Adsorption of two pesticides on a clay surface: a theoretical study

The contamination of water resources with many organic xenobiotic compounds poses a challenge to environmental sciences and technologies [1]. Although in many cases these contaminants are present only in small concentrations, the large variety of such compounds (some of which are classified as priority pollutants) is a matter of concern. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many of these pollutants [2]. In this regard, the choice of adsorbent materials is crucial, which requires an understanding of the details involved in the adsorption of more or less complex organic molecules by a variety of surfaces of different types. In addition to laboratory studies, computational studies may be valuable in this study [3]. MCPA (2-methyl-4-chlorophenoxyacetic acid, a herbicide) and Clofibric acid (2-(4-chlorophenoxy)-2-methylpropanoic, the metabolite of a pharmaceutical, clofibrate, and also a herbicide) are two phenoxy acids that differ only slightly in their structures. However, a quite distinct behavior in adsorption phenomena on clay materials has been observed in past studies [4]. By relating those differences with the molecules' structural features through atomistic computational studies, some insight may be gained into the respective adsorption processes of this type of compounds. In the present work quantum chemical calculations at density functional theory level have been performed to study the adsorption of MCPA and Clofibric acid by a clay surface model. Since hydration plays an important role for the adsorption process of these species, solvent effects were considered by inclusion of water molecules explicitly into the quantum chemical calculations. The deprotonated negatively charged species were found to strongly interact with the surface and the distinct behavior of both species upon adsorption was compared with experimental evidences

Phytoremediation: An Option for Removal of Organic Xenobiotics from Water

Pollution by persistent organic pollutants (pesticides, pharmaceuticals, petroleum hydrocarbons, PAHs, PCBs, etc.) is an environmental problem that is recognized worldwide. In order to address this problem, cost effective technologies have been developed and evaluated for the decontamination of soil and water resources. Phytoremediation is a promising technology that uses plants and the associated rhizosphere microorganisms to remove, transform/detoxify, or accumulate organic and inorganic pollutants present in soils, sediments, surface or ground water, wastewater, and even the atmosphere. In fact, as a result of their sedentary nature, plants have evolved diverse abilities for dealing with toxic compounds in their environment. They, therefore, possess a variety of pollutant attenuation mechanisms that makes their use in remediating contaminated land and water more feasible than physical and chemical remediation. Currently, phytoremediation is used for treating many classes of organic xenobiotics including petroleum hydrocarbons, chlorinated solvents, polycyclic aromatic hydrocarbons, pesticides, explosives, pharmaceutical compounds and their metabolites, and it involves several decontamination mechanisms. There are several different types of phytotechnologies such as, for instance, treatment constructed wetlands. The aim of this work is to present a review on the application of phytoremediation technologies for water decontamination from persistent organic pollutants, with special emphasis focused on the removal of a class of emergent pollutants that has recently been receiving a lot of attention, the pharmaceutically active compounds. Within the realm of phytotechnologies, constructed wetlands for wastewater treatment are dedicated a special focus as these systems have been used with success for the removal of several different types of organic xenobiotics

