A Chemical System that Mimics Decoding Operations

The chemical information stored in equilibrium mixtures of molecular species is larger than the sum of information carried by the individual molecules. Protonation equilibria in dilute dichloromethane solution of a shape‐persistent macrocycle bearing two 2,2′‐bipyridine units and two Coumarin 2 moieties (see figure) can be exploited to mimic decoding operations.

     

C?X⋅⋅⋅O Halogen Bonding: Interactions of Trifluoromethyl Halides with Dimethyl Ether

The formation of weakly bound molecular complexes between dimethyl ether (DME) and the trifluoromethyl halides CF₃Cl, CF₃Br and CF₃I dissolved in liquid argon and in liquid krypton is investigated, using Raman and FTIR spectroscopy. For all halides evidence is found for the formation of C? X???O halogen‐bonded 1:1 complexes. At higher concentrations of CF₃Br, a weak absorption due to a 1:2 complex is also observed. Using spectra recorded at temperatures between 87 and 125 K, the complexation enthalpies for the complexes are determined to be ?6.8(3) kJ mol^?1 (DME?CF₃Cl), ?10.2(1) kJ mol^?1 (DME?CF₃Br), ?15.5(1) kJ mol^?1 (DME?CF₃I), and ?17.8(5) kJ mol^?1 [DME(?CF₃Br)₂]. Structural and spectral information on the complexes is obtained from ab initio calculations at the MP2/ 6‐311++G(d,p) and MP2/6‐311++G(d,p)+LanL2DZ* levels. By applying Monte Carlo free energy perturbation calculations to account for the solvent influences, and statistical thermodynamics to estimate the zero‐point vibrational and thermal influences, the ab initio complexation energies are converted into complexation enthalpies for the solutions in liquid argon. The resulting values are compared with the experimental data deduced from the cryosolutions.     

Packet loss characteristics for <Emphasis Type="Italic">M</Emphasis>/<Emphasis Type="Italic">G</Emphasis>/1/<Emphasis Type="Italic">N</Emphasis> queueing systems

In this contribution we investigate higher-order loss characteristics for M/G/1/N queueing systems. We focus on the lengths of the loss and non-loss periods as well as on the number of arrivals during these periods. For the analysis, we extend the Markovian state of the queueing system with the time and number of admitted arrivals since the instant where the last loss occurred. By combining transform and matrix techniques, expressions for the various moments of these loss characteristics are found. The approach also yields expressions for the loss probability and the conditional loss probability. Some numerical examples then illustrate our results.     

Advanced finite element formulations for modeling thin piezoelectric structures

This contribution is concerned with mixed finite element formulations for modeling piezoelectric beam and shell structures. Due to the electromechanical coupling, specific deformation modes are joined with electric field components. In bending dominated problems incompatible approximation functions of these fields cause incorrect results. These effects occur in standard finite element formulations, where interpolation functions of lowest order are used. A mixed variational approach is introduced to overcome these problems. The mixed formulation allows for a consistent approximation of the electromechanical coupled problem. It utilizes six independent fields and could be derived from a Hu-Washizu variational principle. Displacements, rotations and the electric potential are employed as nodal degrees of freedom. According to the Timoshenko theory (beam) and the Reissner-Mindlin theory (shell), the formulations account for constant transversal shear strains. To incorporate three dimensional constitutive relations all transversal components of the electric field and the strain field are enriched by mixed finite element interpolations. Thus the complete piezoelectric coupling is appropriately captured. The common assumption of vanishing transversal stress and dielectric displacement components is enforced in an integral sense. Some numerical examples will demonstrate the capability of the presented finite element formulation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Towards perfunctionalized dodecahedranes--en route to C20 fullerene

