Rapid Autoxidation Forms Highly Oxidized RO2 Radicals in the Atmosphere

Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO₂ radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O₂ addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.     

Amphiphilic Polymethacrylate‐ and Polystyrene‐Based Chemical Delivery Systems for Damascones

Amphiphilic polystyrene‐ and polymethacrylate‐based β‐acyloxy ketones were investigated as potential delivery systems for the controlled release of damascones by retro‐1,4‐addition in applications of functional perfumery. A series of random copolymers being composed of the hydrophobic damascone‐release unit and a second hydrophilic monomer were obtained by radical polymerization in organic solution by using 2,2′‐azobis[2‐methylpropanenitrile] (AIBN) as the radical source (Schemes 2 and 3). A first evaluation of the polymer conjugates in acidic or alkaline buffered aqueous solution, and in the presence of a surfactant, showed that polymethacrylates and polystyrenes having a carboxylic acid function as hydrophilic group are particularly interesting for the targeted applications (Table 2). The release of δ‐damascone ( 1 ) from polymers with poly(methacrylic acid) and poly(vinylbenzoic acid) comonomers in different stoichiometric ratios was thus followed over several days at pH 4, 7, and 9 by comparison of fluorescence probing, solvent extraction, and particle‐size measurements (Tables 3 and 4). In acidic media, the polymers were found to be stable, and almost no δ‐damascone ( 1 ) was released. In neutral or alkaline solution, where the carboxylic acid functions are deprotonated, the concentration of 1 increased over time. In the case of the polymethacrylates, the fluorescence probing experiments showed an increasing hydrophilicity of the polymer backbone with increasing fragrance release, whereas in the case of the polystyrene support, the hydrophilicity of the environment remained constant. These results suggest that the nature of the polymer backbone may have a stronger influence on the fragrance release than the ratio of hydrophilic and hydrophobic monomers in the polymer chain.     

Experimental setup and first measurement of DNA damage induced along and around an antiproton beam

Radiotherapy employs ionizing radiation to induce lethal DNA lesions in cancer cells while minimizing damage to healthy tissues. Due to their pattern of energy deposition, better therapeutic outcomes can, in theory, be achieved with ions compared to photons. Antiprotons have been proposed to offer a further enhancement due to their annihilation at the end of the path. The work presented here aimed to establish and validate an experimental procedure for the quantification of plasmid and genomic DNA damage resulting from antiproton exposure. Immunocytochemistry was used to assess DNA damage in directly and indirectly exposed human fibroblasts irradiated in both plateau and Bragg peak regions of a 126 MeV antiproton beam at CERN. Cells were stained post irradiation with an anti-γ-H2AX antibody. Quantification of the γ-H2AX foci-dose relationship is consistent with a linear increase in the Bragg peak region. A qualitative analysis of the foci detected in the Bragg peak and plateau region indicates significant differences highlighting the different severity of DNA lesions produced along the particle path. Irradiation of desalted plasmid DNA with 5 Gy antiprotons at the Bragg peak resulted in a significant portion of linear plasmid in the resultant solution.     

Search for kaonic nuclear state, K − pp, in the p + p → X + K + reaction with FOPI

We search for the most fundamental kaonic nuclear state, K ^??? pp by employing the reaction p?+?p→K ^?+??+?X at 3.0 GeV incident beam energy. The experiment makes use of the SIS-18 synchrotron and the ~4π acceptance FOPI apparatus in the cave-B at the GSI, Darmstadt, Germany and aims to collect full kinematics information of the reaction. We look for a signature of the X (?≡?K ^??? pp) in both missing mass spectrum by measuring K ^?+?, and invariant mass spectrum by measuring decay particles; X?→?Λ?+?p. The experiment is planned to take place in 2009.     

Ruthenium alkylidenes: modulation of a new class of catalysts for controlled radical polymerization of vinyl monomers

Air-stable and readily available ruthenium benzylidene complexes of the general type [RuCl2(=CHPh)(L)(L')] (L, L' = PCy3 and/or N-heterocyclic carbene) constitute a new class of catalyst precursors for atom-transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy3 and/or N-heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl2(=CHPh)(L)(L')] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N-heterocyclic carbene ligands remain bound to the metal center. Polymerization of n-butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox-initiated free-radical process.     

Restructuring of force networks

The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent the evolving force network that percolates through the system by an inverse fiber rupture model. Received 15 March 2002 and Received in final form 29 July 2002     

Combinatorial Chemistry for Ligand Development in Catalysis: Synthesis and Catalysis Screening of Peptidosulfonamide Tweezers on the Solid Phase

On the basis of a pyrrolidine tweezer 1, a library of peptidosulfonamide tweezers (15a-e, 16a-e) was synthesized on the solid phase. This library was screened in a simultaneous substrate screening procedure for the ability to enantioselectively catalyze the Ti(O-i-Pr)(4)-mediated addition of diethylzinc to aldehydes. One of the best solid-phase tweezer catalyst (i.e., 16d, giving an ee of 32% in solid-phase catalysis) was resynthesized in solution (compounds 20 and 21). The now homogeneous solution-phase catalysis showed even better enantioselectivity (i.e., up to 66%).     

Density fluctuations in a model for vibrated granular media

This paper presents the study of density fluctuations in a model for vibrated granular media. Their microscopic origin is shown to be linked to the microscopic disorder in grains packing. Varying vibrations amplitude and duration, several regimes are found for density relaxation. Its power spectrum is well described by power laws.