Structure-SONLO Property Relationship On Nickel Complexes: A TD-DFT Study

The search on organometallic compounds for the development of novel nonlinear optical (NLO) materials with large second-order nonlinearities (SONLO) is currently the subject of significant interest in view of their potential application in the area of integrated optics [1]. Experimental and computational systematic studies were made on half-sandwich organometallic complexes presenting the typical push-pull feature in which the metal centre, bound to a highly polarizable conjugated backbone, acts as an electron-releasing or withdrawing group. With this feature, large quadratic hyperpolarizabilities arise from small energy gaps between excited and ground states, large changes in dipole moment upon molecular excitation and large transition dipole moments. The results revealed that h5-monocyclopentadienylmetal organometallic moieties can be very efficient electron-donor groups in complexes presenting thiophene-based ligands with a nitro group as an electron acceptor [2-4]. Nevertheless, the understanding of the relationship between the structure and experimental molecular NLO phenomena is not completely clear, namely the effect of the conjugation length of the chromophores. The time-dependent density functional theory (TD-DFT) method within the DFT frame provides the satisfactory molecular orbital explanation for the electronic excitation, which is usually recommended for calculating the excited-state behaviours. In the case of organometallic complexes, the TD-DFT method is one of the most suitable choices to calculate accurately the excited energy and first hyperpolarizabilities. In order to contribute to a clarification on the molecular organometallic structure-SONLO properties relationship and to enhance the SONLO performance of half-sandwich complexes with substituted thienyl chromophores, we report herein a DFT and TD-DFT study on the nickel complexes [Ni(η5-C5Y5)(PR3)(XC{SC4H2}nNO2)] and [Ni(η5-C5H5)(PH3)(CC{SC4H}(NO2)2] (Y=H, Me; R=H, Ph; X= N, C; n=1,2) using the Gaussian03W program package. The effect of different monocyclopentadienyl and phosphine co-ligands, the conjugated length of the chromophore and its coordination mode to the metal centre and the number of nitro substitutents on the first hyperpolarizability will be evaluated

First hyperpolarizabilities of half-sandwich iron (II) complexes with thiophene acetylide ligands: a DFT study

Organometallic complexes have been studied as potential building blocks for second-order nonlinear optical (SONLO) materials in view of their potential application in the area of integrated optics.1 Experimental work on 5-monocyclopentadienyliron(II) complexes with acetylide and nitrile benzene-based chromophores showed that acetylides have higher first hyperpolarizabilities (β) than the corresponding nitriles.2 Also, studies on a series of similar complexes with substituted oligo-thiophene nitrile ligands showed that these complexes have better NLO properties than the corresponding benzenoid structures.3 These results suggest that combination of acetylide thiophene ligands with 5-monocyclopentadienyliron moiety would maximize the NLO response. In order to predict the first hyperpolarizabilities and for a better understanding on the electronic factors that may be responsible for the second-order nonlinear optical behavior of 5-monocyclopentadienyliron(II) complexes with substituted thienyl-acetylide ligands, density functional theory (DFT) based calculations as well as time dependent DFT (for the prediction of UV/Vis absorption spectra) were performed for the model complexes [FeCp(H2PCH2CH2PH2)(CC{SC4H2}Y)] (Y=NMe2, NH2, OMe, H, Br, CHO, CN, NO2). Spatial localization of electron charge by means of topological analysis of the electron localization functions (ELF) has been performed to gain insight into the nature of bonding between the acetylide ligands and the organometallic moiety. Calculations were also made in the free acetylide ligands in order to study the role played by the organometallic fragment in the second-order NLO properties of the studied complexes

Removal of Antibiotics by “Green” Clay Sorbents

Contamination of water resources with pharmaceuticals has been one of the top concerns of environmental sciences in the latest years [1], the matter having received very significant media coverage recently [2]. Antibiotics in particular have been gathering considerable attention and are amongst the most serious worries due to the development of antibiotic resistant bacteria as result of prolonged exposure [1, 2]. Because most wastewater treatment plants were only designed for removing bulk pollutants, many other more specific pollutant types that are present in low concentrations in the wastewaters are often inefficiently treated and end up being released into receiving water bodies. Although in many cases these contaminants are detected only at small concentrations in environmental samples, the large variety of such compounds and the high potential for adverse interactions with living organisms (due to the nature of their action) is a matter of serious concern. Several advanced technologies have been evaluated as options to treat these contaminants, e.g. advanced oxidative processes or membrane filtration, but despite the sometimes high removal efficiencies attained, these technologies are too expensive to be considered as viable solutions on a large scale. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many organic xenobiotic pollutants [3]. In this regard, the choice of adsorbent materials is crucial. However, pollutants removal efficiency is not the sole selection criterion, as the cost of the materials may provide or preclude economic viability of the water/wastewater treatment system. Therefore, the quest for efficient adsorbents that are widely available, and do not require expensive processing in order to be used (thereby allowing lower production costs) is a very important aspect of research aimed to manage this environmental problem. In this work we present the study of sorption properties of clay materials (LECA and vermiculite) for the removal of some pharmaceuticals two antibiotics (sulfametoxanol and oxytetracycline) from water. The dependence of removal efficiencies on pollutants initial concentrations, contact time with the adsorbents and other system/environment conditions was assessed. The two clay materials were compared in terms of their more balanced performance towards the removal of the pharmaceuticals tested and the materials are suggested as a useful component of a water or wastewater treatment system designed for the removal of pharmaceutical contaminants

