The contact interface of a 120 kD CheA-CheW complex by methyl TROSY interaction spectroscopy

During bacterial chemotaxis, the histidine autokinase CheA interacts with the chemotaxis receptors with the help of the coupling protein CheW. This interaction is typical of many macromolecular complexes where protein-protein interactions play an important role. In this case, a relatively small protein, CheW, becomes part of a much larger complex. Here we describe a new method to map the residues at a protein-protein interface for macromolecular complexes of molecular weight greater than 100 kD.     

Enhancing Energetic Properties and Sensitivity by Incorporating Amino and Nitramino Groups into a 1,2,4‐Oxadiazole Building Block

A single nitrogen‐rich heterocyclic ring with many energetic groups is expected to exhibit excellent detonation performance. We report an effective approach for the synthesis of 3‐amino‐5‐nitramino‐1,2,4‐oxadiazole, which has nitramino and amino groups in the same building block. The single‐crystal X‐ray structure shows layered hydrogen‐bonding pairs as well as the presence of a water molecule which ensure insensitivity. Through incorporation of a cation, the hydrazinium or hydroxylammonium salts exhibit good energetic performance and acceptable sensitivities.     

Potassium 4,4′‐Bis(dinitromethyl)‐3,3′‐azofurazanate: A Highly Energetic 3D Metal–Organic Framework as a Promising Primary Explosive

Environmentally acceptable alternatives to toxic lead‐based primary explosives are becoming increasingly important for energetic materials. In this study, potassium 4,4′‐bis(dinitromethyl)‐3,3′‐azofurazanate, comprising two dinitromethyl groups and an azofurazan moiety, was synthesized and isolated as a new energetic 3D metal–organic framework (MOF). Several attractive properties, including a density of 2.039 g cm^?3, a decomposition temperature of 229 °C, a detonation velocity of 8138 m s^?1, a detonation pressure of 30.1 GPa, an impact sensitivity of 2 J, and friction sensitivity of 20 N make 4 a good candidate as a green primary explosive.     

A Simple Model of Stability in Critical Mass Dynamics

Collective behaviors often spread via the self-reinforcing dynamics of critical mass. In collective behaviors with strongly self-reinforcing dynamics, incentives to participate increase with the number of participants, such that incentives are highest when the full population has adopted the behavior. By contrast, when collective behaviors have weakly self-reinforcing dynamics, incentives to participate “peak out” early, leaving a residual fraction of non-participants. In systems of collective action, this residual fraction constitutes free riders, who enjoy the collective good without contributing anything themselves. This “free rider problem” has given rise to a research tradition in collective action that shows how free riding can be eliminated by increasing the incentives for participation, and thereby making cooperation strongly self-reinforcing. However, we show that when the incentives to participate have weakly self-reinforcing dynamics, which allow free riders, collective behaviors will have significantly greater long term stability than when the incentives have strongly self-reinforcing dynamics leading to full participation.     

Dead-beat full state hybrid projective synchronization for chaotic maps using a scalar synchronizing signal

This paper provides a contribution to the topic of full state hybrid projective synchronization (FSHPS) by introducing an observer-based approach that enables synchronization to be achieved via a scalar synchronizing signal. The method is based on a theorem that assures dead-beat synchronization (i.e., exact synchronization in finite time) to a wide class of discrete-time chaotic (hyperchaotic) systems. Two examples, involving the hyperchaotic Grassi-Miller map and the hyperchaotic double scroll map, show that FSHPS can be effectively achieved in finite time using a scalar synchronizing signal only.     

Experimental investigation of the complete inner shell hydration energies of Ca2+: threshold collision-induced dissociation of Ca(2+)(H2O)x Complexes (x = 2-8)

The sequential bond energies of Ca(2+)(H(2)O)(x) complexes, where x = 1-8, are measured by threshold collision-induced dissociation (TCID) in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Ca(2+)(H(2)O)(x) complexes where x = 6-8, complexes down to x = 2 are formed using an in-source fragmentation technique. Ca(2+)(H(2)O) cannot be formed in this source because charge separation into CaOH(+) and H(3)O(+) is a lower energy pathway than simple water loss from Ca(2+)(H(2)O)(2). The kinetic energy dependent cross sections for dissociation of Ca(2+)(H(2)O)(x) complexes, where x = 2-9, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Ca(2+) for x = 1-8 and the first experimental values for x = 1-4. Additionally, the thermodynamic onsets leading to the charge separation products from Ca(2+)(H(2)O)(2) and Ca(2+)(H(2)O)(3) are determined for the first time. Our experimental results for x = 1-6 agree well with previously calculated binding enthalpies as well as quantum chemical calculations performed here. Agreement for x = 1 is improved when the basis set on calcium includes core correlation.     

Factors affecting primary ionization in dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS

The sensitivity of dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS is generally reduced at higher solvent flow rates. Theory suggests that quenching of excited-state precursors to the dopant ions, via collisions with vaporized solvent molecules, may be one mechanism responsible for this trend. To ascertain if the primary rate of ionization is affected by quenching, experiments were performed utilizing an ionization detector to determine the primary ion current generated by irradiating vaporized mixtures of toluene dopant and methanol solvent. The results indicate that no loss of primary ion current occurs as the solvent flow is increased, provided the dopant-to-solvent ratio is held constant. Additional primary ion current can always be generated by increasing the dopant flow rate and/or the lamp power. Thus, quenching of excited-state precursors to the dopant ions, leading to a reduction in the primary rate of ionization, is not the mechanism responsible for the observed loss of sensitivity at higher liquid solvent flow rates.     

Thermally Stable 3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐based Energetic Materials

3,6‐Dinitropyrazolo[4,3‐c]pyrazole was prepared using an efficient modified process. With selected cations, ten nitrogen‐rich energetic salts and three metal salts were synthesized in high yield based on the 3,6‐dinitropyrazolo[4,3‐c]pyrazolate anion. These compounds were fully characterized by IR and multinuclear NMR spectroscopies, as well as elemental analyses. The structures of the neutral compounds 4 and its salt 16 were confirmed by single‐crystal X‐ray diffraction showing extensive hydrogen‐bonding interactions. The neutral pyrazole precursor and its salts are remarkably thermally stable. Based on the calculated heats of formation and measured densities, detonation pressures (22.5–35.4 GPa) and velocities (7948–9005 m s^?1) were determined, and they compare favorably with those of TNT and RDX. Their impact and friction sensitivities range from 12 to >40 J and 80 to 360 N, respectively. These properties make them competitive as insensitive and thermally stable high‐energy density materials.     

Preparation of Cyan Dyes from 6-Diethylaminobenzo[b]furan-2-carboxaldehyde

6-Diethylaminobenzo[b]furan-2-carboxaldehyde was synthesized in four steps and 48% overall yield starting from 4-diethylaminosalicylaldehyde. Five cyan dyes were made from this aldehyde using malononitrile dimer and 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran. The crystal structures of two dyes are included.