Indium complexes oxygen ligands

Two other types of unusual indium(II)-oxygen ligand complexes are known. The polar-ographic reduction of In(acac)3, In(tropolonate)3 or In(pyronate)3 (pyronate = 3-hydroxy-2-methyl-4-pyronate anion) in non-aqueous solution shows a one-electron reduction in each case, corresponding to the formation of a (formally) In complex. Similar behaviour was observed with In(oxine)3, and in some cases a second one-electron reduction was also observed, implying the formation of In species, although in no case was the site of the reduction identified, so that the product may be either [In (acac)3] or [In (acac)2(acac )] (c/. sulfur ligands. Section 25.2.3.4). 

Comparisons to the known structure of indium DTPA and to other divalent metal DTPA bis-amide complexes indicate that the indium cation binds to the three amine nitrogen atoms, the four carboxylate oxygen atoms, and the one carboxairdde oxygen atom of the DTPA monoamide ligand. Addition of an acidic In chloride solution to a ly-ophilized DTPA-octreotide pellet at room temperature readily fomis In DTPA-octreotide, known clinically as OctreoScan. In a rat model of pancreatic carcinoma In DTPA-octreotide showed clear visualization of the tumors and rapid, primarily renal, clearance of the radiophamiaceutical/ Moreover, pretreatment with 1 mg of octreotide prevents uptake of " in DTPA-octreotide in the tumors and adrenal glands, an observation that verifies that this radiolabeled peptide binds to receptor sites. 

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