Papers by Alfredo J P Carvalho
Constructed Wetlands for Industrial Wastewater Treatment
Over the latest years the occurrence of pharmaceutical residues in the environment has been motiv... more Over the latest years the occurrence of pharmaceutical residues in the environment has been motivating an increasing concern over the possible harmful effects of many of these pollutants to living organisms. In fact many reports are available in the literature about the detection of several of the most consumed pharmaceuticals, their metabolites and transformation products in
Influence of Ionic Liquids on the Aggregation and Pre-aggregation Phenomena of Asphaltenes in Model Solvent Mixtures by Molecular Dynamics Simulations and Quantum Mechanical Calculations
Energy & Fuels
Bioconversion reactions involving whole cells are usually characterized by low volumetric product... more Bioconversion reactions involving whole cells are usually characterized by low volumetric productivities in aqueous media, due to the low solubility of both the substrates and the reaction products in water. In order to overcome this problem, organic solvents have been used as substrate/product pools, including some environmentally friendly substances in view of their low volatility and toxicity [1]. Silicone oils have successfully been used as production medium in conversion of sterols to steroids with whole cells in monophasic and biphasic systems [1]. For the process scale-up, a number of physical properties of the system are needed, such as viscosity of the production medium and solubility of metabolic gases (oxygen and carbon dioxide) in the organic solvent. Polydimethylsiloxane (PDMS) and polymethylphenylsiloxane have been the most used silicone oils in production media for bioconversion reactions. In the case of polydimethylsiloxane, oils with kinematic viscosities of around ...
Aqueous mixtures of 2,2,2-trifluoroethanol have received significant attention in the last years ... more Aqueous mixtures of 2,2,2-trifluoroethanol have received significant attention in the last years because their applications, such as working fluid in Rankine cycle thermal engines or as solvent in studies of protein stability (protein folding). From the fundamental point of view, fluoroalcohols have an amphyphile character, due to the simultaneous presence of a hydrophobic (and alkane-phobic) fluorinated surface and a hydroxyl group. Mixtures of 2,2,2-trifluoroethanol with hydrogenated alcohols were studied recently in our research group (experimental determination of pVT surfaces as well as thermal, volumetric and structural properties by computer simulation) [1]. In the case of 2,2,2-trifluoroethanol/water this study suggested a preference of cross hydrogen bond. Hydrogen bonds play a determinant role in the structure of aqueous mixtures of alcohols, and should influence the dynamic properties of binary systems of fluorinated alcohols with water. The goal of this work is to study ...
Artificial or Constructed Wetlands, 2018
The contamination of aquatic environments with organic micropollutants (OMPs) resulting from huma... more The contamination of aquatic environments with organic micropollutants (OMPs) resulting from human activities is becoming a widespread, serious environmental issue. The problem is mainly rooted in a general inefficiency of conventional wastewater treatment plants to deal with this type of pollutants, which causes treated wastewaters to still contain significant amounts of
The fate of three common plastic nanoparticles in water. A molecular dynamics study
Journal of Molecular Structure, 2021
Abstract The widespread contamination of aqueous environments with micro and nanoplastics (MNPs) ... more Abstract The widespread contamination of aqueous environments with micro and nanoplastics (MNPs) is an emergent environmental problem that has been gathering increasing public concern. In addition to the known harmful effects on the ecosystems and living organisms, there have been raising worries that MNPs may adsorb trace pollutants such as heavy metals and organics, accumulate them and substantially concentrate them relative to their concentrations in the original aqueous medium. The tendency of MNPs to adsorb compounds may be linked to the particle sizes as well as to their final shapes. In order to assess MNPs behavior in the water environment, namely in terms of particle shapes, structures, interactions and aggregation, differently sized nanoparticles of three common plastics, polyethylene, polyethylene terephthalate and the polyamide nylon 6, were analyzed by molecular dynamics simulations. In all cases, a fast and spontaneous aggregation of the initially dispersed nanoparticles was observed yielding one single larger nanoparticle. In spite of the differences in the type of interactions between each plastic and water, no dispersal and solubilization of any plastic chains was observed during the simulations. The form of aggregation of the various nanoclusters was however very different: compact and ordered for polyethylene, globular and stringy for nylon6, while the PET bent chains form entangled piled-up structures with the aromatic rings preferentially oriented in a parallel-wise ordered way. In addition to the observed aggregation of all the smaller nanoparticles, a rearrangement and a spontaneous self-assembling ordering of the chains was observed as well, particularly in the polyethylene case. The results reinforce the observed tendency of the plastic chains to remain stably associated in clusters with a significant size, in the form of nanoparticles that resist further fragmentation and degradation for all the types of plastic, although the shapes of the particles differ among plastic types.
