2,054 research outputs found

    J Fluorescence

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    The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards

    Estimation of GCM Temperature Trends for Different Emission Scenarios with the help of the Integrated Model to Assess the Greenhouse Effect (IMAGE)

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    How useful are General Circulation Models (GCMs) for policy makers? Of course, they are considered to be the most powerful models that are presently available for predicting future climates and for carrying out research. Their disadvantage is that they are very time-consuming and very expensive to run for any greenhouse gas emission or concentration scenario. For that reason, GCMs have been run only for a small number of scenarios. However, policy makers are interested in being able to analyze a large number of scenarios. The Integrated Model to Assess the Greenhouse Effect (IMAGE) developed by the National Institute for Public Health and Environmental Protection (RIVM) in the Netherlands is a scientifically based, policy oriented model that can calculate the effect of different greenhouse gas emissions on global surface air temperature and sea level rise. The major advantage of IMAGE is its quick turnaround time. Its disadvantage is that it gives only global values of surface temperature and sea level rise, which have insufficient spatial resolution to estimate ecological impacts on a regional basis. We propose a methodology for combining the fast turnaround time and time-dependent surface temperature results of IMAGE with the spatial resolution of GCMs to provide a linkage between IMAGE and models of ecological change that could provide policy-makers with valuable information about the consequences of different levels of reduction of greenhouse gas emissions

    Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality

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    Controlled directional transport of molecules is essential to complex natural systems, exemplified by cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Here we report the transfer of a supramolecular cage with controlled directionality between three phases, based on the cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.European Research Council (695009), UK Engineering and Physical Sciences Research Council (EPSRC, EP/P027067/1

    Pathway-Dependent Post-assembly Modification of an Anthracene-Edged MII4L6 Tetrahedron

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    FeII4L6 tetrahedral cage 1 undergoes post-assembly modification (PAM) via a Diels–Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage 2 possesses an enclosed cavity suitable for encapsulation of the fullerene C60, whereas original cage 1 forms a unique covalent adduct through a Diels–Alder cycloaddition of three of its anthracene ligands with C60. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C60 and TCNE. Modified cage 2 was also able to bind an anionic guest, [Co(C2B9H11)2]−, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts

    Improved Acid Resistance of a Metal-Organic Cage Enables Cargo Release and Exchange between Hosts.

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    The use of di(2-pyridyl)ketone in subcomponent self-assembly is introduced. When combined with a flexible triamine and zinc bis(trifluoromethanesulfonyl)imide, this ketone formed a new Zn4 L4 tetrahedron 1 bearing twelve uncoordinated pyridyl units around its metal-ion vertices. The acid stability of 1 was found to be greater than that of the analogous tetrahedron 2 built from 2-formylpyridine. Intriguingly, the peripheral presence of additional pyridine rings in 1 resulted in distinct guest binding behavior from that of 2, affecting guest scope as well as binding affinities. The different stabilities and guest affinities of capsules 1 and 2 enabled the design of systems whereby different cargoes could be moved between cages using acid and base as chemical stimuli.European Research Council (695009), UK Engineering and Physical Sciences Research Council (EPSRC EP/P027067/1

    Subtle Ligand Modification Inverts Guest Binding Hierarchy in M(II)8L6 Supramolecular Cubes.

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    Zinc(II), a dimolybdenum(II) paddlewheel tetramine A, and 2-formylpyridine self-assembled to generate a cubic Zn(II)8(L(A))6 assembly. The paddlewheel faces of this assembly exhibited two distinct conformations, whereas the analogous Fe(II)8(L(A))6 framework displayed no such perturbation to its structure. This variation in behavior is attributed to the subtle difference in ligand rotational freedom between the Zn(II)- and Fe(II)-cornered cubes. The incorporation of a fluorinated Mo(II)2 paddlewheel, B, into analogous Zn(II)8(L(B))6 and Fe(II)8(L(B))6 structures resulted in changes to the rotational dynamics of the ligands. These differing dynamics perturbed the energies of the frontier orbitals of these structures, as determined through spectroscopic and electrochemical methods. The result of these perturbations was an inversion of the halide binding preference of the Zn(II)8(L(B))6 host as compared to its Zn(II)8(L(A))6 congener, whereas the Fe(II)8(L(B))6 host maintained a similar binding hierarchy to Fe(II)8(L(A))6.Seventh Framework ProgrammeThis is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/jacs.6b0385
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