“One‐pot” substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C₂₀H₂₀) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C₂₀(OH)₂₀, in complex polyol mixtures (up to C₂₀H₁₀(OH)₁₀ decols, a trace of C₂₀H(OH)₁₉?). Perfluorination was successful in a NaF matrix but (nearly pure) C₂₀F₂₀ could be secured only in very low yield. “Brute‐force” photochlorination (heat, light, pressure, time) provided a mixture of hydrogen‐free, barely soluble C₂₀Cl₁₆ dienes in high yield and C₂₀Cl₂₀ as a trace component. Upon electron‐impact ionization of the C₂₀Cl₁₆ material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine‐free C₂₀⁺ ions. “Brute‐force” photobrominations delivered an extremely complex mixture of polybromides with C₂₀HBr₁₃ trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C₂₀H_4–0^+(2+)(3+) ions. The insoluble ～C₂₀HBr₁₃ fraction (C₂₀Br₁₄ trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C₂₀^? ions. The C₂₀Cl₁₆ dienes and C₂₀H_0–3Br_14–12 tri‐/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH₂N₂ smoothly. Dehalogenation of the respective cycloaddition products through electron‐impact ionization resulted in C_22–24H_4–8⁺⁽²⁺⁾ ions possibly constituting bis‐/tris‐/tetrakis‐methano‐C₂₀ fullerenes or partly hydrogenated C₂₂, C₂₃, and C₂₄ cages.     

Effective solvation of alkaline earth ions by proline-rich proteolytic peptides of galectin-3 upon electrospray ionisation

In an analysis of a combined chymotrypsin/AspN digest of galectin-3 by positive ion nano-electrospray ionisation mass spectrometry (nanoESI-MS) several peptides were observed which showed metal adduct ions as their most abundant ion signals. The most prominent adduct ions were observed at m/z values corresponding to [M+40]2+, [M+41]3+, and [M+42]4+ ions. Detailed investigation of the [M+40]2+ ion of the peptide GAPAGPLIVPY showed that it was not, as originally expected, a [M+H+39K]2+ adduct ion but had the composition [M+40Ca]2+. This was verified by several approaches: (i) nanoESI-MS/MS of the [M+Ca]2+ adduct ions resulted in the virtually exclusive formation of doubly charged fragment ions; (ii) mass determination by quadrupole time-of-flight (QTOF)-MS provided a preliminary identification; and (iii) accurate mass measurement using nanoESI Fourier transform ion cyclotron resonance (FTICR)-MS at a mass resolving power of 500 000 allowed the specific detection and identification of the isobaric ion pairs [M+40Ca]2+/[M+H+39K]2+ and [M+24Mg]2+/[M+H+23Na]2+. All peptides in the chymotryptic galectin-3 digest without a basic residue (K or R) showed addition of calcium as the most prominent ionisation principle. A further common feature of these nonbasic peptides was the presence of several proline residues, which is assumed to be a factor promoting the intense addition of calcium. It was observed that the common trace levels of sodium and calcium in analytical grade solvents (about 1-10 microM) are sufficient to generate the [M+H+23Na]2+ and [M+40Ca]2+ ions as the most prominent species of the peptide GAPAGPLIVPY. We conclude that the sequence motifs P-XX-P and P-XXX-P favour the solvation of alkaline earth ions in ESI-MS. In view of the successful detection of physiological Ca/protein interactions by ESI-MS, this finding may point to a solvation of Ca2+ by galectin in solution. The findings open new routes of research in the study of metal/protein and metal/peptide interactions     

Preservation of the biofunctionality of DNA and protein during microfabrication

Microfabrication processes, especially in silicon, are not compatible with biomolecules. Silicon and metal-based materials having crystalline structures are manipulated under harsh conditions with acids, bases, and organic solvents at high temperature. In comparison, organic biomolecules such as DNA and proteins have complex, three-dimensional structures and are sensitive to denaturation, oxidation, hydrolysis, and thermal destruction. Here, we report on the integration of DNA and the biotin-binding protein NeutrAvidin into microfabrication processes by using a novel approach based on a gold passivation mask. Our data show that this passivation method preserves approximately 84% of the biofunctionality of DNA and approximately 30% of that of NeutrAvidin under harsh process conditions. This novel technology enables the integration of DNA, proteins, and potentially other biological molecules into mass scalable microfabrication processes for biomedical devices, biochips, biosensors, and microelectromechanical systems with biomolecules (BioMEMS).