Solutions relaxation enhancement

Carotenoid radical intermediates generated electrochemically, chemically, and photochemically in solutions, on oxide surfaces, and in mesoporous materials have been studied by a variety of advanced EPR techniques such as pulsed EPR, ESEEM, ENDOR, HYSCORE, and a multifrequency high-held EPR combined with EPR spin trapping and DFT calculations. EPR spectroscopy is a powerful tool to characterize carotenoid radicals to resolve -anisotropy (HF-EPR), anisotropic coupling constants due to a-protons (CW, pulsed ENDOR, HYSCORE), to determine distances between carotenoid radical and electron acceptor site (ESEEM, relaxation enhancement). 

The relaxivity enhancement of water protons in the aqueous solutions of paramagnetic complexes arises from time fluctuation of the dipolar coupling between the electron magnetic moment of the metal ion and the nuclear magnetic moment of the solvent nuclei (13,14). The dipolar interaction... 

Zeolite X and A with Gd(III) complexed by 8-hydroxyquinoline (8-HQ) was prepared either by the introduction of Gd(III)(8-HQ)2Cl complex into the zeolite synthesis gel or by stirring the Gd(III)-exchanged zeolite X in an ethanolic solution of 8-HQ (85). In vitro MRI studies showed signal enhancement (Ti shortening). However, the data cannot be compared with the previous results obtained with Gd(III)-loaded, but uncomplexed zeolites (because of partial complexation of Gd(III), different methods for determining the relaxivity enhancement, etc.)... 

H2O] is the molarity of water in the protein solution, Tij,r and Tiw are the relaxation times for protons in the hydration spheres of the protein and in the bulk water, [Pr] is the protein concentration in mol/1, n the number of waters bound to each protein molecule, and rvr the residence time for water protons on the protein molecule. In writing Eq. (19) it was assumed for simplicity that there is only one type of hydration site with characteristic rpr and Tipr- It is seen that the relaxation enhancement through the presence of the protein is... 

Fig. 5.6. Water H NMRD profiles for a solution of methemoglobin ( ) and fluoro-methe-moglobin ( ) at 279 K. In the latter case, fast exchange is responsible for water proton relaxation enhancements which are quenched by slow exchange in the former case [12].

Paramagnetic ion probes have been successfully used to study the binding characteristics and solution conformations of a number of biochemically important molecules. These include vitamin D, (533) penicillins, (534) and the antibiotics tetracycline, (535-537) vancomycin, (632) and bacitracin. (633) Antibodies and antibody fragments (immunoglobulins, IgG) have been studied by proton relaxation enhancement methods when lanthanide ions, particularly Gd(m), are bound to the proteins. (746-748). 

Liang B, Bushweller JH, Tamm LK. Site-directed parallel spinlabeling and paramagnetic relaxation enhancement in structure determination of membrane proteins by solution NMR spectroscopy. J. Am. Chem. Soc. 2006 128 4389-4397. 

The large decreases in spin-lattice relaxation times of nuclei surrounding Mn (3d , five unpaired electrons) can be interpreted to give structural information. The ion is widely used in all three of the above categories. Table 3.1 illustrates some recent experiments. Many are concerned with relaxation-enhancement studies. The spin-lattice relaxation times of water ( H or O) are usually enhanced when water is bound to a Mn -macromolecule, compared with an identical solution without the macromolecule. It is often possible to calculate Mn hydration numbers, Mn -water bond lengths, and solvent accessibilities [11]. 

Iwahara J, Tang C, Marius Clore G (2007) Practical aspects of H transverse paramagnetic relaxation enhancement measurements on macromolecules. J Magn Reson 184 185-195 Bertini I, Ciurli S, Dikiy A et al (2001) The first solution structure of a paramagnetic copper (II) protein the case of oxidized plastocyanin from the cyanobacterium Synechocystis PCC6803. J Am Chem Soc 123 2405-2413... 

C, however, Ca + does not have a dehydrating effect on Li+ since these ions possess similar enthalpies of hydration in saturated aqueous solutions. The nuclear magnetic relaxation rates and shifts of Li+ and Cs+ in aqueous solutions containing Fe + and various counter-anions are interpreted in terms of a dipolar attraction between Li+ and the unpaired electrons on the Fe + ion, and the formation of an ion pair between Cs+ and ferric halide complex. An increase of pressure in the range 0—1000 bar results in an enhancement in the hydration of the ions Na+ and K+ in their aqueous chloride solutions. The enhancement is more pronounced at 20 than at 45 °C. These conclusions... 

Sham et have used paramagnetically-induced relaxation enhancements as distance constraints for a solution molecular model of the ferredoxin of P. furiosus. Kostic et have used H Overhauser enhancements to compare the functional C-terminal domains of three vertebrate-type ferredoxins. 

ABSTRACT. The interaction of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) with amylose and its related compounds in aqueous solution has been studied by both steady-state and transient fluorescence measurements. The fluorescence of TNS aqueous solution was enhanced by the addition of amylose, 3-limit dextrin, and amylopectin. The fluorescence decay of TNS bound to these polysaccharides were well described as a sum of two-exponential functions. This suggests that there are two different microenvironments at the binding sites. The fluorescence lifetime of major component for TNS-amylose system agreed with that of major component for TNS-y-cyclodextrin system. The mean rotational relaxation time of TNS bound to amylose is similar to that of the segmental motion of amylose chain. Based on these results, a configurational model for TNS-amylose complex has been proposed. 

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