NMR Spectroscopic Assignment of Backbone and Side‐Chain Protons in Fully Protonated Proteins: Microcrystals,Sedimented Assemblies,and Amyloid Fibrils

We demonstrate sensitive detection of alpha protons of fully protonated proteins by solid‐state NMR spectroscopy with 100–111 kHz magic‐angle spinning (MAS). The excellent resolution in the Cα‐Hα plane is demonstrated for 5 proteins, including microcrystals, a sedimented complex, a capsid and amyloid fibrils. A set of 3D spectra based on a Cα–Hα detection block was developed and applied for the sequence‐specific backbone and aliphatic side‐chain resonance assignment using only 500 μg of sample. These developments accelerate structural studies of biomolecular assemblies available in submilligram quantities without the need of protein deuteration.     

Low temperature crystallization behavior of TiO<Subscript>2</Subscript> derived from a sol–gel process

TiO₂ nanoparticles are widely used for many applications and an understanding of the crystallization behavior of TiO₂ is essential, so that heat treatment conditions can be optimized for particular applications. The effect of sol–gel synthesis conditions on the crystallization behavior of TiO₂ has, therefore, been investigated. Complete crystallization to the anatase phase (determined by XRD and TEM analysis) was achieved during drying of the synthesis product at 95 °C. The nanoparticles grew during heat treatment, reaching ∼10–15 nm in diameter with a heat treatment at 450 °C. Explanations are offered for the observed differences in the crystallization and particle growth behavior of TiO₂ synthesized under various conditions.     

Irreversible versus reversible aggregation: mean field theory and experiments

Colloidal aggregation processes arising at different electrolyte concentrations were studied by means of experiments and confronted with theoretical predictions of different kinetic aggregation models. For this purpose, aqueous dispersions of relatively large polystyrene microspheres were chosen as experimental systems. Aggregation was induced by adding KBr electrolyte to the initially stable particle dispersions. During the aggregation processes, the cluster-size distribution was monitored by means of single cluster light scattering. Analyzing the time evolution of the monomer concentration, we found that the processes arising even at moderate electrolyte concentrations cannot be described by pure time-independent irreversible aggregation models. Hence, alternative models such as time-dependent irreversible aggregation and several reversible aggregation models were also tested. The model that considers a time-dependent sticking probability was found to fit the data quite satisfactorily. Nevertheless, the fitted was so slow that it seems not very likely to find such a behavior in real systems. The aggregation-fragmentation models reported in the literature were unable to reproduce the experimental observations. Hence, a more realistic reversible aggregation model was developed. This model accounts also for reenforced or double bonds between the constituent particles. The corresponding fit improved significantly and reached the same quality as the time-dependent model. Moreover, the obtained fitting parameters were in qualitative agreement with the DLVO predictions and so, reversible aggregation seems to be a more reasonable explanation for the experimental data than time-dependent irreversible aggregation. However, no definite statement on the possible secondary bond fragmentation mechanism may be made since both the applied shear stress in the measuring cell and thermal fluctuations can cause weaker bonds to break.     

Synthesis, structure and magnetism of new single molecule magnets composed of MnII2MnIII2 alkoxo-carboxylate bridged clusters capped by triethanolamine ligands

