Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Opening

  • channel opening
  • crack opening
  • eye opening
  • follicular opening
  • gap opening
  • gland opening
  • glottic opening
  • jaw opening
  • large opening
  • market opening
  • mouth opening
  • nucleophilic ring opening
  • pore opening
  • reductive ring opening
  • regioselective ring opening
  • ring opening
  • stomatal opening
  • vaginal opening

  • Terms modified by Opening

  • opening angle
  • opening displacement
  • opening polymerization
  • opening pressure
  • opening reaction

  • Selected Abstracts


    EDUCATIONAL THEORY, Issue 2 2000
    Steve Bramall
    First page of article [source]


    Samples (n= 100) of freshly harvested clams (Galatea paradoxa Born) from the Cross River, Nigeria, were subjected after 24 h depurations to heat treatment (steam and water at 60, 70, 80, 90, 100C) for 1,6 min to evaluate the effects of level of heat treatment on opening, meat yield, sensory properties, proximate composition, pH and electrical conductivity (EC). Observations were also made on the effects of some chemical shucking aids (NaOH, NaHCO3, Na2CO3, NaCl) in 60C water on these parameters. Results showed that boiling water was most effective in opening the clams, with 100% shucking achieved in 1 min. Steam was least effective, requiring 6 min for 100% opening. Temperature significantly and strongly influenced meat yield (p<0.05;r=-0.92). pH (p<0.01; r=0.97), EC (p<0.05; r =0.65) and sensory properties (p<0.05). In general, shucking aids reduced opening time, significantly p<0.05) raised meat pH and EC, and with the exception of NaCl, insignificantly (P>0.05) improved yield. NaHCO3, and Na2CO3, which cut time for 100% opening from 5 min to 2 min were most effective. There were slight but significant (P <0.05) drops in meat moisture, crude protein and ash contents with increase in temperature (T). the model equations, pH = 4.69 + 0.021 T and % yield = 39.95,0.172 T were found to reliably predict meat pH and yield, with insignificant differences (P>0.05) between predicted and experimental values. [source]


    ABSTRACT The dynamic shear modulus (elastic and viscous modulus) development of dough during baking was studied. Flooded parallel plate geometry was used to monitor the rheological changes of commercially available canned doughs (bread dough, bun dough and biscuit dough). The normal force exerted on the upper plate by the expanding dough was measured to study the cell-opening event. The dough-baking process was simulated in a rheometer oven. The morphology of baked dough was studied using a scanning electron microscope to elucidate the effect of ingredients and process parameters on the properties of the final baked product. Three stages of modulus development were observed during the baking process: bubble growth and packing, rapid expansion/starch gelatinization and final curing. The cell opening coincided with the sudden rise in modulus caused by starch gelatinization. The rate at which starch gelatinization takes place controls the temperature of the cell opening. The type and concentration of various ingredients have a greater effect on the modulus and on the cell opening than the heating rates. Frequency dependence was observed during baking, but the effect on modulus development diminished at higher frequencies. [source]

    Opening up the Solution Space: The Role of Analogical Thinking for Breakthrough Product Innovation

    Oliver Gassmann
    The purpose of this paper is to investigate the approach of analogical thinking for product innovation. We collected data on projects from four engineering firms where analogical thinking was successfully applied for the development of breakthrough innovations. Results show that abstracting the problem by in-depth technical and contextual analysis is pivotal when searching for analogical solutions. Furthermore, the chances of identifying highly novel analogous solutions are increased if the problem is abstracted to the level of its structural similarities to other settings. We also found that the identification of structural similarities is supported when firms not only rely on the cognitive abilities of the individual but also employ an active search based on abstract search terms. Based on these insights, we propose a process model for the development of product innovations by means of analogical thinking. [source]

    Opening Up the Investor,Investee Dyad: Syndicates, Teams, and Networks

    Andy Lockett
    First page of article [source]

