Distribution by Scientific Domains
Distribution within Engineering

Kinds of Scheme

  • access scheme
  • accurate scheme
  • acquisition scheme
  • adaptive control scheme
  • adaptive scheme
  • advection scheme
  • agglomeration scheme
  • aggregation scheme
  • agri-environment scheme
  • agri-environmental scheme
  • allocation scheme
  • analysis scheme
  • approximation scheme
  • ascertainment scheme
  • assessment scheme
  • assimilation scheme
  • assistance scheme
  • assurance scheme
  • audit scheme
  • benefit scheme
  • calculation scheme
  • cancellation scheme
  • carbon pollution reduction scheme
  • carlo sampling scheme
  • carlo scheme
  • categorization scheme
  • certification scheme
  • channel allocation scheme
  • classification scheme
  • coding scheme
  • collection scheme
  • collocation scheme
  • combination scheme
  • communication scheme
  • compensation scheme
  • computation scheme
  • computational scheme
  • conceptual scheme
  • congestion control scheme
  • contribution pension scheme
  • control scheme
  • convection scheme
  • coordination scheme
  • correction scheme
  • corrector scheme
  • coupling scheme
  • data assimilation scheme
  • decision scheme
  • decomposition scheme
  • design scheme
  • detection scheme
  • difference scheme
  • different scheme
  • diffusion scheme
  • discrete scheme
  • discretization scheme
  • distribution scheme
  • diversity scheme
  • efficient scheme
  • element scheme
  • emission trading scheme
  • energy decomposition scheme
  • eqa scheme
  • estimation scheme
  • euler scheme
  • existing scheme
  • explicit scheme
  • external quality assessment scheme
  • extrapolation scheme
  • financing scheme
  • finite difference scheme
  • finite element scheme
  • finite volume scheme
  • finite-difference scheme
  • finite-element scheme
  • funding scheme
  • general scheme
  • generation scheme
  • godunov scheme
  • grading scheme
  • hierarchical scheme
  • hybrid scheme
  • implicit scheme
  • incentive scheme
  • insurance scheme
  • integration scheme
  • interaction scheme
  • interpolation scheme
  • interpretative scheme
  • inversion scheme
  • irrigation scheme
  • isolation scheme
  • iteration scheme
  • iterative scheme
  • kinetic scheme
  • kutta scheme
  • level scheme
  • management scheme
  • modeling scheme
  • modulation scheme
  • monitoring scheme
  • monte carlo sampling scheme
  • monte carlo scheme
  • new scheme
  • nicholson scheme
  • non-standard finite difference scheme
  • novel scheme
  • numerical integration scheme
  • numerical scheme
  • occlusal scheme
  • optimization scheme
  • ordering scheme
  • partitioning scheme
  • payment scheme
  • pension scheme
  • pharmaceutical benefit scheme
  • placement scheme
  • pollution reduction scheme
  • possible scheme
  • present scheme
  • previous scheme
  • pricing scheme
  • processing scheme
  • projection scheme
  • proposed control scheme
  • proposed scheme
  • protection scheme
  • public pension scheme
  • pumping scheme
  • purification scheme
  • quadrature scheme
  • quality assessment scheme
  • quick scheme
  • reaction scheme
  • reconstruction scheme
  • reduction scheme
  • regularization scheme
  • regulatory scheme
  • representation scheme
  • resolution scheme
  • resource management scheme
  • restoration scheme
  • routing scheme
  • sampling scheme
  • scheduling scheme
  • scoring scheme
  • see scheme
  • selection scheme
  • semi-lagrangian scheme
  • simple scheme
  • solution scheme
  • spatial discretization scheme
  • splitting scheme
  • staging scheme
  • synchronization scheme
  • synthetic scheme
  • tax scheme
  • time integration scheme
  • time scheme
  • time-stepping scheme
  • tracking scheme
  • trading scheme
  • training scheme
  • transfer scheme
  • transmission scheme
  • treatment scheme
  • truncation scheme
  • various scheme
  • volume scheme
  • weighting scheme
  • worker scheme

