Optical assaying metal ions

An example of a CILA using optical fibers has been described by Wang et al. [114] for the analysis of 6-mercaptopurine (6-MP). The template, 6-MP, was oxidized to a strong fluorescent compound by H202 in alkaline solution. Upon optimization of the H202 and NaOH concentrations and of the assay temperature, the sensor showed a linear response in the 1.0 x 10 s to 6.0 x 10 6 g mL-1 range with a detection limit of 3.0 x 10-9 g mL-1. Cross reactivity to metal ions, amino acids, and carbohydrates was tested and the sensor was applied to the analysis of 6-MP in spiked serum. 

Some of the most definitive studies of Mg(II)-activated enzymes have been performed by mangetic resonance (NMR, ESR) methods with the Mn(ll)-substituted species. An integrated picture of the role of the metal ion in catalysis in almost all cases also includes data from kinetics (steady state and pre-steady state), equilibrium binding, and optical spectroscopic methods. As stated above, there are but a few examples of true Mn-containing enzymes, especially in mammalian sytems. Table 1 provides a non-exhaustive list of examples of both Mn-specific and Mn/Mg-activated enzymes. Within the latter category are enzymes that show a preference for but not absolute specificity for one ion or the other. The distinction between these categories is not simple, often being dependent upon the source or form of the enzyme and various parameters as the type of assay used, temperature, pH, and others. 

A series of dihydroxamic acid chelators have been designed as hydrophobic carriers of vanadyl. In an assay of lipogenic stimulation in rat adipocytes, RL-252 was maximally effective at molar ratios of 10 1 vanadyl sulfate chelator, suggesting a shuttle mechanism of action. These compounds were electrically neutral, lipid-soluble, and optically chiral they released the bound metal ion when treated with aqueous glutathione solutions. 

Optical Sensing Assays of Metal Ions Using Nanosensors... 

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