Spectral modifications

Figure 9.22—Spin decoupling experiment on butanone. Spectral modification a) by irradiating the CHj group at 2.47 ppm b) by irradiating the CH3 group (of ethyl) at 1.07 ppm, compared to the spectrum shown in Fig. 9.1. For such a simple compound, these experiments are only used to illustrate the principle. On the other hand, a double resonance experiment would be useful to precisely determine the coupling in aspirin (shown in Fig. 9.20).

There are instruments that have used higher order filtering schemes to allow more complex spectral modifications. The E-mu Morpheus sound module uses 14th order... 

The Phase Vocoder. The Phase Vocoder [Flanagan and Golden, 1966][Gordon and Strawn, 1985] is a common analysis technique because it provides an extremely flexible method of spectral modification. The phase vocoder models the signal as a bank of equally spaced bandpass filters with magnitude and phase outputs from each band. Portnoff s implementation of the Short Time Fourier Transform (STFT) provides a time-efficient implementation of the Phase Vocoder. The STFT requires a fast implementation of the Fast Fourier Transform (FFT), which typically involves bit addressed arithmetic. 

NADH is highly fluorescent, with absorption and emission maxima located at 340 and 450 nm, respectively, while NAD+ and NADH+ are not fluorescent (Figures 7.14 and 7.15). Schauenstein et al. (1980) explained the spectral modification of NADH+ by a higher percentage of the stacked conformation at a lower pH. 

Students will follow the absorption and fluorescence spectral modifications of ethidium bromide in the presence of different DNA concentrations. Then, they will calculate the number of binding sites and the mean association constant. Before coming to the lab, students should determine the absorption and emission spectra of ethidium bromide bound to DNA. 

MVH is inhibited by CO, cyanide, arsenite, and sulfide. Carbon monoxide, cyanide, and arsenite react only with the reduced enzyme. Spectral modifications of the heme and other results have indicated that the heme is the site of action of these inhibitors as well as the site at which sulfite, nitrite, and hydroxylamine are reduced. The Michaelis constants of the enzyme for sulfite and NADPH are both about 4r-5 itM. 

Tot( ls) hy Maad Mio This is an important result, since it means that, as far as the total fluorescence intensity is concerned, any spectral modification can in a first approximation be ignored, and a one-wavelength model (at the fi-equency of the fluorescence peak (Op ) can be used. Hence, the... 

The SPMs observed in Figs 2.5, 2.6, 2.7 are sufficiently large and unambiguous to render a clear-cut identification of spectral modifications of the emission. The agreement between experimental and predicted spectra is also sufficiently satisfactory to support the interpretations and validate the models (despite their simplicity). Nonetheless, a more accurate agreement would be desirable for subtler effects, such as a clear distinction between SDMEF and (U)FDMEF. This is, however, prevented by a number of issues which we highlight here as a prerequisite towards improved future experiments. 

FIG. 2 Spectral modifications in the absorbance spectrum of chlorophyll a (full line) triggered by the replacement of the methyl side-group at the C7 position by an aldehyde side-group, yielding chlorophyll b (<dashed line). The structures of chlorophyll a and chlorophyll b molecules are also presented. 

FIG. 5 Effect of processing on the color of pineapple flesh. The structure and spectral modifications occurring during the processing are displayed. 

In spite of the fact that they do not lead to optical data, Raman, IR and FTIR [65] spectroscopies are choice methods to characterize the polymers and to study their chemical modifications. IR spectroscopy has the disadvantage of being used only with technical complexities in the presence of an electrolyte, while Raman spectroscopy proved from the pioneer papers published in 1987 [60,66] to be a very reliable technique for the study of PANI, and can be used very easily in situ. The spectral modifications associated with the percentage of doping [67], with pH [68], with the physico-chemical treatments of as-prepared PANI [36] or with the polymer degradation following the electrochromic cycles [69,70,71] have been studied by Raman spectroscopy. Finally, RS and Optical Spectroscopy were associated several times [40,71,72], by reason of their mutual contribution. 

Electron transfer between electron donor and acceptor located in two different proteins or within the same protein induces a spectral modification in the absorption of both redox centers and thus kinetics parameters and electron transfer data can be studied with absorption. Figure 1.23 displays the absorption spectra of oxidized (a) and reduced (b) forms of cytochrome b2 core extracted from the yeast Hansenula anomala. Reduction of cytochrome c with cytochrome b2 core is followed at the isobestic point of cytochrome b2 equal to 416.5 nm. At this wavelength, only absorption of cytochrome c increases upon reduction. 

In the i.r. range usually investigated (0.5-0.1 eV), besides the vibrational contributions of adsorbed species and multiphonon modes, plasmonic contributions associated with free electrons in the conduction band and defect excitations can also contribute, whose relative intensity is strongly influenced by the pretreatment conditions. In particular when the conduction band is extensively populated, the plasmonic modes couple with the vibrational ones (due to both adsorbed species and multiphonon lattice vibrations) causing a dramatic spectral modification and loss of any vibrational detail. 

Depending on the X-ray source and the spectral modification devices, the LD are in the pg range for 2—3 kW X-ray tubes and in the fg range with excitation by means of synchrotron radiation. Figure 11.15 shows a typical TXRF spectrum the absolute detection limit values of typical TXRF instruments are shown in Fig. 11.10. Thus, TXRF permits to simultaneously determine trace elements in samples of small volume. Additional advantages are insensitivity to matrix effects, easy cahbration, fast analysis times and low cost. In practice, the method is in particular apphed for multi-element determinations in water samples of various nature and for the routine analysis of Si-wafer surfaces employed in the microelectronics industry. 

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