Transition metal ions detection

Bargossi, C. Fiorini. M.C. Montalti. M. Prodi. L. Zaccheroni, N. Recent developments in transition metal ion detection by luminescent chemosensors. Coord. Chem. Rev. 2000. 208. 17-32. 

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

Unpaired electrons and magnetism - One of the consequences of the open (incompletely filled) d" configuration of transition-metal ions may be the presence of one or more unpaired electrons. Such compounds could be described as radicals, and they are detected by techniques such as electron spin resonance spectroscopy. 

Although atherosclerosis and rheumatoid arthritis (RA) are distinct disease states, both disorders are chronic inflammatory conditions and may have common mechanisms of disease perpetuation. At sites of inflammation, such as the arterial intima undergoing atherogen-esis or the rheumatoid joint, oxygen radicals, in the presence of transition-metal ions, may initiate the peroxidation of low-density lipoprotein (LDL) to produce oxidatively modified LDL (ox-LDL). Ox-LDL has several pro-inflammatory properties and may contribute to the formation of arterial lesions (Steinberg et /., 1989). Increased levels of lipid peroxidation products have been detected in inflammatory synovial fluid (Rowley et /., 1984 Winyard et al., 1987a Merry et al., 1991 Selley et al., 1992 detailed below), but the potential pro-inflammatory role of ox-LDL in the rheumatoid joint has not been considered. We hypothesize that the oxidation of LDL within the inflamed rheumatoid joint plays a pro-inflammatory role just as ox-LDL has the identical capacity within the arterial intima in atherosclerosis. 

Another type of spin traps, which have been recommended for the detection of superoxide, are the derivatives of hydroxylamine. In 1982, Rosen et al. [25] showed that superoxide is able to oxidize the hydroxylamine derivative 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazoli-dine (OXANOH) to corresponding free radical 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidinoxyl (OXANO). Although this radical is very stable and easily identified by its ESR spectrum, it is also easily reduced by ascorbic acid and other reductants. Furthermore, OXANOH and other hydroxylamines are oxidized by dioxygen in the presence of transition metal ions to form superoxide, and therefore, superoxide detection must be carried out in the presence of chelators. 

For cations, various examples have been realized mostly concerned with the detection of the already mentioned heavy and transition metal ions. One of the first examples published involves the Cu2+-induced hydrolysis of a rhodamine B hydra-zide 44 to rhodamine B 45, which can be employed in water to detect Cu2+ down to 10 nM with a linear response up to 2 pM (Fig. 16) [135]. 

Epr is most effective for detecting free radicals that may occur as intermediates in oxidation and reduction reactions involving transition metal ions. Since these transients are invariably quite labile, epr is combined with continuous flow, (more conveniently) stopped-flow, flash photolysis, and pulse radiolysis. 

Many inorganic ions are not readily detected because they have orbitally degenerate ground states. Spin relaxation in these states is so rapid that the EPR spectrum cannot be observed at typical temperatures where electrochemical experiments are carried out. Temperatures of 4 K or lower are required to observe these ions. Table 29.1 lists transition metal ions that occur in nondegenerate ground states due to crystal field splittings and as such are amenable to observation. 

Inorganic radicals and transition metal ions typically exhibit broad lines, and hence diminished sensitivity in the EPR method. Consequently, when dealing with small quantities of paramagnetic material, it is often more difficult to detect inorganic species. Several important studies have been reported, however. Kastening s study [64] of the reduction of S02 in dimethylformamide showed that an equilibrium was established between the SO radical ion and the dimer S20, ... 

Cells contain low concentrations of transition-metal ions, notably iron and copper. For example, the DNA scaffolding protein is reported to contain copper (Lewis and Laemmli 1982). However, no intracellular free copper is detectable (Rae et al. 1999). The intracellular labile iron pool is reported to be around mi-... 

With d(TpA) and d(GpC) the same products as observed to be formed by ionizing radiation were detected upon autoxidation induced by ascorbate plus phosphate buffer (low amounts of transition metal ions are omnipresent Ara-kali et al. 1988). 

This effect is essentially similar to the spin-polarization effects which are responsible for the small s-character nearly always detected for radicals and transition metal ions having electrons primarily in p or d atomic levels. It has been discussed by McConnell et al. (1960) who explain why the spin density on the proton is negative when the major... 

Certain inorganic substances also contribute to COD. These include oxidiz-able anions such as S2-, SO,2. NO . P033. AsO . CIO-, C102, C103, Br03-, I03-, and Se032- and such metal ions as Fe2+, Cu1+, Co2+, Sn2+, Mn2+, Hg1+, and Cr3- (mostly transition metal ions in their lower oxidation states). If any of these ions is present in detectable concentration, its COD can be calculated from the balanced equation ... 

Stadler N, Lindner RA, Davies MJ. Direct detection and quantification of transition metal ions in human atherosclerotic plaques evidence for the presence of elevated levels of iron and copper. Arterioscler Thromb Vase Biol 2004 24(5) 949-954. 

Chapter 10 describes how spectral measurements of sunlight reflected from surfaces of planets, when correlated with experimental visible to near-infrared spectra of rock-forming minerals, have been used to detect transition metal ions, to identify constituent minerals, and to determine modal mineralogies of regoliths on terrestrial planets. 

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