminated with the result that the metal complex formed has the stereochemistry expected for the monomeric acetylacetonate complex of that metal ion. For example, nickel(II) acetylacetonate is trimeric as a solid and in solution (11), but the dipivaloylmethane complex is a monomeric, undoubtedly planar species, in solution, as well as in the solid state (37), This stereochemistry occurs with the monomeric acetylacetonate in dilute solution or in the vapor phase, as indicated by absorption spectra and electron diffraction (SO). 

Consequently, synthetic hydrophilic polymers such as polyvinyl alcohol, and polyvinylpyrrolidone, and polyvinylmethyl ester are interesting for two reasons i.e. (1) they coordinate with metal ions thereby decreasing the rate of metal reduction, and (2) they prevent aggregation of colloidal particles. The simplicity of preparation of colloidal metal dispersions, the feasibility of controlling particle sizes, and some other advantages place these polymers as promising catalytic systems [32,53, S3 a]. 

Metal ion can form complex through coordination with unsaturated compounds such as olefin. Through coordination with metal ion, two olefins can be positioned in close proximity, and olefin photochemistry may be caused upon irradiation at longer wavelengths by exciting the charge-transfer band of the resultant complex. Evers and Mackor investigated the intramolecular [2-h2] photocycloaddition of diene 148, which is photochemi-cally catalyzed by copper(l) trifluoromethanesulphonate. In the presence of the copper... 

Semiconducting nanorods and nanowires were synthesized by y-irradiation at room temperature and the atmospheric pressure. The experiment was carried out in ethylenediamine and pyridine as solvents. Ethylenediamine (en) and pyridine (py) molecules were coordinated with metal ions and had an effect on the shape like nanorods and nanowires (Jo et al. 2006). Semiconducting nanorod and pearl necklace-like nanowire of CdS and CdSe were successfully synthesized by irradiation with a dose of 90 kGy at room temperature and the atmospheric pressure. When nanorods and nanowires were prepared in en and py, the solvent molecules controlled their morphology. From XRD data, the synthesized CdS and CdSe could be observed on the information of crystallinity of them. In nanorod CdS and CdSe, the intensity of the (0 0 2) diffraction peak was extraordinarily strong. This result indicates that the CdS obtained in py have a preferential [0 0 1] orientation. TEM images displayed rod and pearl necklace like morphology with diameters of several nanometers and lengths of upto several microns. For the shape control, en and py were successfully used to replace the surfactant molecules on the surface of nanoparticles. 

In such MCMs the carboxylic group can take the part of mono-, bi-, tri- and even tetradentate ligand during coordination with metal ions to form 34-40. 

Vinyl ethers of ethanolamine 66 may coordinate with metal ions via both the ester oxygen atom and the amine group to form two five-membered rings. 

Infrared studies on DjO solutions of carbamyl phosphate led to the same conclusioa Table 19.7 shows infrared bands of acetyl phosphate and carbamyl phosphate in the presence and absence of Mg ions. The carbonyl group in acetyl phosphate dianion and carbamyl phosphate dianion absorbs at 1708 and 1666 cm , respectively. Table 19.7 shows that the positions of these bands are increased only slightly in the presence of Mg ions. These very small increases contrast sharply with large decreases in the infrared stretching frequencies of the carbonyl group when it coordinates with metallic ions. 

In order to enhance the efficiency of biotransformations, chemical modulation can be used, on a case by case basis, to tune the enzyme activity, selectivity, and stability under specific reaction conditions. General methods could be used to improve reaction efficiency, for example, the selection of solvent systems, buffer salts, certain metal ions, and pH adjustments have been reported to work well. The structures and properties of enzymes can be readily regulated in the presence of small-molecule modulators. For example, it is well known that enzymes are able to coordinate with metal ions, which leads to some changes in their properties. In this context, the design and application of chemical modulators in enzymatic reactions is a typical example of chemical biotechnology, as detailed in Chapter 2. 

The NMR has proved to be a very useful technique to achieve a better understanding of the hydrolysis and condensation process and to elucidate their molecular structures at room temperature. The resonance peaks indicate that the molecules are slightly fluxional and remain mononuclear in solution. The up field chemical shift was observed for nuclei due to their coordination with metal ion through tt bonding. 

The formation of complexes Ni(L )2 with L 18C6 or R NBr was also proved by spectrophotometry under analysis of UV spectra of absorption of Ni(L )2 and R NBr (18C6) mixtures solutions. At that coordinate with metal ion with preservation of ligand L in internal coordination sphere of complex [90, 92]. Under formation of complexes of Ni(L )2 with U in spite of axial coordination by the fifth coordination place of nickel (II) ion the outer sphere coordination of (H-bonding) with acetylacetonate-ion is also possible. 

Capping agents that strongly coordinate with metal ions significantly promote the oxidative etching of zero-valent metal atoms. Equation 6.3 shows an example of the oxidative etching of Pd. 

Porphyrins are well known for their ligation with various metal centers to form metalloporphyrins. Coordination of the metal ions typically has a dramatic effect on the It delocalization in the molecule. Inherited changes are very obvious in spectroscopic analysis and in their properties. Especially, the electronic spectra of metalloporphyrins are dependent on the identity of the metal ion, axial ligation, oxidation level, and spin state. Typically, metal coordination reduces the number of observed Q bands of porphyrin, indicating the acquisition of higher symmetry of the chromophore relative to the free base. X-ray structural determinations reveal that the bond length of porphyrin changes upon coordination with metal ions [39]. 

The water molecule can coordinate with metal ions in two different forms, viz, OH2 and OH. The substitution reaction, in which the water molecule replaces any other l%and, is called hydrolysis. The replacement of a ligand by a water molecule as OH yields a hydroxo complex, and the... 

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