In Situ Monitoring of Unique Switching Transitions in the Pressure Amplifying Flexible Framework Material DUT 49 by High Pressure 129Xe NMR Spectroscopy

The pronounced flexibility of special metal amp; 8722;organic frameworks MOFs , so called soft porous crystals, is attracting increasing research interest. Studies of host amp; 8722;guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR spectroscopy is favorable because it provides characteristic, structure sensitive parameters such as chemical shifts. The combination of highpressure xenon adsorption with 129Xe NMR spectroscopy was used to elucidate the adsorption induced phase transitions in the recently discovered pressure amplifying framework material DUT 49, showing a unique negative gas adsorption NGA transition. In the open pore state, DUT 49op exhibits a hierarchical pore system involving both micro and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increase of the pressure initiates the recovery of the mesopores without any indication of a structural intermediate in the NMR spectra. According to the NMR data, the structural transition induced by xenon is a collective, stepwise phenomenon rather than a continuous process. This is the first time that NGA has been studied by directly monitoring the guest and its interaction with the host framewor

Exceptional adsorption induced cluster and network deformation in the flexible metal organic framework DUT 8 Ni observed by in situ X ray diffraction and EXAFS

The gate opening mechanism in the highly flexible MOF Ni2 2,6 ndc 2dabco DUT 8 Ni , DUT Dresden University of Technology with unprecedented unit cell volume change was elucidated in detail using combined single crystal X ray diffraction, in situ XRD and EXAFS techniques. The analysis of the crystal structures of closed pore cp and large pore lp phases reveals a drastic and unique unit cell volume expansion of up to 254 , caused by adsorption of gases, surpassing other gas pressure switchable MOFs significantly. To a certain extent, the structural deformation is specific for the guest molecule triggering the transformation due to subtle differences in adsorption enthalpy, shape, and kinetic diameter of the guest. Combined adsorption and powder diffraction experiments using nitrogen 77 K , carbon dioxide 195 K , and n butane 272.5 K as a probe molecules reveal a one step structural transformation from cp to lp. In contrast, adsorption of ethane 185 K or ethylene 169 K results in a two step transformation with the formation of intermediate phases. In situ EXAFS during nitrogen adsorption was used for the first time to monitor the local coordination geometry of the metal atoms during the structural transformation in flexible MOFs revealing a unique local deformation of the nickel based paddle wheel nod

Workflow and Tools for Crystallographic Fragment Screening at the Helmholtz Zentrum Berlin

Fragment screening is a technique that helps to identify promising starting points for ligand design. Given that crystals of the target protein are available and display reproducibly high resolution X ray diffraction properties, crystallography is among the most preferred methods for fragment screening because of its sensitivity. Additionally, it is the only method providing detailed 3D information of the binding mode of the fragment, which is vital for subsequent rational compound evolution. The routine use of the method depends on the availability of suitable fragment libraries, dedicated means to handle large numbers of samples, state of the art synchrotron beamlines for fast diffraction measurements and largely automated solutions for the analysis of the results. Here, the complete practical workflow and the included tools on how to conduct crystallographic fragment screening CFS at the Helmholtz Zentrum Berlin HZB are presented. Preceding this workflow, crystal soaking conditions as well as data collection strategies are optimized for reproducible crystallographic experiments. Then, typically in a one to two day procedure, a 96 membered CFS focused library provided as dried ready to use plates is employed to soak 192 crystals, which are then flash cooled individually. The final diffraction experiments can be performed within one day at the robot mounting supported beamlines BL14.1 and BL14.2 at the BESSY II electron storage ring operated by the HZB in Berlin Adlershof Germany . Processing of the crystallographic data, refinement of the protein structures, and hit identification is fast and largely automated using specialized software pipelines on dedicated servers, requiring little user input. Using the CFS workflow at the HZB enables routine screening experiments. It increases the chances for successful identification of fragment hits as starting points to develop more potent binders, useful for pharmacological or biochemical application

Formation of Periodically Arranged Nanobubbles in Mesopores Capillary Bridge Formation and Cavitation during Sorption and Solidification in an Hierarchical Porous SBA 15 Matrix

