Paramagnetic substance

Bertini I, Luchinat C and Aime S 1996 NMR of Paramagnetic Substances (Amsterdam Elsevier)... 

Other forms of permeabiHty oftea ate quoted as related to specific appHcatioas (9). A term closely related to the permeabiHty is the volume susceptibiHty k = M/H which particularly characterizes diamagaetic and paramagnetic substances. A variety of definitions of susceptibiHties is given ia Refereace 5. 

Paramagnetic substances have a magnetic entropy associated with the random orientation of the spin of the unpaired electrons as shown in (a) below ... 

A Gouy balance is used to observe the magnetic character of a sample by detecting the extent to which it is drawn into (paramagnetic substances) or driven out of (diamagnetic substances) a magnetic field. 

The low intensities of nonprotonated carbons is usually due to their long relaxation times. The addition of a paramagnetic substance such as... 

The temperature dependence of the molar susceptibility of a paramagnetic substance follows the Curie-Weiss law (if the magnetic field is not too strong) ... 

The function (a) is known as the Langevin function, after Paul Langevin, French physicist (1872-1946). The magnetic susceptibility of a paramagnetic substance can be expressed as (jim(B/kT). where fim is the magnetic moment, (S the magnetic flux, k the B and T die absolute temperature. 

The general theory of solvent nuclear relaxation in the presence of paramagnetic substances was described by Bloem-bergen, Solomon, Morgan, and others (11-16). During the last 10 years, it has been substantially reviewed in the context of MRI contrast agents (1-7,17,18). 

Although ESR has the advantage over NMR of its high sensitivity toward low concentrations of active sites and intermediates, this method is only applicable to the characterization of paramagnetic substances. In addition, the widths of the ESR signals increase dramatically with increasing... 

Magnetic susceptibilities of solutions — These are useful parameters for determining equilibrium constants for reactions involving spin changes. The Evans nmr method utilizes the observed shift in the resonance line (say of a proton of t-BuOH or hexamethyldisilox-ane) in solution when a paramagnetic substance is added. The paramagnetic shift A/ is related to the magnetic moment (jj, of the solution at TK by the approximate expression... 

I have invited Professor Ivano Bertini (University of Florence, Italy), who is an expert in this field, to be the co-editor of this volume. Professor Bertini is a well-known inorganic chemist that has significantly contributed, both experimentally and theoretically, to the understanding of the relations between water relaxation and unpaired electron relaxation. On its turn, electron relaxation determines the high resolution NMR behavior of paramagnetic substances, a field in which he is quite active. 

The analysis of the paramagnetic enhancement of the relaxation rates must be done after subtraction of the diamagnetic contribution from the relaxation rates of the paramagnetic sample, obtained by performing measurements on the diamagnetic analog. It is customary to refer to 1 mM concentration of paramagnetic substances to define the relaxivity of the sample. 

The earliest and most widely studied particulate carriers for paramagnetic substances are the liposomes, either entrapping hydrophilic contrast agents within the internal aqueous phase, or incorporating lipophilic complexes in their phospholipidic bilayer membrane 100,101). 

The tendency of the magnetic lines of force to pass through a medium relative to their tendency to pass through a vacuum is the magnetic permeability, p. This is one of the parameters that distinguishes a diamagnetic material from a paramagnetic substance. Permeability is defined as. 

A second possibility is the modification (conjugation) of an antibody by a label, e.g., biotin, which is detected later on by a specific receptor, e.g., (strept)avidin. In each case the last part of such a cascade has to carry a measurable label. Such labels are enzymes, fluorescent dyes, colloids, radioactive isotopes, paramagnetic substances, and others. 

FIGURE 9.2 Variation of magnetic susceptibility with temperature for (a) a paramagnetic substance, (b) a ferromagnetic substance, and (c) an antiferromagnetic substance. 

For paramagnetic substances the condition 7 1 is applicable, in which case... 

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