A family of tetranuclear mixed-valent Mn(II)(2)/Mn(III)(2) complexes of type [Mn(4)(LH(2))(2)(LH)(2)(H(2)O)(x)(RCO(2))(2)](Y)2.nS has been synthesised and structurally characterised, where LH(3) = triethanolamine (N(CH(2)CH(2)OH)(3)), (R=CH(3), x=2, Y = CH(3)CO(2)-, n=2, S = H(2)O; 1), (R=C(6)H(5), x=0, Y=C(6)H(5)CO(2)-, n=1, S = CH(3)CN; 2), (R=C(2)H(5), x=0, Y=ClO(4)(-), n=0; 3). A common structural core was deduced from X-ray crystallography and consists of a rhomboidal (planar-diamond) array with two 7-coordinate Mn(II) "wingtip (w)" centres and two 6-coordinate Mn(III) "body (b)" centres. The Mn(III) ions are bridged to the Mn(II) ions by mu3-oxygen atoms from a deprotonated alcohol "arm" of each tridentate LH(2-) ligand and by mu2-oxygen atoms from each tetradentate LH(2)(-) ligand. The four nitrogen atoms from LH(2-) and LH(2)(-) groups, together with bridging and terminal carboxylates oxygens complete the outer coordination sites around the Mn atoms. A feature of these clusters is that they are linked together in the crystal lattice by hydrogen-bonding interactions involving a non-coordinated hydroxyl arm on each LH(2-) group. Detailed DC and AC magnetic susceptibility measurements and magnetisation isotherms have been made on the three complexes and show that intra-cluster ferromagnetic coupling is occurring between the S = 2 Mn(III) and S = 5/2 Mn(II) ions to yield S = 9 ground states. The g, J(bb) and J(wb) parameters have been deduced. Inter-cluster antiferromagnetic coupling was noted in and this influences the magnetisation versus field behaviour and the temperature and magnitude of the out-of-phase AC chi"M maxima in comparison to those observed for and. An Arrhenius plot of the reciprocal temperature of the maxima in chi"M obtained at different frequencies (10 to 1500 Hz), in the range 1.75 K to 4 K, against the natural logarithm of the magnetization relaxation rate (1/tau) yielded values of the activation energies and pre-exponential factors for two of these new tetranuclear single-molecule magnets (SMMs), and. The activation energies were compared with the potential energy barrier height, U, for magnetisation direction reversal (U = DS(2)) using the axial zero-field splitting parameter, D, deduced from the DC M/H isotherm analysis for these S = 9 species. The very small separation of S = 9 and 8 levels for these clusters highlights the limitations in the determination of D values from M/H data at low temperatures.     

Tunable laser photodissociation: quantum yield of I★(2P12) from Ch2I2

Tunable laser I^★(²P_{$\text{1}\text{2}$}) quantum-yield measurements are presented for CH₂I₂ in the wavelength range 248–340 nm. The results suggest that a curve-crossing mechanism is operative in the dissociation.     

Interpolation of relative retentions as a tool for identification of perhalogenated compounds

Summary Separation of perhalogenated compounds resulting from thermolysis, photolysis or radiolysis of mixtures of halogens in carbon tetrachloride was carried out by programmed temperature gas chromatography. Plots of relative retentions (to CBr₄) vs the number of bromine atoms present for known compounds of the general formula C_xBr_yCl_z (x=1 and 2; y+z=4 or 6) gave three linear correlations (all with r>0.99). These correlations permitted projections of the identities of reaction products for which no standards were available. These projections were later confirmed by CG-MS. *** DIRECT SUPPORT *** A0732166 00010     

Optimization of power production and costs in microgrids

This paper proposes a mathematical formulation for energy management in a connected microgrid. The aim is determining the optimal operating strategy for energy storage, to fulfil a time-varying energy demand and operational constraints while achieving a tradeoff between microgrid running costs and energy storage system life. The microgrid is composed by various renewable power production plants, storage devices and controllable loads, and has the ability to increase energy efficiency and reduce costs for energy purchasing from the main grid. The problem is formulated as a mixed-integer linear optimization problem. The optimization is aimed at minimizing the overall cost function of the system while satisfying the customer demand and safety of the electrical network. A case study of an existing microgrid is investigated: the microgrid consists of a photovoltaic and a hydroelectric power plant, a battery storage, an office building and an industrial facility. The optimization problem is solved in an efficient way by using commercial software. Simulation results show the feasibility and the effectiveness of the proposed approach to satisfy the load and reduce total costs.     

广义Bethe树上奇偶马尔可夫链场上的若干极限性质

通过构造两个非负鞅证明了一个强极限定理,然后把它应用到本文所定义的广义Bethe树上的奇偶马尔可夫链场上,从而获得了此马氏链场上的一类强极限定理.