Baryonic channels of dilepton production

A calculation of the Dalitz-decay width of baryon resonances is presented and applied to dilepton production in proton-proton collisions in the BEVALAC/SIS energy range. The results indicate, that for these energies the contribution of Dalitz decay of higher baryon resonances (i.e. other that the δ(1232)) are negligible.     

Determination of critical micelle concentration with the rotating sample system

A novel experimental approach using the rotating sample system (RSS) is proposed here for the determination of the critical micelle concentration (CMC) of surfactants. The RSS has been conceived in our laboratory as a convection platform for physicochemical studies and analyses in microliter-sized sample drops. The scheme allows for vigorous rotation of the drop despite its small size through efficient air-liquid mechanical coupling. Thus, changes in surface properties of aqueous samples result in corresponding modulation of the hydrodynamic performance of the RSS, which can be utilized to investigate interfacial phenomena. In this work, we demonstrate that the RSS can be used to study the effects of surfactants on the surface and in the bulk of very small samples with hydrodynamic electrochemistry. Potassium ferrocyanide is employed here with cyclic voltammetry to probe the air-water interface of solutions containing Triton X-100. The CMC of this surfactant determined using this approach is 140 ppm, which agrees well with reported values obtained with conventional methods in much larger samples. The results also demonstrate that besides the CMC, variations in bulk rheological properties can also be investigated in very small specimens using the RSS with a simple method.     

A Simple Green Protocol for the Condensation of Anthranilic Hydrazide with Cyclohexanone and N‐Benzylpiperidinone in Water

An environmentally benign condensation of anthranilic hydrazide with cyclohexanone or N‐benzylpiperidin‐4‐one in aqueous medium has been developed for the synthesis of benzoylhydrazones A. The thermal rearrangements of hydrazones A yielded 3′‐aminospiro‐quinazolinones B. When A or B was reacted repeatedly with cyclohexanone or N‐benzylpiperidin‐4‐one, spiroquinazoline‐hydrazones C were formed. From aqueous suspensions, products could be isolated in high purity by simple filtration.     

Energy-variable collision-induced dissociation study of 1,3,5-trisubstituted 2-pyrazolines by electrospray mass spectrometry

The pathways of the ([M+H](+)) ions generated from electrosprayed solutions of nine 1,3,5-trisubstituted 2-pyrazoline derivatives were studied using energy-variable collision-induced dissociation (CID) and pseudo-MS(3) (in-source CID combined with MS/MS) methods. It was shown that under CID conditions several structurally important product ions such as the 2,4-substituted azete and 1,2-substituted aziridine ions were formed. The compositions of the product ions were unambiguously supported by accurate mass measurement (mass accuracy was within +/- 8 ppm). The fragmentation pathways of 1,3,5-trisubstituted 2-pyrazolines were established by means of pseudo-MS(3). It was found that a substituent at the N-1 position greatly affects the fragmentation pathways of the 2-pyrazoline derivatives. The 1-acetyl- and 1-propionyl-2-pyrazoline derivatives dissociate mainly through formation of a pyrazolium cation, while in the case of 1-phenyl-2-pyrazoline derivatives product ions arising from the consecutive fragmentation of 2,4-substituted azete and 1,2-substituted aziridine ions dominate. Another interesting finding is the formation of a radical cation from the 2,4-substituted azete by loss of a methyl radical. The fragmentation yield as a function of the collision energy for each of the 1,3,5-trisubstituted 2-pyrazolines was determined. Based on the fragmentation yield versus collision energy curves the relative fragmentation stabilities for the 1,3,5-trisubstituted 2-pyrazoline derivatives were also evaluated.     

