Spacer Length Effect on the Photoinduced Electron Transfer Fluorescent Probe for Alkali Metal Ions

Abstract— We have synthesized four derivatives of aikyi pyrene covalently bonded to aza-lS-crown-6 at the nitrogen position, Py(CH₂)_n, (n = 1–4), to study the effect of spacer length on the emission properties of pyrene fluorophore upon complication of alkali metal ions by the crown moiety. In the absence of alkali metal ions, the parent molecule is weakly fluorescent because its emission is partially quenched by photoinduced electron transfer (PET) from nitrogen lone pairs to the excited singlet state of pyrene. Complication of alkali metal ions (e.g. K⁺) by the crown moiety prevents the nitrogen lone pair from participating in PET and results in an enhancement in the observed emission from pyrene (fluorescent turn on). Because the PET effect could be exerted through bonds as well as space, its magnitude may show a dependence on chain length. We have examined the fluorescence behavior of these pyrene aza-crown ether derivatives in the presence of alkali metal ions to determine the magnitude of such an effect and its impact on the sensitivity of the fluorescent probe for detection purposes. Our results indicate that maximum efficiency for PET between the pyrene moiety and aza-crown ether is achieved when n ≤ 3.     

A heuristic for the multi-satellite,multi-orbit and multi-user management of Earth observation satellites

Earth observation satellites are platforms equipped with optical instruments that orbit the Earth in order to take photographs of specific areas at the request of users. This article is concerned with the management of several satellites performing multiple orbits over a given planning horizon. It describes a tabu search heuristic for the problem of selecting and scheduling the requests to be satisfied, under operational constraints. An upper bounding procedure based on column generation is used to evaluate the quality of the solutions. The results of extensive computational experiments performed on data provided by the French Centre National d’Études Spatiales are reported.     

Blutuntersuchung

Ohne Zusammenfassung     

Über ein Dimethyltetraoxyanthrachinon

Ohne ZusammenfassungDie Arbeit wurde 1914 durch den Krieg unterbrochen und nach 1919 an der Universität Zagreb beendigt.     

Coordination of stocking decisions in an assemble-to-order environment

This paper examines an assemble-to-order environment involving a short-life-cycle product that is sold in two different configurations, each requiring a unique component that must be stocked in advance. Both configurations of the product are assembled on the same equipment which has limited capacity. The focus of the analysis is on the determination of the appropriate stocking quantities for each of the configuration specific components. Because the same assembly capacity is often reused for different instances of the component stocking problem, we treat assembly capacity as exogenous. This represents the fact that capacity decisions are often made less frequently than are procurement/production quantity decisions. We first solve for the first-best stocking policy when the components are produced internally. We then consider the case when the components are procured from external suppliers, and investigate how different forms of contract between the assembler and the component suppliers affect coordination of the supply chain as well as each party’s profit. One particularly interesting finding is that it is possible to coordinate the supply chain with a single-price contract between each supplier and the assembler while awarding all parties positive profit.     

Conditions to obtain precise and true measurements of the intramolecular C distribution in organic molecules by isotopic C nuclear magnetic resonance spectrometry

Intramolecular ¹³C composition gives access to new information on the (bio) synthetic history of a given molecule. Isotopic ¹³C NMR spectrometry provides a general tool for measuring the position-specific ¹³C content. As an emerging technique, some aspects of its performance are not yet fully delineated. This paper reports on (i) the conditions required to obtain satisfactory trueness and precision for the determination of the internal ¹³C distribution, and (ii) an approach to determining the “absolute” position-specific ¹³C content. In relation to (i), a precision of <1% can be obtained whatever the molecule on any spectrometer, once quantitative conditions are met, in particular appropriate proton decoupling efficiency. This performance is a prerequisite to the measurement of isotope fractionation either on the transformed or residual compound when a chemical reaction or process is being studied. The study of the trueness has revealed that the response of the spectrometer depends on the ¹³C frequency range of the studied molecule, i.e. the chemical shift range. The “absolute value” and, therefore, the trueness of the ¹³C NMR measurements has been assessed on acetic acid and by comparison to the results obtained on the fragments from COOH and CH₃ by isotopic mass spectrometry coupled to a pyrolysis device (GC-Py–irm-MS), this technique being the reference method for acetic acid. Of the two NMR spectrometers used in this work, one gave values that corresponded to those obtained by GC-Py–irm-MS (thus, the “true” value) while the other showed a bias, which was dependent to the range covered by the resonance frequencies of the molecule. Therefore, the former can be used directly for studying isotope affiliations, while the latter can only be used directly for comparative data, for example in authenticity studies, but can also be used to obtain the true values by applying appropriate correction factors. The present study assesses several key protocol steps required to enable the determination of position-specific ¹³C content by isotopic ¹³C NMR, irrespective of the NMR spectrometer: parameters to be adjusted, performance test using [1,2-¹³C₂]acetic acid, generation of correction factors.