Publications

A novel tetrameric tetra[O-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)]-pentaerythritol (TBTP) has been synthesized using click chemistry strategy. TBTP was characterized and used as ligand to form new Cu(II) complexes, forming 1-D coordination polymers. Two square planar complexes were characterized by single-crystal X-ray diffraction, presenting formula [Cu(TBTP)][Cu(NO3)4] (1) and [Cu(TBTP)](NO3)2 (2). In both structures, a cationic 1-D coordination polymer (CP) has been formed. The CP contain a 1:1 Cu(II)/TBTP ratio with four neutral triazole groups coordinating the Cu(II) center, forming a CuN bonds ranging 1.988(2)–2.001(2) Å. The study of the magnetic properties of compounds 1 and 2 pointed to an antiferromagnetic behavior for both compounds, defined by inter- and intra-chain dipolar interactions among their metallic centers. In addition, the complex 1 was found to be an efficient catalyst for selective oxidation of aniline to azobenzene under mild reaction conditions.

We employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.

Calcium phosphates are suggested as a CO2 adsorbent via pressure swing adsorption. Amorphous calcium phosphate (ACP) and biphasic calcium phosphate (BCP) (composed of hydroxyapatite and beta-tricalcium phosphate) were investigated for the capture/immobilization of the gas. A fluidized bed was set up to assess the levels of CO2 adsorption by ACP and BCP. A gaseous mixture was synthesized, mimicking the conditions for possible industrial use. The results show a significant reduction in CO2 concentrations. Using DFT calculations, we show that CO2 adsorption increases the stability by reducing the surface energy. The energies involved and preferential adsorption sites were also theoretically predicted.

Four new organoruthenium complexes with formula [RuCl(η6-p-cymene)(μ-FCZ)]2[Cl]2 (1), [RuCl(FCZ)(η6-p-cymene)(PPh3)]PF6 (2), [RuCl(CTZ)(η6-p-cymene)(PPh3)]PF6 (3) and [RuCl(KTZ)(η6-p-cymene)(PPh3)]PF6 (4) (where FCZ: 2-(2,4-difluorophenyl)-1,3-di(1H-1,2,4-triazol-1-yl)-2-propanol, CTZ: 1-[(2-chlorophenyl)-diphenylmethyl-1H-imidazole] and KTZ: cis-1-acetyl-4-[4-[[2-(2,4-dichlorophenyl)-2-(1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl]piperazine) were synthesized, characterized and evaluated as potential inhibitors for Leishmania amazonensis growth by widely reported methods. Complexes 3 and 4 displayed effective IC50 activities against Leishmania amazonensis promastigotes and intracellular amastigotes in the range of nanomolar concentration. Scanning and transmission electron microscopy analysis of Leishmania amazonensis promastigotes after treatment with 300 or 500 nM of complexes 3 and 4 for 48 h showed morphological alterations in the cell surface, a shortening of the flagellum, loss of mitochondrial matrix, disorganization of the kDNA and abnormal chromatin condensation. Thus, our strategy of incorporating a ruthenium atom into the structure of clinical drugs to improve their efficacy continues to demonstrate suitability for metallodrug discovery purposes.

The phase behavior of a two dimensional fluid confined within hydrophobic walls is obtained by Monte Carlo simulations. The fluid is described by the associating lattice gas model which reproduces the density and diffusion anomalous behavior of water. The confined fluid exhibits a liquid-liquid critical temperature which decreases with the decrease of the distance between the confining walls. In contact with the wall a dewetting is observed. The thickness of this interfacial layer is independent of the distance between the two walls. Even for very small distances between the two walls no total depletion is observed and consequently no drying transition is present.

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of eccentricity at 300 K. We found a water structural transition between tubular-like to single-file for (7,7) nanotubes associated with change from a high to low mobility regimes. Water is frozen when confined in a perfect (9,9) nanotube and it becomes liquid if such a nanotube is deformed above a certain threshold. Water diffusion enhancement (suppression) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is an important ingredient when considering the dynamical and structural properties of confined water.

Phenazine derivative molecules were studied using steady state and time resolved fluorescence techniques and demonstrated to lead to strong formation of aggregated species, identified as dimers by time dependent density functional theory calculations. Blended films in a matrix of Zeonex®, produced at different concentrations, showed different contributions of dimer and monomer emissions in a prompt time frame, e.g. less than 50 ns. In contrast, the phosphorescence (e.g. emission from the triplet state) shows no significant effect on dimer formation, although strong dependence of the phosphorescence intensity on concentration is observed, leading to phosphorescence being quenched at higher concentration.

