Two new chiral EDTA-based metal chelates for weak alignment of proteins in solution

[structure: see text] A short synthesis of EDTA-based metal chelates that can be attached to the cysteine residue of a protein via a disulfide bond is described. The complexes were used after coordination of lanthanides to align trigger factor and apo-calmodulin in solution to yield residual dipolar couplings and pseudocontact shifts. Alignment tensors for the new tags are linearly independent compared to those of previously published tags.     

Computational modeling of polyoxotungstates by relativistic DFT calculations of (183)W NMR chemical shifts

The (183)W nuclear shielding in a variety of tungsten polyoxometalates (POM) (Lindqvist, Anderson, decatungstates, Keggin) of different shapes and charges has been modeled by DFT calculations that take into account relativistic effects, by means of the zero-order regular approximation (ZORA), and solvent effects, by the conductor-like screening model (COSMO) continuum method. The charge/surface area ratio (q/A) is proposed as an indicator of the charge density to which the solvation energies of all POMs are correlated in a satisfactory way. Among the various theoretical levels tested (ZORA scalar or spin-orbit, frozen-core or all-electron basis set, geometry optimization in the gas phase or in the continuum solvent, etc.), the best results are obtained when both geometry optimization in solvent and spin-orbit shielding are included (mean absolute error of delta=35 ppm). The quality of the computed chemical shifts depends systematically on the charge density as expressed by q/A; thus, POMs with low q/A ratios display the best agreement with experimental data. The performance of the method is such that computed values can aid the assignment of the (183)W NMR spectra of polyoxotungstates, as shown by the case of alpha-[PW(11)TiO(40)](5-), whose six signals are ranked computationally so as to almost reproduce the experimental ordering even though the signals are spaced by as little as 5 ppm.     

Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary material by COSIMA onboard ROSETTA

Chemometric data evaluation methods for time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been tested for the characterization and classification of minerals. Potential applications of these methods include the expected data from cometary material to be measured by the COSIMA instrument onboard the ESA mission ROSETTA in the year 2014. Samples of the minerals serpentine, enstatite, olivine, and talc have been used as proxies for minerals existing in extraterrestrial matter. High mass resolution TOF-SIMS data allow the selection of peaks from inorganic ions relevant for minerals. Multivariate cluster analysis of peak intensity data by principal components analysis and the new method CORICO showed a good separation of the mineral classes. Classification by k nearest-neighbor classification (KNN) or binary decision trees (CART method) results in more than 90% correct class assignments in a leave-one-out cross validation.     

Density functional study of the 13C NMR chemical shifts in small-to-medium-diameter infinite single-walled carbon nanotubes

NMR chemical shifts were calculated for semiconducting (n,0) single-walled carbon nanotubes (SWNTs) with n ranging from 7 to 17. Infinite isolated SWNTs were calculated using a gauge-including projector-augmented plane-wave (GIPAW) approach with periodic boundary conditions and density functional theory (DFT). In order to minimize intertube interactions in the GIPAW computations, an intertube distance of 8 A was chosen. For the infinite tubes, we found a chemical shift range of over 20 ppm for the systems considered here. The SWNT family with lambda = mod(n, 3) = 0 has much smaller chemical shifts compared to the other two families with lambda = 1 and lambda = 2. For all three families, the chemical shifts decrease roughly inversely proportional to the tube's diameter. The results were compared to calculations of finite capped SWNT fragments using a gauge-including atomic orbital (GIAO) basis. Direct comparison of the two types of calculations could be made if benzene was used as the internal (computational) reference. The NMR chemical shifts of finite SWNTs were found to converge very slowly, if at all, to the infinite limit, indicating that capping has a strong effect (at least for the (9,0) tubes) on the calculated properties. Our results suggest that (13)C NMR has the potential for becoming a useful tool in characterizing SWNT samples.     

Dissolution kinetics of titanium dioxide nanoparticles: the observation of an unusual kinetic size effect

Different types of industrially produced titanium dioxide nanoparticles and a precipitated titanium dioxide have been dissolved in aqueous NaCl solutions at temperatures of 25 and 37 degrees C. The titanium concentration in solution with regard to dependence on time has been determined up to 3000 h after starting the dissolution experiment. The effect of particle size, pH value, temperature, background electrolyte concentration, and mass concentration of titanium dioxide exposed to the liquid phase has been studied. The nanoparticles have been characterized by N2 physisorption measurements and XRD. The total dissolved titanium in solution has been determined by adsorptive stripping voltammetry (AdSV) and inductively coupled plasma mass spectrometry (ICP-MS). A new kinetic size effect has been observed. It turns out that this effect can be explained by applying an already existing phenomenological thermodynamic and kinetic model. The model describes all possible phenomena in a colloidal dispersion, nucleation, growth of particles, Ostwald ripening, and dissolution of particles using a uniform concept.     

Low-dimensional compounds containing cyano groups. XVII. Crystal structure, spectroscopic, thermal and magnetic properties of [Cu(bmen)2][Pt(CN)4] (bmen=N,N′-dimethylethylenediamine)

The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {[Cu(bmen)₂][Pt(CN)₄]}_n (bmen=N,N′-dimethylethylenediamine) are presented. X-ray crystal-structure analysis revealed that the [Pt(CN)₄]²⁻ building blocks are combined with [Cu(bmen)₂]²⁺ units to form a chain-like structure along the a axis. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane belonging to two molecules of bidentate bmen ligands with average Cu-N distance of 2.043(18) Å. The axial positions are occupied by two nitrogen atoms from bridging [Pt(CN)₄]²⁻ anions at a longer axial Cu-N distance of 2.490(4) Å. The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/k_B=0.6 K. Despite the one-dimensional (1D) character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen)₂][Pt(CN)₄] behaves as a two-dimensional (2D) square-lattice Heisenberg magnet with weak interlayer coupling.     

Thermodynamic aspects of the host-guest chemistry of pyrogallol[4]arenes and peralkylated ammonium cations

The stability constants (K), standard free energy (ΔG^o), enthalpy (ΔH^o), and entropy changes (ΔS^o) for the complexation of pyrogallol[4]arenes with ammonium cations of different size and shape have been determined in ethanol at 298 K by isothermal titration calorimetry. The trends observed in the thermodynamic parameters for 1:1 and/or 1:2 host-guest complexation correspond to the systematic structural changes of the guest molecules. On the basis of the results obtained we compare the complexation properties with two other resorcin[4]arenes and discuss the thermodynamic aspects of this supramolecular host-guest interactions.     

Hydrogen–Deuterium Exchange Reactions of Aromatic Compounds and Heterocycles by NaBD4‐Activated Rhodium,Platinum and Palladium Catalysts

Conventional thermal and microwave conditions were compared for hydrogen–deuterium (H/D) exchange reactions of aminobenzoic acids catalysed by NaBD₄‐activated Pd/C or RhCl₃ with D₂O as the deuterium source. We also investigated different NaBD₄‐activated metal catalysts (including Pd/C, RhCl₃ and Pt/C) under microwave conditions for an efficient H/D exchange of aromatic and heterocyclic compounds. Even higher deuterium incorporations were obtained for Pd/C and Pt/C catalyst mixtures due to the previously observed synergistic effect. Finally, we have applied these optimised conditions for one‐step syntheses of the MS standards of several pharmaceutically active compounds.