    Asymmetric Synthesis of Isoquinoline Derivatives from Amino Acids

    Oxana Sieck
    Abstract Reaction of isoquinolines 1 with N -arylsulfonylamino acid fluorides 2 provides a highly stereoselective access to new dihydroimidazo[2,1 -a]isoquinolin-3-ones 5 via intermediate N -acylisoquinolinium salts 3. Addition reactions to the en-amine double bond, such as hydrogenation or epoxidation with dimethyldioxirane, leads to tetrahydroimidazo[2,1 -a]isoquinoline-3-ones 6, 7 and oxiranes 8, respectively. Opening of the oxirane ring of the 8 with nucleophiles allows the synthesis of hydroxytetrahydroimidazo[2,1 -a]isoquinolin-3-ones 10 or 12 or of the polycyclic 1,4-dioxane 13 in high stereoselectivity. The regioselectivity of the oxiran ring opening depends on the kind of nucleophile and the conditions. Reaction of dihydroisoquinoline with O -TBDMS-mandelic acid chloride 15 leads to a tetrahydrooxazolo[2,3 -a]isoquinoline 17 with opposite facial selectivity as compared with dihydroimidazo[2,1 -a]isoquinolin-3-ones 5. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Regioselective SN2 Opening of Vinylic Epoxides with Trialkylzincates and Trialkylaluminates

    Olivier Equey
    Abstract The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti -substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products' ratio. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Intramolecular Opening of ,-Lactams with Amines as a Strategy Toward Enzymatically or Photochemically Triggered Activation of Lactenediyne Prodrugs

    Luca Banfi
    Abstract In order to develop a general strategy for selective activation of designed enediyne prodrugs belonging to the "lactenediyne" family, we studied the scope of intramolecular transamidation of simple monocyclic ,-lactams bearing a tethered amine. The effect of substituents, of reaction media, and of the type of tether, on the rate of transamidation is disclosed. The possibility of triggering the transamidation event under mild conditions by the action of suitable enzymes or UV light was demonstrated on model monocyclic ,-lactams. Finally, the strategy of intramolecular opening of the ,-lactam leading to a larger seven-membered ring was employed on a lactenediyne, demonstrating that ring enlargement could unleash the reactivity of the enediyne moiety. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Photochromic Polymers Based on the Photoinduced Opening and Thermal Closing of [1,3]Oxazine Rings

    Massimiliano Tomasulo
    Abstract Two macromolecular constructs incorporating a single polymer backbone with multiple photochromic side chains are developed. Both systems are prepared from preformed photochromic [1,3]oxazines after the ring-opening polymerization of their norbornene appendages. In solution, UV illumination of these polymers opens the [1,3]oxazine rings in their side chains in less than 6,ns and with a quantum yield of 0.09 in both instances. The photogenerated species incorporate a 4-nitrophenolate chromophore, and hence, their formation is accompanied by the appearance of an intense band in the visible region of the absorption spectrum. The photoproducts revert spontaneously to the original state with first-order kinetics in microseconds. Furthermore, both photochromic polymers tolerate hundreds of switching cycles with no sign of degradation, even in the presence of molecular oxygen. Thus, this design logic and choice of functional building blocks can translate into the realization of innovative photoresponsive materials with excellent photochromic performance. [source]

    Analysis of hopanes and steranes in single oil-bearing fluid inclusions using time-of-flight secondary ion mass spectrometry (ToF-SIMS)

    GEOBIOLOGY, Issue 1 2010
    Steranes and hopanes are organic biomarkers used as indicators for the first appearance of eukaryotes and cyanobacteria on Earth. Oil-bearing fluid inclusions may provide a contamination-free source of Precambrian biomarkers, as the oil has been secluded from the environment since the formation of the inclusion. However, analysis of biomarkers in single oil-bearing fluid inclusions, which is often necessary due to the presence of different generations of inclusions, has not been possible due to the small size of most inclusions. Here, we have used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to monitor in real time the opening of individual inclusions trapped in hydrothermal veins of fluorite and calcite and containing oil from Ordovician source rocks. Opening of the inclusions was performed by using a focused C60+ ion beam and the in situ content was precisely analysed for C27,C29 steranes and C29,C32 hopanes using Bi3+ as primary ions. The capacity to unambiguously detect these biomarkers in the picoliter amount of crude oil from a single, normal-sized (15,30 ,m in diameter) inclusion makes the approach promising in the search of organic biomarkers for life's early evolution on Earth. [source]

    Lewis Acid Catalyzed, Selective Cyclopropane-Ring Opening in Ingol Diterpene Derivatives

    Masuna Srinivasulu
    Lewis acid mediated skeletal rearrangement of the ingol diterpenoids 1 and 4via regio- and stereospecific cyclopropane-ring opening afforded the four new compounds 2, 3, 5, and 6, named nivulianol A,D (Scheme,1). Their structures were established by means of IR, MS, and in-depth NMR spectroscopic analyses. The rearranged congeners were tested for lipopolysaccharide (LPS)-induced prostaglandin (PG) E2 (cyclooxygenase-2) inhibition. Thereby, nivulianol B (=(1S*,2E,4R*,5S*,7Z,9S*,11R,13S*,14S*)-14-acetoxy-5-methoxy-3,9,13-trimethyl-6-(1-methylethenyl)-10-oxo-15-oxatricyclo[,11]pentadeca-2,7-dien-4-yl (2Z)-2-methylbut-2-enoate; 3) was found to be significantly active, with an IC50 value of 36.3,,g/ml. [source]

