Library of dispersion-corrected atom-centered potentials for generalized gradient approximation functionals: Elements H, C, N, O, He, Ne, Ar, and Kr

Parameters for analytical dispersion-corrected atom-centered potentials (DCACPs) are presented to improve the description of London dispersion forces within the generalized gradient approximation functionals BLYP, BP, and PBE. A library of DCACPs for hydrogen, carbon, nitrogen, oxygen, helium, neon, argon, and krypton was obtained by calibrating against high-level CCSD(T) or configuration interaction references. The performance and transferability of DCACPs were tested on weakly bound complexes and provide excellent results throughout all investigated systems

Controlo integrado da Lagarta das Pastagens Mythimna unipuncta (Haworth)

II Jornadas Agronómicas Açorianas, Outubro, 1991, Ponta Delgada, Açores.No Arquipélago dos Açores, desde 1970 e com maior incidência na ilha de S. Miguel, devido ao aumento da área de pastagem, com vista ao desenvolvimento da bovinocultura, uma das espécies de Noctuídeos, Mythimna unipuncta (Haworth) (Lepidoptera, Noctuidae), assinalada na região desde 1810 por GODMAN, tornou-se num grave problema económico, estimando-se os seus prejuízos em cerça de 8% da produção anual das pastagens (TAVARES, 1989)

Antimalarial Activity of Potential Inhibitors of Plasmodium falciparum Lactate Dehydrogenase Enzyme Selected by Docking Studies

The Plasmodium falciparum lactate dehydrogenase enzyme (PfLDH) has been considered as a potential molecular target for antimalarials due to this parasite's dependence on glycolysis for energy production. Because the LDH enzymes found in P. vivax, P. malariae and P. ovale (pLDH) all exhibit ∼90% identity to PfLDH, it would be desirable to have new anti-pLDH drugs, particularly ones that are effective against P. falciparum, the most virulent species of human malaria. Our present work used docking studies to select potential inhibitors of pLDH, which were then tested for antimalarial activity against P. falciparum in vitro and P. berghei malaria in mice. A virtual screening in DrugBank for analogs of NADH (an essential cofactor to pLDH) and computational studies were undertaken, and the potential binding of the selected compounds to the PfLDH active site was analyzed using Molegro Virtual Docker software. Fifty compounds were selected based on their similarity to NADH. The compounds with the best binding energies (itraconazole, atorvastatin and posaconazole) were tested against P. falciparum chloroquine-resistant blood parasites. All three compounds proved to be active in two immunoenzymatic assays performed in parallel using monoclonals specific to PfLDH or a histidine rich protein (HRP2). The IC50 values for each drug in both tests were similar, were lowest for posaconazole (<5 µM) and were 40- and 100-fold less active than chloroquine. The compounds reduced P. berghei parasitemia in treated mice, in comparison to untreated controls; itraconazole was the least active compound. The results of these activity trials confirmed that molecular docking studies are an important strategy for discovering new antimalarial drugs. This approach is more practical and less expensive than discovering novel compounds that require studies on human toxicology, since these compounds are already commercially available and thus approved for human use

The ground state tunneling splitting and the zero point energy of malonaldehyde: A quantum Monte Carlo determination

Viel A, Coutinho-Neto MD, Manthe U. The ground state tunneling splitting and the zero point energy of malonaldehyde: A quantum Monte Carlo determination. JOURNAL OF CHEMICAL PHYSICS. 2007;126(2): 24308

Multi Dimensional Quantum Dynamics of Chemical Reaction Processes

International audienc

Multiconfigurational time-dependent Hartree calculations for tunneling splittings of vibrational states: Theoretical considerations and application to malonaldehyde

Hammer T, Coutinho-Neto MD, Viel A, Manthe U. Multiconfigurational time-dependent Hartree calculations for tunneling splittings of vibrational states: Theoretical considerations and application to malonaldehyde. JOURNAL OF CHEMICAL PHYSICS. 2009;131(22):224109

Predicting noncovalent interactions between aromatic biomolecules with London-dispersion-corrected DFT

Within the framework of Kohn-Sham density functional theory, interaction energies of hydrogen bonded and pi-pi stacked supramolecular complexes of aromatic heterocycles, nuclcobase pairs, and complexes of nucleobases with the anti-cancer agent ellipticine as well as its derivatives are evaluated. Dispersion-corrected atom-centered potentials (DCACPs) are employed together with a generalized gradient approximation to the exchange correlation functional. For all systems presented, the DCACP calculations are in very good agreement with available post Hartree-Fock quantum chemical results. Estimates of 3-body contributions (&lt; 15% of the respective interaction energy) and deformation energies (5-15% of the interaction energy) are given. Based on our results, we predict a strongly bound interaction energy profile for the ellipticine intercalation process with a stabilization of nearly 40 kcal/mol (deformation energy not taken into account) when fully intercalated. The frontier orbitals of the intercalator-nucleobase complex and the corresponding non-intercalated nucleobases are investigated and show significant changes upon intercalation. The results not only offer some insights into the systems investigated but also suggest that DCACPs can serve as an effective way to achieve higher accuracy in density functional theory without incurring an unaffordable computational overhead, paving ways for more realistic studies on biomolecular complexes in the condensed phase

