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.     

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.     

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.     

Electronic band gap of SrSe at high pressure

The electronic band gap of SrSe, in the CsCl-stuctured phase, was measured to 42 GPa via optical absorption studies. The indirect electronic band gap was found to close monotonically with pressure for the range of pressures studied. The change in band gap with respect to pressure, dE_gap/dP, was determined to be −6.1(5)×10⁻³ eV/GPa. By extrapolation of our line fit, we estimate band gap closure to occur at 180(20) GPa.     

Airborne ultrasound for the precipitation of smokes and powders and the destruction of foams

Sonochemistry is generally associated with the use of power ultrasound in liquid media. Under such circumstances acoustic cavitation can drive a range of reactions and processes. The use of airborne ultrasound in processing is less familiar because of the difficulties that relate to the use of ultrasound in gaseous systems. Firstly there is a greater attenuation (power loss) in the transmission of sound through air compared with that through liquid. Secondly the transfer of acoustic energy generated in air into a liquid or solid material is inefficient due to the mismatch between acoustic impedances of gases and solids or liquids. Despite this, applications do exist for airborne ultrasound but the source must be very powerful and efficient. In this way one can obtain levels of intensities at which it is possible to use ultrasound for specific applications such as to agglomerate fine dusts and to break down foams.     

Spectral beam combining of 2 μm Tm fiber laser systems

Output beams from three independently frequency-stabilized thulium master-oscillator power-amplifier fiber laser systems were spectrally combined using a plane-ruled metal diffraction grating. Two laser channels were frequency-stabilized with guided mode resonance filters and the third was stabilized using a plane-ruled metal diffraction grating. The systems had output wavelengths between 1984 and 2015 nm, each with a spectral width of 100-450 pm and output powers between 40-120 W. The combined beam had powers up to 49 W and was 32% efficient with respect to the launched pump power.     

The magnetic part of the Weyl tensor,and the expansion of discrete universes

We examine the effect that the magnetic part of the Weyl tensor has on the large-scale expansion of space. This is done within the context of a class of cosmological models that contain regularly arranged discrete masses, rather than a continuous perfect fluid. The natural set of geodesic curves that one should use to consider the cosmological expansion of these models requires the existence of a non-zero magnetic part of the Weyl tensor. We include this object in the evolution equations of these models by performing a Taylor series expansion about a hypersurface where it initially vanishes. At the same cosmological time, measured as a fraction of the age of the universe, we find that the influence of the magnetic part of the Weyl tensor increases as the number of masses in the universe is increased. We also find that the influence of the magnetic part of the Weyl tensor increases with time, relative to the leading-order electric part, so that its contribution to the scale of the universe can reach values of \(\sim \)1%, before the Taylor series approximation starts to break down.