    Ring Opening of 1-Azabicyclo[1.1.0]butanes with Hydrazoic Acid , a Facile Access to N -Unsubstituted Azetidin-3-Amines

    Grzegorz Mlosto
    Sterically congested 1-azabicyclo[1.1.0]butanes 1 add hydrazoic acid smoothly at 0,5°, giving 3-azidoazetidines 2 in good to excellent yields. After hydrogenolysis over Pd/C catalyst, compounds 2 were converted into N -unsubstituted azetidin-3-amines 4. Attempted reduction of 2a with Raney -Ni led to a mixture of the expected azetidin-3-amine 4a and the ring-enlarged 2,5-dihydro-1H -imidazole derivative 5. [source]

    Synthesis of the Spermidine Alkaloids (,)-(2R,3R)- and (,)-(2R,3S)-3-Hydroxycelacinnine: Macrocyclization with Oxirane-Ring Opening and Inversion via Cyclic Sulfamidates

    The two epimers (,)- 1a and (,)- 1b of the macrocyclic lactam alkaloid 3-hydroxycelacinnine with the (2R,3R) and (2R,3S) absolute configurations, respectively, were synthesized by an alternative route involving macrocyclization with the regio- and stereoselective oxirane-ring opening by the terminal amino group (Schemes,2 and 6). Properly N -protected chiral trans -oxirane precursors provided (2R,3R)-macrocycles after a one-pot deprotection-macrocyclization step under moderate dilution (0.005,0.01M). The best yields (65,85%) were achieved with trifluoroacetyl protection. Macrocyclization of the corresponding cis -oxiranes was unsuccessful for steric reasons. Inversion at OHC(3) via nucleophilic displacement of the cyclic sulfamidate derivative with NaNO2 led to (2R,3S)-macrocycles. The synthesized (,)-(2R,3S)-3-hydroxycelacinnine ((,)- 1b) was identical to the natural alkaloid. [source]

    Focused-Ion-Beam-Based Selective Closing and Opening of Anodic Alumina Nanochannels for the Growth of Nanowire Arrays Comprising Multiple Elements,

    ADVANCED MATERIALS, Issue 13 2008
    Nai-Wei Liu
    A lithographic process based on focused ion beam bombardment is developed for selectively closing and opening nanochannels on a porous anodic alumina film. This resist-free process is based on the use of focused ion beams with different energies that strike a balance between material sputtering and material relocation. This process is used to selectively grow nanowire patterns of different elements. [source]

    Asymmetric Ring Opening of Benzo-7-oxabicyclo[2.2.1]heptadienes with Cationic Rhodium Complexes

    Angelika Preetz
    Abstract The efficient design of stereochemically challenging ring systems by ring opening of heterobicyclic alkenes has become a very important reaction in the chemistry of CC and CX bond formation. By using the hitherto applied in situ technique for the generation of the ,2 -bridged, dimeric neutral rhodium complexes, however, the catalytically active species and its concentration remained unidentified. Furthermore, the reaction temperature is at least 80,°C. The application of cationic rhodium(I) solvate complexes (that no longer contain blocking diolefins) shows that a much greater activity and enantioselectivity for the synthesis of 1,2-dihydro-1-naphthols can be reached than was described so far, even at ambient temperature. NMR spectroscopy and X-ray analysis show that a product inhibition during the ring opening reaction takes place that is independent of the nucleophile. [source]

    Cascade Reactions: Catalytic Synthesis of Functionalized 1,3-Dihydroisobenzofuran and Tetrahydrofuran Derivatives by Sequential Nucleophilic Ring Opening,Heterocyclization, Oxidative Carbonylation of Alkynyloxiranes

    Nicola Della Ca'
    Abstract Differently substituted alkynyloxiranes were efficiently converted into functionalized 1,3-dihydroisobenzofurans and tetrahydrofuran derivatives in fair to good yields by a new cascade reaction, consisting of a sequential nucleophilic ring opening,heterocyclization,oxidative carbonylation process. Reactions were carried out at 80,100,°C and under a 3:1 mixture of carbon monoxide and air (total pressure=32,42,atm at 25,°C) in methanol or acetonitrile/methanol mixtures in the presence of catalytic amounts of palladium diiodide in conjunction with an excess of potassium iodide. The nucleophilic species beginning the cascade process by regioselective attack to the less hindered carbon of the oxirane ring can be methanol itself or iodide anions. [source]

