Giovana G. Nunes

Synthesis, characterization and chemoprotective activity of polyoxovanadates against DNA alkylation

The alkylation of pUC19 plasmid DNA has been employed as a model reaction for the first studies on chemoprotective action by a mixed-valence (+IV/+V) polyoxovanadate. A new, non-hydrothermal route for the high yield preparation of the test compound is described. The deep green, microcrystalline solid A was isolated after a three-day reaction in water at 80°C and 1 atm, while the reaction at 100°C gave green crystals of B. Both solids were structurally characterized by X-ray diffractometry and FTIR, EPR, NMR and Raman spectroscopies. Product A was identified as (NH(4))(2)V(3)O(8), while B corresponds to the spherical polyoxoanion [V(15)O(36)(Cl)](6-), isolated as the NMe(4)(+) salt. The lack of solubility of A in water and buffers prevented its use in DNA interaction studies, which were then carried out with B. Complex B was also tested for its ability to react with DNA alkylating agents by incubation with diethylsulphate (DES) and dimethylsulphate (DMS) in both the absence and presence of pUC19. For DMS, the best results were obtained with 10 mM of B (48% protection); with DES, this percentage increased to 70%. The direct reaction of B with increasing amounts of DMS in both buffered (PIPES 50 mM) and non-buffered aqueous solutions revealed the sequential formation of several vanadium(IV), vanadium(V) and mixed-valence aggregates of different nuclearities, whose relevance to the DNA-protecting activity is discussed.

Novel double alkoxides of titanium(IV) and iron(II)/(III): synthetic, structural and spectroscopic studies

The first structurally characterised titanium and iron polynuclear isopropoxides [FeCl{Ti2(OPri)9}], 1, and [Ti3(OMe)2(OPri)9][Fe4TiCl4(O)(OPri)9], 2, have been prepared from 2 : 1 : 1 mixtures of [Ti(OPri)4], K(OPri) and FeCl2. Their identity was confirmed by a number of chemical and physical methods including X-ray diffractometry. Semiempirical quantum mechanical calculations were consistent with an S = 2 ground state for 1. Structural and spectroscopic data support a mixed-valence formulation for the unique {Fe4Ti} anion in 2.

Adding remnant magnetization and anisotropic exchange to propeller-like single-molecule magnets through chemical design.

The selective replacement of the central iron(III) ion with vanadium(III) in a tetrairon(III) propeller-shaped single-molecule magnet has allowed us to increase the ground spin state from S=5 to S=13/2. As a consequence of the pronounced anisotropy of vanadium(III), the blocking temperature for the magnetization has doubled. Moreover, a significant remnant magnetization, practically absent in the parent homometallic molecule, has been achieved owing to the suppression of zero-field tunneling of the magnetization for the half-integer molecular spin. Interestingly, the contribution of vanadium(III) to the magnetic anisotropy barrier occurs through the anisotropic exchange interaction with iron(III) spins and not through single ion anisotropy as in most single-molecule magnets.

Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

i ) 9 }) (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO 3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mossbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 o C in the HNO 3 - containing system, leading to the detection of ilmenite (FeTiO 3 ). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.

The first hetero-binuclear alkoxide of iron and vanadium: structural and spectroscopic features

Abstract The immediate reaction between [V2(μ-OPri)2(OPri)6] (A) and [Fe2(μ-I)2I2(HOPri)4] (B) in toluene/propan-2-ol gives the novel mixed-metal [FeI2(μ-OPri)2V(OPri)2(HOPri)] (C). Structural, spectroscopic and magnetochemical characterisation are all consistent with a non-oxo vanadium(IV)/high-spin iron(II) formulation; variable-temperature X-band EPR spectra reveal an S=1/2↔S=1 equilibrium involving the vanadium centres in propan-2-ol solution.

