Cobalt electron absorption spectroscopy

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

Framework charge and, hence, cation exchange capacity and acidity in CoAPO molecular sieves are a function of the concentration of incorporated cobalt(II), which can be monitored quantitatively by means of electron absorption spectroscopy. The maximum framework cobalt acceptance as well as the stability depends on the structure type and decreases in the same order CoAPO -5 > CoAPO -11 > CoAPO —16 > CoAPO -34. Less stable structure types such as CoAPO -16 and —34 suffer from a loss in crystallinity and framework cobalt during calcination and reduction experiments, whereas in stable structures framework cobalt can reversibly undergo redox reactions Co(II) <—> Co(III). In conclusion, CoAPOs have potential for both redox catalysis and acidic catalysis. In the latter case, however, fluctuating acidic properties due to changes in the oxidation state can be a serious restriction in many operations. 

The cobalt(II) corrole anion prepared as above was characterized primarily by electron spin resonance (esr) and absorption spectroscopy. When prepared via sodium film reduction, the cobalt(II) corrole oxidizes rapidly to the corresponding Co(III) corrole on exposure to air. When prepared by the other methods, it is moderately stable in air in the presence of a reducing agent. Attempts to prepare the neutral form of the initial Co(II) corrole anion, by protonation with perchloric acid, resulted in formal oxidation to the Co(III) derivative. Interestingly, further protonation of the Co(III) corrole with perchloric acid led to what appeared to be a protonated Co(III) corrole. Certainly, the absorption spectrum of this species is similar to that of the corresponding neutral nickel(II) corrole complex. However, the exact nature of this protonated material has not been fully elucidated. 

Even more spectacular results in terms of the increasing importance of nanocatalysis for bulk industrial processes have recently been reported by Kuipers and de Jong [32, 33]. By dispersing metallic cobalt nanoparticles of specific sizes on inert carbon nanofibers the authors were able to prepare a new nano-type Fischer-Tropsch catalyst. A combination of X-ray absorption spectroscopy, electron microscopy, and other methods has revealed that zerovalent cobalt particles are the true active centers which convert CO and H2 into hydrocarbons and water. Further, a profound size effect on activity, selectivity, and durability was observed. Via careful pressure-size correlations, Kuipers and de Jong have found that or cobalt particles of 6 or 8nm are the optimum size for Fischer-Tropsch catalysis. The Fischer-Tropsch process (invented in 1925 at the Kaiser-Wilhelm-Institute for... 

Table 1.38 summarises the main features of Mossbauer spectroscopy. The great advantage of Mossbauer spectroscopy for in-polymer additive analysis is that it provides in situ information. An economic advantage is that the technique is relatively inexpensive in comparison to electron microscopy or XPS. The technique is limited to those isotopes that exhibit the Mossbauer effect. The detection limit is 10 atoms of the nuclear isotope studied. Through the Mossbauer effect in iron, it is possible to obtain information on the state of cobalt. Whereas in Mossbauer absorption spectroscopy (MAS) a single-line source is moved and... 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

The reactive intermediates in the charge-transfer photoreactions of carbonyl metallate salts are examined by time-resolved spectroscopy applying a 10-ns pulse of a Q-switched Nd YAG laser at 532 nm [118]. Thus, the charge-transfer excitation of various manganate and cobaltate salts results in the formation of intense transient absorption centered at 800 nm and 780 nm, respectively, which are readily assigned to the 17-electron radicals Mn(CO)5 and Co(CO)4 , respectively (see Figure 12) [168- 170]. 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

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