Hyperbolic groups have flat-rank at most 1

The flat-rank of a totally disconnected, locally compact group G is an integer, which is an invariant of G as a topological group. We generalize the concept of hyperbolic groups to the topological context and show that a totally disconnected, locally compact, hyperbolic group has flat-rank at most 1. It follows that the simple totally disconnected locally compact groups constructed by Paulin and Haglund have flat-rank at most 1.     

2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a ligand for efficient actinide(III)/lanthanide(III) separation

The N-donor complexing ligand 2,6-bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine (C5-BPP) was synthesized and screened as an extracting agent selective for trivalent actinide cations over lanthanides. C5-BPP extracts Am(III) from up to 1 mol/L HNO(3) with a separation factor over Eu(III) of approximately 100. Due to its good performance as an extracting agent, the complexation of trivalent actinides and lanthanides with C5-BPP was studied. The solid-state compounds [Ln(C5-BPP)(NO(3))(3)(DMF)] (Ln = Sm(III), Eu(III)) were synthesized, fully characterized, and compared to the solution structure of the Am(III) 1:1 complex [Am(C5-BPP)(NO(3))(3)]. The high stability constant of log β(3) = 14.8 ± 0.4 determined for the Cm(III) 1:3 complex is in line with C5-BPP's high distribution ratios for Am(III) observed in extraction experiments.     

Stable gas-phase radical cations of dimeric tryptophan and tyrosine derivatives

Stable radical cations of dimeric amino acid derivatives of tryptophan and tyrosine were generated by collision-induced dissociation of [Cu(II)(diethylenetriamine)(amino acid derivative)2]*2+. The yields of the dimer radical cations were dependent on both the auxiliary ligand and the tryptophan or tyrosine derivatives used. Amino acid derivatives with an unmodified carboxylic acid group did not generate dimer radical cations. For the amino acid derivatives Ac-Trp-OMe and Ac-Trp-NH2 (Ac is N-acetyl; OMe and NH2 are the methyl ester and amide modifications of the C-terminal carboxylic group), no auxiliary ligand was required for generating the dimer radical cations. Collision-induced dissociation of the [Cu(II)(amino acid derivative)4]*2+ precursor generated the dimer radical cation [(amino acid derivative)2]*+. Stabilizing interactions, most likely involving hydrogen bonding, between the two amino acid derivatives are proposed to account for observation of the dimer radical cations. Dissociation of these ions yields protonated or radical cationic amino acid derivatives; these observations are consistent with the expectation of proton competition between monomeric units, whose proton affinities were calculated using density functional theory.     

"Tying up loose ends" – silicone surfactants as stabilizing agents for flexible polyurethane foam

This paper is a tribute to the work of Dr. Michael J. Owen and colleagues in revealing the mechanism of the silicone surfactant-driven stabilization of flexible polyurethane foam. This work, performed at Midland Silicones (acquired by Dow Corning Corporation in 1967), was the inspiration for a body of experimental and theoretical research performed by the present authors in the mid-1990's. For flexible polyurethane foam, the surfactant is necessary to stabilize the liquid foamy mass before it hardens into an elastomeric sponge. Owen and coworkers demonstrated that in order to stabilize the foam the surfactant must (1) significantly lower the equilibrium surface tension of the liquid, (2) exhibit a dynamic surface tension within a narrow range of values, and (3) have an appreciable but low surface viscosity. The recent work of the authors has both validated these observations and extended their scope. They have modeled the stabilization process and have found that stability is the result of a delicate interplay of surface viscosity and elasticity which are functions of both structure and excess surface concentration of the surfactant. This modeling work was validated experimentally by investigating the drainage of model polyurethane thin liquid films ("soap films") containing silicone surfactants. The seminal nature of the work done by Owen and coworkers was reinforced by the authors' discovery that many of the original conclusions were validated by the recent work.     

Catalytic C-C bond formation accomplished by selective C-F activation of perfluorinated arenes

The first example of a catalytically active system for Suzuki-type cross-coupling reactions of perfluorinated arenes such as octafluorotoluene and decafluorobiphenyl is presented.     

