Crystal Chemistry of Ordered Rocksalt-Type SrCaNF

Journal of Chemical Crystallography - A new Group 2 bimetallic nitride fluoride phase of approximate composition SrCaNF has been prepared and characterized via high resolution single crystal X-ray...     

Dendritic analogues of engineering plastics - a general one-step synthesis of dendritic polyaryl ethers

The first general single-step route to dendritic or cascade polyaryl ethers analogous to common linear polyaryl ethers is described. The sodium salts of four AB₂ monomers each containing a single phenolic hydroxyl group and two aryl fluorides activated toward nucleophilic substitution by carbonyl, sulphonyl, or tetrafluorophenyl moieties are shown to polymerize in hot N, N-dimethylacetamide. The products are high molecular weight polymers (7000 < M_n < 36000), have narrow polydispersities (1.50 < M_w/M_n < 4.50), and are highly soluble in organic solvents. The molecular weights of two of the polymers increase with monomer concentration. The polymers are thermally stable (500 °C under N₂) and have glass transition temperatures ranging from 135 to 231 °C.     

Photoemission core level and satellite study of TixRu1−xoxide layers

Combined photoemission core level and satellite structure investigations of pyrolytic titanium-rich Ti_xRu_1−x-oxide layers (0.90 ≦ x ≦ 0.97) and RuO₂ layers on titanium are used to gain structural and compositional information about these electro-catalytically active surfaces. By means of this method deviations from stoichiometry, the formation of carbon interstitials and the growth of anatase by ruthenium loss could be pointed out.     

Discovery of an NAD+ analogue with enhanced specificity for PARP1

Among various protein posttranslational modifiers, poly-ADP-ribose polymerase 1 (PARP1) is a key player for regulating numerous cellular processes and events through enzymatic attachments of target proteins with ADP-ribose units donated by nicotinamide adenine dinucleotide (NAD⁺). Human PARP1 is involved in the pathogenesis and progression of many diseases. PARP1 inhibitors have received approvals for cancer treatment. Despite these successes, our understanding about PARP1 remains limited, partially due to the presence of various ADP-ribosylation reactions catalyzed by other PARPs and their overlapped cellular functions. Here we report a synthetic NAD⁺ featuring an adenosyl 3′-azido substitution. Acting as an ADP-ribose donor with high activity and specificity for human PARP1, this compound enables labelling and profiling of possible protein substrates of endogenous PARP1. It provides a unique and valuable tool for studying PARP1 in biology and pathology and may shed light on the development of PARP isoform-specific modulators.

An analogue of nicotinamide adenine dinucleotide (NAD⁺) featuring an azido group at 3′-OH of adenosine moiety is found to possess high specificity for human PARP1-catalyzed protein poly-ADP-ribosylation.     

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction.     

Structure-mechanics statistical learning uncovers mechanical relay in proteins

A protein''s adaptive response to its substrates is one of the key questions driving molecular physics and physical chemistry. This work employs the recently developed structure-mechanics statistical learning method to establish a mechanical perspective. Specifically, by mapping all-atom molecular dynamics simulations onto the spring parameters of a backbone-side-chain elastic network model, the chemical moiety specific force constants (or mechanical rigidity) are used to assemble the rigidity graph, which is the matrix of inter-residue coupling strength. Using the S1A protease and the PDZ3 signaling domain as examples, chains of spatially contiguous residues are found to exhibit prominent changes in their mechanical rigidity upon substrate binding or dissociation. Such a mechanical-relay picture thus provides a mechanistic underpinning for conformational changes, long-range communication, and inter-domain allostery in both proteins, where the responsive mechanical hotspots are mostly residues having important biological functions or significant mutation sensitivity.

Protein residues exhibit specific routes of mechanical relay as the adaptive responses to substrate binding or dissociation. On such physically contiguous connections, residues experience prominent changes in their coupling strengths.     

Etch- and Transmission Electron Microscope Investigations of Microdefects in (001) LEC-GaP Substrates

The etch pattern of (001) and (110) LEC-GaP doped with sulphur (N_DN_A in the range from 3–7 × 10¹⁷ cm⁻³) do not only show dislocation etch pits but fine pits, so-called “saucer pits” (S-pits). The distribution of S-pits, their etching behaviour and transmission electron microscope observations of etched samples indicated a clear correlation between S-pits and microdefects (fauted-, prismatic dislocation loops and precipitates).     

Deposition of InP on GaAs Substrates in the InP/PCl3/H2 System

Vapour phase epitaxial layers of InP were deposited onto (111)A-, (111)B-, (001)-, and (110)-oriented GaAs substrates in the InP/PCl₃/H₂ system using a close-space technique. It is shown that the dependence of the layer quality on the substrate orientation is due to differences in the initial growth stages. Results on the growth rates and the electrical properties of the layers are reported.     

Modeling of pair distribution functions for XAFS in disordered systems

A commonly used expression for modeling the XAFS of highly disordered systems is shown to generate substantial systematic errors in the coordination number in many cases of practical interest. This expression is corrected and generalized. Further, a simpler and more flexible model distribution is proposed, and the corresponding XAFS expression is derived. Comparison with experimental and simulated data show that the new expressions are useful in cases of high disorder for which the cumulant expansion loses its utility, and they explicitly account for the k-dependence of the mean free path.