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      Chemically Reversible Reactions of Hydrogen Sulfide with Metal Phthalocyanines

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          Abstract

          Hydrogen sulfide (H 2S) is an important signaling molecule that exerts action on various bioinorganic targets. Despite this importance, few studies have investigated the differential reactivity of the physiologically relevant H 2S and HS protonation states with metal complexes. Here we report the distinct reactivity of H 2S and HS with zinc(II) and cobalt(II) phthalocyanine (Pc) complexes and highlight the chemical reversibility and cyclability of each metal. ZnPc reacts with HS , but not H 2S, to generate [ZnPc-SH] , which can be converted back to ZnPc by protonation. CoPc reacts with HS , but not H 2S, to form [Co IPc] , which can be reoxidized to CoPc by air. Taken together, these results demonstrate the chemically reversible reaction of HS with metal phthalocyanine complexes and highlight the importance of H 2S protonation state in understanding the reactivity profile of H 2S with biologically relevant metal scaffolds.

          Abstract

          The protonation state of H 2S influences its reactivity with different metal phthalocyanine (Pc) complexes. Both ZnPc and CoPc react with H 2S in a chemically reversible manner, with redox-inactive ZnPc binding HS and redox-active CoPc undergoing reduction. The [ZnPc-SH] product can be reverted to ZnPc by protonation, and [Co IPc] can be redoxidized to CoPc with air.

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          Most cited references 16

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          Rapid planetesimal formation in turbulent circumstellar discs

          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

            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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              The possible role of hydrogen sulfide as an endogenous neuromodulator.

               K Abe,  Richard Kimura (1996)
              Hydrogen sulfide (H2S), which is well known as a toxic gas, is produced endogenously from L-cysteine in mammalian tissues. H2S is present at relatively high levels in the brain, suggesting that it has a physiological function. Two other gases, nitric oxide and carbon monoxide, are also endogenously produced and have been proposed as neuronal messengers in the brain. In this work we show the following: (1) an H2S-producing enzyme, cystathionine beta-synthase (CBS), is highly expressed in the hippocampus; (2) CBS inhibitors hydroxylamine and amino-oxyacetate suppress the production of brain H2S; and (3) a CBS activator, S-adenosyl-L-methionine, enhances H2S production, indicating that CBS contributes to the production of endogenous H2S. We also show that physiological concentrations of H2S selectively enhance NMDA receptor-mediated responses and facilitate the induction of hippocampal long-term potentiation. These observations suggest that endogenous H2S functions as a neuromodulator in the brain.
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                Author and article information

                Affiliations
                Department of Chemistry and Biochemistry, Materials Science Institute, University of Oregon , Eugene, Oregon 97403-1253, United States
                Author notes
                Journal
                Inorg Chem
                Inorg Chem
                ic
                inocaj
                Inorganic Chemistry
                American Chemical Society
                0020-1669
                1520-510X
                01 May 2015
                01 May 2014
                04 August 2014
                : 53
                : 15
                : 7800-7802
                24785654 4123935 10.1021/ic500664c
                Copyright © 2014 American Chemical Society

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                Funding
                National Institutes of Health, United States
                Categories
                Communication
                Custom metadata
                ic500664c
                ic-2014-00664c

                Inorganic & Bioinorganic chemistry

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