In this study, we report on the selective esterification of the carboxyl group in a coordinated ligand based on the Fischer reaction. The new [Ru(N–O)(bipy)(dppb)]PF6 complex 1 was used as a precursor to obtain the ester derivative [Ru(N–Oet)(bipy)(dppb)]PF6 (2), and in order to establish the influence of either the free carboxyl group or the ethoxycarbonyl group on biological properties, the [Ru(pic)(bipy)(dppb)]PF6 complex (3) was synthesized for comparison (dppb = 1,4-bis(diphenylphosphino)butane, bipy = 2,2′-bipyridine, N–O = mono-deprotonated 2,4-pyridinedicarboxylic acid, N–Oet = 4-ethoxycarbonyl-2-pyridinecarboxylic acid). All three complexes interact weakly with human serum albumin (HSA) with Kb values ranging from 101–104 M−1, suggesting a spontaneous interaction with this protein by electrostatic (1–2) or van der Waals interactions (3). Moreover, complex/DNA-binding experiments indicate that complexes 2 and 3 interact weakly with DNA, while no interaction is observed between complex 1 and DNA, probably due to the repulsion involving the free carboxylate group/DNA-phosphate. Anti-Mycobacterium tuberculosis (MTB) activity and cytotoxicity assays against one normal cell line V79 (hamster fibroblast) and three human cancer cell lines A549 (lung), MCF7 and MDA-MB-231 (breast) revealed that complexes 2 and 3 exhibit good activity against MTB and tumor cells, presenting high cytotoxicity (low IC50). On the other hand, complex 1 is practically inactive. Therefore, the best biological results found for complex 2 can be attributed to its esterification, improving the lipophilicity and cellular uptake, in order to facilitate its passive permeation through the tumor cell membranes allowing for cell death, as well as DNA and HSA interactions, when compared with complex 1.

The aim of this work was to study the synthesis of molecularly imprinted polymers (MIPs) for the selective adsorption of β-estradiol (E2). For this, six solvents with different polarities were tested and the results indicated that, for obtaining a good E2 adsorbent, the solvent should be moderately polar to favor the formation of a monomer–template complex during the synthesis. Synthesis with acetonitrile (ACN) or a mixture of chloroform (CFM) and dimethylsulfoxide (DMSO) 1 : 1 led to higher E2 adsorption capacities (from 26 to 37 mg g−1). The use of MIP-CFM:DMSO resulted in better results than that of MIP-ACN relative to their NIPs (about 3 times more for CFM:DMSO, compared to 1.5 times for ACN) for the adsorption capacities. This can be explained by the fact that ACN is a porogen solvent, which on one hand increased the area of the adsorbent material but on the other reduced its selectivity towards E2 adsorption.

This paper presents a new approach for the analysis of AC conductivity, =  + , in disordered solids which brings together the quasi-universal frequency-dependent conductivity and the idea of a Gaussian distributions of probable activation energy barriers for hopping carriers. An explicit expression for AC conductivity was obtained using a complex dielectric response function and a continuous time random walk treatment applied to a lattice obeying the Kubo’s fluctuation-dissipation theorem. This expression provides an insight into the universality of the form and (k is the dielectric constant), as well into the effect of the Gaussian disorder on exponent s. We discuss the similarities and differences with the Random Free Energy Barrier model equivalent to the long-used box model, and it brings support to an extending expression proposed by J C Dyre and one of the authors. The applicability of the model to experimental observations on poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] reveals the dielectric constant, mean energy and variance of the Gaussian distribution for hopping carriers in this disordered conjugated polymer.

Conducting polymers such as polyaniline (PANi) have been widely investigated as ammonia gas sensors due to their intrinsic redox states, good environmental stability, and suitability for low-cost and variable changing in electrical conductivity when exposed to acid and basic gases. In this paper we used both a hybrid PANi derivative, poly(o-methoxyaniline) (POMA)-vanadium pentoxide (V2O5) film, and new ac electrical measurement strategies to increase the ammonia gas sensor performance. Complex impedance measurements of POMA/V2O5 hybrid film showed linearity in response and a high sensitivity to ammonia in the 0–20 ppm range in both real (around 800%) and imaginary (around 3000%) components, which indicated that the film is a good candidate to use as an ammonia sensing material. FTIR spectra presented typical V2O5 and POMA bands and also presented a shifting to higher wave numbers in bands referring to the vanadyl group and primary amines, which indicated the presence of hydrogen bonds between oxide and polymer. Finally, the Cole–Cole theoretical model with an interface effect provided a good fit for the experimental results from electrical ac measurements.

