DNA recognition site of anticancer tinidazole copper(II) complexes.

This paper describes the recognition process of tetrahedral [CuII(tnz)2X2] (X = Cl, Br) complexes by a DNA chain, analyzing the specific interaction between the DNA bases and backbone with the metal and the tinidazole (tnz) ligand. We identified the coordination of the copper metal center with one or two phosphates as the first recognition site for the tinidazole copper(II) complexes, while the ligands present partial intercalation into the minor groove. Also, we discuss a novel trigonal copper(I) tnz bromide complex, obtained by reducing the previously reported [Cu(tnz)2Br2]. This complex sheds light on the mechanism of action of tnz metal complexes as one of the most stable DNA-complex adducts depicts a trigonal geometry around the copper ion.

Intermediate Detection in the Casiopeina-Cysteine Interaction Ending in the Disulfide Bond Formation and Copper Reduction.

A strategy to improve the cancer therapies involves agents that cause the depletion of the endogenous antioxidant glutathione (GSH), increasing its efflux out of cells and inducing apoptosis in tumoral cells due to the presence of reactive oxygen species. It has been shown that Casiopeina copper complexes caused a dramatic intracellular GSH drop, forming disulfide bonds and reducing CuII to CuI. Herein, through the determination of the [CuII]-SH bond before reduction, we present evidence of the adduct between cysteine and one Casiopeina as an intermediate in the cystine formation and as a model to understand the anticancer activity of copper complexes. Evidence of such an intermediate has never been presented before.

Self-Assembly of Aluminum- and Gallium-Based meso-Metallaporphyrins.

The molecular meso-metallaporphyrin has been obtained from the reaction of AlMe3 with the bulky 4,5-(Ph2(HO)C)2-1,2,3-triazole (1). The presence of Al-Me groups coordinated to the triazole rings creates three different stereoisomers that were identified by single-crystal X-ray diffraction. Further studies revealed that, for steric reasons, only one of the two main stereoisomers is active in the polymerization of ε-caprolactone. When GaMe3 is used instead of AlMe3, a trimetallic species is formed instead of the meso-metallaporphyrin pointing to a metal-directed self-assembly. On the other hand, the reaction of the monolithium salt [{Li(THF)2}{κ2- N, N'-4,5-(Ph2(HO)C)-1,2,3-triazole}]2 (2; THF = tetrahydrofuran) with MCl3 (M = Al, Ga) yields meso-metallaporphyrin species with a lithium atom in the center of the metallacycle. While the gallium derivative is rather stable in solution, the aluminum analogue decomposes rapidly. In the solid state, continuous cationic columns running throughout the whole crystal are formed from alternating Li⊂[M]4 (M = Al, Ga) meso-metallaporphyrin and [Li(THF)4]+ cations. Density functional theory calculations determined that the weak Cl···H, H···H, N···H, and Cl···O interactions with a total interaction energy of -38.6 kcal·mol-1 are responsible for this unusual packing.

Origin of the Photoinduced Geometrical Change of Copper(I) Complexes from the Quantum Chemical Topology View.

Copper(I) complexes (CICs) are of great interest due to their applications as redox mediators and molecular switches. CICs present drastic geometrical change in their excited states, which interferes with their luminescence properties. The photophysical process has been extensively studied by several time-resolved methods to gain an understanding of the dynamics and mechanism of the torsion, which has been explained in terms of a Jahn-Teller effect. Here, we propose an alternative explanation for the photoinduced structural change of CICs, based on electron density redistribution. After photoexcitation of a CIC (S0 →S1 ), a metal-to-ligand charge transfer stabilizes the ligand and destabilizes the metal. A subsequent electron transfer, through an intersystem crossing process, followed by an internal conversion (S1 →T2 →T1 ), intensifies the energetic differences between the metal and ligand within the complex. The energy profile of each state is the result of the balance between metal and ligand energy changes. The loss of electrons originates an increase in the attractive potential energy within the copper basin, which is not compensated by the associated reduction of the repulsive atomic potential. To counterbalance the atomic destabilization, the valence shell of the copper center is polarized (defined by ∇2 ρ(r) and ∇2 Vne (r)) during the deactivation path. This polarization increases the magnitude of the intra-atomic nuclear-electron interactions within the copper atom and provokes the flattening of the structure to obtain the geometry with the maximum interaction between the charge depletions of the metal and the charge concentrations of the ligand.

Synthesis of Cyclic and Cage Borosilicates Based on Boronic Acids and Acetoxysilylalkoxides. Experimental and Computational Studies of the Stability Difference of Six- and Eight-Membered Rings.

A series of borosilicates was synthesized, where the structure of the borosilicate core was easily modulated using two strategies: blocking of condensation sites and controlling the stoichiometry of the reaction. Thus, on the one hand, the condensation of phenylboronic or 3-hydroxyphenylboronic acid with diacetoxysilylalkoxide [(tBuO)(Ph3CO)Si(OAc)2] led to the formation of borosilicates (tBuO)(Ph3CO)Si{(µ-O)BPh}2(µ-O) (1), [{(tBuO)(Ph3CO)Si(µ-O)BPh(µ-O)}2] (2), and [{(tBuO)(Ph3CO)Si(µ-O)B(3-HOPh)(µ-O)}2] (3) with a cyclic inorganic B2SiO3 or B2Si2O4 core, respectively. On the other hand, the reaction of phenylboronic acid with triacetoxysilylalkoxide (Ph3CO)Si(OAc)3 in 3:2 ratio resulted in the formation of a cagelike structure [{(Ph3CO)Si(µ-O)2BPh(µ-O)}2] (4) with B4Si4O10 core, while the reaction of the boronic acid with silicon tetraacetate generated an unusual 1,3-bis(acetate)-1,3-diphenyldiboraxane PhB(µ-O)(µ-O,O'-OAc)2BPh (5). Additionally, compound 1 was used to evaluate the possibility to form N→B donor-acceptor bond between the boron atom in the borosilicates and a nitrogen donor. Thus, coordination of 1 with piperazine yielded a tricyclic [{(tBuO)(Ph3CO)Si(OBPh)2(µ-O)}2·C4H10N2] compound 6 with two borosilicate rings bridged by a piperazine molecule. Finally, the processes involved in the formation of the six- and eight-membered rings (B2SiO3 and B2Si2O4) in compounds 1 and 2 were explored using solution 1H NMR studies and density functional theory calculations. These molecules represent to the best of our knowledge first examples of cyclic molecular borosilicates containing SiO4 units.