Indium, complex dissociation

Direct. Some radionucHdes are packaged in solution for direct sampling (qv) via a septum and injection into the patient. GalHum-67 is a marker of inflammation, infection, and various tumor types. Its half-life is 78.3 h and it is suppHed as the gallium citrate salt. Indium-111 chloride is suppHed for the labeling of white blood ceUs. The In chloride is mixed with oxine (9-hydroxyquinoline) to form a lipophilic, cationic In oxine complex, which enters the white blood ceU. The complex dissociates within the ceU, and the cationic In " ion is trapped within the ceU, owing to its charge. 

A further prerequisite for an indium complex to be useful for nuclear medicine applications is that it be resistant to exchange with the plasma protein transferrin. Indium binds to transferrin at the Fe binding site with a stability constant (/f ) of lO in the presence of bicarbonate [7]. The formation constants of indium with ethylenediaminetetraacetic acid (EDTA) (log = 25.0) and DTPA (log Ki = 29.0) are such that at infinite dilution equilibrium would favor the formation of indium transferrin [8J. The slow dissociation of indium from these complexes hinders the formation of indium transferrin. 

Initial work on radiolabeling of autologous polymorphonuclear leukocytes was performed by McAfee and Thakur [30]. One of the compounds they examined was the nonpolar, lipid-soluble complex 8-hydroxyquinoline (oxine) (Fig. 2). Indium forms a neutral, lipid-soluble complex with oxine which will penetrate cellular membranes. Subsequently, studies showed that this technique could be used to label leukocytes and platelets with retention of biological activity [31]. After diffusing intracellularly, the ln-oxine complex dissociates and the " In is bound to nuclear and cytoplasmic proteins (Fig. 3) [32-34]. Due to the high stability of indium with the blood protein transferrin, it is necessary to label platelets or WBCs in the absence of plasma. In addition, a final wash of the labeled cells using plasma will remove any loosely bound indium by complexation with transferrin [35,36]. 

The kinetics in the basic media are summarised in the table. Since the rate is not affected by the buffer under due conditions, the reaction mechanism seems to involve essentially that of hydroxo complexes except for thallium, and the attack of hydroxide ions upon the complex appears to play an important role. The fact that the rate of the indium complex is proportional to the square of the hydroxide ion concentration tells that indium is the most inert among the three. Such an inertness of indium complexes may be reflected in the small value of its apparent dissociation constant of the coordinated water molecule, K. ... 

In two independent studies, InP was grown from the precursor complex [(CH3)2In /i-P(But)2 ]2.255 256 262 First, Cowley et al. employed the use of a cold-wall reactor to deposit InP using H2 or He as the carrier gas, with substrate temperatures between 450 °C and 700 °C. Using an MBE reactor, Bradley and co-workers found that stoichiometric growth was only possible at 480 °C and only when a simultaneous secondary incident flux of dissociated phosphine was added. Lower growth temperatures resulted in indium-rich deposits. 

A tetracobalt anionic complex, viz. [In Co(CO)4 4] (27) (37,37a), has been briefly described together with the thallium analogue (28) (37a), both formed by addition of [Co(CO)4] to either 25 or 26. No structural details have been reported although the indium and thallium centers are presumably tetrahe-drally coordinated by the four cobalt atoms. Mention is also made (37a) of the facile heterolytic bond dissociation (In—Co or Tl—Co) observed in polar solvents. Little has been reported about the reactivity of these complexes, although a discussion on the use of 25 as a catalyst in the dimerization of norbornadiene has appeared (58). 

In contrast to the behavior of comparable aluminum, gallium, and indium compounds, the hitherto known alkynyl thallium(III) compounds (170) of the type R2T1C=CR show no tendency to dimerize via n complexation. Molecular weight determinations performed in aniline show the monomeric character of these species, which behave as weak electrolytes due to partial dissociation into R2T1+ and C=CR" (170). 

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