The 5,8-π-extended quinoxaline derivatives are widely studied due to their well-known photophysical and electrochemical properties. In order to investigate the structure-property relationship, a novel series of fluorescent calamitic liquid crystals based on the quinoxaline heterocycle was successfully synthesized and characterized. The final molecules presented calamitic mesomorphism with nematic and smectic phases. These compounds displayed intense green photoluminescence under UV light excitation in solution and in the solid state. In chloroform solution, the fluorescence quantum yields (ΦFL = 0.54–0.62) of the quinoxaline-based derivatives were significantly higher than those previously described for similar benzothiadiazoles. The maximum emission peaks were between 511 and 520 nm with singlet excited-state lifetimes in the nanosecond timescale. The solvatochromism studies showed a significant dependence of the emission on the polarity of the solvent. Doping of the quinoxalines with fullerene C60 suggests a charge transfer process, this being dependent on the π-conjugate core. The energy band gaps predicted with DFT calculations are in excellent agreement with the experimental data.

Topological phase transitions such as the Berezinskii-Kosterlitz-Thouless (BKT) transition are difficult to characterize due to the difficulty in defining an appropriate order parameter or to unravel its critical properties. In this paper, we discuss the application of a newly introduced numerical algorithm that was inspired by the Fisher zeros of the partition function and is based on the partial knowledge of the zeros of the energy probability distribution (EPD zeros). This iterative method has proven to be quite general, furnishing the transition temperature with great precision and a relatively low computational effort. Since it does not need the a priori knowledge of any order parameter it provides an unbiased estimative of the transition temperature being convenient to the study of this kind of phase transition. Therefore, we applied the EPD zeros approach to the 2D XY model, which is well known for showing a BKT transition, in order to demonstrate its effectivity in the study of the BKT transition. Our results are consistent with the real and imaginary parts of the pseudo-transition temperature, T(L), having a different asymptotic behavior, which suggests a way to characterize a BKT like transition.

Luminescent boron(III) complexes have recently been employed as emitters in organic light-emitting diodes (OLEDs) with reasonable success. They are easy to prepare and sufficiently stable to be used in such devices, being of great interest as a simple molecular emissive layer. Although emitters for this class with all colors have already been reported, highly efficient and stable blue emitters for applications in solution processed devices still pose a challenge. Here, we report the design, synthesis, and characterization of new boron complexes based on the 2-(benzothiazol-2-yl)phenol ligand (HBT), with different donor and acceptor groups responsible for modulating the emission properties, from blue to red. The molecular design was assisted by calculations using our newly developed formalism, where we demonstrate that the absorption and fluorescence spectra can be successfully predicted, which is a powerful technique to evaluate molecular photophysical properties prior to synthesis. In addition, density functional theory (DFT) enables us to understand the molecular and electronic structure of the molecules in greater detail. The molecules studied here presented fluorescence efficiencies as high as Φ = 0.88 and all solution processed OLEDs were prepared and characterized under an ambient atmosphere, after dispersion in the emitting layer. Surprisingly, even considering these rather simple experimental conditions, the blue emitters displayed superior properties compared to those in the present literature, in particular with respect to the stability of the current efficiency.

We report on chemistry and cytotoxic studies of four new ruthenium (II) complexes containing uracil derivatives. All compounds are neutral, presenting the formula [Ru(PPh3)2(2TU)2] (1), [Ru(PPh3)2(6m2TU)2] (2), [Ru(dppb)(2TU)2] (3) and [Ru(dppb)(6m2TU)2] (4), where PPh3 = triphenylphosphine; dppb = 1,4-bis(diphenylphosphino)butane, 2TU = 2-thiouracil and 6m2TU = 6-methyl-2-thiouracil. They were characterized using NMR, UV–vis and IR spectroscopies, microanalytical analysis and mass spectrometry. Furthermore, the crystal structures of 1–4 were determined by single-crystal X-ray diffraction. The coordination of 2-thiouracil derivatives with ruthenium increases regions able to carry out hydrogen bonds with the biological targets, such as DNA. We evaluated the interaction of the complexes with DNA by UV/Vis spectrophotometric titration, and as a result, the values of DNA-binding constants are in the range of 0.8–1.8 × 104 M−1. Moreover, the interaction of the complexes with BSA was investigated. In vitro, activities against B16-F10 (mouse melanoma), HepG2 (human hepatocellular carcinoma), HL-60 (human promyelocytic leukemia) and K562 (human chronic myelocytic leukemia) and non-tumor cells: PBMC (human peripheral blood mononuclear cells activated with concanavalin A – human lymphoblast) were carried out. Cytotoxicity assays revealed that complexes (2) and (4) present biological activity against tumor cells comparable with oxaliplatin, the reference platinum drug, revealing that they are promising molecules for developing new antitumor compounds.