    Public Organizations in an Emergency: The 1995 Hanshin-Awaji Earthquake and Municipal Government

    Nobuyuki Hashimoto
    A magnitude 7.2 earthquake hit one of the major metropolitan areas of Japan at 5:46 am on 17 January 1995. This paper examines the behaviour of public organizations during this event in four municipal governments. Opening and managing shelters, reception of relief goods and cooperation with volunteers are, especially, studied in detail. Some of the programmes implemented by the national government and Hyogo prefectural government are also studied. Based on these studies, characteristics of the organizations' responses during the emergency are analyzed. It is argued that the structure of organizations or the disaster response programmes are formulated or changed by using more stable structures or procedures. [source]

    Opening up: psychiatric nurses' experiences of participating in reflection groups focusing on the use of coercion

    B. OLOFSSON rn phd
    Psychiatric staff report that the use of coercion towards patients in psychiatric care engenders feelings of discomfort and conflicts. The aim of this study was to describe psychiatric nurses' experiences of participating in reflection groups focused on the use of coercion, in relation to their views regarding systematic clinical supervision and staff support. Twenty-one nurses who had participated in reflection groups were interviewed retrospectively. The structured interview focused on: (i) their views of clinical supervision and support in general; (ii) their views of clinical supervision and support specifically concerning the use of coercion; and (iii) their experiences of participating in groups reflecting the use of coercion. Nurses were largely positive about participating in reflection groups, as expressed in the subthemes: having time for reflection; being confirmed; gaining new perspectives; sharing fellowship with colleagues; and relating more effectively to patients. Complications concerning participation in the reflection groups and other forms of clinical supervision as reported by nurses were: providing time for participation; having a common aim; being vulnerable in difficult situations; and assuming that the need for supervision and support could indicate that they were not coping with their job. [source]

    Thinking Outside the (Ballot) Box: Informal Electoral Institutions and Mexico's Political Opening

    Todd A. Eisenstadt
    ABSTRACT This article studies the development of informal bargaining tables to mitigate postelectoral conflicts in some 15 percent of Mexico's local elections between 1989 and 2000, even as formally autonomous electoral commissions and courts were being constituted. By documenting the dual institutions that resulted, the study qualifies theories of institutional design that take actor consent for granted. It argues that in the Mexican case and perhaps others, elections, particularly subnational elections, are focal points for informal bargaining over rules that are the true motors of protracted transitions. It finds electoral institutions to be critical to democratization, but for reasons beyond those given by most institutionalists. [source]

    Opening Up Ownership: Community Belonging, Belongings, and the Productive Life of Property

    LAW & SOCIAL INQUIRY, Issue 3 2007
    Davina Cooper
    Drawing on empirical data and property theory, this article explores the property structure of a "free school" and the work property performs there. At Summerhill, we can see a tension between two property registers. On the one hand, the founder and present members stress the importance of individual ownership; at the same time the school's property regime involves property-limitation rules, a dispersal of rights, collective forms of property, and cross-cutting, pluralized sites of institutional recognition. In exploring how this tension is manifested through property's work, the article focuses on property's contribution to a variegated social life at the school, analyzed in terms of personal, civic, and boundary relations. With belonging treated as the central component of property rather than exclusion or control, ways of understanding what constitutes property and how it works shift. [source]

    Turkey's New Kurdish Opening: Religious Versus Secular Values

    MIDDLE EAST POLICY, Issue 2 2010
    Murat Somer
    First page of article [source]

    Strange Wonder: The Closure of Metaphysics and the Opening of Awe , By Mary,Jane Rubenstein

    MODERN THEOLOGY, Issue 2 2010
    Catherine Keller
    First page of article [source]

    Opening up the innovation process: the role of technology aggressiveness

    R & D MANAGEMENT, Issue 1 2009
    Ulrich Lichtenthaler
    Besides acquiring external knowledge, many firms have begun to actively commercialize technology, for example, by means of out-licensing. This increase in inward and outward technology transactions reflects the new paradigm of open innovation. Most prior research into open innovation is limited to theoretical considerations and case studies, whereas other lines of research have focused either on external technology acquisition or exploitation. In an integrative view, we consider inward and outward technology transactions as the main directions of open innovation. Moreover, technology aggressiveness, which constitutes an important dimension of technology strategy, is identified as a major determinant of open innovation. Data from a survey of 154 industrial firms are used to test three hypotheses relating technology aggressiveness, external technology acquisition, and external technology exploitation. In addition, clusters of firms with homogeneous strategies regarding technology aggressiveness and open innovation are identified. [source]