  • Terms modified by Scheme

  • scheme shows
  • scheme used

  • Selected Abstracts

    SPECIAL SECTION: EVALUATION OF THE WESTERN AUSTRALIAN CANNABIS INFRINGEMENT NOTICE SCHEME,PHASE 1: Community attitudes towards cannabis law and the proposed Cannabis Infringement Notice scheme in Western Australia

    Abstract Western Australia (WA) became the fourth Australian jurisdiction to adopt a prohibition with civil penalties scheme for minor cannabis offences when its Cannabis Infringement Notice (CIN) scheme became law on 22 March 2004. Previous criminological research has demonstrated the importance of public attitudes towards the law in determining the effectiveness of legislation. This survey represents the first phase of a pre-post study that attempted to gauge public attitudes towards the legal status of cannabis, the proposed legislative reforms surrounding the drug and their likely effects. A random telephone survey of 809 members of the WA population was conducted prior to the implementation of the new laws with a view to exploring contemporary views of the existing legal status of cannabis, attitudes to the proposed legislative model and respondent perceptions of its likely effects. Despite cannabis being viewed negatively by large numbers of the sample, criminal penalties for minor cannabis offences were viewed as inappropriate and ineffective. Once explained, the proposed civil penalty scheme was viewed as ,a good idea' by 79% of the sample, despite significant differences due to personal experience of cannabis use, political affiliation, religiosity and age of offspring. Most believed that the legislative change would not result in changes to levels of cannabis use (70%) or ease of obtaining cannabis (59%). These data suggest that prior to its implementation the new legislation was highly acceptable to the majority of the community. These baseline data will be compared with data to be collected at the post-change phase of the study to allow empirical observations of attitudinal and behavioural changes occurring in the community. [source]


    Pam McGrath
    ABSTRACT: This article presents findings from State-wide research in Queensland on experiences with the Patient Transit Assistance Scheme (PTAS) from the point of view of patients with a haematological malignancy who travelled for specialist treatment. The findings indicate that the PTAS is of crucial importance to patients and their families and goes some way to buffering the financial hardship incurred from relocation. However, there are also strong indications that there is insufficient community awareness of the scheme, with the consequence that it is not appropriately accessed by those in need. The results confirm previous research that points to the hardship, both financial and emotional, associated with the experience of relocation for specialist treatment. [source]


    Hamed Kebriaei
    In this paper, an agent matching method for bilateral contracts in a multi-agent market is proposed. Each agent has a hierarchical representation of its trading commodity attributes by a tree structure of fuzzy attributes. Using this structure, the similarity between the trees of each pair of buyer and seller is computed using a new ordered fuzzy similarity algorithm. Then, using the concept of Stackelberg equilibrium in a leader,follower game, matchmaking is performed among the sellers and buyers. The fuzzy similarities of each agent with others in its personal viewpoint have been used as its payoffs in a bimatrix game. Through a case study for bilateral contracts of energy, the capabilities of the proposed agent-based system are illustrated. [source]


    ECONOMIC AFFAIRS, Issue 4 2006
    Nick Silver
    The decline in final salary pension schemes (FSS) is a result of increasing costs caused in part by legislative interference. In this paper it is argued that FSS have always been detrimental to the economy. In a misguided attempt to save FSS, the government risks bankrupting large sections of the British corporate sector. Other policy measures could allow greater flexibility for trustees of pension schemes and remove counter-productive legislation and encourage innovative market-based solutions to pensions problems. [source]


    Valentina Corradi
    We introduce block bootstrap techniques that are (first order) valid in recursive estimation frameworks. Thereafter, we present two examples where predictive accuracy tests are made operational using our new bootstrap procedures. In one application, we outline a consistent test for out-of-sample nonlinear Granger causality, and in the other we outline a test for selecting among multiple alternative forecasting models, all of which are possibly misspecified. In a Monte Carlo investigation, we compare the finite sample properties of our block bootstrap procedures with the parametric bootstrap due to Kilian (Journal of Applied Econometrics 14 (1999), 491,510), within the context of encompassing and predictive accuracy tests. In the empirical illustration, it is found that unemployment has nonlinear marginal predictive content for inflation. [source]