We report synchrotron based small angle X ray scattering experiments on a template grown porous silica matrix Santa Barbara Amorphous 15 upon in situ sorption of fluorinated pentane C5F12 along with volumetric gas sorption isotherm measurements. Within the mean field model of Saam and Cole for vapor condensation in cylindrical pores, a nitrogen and C5F12 sorption isotherm is well described by a bimodal pore radius distribution dominated by meso and micropores with 3.4 and 1.6 nm mean radius, respectively. In the scattering experiments, two different periodicities become evident. One of them d1 11.5 nm reflects the next nearest neighbor distance in a 2D hexagonal lattice of tubular mesopores. A second periodicity d2 11.4 nm found during in situ sorption and freezing experiments is traced back to a superstructure along the cylindrical mesopores. It is compatible with periodic pore corrugations found in electron tomograms of empty SBA 15 by Gommes et al. Chem. Mater. 2009, 21, 1311 amp; 8722;1317 . A Rayleigh amp; 8722;Plateau instability occurring at the cylindrical blockcopolymer micelles characteristic of the SBA 15 templating process quantitatively accounts for the superstructure and thus the spatial periodicity of the pore wall corrugation. The consequences of this peculiar morphological feature on the spatial arrangement of C5F12, in particular the formation of periodically arranged nanobubbles or voids upon adsorption, desorption, and freezing of liquids, are discussed in terms of capillary bridge formation and cavitation in tubular but periodically corrugated pore

Coherent Analysis of Disordered Mesoporous Adsorbents using Small Angle X Ray Scattering and Physisorption Experiments

Characterization of mesoporous adsorbents is traditionally performed in terms of the pore size distribution with bulk methods like physisorption and mercury intrusion. But their application relies on assumptions regarding the basic pore geometry. Although novel tools have enabled the quantitative interpretation of physisorption data for adsorbents having a well defined pore structure the analysis of disordered mesoporosity still remains challenging. Here we show that small angle X ray scattering SAXS combined with chord length distribution CLD analysis presents a precise and convenient approach to determine the structural properties of two phase solid void systems of mesopores. Characteristic wall solid and pore void sizes as well as surface areas are extracted without the need to assume a certain pore shape. The mesoporous structure of modern, commercially available fully porous and core shell adsorbent particles is examined by SAXS CLD analysis. Mean pore size and surface area are compared with results obtained from nitrogen physisorption data and show excellent agreemen

Structural peculiarities in the beta phase of the La0.75Ce0.25Ni4.8Al0.2 deuterides

In this contribution the structural, magnetic and sorption properties of the novel La0.75Ce0.25Ni4.8Al0.2 alloy and its deuterides are discussed. The collected data indicate good stability of the alloy during the cycle life and thermal treatment tests. Particularly, the desorption pressure is almost constant versus the cycle number. The results of the in situ neutron diffraction studies show the unusual behaviour of the deuterium rich b phase. Unexpectedly, the b phase belongs to the same P6 mmm space group as the hydrogen poor a phase. Moreover, the b phase behaves like a solid solution on the plateau of the pressure composition temperature PCT curve. The deuterium sites and their occupations in both a and b phases are determined from the neutron diffraction data, giving the first hand insight into the mechanism of the PCT hysteresis. As far as the magnetic properties are concerned, cerium is trivalent in the investigated alloy. However, no magnetic ordering down to 3 K is observed. It can be concluded that the sorption properties of the crystal depend on the cerium valence, what distinguishes the alloy from the other composition

Magnetic order in YbMn2Si2 - Neutron scattering investigation

Several mechanisms have been proposed to account for the structural and magnetic behaviour of the rare earth intermetallic compound YbMn2Si2 below the transition that occurs around ∼30 K. We have carried out detailed neutron diffraction measurements over the temperature range ∼0.3-52 K and confirm both an antiferromagnetic structure with ferromagnetic Mn (001) planes coupled antiferromagnetically along the c-axis above ∼30 K and the absence of ordering of the Yb sublattice down to 0.3 K. The decrease in intensity of the (111) reflection around ∼30 K together with the appearance of satellite reflections of propagation vector k = 001/2 confirm that the magnetic unit cell doubles along the c axis below T N2. The resultant molecular field acting on half of the ions below ∼30 K removes the degeneracy of the Kramers doublets of the Yb3+ ions and accounts for the additional excitations observed below ∼30 K compared with the inelastic neutron scattering above ∼30 K

