Sorption of platinum on immobilized microorganisms for its on-line preconcentration and chemiluminescent determination in water samples

Fungi of the type Aspergillus sp. were immobilized on a cellulosic resin and used as a biosorbent for the on-line preconcentration and separation of Pt(IV) ions prior to their chemiluminescent determination via flow injection analysis. Biosorption and elution conditions were optimized, and the results compared to biosorbents based on the use of Chlorella vulgaris algae and Saccharomyces cerevisiae yeast in terms of preconcentration and selective retention of Pt(IV). The immobilized fungi presented here have a high potential for use in platinum biosorption. The procedure exhibits the currently lowest limit of detection (0.02 ng mL−1 of Pt) and very high selectivity. The procedure was applied to the determination of Pt(IV) in river water, road run-off, and wastewater samples

Cloud computing - the Benefits and risks

More and more frequently companies decide to get rid of certain functions of their structures by using outside firms to provide components and services. Outsourcing, very popular in recent years, has the purpose of reducing spendings in departments of a company. However, it this goal achieved? Often, such cost reduction is connected with the dependence of the customer on the supplier - which can, in the long run, globally contribute to raising costs. Will such delegation of certain responsibilities not cause a significant danger of losing its independence and a gradual increase in spendings in such a way that, in a broader perspective, they will be much higher than the costs before outsourcing? What will happen when a company dependent on its supplier or provider wants to pass another or a different company a particular job? Furthermore, if the company management decided to dispense with the services offered by a third party - would we be able to import the data that we receive into any other system? The compilation is an attempt at familiarizing the reader with the meaning of Cloud computing, as well as the concepts directly related to it. An attempt has been made to systemise the knowledge of the subject and present the main premises and hazards that are associated with the implementation of solution

Hydrogen atoms can be located accurately and precisely by x-ray crystallography

Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A–H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A–H bond lengths with those from neutron measurements for A–H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors

Ab Initio Modeling of Graphene Functionalized with Boron and Nitrogen

We investigate theoretically the electronic properties of graphene functionalized with nitrogen and boron atoms substituted into the graphene monolayer. Our study is based on the ab initio calculations in the framework of the density functional theory. We predict the dependence of the energy band gap, binding energy per atom, and the shift of the Fermi level on the concentration of dopants. Moreover, we examine the influence of the distribution of B/N atoms on the specified properties

Monte Carlo Simulations of Ferromagnetic Nanocomposites

We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic field. In our simulations we take into account the interaction with the external magnetic field, the energy of crystallographic anisotropy and the dipole-dipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature $T_{B}$ on particle and cluster size

On the accuracy and precision of X-ray and neutron diffraction results as a function of resolution and the electron density model

X-ray diffraction is the main source of three-dimensional structural information.In total, more than 1.5 million crystal structures have been refined and depositedin structural databanks (PDB, CSD and ICSD) to date. Almost 99.7% of themwere obtained by approximating atoms as spheres within the independent atommodel (IAM) introduced over a century ago. In this study, X-ray datasets forsingle crystals of hydrated-oxalic acid were refined using several alternativeelectron density models that abandon the crude spherical approximation: themultipole model (MM), the transferable aspherical atom model (TAAM) andthe Hirshfeld atom refinement (HAR) model as a function of the resolution ofX-ray data. The aspherical models (MM, TAAM, HAR) give far more accurateand precise single-crystal X-ray results than IAM, sometimes identical to resultsobtained from neutron diffraction and at low resolution. Hence, asphericalapproaches open new routes for improving existing structural informationcollected over the last century

Validation of X-ray Wavefunction Refinement

In this work, the quality of the electron density in crystals reconstructed by the multipolar model (MM) and by X-ray wavefunction refinement (XWR) is tested on a set of high-resolution X-ray diffraction data sets of four amino acids and six tripeptides. It results in the first thorough validation of XWR. Agreement statistics, figures of merit, residual- and deformation-density maps, as well as atomic displacement parameters are used to measure the quality of the reconstruction relative to the measured structure factors. Topological analysis of the reconstructed density is carried out to obtain atomic and bond-topological properties, which are subsequently compared to the values derived from benchmarking periodic DFT geometry optimizations. XWR is simultaneously in better agreement than the MM with both benchmarking theory and the measured diffraction pattern. In particular, the obvious problems with the description of polar bonds in the MM are significantly reduced by using XWR. Similarly, modeling of electron density in the vicinity of hydrogen atoms with XWR is visibly improved

Hirshfeld atom refinement for modelling strong hydrogen bonds

High-resolution low-temperature synchrotron X-ray diffraction data of the salt L-phenylalaninium hydrogen maleate are used to test the new automated iterative Hirshfeld atom refinement (HAR) procedure for the modelling of strong hydrogen bonds. The HAR models used present the first examples of Z' > 1 treatments in the framework of wavefunction-based refinement methods. L-Phenylalaninium hydrogen maleate exhibits several hydrogen bonds in its crystal structure, of which the shortest and the most challenging to model is the O-H...O intramolecular hydrogen bond present in the hydrogen maleate anion (O...O distance is about 2.41 Å). In particular, the reconstruction of the electron density in the hydrogen maleate moiety and the determination of hydrogen-atom properties [positions, bond distances and anisotropic displacement parameters (ADPs)] are the focus of the study. For comparison to the HAR results, different spherical (independent atom model, IAM) and aspherical (free multipole model, MM; transferable aspherical atom model, TAAM) X-ray refinement techniques as well as results from a low-temperature neutron-diffraction experiment are employed. Hydrogen-atom ADPs are furthermore compared to those derived from a TLS/rigid-body (SHADE) treatment of the X-ray structures. The reference neutron-diffraction experiment reveals a truly symmetric hydrogen bond in the hydrogen maleate anion. Only with HAR is it possible to freely refine hydrogen-atom positions and ADPs from the X-ray data, which leads to the best electron-density model and the closest agreement with the structural parameters derived from the neutron-diffraction experiment, e.g. the symmetric hydrogen position can be reproduced. The multipole-based refinement techniques (MM and TAAM) yield slightly asymmetric positions, whereas the IAM yields a significantly asymmetric position