    METROECONOMICA, Issue 2 2008
    Sandro Gronchi
    ABSTRACT The paper inquires into notional defined contribution pension schemes, which retain the pay-as-you-go financing method while adopting the award and indexation formulas typical of funded, defined-contribution systems. It examines the properties of the new arrangement and compares them with those of the traditional defined-benefit pay-as-you-go schemes. [source]

    An Adaptive Sampling Scheme for Out-of-Core Simplification

    Guangzheng Fei
    Current out-of-core simplification algorithms can efficiently simplify large models that are too complex to be loaded in to the main memory at one time. However, these algorithms do not preserve surface details well since adaptive sampling, a typical strategy for detail preservation, remains to be an open issue for out-of-core simplification. In this paper, we present an adaptive sampling scheme, called the balanced retriangulation (BR), for out-of-core simplification. A key idea behind BR is that we can use Garland's quadric error matrix to analyze the global distribution of surface details. Based on this analysis, a local retriangulation achieves adaptive sampling by restoring detailed areas with cell split operations while further simplifying smooth areas with edge collapse operations. For a given triangle budget, BR preserves surface details significantly better than uniform sampling algorithms such as uniform clustering. Like uniform clustering, our algorithm has linear running time and small memory requirement. [source]

    Native wildlife on rangelands to minimize methane and produce lower-emission meat: kangaroos versus livestock

    George R. Wilson
    Abstract Ruminant livestock produce the greenhouse gas methane and so contribute to global warming and biodiversity reduction. Methane from the foregut of cattle and sheep constitutes 11% of Australia's total greenhouse gas emissions (GHG). Kangaroos, on the other hand, are nonruminant forestomach fermenters that produce negligible amounts of methane. We quantified the GHG savings Australia could make if livestock were reduced on the rangelands where kangaroo harvesting occurs and kangaroo numbers increased to 175 million to produce same amount of meat. Removing 7 million cattle and 36 million sheep by 2020 would lower Australia's GHG emissions by 16 megatonnes, or 3% of Australia's annual emissions. However, the change will require large cultural and social adjustments and reinvestment. Trials are underway based on international experiences of managing free-ranging species. They are enabling collaboration between farmers, and if they also show benefits to sustainability, rural productivity, and conservation of biodiversity, they could be expanded to incorporate change on the scale of this article. Farmers have few options to reduce the contribution that livestock make to GHG production. Using kangaroos to produce low-emission meat is an option for the Australian rangelands which would avoid permit fees under Australia's Emissions Trading Scheme, and could even have global application. [source]

    Application of the 3D Finite Difference Scheme to the TEXTORDED Geometry

    R. Zagórski
    First page of article [source]

    EMAS and its local diffusion in Italy

    Rita Jirillo
    Due to the growing awareness among enterprises of the relevance of ,sustainable development', applications of the Environmental Management and Audit Scheme (EMAS) in Italy are expanding. With the second era of EMAS (EMAS II), this scheme will become a global instrument, enabling Italian small and medium enterprises (SMEs) to master environmental challenges while improving their competitive position. This report intends to demonstrate that area and local agreements between local government units and research centres, such as universities or energy and environmental boards, can simplify and improve the diffusion of EMAS in the country. Reported examples of some small Italian municipalities that have applied EMAS are demonstrations of how government units can increase all citizens' quality of life while taking care of environmental aspects. Since 1993, the year of the first applications of Regulation 1836/93, local government units have understood the important role they can play in this subject. This work illustrates that the development of ISO and EMAS local applications must be based on government's local promotion aimed at encouraging enterprises to voluntarily adopt these instruments for environmental safeguard. Copyright © 2003 John Wiley & Sons, Ltd. and ERP Environment. [source]

    A Development Delivery Institution for the Tribal Communities: Experience of the National Rural Employment Guarantee Scheme in India

