MOLECULAR AND CRYSTAL-STRUCTURES OF 2 CHELATING-AGENTS FOR USE IN MRI CONTRAST AGENTS

1,7-Bis-[(N-benzylcarbamoyl)methyl]-1,4,7-triazaheptane-1,4,7-triacetic acid dihydrate, DTPA-BBA, C28H41N5O10, crystallizes in the monoclinic space group P2(1)/a, Z = 4 with unit cell dimensions a = 18.019(5), b = 7.204(1), c = 24.288(7) angstrom, beta = 99.26(2)-degrees. R = 0.034 for 1916 unique reflections. 1,7-Bis-[(N-methyl-carbamoyl)methyl]-1,4,7-triazaheptane-1,4,7-triacetic acid dihydrate, DTPA-BMA, C16H33N5O10, crystallizes in the monoclinic space group P2(1)/c, Z = 4 with unit cell dimensions a = 17.472(4), b = 7.110(2), c = 17.846(2) angstrom, beta = 96.02(1)-degrees. R = 0.043 for 4513 unique reflections. There are two intramolecular hydrogen bonds in both molecules, which give them a folded conformation. The molecules crystallize as zwitterions with the central of the three amine nitrogen atoms (N3) protonated. An extensive hydrogen-bonding network is found for both structures, including a short unsymmetrical carboxyl-carboxylate hydrogen bond, 2.522(3) angstrom (DTPA-BBA) and 2.504(2) angstrom (DTPA-BMA), respectively, and an almost equally short carboxyl-water hydrogen bond, 2.570(4) angstrom (DTPA-BBA) and 2.575(2) angstrom (DTPA-BMA), respectively.