Spin gap and Luttinger liquid description of the NMR relaxation in carbon nanotubes

Recent NMR experiments by Singer et al. [Singer, Phys. Rev. Lett. 95, 236403 (2005).] showed a deviation from Fermi-liquid behavior in carbon nanotubes with an energy gap evident at low temperatures. Here, a comprehensive theory for the magnetic field and temperature dependent NMR 13C spin-lattice relaxation is given in the framework of the Tomonaga-Luttinger liquid. The low temperature properties are governed by a gapped relaxation due to a spin gap ( approximately 30 K), which crosses over smoothly to the Luttinger liquid behavior with increasing temperature.     

Anion‐, Solvent‐, Temperature‐, and Mechano‐Responsive Photoluminescence in Gold(I) Diphosphine‐Based Dimers

A series of [Au₂(nixantphos)₂](X)₂ (nixantphos=4,6‐bis(diphenylphosphino)‐phenoxazine; X=NO₃, 1 ; CF₃COO, 2 ; CF₃SO₃, 3 ; [Au(CN)₂], 4 ; and BF₄, 5 ) complexes that exhibit intriguing anion‐switchable and stimuli‐responsive luminescent photophysical properties have been synthesized and characterized. Depending on their anions, these complexes display yellow ( 3 ), orange ( 4 and 5 ), and red ( 1 and 2 ) emission colors. They exhibit reversible thermo‐, mechano‐, and vapochromic luminescence changes readily perceivable by the naked eye. Single‐crystal X‐ray studies show that the [Au₂(nixantphos)₂]²⁺ cations with short intramolecular Au ??? Au interactions are involved as donors in an infinite N?H ??? X (X=O and N) hydrogen‐bonded chain formation with CF₃COO^? ( 2 C ) and aurophilically linked [Au(CN)₂]^? counterions ( 4 C ). Both crystals show thermochromic luminescence; their room temperature red ( 2 C ) and orange ( 4 C ) emission turns into yellow upon cooling to 77 K. They also exhibit reversible mechanochromic luminescence by changing their emission color from red to dark ( 2 C ), and orange to red ( 4 C ). Compounds 1 – 5 also display reversible mechanochromic luminescence, altering their emission colors between orange ( 1 ) or red ( 2 ) to dark, as well as between yellow ( 3 ) or orange ( 4 and 5 ) to red. Detailed photophysical investigations and correlation with solid‐state structural data established the significant role of N?H ??? X interactions in the stimuli‐responsive luminescent behavior.     

The exact Schrieffer–Wolff transformation

The effective s–d spin interaction is derived exactly for the single-impurity Anderson model via a unitary transformation. This unitary transformation was calculated up to infinite order and no restrictions were imposed upon the coefficients of the Hubbard interaction and the hybridization. We also discuss briefly the impact of the obtained result on the magnetic properties of several Kondo compounds. This will shed new light on the understanding of the competition between the Kondo effect and the Ruderman–Kittel–Kasuya–Yosida interaction and reinterpret the Doniach diagram.     

Electrospray Post-Ionization Mass Spectrometry of Electrosurgical Aerosols

The feasibility of electrospray (ES) ionization of aerosols generated by electrosurgical disintegration methods was investigated. Although electrosurgery itself was demonstrated to produce gaseous ions, post-ionization methods were implemented to enhance the ion yield, especially in those cases when the ion current produced by the applied electrosurgical method is not sufficient for MS analysis. Post-ionization was implemented by mounting an ES emitter onto a Venturi pump, which is used for ion transfer. The effect of various parameters including geometry, high voltage setting, flow parameters, and solvent composition was investigated in detail. Experimental setups were optimized accordingly. ES post-ionization was found to yield spectra similar to those obtained by the REIMS technique, featuring predominantly lipid-type species. Signal enhancement was 20- to 50-fold compared with electrosurgical disintegration in positive mode, while no improvement was observed in negative mode. ES post-ionization was also demonstrated to allow the detection of non-lipid type species in the electrosurgical aerosol, including drug molecules. Since the tissue specificity of the MS data was preserved in the ES post-ionization setup, feasibility of tissue identification was demonstrated using different electrosurgical methods.