On the stability, electronic structure, and nonlinear optical properties of HXeOXeF and FXeOXeF

The electronic ground state, stability, and linear and nonlinear optical properties of HXeOXeF and FXeOXeF have been studied theoretically by employing complete active space valence bond (CASVB), multistate complete active space perturbation theory (MS-CASPT2), and coupled cluster methods. It is shown that the oxygen inserted between the two Xe atoms significantly modifies the ground-state electronic configuration of the formed derivative by increasing the closed-shell contribution (σ(2)) and removing the diradicaloid character observed in HXe(2)F. The electronic charge distribution has been analyzed by employing the atoms-in-molecules (AIM) method. The dissociation channels of HXeOXeF and FXeOXeF have been studied in detail. It was found that these compounds are metastable, protected by substantial energy barriers and, thus, they can be prepared under appropriate conditions. Both two- and three-body dissociation reactions have been considered. The effects of inserting O in HXe(2)F and substituting H (HXeOXeF) by F, leading to FXeOXeF, on the energy barriers are discussed. The significant effects of the inserted oxygen on the polarizability and even more on the first hyperpolarizability have been computed and rationalized.     

Concentration of 238U and 232Th among constituent minerals of two igneous plutonic rocks exhibiting elevated natural radioactivity levels

The concentrations of ²³⁸U and ²³²Th of the constituent minerals in two plutonic rock samples, from N. Greece, exhibiting elevated levels of bulk rock natural radioactivity were determined by using LA-ICP-MS. The available data of whole rock ²³⁸U and ²³²Th concentrations were also used. The minerals were separated using a combination of heavy liquids of various densities, shaking table and magnetic separation techniques. The great variation in the concentrations of ²³⁸U and ²³²Th is probably indicative of the different distribution of U and Th within the same rock, as well as to secondary post-magmatic processes that were responsible for the redistribution of U and Th. An estimation of the contribution of each mineral constituent to the natural radioactivity levels of the bulk rock is attempted. Thorite and zircon contribute the most to the whole rock ²³⁸U and ²³²Th content, while the contribution of apatite is moderate. The contribution of the rest of the minerals examined (fluorite, quartz, plagioclase, K-feldspar, amphibole, pyroxene, magnetite and biotite) is not important.     

Estimating uncertainty in matrix solid phase extraction methodology for the determination of chlorinated compounds in fish

In this study, a detailed process of uncertainty estimation associated with matrix solid phase dispersion method (MSPD) for the extraction of organochlorinated compounds from fish coupled with gas chromatography is given. The evaluation of uncertainty arising from trueness using fully nested experimental designs is presented by estimating proportional bias, in terms of recovery. The uncertainty of measurements associated with the actual chromatographic process was also estimated. The methodology was applied for the determination of selected organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in real fish samples, from selected study locations in Western Greece (Mesologgi lagoon and Trichonida lake), based on chromatographic techniques. The sources of uncertainty are presented along with the calculated combined uncertainty terms derived from the analytical procedure and chromatographic process. The estimation of uncertainty was included in the presentation of final determinations.     

Experimental and First‐Principles Characterization of Functionalized Magnetic Nanoparticles

Magnetic iron oxide nanoparticles synthesized by coprecipitation and thermal decomposition yield largely monodisperse size distributions. The diameters of the coprecipitated particles measured by X‐ray diffraction and transmission electron microscopy are between approximately 9 and 15 nm, whereas the diameters of thermally decomposed particles are in the range of 8 to 10 nm. Coprecipitated particles are indexed as magnetite‐rich and thermally decomposed particles as maghemite‐rich; however, both methods produce a mixture of magnetite and maghemite. Fourier transform IR spectra reveal that the nanoparticles are coated with at least two layers of oleic acid (OA) surfactant. The inner layer is postulated to be chemically adsorbed on the nanoparticle surface whereas the rest of the OA is physically adsorbed, as indicated by carboxyl O? H stretching modes above 3400 cm^?1. Differential thermal analysis (DTA) results indicate a double‐stepped weight loss process, the lower‐temperature step of which is assigned to condensation due to physically adsorbed or low‐energy bonded OA moieties. Density functional calculations of Fe–O clusters, the inverse spinel cell, and isolated OA, as well as OA in bidentate linkage with ferrous and ferric atoms, suggest that the higher‐temperature DTA stage could be further broken down into two regions: one in which condensation is due ferrous/ferrous– and/or ferrous/ferric–OA and the other due to condensation from ferrous/ferric– and ferric/ferric–OA complexes. The latter appear to form bonds with the OA carbonyl group of energy up to fivefold that of the bond formed by the ferrous/ferrous pairs. Molecular orbital populations indicate that such increased stability of the ferric/ferric pair is due to the contribution of the low‐lying Fe³⁺ t_2g states into four bonding orbitals between ?0.623 and ?0.410 a.u.     

