Electron paramagnetic resonance environment

Since cupric ions are paramagnetic, it is possible by electron paramagnetic resonance (EPR) to obtain information on the status and the environment of the Cu ions adsorbed on uronic acids [4, 5]. Nitella cell walls with uronate charges compensated to 9 or 100% with copper in equilibrium with mixed copper and zinc chloride solutions had their EPR spectra recorded at two different temperatures, 93 and 293 °K (Fig. 3.a, b). 

In general, several spectroscopic techniques have been applied to the study of NO, removal. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are currently used to determine the surface composition of the catalysts, with the aim to identify the cationic active sites, as well as their coordinative environment. 

The crystallographic structure of rubredoxin from Clostridium pasteurianum at 2.5 A, a resolution sufficient to reveal the sequence of several of the bulky amino acid side chains, shows the iron coordinated to two pairs of cysteine residues located rather near the termini of the polypeptide chain (Fig. 1). A related rubredoxin, with a three times larger molecular weight, from Pseudomonas oleovorans is believed to bind iron in a similar fashion. This conclusion is based on physical probes, especially electron paramagnetic resonance spectroscopy, all of which indicate that the iron is in each case situated in a highly similar environment however, the proteins display some specificity in catalytic function. 

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... 

Analysis of antioxidant properties relative to the DPPH" radical involves observation of colour disappearance in the radical solution in the presence of the solution under analysis which contains antioxidants. A solution of extract under analysis is introduced to the environment containing the DPPH radical at a specific concentration. A methanol solution of the DPPH radical is purple, while a reaction with antioxidants turns its colour into yellow. Colorimetric comparison of the absorbance of the radical solution and a solution containing an analysed sample enables one to make calculations and to express activity as the percent of inhibition (IP) or the number of moles of a radical that can be neutralised by a specific amount of the analysed substance (mmol/g). In another approach, a range of assays are conducted with different concentrations of the analysed substance to determine its amount which inactivates half of the radical in the test solution (ECso). The duration of such a test depends on the reaction rate and observations are carried out until the absorbance of the test solution does not change [4]. If the solution contains substances whose absorbance disturbs the measurement, the concentration of DPPH radical is measured directly with the use of electron paramagnetic resonance (EPR) spectroscopy. 

The substitution of a different metal into an enzyme provides a very useful method for studying the immediate environment of the metal site. In addition to the use of Co2 for spectral studies, appropriate substitution allows the use of physical methods such as electron paramagnetic resonance (Co . Cu2 ). the Mdssbauer effect tFe2 ). proton magnetic resonance relaxation techniques (Mir ), or X-ray crystallography (with a heavy metal atom to aid in the structure solution). ... 

When one looks for methods to detect OH, one always has two keep in mind that these radicals are very reactive, and in the presence of substrates their steady-state concentrations are extremely low even at a high rate of OH production. The fact that OH only absorbs far out in the UV region (Hug 1981) is thus not the reason why an optical detection of OH is not feasible. Electron paramagnetic resonance (EPR) must also fail because of the extremely low steady-state concentrations that prevail in the presence of scavengers. The only possibility to detect their presence is by competition of a suitable OH probe that allows the identification of a characteristic product [probe product, reaction (41)]. When this reaction is carried out in a cellular environment, the reaction with the probe is in competition with all other cellular components which also readily react with OH [reaction (42)]. The concentration of the probe product is then given by Eq. (43), where [ OH ] is the total OH concentration that has been formed in this cellular environment and q is the yield of the probe product per OH that has reacted with the probe. 

The possibility of using the electron paramagnetic resonance properties of Gd3+ to probe its environment in and interactions with biological molecules has previously received little attention in the literature (40). However, the possibility exists that Gd2+ will be a sensitive EPR probe for characterizing macromolecular biological systems such as the Ca2+-ATPase. The EPR spectra of Gd3+, which has S = 7/2. in neutral water and in two different buffers are shown in Figure 13A. The linewidths were found to be independent of pH over the usable range of these buffers and independent of temperature between 4 and 30°C, The spectrum of Gd2+ in neutral water is centered around 3248 G, with a linewidth of 530 G. As shown, Gd3+ in Pipes buffer, but not in Tes buffer, yielded a spectrum similar to that of the aqueous Gd2+ solution. On this basis, all of our Gd3+ EPR and NMR studies... 

Depending on concentration of a hydrochloric acid during lixiviation of powders the process of saturation by gas develops ambiguously it has a sine wave character. The established dependence of an output in a solution of ions trivalent titanium on the concentration of a solution according to data, obtained by the method of electronic paramagnetic resonance, has shown that at small time of exposure (50-100 hrs) the output of ions of titanium in a solution proceeds with the increasing speed. The pure powders react with environment less actively, polluted -more intensively. The speed of saturation of powders by gas at corrosion in solutions of a hydrochloric acid is increased with growth of concentration, and then is sharply reduced. 

The paramagnetism of many lanthanide ions finds practical application in NMR shift reagents and, increasingly, in MRI contrast agents. EPR (see Electron Paramagnetic Resonance) spectra are only readily obtained from Gd +, with its ground state, as yet there has been little study of the effects of environment upon the spectra. 

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