Cyano-bridged coordination polymer nanoparticles with high nuclear relaxivity: toward new contrast agents for MRI

New water-soluble paramagnetic Gd-containing cyano-bridged metallic coordination polymer nanoparticles with a chitosan shell show high nuclear relaxivity in acidic water which is up to six times higher than that of the actually used Gd-chelates.     

Total syntheses of brominated marine sponge alkaloids

Total syntheses of six brominated marine sponge bis(indole) alkaloids of the hamacanthin, spongotine, and topsentin classes are described. Retrosynthetic analysis shows that their structures all include the 1-(6'-bromoindol-3'-yl)-1,2-diaminoethane unit 13a. This key moiety has been prepared from brominated indolic N-hydroxylamine 5b via synthetic intermediate 8b.     

Efficient synthetic approaches to the common scaffold of indole alkaloids

Birch reductive alkylation of 2-aminobiphenyls affords access to highly functionalized polyenes that react through a Pd(II)-catalyzed oxidative amination cascade or through a double 1,4-addition process to provide the tetracyclic skeleton of indole alkaloids with up to four stereogenic centers created in a single-pot operation.     

Enantiospecific Syntheses of Congested Atropisomers through Chiral Bis(aryne) Synthetic Equivalents

The synthetic equivalents of the enantiopure binaphthyl bis(aryne) atropisomers derived from BINOL (1,1′-bi-2,2′-naphtol) featuring a stereogenic axis vicinal to the two reactive triple bonds can be generated for the first time in solution in an enantiospecific manner. Using a two-step sequence based on the bidirectional [4+2] cycloaddition of furan derivatives followed by an aromatizative deoxygenation reaction, several 9,9’-bianthracenyl-based atropisomers could be prepared enantiospecifically in high enantiomeric purity. Alternatively, bidirectional reactions with anthracene, 2-bromostyrene, and perylene as the arynophiles afforded very congested bis(benzotriptycene), bis(tetraphene) and bis(anthra[1,2,3,4-ghi]perylene) nanocarbon atropisomers in equally high enantiomeric purity. In complement, cross reactions with two different arynophiles revealed possible. The unusual atropisomer prototypes described in this study open the way to enantiopure nanographene atropisomers designed for functions.     

Phosphorus Compounds for the Formation of Unprecedented Anionic Zirconium Complexes

Using the nucleophilic ability of tertiary phosphines we have been able to prepare a large variety of unprecedented stable phosphonium anionic zirconocene(IV) complexes.     

Interorganizational Networking Patterns Among Development Organizations

This research seeks to explain the structure of the interorganizational network of international development organizations, including international nongovernmental organizations (INGOs) and intergovernmental organizations (IGOs). The study uses a multitheoretical, multilevel model to examine the endogenous and exogenous influences on the international development organization network. Results indicate that homophily, mutuality, transitivity, and centralization influence the configuration of the international development organizational network. In particular, IGOs tended to collaborate with IGOs; both INGOs and IGOs were likely to seek joint dependencies over asymmetric dependencies; some organizations acted as intermediary coordinators; and organizations were more likely to form collaborations with partners of partners. Implications for executive directors of INGOs and policymakers are drawn from the results.     

Periodic Behavior of Lanthanide Coordination within Reverse Micelles

Trends in lanthanide(III) (Ln^III) coordination were investigated within nanoconfined solvation environments. Ln^III ions were incorporated into the cores of reverse micelles (RMs) formed with malonamide amphiphiles in n‐heptane by contact with aqueous phases containing nitrate and Ln^III; both insert into pre‐organized RM units built up of DMDOHEMA (N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide) that are either relatively large and hydrated or small and dry, depending on whether the organic phase is acidic or neutral, respectively. Structural aspects of the Ln^III complex formation and the RM morphology were obtained by use of XAS (X‐ray absorption spectroscopy) and SAXS (small‐angle X‐ray scattering). The Ln^III coordination environments were determined through use of L₃‐edge XANES (X‐ray absorption near edge structure) and EXAFS (extended X‐ray absorption fine structure), which provide metrical insights into the chemistry across the period. Hydration numbers for the Eu species were measured using TRLIFS (time‐resolved laser‐induced fluorescence spectroscopy). The picture that emerges from a system‐wide perspective of the Ln? O interatomic distances and number of coordinating oxygen atoms for the extracted complexes of Ln^III in the first half of the series (i.e., Nd, Eu) is that they are different from those in the second half of the series (i.e., Tb, Yb): the number of coordinating oxygen atoms decrease from 9 O for early lanthanides to 8 O for the late ones—a trend that is consistent with the effect of the lanthanide contraction. The environment within the RM, altered by either the presence or absence of acid, also had a pronounced influence on the nitrate coordination mode; for example, the larger, more hydrated, acidic RM core favors monodentate coordination, whereas the small, dry, neutral core favors bidentate coordination to Ln^III. These findings show that the coordination chemistry of lanthanides within nanoconfined environments is neither equivalent to the solid nor bulk solution behaviors. Herein we address atomic‐ and mesoscale phenomena in the under‐explored field of lanthanide coordination and periodic behavior within RMs, providing a consilience of fundamental insights into the chemistry of growing importance in technologies as diverse as nanosynthesis and separations science.     

Fractional Laplacian phase transitions and boundary reactions: A geometric inequality and a symmetry result

We deal with symmetry properties for solutions of nonlocal equations of the type

     

ICA-based and second-order separability of nonlinear models involving reference signals: General properties and application to quantum bits

Relatively few results have been reported about the separability of given classes of nonlinear mixtures by means of statistical criteria such as ICA. We here first prove the ICA separability of a wide class of nonlinear global (i.e. mixing+separating) models involving “reference signals”, i.e. unmixed signals. We also show the second-order separability of sub-classes of the above class of models. This work therefore concerns nonlinear extensions of (linear) adaptive noise cancellation. We illustrate the usefulness of our general results by applying them to a quantum information processing problem, which involves a model of Heisenberg-coupled quantum states (i.e. qubits). This paper opens the way to practical ICA-based and second-order blind source separation (BSS) methods for nonlinear mixtures encountered in various applications. These BSS methods are also outlined in this paper.     

Development of Domino Processes by Using 7‐Silylcycloheptatrienes and Its Analogues

7‐Silyl‐ and 7‐silylmethylcycloheptatrienes were shown to react with acylnitroso reagents at room temperature, through their norcaradiene forms, to generate the corresponding cycloadducts 5 a – b and 6 a – b as single diastereomers. The course of the reaction was dramatically modified by changing the reaction conditions. Using a polar medium, functionalized cyclohexa‐1,3‐dienes 7 a – b and bicyclic compounds 13 a – b were instead generated, incorporating one or two amino groups. Similar behavior was observed by using other dienophiles, including triazolinedione, but also activated aldehydes and ketones. A tentative mechanism has been proposed to rationalize the formation of both classes of products that relies on a domino process involving four consecutive elementary steps, in this order: 1) electrocyclic process, 2) hetero‐Diels–Alder reaction, 3) cyclopropane ring opening, and 4) hetero‐Diels–Alder reaction. Trapping of the cationic intermediate and isolation of the primary cycloadduct provide support for this hypothesis. An enantioselective version of the cascade using cycloheptatriene 4 b and aldehydes and ketones, under copper(II) catalysis was also carried out, leading to cyclohexa‐1,3‐dienes 21 , 28 , and 30 with enantioselectivities up to 93 % ee. Finally, elaboration of the intermediates above has been carried out, opening a straightforward access to sugar mimics 42 – 43 and complex polycyclic systems 36 and 39 .