    Pulak Mishra
    This article examines the varied impacts of the National Rural Employment Guarantee Scheme (NREGS) as a development delivery institution for the tribal communities vis-ą-vis other social groups across the Indian States, using the framework of new institutional economics. A number of State-specific, socio-economic institutional factors seem to be responsible for these variations. The article therefore suggests institutional reforms and convergence of the development initiatives of the Ministry of Tribal Affairs with the NREGS in order to realise the optimal potential of the scheme, and, in particular, to ensure greater livelihood opportunities for these marginalised groups and their entitlement to productive resources with greater socio-economic and political empowerment. [source]

    Agro-Food Preferences in the EU's GSP Scheme: An Analysis of Changes Between 2004 and 2006

    Federica DeMaria
    This article examines the extent to which the 2006 revisions to the EU's Generalised System of Preferences improved market-access opportunities for developing-country agro-food exports. It shows that they resulted in only a slight increase in the percentage preferential margin, but that there has been a significant increase in the value of preferential trade and of the preferential margin enjoyed by exporters. This was accompanied by changes in the ranking of beneficiaries. Countries such as China, Brazil, Argentina, India and South Africa maintained their significant shares of GSP agro-food exports, but other countries such as Thailand and Vietnam have now emerged as major GSP beneficiaries. [source]

    Grandfathering and Greenhouse: The Role of Compensation and Adjustment Assistance in the Introduction of a Carbon Emissions Trading Scheme for Australia

    Flavio Menezes
    Q52; Q58 The terms "grandfather clause" and "grandfathering" describe elements of a policy programme in which existing participants in an activity are protected from the impact of regulations, restrictions or charges applied to new entrants. In this paper, the role of grandfathering in the design of a carbon emissions trading scheme in Australia is assessed. It is argued that adjustment assistance policies such as those adopted in conjunction with previous microeconomic reform programmes are preferable to policies based on the free issue of emission permits. The suggestion that owners of capital assets should be compensated for changes in government policy that reduce the expected flow of income from those assets represents a radical, and undesirable, policy innovation. [source]

    Road pricing: lessons from London

    ECONOMIC POLICY, Issue 46 2006
    Georgina Santos
    SUMMARY Road pricing LESSONS FROM LONDON This paper assesses the original London Congestion Charging Scheme (LCCS) and its impacts, and it simulates the proposed extension which will include most of Kensington and Chelsea. It also touches upon the political economy of the congestion charge and the increase of the charge from £5 to £8 per day. The possibility of transferring the experience to Paris, Rome and New York is also discussed. The LCCS has had positive impacts. This was despite the considerable political influences on the charge level and location. It is difficult to assess the impacts of the increase of the charge from £5 to £8, which took place in July 2005, because no data have yet been released by Transport for London. The proposed extension of the charging zone does not seem to be an efficient change on economic grounds, at least for the specific boundaries, method of charging and level of charging that is currently planned. Our benefit cost ratios computed under different assumptions of costs and benefits are all below unity. Overall, the experience shows that simple methods of congestion charging, though in no way resembling first-best Pigouvian taxes, can do a remarkably good job of creating benefits from the reduction of congestion. Nevertheless, the magnitude of these benefits can be highly sensitive to the details of the scheme, which therefore need to be developed with great care. , Georgina Santos and Gordon Fraser [source]

    A LiMn2O4 Based Electrochemical Scheme for Selective Measurement of Dopamine

    ELECTROANALYSIS, Issue 3 2006
    Hoang, Jyh Leu
    Abstract A new cathodic scheme was developed for the determination of dopamine by flow injection analysis (FIA). A mild oxidizing agent, lithium manganese (III, IV) oxide (LiMn2O4), as an upstream modifier can oxidize the dopamine to produce the dopaminequinone, and then the oxidized product is subsequently detected by the downstream detector at ,0.1,V (vs. Ag/AgCl). In this work, the significant feature of LiMn2O4 based sensing scheme possesses no interference from other tested biological amines including acetylcholine, epinephrine, glutamate, and histamine. Otherwise, there is no detectable interference from ascorbic acid, but 2% and 1% negligible interferences were found from uric acid and acetaminophen, respectively. [source]

    Preparing for the ,real' market: national patterns of institutional learning and company behaviour in the European Emissions Trading Scheme (EU ETS)

