{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T05:25:21Z","timestamp":1791177921535,"version":"4.1.0"},"reference-count":65,"publisher":"Wiley","issue":"4","license":[{"start":{"date-parts":[[2005,11,28]],"date-time":"2005-11-28T00:00:00Z","timestamp":1133136000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Chemistry A European J"],"published-print":{"date-parts":[[2006,1,23]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>The heterotritopic ligand [bpy(DTTA)<jats:sub>2<\/jats:sub>]<jats:sup>8\u2212<\/jats:sup> has two diethylenediamine\u2010tetraacetate units for selective lanthanide(<jats:sc>III<\/jats:sc>) coordination and one bipyridine function for selective Fe<jats:sup>II<\/jats:sup> coordination. In aqueous solution and in the presence of these metals, the ligand is capable of self\u2010assembly to form a rigid supramolecular metallostar structure, {Fe[Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sub>3<\/jats:sub>}<jats:sup>4\u2212<\/jats:sup>. We report here the physicochemical characterization of the dinuclear complex [Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sup>2\u2212<\/jats:sup> and the metallostar {Fe[Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sub>3<\/jats:sub>}<jats:sup>4\u2212<\/jats:sup> with regard to potential MRI contrast agent applications. A combination of pH potentiometry and <jats:sup>1<\/jats:sup>H NMR spectroscopy has been used to determine protonation constants for the ligand [bpy(DTTA)<jats:sub>2<\/jats:sub>]<jats:sup>8\u2212<\/jats:sup> and for the complexes [Fe{bpy(DTTA)<jats:sub>2<\/jats:sub>}<jats:sub>3<\/jats:sub>]<jats:sup>22\u2212<\/jats:sup> and [Y<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>]<jats:sup>2\u2212<\/jats:sup>. In addition, stability constants have been measured for the dinuclear chelates [M<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>]<jats:sup><jats:italic>n<\/jats:italic>\u2212<\/jats:sup> formed with M = Gd<jats:sup>3+<\/jats:sup> and Zn<jats:sup>2+<\/jats:sup> (log\u2009<jats:italic>K<\/jats:italic><jats:sub>GdL<\/jats:sub> = 18.2; log\u2009<jats:italic>K<\/jats:italic><jats:sub>ZnL<\/jats:sub> = 18.0; log\u2009<jats:italic>K<\/jats:italic><jats:sub>ZnHL<\/jats:sub> = 3.4). A multiple field, variable\u2010temperature <jats:sup>17<\/jats:sup>O NMR and proton relaxivity study on [Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sup>2\u2212<\/jats:sup> and {Fe[Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sub>3<\/jats:sub>}<jats:sup>4\u2212<\/jats:sup> yielded the parameters for water exchange and the rotational dynamics. The <jats:sup>17<\/jats:sup>O chemical shifts are indicative of bishydration of the lanthanide ion. The exchange rates of the two inner\u2010sphere water molecules are very similar in the dinuclear [Gd<jats:sub>2<\/jats:sub>bpy(DTTA)<jats:sub>2<\/jats:sub>(H<jats:sub>2<\/jats:sub>O)<jats:sub>4<\/jats:sub>]<jats:sup>2\u2212<\/jats:sup> and in the metallostar (<jats:italic>k<\/jats:italic><jats:sub>ex<\/jats:sub><jats:sup>298<\/jats:sup> = 8.1\u00b10.3\u00d710<jats:sup>6<\/jats:sup> and 7.4\u00b10.2\u00d710<jats:sup>6<\/jats:sup> s<jats:sup>\u22121<\/jats:sup>, respectively), and are comparable to <jats:italic>k<\/jats:italic><jats:sub>ex<\/jats:sub><jats:sup>298<\/jats:sup> for similar Gd<jats:sup>III<\/jats:sup> poly(amino carboxylates). The rotational dynamics of the metallostar has been described by means of the Lipari\u2013Szabo approach, which involves separating global and local motions. The difference between the local and global rotational correlation times, <jats:italic>\u03c4<\/jats:italic><jats:sub>lO<\/jats:sub><jats:sup>298<\/jats:sup> = 