Solubility of xenon in liquid n-alkanes and cycloalkanes by computer simulation. Towards the perfect anaesthetic
Journal of Molecular Liquids, 2021
Abstract The solubility (Henry’s constant) of xenon in a series of n-alkanes (n-heptane, n-octane... more Abstract The solubility (Henry’s constant) of xenon in a series of n-alkanes (n-heptane, n-octane, n-nonane, n-dodecane and n-hexadecane) and in two cycloalkanes (cyclopentane and cyclohexane) has been obtained by Monte Carlo computer simulations as a function of temperature, at a reference pressure of 100 kPa and compared with experimental results from literature. The n-alkanes and cycloalkanes were modelled with the united atom TraPPE force field, using optimized non-bonded parameters in a transferable fashion for each solvent family. Standard enthalpies of solvation were calculated from the temperature dependence of the Henry’s constants. Solute-solvent interaction energies were also estimated for all systems by Molecular Dynamics. The agreement between the simulated Henry’s constants and experimental data from the literature is excellent in all cases. For all systems involving n-alkanes, the temperature dependence of the standard enthalpies of solvation displays a maximum at very similar reduced temperatures, 0.51 Structural details of the solutions were also studied calculating the radial distribution functions xenon/CHn for all the systems at similar thermodynamic states. The results confirm the enrichment of methyl groups within xenon’s first coordination sphere relatively to methylene groups. The effect is more pronounced the longer the n-alkane chain.
Journal of Computational Chemistry, 2019
Thirty-six stable complexes of formic acid with formaldehydes and thioformaldehydes were determin... more Thirty-six stable complexes of formic acid with formaldehydes and thioformaldehydes were determined on the potential energy surface, in which the XCHOÁÁÁHCOOH complexes are found to be more stable than the XCHSÁÁÁHCOOH counterparts, with X = H, F, Cl, Br, CH 3 , NH 2 . All complexes are stabilized by hydrogen bonds, and their contribution to the total stabilization energy of the complexes increases in going from C-HÁÁÁS to C-HÁÁÁO to O-HÁÁÁS and finally to O-HÁÁÁO. Remarkably, a significant blueshift of C sp2 -H bond by 81-96 cm -1 in the C sp2 -HÁÁÁO hydrogen bond has hardly ever been reported, and a considerable redshift of O-H stretching frequency by 206-544 cm -1 in the O-HÁÁÁO/S hydrogen bonds is also predicted. The obtained results in our present work and previous literatures support that a distance contraction and a stretching frequency blueshift of C-H bond involving hydrogen bond depend mainly on its polarity and gas phase basicity of proton acceptor, besides the rearrangement of electron density due to complex formation. Markedly, we suggest the ratio of deprotonation enthalpy to proton affinity (R c ) as an indicator to prospect for classification of hydrogen bonds. The symmetry adapted perturbation theory results show a larger role of attractive electrostatic term in XO-n as compared to that in XS-n and the electrostatic interaction is overwhelming dispersion or induction counterparts in stabilizing XO-n and XS-n, with n = 1, 2, 3.
Insight into the adsorption of chloramphenicol on a vermiculite surface
Chemical Physics Letters, 2018
Abstract Four stable configurations were found upon adsorption of the chloramphenicol on a period... more Abstract Four stable configurations were found upon adsorption of the chloramphenicol on a period slab model of the vermiculite surface, using the PBE and C09-vdW functionals in a projector-augmented wave (PAW) method approach. The adsorption is a strong chemisorption process, characterized by an adsorption energy of −106.5 kcal mol−1 at the most stable configuration. Stability of configurations contributed mainly by Mg⋯O/Cl attractive electrostatic interactions and C/O H⋯O hydrogen bonds. It is remarkable that the vermiculite is found to be a solid material with good potential to be used for adsorption and consequent removal of this type of antibiotic drugs.
Biochimica et biophysica acta, Jan 27, 2016
Fluorescence spectroscopy and microscopy have been utilized as tools in membrane biophysics for d... more Fluorescence spectroscopy and microscopy have been utilized as tools in membrane biophysics for decades now. Because phospholipids are non-fluorescent, the use of extrinsic membrane probes in this context is commonplace. Among the latter, 1,6-diphenylhexatriene (DPH) and its trimethylammonium derivative (TMA-DPH) have been extensively used. It is widely believed that, owing to its additional charged group, TMA-DPH is anchored at the lipid/water interface and reports on a bilayer region that is distinct from that of the hydrophobic DPH. In this study, we employ atomistic MD simulations to characterize the behavior of DPH and TMA-DPH in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and POPC/cholesterol (4:1) bilayers. We show that although the dynamics of TMA-DPH in these membranes is noticeably more hindered than that of DPH, the location of the average fluorophore of TMA-DPH is only ~3-4Å more shallow than that of DPH. The hindrance observed in the translational and rotati...