A DFT Study on the Adsorption of Benzodiazepines to Clay Surfaces

Benzodiazepines (BDZ) belong to the group of psychiatric substances which act on the central nervous system, having anxiolytic, sedative and hypnotic effects and is one of the most prescribed groups of pharmaceuticals throughout the world. These compounds are not exclusively used for human therapeutics, their prescription is also common in veterinary treatments for anxiolytic and appetite stimulation effects. Nowadays, there are several benzodiazepines under international control for therapeutic use. The widespread use of these compounds doesn’t come without a cost and trace levels of it can now be found disseminated on the environment, what is a matter of ecological concern. In fact, over the last decade, there has been a significant number of studies reporting the occurrence of BDZ in environmental matrices, namely in wastewater treatment plants influents and effluents, surface waters and drinking waters . Some of the more frequently detected BDZ include alprazolam, diazepam, lorazepam and oxazepam . The main reason for the ubiquitous presence of BDZ in the environment is associated not only with the large use but also the generally low efficiency of conventional biological wastewater treatment to remove these pharmaceutical residues. It has been suggested that this inefficiency is due to the halogenated structure of these compounds that significantly reduces their susceptibility to biodegradation . Adsorption processes are the most promising and cheap alternative for removal of these kind of organic xenobiotic from wastewaters. In recent years, inexpensive widely available materials have been investigated for the selection of efficient adsorbents that can make adsorption processes an attractive solution at reasonable costs. Among some of the adsorbents studied, clay-based materials have received some attention due to their interesting properties such as the high cation exchange capacity, swelling properties and high specific surface areas. In particular for the treatment of wastewaters, these materials can overcome the limitations of biological processes, as used in conventional wastewater treatment. A better understanding of the interactions of these organic molecules with clay minerals may thus allow a more judicious selection of materials for water/wastewater treatment filters that present significant enhancements in the removal of BDZ. In this work, electronic structure calculations based on the density functional theory (DFT) are presented on the interaction of two BDZ molecules (diazepam and alprazolam) with a periodic model surface of the vermiculite mineral. Geometry changes of the molecules upon adsorption were compared and the interaction energies with the surfaces were determined for a few different molecular orientations in order to understand the way these molecules interact with the clay surface and the essential factor governing the adsorption processes

T-20 and T-1249 HIV fusion inhibitors’ structure and conformational behavior in solution: a molecular dynamics study

Fusion of the HIV envelope with the target cell membrane is a critical step of HIV entry into the target cell. Several peptides based on the C-region of HIV gp41 have been used in clinical trials as possible HIV fusion inhibitors. Among these are T-1249 and T-20 (also known as enfurvitide; see fig. 1). Despite recent works, a detailed molecular picture of the inhibitory mechanism of these molecules is still lacking. These peptides are usually depicted as α-helices by analogy with the structure of the sequence of the gp41 protein with which they are homologous. However, structures like these would not explain the ability that the two fusion inhibitors have to both become solvated by water and interact effectively with cell membranes. This led us to study the structure and conformational behavior of all these peptides. To this effect, extensive molecular dynamics simulations (total time 400 ns) with explicit solvent (SPC water) were carried out to investigate the structure and conformational behavior of T-1249 and T-20, as well as shorter homologous peptides CTP and 3f5 (see fig. 1), which show no inhibitory action. The monitored parameters include mean square displacement relative to the initial conformation (α-helix structures in all cases), secondary structure, solvent accessible surface and radius of gyration. We found that the studied peptides have no stable structure in solution in the time scale studied. Additionally, the solvent accessible area varies significantly during the simulation. Our findings suggest that these peptides may assume not only one but several possible sets of structures in solution, some of which more adequate to interact with the solvent, whereas others might be better suited to interact with cell membranes

