Effect of scale and surface chemistry on the mechanical properties of carbon nanotubes‐based composites

In this article, Multi‐Walled Carbon Nanotubes (MWCNTs) of varying diameters, both untreated and polycarboxylated, were dispersed at constant weight percentage in an epoxy matrix, and resulting fracture toughnesses (K_Ic) were measured in each case. We show that changing the MWCNT diameter has two effects on the composite fracture toughness: (i) a small MWCNT diameter enables larger interfacial surface for adhesion maximization, which increases toughness; (ii) at the same time, it limits the available pull‐out energy and reduces the MWCNT ability to homogeneously disperse in the matrix due to this same large active surface: this decreases toughness. Most commercially available MWCNTs have a length range of several μm, thus an optimal diameter exists which depends on MWCNT wall thickness and surface treatment. Such optimal diameter maximizes pull‐out energy and thus composite fracture toughness. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Automated chemical resonance generation and structure filtration for kinetic modeling

This work discusses efficient and automated methods for constructing a set of representative resonance structures for arbitrary chemical species, including radicals and biradicals, consisting of the elements H, C, O, N, and S. Determining the representative reactive structures of chemical species is crucial for identification of reactive sites and consequently applying the correct reaction templates to generate the set of important reactions during automated chemical kinetic model generation. We describe a fundamental set of resonance pathway types, accounting for simple resonating structures, as well as global approaches for polycyclic aromatic species. Automatically discovering potential localized structures along with filtration to identify the representative structures was shown to be robust and relatively fast. The algorithms discussed here were recently implemented in the Reaction Mechanism Generator (RMG) software. The final structures proposed by this method were found to be in reasonable agreement with quantum chemical computation results of localized structure contributions to the resonance hybrid.     

Weak closure and Oliver’s p-group conjecture

To date almost all verifications of Oliver’s p-group conjecture have proceeded by verifying a stronger conjecture about weakly closed quadratic subgroups. We construct a group of order 3⁴⁹ which refutes the weakly closed conjecture but satisfies Oliver’s conjecture.     

Rigid Support Materials for the Immobilization of Enzymes

The purpose of the work presented here was to prepare a support material for enzymes and “affinity ligands” with the following characteristics: low cost, durability, rigidity, and high capacity. Our study encompassed conjugates of porous and nonporous silicas with organic polymers and macroporous ion-exchange resins. Poly-ethyleneimine (PEI), polyacrylic acid (PAA), poly (methyl vinyl ether/maleic anhydride) were attached to porous glass and silica in various combinations. The composite of silica beads with PEI and PAA is a good support for the enzyme trypsin as judged by the activity against N-α-benzoyl-L-arginine ethyl ester.

Amberlyst (macroporous, sulfonated polystyrene) was activated by treatment with thionyl chloride; the resulting resin was either used directly or reacted with a diamine. The diamine derivative was used for enzyme coupling or transformed further to the succinyl or p-aminobenzoyl derivative. None of these derivatives were particularly good as supports for the enzyme trypsin. Duolite converted to a PAA, succinyl, or succinimide derivative was a good support. The enzyme-resin adduct has good activity and stability.

The resin is quite durable and of low cost. The Duolite-trypsin has good activity against protein. In addition, this derivative was active in 7 M urea. The proteolytic activity was nearly doubled by urea, presumably as a result of substrate (casein) denaturation. The michaelis constants and pH dependences are compared for trypsin conjugates with Duolite A-7, Silica-PEI-PAA, agarose, and porous glass. A cost comparison reveals that the Duolite and silica derivatives are much less expensive than agarose and glass.     

