The thermodynamic stability of Fe(III) complexes with a new hexadentate tripodal ligand (O-TRENSOX) incorporating three 8-hydroxyquinoline ("oxine") subunits, linked to a tetraamine ("TREN") via an amide connection, has been investigated by the use of UV-vis spectrophotometry and potentiometric methods. O-TRENSOX has been found to form, at pH < 1, a protonated complex FeLH 5 2+ (orange color) which deprotonates, over the pH range 1-2, to a green complex FeLH 2through a four-proton process. The first protonation constant of ferric O-TRENSOX has been determined to be 5.60. The stability constant log β 110 has been determined to be 30.9. A pFe (pFe ) -log [Fe 3+ ]) value of 29.5 has been calculated at pH ) 7.4, [ligand] tot ) 10 µΜ, and [Fe 3+ ] tot ) 1 µM, indicating that O-TRENSOX is one of the most powerful among the iron synthetic chelators. Cyclic voltammetry experiments have shown that the system Fe III -O-TRENSOX/Fe II -O-TRENSOX is quasi reversible, with a redox potential of 0.087 V vs NHE. This value is related to the high complexing ability of O-TRENSOX for both the ferric and ferrous iron redox states, making it relevant for biological uses. The kinetics of formation and acid hydrolysis of the ferric O-TRENSOX complex have been investigated in acidic medium using the diode array stopped-flow spectrophotometry technique in 2.0 M NaClO 4 /HClO 4 at 25 °C. The determining step for the complex formation involves the reaction of FeOH 2+ with the LH 7 + ligand species, with a rate constant of 789 ( 17 M -1 s -1 . The acid hydrolysis of the FeLH 2complex in 0.02-1.0 M HClO 4 and ionic strength 2.0 M NaClO 4 /HClO 4 leads to the FeLH 5 2+ complex, indicating that O-TRENSOX is a very strong chelating agent for Fe(III) in acidic medium. The kinetic data have been interpreted by a stepwise mechanism related to the successive protonation of four binding sites. The spectroscopic change is consistent with removal of one arm of the ligand followed by a shift from a bis(oxinate) to a bis(salicylate) mode of coordination.

A novel type of cryptation involving only the r-binding sites of the cavity [2.2.2]paracyclophane is evidenced through solubility and 'H NMR studies. The stability constant, in methanol, of the 1:l complex of [2.2.2]paracyclophane with silver triflate is approximately 100-fold higher than those of the usual r-charge-transfer complexes of arenes with silver cation. The well-defined, sharp-melting, crystalline, 1 : 1 complex has been isolated and characterized.

We investigated the effects of a new iron chelator, O-Trensox (TRX), compared with desferrioxamine (DFO), on proliferation and apoptosis in cultures of the human hepatoblastoma HepG2 and hepatocarcinoma HBG cell lines. Our results show that TRX decreased DNA synthesis in a time- and dose-dependent manner and with a higher efficiency than DFO. Mitotic index was also strongly decreased by TRX and, unexpectedly, DFO inhibited mitotic activity to the same extent as TRX, thus there is a discrepancy between the slight reduction in DNA synthesis and a large decrease in mitotic index after DFO treatment. In addition, we found that TRX induced accumulation of cells in the G(1) and G(2) phases of the cell cycle whereas DFO arrested cells in G(1) and during progression through S phase. These data suggest that the partial inhibition of DNA replication observed after exposure to DFO may be due to a lower efficiency of metal chelation and/or that it does not inhibit the G(1)/S transition but arrests cells in late S phase. The effects of both TRX and DFO on DNA synthesis and mitotic index were reversible after removing the chelators from the culture medium. An apoptotic effect of TRX was strongly suggested by analysis of DNA content by flow cytometry, nuclear fragmentation and DNA degradation in oligonucleosomes and confirmed by the induction of a high level of caspase 3-like activity. TRX induced apoptosis in a dose- and time-dependent manner in proliferating HepG2 cells. In HBG cells, TRX induced apoptosis in proliferating and confluent cells arrested in the G(1) phase of the cell cycle, demonstrating that inhibition of proliferation and induction of apoptosis occurred independently. DFO induced DNA alterations only at concentrations >100 microM and without induction of caspase 3-like activity, indicating that DFO is not a strong inducer of apoptosis. Addition of Fe or Zn to the culture medium during TRX treatment led to a complete restoration of proliferation rate and inhibition of apoptosis, demonstrating that Fe/Zn-saturated TRX was not toxic in the absence of metal depletion. These data show that TRX, at concentrations of 20-50 microM, strongly inhibits cell proliferation and induces apoptosis in proliferating and non-proliferating HepG2 and HBG cells, respectively.

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The interest in synthetic siderophore mimics includes therapeutic applications (iron chelation therapy), the design of more effective agents to deliver Fe to plants and the development of new chemical tools for studies of iron metabolism and for a better understanding of iron assimilation processes in living systems. The 8-hydroxyquinoline bidentate chelate moiety offers an alternative to the usual hydroxamic acid, catechol and/or alpha-hydroxycarboxylic acid metal-binding groups encountered in natural siderophores. The promising results obtained by the tris hydroxyquinoline-based ligand O-TRENSOX are summarized. O-TRENSOX exhibits a high and selective affinity for Fe(III) complexation. Its efficiency in delivering Fe to plants as well as its efficiency for iron mobilization, cellular protection and antiproliferative effects have been evidenced. Other chelators of the O-TRENSOX family (mixed catechol / 8-hydroxyquinoline ligands, lipophilic ligands) are also described. Some results question whether the use of partition coefficients is pertinent to foresee the activity of iron chelators. The development of probes (fluorescent, radioactive, spin labelled) based on the O-TRENSOX backbone is in progress. 8-hydroxyquinoline iron chelators seem to have a promising future.

tures were refined to R values of 0.076 (I) and 0.062 (It) for 1245 and 1495 intensities respectively. In both cases, the conformations of the paracyclophane molecules are similar with respect to the orientation of the three aromatic rings around a threefold pseudo-axis of symmetry, the rings being parallel to that axis. In the complex, the Ag + ion lies on the threefold pseudo-axis, slightly off the cavity formed by the three rings.

New tripodal gem-(bis-phosphonates) uranophiles were discovered by a screening method that allowed for the selection of ligands with strong uranyl-binding properties in a convenient microtiter-plate format. The method is based on competitive uranium binding by using Sulfochlorophenol S as chromogenic chelate. This dye compound was found to present high uranyl complexation properties and allowed to highlight ligands presenting association constants for UO(2+)(2) up to 10(18) at pH 7.4 and 10(20) at pH 9. A collection of 40 known ligands including polycarboxylate, hydroxamate, catecholate, hydroxypyridonate and hydroxyquinoline derivatives was tested. Also screened was a combinatorial library prepared from seven amine scaffolds and eight acrylates bearing diverse chelating moieties. Among these 96 tested candidates, a tripod derivative bearing gem-bis-phosphonates moieties was found to present the highest complexation properties over a wide range of pH and was further studied.