New titanium(IV) and vanadium(IV) haloalkoxides: synthetic route and structural characterisation

The novel binuclear titanium(IV) complex [{TiCl(OPri)2(HOPri )}2(m-OPri)2], 1, and the first mononuclear vanadyl(IV) chloroalcoholate [VCl(O)(HOPri)4]Cl, 2, have been prepared from 2:1:1 mixtures of [Ti(OPri)4], KOPri and VCl3. Products were characterised by elemental analysis, FTIR, EPR, NMR and electronic spectroscopies, magnetic susceptibility measurements and single crystal X-ray diffractometry. A third product was found to be polynuclear and to contain both titanium and vanadium. Semi-empirical quantum-mechanical calculations were carried out for the evaluation of the electronic structure of 1.

Catalytic Activity of a Titanium(IV)/Iron(II) Heterometallic Alkoxide in the Ring‑Opening Polymerization of ε‑Caprolactone and rac‑Lactide

The activity of the heterometallic alkoxide [FeCl{Ti2(OiPr)9}] (1) towards polymerization of rac-lactide (rac-LA) and e-caprolactone (e-CL) was investigated in toluene solution and in bulk at various temperatures, monomer/heterometallic alkoxide molar ratio and reaction times. The alkoxide 1 was active in solution for e-CL and in bulk for both monomers. Polymers were obtained in good yields with molecular weights ranging from 3890 to 15000 g moL-1 and polydispersity indexes (PDI) values varying from 1.3 to 2.5. Based on the 1H nuclear magnetic resonance (NMR) end-group analysis of polymers, a coordination-insertion mechanism was suggested for both monomers. The average number of growing chains per molecule of initiator (4 to 5 for rac-LA and 7 to 8 for e-CL) indicates that both bridging and terminal isopropoxides are active initiating groups. Kinetic studies with e-CL indicated that the polymerization rate is first order with respect to monomer concentration. The catalytic properties of 1 were compared to those found for other titanium(IV) and iron(II) complexes using e-CL as a model monomer.

Magneto-V1: um programa para o cálculo de correções diamagnéticas e de momentos magnéticos efetivos

A new computer program has been developed to help the users of force methods for magnetic moment determination. It provides a user-friendly interface for the calculation of corrected magnetic susceptibilities of paramagnetic materials and enables the user to simulate a number of chemical formulations for the sample under study. The program is written in the Perl scripting language and runs on a Unix platform.

Crystal structures of two deca­vanadates(V) with penta­aqua­manganese(II) pendant groups: (NMe4)2[V10O28{Mn(H2O)5}2]·5H2O and [NH3C(CH2OH)3]2[V10O28{Mn(H2O)5}2]·2H2O

Two heterometallic decavanadate(V) hydrated salts with tetramethylammonium and [tris(hydroxymethyl)methyl]ammonium counter-cations have been synthesized under mild reaction conditions in an aqueous medium. Both polyanions present two [Mn(OH2)5]2+ complex units bound to the decavanadate cluster through oxide bridges.

Termocromismo em soluções de alcóxidos de Vanádio(IV): uma abordagem pela modelagem molecular

The thermochromic behavior exhibited by vanadium(IV) alkoxides, [V2(μ-OPri)2(OPri) 6] and [V2(μ-ONep)2(ONep)6 ], OPri = isopropoxide and ONep = neopentoxide, was studied by molecular modeling using DFT, TDDFT and INDO/S methods. The vibrational and electronic spectra calculated for [V2(μ-OPri)2(OPri) 6] were very similar to the experimental data registered for crystalline samples of the complex and for its solutions at low temperature ( 315 K) were compatible with those calculated for the monomeric form, [V(OPri)4]. These results consistently point to a monomer/dimer equilibrium as an explanation for the solution thermochromism of {V(OPri)4}n. In spite of the structural similarity between [V2(μ-ONep)2(ONep)6 ] and [V2(μ-OPri)2(OPri) 6] in the solid state, the thermochromic behavior of the former could not be explained by the same model, and the possibility of tetranuclear aggregation at low temperatures was also investigated.