Characterization of the metal-organic framework compound Cu3(benzene 1,3,5-tricarboxylate)2 by means of 129Xe nuclear magnetic and electron paramagnetic resonance spectroscopy

129Xe NMR measurements of adsorbed xenon are shown for the first time to be a suitable tool to characterize the porosity and the properties of the metal-organic framework Cu3(BTC)2(H2O)3 (BTC = benzene 1,3,5-tricarboxylate). The NMR experiments are performed at room temperature and over a wide range of xenon pressure and on two different synthesized Cu3(BTC)2 samples. 129Xe NMR results reveal that in dependence on the kind of the synthesis pathway either one or two signals are observed which can be attributed to two kinds of fast exchange of xenon atoms in two pores with different pore sizes. Coadsorption experiments of xenon and ethylene demonstrate that the xenon atoms prefer to fill the greater pores of the material because the smaller pores are occupied with residual molecules from the synthesis procedure and additionally adsorbed ethylene. Besides the NMR experiments a series of electron paramagnetic resonance (EPR) measurements are performed to estimate the state of copper having a strong influence on the chemical shift of the adsorbed xenon. The EPR experiments demonstrate that spin exchange between the interconnected copper dimers is taking place across the BTC linker molecules in the Cu3(BTC)2 framework.     

Self-assembly of nanoparticles into rings: a lattice-gas model

A coarse-grained lattice-gas model in three dimensions is developed to study the self-assembly of nanoparticles into micrometer-sized rings from a thin liquid film containing the nanoparticles. The model describes the nanoparticles as well as the solvent on length scales that are typical of the solvent bulk correlation length. Morphologies obtained from simulations of the model resemble recent experiments and provide a microscopic picture for the formation of nanoparticle rings. The role of evaporation rate, film thickness, diffusion rate, and nanoparticle coverage is discussed and compared to other continuum theories. Predictions of novel structures resulting from low nanoparticle mobility are analyzed.     

Hydrophilic-Interaction Planar Chromatography of Some Water-Soluble Co(III) Complexes on Different Adsorbents

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of twelve neutral, mixed cobalt(HI) complexes of the uns-cis-edda-type has been investigated in six...     

Adiabatic pumping in interacting systems

A dc current can be pumped through an interacting system by periodically varying two independent parameters such as the magnetic field and a gate potential. We present a general expression for the adiabatic pumping current in interacting systems, written in terms of instantaneous properties of the system at equilibrium, and find the limits of its applicability. This expression generalizes the scattering approach for noninteracting particles. We apply our formula for a quantum critical system that exhibits the two-channel Kondo effect, where single particle excitations are not well defined. We find that if the quantum critical point is contained in the pumping trajectory, the pumped spin between the channels approaches h, and if it is not contained in the trajectory, the spin approaches zero when the temperature T --> 0. We discuss the non-Fermi liquid features of this system at finite T.     

Spectral techniques applied to sparse random graphs

We analyze the eigenvalue gap for the adjacency matrices of sparse random graphs. Let λ₁ ≥ … ≥ λ_n be the eigenvalues of an n‐vertex graph, and let λ = max[λ₂,|λ_n|]. Let c be a large enough constant. For graphs of average degree d = c log n it is well known that λ₁ ≥ d, and we show that . For d = c it is no longer true that , but we show that by removing a small number of vertices of highest degree in G, one gets a graph G′ for which . Our proofs are based on the techniques of Friedman Kahn and Szemeredi from STOC 1989, who proved similar results for regular graphs. Our results are useful for extending the analysis of certain heuristics to sparser instances of NP‐hard problems. We illustrate this by removing some unnecessary logarithmic factors in the density of k‐SAT formulas that are refuted by the algorithm of Goerdt and Krivelevich from STACS 2001. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005     

Depth-resolved multiphoton polarization microscopy by third-harmonic generation

We achieve depth-resolved polarization microscopy by measuring third-harmonic generation induced by a tightly focused circularly polarized beam. In crystals exhibiting strong birefringence this signal is dominated by positively phase-matched third-harmonic generation. This process occurs in only optically anisotropic media, in which the birefringence compensates for the phase mismatch between the fundamental and the third harmonic induced by dispersion. Both the intensity and the polarization of the emitted signal provide information on the local optical anisotropy. We demonstrate the technique by imaging biogenic crystals in sea urchin larval spicules.     

Unusual Electro‐Optic Kerr Response in a Self‐Stabilized Amorphous Blue Phase with Nanoscale Smectic Clusters

We investigated the electro‐optic response in the “foggy” amorphous blue phase (BPIII) as well as in the isotropic phase. To the best of our knowledge, such a study has not yet been performed due to the very limited thermal range of BPIII. In this study, we used a single‐component chiral bent‐core liquid crystal with a self‐stabilized BPIII, which is stable over a wide temperature range. The results show that the response time is on the order of hundreds of microseconds in the isotropic phase and increases to 1–2 ms in the BPIII (at T_I?BP–T <1), then drastically increases up to a few tens of milliseconds upon further cooling in BPIII. Such an unusual behavior was explained on the basis of the high rotational viscosity and/or the existence of nanoscale smectic (Sm) clusters. The Kerr constant was also measured and found to be ～500 pm V^?2, which is the largest among bent‐core BP systems reported so far and comparable with that of polymer‐stabilized BPs.     

Homoleptic Two‐Coordinate Silylamido Complexes of Chromium(I), Manganese(I), and Cobalt(I)

Anionic two‐coordinate complexes of first‐row transition‐metal(I) centres are rare molecules that are expected to reveal new magnetic properties and reactivity. Recently, we demonstrated that a N(SiMe₃)₂^? ligand set, which is unable to prevent dimerisation or extraneous ligand coordination at the +2 oxidation state of iron, was nonetheless able to stabilise anionic two‐coordinate Fe^I complexes even in the presence of a Lewis base. We now report analogous Cr^I and Co^I complexes with exclusively this amido ligand and the isolation of a [Mn^I{N(SiMe₃)₂}₂]₂^2? dimer that features a Mn?Mn bond. Additionally, by increasing the steric hindrance of the ligand set, the two‐coordinate complex [Mn^I{N(Dipp)(SiMe₃)}₂]^? was isolated (Dipp=2,6‐iPr₂‐C₆H₃). Characterisation of these compounds by using X‐ray crystallography, NMR spectroscopy, and magnetic susceptibility measurements is provided along with ligand‐field analysis based on CASSCF/NEVPT2 ab initio calculations.     

Kinetics of the Antibody Recognition Site in the Third IgG‐Binding Domain of Protein G

Protein dynamics occurring on a wide range of timescales play a crucial role in governing protein function. Particularly, motions between the globular rotational correlation time ( ) and 40 μs (supra‐ window), strongly influence molecular recognition. This supra‐ window was previously hidden, owing to a lack of experimental methods. Recently, we have developed a high‐power relaxation dispersion (RD) experiment for measuring kinetics as fast as 4 μs. For the first time, this method, performed under super‐cooled conditions, enabled us to detect a global motion in the first β‐turn of the third IgG‐binding domain of protein G (GB3), which was extrapolated to 371±115 ns at 310 K. Furthermore, the same residues show the plasticity in the model‐free residual dipolar coupling (RDC) order parameters and in an ensemble encoding the supra‐ dynamics. This β‐turn is involved in antibody binding, exhibiting the potential link of the observed supra‐ motion with molecular recognition.