    Effect of Testosterone on Potassium Channel Opening in Human Corporal Smooth Muscle Cells

    Deok Hyun Han MD
    ABSTRACT Introduction., In humans, the role of testosterone in sexual functions, including sexual desire, nocturnal penile erections, and ejaculatory volume, has been relatively well established. However, the effects of testosterone on intrapenile structure in humans remains controversial. Aim., We assessed the direct effects of testosterone on potassium channels in human corporal smooth muscle cells, in an effort to understand the mechanisms inherent to the testosterone-induced relaxation of corporal smooth muscle cells at the cellular and molecular levels. Methods., We conducted electrophysiologic studies using cultured human corporal smooth muscle cells. We evaluated the effects of testosterone on potassium channels,BKCa and KATP channels,by determining the whole-cell currents and single-channel activities. For the electrophysiologic recordings, whole-cell and cell-attached configuration patch-clamp techniques were utilized. Main Outcome Measures., Changes in whole-cell currents and channel activities of BKCa and KATP channels by testosterone. Results., Testosterone (200 nM) significantly increased the single-channel activity of calcium-activated potassium (BKCa) channels and whole-cell K+ currents by 443.4 ± 83.4% (at +60 mV; N = 11, P < 0.05), and this effect was abolished by tetraethylammonium (TEA) (1 mM), a BKCa channel blocker. The whole-cell inward K+ currents of the KATP channels were also increased by 226.5 ± 49.3% (at ,100 mV; N = 7, P < 0.05). In the presence of a combination of vardenafil (10 nM) and testosterone (200 nM), the BKCa channel was activated to a significantly higher degree than was induced by testosterone alone. Conclusions., The results of patch-clamp studies provided direct molecular evidence that testosterone stimulates the activity of BKCa channels and KATP channels. An understanding of the signaling mechanisms that couple testosterone receptor activation to potassium channel stimulation will provide us with an insight into the cellular processes underlying the vasorelaxant effects of testosterone. Han DH, Chae MR, Jung JH, So I, Park JK, and Lee SW. Effect of testosterone on potassium channel opening in human corporal smooth muscle cells. J Sex Med 2008;5:822,832. [source]

    Nucleophilic Opening of Oxabicyclic Ring Systems,

    ANGEWANDTE CHEMIE, Issue 34 2009
    Mit Leichtigkeit gingen auch gesättigte [2.2.1]Oxabicyclo-Systeme 1 eine Lewis-Säure-vermittelte nucleophile Ringöffnung ein, die auf direktem Weg zu hoch funktionalisierten Perhydroindolen (n=1) oder Perhydrochinolinen (n=2) führt (siehe Schema). Sowohl Amin- als auch Amidsubstituenten kamen bei dieser effizienten und allgemeinen Umsetzung als Nucleophile zum Einsatz. [source]

    Opening up Public Services to Competition by Putting Them Out to Tender: An Evaluation

    P. Bance
    This article examines the effects of systematizing tendering procedures when awarding public service concessions. The opening up of the water supply industry to competition is used by way of illustration. Results show that arguments in favour of systematization are not robust when focusing solely on the expected benefits of the liberalization process. The peculiarities of the contract relationship in the delegation of public services, the mobilization of specific assets, and the long duration and incompleteness of the contracts invalidate this type of argument and expose public authorities to the opportunism of operators. The efficiency of awarding public services concessions relies on cost,benefit analysis, taking into account sectoral aspects as well as specificities of the contracting organizations and structures. The public service culture of these organizations is in this respect a key factor in the choice of efficient organizations since it conditions their ability to internalize the mission of fulfilling the public interest. [source]

    Opening up the secret city of Stepnogorsk: biological weapons in the Former Soviet Union