A New Class of Remote N‐Heterocyclic Carbenes with Exceptionally Strong σ‐Donor Properties: Introducing Benzo[c]quinolin‐6‐ylidene

We make the case for benzo[c]quinolin‐6‐ylidene ( 1 ) as a strongly electron‐donating carbene ligand. The facile synthesis of 6‐trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate ( 2 ) gives straightforward access to a useful precursor for oxidative addition to low‐valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin‐6‐ylidene)(CO)₅]⁺ ( 15 ) and [Pd(benzo[c]quinolin‐6‐ylidene)(PPh₃)₂(L)]²⁺ L=THF ( 21 ), OTf ( 22 ) or pyridine ( 23 ). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR‐stretching‐frequency data for the manganese compound suggests benzo[c]quinolin‐6‐ylidene is at least as strong a donor as any heteroatom‐stabilised carbene ligand reported.     

Ultraviolet properties of maximal supergravity

We argue that recent results in string perturbation theory indicate that the four-graviton amplitude of four-dimensional N=8 supergravity might be ultraviolet finite up to eight loops. We similarly argue that the h-loop M-graviton amplitude might be finite for h<7+M/2.     

Indium‐Bridged [1]Ferrocenophanes

Indium‐bridged [1]ferrocenophanes ([1]FCPs) and [1.1]ferrocenophanes ([1.1]FCPs) were synthesized from dilithioferrocene species and indium dichlorides. The reaction of Li₂fc?tmeda (fc=(H₄C₅)₂Fe) and (Mamx)InCl₂ (Mamx=6‐(Me₂NCH₂)‐2,4‐tBu₂C₆H₂) gave a mixture of the [1]FCP (Mamx)Infc ( 4₁ ), the [1.1]FCP [(Mamx)Infc]₂ ( 4₂ ), and oligomers [(Mamx)Infc]_n ( 4 _n ). In a similar reaction, employing the enantiomerically pure, planar‐chiral (S_p,S_p)‐1,1′‐dibromo‐2,2′‐diisopropylferrocene ( 1 ) as a precursor for the dilithioferrocene derivative Li₂fc^iPr2, equipped with two iPr groups in the α position, gave the inda[1]ferrocenophane 5₁ [(Mamx)Infc^iPr2] selectively. Species 5₁ underwent ring‐opening polymerization to give the polymer 5 _n . The reaction between Li₂fc^iPr2 and Ar′InCl₂ (Ar′=2‐(Me₂NCH₂)C₆H₄) gave an inseparable mixture of the [1]FCP Ar′Infc^iPr2 ( 6₁ ) and the [1.1]FCP [Ar′Infc^iPr2]₂ ( 6₂ ). Hydrogenolysis reactions (BP86/TZ2P) of the four inda[1]ferrocenophanes revealed that the structurally most distorted species ( 5₁ ) is also the most strained [1]FCP.     

UV-Induced 1,3,4-Oxadiazole Formation from 5-Substituted Tetrazoles and Carboxylic Acids in Flow

A range of 1,3,4-oxadiazoles have been synthesized using a UV-B activated flow approach starting from carboxylic acids and 5-substituted tetrazoles. The application of UV light represents an attractive alternative to the traditional thermolytic approach and has demonstrated comparable efficiency and versatility, with a diverse substrate scope, including the incorporation of highly substituted amino acids.     

A Highly Selective and Sensitive Chemiluminescent Probe for Real‐Time Monitoring of Hydrogen Peroxide in Cells and Animals

Selective and sensitive molecular probes for hydrogen peroxide (H₂O₂), which plays diverse roles in oxidative stress and redox signaling, are urgently needed to investigate the physiological and pathological effects of H₂O₂. A lack of reliable tools for in vivo imaging has hampered the development of H₂O₂ mediated therapeutics. By combining a specific tandem Payne/Dakin reaction with a chemiluminescent scaffold, H₂O₂‐CL‐510 was developed as a highly selective and sensitive probe for detection of H₂O₂ both in vitro and in vivo. A rapid 430‐fold enhancement of chemiluminescence was triggered directly by H₂O₂ without any laser excitation. Arsenic trioxide induced oxidative damage in leukemia was successfully detected. In particular, cerebral ischemia‐reperfusion injury‐induced H₂O₂ fluxes were visualized in rat brains using H₂O₂‐CL‐510 , providing a new chemical tool for real‐time monitoring of H₂O₂ dynamics in living animals.