Modelling of interactions of polar and nonpolar pollutants with soil minerals and soil organic matter

Environmental pollution of soils by organic contaminants such as pesticides is one of the serious problems of our civilization. Contaminants can undergo various physical, chemical and biological transformation processes in soils governing behaviour, distribution, and fate of organic species in environment and subsequent environmental risks. Mechanistic understanding of molecular interactions of organic pollutants with main soil components represents a key factor for estimating the behaviour of contaminants in soils. Molecular modelling offers an opportunity to investigate and characterize various details of these interactions at molecular level providing specifications, which are difficult to obtain at the experimental level. This work represents a comprehensive overview of our investigations of the molecular interactions of organic contaminants with selected soil components. Particularly, we focused on the characterization of the structure and the surface complexation of the phenoxyacetic acid derivatives (herbicides MCPA and 2,4-D) and typical soil minerals such as clay minerals (kaolinite and montmorillonite) and iron oxyhydroxides (goethite and lepidocrocite). Further, interactions of several representative nonpolar polycyclic aromatic hydrocarbons (e.g. naphthalene, anthracene, pyrene, and phenanthrene) with iron oxyhydroxides were modelled, as well. It was found that in case of polar species, hydrogen bonds and electrostatic interactions play an important role in the formation of the surface complexes. In case of nonpolar PAHs, dispersion forces dominate in the planar stacking of the PAHs molecules on mineral surfaces. Another study focused at a complex 3D model representing humic substances firstly, featuring polar hydrophilic and nonpolar hydrophobic domains and also a nanopore SOM structure. This model was taken to simulate trapping and interactions of MCPA (polar) and naphthalene (nonpolar) species inside of the nanopore. It was found that MCPA is preferentially stabilized close to polar functional groups (carboxyl) whereas naphthalene interacts mostly with nonpolar aliphatic chains through dispersion interactions

A new mechanically-interlocked [Pd2L4] cage motif by dimerization of two peptide-based lemniscates

Most metallo-supramolecular assemblies of low nuclearity adopt simple topologies, with bridging ligands spanning neighboring metal centers in a direct fashion. Here we contribute a new structural motif to the family of host compounds with low metal count (two) that consists of a pair of doubly-interlocked, Figure-eight-shaped subunits, also termed “lemniscates”. Each metal is chelated by two chiral bidentate ligands, composed of a peptidic macrocycle that resembles a natural product with two pyridyl-terminated arms. DFT calculation results suggest that dimerization of the mononuclear halves is driven by a combination of 1) Coulomb interaction with a central anion, 2) π-stacking between intertwined ligand arms and 3) dispersive interactions between the structure's compact inner core bedded into an outer shell composed of the cavitand-type macrocycles. The resulting cage-like architecture was characterized by NMR, MS and X-ray structure analyses. This new mechanically bonded system highlights the scope of structural variety accessible in metal-mediated self-assemblies composed of only a few constituents

Mobility of Cr, Pb, Cd, Cu and Zn in a loamy sand soil : a comparative study

Interest in soil contamination has been growing in recent years due to the ongoing degradation of soil environments. Therefore, the development of remediation techniques and the study of contaminant sorption and migration are areas of intense research. In this study, the authors sought to evaluate the scenario of co-contamination of a loamy sand soil by multiple heavy metals. To that end, the sorption and transport of five metals—Cr, Pb, Cd, Cu and Zn—was evaluated using representative samples of a soil from the north of Portugal. The tests were conducted in batch and continuous systems using single- and multiple-metal acid solutions to evaluate the effect of metal competition. In accordance with the type of assay—batch or continuous—Langmuir or Convection Dispersion Two-Site Nonequilibrium models were adjusted to explain the sorption/transport data. FTIR analyses were performed on the final samples of the continuous systems. Generally, the results revealed good fitting of the tested models for the metals in competitive and noncompetitive scenarios, with the exception of Zn that was originally present in soil samples at higher concentrations. As expected, the influence of competition was observed in both batch and continuous systems, but with different tendencies. The FTIR spectra also revealed a strong influence of clay minerals and organic matter on the sorption of the metals.The PhD grants of Bruna Fonseca and Hugo Figueiredo and the research grant of Joana Rodrigues were financially supported by Fundacao para a Ciencia e Tecnologia, Ministerio da Ciencia e Tecnologia, Portugal and Fundo Social Europeu (FSE)