    Anita Engels
    Abstract European companies have reacted in different ways to the European Emissions Trading Scheme (EU ETS), Phase I. While some companies engaged in an active trading behaviour focused on additional revenues, others adopted a strategy orientated to mere compliance with the scheme and aimed for balanced accounts only. This article provides the outcomes of a survey on company behaviour under the EU ETS in Germany, the United Kingdom, the Netherlands and Denmark from 2005 to 2006, in which cross-national differences in trading behaviour are linked to national patterns of policy implementation and the political economies in which companies operate. Thus, specific country patterns of institutional preparation and institutional learning for the ,real' CO2 allowance market in Phase II of the EU ETS (2008,2012) are sketched. Whereas Phase I is distinguished by a net over-allocation of allowances, Phase II is expected to entail some level of scarcity of allowances. We argue that companies are prepared differently to meet the challenges of the future EU ETS. Copyright © 2008 John Wiley & Sons, Ltd and ERP Environment. [source]

    The need for adaptability in EU environmental policy design and implementation

    Matthieu Glachant
    Is the application of the EU environmentally policy satisfying in the field? In particular, are the environmental objectives set in the directives met? This paper explores the issue of the effectiveness of the European environmental policy. It is based on the results of a recent study, which has consisted in evaluating the implementation of three pieces of EU environmental legislation in France, Germany, Netherlands and United Kingdom. The legislation studied was Directive 89/429 regulating atmospheric emissions from domestic waste incinerators, Directive 88/609 dealing with SO2 and NOx emissions from large combustion plants (LCPs) and Council Regulation 1836/93 concerning the voluntary participation of industrial companies in an EU Eco-Management and Audit Scheme (EMAS). The result of the study suggests that simply posing the problem in terms of ,implementation deficit' is not sufficient. In fact, over-compliance with directive goals is even observed in certain cases. By contrast, the evaluation suggests the prevalence of interactions between the considered implementation process and other parallel policy processes at the implementation stage. The study shows that this interplay between policies has a huge impact on implementation environmental results, which can be either positive or negative. Based on this statement, an important question for EU policy is how implementation can efficiently cope with such interactions, which means finding ways to maximize potential synergies, or alternatively to reduce inconsistencies, with the other policy components. Given that policy interactions are difficult to predict at the policy formulation stage of the policy, adjustments necessarily occur at the implementation stage. In this context, implementing EU environmental policy requires policy systems able to adjust at low costs. In this paper, this property is called adaptability and is given a precise content. Copyright © 2001 John Wiley & Sons, Ltd. and ERP Environment [source]

    EMAS and regulatory relief in Europe: lessons from national experience

    Frank Wätzold
    Apart from in Germany and Austria, corporate participation in the European Eco-Management and Audit Scheme (EMAS) has remained sluggish and far behind involvement in ISO14001. Given the lack of response in most EU member states, the key issue for the current EMAS revision is to increase incentives for companies to join the scheme. One of the proposals in this respect is to encourage member states to consider a lighter regulatory touch for EMAS participants. The aim of this article is to assess the extent to which encouraging regulatory relief may contribute to an increase in the number of EMAS registered companies. For this purpose the regulatory relief already offered to EMAS registered (and ISO14001 certified) companies in France, Germany, The Netherlands and the United Kingdom is described and analysed. Based on this experience, the central conclusion of the article is that regulatory relief can increase participation in EMAS, but that to do so it must be granted exclusively to EMAS registered companies, and that ideally such relief should be substantial and integrated into a comprehensive voluntary policy approach aimed at altering the traditional relationship between government and industry. However, given that some countries treat EMAS registration and ISO14001 certification as equivalent, with respect to regulatory relief, even those deregulation measures that fulfil the above conditions may lead to an increase in ISO14001 certifications rather than EMAS registrations. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment. [source]

    A Clinical Guide to Epileptic Syndromes and their Treatment: Based on the New ILAE Diagnostic Scheme

    EPILEPSIA, Issue 8 2003
    Richard S. McLachlan M.D.
    No abstract is available for this article. [source]

    A Proposed Diagnostic Scheme for People with Epileptic Seizures and with Epilepsy: Report of the ILAE Task Force on Classification and Terminology