Influence of mordants in the colour of natural dyes: theoretical predictions and experimental results

Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile production and a cultural heritage that urges to preserve. The richness of colours displayed by some of the Arraiolos tapestries denotes the likely use of a wide variety of dyes. The different light-fastness of dyes combined with the use of different types of mordants can also explain the appearance of pale shades and fading in some tapestries due to different molecule interactions with the support fibres. The work we present is part of a major project (experimental and theoretical) that envisages the identification of the dyes and mordants used throughout the ages in the production of Arraiolos tapestries and the establishment of the major factors (like mordant, humidity and light) that are responsible for the colour and fading of the natural dyes as well as for the degradation of the fibres. It is well known that the colour of a dye depends on the type of mordant used, due to the formation of metal complexes that cause a change in the molecular orbitals energies and hence a shift in UV/Vis absorption bands. The electronic structure and transitions in the visible spectra of some dyes and mordants identified on Arraiolos rugs were predicted by the ZINDO-INDO/S semi-empirical molecular orbital method [1,2] in order to identify the origin of the colours and characterize the influence of metal coordination on colour modifications. The molecular geometry of each dye-mordant complex was optimized at DFT level using the Gaussian03 package [3] and a simulation of the UV/Vis absorption spectrum was calculated using ZINDO. Another important outcome of this study was the determination of the chromophore properties of fragment molecules produced by the dyes degradation processes that enabled the evaluation of the colour changes of the dyes and subsequent fading. Wool fibres were dyed with previously identified natural dyes and mordants and the colour parameters and the spectra were determined using a UV-Vis portable spectrometer. These parameters were compared with the results from the theoretical predictions

Removal of the Antibiotic Sulfamethoxazole by “Green” Clay Sorbents

Contamination of water resources with pharmaceuticals has been one of the top concerns of environmental sciences in the latest years [1, 2], the matter having received very significant media coverage recently [2, 3]. Antibiotics in particular have been gathering considerable attention and are amongst the most serious worries due to the development of antibiotic resistant bacteria as result of prolonged exposure [1, 2, 3]. In particular, antimicrobials and their metabolites are being detected in significant amounts in water supplies, and although no evidence exists that human health is affected by minute doses of antibiotics over long periods of time, changes have been observed in ecosystem functions [3,4]. In addition to antimicrobial resistance, other effects have been observed such as a delay in cell growth of bacteria, limited denitrification, and shifts in community composition [5]. Sulfamethoxazole (SMX), a broad-spectrum biostatic sulfanilamide, has become a point of interest because of its prevalence in contaminated wastewaters at concentrations correlated to bacterial resistance and genetic mutations in organisms [3,4,5]. Taking into account the widespread use of sulfonamides and their potential environmental effects, there is importance in developing new technologies for removing SMX and similar compounds from points of discharge. In fact, most wastewater treatment plants are inefficient for the removal of most micropollutants, especially hardly biodegradable organic xenobiotics which are present in wastewaters at low concentrations, as these conventional systems were only designed for removing bulk pollutants. Several advanced technologies have been evaluated as options to treat these contaminants, e.g. advanced oxidative processes or membrane filtration, but despite the sometimes high removal efficiencies attained, these technologies are too expensive to be considered as viable solutions on a large scale. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many organic xenobiotic pollutants [6, 7]. In this regard, the choice of adsorbent materials is crucial. However, pollutants removal efficiency is not the sole selection criterion, as the cost of the materials may provide or preclude economic viability of the water/wastewater treatment system. Therefore, the quest for efficient adsorbents that are widely available, and do not require expensive processing in order to be used (thereby allowing lower production costs) is a very important aspect of research aimed to manage this environmental problem. In this work we present the study of sorption properties of clay materials (LECA and vermiculite) for the removal of SMX from water. The dependence of removal efficiencies on the antibiotic initial concentrations, contact time with the adsorbents and other system/environment conditions was assessed. The two clay materials were compared in terms of their more balanced performance towards the removal of the pharmaceutical tested and the materials are suggested as a useful component of a water or wastewater treatment system designed for the removal of this contaminant (and others of similar type). Vermiculite was shown to be more efficient than LECA in the adsorption of the pharmaceutical and the one with faster kinetics. In other to gain a deeper insight into the characteristics that favor the removal of this compound by mineral surfaces, quantum chemical theoretical calculations were performed to illustrate the type of interactions that are responsible for the preferable adsorption of the compound to the vermiculite surface