190\u00b115 ps and <jats:italic>\u03c4<\/jats:italic><jats:sub>gO<\/jats:sub><jats:sup>298<\/jats:sup> = 930\u00b150 ps, respectively, shows that the metallostar is not completely rigid. However, the relatively high value of <jats:italic>S<\/jats:italic><jats:sup>2<\/jats:sup> = 0.60\u00b10.04, describing the restriction of the local motions with regard to the global one, points to a limited flexibility compared with previously reported macromolecules such as dendrimers. As a result of the two inner\u2010sphere water molecules, with their near\u2010optimal exchange rate, and the limited flexibility, the metallostar has a remarkable molar proton relaxivity, particularly at high magnetic fields (<jats:italic>r<\/jats:italic><jats:sub>1<\/jats:sub> = 33.2 and 16.4 m<jats:sc>M<\/jats:sc><jats:sup>\u22121<\/jats:sup>\u2009s<jats:sup>\u22121<\/jats:sup> at 60 and 200 MHz, respectively, at 25\u2009\u00b0C). It packs six efficiently relaxing Gd<jats:sup>III<\/jats:sup> ions into a small molecular space, which leads, to the best of our knowledge, to the highest relaxivity per molecular mass ever reported for a Gd<jats:sup>III<\/jats:sup> complex. The [bpy(DTTA)<jats:sub>2<\/jats:sub>]<jats:sup>8\u2212<\/jats:sup> ligand is also a prime candidate as a terminal ligand for constructing larger sized, Fe<jats:sup>II<\/jats:sup> (or Ru<jats:sup>II<\/jats:sup>)\u2010based metallostars or metallodendrimers loaded with Gd<jats:sup>III<\/jats:sup> on the surface.<\/jats:p>","DOI":"10.1002\/chem.200500969","type":"journal-article","created":{"date-parts":[[2005,11,28]],"date-time":"2005-11-28T04:17:01Z","timestamp":1133151421000},"page":"989-1003","source":"Crossref","is-referenced-by-count":113,"title":["A Starburst\u2010Shaped Heterometallic Compound Incorporating Six Densely Packed Gd<sup>3+<\/sup> Ions"],"prefix":"10.1002","volume":"12","author":[{"given":"Jo\u00e3o Bruno","family":"Livramento","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ang\u00e9lique","family":"Sour","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alain","family":"Borel","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andr\u00e9 E.","family":"Merbach","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"\u00c9va","family":"T\u00f3th","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2006,1,13]]},"reference":[{"key":"e_1_2_6_1_2","doi-asserted-by":"publisher","DOI":"10.1021\/cr00081a003"},{"key":"e_1_2_6_2_2","doi-asserted-by":"publisher","DOI":"10.1021\/cr980440x"},{"key":"e_1_2_6_3_2","volume-title":"The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging","year":"2001"},{"key":"e_1_2_6_4_2","first-page":"45","volume-title":"The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging","author":"T\u00f3th \u00c9.","year":"2001"},{"key":"e_1_2_6_5_2","doi-asserted-by":"publisher","DOI":"10.1039\/b107456n"},{"key":"e_1_2_6_6_2","doi-asserted-by":"publisher","DOI":"10.1039\/B207713B"},{"key":"e_1_2_6_7_2","doi-asserted-by":"publisher","DOI":"10.1002\/chem.200204612"},{"key":"e_1_2_6_8_2","doi-asserted-by":"publisher","DOI":"10.1039\/b506702b"},{"key":"e_1_2_6_9_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic000563b"},{"key":"e_1_2_6_10_2","doi-asserted-by":"publisher","DOI":"10.1002\/1521-3765(20020301)8:5<1040::AID-CHEM1040>3.0.CO;2-D"},{"key":"e_1_2_6_11_2","doi-asserted-by":"publisher","DOI":"10.1002\/chem.200401326"},{"key":"e_1_2_6_12_2","doi-asserted-by":"publisher","DOI":"10.1007\/s00775-002-0353-3"},{"key":"e_1_2_6_13_2","author":"Torres S.","year":"2005","journal-title":"Chem. 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