    EPILEPSIA, Issue 6 2001
    Jerome Engel Jr.
    First page of article [source]

    Synthetic Scheme for the Preparation of 13C-Labeled 3,4-Didehydro-Retinal, 3-Hydroxyretinal, and 4-Hydroxyretinal up to Uniform 13C-Enrichment

    Arjan A. C. van Wijk
    Abstract A modular synthetic scheme has been developed for the synthesis of 13C-labeled naturally occurring visual pigment chromophores; 3,4-didehydroretinal, 3-hydroxyretinal, and 4-hydroxyretinal. These compounds can now be made with > 99% 13C enrichment at any position or combination of positions. We used the common C10+C5+C5 scheme for the synthesis of retinals, and by making variations in the C10 part we can now prepare the desired retinal derivatives with selective or uniform 13C enrichment. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    A Hybrid Interference Cancellation Scheme for Multiuser Systems in Multipath Fading Channels

    Ann-Louise Johansson
    A new hybrid interference cancellation (IC) scheme is proposed for the uplink of multirate direct-sequence code division multiple access (DS-CDMA) systems communicating over mobile radio channels. The hybrid IC scheme includes both non-decision directed and decision directed IC, together with a modified RAKE combiner to utilize the diversity in a frequency-selective channel. The performance is evaluated via computer simulations for the two multiple data rate schemes, mixed modulation and multicode, in a multipath environment. Both known channel parameters and channel estimation using pilot symbols are considered. The results show that rnulticode or a combination of multicode and mixed modulation are preferable when handling multirate system and the loss in performance compared to the single-user bound is small. [source]

    Targeting fuel poverty in England: is the government getting warm?

    FISCAL STUDIES, Issue 3 2002
    Tom Sefton
    Abstract This paper examines the cost-effectiveness of the new Home Energy Efficiency Scheme (HEES), a key component of the UK government's Fuel Poverty Strategy. The impact on the fuel poverty gap is simulated using data on a large-scale and representative sample of households in England. The scope for improving the scheme's targeting is considered by examining the optimal allocation of grants between households. The extent to which these potential gains might be achieved in practice using pragmatic criteria for distributing grants, and the implications of taking into account the dynamics of fuel poverty and the self-selection of grant applicants, are also explored. The current scheme is unlikely to have a very significant impact on fuel poverty, and considerable gains could be achieved by redesigning HEES, although the paper also highlights the difficulties involved in efficient targeting, including some additional complications not encountered in the analysis of more traditional anti-poverty measures. [source]

    Revisiting a Classification Scheme for U.S.-Mexico Alluvial Basin-Fill Aquifers

    GROUND WATER, Issue 5 2005
    Barry J. Hibbs
    Intermontane basins in the Trans-Pecos region of westernmost Texas and northern Chihuahua, Mexico, are target areas for disposal of interstate municipal sludge and have been identified as possible disposal sites for low-level radioactive waste. Understanding ground water movement within and between these basins is needed to assess potential contaminant fate and movement. Four associated basin aquifers are evaluated and classified; the Red Light Draw Aquifer, the Northwest Eagle Flat Aquifer, the Southeast Eagle Flat Aquifer, and the El Cuervo Aquifer. Encompassed on all but one side by mountains and local divides, the Red Light Draw Aquifer has the Rio Grande as an outlet for both surface drainage and ground water discharge. The river juxtaposed against its southern edge, the basin is classified as a topographically open, through-flowing basin. The Northwest Eagle Flat Aquifer is classified as a topographically closed and drained basin because surface drainage is to the interior of the basin and ground water discharge occurs by interbasin ground water flow. Mountains and ground water divides encompass this basin aquifer on all sides; yet, depth to ground water in the interior of the basin is commonly >500 feet. Negligible ground water discharge within the basin indicates that ground water discharges from the basin by vertical flow and underflow to a surrounding basin or basins. The most likely mode of discharge is by vertical, cross-formational flow to underlying Permian rocks that are more porous and permeable and subsequent flow along regional flowpaths beneath local ground water divides. The Southeast Eagle Flat Aquifer is classified as a topographically open and drained basin because surface drainage and ground water discharge are to the adjacent Wildhorse Flat area. Opposite the Eagle Flat and Red Light Draw aquifers is the El Cuervo Aquifer of northern Chihuahua, Mexico. The El Cuervo Aquifer has interior drainage to Laguna El Cuervo, which is a phreatic playa that also serves as a focal point of ground water discharge. Our evidence suggests that El Cuervo Aquifer may lose a smaller portion of its discharge by interbasin ground water flow to Indian Hot Springs, near the Rio Grande. Thus, El Cuervo Aquifer is a topographically closed basin that is either partially drained if a component of its ground water discharge reaches Indian Hot Springs or undrained if all its natural ground water discharge is to Laguna El Cuervo. [source]