Pilot-scale study on the removal of pharmaceuticals by LECA based SSF-constructed wetlands

In recent years, the occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. Some compounds are just resistant to degradation in the sewage treatment plants (STPs) while others, although suffering partial degradation, still end up in receiving water bodies due to the large inputs received in STPs [1]. Clofibric acid (a metabolite from a series of widely used blood lipids lowering agents), ibuprofen (an anti-inflamatory non-prescription drug) and carbamazepine (an anticonvulsant and mood stabilizing drug) are some of the most frequently found PhACs in environmental monitoring studies [1]. Wastewater treatment by sub-surface flow constructed wetland systems (SSF-CWs) is a low-cost technology that has shown some capacity for removal of several organic xenobiotic pollutants, but fewer studies exist on pharmaceuticals behavior. The aim of the present work was to evaluate the efficiency of a pilot SSF-CW assembled with the plants cattail (Typha spp.) and a clay material (LECA 2/4) as support matrix, for the removal of three pharmaceuticals, namely ibuprofen (IB), carbamazepine (CB) and clofibric acid (CA), from contaminated wastewaters. Four beds were planted with pre-grown cattails (density of 80 plants/m2) and four were left unplanted to be used as controls. Experiments were conducted both in batch and in continuous mode with a flooding rate of 100%. Pharmaceutical concentrations were quantified by HPLC with UV detection at 210 nm (CB), 222 nm (IB) and 230 nm (CA). Solid phase extraction was used for sample pre-concentration whenever the measured pharmaceutical concentrations fell under the limit of quantification of the analytical method. The physico-chemical characterization of the support matrix material, LECA, involved the determination of properties such as pH, point of zero charge, electrical conductivity, apparent porosity, bulk density and hydraulic conductivity. In order to shed some light on the tolerance mechanisms developed by Typha spp. in the presence of these pharmaceuticals, biochemical and physiological parameters were evaluated. Typha spp. showed good tolerance to the presence of CA, CB and IB concentrations of 1 mg L-1, which is a value much higher than those usually reported in wastewaters. LECA alone was able to remove about 90% of the initial amounts of CB and IB in solution, and 50% of CA. IB was very susceptible to microbial degradation and up to 80% of the initial concentration could be removed by the microbial population present in the wastewater used. Overall, the CWS shows a higher removal performance for CA, CB and IB than any of its individual components (plants, support matrix, microorganisms) considered separately. CA proved to be the most resilient compound, which comes in agreement with other published data. However, this system enabled the removal of substantially higher amounts of CA than has previously been reported in other studies. The use of systems of this kind for the removal of pharmaceuticals from wastewaters seems like a promising alternative to the less efficient processes of conventional wastewater treatment