Two new heteroleptic pentacoordinated Zn(II) complexes (1 and 2) containing 4,4 0 -disubstituted 2,2 0bipyridines as the main ligand and curcumin (curc) as an ancillary ligand have been synthesized, spectroscopically and structurally characterized, and tested in vitro towards different human cancer cell lines. While the nitrogen ligands are almost inactive, Zn(II) curc derivatives 1 and 2 show promising and selective anticancer properties. In particular the curc Zn(II) complex 1 shows the strongest growth inhibition in all cell lines, being even more effective than the pure curc in the LAN-5 neuroblastoma cell line. Furthermore, the curc moiety makes the complexes 1 and 2 fluorescent, a feature enabling investigation of their interaction with DNA through a new optical method previously tested with the reference fluorescent intercalator ethidium bromide. This analysis demonstrates that the interaction mode of curc, 1 and 2 with DNA in the double helix favors their alignment perpendicular to the DNA axis, suggesting a partial inter-base intercalation of these Zn(II) complexes.

Ammonia is a low-cost and potentially valuable building block for almost every nitrogen-containing compound required by industry. There is an obvious interest in utilizing this chemical as feedstock in catalytic organic transformations to produce higher-value products, an issue that has began to be explored with some degree of success.[1] However, most of late transition metal catalyzed reactions do not occur with ammonia. Several factors have been invoked to explain this lack of reactivity: [2] 1) The high strength of the NÀH bond of ammonia (107 kcal mol À1 ) makes its activation very difficult to achieve by metal centers; 2) the catalyst often deactivates through the formation of stable Werner ammine (M ! NH 3 ) adducts; and 3) the low acidity of ammonia prevents its participation in proton exchange reactions that could lead to NÀH activation.In order to achieve a metal-mediated functionalization of ammonia, an imperative requisite should be the formation of M À NH 2 bonds directly from ammonia (i.e. rather than leading to stable M ! NH 3 adducts).[3] So far, only few early examples involving interaction of NH 3 with iridium complexes followed an oxidative addition profile.[4] This concept was elegantly illustrated by Hartwig et al., who reported on the formal oxidative addition of ammonia to an electron-rich Ir I pincer system, leading to the first structurally characterized terminal amido hydrido Ir III complex. [5] In spite of the efficacy of this N À H activation, uptake and homolytic breakage of ammonia by late transition metal complexes still remains a difficult goal.[6] We assumed that a good approach to induce the formation of M À NH 2 bonds, circumventing the formation of Werner adducts, should rely on an appropriate design of organometallic precursors. Herein we report on a synthetic protocol that uses gaseous ammonia as "NH 2 " source to generate stable novel parent bridging and terminal amido Rh I and Ir I complexes under very mild conditions. We chose as metallic precursors dinuclear complexes bearing alkoxo-bridging ligands, well suited to induce NÀH activation. [7] In this way, treatment of the methoxo-bridged compounds [{M(m-OMe)(tfbb)} 2 ] (M = Rh, Ir; tfbb = tetrafluorobenzobarrelene) with gaseous ammonia in diethyl ether at atmospheric pressure rapidly afforded the parent amidobridged trinuclear complexes [{M(m 2 -NH 2 )(tfbb)} 3 ] (M = Rh (1), Ir (2)) which were isolated in good yields. On the other hand, reactions of the cod complexes [{M(m-OMe)(cod)} 2 ] (cod = 1,5-cycloctadiene) with gaseous ammonia yielded dinuclear amido-bridged complexes [{M(m-NH 2 )(cod)} 2 ] (M = Rh (3), Ir (4)) in excellent yields (Scheme 1). All the reactions leading to complexes 1-4 were found to be reversible. For example, monitoring by NMR spectroscopy the reaction of 3 with MeOH in a 1:1 ratio in [D 6 ]benzene showed upon 10 min, when the equilibrium was considered to be reached, the presence of unchanged 3, the original methoxo-bridged complex [{Rh(m-OMe)(cod)} 2 ] and the mixed amido-alkoxo species [{Rh(co...

Upon cooling, the aperiodic inclusion compound n-nonadecane/urea presents a hexagonal-to-orthorhombic group-subgroup phase transition at T cl that increases the structure's superspace dimensionality from four to five. This paper reports on pretransitional phenomena in such a high-dimensional space, generalizing the critical results previously reported at a lower dimensionality. Very high-resolution diffraction data reveal anomalously large correlation lengths along the aperiodic direction, with all correlation lengths diverging at T cl . This could be explained by low-frequency phason excitations that soften at T cl at the critical wave vector, in accordance with an increase in the critical diffuse scattering intensity. The physics of phase transitions in crystalline materials was studied extensively during the last decades of the 20th century. With respect to group-subgroup structural instabilities, the order parameters, as measures of symmetry breaking, as well as related critical phenomena, were derived and measured.