Subalterne Sozialität. Zur normativen Struktur von Gegengemeinschaften

Der Beitrag exploriert die spezifische Normativität von Gegengemeinschaften. Die dabei zugrunde gelegte These lautet, dass solche Gemeinschaftsformen für unterdrückte oder ausgeschlossene Gruppen keine bloß kompensatorische Funktion erfüllen, sondern ihre Sozialität die der Gesamtgesellschaft transzendiert. Diese These der ›Überlegenheit der Unterlegenen‹ wird mit Bezug auf Hegel eingeführt und ihre sozialtheoretische Relevanz mit Marx und Engels herausgestellt. Es werden zwei mögliche Interpretationen der Überlegenheit subalterner Sozialität diskutiert, eine geschichtsphilosophische (die knechtische Existenzweise antizipiert eine kommende Sozialität) und eine anthropologische (Knechte haben bereits im Hier und Jetzt einen Zugang zu den sozialen Potenzialen ihres menschlichen Gattungswesens, der den Herren abgeht). Nachdem diese beiden Optionen anhand des Proletariats als Beispiel einer subalternen Sozialität abgewogen wurden, skizziert der Beitrag die Konturen einer allgemeinen Theorie subalterner Sozialität. Abschließend werden knapp einige Erfolgsbedingungen von Gegenvergemeinschaftungen identifiziert und sozialtheoretische Implikationen aufgezeigt

Peering into the structural evolution of glass like carbons derived from phenolic resin by combining small angle neutron scattering with an advanced evaluation method for wide angle X ray scattering

The structural evolution of two non graphitizing glass like carbons derived from a liquid resole and a solid novolac type phenolic resin was quantitatively characterized by combining small angle neutron scattering SANS with an advanced evaluation for wide angle X ray scattering WAXS data. Utilizing these two methods allowed for studying the microstructure on the ngstrom level graphene stacks, WAXS and the inaccessible microporosity SANS . The applied WAXS analysis provided uantitative structural parameters for both, size and disorder in the polyaromatic sp2 microstructure. Hence, the combined SANS WAXS analysis yielded comprehensive insights into the relation between the graphene microstructure and the inaccessible porosity upon heat treatment for glass like carbons, i.e. a nongraphitizing class of carbon. In particular, the analogue investigation of a graphitizing mesophase pitch demonstrates the major impact of the chemical composition of the utilized carbon precursor. For the glass like carbons the results revealed different growth rates for the lateral extent of the basic structural units La depending on the temperature range, finally reaching 12 nm, whereas the stack height Lc exhibiting 2.2 nm is hardly affected by the thermal processing up to 3000 C. As a major finding our study thus relates the evolution of microstructure and porosity to changes in chemical compositio

Gaining Insights on the H2 Sorbent Interactions Robust soc MOF Platform as a Case Study

We report on the synthesis and gas adsorption properties i.e., Ar and H2 of four robust 3 periodic metal organic frameworks MOFs having the targeted soc topology. These cationic MOFs are isostructural to the parent indium based MOF, In soc MOF 1a for NO3 , previously reported by us, and likewise are constructed from the assembly of rigid amp; 956;3 oxygen centered trinuclear metal carboxylate clusters, [M3O O2C amp; 8722; 6], where M In3 or Fe3 . Each inorganic trinuclear molecular building block MBB , generated in situ, is bridged by six 3,3 amp; 8242;,5,5 amp; 8242; azobenzenetetracarboxylate ABTC4 ligands to give the extended 4,6 connected MOF, soc MOF. In our previous work, we confirmed that the parent soc MOF, i.e., In soc MOF 1a, possesses unique structural characteristics e.g., vacant In binding sites and narrow pores with higher localized charge density , which led to exceptional hydrogen H2 storage capabilities. Therefore, charged MOFs with soc topology can be viewed collectively as an ideal prototypical platform to examine the impact of specific structural parameters on H2 MOF interactions via systematic gas adsorption studies. We infer that enhanced binding of molecular H2 is primarily governed by the presence and type of vacant metal centers i.e., Fe was shown to exhibit stronger H2 MOF interactions at low H2 loading compared to the In analogues . These findings are evident from the associated isosteric heat of adsorption Qst at low loadings and inelastic neutron scattering INS experiments of the rotational transitions of sorbed H2, as well as, temperature programmed desorption TPD studies for a select compound . The importance of localized charge density is also highlighted, where the extra framework nitrate anions in the Fe soc MOF 1a for NO3 facilitate enhanced binding affinities as compared to the chloride analogu