Generation and dissociation pathways of singly and doubly protonated bisguanidines in the gas phase

Para-bisguanidinyl benzene 1 and its N-permethylated derivative 2 are both sufficiently strong bases to afford not only the monocations [1+H]+ and [2+H]+, but also the doubly protonated ions, [1+2H]2+ and [2+2H]2+, in the gas phase. The title ions generated via electrospray ionization are probed by collision-induced dissociation experiments which inter alia reveal that the dicationic species [1+2H]2+ and [2+2H]2+ can even undergo fragmentation reactions with maintenance of the 2-fold charge. Complementary results from density functional theory predict PAs above 1000 kJ mol(-1) for the neutral compounds, i.e., PA(1) = 1025 kJ mol(-1) and PA(2) = 1067 kJ mol(-1). Due to the stabilization of the positive charge in the guanidinium ions and the para-phenylene spacer separating the basic sites, even the monocations bear sizable proton affinities, i.e., PA([1+H]+) = 740 kJ mol(-1) and PA([2+H]+) = 816 kJ mol(-1).     

Reinigen mit Licht und Regen

After the discovery of the lotus‐effect in the 1970s the attention concerning the field of self‐cleaning surfaces increased rapidly. Besides hydrophobic surfaces which are designed following the example of the lotus flower, superhydrophilic and photocatalytic active coatings play an important role. These coatings are using sunlight to oxidize pollutants and remove residues by rinsing with water. Coatings based on the lotus‐effect suffer from their weak mechanical durability, but are able to work without light. On the other hand, photocatalytic layers are mechanically stable, but they need to be illuminated to become self‐cleaning.     

Eri Jabotinsky,mathematician and politician: a short biography

Aequationes mathematicae - Despite the fact that Eri Jabotinsky (1910–1969) published only few (i.e. fourteen) mathematical papers, some of them had a remarkable influence in iteration...     

Raman study of the polybenzimidazole-phosphoric acid interactions in membranes for fuel cells

Poly(2,5-benzimidazole) (AB-PBI) membranes are investigated by studying the FT-Raman signals due to the benzimidazole ring vibration together with the C-C and C-H out-of- and in-plane ring deformations. By immersion in aqueous ortho-phosphoric acid for different time periods, membranes with various doping degrees, i.e. different molar fractions of acid, are prepared. The chemical-physical interactions between polymer and acid are studied through band shifting and intensity change of diagnostic peaks in the 500-2000 cm(-1) spectral range. The formation of hydrogen bonding networks surrounding the polymer seems to be the main reason for the observed interactions. Only if the AB-PBI polymer is highly doped, the Raman spectra show an additional signal, which can be attributed to the presence of free phosphoric acid molecules in the polymer network. For low and intermediate doping degrees no evidence for free phosphoric acid molecules can be seen in the spectra. The extent of the polymer-phosphoric acid interactions in the doped membrane material is reinvestigated after a period of one month and the stability discussed. Our results provide insight into the role of phosphoric acid as a medium in the conductivity mechanism in polybenzimidazole.     

Structures of medium sized tin cluster anions

The structures of medium sized tin cluster anions Sn(n)(-) (n = 16-29) were determined by a combination of density functional theory, trapped ion electron diffraction and collision induced dissociation (CID). Mostly prolate structures were found with a structural motif based on only three repeatedly appearing subunit clusters, the Sn(7) pentagonal bipyramid, the Sn(9) tricapped trigonal prism and the Sn(10) bicapped tetragonal antiprism. Sn(16)(-) and Sn(17)(-) are composed of two face connected subunits. In Sn(18)(-)-Sn(20)(-) the subunits form cluster dimers. For Sn(21)(-)-Sn(23)(-) additional tin atoms are inserted between the building blocks. Sn(24)(-) and Sn(25)(-) are composed of a Sn(9) or Sn(10) connected to a Sn(15) subunit, which closely resembles the ground state of Sn(15)(-). Finally, in the larger clusters Sn(26)(-)-Sn(29)(-) additional bridging atoms again connect the building blocks. The CID experiments reveal fission as the main fragmentation channel for all investigated cluster sizes. This rather unexpected "pearl-chain" cluster growth mode is rationalized by the extraordinary stability of the building blocks.     

Investigations into the Formation and Stability of Cationic Rhodium Diphosphane η(6) -Arene Complexes

Rhodium-η(6) -arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP*=chelating diphosphane, X=noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy ((31) P, (103) Rh) and X-ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318?K.     

Model‐free multivariate curve resolution combined with model‐based kinetics: algorithm and applications

Multivariate curve resolution techniques are powerful tools to extract from sequences of spectra of a chemical reaction system the number of independent chemical components, their associated spectra, and the concentration profiles in time. Usually, these solutions are not unique because of the so‐called rotational ambiguity. In the present work, we reduce the non‐uniqueness by enforcing the consistency of the computed concentration profiles with a given kinetic model. Traditionally, the kinetic modeling is realized in a separate step, which follows the multivariate curve resolution procedure. In contrast to this, we consider a hybrid approach that combines the model‐free curve resolution technique with the model‐based kinetic modeling in an overall optimization. For a two‐component model problem, the range of possible solutions is analyzed, and its reduction to a single, unique solution by means of the hybrid kinetic modeling is shown. The algorithm reduces the rotational ambiguity and improves the quality of the kinetic fitting. Numerical results are also presented for a multi‐component catalytic reaction system that obeys the Michaelis–Menten kinetics. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigations into the Formation and Stability of Cationic Rhodium Diphosphane η6‐Arene Complexes

Rhodium–η⁶‐arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP*=chelating diphosphane, X=noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy (³¹P, ¹⁰³Rh) and X‐ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318 K.     

On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration

Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet–droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet–droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet–droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet–droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet–droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.     

Molecular vibration spectroscopy studies on novel trinuclear rhodium-7-hydride complexes of the general type {[Rh(PP*)X]3(μ(2-X)3(μ3-X)}(BF4)2 (X = H, D)

Novel trinuclear rhodium-hydride complexes with diphosphine ligands Tangphos, t-Bu-BisP*, and Me-DuPHOS which contain bridging μ(2)- and μ(3)-hydrides as well as terminal hydrides in one molecule have been reported recently. In this work, these different rhodium-hydride bonds are characterized by Raman spectroscopy and the results are compared with those obtained by means of the more commonly applied IR spectroscopy. Density functional theory (DFT) calculations have been carried out to support the experimental findings. The structure of the Rh(3)H(7) core is described in the context of their vibrational stretching modes.