Direct calculation of F�rster orientation factor of membrane probes by molecular simulation
J Mol Struc Theochem, 2010
Geometry optimization of free alizarin, purpurin and luteolin and coordinated Fe(II) complexes wa... more Geometry optimization of free alizarin, purpurin and luteolin and coordinated Fe(II) complexes was performed at DFT/B3LYP level. TD-DFT spectra were also calculated for free and coordinated alizarin and luteolin. For the Fe(II) complexes several spin multiplicities have been calculated and quintuplet spin structures were found to be the most stable. In the luteolin-Fe(II) complex, the coordination of the chromophore with the iron leads to a decrease in the lower energy band. In the case of luteolin complex, a new band emerges due to interactions between the delocalized π electrons of the luteolin molecule with the d metal orbitals.
Journal of Molecular Structure: THEOCHEM, 1996
A Monte Carlo simulation is performed to investigate the role of solvent in the Cu*+/Cu+ electron... more A Monte Carlo simulation is performed to investigate the role of solvent in the Cu*+/Cu+ electron exchange process in water. This study is based on the classical Marcus model using the energy gap between the reactant and product states as the reaction coordinate. Since the process has a rather high activation free energy, conventional simulations are not best suited to its complete description, and thus special sampling techniques are required. In this case, a mapping potential is used to drive the system from the reactants to the transition state, and free energies are computed by thermodynamic perturbation and thermodynamic integration methods. A comparison is made between the results obtained by both methods and conclusions are drawn concerning the applicability of the Marcus model to this kind of process.
Journal of Molecular Structure: THEOCHEM, 2009
Journal of Molecular Structure: THEOCHEM, 2005
Nitrogen adsorption isotherms in infinite hexagonal shaped silica nanopores were obtained by Gran... more Nitrogen adsorption isotherms in infinite hexagonal shaped silica nanopores were obtained by Grand Canonical Monte Carlo simulations and compared with experimental isotherms of this adsorptive on highly regular MCM-41 pure silica materials. The influence of surface irregularity and pore size was analysed. The results indicate that the nitrogen adsorption in MCM-41 is well described by a model using Lennard-Jones N 2 spheres and amorphous hexagonal shaped pores.
The Journal of Physical Chemistry B, 2007
Excess molar enthalpies and excess molar volumes as a function of composition for liquid mixtures... more Excess molar enthalpies and excess molar volumes as a function of composition for liquid mixtures of xenon + ethane (at 161.40 K), xenon + propane (at 161.40 K) and xenon + n-butane (at 182.34 K) have been obtained by Monte Carlo computer simulations and compared with available experimental data. Simulation conditions were chosen to closely match those of the corresponding experimental results. The TraPPE-UA force field was selected among other force fields to model all the alkanes studied, whereas the one-center Lennard-Jones potential from Bohn et al. was used for xenon. The calculated H m E and V m E for all systems are negative, increasing in magnitude as the alkane chain length increases. The results for these systems were compared with experimental data and with other theoretical calculations using the SAFT approach. An excellent agreement between simulation and experimental results was found for xenon + ethane system, whereas for the remaining two systems, some deviations that become progressively more significant as the alkane chain length increases were observed.
Science of The Total Environment, 2013
CW with LECA substrate and Phragmites plants tested with agricultural wastewaters. • High removal... more CW with LECA substrate and Phragmites plants tested with agricultural wastewaters. • High removals of TSS, COD, NH 4 -N, polyphenols, a pharmaceutical and a pesticide. • Contact time of wastewaters with beds ranged from 3 to 9days in batch conditions. • Promising results suggest more studies in full-scale and more realistic conditions.
Journal of Hazardous Materials, 2013
• Substrate of wetlands plays a major role in removal of non-biodegradable pollutants. • Optimiza... more • Substrate of wetlands plays a major role in removal of non-biodegradable pollutants. • Optimization may be attempted by selection of materials with high sorption capacity. • Clay minerals are generally efficient, widely available and cheap options. • Agricultural wastes and by-products have been gaining increasing popularity. • Available lab-scale assays must still be complemented with full-scale field assays.
Path integral Monte Carlo simulations: Study of the efficiency of energy estimators
The Journal of Chemical Physics, 1995
This article presents a study of the relative efficiency of two commonly used energy estimators f... more This article presents a study of the relative efficiency of two commonly used energy estimators for path integral Monte Carlo (MC) simulations; the Barker estimator and the virial estimator. Two different path integral MC algorithms are considered; the simple algorithm augmented ...
Electrochimica Acta, 2013
Uploads
Papers by Alfredo J P Carvalho