Optical spectroscopy, metal ions

Glucose isomerase catalyzes the conversion of D-glucose to D-fructose and has also been used extensively on an industrial scale.1184 Some, but not all, enzymes of this family require Co specifically, while others can function with other divalent ions. Environmental and health issues limit the concentrations of Co in culture media during D-fructose production and other metal ions are being sought as substitutes. Although the active site structure remains unknown, EXAFS, optical and EPR spectroscopy has suggest a low-spin divalent Co ion, bound by N and O-donors only (no S-donors). 

The potential applications of NIR OFCD determination of metal ions are numerous. The detection of metal contaminants can be accomplished in real-time by using a portable fiber optical metal sensor (OFMD). Metal probe applications developed in the laboratory can be directly transferred to portable environmental applications with minimal effort. The response time of the NIR probe is comparable to its visible counterparts and is much faster than the traditional methods of metal analysis such as atomic absorption spectroscopy, polarography, and ion chromatography. With the use of OFMD results can be monitored on-site resulting in a significant reduction in labor cost and analysis time. 

Amine-terminated, full-generation PAMAM and PPI dendrimers, as well as carboxylate-terminated half-generation PAMAM dendrimers, can directly bind metal ions to their surfaces via coordination to the amine or acid functionality. A partial hst of metal ions that have been bound to these dendrimers in this way includes Na+, K+, Cs+, Rb+, Fe +, Fe +, Gd +, Cu+, Cu +, Ag+, Mn +, Pd, Zn, Co, Rh+,Ru +,andPt + [18,19,27,36,54,82-96]. Tuxro et al.have also shown that the metal ion complexes, such as tris(2,2 -bipyridine)ruthenium (Rulbpylj), can be attached to PAMAM dendrimer surfaces by electrostatic attraction [97]. A wide variety of other famihes of dendrimers have also been prepared that bind metal ions to their periphery. These have recently been reviewed [3]. Such surface-bound metal ions can be used to probe dendrimer structure using optical spectroscopy, mass spectrometry, and electron paramagnetic resonance (EPR) [86-88,90,97-99]. 

The heme moiety provides de novo designed heme proteins with an intrinsic and spectroscopically rich probe. The interaction of the amide bonds of the peptide or protein with the heme macrocycle provides for an induced circular dichroism spectrum indicative of protein-cofactor interactions. The strong optical properties of the heme macrocycle also make it suitable for resonance Raman spectroscopy. Aside from the heme macrocycle, the encapsulated metal ion itself provides a spectroscopic probe into its electronic structure via EPR spectroscopy and electrochemistry. These spectroscopic and electrochemical tools provide a strong quantitative base for the detailed evaluation of the relative successes of de novo heme proteins. 

After reviewing the properties and structure of ionic liquids, leading specialists explore the role of these materials in optical, electrochemical, and biochemical sensor technology. The book then examines ionic liquids in gas, liquid, and countercurrent chromatography, along with their use as electrolyte additives in capillary electrophoresis. It also discusses gas solubilities and measurement techniques, liquid-liquid extraction, and the separation of metal ions. The final chapters cover molecular, Raman, nuclear magnetic resonance, and mass spectroscopies. 

The work has largely focused on the coordination chemistry of transition metal ions (i.e., on the description of the nature and symmetry of their environments) (Section 2.1), in line with other spectroscopies, mainly optical (UV-vis), magnetic (EPR and NMR), which take advantage of partly filled d orbitals, and structural (EXAFS) (Sojka and Che, 2009). It has even become possible with PL via well-resolved fine structures to determine the extent of distortion of the environment of tetrahedral species (e.g., vanadium species in zeolites (Section 2.1.2)). It is likely that such information combined with that derived from other spectroscopies, vibrational on one hand, such as IR and Raman, and electronic on the other hand, such as EPR, will be applied by theoreticians to further improve the existing models and our understanding of the nature and role of surface species involved in catalytic processes. 

Bruckner (2001) combined UV-vis with EPR spectroscopy, using online gas chromatography for product analysis. For many transition metal ions, EPR and optical spectra are complementary, in that some states are detectable or distinguishable with only one of the methods. The UV-vis facility was added to a previously described flow reactor system for EPR spectroscopy (Bruckner et al., 1996). A fiber optical probe (Avantes, AVS-PC-2000 plug-in spectrometer) was inserted directly into the reactor via a Teflon -sealed feedthrough and placed in the catalyst bed. UV-vis spectra were reported for temperatures up to 810 K. The design was later expanded to include a third method, Raman spectroscopy (Bruckner, 2005 Bruckner and Kondratenko, 2006). A hole in the... 

The analyst uses ICP-OES (inductively coupled plasma, optical emission spectroscopy) to measure twenty different metal ions in solution. To fully calibrate the instrument requires the preparation and measurement of 100 individual calibration standards (five point calibration per element). It would be impracticable for an analyst to calibrate the instrument daily. The instrument is calibrated at regular intervals (say fortnightly) by the analyst. In the intervening time, the calibration for each metal ion is checked by the use of a set of drift correction standard solutions. Minor corrections can then be made to the calibration to allow for day-to-day drift. 

It is clear from Table III that all transition metal ions other than Cu + have a well-defined six-fold coordination, and on the basis of these results and those from NMR, QENS, optical spectroscopy, and kinetic studies with isotopically enriched species, it can be concluded that they form stable hydration complexes. 

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