10.1021/ic049973g.s002 Wen-Yuan Hsieh Wen-Yuan Hsieh Shuang Liu Shuang Liu Synthesis, Characterization, and Structures of Indium In(DTPA-BA<sub>2</sub>) and Yttrium Y(DTPA-BA<sub>2</sub>)(CH<sub>3</sub>OH) Complexes (BA = Benzylamine):  Models for <sup>111</sup>In- and <sup>90</sup>Y-Labeled DTPA-Biomolecule Conjugates American Chemical Society 2004 BA HPLC benzylamine groups OH square antiprism coordination geometry carbonyl oxygen donors 1 H NMR signals CH Lu complex isomers IR N atom 2004-09-20 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Synthesis_Characterization_and_Structures_of_Indium_In_DTPA_BA_sub_2_sub_and_Yttrium_Y_DTPA_BA_sub_2_sub_CH_sub_3_sub_OH_Complexes_BA_Benzylamine_Models_for_sup_111_sup_In_and_sup_90_sup_Y_Labeled_DTPA_Biomolecule_Conjugates/3324601 To explore structural differences in In<sup>3+</sup>, Y<sup>3+</sup>, and Lu<sup>3+</sup> chelates, we prepared M(DTPA-BA<sub>2</sub>) complexes (M = In, Y, and Lu; DTPA-BA<sub>2</sub> = N,N‘ ‘-bis(benzylcarbamoylmethyl)diethylenetriamine-N,N‘,N‘ ‘-triacetic acid) by reacting the trisodium salt of DTPA-BA<sub>2</sub> with 1 equiv of metal chloride or nitrate. All three complexes have been characterized by elemental analysis, HPLC, IR, ES-MS, and NMR (<sup>1</sup>H and <sup>13</sup>C) methods. ES-MS spectral and elemental analysis data are consistent with the proposed formula for M(DTPA-BA<sub>2</sub>) (M = In, Y, and Lu) and have been confirmed by the X-ray crystal structures of both In(DTPA-BA<sub>2</sub>)·2H<sub>2</sub>O and Y(DTPA-BA<sub>2</sub>)(CH<sub>3</sub>OH) complexes. By a reversed-phase HPLC method, it was found that In(DTPA-BA<sub>2</sub>) is more hydrophilic than M(DTPA-BA<sub>2</sub>) (M = Y and Lu), most likely due to the dissociation of the two carbonyl oxygen donors in solution. The X-ray crystal structure of In(DTPA-BA<sub>2</sub>) revealed a rare example of an eight-coordinated In<sup>3+</sup> complex with DTPA-BA<sub>2</sub> bonding to the In<sup>3+</sup> in a distorted square antiprism coordination geometry. Both benzylamine groups are in the trans position relative to the acetate-chelating arm that is attached to the central N atom. The Y<sup>3+</sup> in Y(DTPA-BA<sub>2</sub>)(CH<sub>3</sub>OH) is nine-coordinated with an octadentate DTPA-BA<sub>2</sub> and a methanol oxygen. The coordination geometry is best described as a tricapped trigonal prism. One benzylamine group is trans and the other cis to the acetate-chelating arm that is attached to the central N atom. All three M(DTPA-BA<sub>2</sub>) complexes (M = In, Y, and Lu) exist as at least three isomers in solution (∼10 mM), as shown by the presence of 6−8 overlapped <sup>1</sup>H NMR signals from the methylene hydrogens of the benzylamine groups. The coordinated DTPA-BA<sub>2</sub> remains rigid even at temperatures >85 °C. The exchange rate between different isomers in M(DTPA-BA<sub>2</sub>) (M = In, Y, and Lu) is relatively slow at high concentrations (>1.0 mM), but it is fast due to the partial dissociation and rapid interconversion of different isomers at lower concentrations (∼10 μM). It is not surprising that M(DTPA-BA<sub>2</sub>) complexes (M = In, Y, and Lu) appear as a single peak in their respective HPLC chromatogram.