Spectra display

Figure C 1.5.7. Surface-eiilianced Raman spectra of a single rhodamine 6G particle on silver recorded at 1 s intervals. Over 300 spectra were recorded from this particle before tlie signals disappeared. The nine spectra displayed here were chosen to highlight several as yet unexplained sudden changes in botli frequency and intensity. Reprinted witli pennission from Nie and Emory [ ]. Copyright 1997 American Association for tlie Advancement of Science.

Table 29 presents IR absorption spectra of the above compounds. All spectra display bimodal absorption in the high frequency range, which is attributed to Nb-0 vibrations. In addition, the Nb-F part of the spectra seems to be different from the typical spectra observed for isolated complex ions. Such differences in the structure of the spectra can be related to vibrations of both the bridge and the terminal ligands. 

In practically all cases, Raman spectra display bands at 699 and 280 cm 1. These bands correspond to v, and v5 of the TaF6 complex ion, respectively. Decrease in the concentration of both HF and tantalum leads to a decrease in the intensity of the band at 699 cm" and to an increase in the intensity of the band at 645 cm 1. A further decrease in HF or/and tantalum concentrations initiates the appearance of a band at 674 cm 1. These changes in the Raman spectra attest to the fact that with the decrease in HF or/and tantalum concentrations, TaF6 is replaced by TaF72 complex ion. Fig. 49 shows typical changes in Raman spectra versus HF concentration. 

In this section, the characteristics of the spectra displayed by the different types of iron—sulfur centers are presented, with special emphasis on how they depend on the geometrical and electronic structure of the centers. The electronic structure is only briefly recalled here, however, and interested readers are referred to the excellent standard texts published on this topic (3, 4). Likewise, the relaxation properties of the centers are described, but the nature of the underlying spin-lattice relaxation processes is not analyzed in detail. However, a short outline of these processes is given in the Appendix. The aim of this introductory section is therefore mainly to describe the tools used in the practical applications presented in Sections III and IV. It ends in a discussion about some of the issues that may arise when EPR spectroscopy is used to identify iron-sulfur centers. 

Fig. 6. Representative EPR spectra displayed by trinuclear and tetranucleEir iron-sulfur centers, (a) and (b) [3Fe-4S] + center in the NarH subunit of Escherichia coli nitrate reductase and the Ni-Fe hydrogenase fromD. gigas, respectively, (c) [4Fe-4S] + center in D. desulfuricans Norway ferredoxin I. (d) [4Fe-4S] center in Thiobacillus ferrooxidans ferredoxin. Experimental conditions temperature, 15 K microwave frequency, 9.330 GHz microwave power, (a) 100 mW, (b) 0.04 mW, (c) smd (d) 0.5 mW modulation amplitude (a), (c), (d) 0.5 mT, (b) 0.1 mT.

The heterogeneous character of the EPR spectra given by some HIPIP is probably due to the heterogeneous location of the mixed-valence pair in the [4Fe-4S] centers, which was established in detailed NMR studies (121, 122). Since a heterogeneous location of the mixed-valence pair was also observed in the case of the [4Fe-4S] centers of Chromatium vinosum ferredoxin (123), the same phenomenon may account for the complex EPR spectra displayed by these centers in some proteins (124-126). 

Sine-beU An apodization function employed for enhancing resolution in 2D spectra displayed in the absolute-value mode. It has the shape of the first halfcycle of a sine function. 

Makharia et al., 2005]. These spectra display a major loop in the Z" versus Z plot that cuts the Z axis at some frequency in the range 0.1-1 Hz, followed by an inductive loop that cuts the Z axis again at a much lower frequency. This frequency response of the interfacial faradaic process likely reflects variations of ORR current in response to a cychc potential perturbation, originating from two effects of the potential on ORR rate, which are well resolved by their different response times. A relevant expression describing this behavior is likely of the form... 

Upon displacement of the NBD ligand with parahydrogen according to Scheme 12.3, the 1H-PHIP-NMR spectra displayed in Figure 12.12 were observed, whereby the details of their parameters depended on the type and polarity of the solvent. 

Figure 1.15 Diffuse reflectance UV-Vis spectra from a series of chromia/alumina catalysts after various treatments [115], All these spectra display a shoulder at about 16,700 cm-1 corresponding to the first d-d transition of Cr3+, but the main feature seen in the hydrated and calcined samples at about 26,000 cm-1 due to a Cr6+ charge transition is absent in the data for the reduced sample. This points to a loss of the catalytically active Cr6+ phase upon reduction. (Reproduced with permission from Elsevier.)...

At low extraction voltages, the in-source CID process is greatly inhibited and the spectra display intense signals for the protonated molecular ions. By raising the extraction voltage, in-source CID spectra were obtained. Neutral losses of the carboxylated ethoxy chain and... 

Fig. 5.3 Proton one-dimensional spectra displaying the region of amide resonances of 0.5 mM Ala31, Pro32-NPY recorded in 300 mM SDS (left) or 300 mM DPC (right) at various values of the pH.

Fig. 3.6 Single chain structure factor from PEE melts as a function of the Rouse scaling variable. The dashed line displays the Rouse prediction for infinite chains, the solid lines incorporate the effect of translational diffusion. The different symbols relate to the spectra displayed in Fig. 3.5. (Reprinted with permission from [40]. Copyright 2003 Springer, Berlin)...

Spectra of G4-OH(Pt)n, n= 12, 40, and 60, obtained between 280 nm and 700 nm and normalized to A = 1 at A = 450 nm, are shown in Fig. 12 b all of these spectra display the interband transition of Pt nanoparticles. Control experiments clearly demonstrate that the Pt clusters are sequestered within the G4-OH dendrimer. For example, BH4 reduction of the previously described G4-NH2(Pt +)n emulsions results in immediate precipitation of large Pt clusters. Importantly, the dendrimer-encapsulated particles do not agglomerate for up to 150 days and they redissolve in solvent after repeated solvation/drying cycles. 

The calibration spectra displayed in Figure 5.33 reveal a random baseline offset for these data. No other anomalous behavior is observed. The concentration design has seven independent standards (see Figure 3.32), which are sufficient for estimating the three pure spectra. 

The solution compositions of a number of methyhnagnesium aUcoxides have been studied in some detail by Ashby and coworkers using a variety of physicochemical methods, including H NMR spectroscop) . The NMR spectra displayed broad signals due to the Mg—CH3 groups in the region —1 to —2 ppm (Table 8), which are strongly solvent, concentration and time dependent. 

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