Gadolinium complexes relativity

In this procedure the pentameglumine salt of the ligand DTPA was added to prevent any undesired release of the gadolinium ion from the chelate. Gadolinium-complex formulations normally contain a small amount of excess ligand either in its free or calcium-complexed form. As mentioned above, Pro-Hance (gadoteridol) contains calteridol, the calcium salt of the relatively weak calcium complex of the ligand for instance. 

T (H2O) = 2. 75 ms. The photophysical characteristics are weU documented (luminescence decay in D2O and at 77 K) residual water molecules ( H20 0.2-0.4) and triplet state energy of gadolinium complex (25,150 cm ) however the actual expected brightness upon laser excitation cannot be compared with other complexes since the absorbance at 337 nm is not reported. The conjugation of the complex with biomolecules was performed by its derivatization (as isothiocyanate) in relatively low yield using a tedious synthetic protocol. Unfortunately, for either the bis-pyrazolylpyridine or the bis-pyrazolylpyrimidine lanthanide complexes, no data are available concerning the stability in the presence of EDTA or competing ions (Mn Ca " ) or in potentially troublesome but basic buffer as phosphate buffer therefore, it is hard to evaluate the real usefulness of these complexes in a real bioassay, as in the HTS context. 

Outer sphere relaxation arises from the dipolar intermolecular interaction between the water proton nuclear spins and the gadolinium electron spin whose fluctuations are governed by random translational motion of the molecules (106). The outer sphere relaxation rate depends on several parameters, such as the closest approach of the solvent water protons and the Gdm complex, their relative diffusion coefficient, and the electron spin relaxation rate (107-109). Freed and others (110-112) developed an analytical expression for the outer sphere longitudinal relaxation rate, (l/Ti)os, for the simplest case of a force-free model. The force-free model is only a rough approximation for the interaction of outer sphere water molecules with Gdm complexes. 

The modified Florence program is well-suited for fitting the experimental NMRD profiles for slowly-rotating complexes of gadolinium(HI), an S = 7/2 ion characterized by relatively low ZFS, whose electron spin relaxation can be considered to be in the Redfield limit. An example of fitting an NMRD profile for aqueous protons, using different methods, for a protein adduct of a Gd(HI) chelate capable of accommodating one water molecule in the first coordination sphere, is displayed in Fig. 11. Other examples will be provided in Chapter 3. 

The relative concentration of gadolinium can be significantly increased as compared to that achievable with liposomes because the physical stability of the mixed micelles is reached for relatively low amounts of additional lipids and surfactants. It is also worth mentioning that the gadolinium-heads of the complexes embedded in micelles are all exposed to the aqueous phase and can interact directly with the water molecules of the bulk, a situation which is usually not met with liposome systems. 

In addition to wrong-way shifts, there are other methods to assess whether contact shifts occur for a nucleus. One is to compute sets of internal ratios of the shifts of protons for different metals or for directly attached H or C nuclei. Anomalies in these ratios are indicative of a contact contribution. Chelates of gadolinium, which has an isotropic f configuration, can only produce shifts by complexation or contact effects . Theoretical parameters for the relative contributions of contact and dipolar shifts for different lanthanide metals can be used to construct plots that indicate whether or not the shifts of a particular nucleus are purely dipolar or have a contact contribution Theoretical parameters indicate that the proportion of contact contribution to the shifts occurs in the order Eu > Nd > Ho > Er > Tb > Dy > Tm > Using the theoretical values... 

Relaxation times measured with isotropic Gd(III) chelates can also be incorporated into the fitting process . Changes in relaxation times vary only with the distance (1/r ) from the gadolinium ion. Therefore, relative relaxation rates of the nuclei of the substrate provide relative distances from the gadolinium ion. Incorporation of relaxation data into the fitting process requires that the geometry of the gadolinium-substrate complex be identical to that of the other lanthanide-substrate complex used to measure shift data, which must be assumed with care . ... 

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