    AREA, Issue 1 2010
    Caitríona McLeish
    For almost 30 years, the Soviet government hid a large part of its biological weapons programme behind the façade of a network of civilian bio-technology facilities, called the All-Union Production Association Biopreparat, which were established to overcome deficiencies in molecular biology and genetics research. This paper, which is developed from a presentation given during an ESRC-sponsored seminar series, ,Locating Technoscience: The Geographies of Science, Technology and Politics', details the secret geography of one of those Biopreparat facilities located in Stepnogorsk, Kazakhstan. In doing this the paper illustrates how secret geographies can operate simultaneously, and at multiple scales. In the case of the Soviet bio-weapons programme, enacting secrecy at these multiple scales was made possible by the purposeful exploitation of ,dual use' technologies. By recounting a trip made to the Kazak facility, and using personal communications with UK and US experts involved with uncovering the Soviet bio-warfare programme, the author addresses some of the methodological challenges involved with researching secret geographies. This case study therefore looks in several directions , to work on the geographies of scale, research on the geographies of knowledge and work on secrecy in science and technology studies. [source]

    Opening up Australian preschoolers' lunchboxes

    Bridget Kelly
    Abstract Objective: Early childhood services have been identified as key settings for promoting healthy eating and obesity prevention. However, little is known about the obesity-related behaviours of preschool-aged children or food-related policies in these settings. The purpose of this study was to describe the contents of preschoolers' lunchboxes to inform future interventions. Methods: Cross-sectional survey of 259 children attending preschools in the Sydney West and Sydney South West regions of New South Wales in 2008. Lunchbox data were collected using a purpose-designed audit tool. Food and beverages were classified as fruit, vegetables, dairy, breads and cereals, ,extra' (energy-dense) foods, ,extra' drinks or water. Results: Sandwiches and home-cooked meals were the most frequently identified food item, found in 92% of children's lunchboxes, followed by fresh fruit. However, 60% of lunchboxes contained more than one serve of extra food or drink. Conclusion: While nutrition guidelines allow one to two serves of extra foods per day for preschool-aged children, the majority of children appear to consume most of this allocation during their school day, potentially contributing to over-consumption of extra foods and excess kilojoule intake. Implications: Preschool food policies may help to guide the content of children's lunchboxes, however this study emphasises the need for better communication and enforcement of these policies, as well as broader public policy changes. [source]

    A Proposed Mechanism for the Reductive Ring Opening of the Cyclodiphosphate MEcPP, a Crucial Transformation in the New DXP/MEP Pathway to Isoprenoids Based on Modeling Studies and Feeding Experiments

    CHEMBIOCHEM, Issue 3 2004
    Wolfgang Brandt Dr.
    Abstract Experimental and theoretical investigations concerning the second-to-last step of the DXP/MEP pathway in isoprenoid biosynthesis in plants are reported. The proposed intrinsic or late intermediates 4-oxo-DMAPP (12) and 4-hydroxy-DMAPP (11) were synthesized in deuterium- or tritium-labeled form according to new protocols especially adapted to work without protection of the diphosphate moiety. When the labeled compounds MEcPP (7), 11, and 12 were applied to chromoplast cultures, aldehyde 12 was not incorporated. This finding is in agreement with a mechanistic and structural model of the responsible enzyme family: a three-dimensional model of the fragment L271,A375 of the enzyme GcpE of Streptomyces coelicolor including NADPH, the Fe4S4cluster, and MEcPP (7) as ligand has been developed based on homology modeling techniques. The model has been accepted by the Protein Data Bank (entry code 1OX2). Supported by this model, semiempirical PM3 calculations were performed to analyze the likely catalysis mechanism of the reductive ring opening of MEcPP (7), hydroxyl abstraction, and formation of HMBPP (8). The mechanism is characterized by a proton transfer (presumably from a conserved arginine 286) to the substrate, accompanied by a ring opening without high energy barriers, followed by the transfer of two electrons delivered from the Fe4S4cluster, and finally proton transfer from a carboxylic acid side chain to the hydroxyl group to be removed from the ligand as water. The proposed mechanism is in agreement with all known experimental findings and the arrangement of the ligand within the enzyme. Thus, a very likely mechanism for the second to last step of the DXP/MEP pathway in isoprenoid biosynthesis in plants is presented. A principally similar mechanism is also expected for the reductive dehydroxylation of HMBPP (8) to IPP (9) and DMAPP (10) in the last step. [source]

    ChemInform Abstract: Ring Opening of Cyclic Vinylogous Acyl Triflates Using Stabilized Carbanion Nucleophiles: Claisen Condensation Linked to Carbon,Carbon Bond Cleavage.

    CHEMINFORM, Issue 37 2010
    David M. Jones
    Abstract Treatment of the cyclic triflates (I) and (VII) with carbanion nucleophiles provides acyclic alkynes bearing 1,3-diketone, ,-keto ester, ,-keto phosphonate, or ,-keto phosphine oxide moieties. [source]