Spectroscopic absorption spectra

The equilibrium constants obtained using the metal-ion induced shift in the UV-vis absorption spectrum are in excellent agreement with the results of the Lineweaver-Burke analysis of the rate constants at different catalyst concentrations. For the copper(II)ion catalysed reaction of 2.4a with 2.5 the latter method gives a value for of 432 versus 425 using the spectroscopic method. 

EXAFS analysis is a powerful spectroscopic method for structural analysis which has been extensively applied to the problem of structure determination in nanoparticles, and especially bimetallic nanoparticles [170-172]. The X-ray absorption spectrum of an element contains absorption edges corresponding to the excitation of electrons from various electronic states at energies characteristic of that element, i.e., K edges arise from the excitation of electrons from Is states, and LI, II, III edges from excitations from 2s, 2p 1/2, and 2p3/2 states. When the X-ray energy is increased above an edge, oscillations (fine... 

The absorption spectrum of folded AvGFP in the visible region displays two well-separated peaks at 395 nm and 475 nm, whose relative intensity depends on pH (Fig. 4b). The chromophore states associated to these two peaks have been termed, respectively, A and B [81]. Although this has been initially debated [78, 82, 83], accumulated spectroscopic and theoretical evidences indicate that these two absorption bands, respectively, arise from the neutral (A) and anionic (B) forms of the HBI chromophore [10, 11, 69-71, 84-87]. 

FRET is a nonradiative process that is, the transfer takes place without the emission or absorption of a photon. And yet, the transition dipoles, which are central to the mechanism by which the ground and excited states are coupled, are conspicuously present in the expression for the rate of transfer. For instance, the fluorescence quantum yield and fluorescence spectrum of the donor and the absorption spectrum of the acceptor are part of the overlap integral in the Forster rate expression, Eq. (1.2). These spectroscopic transitions are usually associated with the emission and absorption of a photon. These dipole matrix elements in the quantum mechanical expression for the rate of FRET are the same matrix elements as found for the interaction of a propagating EM field with the chromophores. However, the origin of the EM perturbation driving the energy transfer and the spectroscopic transitions are quite different. The source of this interaction term... 

The pyrene-like aromatic chromophore of BaPDE is characterized by a prominent and characteristic absorption spectrum in the A 310-360 nm spectral region, and a fluorescence emission in the X 370-460 nm range. These properties are sensitive to the local microenvironment of the pyrenyl chromophore, and spectroscopic techniques are thus useful in studies of the structures of the DNA adducts and in monitoring the reaction pathways of BaPDE and its hydrolysis products in DNA solutions. 

Both infrared and Raman are vibrational spectroscopic techniques, and the Raman scattering spectrum and infrared absorption spectrum for a given species often resemble one another quite closely. There are, however, sufficient differences... 

Absorption Spectrum The polarized absorption spectrum of a single crystal of aspirin was measured which indicated that aspirin may be spectroscopically treated as perturbed benzoic acid.59... 

The structure of HRP-I has been identified as an Fe(IV) porphyrin -ir-cation radical by a variety of spectroscopic methods (71-74). The oxidized forms of HRP present differences in their visible absorption spectra (75-77). These distinct spectral characteristics of HRP have made this a very useful redox protein for studying one-electron transfers in alkaloid reactions. An example is illustrated in Fig. 2 where the one-electron oxidation of vindoline is followed by observing the oxidation of native HRP (curve A) with equimolar H202 to HRP-compound I (curve B). Addition of vindoline to the reaction mixture yields the absorption spectrum of HRP-compound II (curve C) (78). This methodology can yield useful information on the stoichiometry and kinetics of electron transfer from an alkaloid substrate to HRP. Several excellent reviews on the properties, mechanism, and oxidation states of peroxidases have been published (79-81). 

Extensive studies into the association of this cytochrome b with CGD neutrophils were performed by Segal and Jones, and by other workers, in the late 1970s and early 1980s. The cytochrome was completely absent (as determined by the absence of a distinctive absorption spectrum in spectroscopic studies) in almost all cases of X-linked CGD, but present at decreased levels in female relatives of these patients. In almost all cases of autosomal recessive CGD, the cytochrome was present but non-functional, in that it did not become reduced upon cellular activation. This indicated both the heterogeneous nature of the disease and also that some other biochemical defect was responsible for impaired function in these patients. Hence, the search was on for other components of the NADPH oxidase. 

As the odd number of hydrogen atoms already shows, triphenylmethyl, C19H16, known in solution only, contains a tervalent carbon atom. In contrast to the colourless hexaphenylethane, which can be isolated in the crystalline state, triphenylmethyl is intensely yellow. Its absorption spectrum exhibits characteristic bands (examine the spectrum in a spectroscope). 

We suggest that these results can be explained if the aggregation process in these solid TTF polymers proceeds by means of a two-step mechanism (Figure 7) in which the fast oxidative electron transfer step is followed by a slow process of ion clustering/reorganization which is favored by a low viscosity environment. This mechanism is consistent with the fact that the starting neutral homopolymer shows no spectroscopic evidence for site-site interaction between the pendant donors. The absorption spectrum of the polymer is... 

The interpretation of these effects as the formation of a proton addition complex was further supported by Plattner et al. (1952) by means of spectroscopic and conductimetric investigations. In these interactions the change of the absorption spectrum is characteristic, since the blue colour of the azulene in organic solvents is changed to a yellow colour in... 

In flash spectroscopy a second spectroscopic flash is fired a short time after the photolysis flash and the transient absorption spectrum is registered on a photographic plate (Fig. 13). Repeating the experiments with different delay times gives complete information about the wavelength and the time behavior of the intermediate absorptions. 

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