Circular dichroism, paramagnetic

Labrude, P., Rasolomana, M. Atomization of oxyhemoglobin in the presence of sucrose. Study by circular dichroism and electronic paramagnetic resonance, comparison with freezedrying. S. T. P. Pharma 4 (6), p. 472 80, 1988... 

Before the availability of a high-resolution structure of P. aeruginosa CCP, the properties and environments of the two hemes had been probed using a range of solution spectroscopies. These include electron paramagnetic resonance (EPR) (51, 57, 58, 61), resonance Raman (59), circular dichroism (CD) 71, 72), MCD 58, 61, 73, 74). Until the demonstration by Ellfolk and colleagues that it is the mixed-valence form of the... 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

In some cases large extinction coefficient allows sensitive detection Circular dichroism (CD) spectra Coordination geometry metal ligands Electron paramagnetic resonance (EPR) spectra... 

The discussion of activity from X-ray data in conjunction with kinetic data is also difficult because, apart from considerations of dynamics, these techniques do not provide the essential knowledge about the energy states of given atoms or groups. It is necessary to inspect the electronic structure of at least certain regions of the protein. Methods exist for this inspection, and these include electron paramagnetic resonance, ultraviolet, circular dichroism, Raman and Mossbauer spectroscopies. The full understanding of activity can only come when the information derived from all available methods is assimilated and rationalized. 

Fig. 7. Optical absorption and magnetic circular dichroism spectra of oxidized hydrogenase from M. thermoautotrophicum (AH strain), nickel concentration 120 pM. (a) Optical absorption spectrum, at room temperature the absorption is predominantly due to iron-sulfur clusters, (b) MCD spectra recorded at 1.53, 4.22, and 8.9 K, in a magnetic field of 4.5 T MCD is predominantly due to Ni(III), which is the only paramagnetic species in the oxidized enzyme. Reproduced, with permission, from Ref. 57.

The nature of the Jahn-Teller interaction is such as to yield several vibronic states, within just a few wave numbers of the ground state. These states have very different expectation values for the electronic and nuclear co-ordinates, and we shall now examine how the low-lying vibronic structure may be elucidated by the followings modem physical techniques high-field, multifrequency electron paramagnetic resonance (HFMF EPR) magnetic circular dichroism (MCD), and extended X-ray absorption fine stmcture spectroscopy (EXAFS). The recent advent of HFMF EPR... 

Of the paramagnetic techniques listed above, magnetic circular dichroism (MCD) is one of the few techniques that can identify electronic structure specific to the dithiolene chelate bound to Mo/W (111, 112). Since at this point only a handful of studies have been accomplished, the salient points of each will be summarized. 

P. aer. = Pseudomonas aeruginosa A. den. = Alcaligenes denitrificans MCD = magnetic circular dichroism EPR = electron paramagnetic resonance XAS = X-ray absorption spectroscopy NMR = nuclear magnetic resonance EXAFS = extended X-ray absorption fine structure. 

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