Synthesis of substituted benzoxacycles via a domino ortho-alkylation/Heck coupling sequence

The synthesis of a variety of alkylidene benzoxacycles via a domino palladium-catalyzed ortho-alkylation/intramolecular Heck reaction is described. Under the optimized conditions [Pd(OAc)2 (10 mol %), P(2-Furyl)3 (20 mol %), norbornene (4 equiv), Cs2CO3 (2 equiv), CH3CN, 80 degrees C], aryl iodides with oxygen-tethered Heck acceptors are coupled with alkyl bromides (5 equiv) to generate a variety of six- and seven-membered-ring benzoxacyclic products.     

Solvent- and temperature-tuned orientation of ferrocenyl azide inside beta-cyclodextrin

An induced circular dichroism (ICD) solution study on the orientation of ferrocenyl azide within the beta-cyclodextrin cavity is described. In DMSO, ferrocenyl azide prefers an axial inclusion, whereas in ethylene glycol and DMSO/H2O = 50/50 an equatorial alignment dominates. As shown by temperature-dependent ICD spectra, at lower temperatures ferrocenyl azide adopts preferentially an equatorial arrangement, whereas at higher temperatures an axial one is favored. Temperature and solvent effects on the co-conformation of ferrocene noncovalently bound to cyclodextrin have never been observed before.     

Assessment of acetone as an alternative to acetonitrile in peptide analysis by liquid chromatography/mass spectrometry

Acetonitrile as a solvent used in liquid chromatography/mass spectrometry (LC/MS) of peptides and proteins is a relatively toxic solvent (LD₅₀ oral; rat; 2,460 mg/kg) compared to alternatives like methanol (LD₅₀ oral; rat; 5,628 mg/kg) and acetone (LD₅₀ oral; rat; 5,800 mg/kg). Strategies to minimize its consumption in LC are either to reduce the inner diameter of the column or replace acetonitrile with a suitable alternative. Methanol is often recommended to replace acetonitrile in peptide analysis. In this study however, the main focus lies on another alternative solvent for LC/MS of peptides; acetone. A number of model proteins were tryptically digested and the peptide solutions were analyzed on a linear trap quadrupole (LTQ) mass spectrometer. The performances of acetonitrile, methanol and acetone were compared according to the quality of the chromatograms obtained and identification of the peptides using the BioWorks? software developed by Thermo Scientific. In accordance to the elutropic series, acetone was found to significantly reduce the retention times of peptides separated by C18 column material with regard to acetonitrile while methanol led to increased retention times. Acetone was the superior solvent to methanol for most of the tested model proteins reaching similar sequence coverage and numbers of identified peptides as acetonitrile. We therefore propose acetone as an alternative to acetonitrile in LC/MS of peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Fragmentation of size-selected Xe clusters: Why does the monomer ion channel dominate the Xen and ionization?

The fragmentation of the small Xe_n n=2−5 clusters following 70 eV electron impact ionization has been investigated in a size selective experiment and simulated using non-adiabatic dynamics. The experimental results show that the clusters strongly fragment to yield monomer Xe⁺ (more than 90%) and dimer Xe₂⁺ fragments (the remaining few percent). Trimer Xe₃⁺ fragments first occur from the neutral pentamers Xe₅ in a very low yield of approximately 0.3%. The present results are compared with the previous ones for Kr and Ar clusters. It is shown that the Xe and Kr clusters exhibit a qualitatively similar behavior with a strong propensity for monomer fragments, while in the Ar case dimers prevail. The theoretical calculations also reveal a strong fragmentation to the dimer and monomer fragments. However, the dimer Rg₂⁺ is predicted to be the major product for all rare gases (Rg ≡ Ar, Kr, Xe). Possible reasons for the discrepancy between theory and experiment are discussed.     

Activity Monitoring for a Polymerization Catalyst System

Summary: Catalyst systems for polymerization often exhibit variable and poorly controllable activity because of strong influences of trace components and catalyst preparation conditions. In cationic polymerizations in particular, determining catalytic activity and hence the amount of catalyst to be used is challenging. The assessment of a given initiator system typically requires testing it in polymerization reactions. Determining catalytic activity before using the initiator in a polymerization reaction is a desirable approach. This contribution describes the development of such an activity monitoring tool. In the first part, results from a fundamental characterization of the system diethylaluminum chloride/ethylaluminum dichloride/water by different NMR measurements and elemental analysis are reported. Structures characteristic of catalytically active systems are presented. The second part describes the application of transmission IR to the characterization of this system and the correlation of IR results to catalytic activity in dimerization and polymerization reactions. Implementation of the IR analysis as an on-line measurement is demonstrated.