An autonomous chemically fuelled small-molecule motor

Molecular machines are among the most complex of all functional molecules and lie at the heart of nearly every biological process. A number of synthetic small-molecule machines have been developed, including molecular muscles, synthesizers, pumps, walkers, transporters and light-driven and electrically driven rotary motors. However, although biological molecular motors are powered by chemical gradients or the hydrolysis of adenosine triphosphate (ATP), so far there are no synthetic small-molecule motors that can operate autonomously using chemical energy (that is, the components move with net directionality as long as a chemical fuel is present). Here we describe a system in which a small molecular ring (macrocycle) is continuously transported directionally around a cyclic molecular track when powered by irreversible reactions of a chemical fuel, 9-fluorenylmethoxycarbonyl chloride. Key to the design is that the rate of reaction of this fuel with reactive sites on the cyclic track is faster when the macrocycle is far from the reactive site than when it is near to it. We find that a bulky pyridine-based catalyst promotes carbonate-forming reactions that ratchet the displacement of the macrocycle away from the reactive sites on the track. Under reaction conditions where both attachment and cleavage of the 9-fluorenylmethoxycarbonyl groups occur through different processes, and the cleavage reaction occurs at a rate independent of macrocycle location, net directional rotation of the molecular motor continues for as long as unreacted fuel remains. We anticipate that autonomous chemically fuelled molecular motors will find application as engines in molecular nanotechnology.</p

Evaluation of interactive in-car systems in immersive environments

In the coming few years, electronic innovation like driver assistance and information system as well as driving X-by-wire will radically change the development of car technology and the face of driving. Short development cycles and changing market demands require a fast and flexible prototyping, while the introduction of further communication, information and entertainment technology in cars makes it necessary to adjust their human machine interface into the driving context. For answering these demands the Fraunhofer Institute of Industry Engineering IAO developed a highly flexible virtual prototyping and testing system based on driving simulators. These systems can integrate several further interfaces via "Switchboard and therefore allow to flexibly introduce further data sources allowing a fast adaptability testing scenarios. This virtual prototyping and testing system has already been effective, tried and tested in several international research projects: Within SAVE, IN-ARTE and COMUNICAR a human-machine interface has been created for driver assistance systems and advanced media interaction devices. These interfaces were developed from the very beginning parallel to the technological system concept. A virtual prototype was designed after analyzing the user requirements and consequently run through a user test. The list of defects obtained from this trial will help to optimize the prototype and serves as input for further development phases

The response of soil nitrogen and 15N natural abundance to different amendments in a long-term experiment at Ultuna, Sweden

In a long-term field experiment on a clay loam soil at Uppsala, Sweden, changes in nitrogen contents, natural abundance of 15N in the topsoils receiving various organic amendments at the rate of 2 000 kg C ha-1year -1 and different rates of nitrogen mineralisation were studied. Cropping resulted in clearly lower N losses from the topsoil (0-20 cm) compared to the bare fallow plots. Green manure, animal manure and sewage sludge increased the Nt inventory significantly; for the latter two treatments an equilibrium of N input and N output was not reached within 35 years of application. The highest N efficiency with respect to plant uptake and the highest N losses were recorded for the mineral N-treated plots. 15N abundances were clearly affected by N input, differing in isotopic signature introduced through the amendments. This effect was used to derive the relative input of 'stable' N from green manure and peat in comparison with the difference method. (© Inra/Elsevier, Paris.)Réponse de l'azote du sol et de l'abondance naturelle de 15N à différents amendements organiques dans une expérience à long terme à Ultuna, Suède. Une expérience à long terme a été conduite sur un sol limonoargileux à Uppsala, Suède. Les modifications de la teneur en azote et de l'abondance naturelle de 15N dans la couche superficielle ont été étudiées en fonction des apports de différents amendements organiques correspondant à 2 000 kg C ha-1·an -1 avec différents taux de minéralisation de l'azote. Sous culture il apparaît clairement une plus faible perte en azote de la couche superficielle comparativement à un sol nu non cultivé. Les apports d'engrais vert, de fumier et de boues de station d'épuration ont accru significativement la teneur totale en azote Nt et pour les deux premiers traitements l'équilibre entre les apports et les pertes d'azote n'a pas été atteint au cours de 35 ans d'application. La meilleure efficience de l'azote en ce qui concerne l'extraction par la plante et la perte la plus élevée furent enregistrées pour les parcelles qui recevaient un apport d'azote minéral. L'abondance de 15N a été clairement affectée par les types d'apport d'amendements dont les signatures isotopiques étaient différentes. Cette particularité a été utilisée pour déduire l'apport relatif d'azote «stable» à partir d'un engrais vert et de la tourbe comparativement à la méthode différentielle. (© Inra/Elsevier, Paris.