Charge inversion as a structural probe for C6H 5 + and C6H 6 +· cations

Charge reversal (⁺CR⁻) of cations to anions can be used to structurally differentiate isomeric C₆H₅⁺ and C₆H₆^+· hydrocarbon ions by means of tandem mass spectrometry. In view of the manifold of possible isomers, only a few prototype precursors are examined. Thus, charge inversion demonstrates that electron ionization of 2,4-hexadiyne yields an intact molecular ion, whereas the charge inversion spectra of C₆H₆^+· obtained from benzene, 1,5-hexadiyne, and fulvene are identical within experimental error. Similarly, the ⁺CR⁻ spectrum of the C₆H₅⁺ cation generated by dissociative ionization of 2,4-hexadiyne is significantly different from the ⁺CR⁻ spectrum of C₆H₅⁺ obtained from iodobenzene, suggesting the formation of a 2,4-hexadiynyl cation from the former precursor. Although charge inversion of cations to anions has a low efficiency and requires large precursor ion fluxes, the particular value of this method is that the spectra may not just differ in fragment ion intensities, but these differences can directly be related to the underlying ion structures.     

Tuning optical properties of water-soluble CdTe quantum dots for biological applications

In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.

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Statistical investigation of the nonlinear dynamical behavior of offshore structures

The increasing amount of reports concerning damages of ships, structures and loss of cargo due to wave structure interaction demand the development of systems to predict critical situations in the offshore environment. Within the last years, research has been done to predict encounter with critical wave or wave groups such as “rogue waves” or the so–called “three sisters”. The aim of such research is to develop programs that predict dangerous incidents and possibly alert the crew in time. The dangers of such extreme wave situations are severe, but occurrence of them is rather rare. Additionally and more often, structures are endangered because of fluid–structure–interaction leading to critical dynamical system behaviour in a wave environment that shows no extreme wave heights. The severeness of these incidents then depends on the experience and correctness of decision concerning the evasive actions of the master and his crew. Taking nonlinear effects into account, the statistical investigation of structures in waves shows critical behaviour of ships and structures without the absolute necessity of heavy sea conditions or the occurrence of dangerous sea phenomena. This paper describes the development of a program that uses a Monte–Carlo–Simulation technique based on a common panel–method for the creation of added masses and added dampings to predict the behaviour of the structure in several wave conditions. It shows possible ways to prevent the occurrence using similar early warning systems to those in development for critical wavegroups. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

New Polyolefin-Nanocomposites by In Situ Polymerization with Metallocene Catalysts

Summary: Polypropylene-nanocomposites were prepared by in-situ polymerization with the catalysts systems rac[Et(IndH₄)₂]ZrCl₂, Me₂Si(Flu)(Ind)ZrCl₂ and rac[Me₂Si(2-Me-4-(1-Naph)Ind)₂]ZrCl₂. The type and size of the nanoparticles and the concentration of the propene were varied. The activity is independent of the type and the size of the filler. It was observed that the filler contents in the polypropylene-nanocomposites depend on the catalysts system used. The morphology results using TEM revealed that the nanoparticles are uniformly distributed in the isotactic polypropylene matrix. Additionally, the melting points, glass temperatures and crystallization temperatures changed with the amount of the fillers.     

Measurement of the absolute branching fraction of D0-->K-pi+

We measure the absolute branching fraction for D(0)-->K(-)pi(+) using partial reconstruction of B(0)-->D(*+)Xl(-)nu(l) decays, in which only the charged lepton and the pion from the decay D(*+)-->D(0)pi(+) are used. Based on a data sample of 230 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D(0)-->K(-)pi(+)) = (4.007+/-0.037+/-0.072)%, where the first uncertainty is statistical and the second is systematic.     

Total Synthesis and Biological Evaluation of Heliolactone

Strigolactones are phytohormones, which affect diverse aspects of plant growth and development with potential application in modern agriculture. Recently, heliolactone has been isolated as a non‐canonical type of strigolactone from the root exudates of sunflower, and it could be involved in signaling in the rhizosphere as well as in planta. However, its biological activity is yet to be evaluated, due to its relative chemical instability and its low natural abundance. Herein, we describe the gram‐scale synthesis of heliolactone and its derivatives by using Stille cross‐coupling as the key bond‐forming reaction, and we disclose some of their biological activities (soil stability, binding ability to strigolactone receptor, corn germination, sunflower germination, Orobanche cumana germination and leaf senescence) in comparison with other canonical and non‐canonical strigolactones.     

The unusual fragmentation of long‐chain feruloyl esters under negative ion electrospray conditions

Long‐chain ferulic acid esters, such as eicosyl ferulate ( 1 ), show a complex and analytically valuable fragmentation behavior under negative ion electrospay collision‐induced dissociation ((?)‐ESI‐CID) mass spectrometry, as studied by use of a high‐resolution (Orbitrap) mass spectrometer. In a strong contrast to the very simple fragmentation of the [M + H]⁺ ion, which is discussed briefly, the deprotonated molecule, [M – H]^?, exhibits a rich secondary fragmentation chemistry. It first loses a methyl radical (MS²) and the ortho‐quinoid [M – H – Me]^‐? radical anion thus formed then dissociates by loss of an extended series of neutral radicals, C_nH_2n + 1^? (n = 0–16) from the long alkyl chain, in competition with the expulsion of CO and CO₂ (MS³). The further fragmentation (MS⁴) of the [M – H – Me – C₃H₇]^? ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M – H – Me – CO]^‐? and [M – H – Me – CO₂]^‐? ions provide some mechanistic and structural insights.     

An Integrated Model-Based Analysis of Polymer Chemistry and Polymerisation Reactors

In this paper, a simple demonstration is presented on the analysis of the combined effect of polymer chemistry and the polymerisation reactor on the polymer properties. The model would ideally account for the raw material and end-product characteristics and properties on the one hand; the polymerisation kinetics and reaction engineering on the other hand. This system-wide model-driven approach enables the interlinking of the widely disparate facets of polymer science and engineering, and thereby provides a tool for rapid and efficient identification and scale-up of new polymeric materials that would be exploited in future studies. The ideas are demonstrated with regard to a hyper-branched polymerisation chemistry.     

The clusters [Ma(ECp*)b] (M=Pd, Pt; E=Al, Ga, In): structures, fluxionality, and ligand exchange reactions

The synthesis and structural characterization of the novel homoleptic cluster complexes [Pd2(GaCp*)2(mu2-GaCp*)3] (1c), [Pd3(GaCp*)4(mu2-GaCp*)4] (2b) and [Pd3(AlCp*)2(mu2-AlCp*)2(mu3-AlCp*)2] (3) (Cp*=C5Me5) are presented. Furthermore, ligand exchange reactions of these cluster complexes are explored. In contrast to the electronically and sterically saturated complexes [M(ECp*)4] (M=Ni, Pd, Pt), the new unsaturated analogues [M(a)(ER)b] (E=Al, Ga, In) react with a variety of typical ligands (Cp*Al, CO, phosphines, isonitriles) to give new di- and tri-substituted compounds like [Pt2(GaCp*)2(mu2-AlCp*)3] (1d), [PdPt(GaCp*)(PPh3)(mu2-GaCp*)3] (4b), or [Pd3(PPh3)3(mu2-InCp*)(mu3-InCp*)2] (8). The trends of the reactivity of [M(a)(ER)b] as well as their fluxional behavior in solution has been elucidated by NMR spectroscopy, resulting in a mechanistic rationale for the ligand exchange reactions as well as the fluxional processes.