Reduction difference spectra

Another example from the same paper16 involves the cyanocarbon anion, 1,1,2,3,3-pentacyanopropene. One-electron reduction produces the expected dianion radical, the spectrum of which is shown in Figure 2.9. However, further reduction leads to a very different spectrum, which results from loss of CN from position 2, and attachment of a proton (presumably from the solvent A-,A -dimethy 1 lbrmamide) to produce the 1,1,3,3,-tetracyanopropene dianion radical the spectrum of which is also shown in Figure 2.9. 

Despite the reduction in symmetry, no additional bands have ever been unambiguously assigned to internal fullerene active vibrations. For multiple addition adducts, the severe disruption to the cage structure results in a markedly different spectrum. 

Kg. 4.1.9. Difference spectrum of oak (Quercus obtusata) obtained by subtracting the spectrum of MWL from the spectrum of the same MWL after NaBH4 reduction. (Instrument Nicolet 20SX D, 4cm 1 resolution, 32 scans, KBr pellet technique)... 

Protection of the reductase by NADH from inhibition by thiol group reagents suggested that the enzyme formed a stable complex with pyridine nucleotide (353). Such a complex was readily demonstrated by difference spectroscopy. When the enzyme was reduced by NADH or AcPyADH a prominent positive band was observed at 317 nm (Fig. 16) this band was very small (and blue-shifted) when NADPH, a very poor substrate, was the reductant. Furthermore, addition of NAD+ following NADPH resulted in a difference spectrum identical with that produced by NADH. The dashed line in Fig. 15 represents the absorption resulting from NAD" binding. Thus, this band was attributed to a reduced enzyme-NAD complex (350). 

The reduced minus oxidized difference spectrum of Pheo photoaccumulated in PS II, showing large changes in the blue and red and in particular a small bleaching at 545 nm, is typical of Pheo reduction compared to spectra obtained in vitro [109,140]. The EPR spectrum from Pheo is split by when it is present... 

Another method of analysis makes use of a subtraction procedure and has been applied to investigate the oxidation state of a series of Ce-Zr mixed oxides during a temperature programmed process [195]. A difference spectrum between the sample at a defined state and the calcined, fully oxidized material displays a positive peak at the position of feature Bo, characteristic of Ce, and a negative peak at the position of feature C, characteristic of Ce. The overall peak-to-peak amplitude is then proportional to the average reduction degree of Ce in the sample. 

The catalytic activity toward hydrogenation reactions has been indeed observed in such bimetallic colloidal systems. The SERS spectrum of p-nitrobenzoate (PNBA) adsorbed on colloidal silver and the SERS spectra observed on Ag/Pd nanoparticles, immediately after the addition of PNBA and after 1 week, are shown in Fig. 20.7 A, B, and C, respectively. In the bimetallic colloid, instead of the SERS spectrum of PNBA (spectrum A), a different spectrum is obtained (spectrum B) that slowly evolves toward a different spectral feature, which becomes predominant after a week (spectrum C). This modification may be related to the initial formation of p-aminobenzoate as a result of the catalytic reduction of the nitro group, followed by slow oxidation to azodibenzoate by atmospheric oxygen (see Fig. 20.8). 

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