Water formation at low temperatures by surface O2 hydrogenation I: characterization of ice penetration

Water is the main component of interstellar ice mantles, is abundant in the solar system and is a crucial ingredient for life. The formation of this molecule in the interstellar medium cannot be explained by gas-phase chemistry only and its surface hydrogenation formation routes at low temperatures (O, O2, O3 channels) are still unclear and most likely incomplete. In a previous paper we discussed an unexpected zeroth-order H2O production behavior in O2 ice hydrogenation experiments compared to the first-order H2CO and CH3OH production behavior found in former studies on hydrogenation of CO ice. In this paper we experimentally investigate in detail how the structure of O2 ice leads to this rare behavior in reaction order and production yield. In our experiments H atoms are added to a thick O2 ice under fully controlled conditions, while the changes are followed by means of reflection absorption infrared spectroscopy (RAIRS). The H-atom penetration mechanism is systematically studied by varying the temperature, thickness and structure of the O2 ice. We conclude that the competition between reaction and diffusion of the H atoms into the O2 ice explains the unexpected H2O and H2O2 formation behavior. In addition, we show that the proposed O2 hydrogenation scheme is incomplete, suggesting that additional surface reactions should be considered. Indeed, the detection of newly formed O3 in the ice upon H-atom exposure proves that the O2 channel is not an isolated route. Furthermore, the addition of H2 molecules is found not to have a measurable effect on the O2 reaction channel.Comment: 1 page, 1 figur

Water formation at low temperatures by surface O2 hydrogenation II: the reaction network

Water is abundantly present in the Universe. It is the main component of interstellar ice mantles and a key ingredient for life. Water in space is mainly formed through surface reactions. Three formation routes have been proposed in the past: hydrogenation of surface O, O2, and O3. In a previous paper [Ioppolo et al., Astrophys. J., 2008, 686, 1474] we discussed an unexpected non-standard zeroth-order H2O2 production behaviour in O2 hydrogenation experiments, which suggests that the proposed reaction network is not complete, and that the reaction channels are probably more interconnected than previously thought. In this paper we aim to derive the full reaction scheme for O2 surface hydrogenation and to constrain the rates of the individual reactions. This is achieved through simultaneous H-atom and O2 deposition under ultra-high vacuum conditions for astronomically relevant temperatures. Different H/O2 ratios are used to trace different stages in the hydrogenation network. The chemical changes in the forming ice are followed by means of reflection absorption infrared spectroscopy (RAIRS). New reaction paths are revealed as compared to previous experiments. Several reaction steps prove to be much more efficient (H + O2) or less efficient (H + OH and H2 + OH) than originally thought. These are the main conclusions of this work and the extended network concluded here will have profound implications for models that describe the formation of water in space.Comment: 1 page, 1 figur

Total Synthesis of Solandelactone I

Since the marine natural products solandelactones A–I were isolated from the hydroid Solanderia secunda and investigated by Seo et al. in 1996, considerable synthetic efforts toward these marine oxylipins followed. However, the structure elucidation of solandelactone I remained incomplete, and no synthesis has been reported. On the basis of our retrosynthetic analysis, the key building blocks were combined in a Horner–Wadsworth–Emmons reaction to create two common intermediates for the stereodivergent synthesis of all four diastereomers 1–4 matching the proposed structure of solandelactone I. Comparison of the published analytical data of natural product solandelactone I and data obtained from the synthetic endeavor toward diastereomers 1–4 enabled the structure assignment of isomer 3; the proposed biosynthetic pathway for marine oxylipins also supports the result

How to use oxygen and atomic hydrogen to prepare atomically flat fcc Co(110) films

It is shown that atomic hydrogen from a specially designed atomic beam source is well suited for removing chemisorbed oxygen from an fcc Co(110) film that has been grown on a Cu(110) substrate using oxygen as a surfactant. Exposing the oxygen-terminated Co surface to atomic hydrogen leads to a surface reaction which destroys the (3×1) ordered-O induced surface reconstruction of the Co film. Upon annealing at 380 K, the hydrogen remaining on the O-free Co surface can be completely desorbed. With this technique, it is possible for the first time to prepare about 15 monolayers thick, atomically-flat fcc Co(110) films

Total Synthesis of Solandelactones A and B

The total synthesis of solandelactones A and B is presented. The eastern cyclopropyl moiety was prepared following an exceptionally short chemoenzymatic approach whereas enantioselective synthesis of the western side-chain relied on the application of diastereomerically pure allyl boronates. The natural products solandelactones A and B were isolated in good overall yields following convergence of each eastern and western element by application of the Nozaki–Hiyama–Kishi reaction

Who Got All of My Personal Data? Enabling Users to Monitor the Proliferation of Shared Personally Identifiable Information

Part 4: Privacy and Transparency in the Age of Cloud ComputingInternational audienceThe risk involved when users publish information, which becomes available to an unintentional broad audience via online social networks is evident. It is especially difficult for users of social networks to determine who will get the information before it is shared. Moreover, it is impossible to monitor data flows or to control the access to personal data after sharing the information. In contrast to enterprise identity management systems, in which provider-engineered processes control the access to and flow of data, the users of social networks themselves are responsible for information management. Consequently, privacy requirements have become important so that users can control the flow of their personal data across social networks and beyond. In particular, this kind of user-based information management should provide the capability to control data flows in a proactive manner, as well as reactive components to monitor the proliferation of data. In this conceptual paper, we motivate the necessity of a dedicated user-based information management on the basis of studies that we conducted on information that users share publicly in online social networks. Moreover, we outline the building blocks of user-based information management on the basis of existing approaches, which support users in managing data flows and an investigation that we did on the linkability of social network profiles. Furthermore, we contrast user-based information management with our experiences in developing and operating federated identity management services at the Karlsruhe Institute of Technology (KIT)

Surface formation routes of interstellar molecules: Hydrogenation reactions in simple ices

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Bromostibine complexes of iron(II): hypervalency and reactivity

The halostibine complexes [CpFe(CO)2(SbMe2Br)][CF3SO3] and [CpFe(CO)2(SbMe2Br)][BF4] both contain significant interactions between the anion and the formally neutral Sb(III) ligand, which simultaneously displays Lewis acidic and Lewis basic properties. The unexpected secondary product [CpFe(CO)(Me2BrSb-?-Br-SbBrMe2)] is formed in the presence of excess ligand, the strongly associated Br– anion bridging the two Sb donors to form a four-membered FeSb2Br ring.<br/