    An Improved Preparation of D -Glyceraldehyde 3-Phosphate and Its Use in the Synthesis of 1-Deoxy- D -xylulose 5-Phosphate

    Heng Li
    Abstract D -Glyceraldehyde 3-phosphate (=D -GAP; 2) was prepared by an improved chemical method (Scheme,2), and it was then employed to synthesize 1-deoxy- D -xylulose 5-phosphate (=DXP; 3) which is enzymatically one of the key intermediates in the MEP (4) terpenoid biosynthetic pathway (Scheme,1). The recombinant DXP synthase of Rhodobacter capsulatus was used to catalyze the condensation of D -glyceraldehyde 3-phosphate (2) and pyruvate (=2-oxopropanoate; 1) to produce the sugar phosphate 3 (Scheme,2). The simple two-step chemoenzymatic route described affords DXP (3) with more than 70% overall yield and higher than 95% purity. The procedure may also be used for the synthesis of isotope-labeled DXP (3) by using isotope-labeled pyruvate. [source]

    Stereochemical Models for Discussing Additions to ,,, -Unsaturated Aldehydes Organocatalyzed by Diarylprolinol or Imidazolidinone Derivatives , Is There an ,(E)/(Z)-Dilemma'?

    Dieter Seebach
    Abstract The structures of iminium salts formed from diarylprolinol or imidazolidinone derivatives and ,,, -unsaturated aldehydes have been studied by X-ray powder diffraction (Fig.,1), single-crystal X-ray analyses (Table,1), NMR spectroscopy (Tables,2 and 3, Figs.,2,7), and DFT calculations (Helv. Chim. Acta2009, 92, 1, 1225, 2010, 93, 1; Angew. Chem., Int. Ed.2009, 48, 3065). Almost all iminium salts of this type exist in solution as diastereoisomeric mixtures with (E)- and (Z)-configured +NC bond geometries. In this study, (E)/(Z) ratios ranging from 88,:,12 up to 98,:,2 (Tables,2 and 3) and (E)/(Z) interconversions (Figs.,2,7) were observed. Furthermore, the relative rates, at which the (E)- and (Z)-isomers are formed from ammonium salts and ,,, -unsaturated aldehydes, were found to differ from the (E)/(Z) equilibrium ratio in at least two cases (Figs.,4 and 5,,a, and Fig.,6,,a); more (Z)-isomer is formed kinetically than corresponding to its equilibrium fraction. Given that the enantiomeric product ratios observed in reactions mediated by organocatalysts of this type are often ,99,:,1, the (E)-iminium-ion intermediates are proposed to react with nucleophiles faster than the (Z)-isomers (Scheme,5 and Fig.,8). Possible reasons for the higher reactivity of (E)-iminium ions (Figs.,8 and 9) and for the kinetic preference of (Z)-iminium-ion formation are discussed (Scheme,4). The results of related density functional theory (DFT) calculations are also reported (Figs.,10,13 and Table,4). [source]

    Synthesis of 1,3-Selenazol-2(3H)-imines

    Abstract The reaction of N,N, -diarylselenoureas 16 with phenacyl bromide in EtOH under reflux, followed by treatment with NH3, gave N,3-diaryl-4-phenyl-1,3-selenazol-2(3H)-imines 13 in high yields (Scheme,2). A reaction mechanism via formation of the corresponding Se -(benzoylmethyl)isoselenoureas 18 and subsequent cyclocondensation is proposed (Scheme,3). The N,N, -diarylselenoureas 16 were conveniently prepared by the reaction of aryl isoselenocyanates 15 with 4-substituted anilines. The structures of 13a and 13c were established by X-ray crystallography. [source]