Binding of novel fullerene inhibitors to HIV-1 protease: insight through molecular dynamics and molecular mechanics Poisson–Boltzmann surface area calculations

The objectives of this study include the design of a series of novel fullerene-based inhibitors for HIV-1 protease (HIV-1 PR), by employing two strategies that can also be applied to the design of inhibitors for any other target. Additionally, the interactions which contribute to the observed exceptionally high binding free energies were analyzed. In particular, we investigated: (1) hydrogen bonding (H-bond) interactions between specific fullerene derivatives and the protease, (2) the regions of HIV-1 PR that play a significant role in binding, (3) protease changes upon binding and (4) various contributions to the binding free energy, in order to identify the most significant of them. This study has been performed by employing a docking technique, two 3D-QSAR models, molecular dynamics (MD) simulations and the molecular mechanics Poisson–Boltzmann surface area (MM–PBSA) method. Our computed binding free energies are in satisfactory agreement with the experimental results. The suitability of specific fullerene derivatives as drug candidates was further enhanced, after ADMET (absorption, distribution, metabolism, excretion and toxicity) properties have been estimated to be promising. The outcomes of this study revealed important protein–ligand interaction patterns that may lead towards the development of novel, potent HIV-1 PR inhibitors.     

Quantitative analysis of infrared absorption coefficient of spider silk fibers

Spider silk has a high degree of crystallinity comprising nanocrystals which are interlinked by amorphous regions containing pre-strained spidroin chains. Both, crystal volume fraction and crystal size were shown to be critical for the macroscopic mechanical properties of silk. In this study, for the first time, quantitative results were obtained from absorption IR spectra. Two main difficulties must be overcome: the cylindrical sample geometry and the absence of suitable reference spectra. We show that it is possible to get reproducible absorption coefficient spectra from dense parallel fiber grids immersed in a refractive index matching liquid. Comparison with model polypeptides yields the nanocrystal volume fraction that is close to the crystallinity values given by solid-state NMR or X-ray scattering.     

Combining glycomimetic and multivalent strategies toward designing potent bacterial lectin inhibitors

As part of ongoing activities toward the design of potent and selective ligands against galactoside-binding proteins from animal, bacterial, and plant lectins, a systematic investigation involving the synthesis and binding evaluations of a series of original β-C-galactopyranoside mimetics is described. The multivalent presentation of partly optimized candidates on various dendritic scaffolds through Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) has also been achieved. Biophysical investigations based on isothermal titration calorimetry (ITC) have indicated a dissociation constant in the low micromolar range for the best optimized monovalent conjugate (K(d)=37 μM). The results thus confirmed that stable C-galactosides could represent efficient synthetic glycomimetics of natural α-linked oligosaccharidic inhibitors of PA-IL lectin (Lec A) from the pathogenic Pseudomonas aeruginosa. Striking enhancements in the avidity of the glycoconjugates were also observed for tri-, hexa-, and nonavalent derivatives, among which the most potent exhibited dissociation constants below 500 nM, corresponding to a 400-fold increase in affinity compared with the β-D-Gal-O-Me used as reference. To deepen our understanding of the binding mode of the best glycomimetics involved in the recognition process, molecular modeling studies, docking calculations, and NMR diffusion measurements have been performed. Although favorable complementary interactions induced by the addition of the hydrophobic aglycon might explain the affinity enhancement, experimental determination of the size and the topology of the multivalent conjugates further supported the formation of aggregative complexes as a major multivalent binding mode. This work represents a systematic and comprehensive study towards a thorough understanding of the protein-carbohydrate interactions involved in Pseudomonas aeruginosa infection, and as such should prove useful for the development of stable and optimized anti-adhesive agents.     

分子内结构环境对解离能的影响

为了理解化学键的这一结构效应, 本文对具有相同化学键而分子内结构环境不同的系列分子进行了计算研究, 讨论了化学键结构环境对解离能的影响.