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      Synthesis of cyclic adenosine 5′-diphosphate ribose analogues: a C2′ endo/ syn “southern” ribose conformation underlies activity at the sea urchin cADPR receptor†

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          Abstract

          Conformational analysis of cyclic ADP-ribose analogues reveals a correlation between a C2′ endo/ syn “southern” ribose conformation and activity in sea urchin egg homogenates.

          Abstract

          Novel 8-substituted base and sugar-modified analogues of the Ca 2+ mobilizing second messenger cyclic adenosine 5′-diphosphate ribose (cADPR) were synthesized using a chemoenzymatic approach and evaluated for activity in sea urchin egg homogenate (SUH) and in Jurkat T-lymphocytes; conformational analysis investigated by 1H NMR spectroscopy revealed that a C2′ endo/ syn conformation of the “southern” ribose is crucial for agonist or antagonist activity at the SUH-, but not at the T cell-cADPR receptor.

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          Rapid planetesimal formation in turbulent circumstellar discs

          Anders Johansen, Jeffrey S. Oishi, Mordecai-Mark Mac Low … (2007)
          The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.
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            The Dicke Quantum Phase Transition with a Superfluid Gas in an Optical Cavity

            Ferdinand Brennecke, Tilman Esslinger, Christine Guerlin … (2009)
            A phase transition describes the sudden change of state in a physical system, such as the transition between a fluid and a solid. Quantum gases provide the opportunity to establish a direct link between experiment and generic models which capture the underlying physics. A fundamental concept to describe the collective matter-light interaction is the Dicke model which has been predicted to show an intriguing quantum phase transition. Here we realize the Dicke quantum phase transition in an open system formed by a Bose-Einstein condensate coupled to an optical cavity, and observe the emergence of a self-organized supersolid phase. The phase transition is driven by infinitely long-ranged interactions between the condensed atoms. These are induced by two-photon processes involving the cavity mode and a pump field. We show that the phase transition is described by the Dicke Hamiltonian, including counter-rotating coupling terms, and that the supersolid phase is associated with a spontaneously broken spatial symmetry. The boundary of the phase transition is mapped out in quantitative agreement with the Dicke model. The work opens the field of quantum gases with long-ranged interactions, and provides access to novel quantum phases.
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              Versatile Photocatalytic Systems for H2 Generation in Water Based on an Efficient DuBois-Type Nickel Catalyst

              Manuela Groß, Anna Reynal, James R. Durrant … (2013)
              The generation of renewable H2 through an efficient photochemical route requires photoinduced electron transfer (ET) from a light harvester to an efficient electrocatalyst in water. Here, we report on a molecular H2 evolution catalyst (NiP) with a DuBois-type [Ni(P2 R′N2 R″)2]2+ core (P2 R′N2 R″ = bis(1,5-R′-diphospha-3,7-R″-diazacyclooctane), which contains an outer coordination sphere with phosphonic acid groups. The latter functionality allows for good solubility in water and immobilization on metal oxide semiconductors. Electrochemical studies confirm that NiP is a highly active electrocatalyst in aqueous electrolyte solution (overpotential of approximately 200 mV at pH 4.5 with a Faradaic yield of 85 ± 4%). Photocatalytic experiments and investigations on the ET kinetics were carried out in combination with a phosphonated Ru(II) tris(bipyridine) dye (RuP) in homogeneous and heterogeneous environments. Time-resolved luminescence and transient absorption spectroscopy studies confirmed that directed ET from RuP to NiP occurs efficiently in all systems on the nano- to microsecond time scale, through three distinct routes: reductive quenching of RuP in solution or on the surface of ZrO2 (“on particle” system) or oxidative quenching of RuP when the compounds were immobilized on TiO2 (“through particle” system). Our studies show that NiP can be used in a purely aqueous solution and on a semiconductor surface with a high degree of versatility. A high TOF of 460 ± 60 h–1 with a TON of 723 ± 171 for photocatalytic H2 generation with a molecular Ni catalyst in water and a photon-to-H2 quantum yield of approximately 10% were achieved for the homogeneous system.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Org Biomol Chem
                Title: Organic & Biomolecular Chemistry
                Publisher: Royal Society of Chemistry
                ISSN (Print): 1477-0520
                ISSN (Electronic): 1477-0539
                Publication date (Print): 7 January 2011
                Publication date (Electronic): 25 October 2010
                Volume: 9
                Issue: 1
                Pages: 278-290
                Affiliations
                [a ] Wolfson Laboratory of Medicinal Chemistry , Department of Pharmacy and Pharmacology , University of Bath , Bath , UK BA2 7AY . Email: b.v.l.potter@ 123456bath.ac.uk ; Fax: +44 1225 386114 ; Tel: +44 1225 386639
                [b ] Department of Pharmacology , University of Oxford , Mansfield Road , Oxford , UK OX1 3QT
                [c ] Institute of Biochemistry and Molecular Biology I: Cellular Signal Transduction , University Medical Center Hamburg-Eppendorf , Germany
                Article
                Publisher ID: c0ob00396d
                DOI: 10.1039/c0ob00396d
                PMC ID: 3172588
                PubMed ID: 20976353
                SO-VID: 79ef0ad6-bdc7-4381-b508-99d271ef5f93
                Copyright © This journal is © The Royal Society of Chemistry 2010
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 7 July 2010
                Date accepted : 14 September 2010
                Categories
                Subject: Chemistry

                Notes

                †This paper is part of an Organic & Biomolecular Chemistry web theme issue on chemical biology.


                ScienceOpen disciplines: Organic & Biomolecular chemistry
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                ScienceOpen disciplines: Organic & Biomolecular chemistry

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