    Trichocarpinine, a Novel Hetidine,Hetisine Type Bisditerpenoid Alkaloid from Aconitum tanguticum var. trichocarpum

    Ling Lin
    Abstract Trichocarpinine (1), the first hetidine,hetisine type bisditerpenoid alkaloid, was isolated from the whole herbs of Aconitum tanguticum var. trichocarpum. Its structure was determined by a combination of spectroscopic techniques, including HR-ESI-MS and 1D- and 2D-NMR experiments. Its plausible biogenetic pathway was proposed as well (Scheme). [source]

    Minocycline-Based Europium(III) Chelate Complexes: Synthesis, Luminescent Properties, and Labeling to Streptavidin

    Takuya Nishioka
    Abstract Two chelate ligands for europium(III) having minocycline (=(4S,4aS,5aR,12aS)-4,7-bis(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,10,12,12a-tetrahydroxy-1,11-dioxonaphthacene-2-carboxamide; 5) as a VIS-light-absorbing group were synthesized as possible VIS-light-excitable stable Eu3+ complexes for protein labeling. The 9-amino derivative 7 of minocycline was treated with H6TTHA (=triethylenetetraminehexaacetic acid=3,6,9,12-tetrakis(carboxymethyl)-3,6,9,12-tetraazatetradecanedioic acid) or H5DTPA (=diethylenetriaminepentaacetic acid=N,N -bis{2-[bis(carboxymethyl)amino]ethyl}glycine) to link the polycarboxylic acids to minocycline. One of the Eu3+ chelates, [Eu3+(minocycline-TTHA)] (13), is moderately luminescent in H2O by excitation at 395,nm, whereas [Eu3+(minocycline-DTPA)] (9) was not luminescent by excitation at the same wavelength. The luminescence and the excitation spectra of [Eu3+(minocycline-TTHA)] (13) showed that, different from other luminescent EuIII chelate complexes, the emission at 615,nm is caused via direct excitation of the Eu3+ ion, and the chelate ligand is not involved in the excitation of Eu3+. However, the ligand seems to act for the prevention of quenching of the Eu3+ emission by H2O. The fact that the excitation spectrum of [Eu3+(minocycline-TTHA)] is almost identical with the absorption spectrum of Eu3+ aqua ion supports such an excitation mechanism. The high stability of the complexes of [Eu3+(minocycline-DTPA)] (9) and [Eu3+(minocycline-TTHA)] (13) was confirmed by UV-absorption semi-quantitative titrations of H4(minocycline-DTPA) (8) and H5(minocycline-TTHA) (12) with Eu3+. The titrations suggested also that an 1,:,1 ligand Eu3+ complex is formed from 12, whereas an 1,:,2 complex was formed from 8 minocycline-DTPA. The H5(minocycline-TTHA) (12) was successfully conjugated to streptavidin (SA) (Scheme,5), and thus the applicability of the corresponding Eu3+ complex to label a protein was established. [source]

    2-(2,4-Dinitrobenzyl)pyridine (DNBP): A Potential Light-Activated Proton Shuttle

    Catrin Goeschen
    Abstract The well-known photochromic tautomerism of 2-(2,4-dinitrobenzyl)pyridine (1; CH; Scheme,1) was re-investigated by flash photolysis in aqueous solution in view of its potential application as a light-activated proton pump. Irradiation of 1 yields the enamine tautomer NH (,max=520,nm) that rapidly equilibrates with its conjugate base CNO, (,max=420,nm). The pH,rate profile for the first-order decay of NH and CNO, provides a direct determination of the acidity constant of NH, pK=5.94±0.12 (I=0.1M) and serves to clarify the mechanisms of proton transfer prevailing in aqueous solutions. The acidity constant of protonated 1 (CHNH+), pK=4.18±0.02, was determined by spectrophotometric titration. [source]