Francisco A. M. Sales

Anhydrous crystals of DNA bases are wide gap semiconductors.

We present the structural, electronic, and optical properties of anhydrous crystals of DNA nucleobases (guanine, adenine, cytosine, and thymine) found after DFT (Density Functional Theory) calculations within the local density approximation, as well as experimental measurements of optical absorption for powders of these crystals. Guanine and cytosine (adenine and thymine) anhydrous crystals are predicted from the DFT simulations to be direct (indirect) band gap semiconductors, with values 2.68 eV and 3.30 eV (2.83 eV and 3.22 eV), respectively, while the experimentally estimated band gaps we have measured are 3.83 eV and 3.84 eV (3.89 eV and 4.07 eV), in the same order. The electronic effective masses we have obtained at band extremes show that, at low temperatures, these crystals behave like wide gap semiconductors for electrons moving along the nucleobases stacking direction, while the hole transport are somewhat limited. Lastly, the calculated electronic dielectric functions of DNA nucleobases crystals in the parallel and perpendicular directions to the stacking planes exhibit a high degree of anisotropy (except cytosine), in agreement with published experimental results.

L-asparagine crystals with wide gap semiconductor features: Optical absorption measurements and density functional theory computations

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.

Controlled Release of Nor-β-lapachone by PLGA Microparticles: A Strategy for Improving Cytotoxicity against Prostate Cancer Cells.

Prostate cancer is one of the most common malignant tumors in males and it has become a major worldwide public health problem. This study characterizes the encapsulation of Nor-β-lapachone (NβL) in poly(d,l-lactide-co-glycolide) (PLGA) microcapsules and evaluates the cytotoxicity of the resulting drug-loaded system against metastatic prostate cancer cells. The microcapsules presented appropriate morphological features and the presence of drug molecules in the microcapsules was confirmed by different methods. Spherical microcapsules with a size range of 1.03 ± 0.46 μm were produced with an encapsulation efficiency of approximately 19%. Classical molecular dynamics calculations provided an estimate of the typical adsorption energies of NβL on PLGA. Finally, the cytotoxic activity of NβL against PC3M human prostate cancer cells was demonstrated to be significantly enhanced when delivered by PLGA microcapsules in comparison with the free drug.

Optical Absorption of the Antitrypanocidal Drug Benznidazole in Water

UV-vis optical absorption spectra of the antitrypanocidal drug benznidazole solvated in water were measured for various concentrations. The spectra show a prominent peak around 3.80 eV, while deconvolution of the UV-vis optical absorption spectra revealed six bands centered at 3.60, 3.83, 4.15, 4.99, 5.60, and 5.76 eV. Benznidazole electronic transitions were obtained after density functional theory (DFT) calculations within the polarized continuum (PCM) model for water solvation. Molecular geometry optimizations were carried out, and the measured absorption peaks were related to specific molecular orbital transitions obtained within the time dependent DFT (TD-DFT) with excellent agreement between theory and experiment.

Synthesis, Inhibition of Mycobacterium tuberculosis Enoyl-acyl Carrier Protein Reductase and Antimycobacterial Activity of Novel Pentacyanoferrate(II)-isonicotinoylhydrazones

Tuberculosis remains among the top causes of death triggered by a single pathogen. Herein, a greener synthetic approach for isonicotinoylhydrazones is described using ultrasound energy. These compounds were used as starting materials for synthesizing pentacyanoferrate(II)isonicotinoylhydrazones, which inhibited the reaction catalyzed by Mycobacterium tuberculosis 2-trans-enoyl-ACP(CoA) reductase (MtInhA) in a time-dependent manner. The most active coordination complex showed an increase of more than ten-fold in the MtInhA inhibition rate constant compared with lead pentacyano(isoniazid)ferrate(II) (IQG607). Additionally, the new series of metal-based compounds demonstrated antitubercular activity against a drug-susceptible Mycobacterium tuberculosis (Mtb) strain and was devoid of toxicity to mammalian cells (IC50 > 20 μmol L, half maximal inhibitory concentration). Finally, one of the synthesized compounds showed intracellular activity similar to isoniazid in a macrophage model of Mtb infection, indicating that this chemical class may furnish novel structures to embark on the preclinical phase of anti-tuberculosis drug development.

First-generation antipsychotic haloperidol: optical absorption measurement and structural, electronic, and optical properties of its anhydrous monoclinic crystal by first-principle approaches

The fifty years old first-generation antipsychotic drug haloperidol is very effective in the therapy of the positive symptoms of schizophrenia and mania, but its solid-state properties remain veiled. To fill this gap, the anhydrous monoclinic crystal of haloperidol, was investigated through calculations employing density functional theory (DFT) within the generalized gradient approximation (GGA) and including the dispersion effects (TS). The optical absorption measurements revealed that the anhydrous monoclinic haloperidol crystal is a wide band gap material with a 3.8 eV indirect main gap energy and an optical absorption onset due to a Frenkel exciton with a binding energy of 1.1 eV and charge-transfer excitons with a binding energy of 0.2–0.5 eV. The DFT-GGA+TS modeling produced structural parameters in very good agreement with the X-ray data, with the calculated band gap energy smaller than the experimental data by about 36%, with an indirect band gap corresponding to α1 → β1 transition. After applying the Δ-sol gap correction scheme, the main gap increased to 3.72 eV, almost matching the experimental gap estimation. Theoretical simulations within the time-dependent DFT formalism, on the other hand, predicted a Frenkel exciton with a binding energy of 1.6 eV, about 45% larger than the experimental estimation. It was found that electronic wavefunctions mainly originating from the 2p states of oxygen (O1) and nitrogen (N1) atoms contribute to the highest valence energy band, while the 2p states of C15, C16, C19, C21, and O2 atoms contribute most significantly to the lowest conduction energy bands. Analysis showed that the unit cell was less stiff along the b direction than the a and c directions. Finally, calculations pointed to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 001 directions.