Chelation and other forms of complexation

Sodium sulfadiazine and sulfafurazole diolamine in therapeutic doses (1 mg) added to 5% dextrose and 5% dextrose and saline solution have been found to be compatible, yet when added to commercial polyionic solutions (such as Abbott lonosol B, Baxter electrolyte No.2) both rapidly form heavy precipitates. pH and temperature are two vital parameters, but the pH effect is not simply a solubility-related phenomenon. Polyionic solutions of a lower initial pH (4.4-4.6) cause crystallisation of sulfafurazole at room temperature within 2.5 h, the pH values of the admixtures being 5.65 and 5.75 respectively. Other solutions with slightly higher initial pH levels (6.1-6.6) formed crystals only after preliminary cooling to 20°C at pH values from 4.25 to 4.90. If the temperature remains constant, the intensity of precipitation varies with the composition and initial pH of the solution used as a vehicle. 

Most physicochemically based drug interactions can take place in the body, or outside it, or during concomitant dmg administration, so it is probably not profitable to consider them separately. Some interactions, such as complexation, which are probably more important in vivo than in vitro are discussed in detail below. 

The extensive clinical use of polyionic solutions for intravenous therapy means that dmgs are frequently added to systems of a complex ionic namre. Reduction in the solubility of 

The term chelation (derived from the Greek chele meaning lobster s claw) relates to the 

Tetracyclines have similar chelating groups in their stmcture. Therapeutic chelators are used in syndromes where there is metal ion overload. EDTA (ethylenediaminetetraacetic 

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Based on preliminary results from Helfferich130, further developments by Davankov and co-workers5 131 133 turned the principle of chelation into a powerful chiral chromatographic method by the introduction of chiral-complex-forming synlhetie resins. The technique is based on the reversible chelate complex formation of the chiral selector and the selectand (analyte) molecules with transient metal cations. The technical term is chiral ligand exchange chromatography (CLEC) reliable and complete LC separation of enantiomers of free a-amino acids and other classes of chiral compounds was made as early as 1968 131. 

The speciation and chemical form of Pu in this sediment system has not been determined, but a fraction of the sediment-plutonium inventory may be in a chemical form (i.e., chelated, associated with organic matter, complexed with inorganic substances, or soluble) that is more mobile in the system than the balance of the inventory. While ingestion of sediment appears responsible for the highest levels of Pu (body burden) in fish, this mechanism apparently has not enhanced availability of Pu to biota because concentration factors for biota in WOL were relatively low compared to those observed at other study sites. Concentration factors for biota of WOL were low even though 12% of the plutonium in the water column was a soluble form (Table VI). 

The chelate complex is shown in Figure 9. As the crystal is centrosymmetric, d and 1 forms of optically active Co(en)g are present in the structure in equal amounts. The" atom of cobalt is in an almost regular octahedron composed of nitrogen atoms. Each atom of chelate cycle is located in the tetrahedron two tops of which are occupied by the neighbouring atoms of the ethylenediamine ring and the two others by the hydrogen atoms. 

Co" -DOTATOC shows the best binding affinity of this series, which is even higher than the one of native somatostatin 28. This effect is not yet fully understood. As both Co" and Ga form hexacoordinated complexes with DOTA, the biomolecule bound carboxymethyl arm remains not coordinated to the metal (Heppeler et al. 1999a). It keeps its flexibility and could play the role of a spacer between the biomolecule and the chelator, reducing the influence of the bulky BFC. In addition, Co" also has a different charge compared to the other metals. Y" shows an octacoordinated structure with DOTA, the biomolecule bound carboxymethyl arm is coordinated to the metal as well the chelator is more fixed in its position relative to the biomolecule. 

The rate of autoxidation is thus proportional to the square root of the metal ion concentration. However, this rate does not hold when the concentration of metal initiator is too small to measure. In many food and biological systems, metal catalysts may be coordinated with ligands as complexes or may exist as dimers or higher molecular weight compounds. Other chelating materials may form strong complexes with metals and inactivate their catalytic effects in promoting hydroperoxide decomposition (Chapter 4). 

The chemistry of antioxidant activity of nitrite is complex and not completely understood. Although much of the literature evidence for this activity is based on the notoriously imreliable TBA test (see Chapter 5), there is more specific evidence based on GC volatile analyses indicating significant reduction of hexanal and other decomposition products of polyunsaturated fatty acids. A number of mechanisms have been suggested for the antioxidant activity of nitrite it inhibits heme-catalysed lipid oxidation by forming a complex with the iron porphyrins, stabilizes the polyunsaturated lipids in membranes, chelates catalytic metals, forms inactive complexes with nonheme iron and copper, or low molecular weight iron fractions, produces... 

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