The assembly of Cd(L1)— {L13— = NCH2CH2N=C(CH3)COO—3} into the tetranuclear cluster {Cd(L1)Na(H2O)2}2 in the presence of Na+ is mediated by Na+‐carboxylate interactions; in contrast In3+ and Fe3+ ...induce the partial hydrolysis of L13— to afford the complexes In(L2)Cl and {Fe(L2)2O} {L22— = NCH2CH2NH2CH2CH2N=C(CH3)COO—2} which aggregate via intermolecular H‐bonding.
Der Effekt partieller Hydrolyse beim Wechsel der Art der intermolekularen Bindung zwischen Metall‐Komplexen
Die Umwandlung von Cd(L1)— (L13— = NCH2CH2N=C(CH3)COO—3) in den vierkernigen Cluster {Cd(L1)Na(H2O)2}2 in Anwesenheit von Na+ wird durch Na+‐Carboxylat‐Wechselwirkungen vermittelt. Im Gegensatz hierzu induzieren In3+ und Fe3+ die partielle Hydrolyse von L13— unter Bildung der Komplexe In(L2)Cl und {Fe(L2)2O} (L22— = NCH2CH2NH2CH2CH2N=C(CH3)COO—2 ), die über intermolekulare Wasserstoffbrücken‐Bindungen aggregieren.
Tris(2‐succinimidoethyl)amine hydrate (1/0.075) Blake, Alexander J.; Doble, Dan M. J.; Li, Wan‐Sheung ...
Acta crystallographica. Section E, Structure reports online,
August 2001, Letnik:
57, Številka:
8
Journal Article
Recenzirano
The title compound, C18H24N4O6·0.075H2O, (I), was prepared as part of a research programme to prepare and identify new tripodal ligands which exhibit instability at low pH, thereby releasing ...coordinated metal cations under such conditions. Each molecule lies on a crystallographic threefold axis with the three arms arranged in the form of a claw. Angles within the five‐membered succinimide ring, where the r.m.s. deviation of the five atoms from the least‐squares ring plane is only 0.004 Å, vary from 104.8 (3)° at a methylene C atom to 112.7 (3)° at the formally sp2 N atom. The structure contains a partially occupied disordered water molecule, the source of which is presumably the water produced as a by‐product of the synthetic reaction.
The thermodynamic selectivity for Gd3+ relative to Ca2+, Zn2+, and Fe3+ of two ligands of potential interest as magnetic resonance imaging (MRI) contrast agents has been determined by NMR ...spectroscopy and potentiometric and spectrophotometric titration. The two hexadentate ligands TREN-6-Me-3,2-HOPO (H3 L2) and TREN-bisHOPO-TAM-EA (H4 L3) incorporate 2,3-dihydroxypyridonate and 2,3-dihydroxyterephthalamide moieties. They were chosen to span a range of basicity while maintaining a structural motif similar to that of the parent ligand, TREN-1-Me-3,2-HOPO (H3 L1), in order to investigate the effect of the ligand basicity on its selectivity. The 1:1 stability constants (β110) at 25 °C and 0.1 M KCl are as follows. L2: Gd3+, 20.3; Ca2+, 7.4; Zn2+, 11.9; Fe3+, 27.9. L3: Gd3+, 24.3; Ca2+, 5.2; Zn2+, 14.6; Fe3+, 35.1. At physiological pH, the selectivity of the ligand for Gd3+ over Ca2+ increases with the basicity of the ligand and decreases for Gd3+ over Fe3+. These trends are consistent with the relative acidities of the various metal ions; more basic ligands favor harder metals with a higher charge-to-radius ratio. The stabilities of the Zn2+ complexes do not correlate with basicity and are thought to be more influenced by geometric factors. The selectivities of these ligands are superior to those of the octadentate poly(aminocarboxylate) ligands that are currently used as MRI contrast agents in diagnostic medicine.
The synthesis and relaxometric properties of hetero-tripodal hydroxypyridonate-terephthalamide gadolinium (Gd3+) chelates with differing structural features for probing human serum albumin (HSA) ...interactions are reported. The Gd3+ complexes are divided into two series. The first series (3−5) features a benzyl derivative connected to the hydroxypyridonate (HOPO) moiety. The second series of complexes (6−10) has the common feature of a poly(ethylene glycol) (PEG) attached to the terephthalamide (TAM) moiety and is nonbenzylated. The water exchange of the complexes is in the fast exchange regime with rates (k ex) in the range 0.45−1.11 × 108 s-1. The complexes have a moderate interaction with HSA with association constants (K A's) in the range 0.7−8.6 × 103 M-1. Protein binding results in an enhancement in proton relaxivity from 7.7−10.4 mM-1 s-1 (r 1p) to 15−29 mM-1 s-1 (r 1p b). It is concluded that the interaction of the complexes with HSA (i) is enhanced by the presence of benzyl groups, (ii) is entropically driven, and (iii) results in a lower hydration number (q).
Template in Form von Lanthanoid‐, Hauptgruppen‐ und Nebengruppenmetallionen ermöglichen die Bildung verschiedener mehrkerniger Käfige aus M(L) (M=Ni, Mn; (L)2−=CH2CH2N=C(CH3)COO−2). Mit Lanthan führt ...die Templatsynthese zu einem ikosaedrisch koordinierten LaIII‐Ion, das von sechs Ni(L)‐Einheiten eingeschlossen wird. Mit Natrium hingegen entsteht ein dreifach überdachter, prismatischer {Ni(L)}9‐Käfig, der vier Na+‐Ionen im Innern enthält. Mit Mangan schließlich konnte ein von sechs Mn(L)‐Fragmenten koordiniertes MnII‐Ion erhalten werden, das in eine verzerrte, trigonal‐prismatische Anordnung eingebettet ist (siehe Bild).
The aggregates {Zn(L
1)H
2O}
∞ and {Y(L
2)
4Na
3(H
2O)
2(MeOH)
1.2}(NO
3)
3·2H
2O·5.6MeOH have been assembled from complexes of imino–phosphonate monoester ligands L
1
2− {CH
2CH
2NC(CH
3)PO
2(OMe)
...2}
2− and L
2
3− {NCH
2CH
2NC(CH
3)PO
2(OMe)
3}
3−, the topology of these materials differing from that of their imino–carboxylate analogues.
The aggregation of complexes of imino–phosphonate monoester ligands has been investigated. The aggregates {Zn(L
1)H
2O}
∞ and {Y(L
2)
4Na
3(H
2O)
2(MeOH)
1.2}(NO
3)
3·2H
2O·5.6MeOH, assembled from complexes of imino–phosphonate monoester ligands L
1
2− {CH
2CH
2NC(CH
3)PO
2(OMe)
2}
2− and L
2
3− {NCH
2CH
2NC(CH
3)PO
2(OMe)
3}
3−, show chain structures controlled by the hybridisation at the phosponate ligands.