Weakly bonded complexes of aliphatic and aromatic carbon compounds described with dispersion corrected density functional theory

Interaction energies and structural properties of van der Waals complexes of aliphatic hydrocarbons molecules and crystals of aromatic hydrocarbon compounds are studied using density functional theory augmented with dispersion corrected atom centered potentials (DCACPs). We compare the performance of two sets of DCACPs, (a) DCACP-MP2, a correction for carbon only, generated using MP2 reference data and a penalty functional that includes only equilibrium properties and (b) DCACP-CCSD(T), a set that has been calibrated against CCSD(T) reference data using a more elaborate penalty functional that explicitly takes into account some long-range properties and uses DCACP corrections for hydrogen and carbon atoms. The agreement between our results and high level ab initio or experimental data illustrates the transferability of the DCACP scheme for the gas and condensed phase as well as for different hybridization states of carbon. The typical error of binding energies for gas-phase dimers amounts to 0.3 kcal/mol. This work demonstrates that only one DCACP per element is sufficient to correct for weak interactions in a large variety of systems, irrespective of the hybridization state

Self-Assembly of Peptide Nanostructures onto an Electrode Surface for Nonenzymatic Oxygen Sensing

We report here the fabrication of a biomimetic sensor for direct oxygen reduction; the sensor consists of multicopper oxidases derived from cyclic-tetrameric copper­(II) species containing the ligand (4-imidazolyl)­ethylene-2-amino-1-ethylpyridine (apyhist) that are self-assembled with l-diphenylalanine micro/nanostructures (FF-MNTs). The [Cu₄(apyhist)₄]⁴⁺/FF-MNT complex was immobilized onto the surface of a glassy carbon (GC) electrode by poly ion complex formation with a Nafion film. This hybrid membrane allows regular proton transport to a Cu-based molecular oxygen reduction reaction catalyst, and the imidazole group in the imine ligand (apyhist) acts as a local buffer in the vicinity of the O₂ reducing center, thus aiding the catalyst in retaining its selectivity for 4e^–/4H⁺ oxygen reduction reaction. This nanocomposite provided improved sensing characteristics in the electrode interface with respect to the electroactive surface area, the diffusion coefficient, and the electron transfer kinetics. In addition, the hybrid film [Cu₄(apyhist)₄]⁴⁺/FF-MNT-coated GC electrode was successfully used as an enzymeless electrochemical sensor for the detection of dissolved oxygen in aqueous media at two concentration intervals, viz., 0.2–3.0 mg L^–1 and greater than 3.0 mg L^–1, with sensitivities of 25.0 and 80.2 μA L mg^–1 cm^–2, respectively, and a detection limit of 0.1 mg L^–1. Evaluated in terms of relative standard deviation, the repeatability of the proposed sensor was less than 9.0% for ten measurements of a solution of 6.5 mg L^–1 oxygen. Experimental efforts were conducted to use this proposed platform for O₂ determination with real samples. Results from theoretical investigations using density functional theory support the hypothesis that the [Cu₄(apyhist)₄]⁴⁺ complex can act as the sole source of protons and electrons in the O₂ reduction reaction

Naphthenic Acids Aggregation: The Role of Salinity

Naphthenic Acids (NA) are important oil extraction subproducts. These chemical species are one of the leading causes of marine pollution and duct corrosion. For this reason, understanding the behavior of NAs in different saline conditions is one of the challenges in the oil industry. In this work, we simulated several naphthenic acid species and their mixtures, employing density functional theory calculations with the MST-IEFPCM continuum solvation model, to obtain the octanol&ndash;water partition coefficients, together with microsecond classical molecular dynamics. The latter consisted of pure water, low-salinity, and high-salinity environment simulations, to assess the stability of NAs aggregates and their sizes. The quantum calculations have shown that the longer chain acids are more hydrophobic, and the classical simulations corroborated: that the longer the chain, the higher the order of the aggregate. In addition, we observed that larger aggregates are stable at higher salinities for all the studied NAs. This can be one factor in the observed low-salinity-enhanced oil recovery, which is a complex phenomenon. The simulations also show that stabilizing the aggregates induced by the salinity involves a direct interplay of Na+ cations with the carboxylic groups of the NAs inside the aggregates. In some cases, the ion/NA organization forms a membrane-like circular structural arrangement, especially for longer chain NAs