Push–Pull Bisnaphthyridylamine Supramolecular Nanoparticles: Polarity-Induced Aggregation and Crystallization-Induced Emission Enhancement and Fluorescence Resonance Energy Transfer

Emissive push–pull-type bisnaphthyridylamine derivatives ( BNA-X : X=Me, Et, Bzl, Ph, BuBr, and BuTEMPO) aggregate in aqueous methanol. Furthermore, a two-step emission and aggregation process is controllable by varying the methanol-to-water ratio. At 2:3 MeOH/H₂O, crystallization-induced emission enhancement (CIEE) occurs via formation of an emissive crystal phase, whereas, at 1:9 MeOH/H₂O, aggregation-induced emission enhancement (AIEE) occurs, induced by emissive supramolecular nanoparticles (NPs). For BNA-Ph , the emission quantum yield was 25 times higher in aqueous methanol than that in pure methanol. Despite the high hydrophobicity of BNA-X (C log P=6.1–8.0), the spherical NPs were monodisperse (polydispersity indices <0.2). Moreover, the emissive NPs exhibited fluorescence resonance energy transfer (FRET) with pyrene; however, for BNA-X bearing the TEMPO radical ( BNA-BuTEMPO ), no FRET was observed because of quenching. In particular, the BNA-BuTEMPO NPs have a slow rotational correlation time (1.3 ns), suggesting applications as magnetic resonance imaging contrast agents with large relaxivity.     

Thermosensitive, soft glassy and structural colored colloidal array in ionic liquid: colloidal glass to gel transition

A novel soft material comprising thermosensitive poly(benzyl methacrylate)-grafted silica nanoparticles (PBnMA-g-NPs) and the ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C(2)mim][NTf(2)]), was fabricated. The thermosensitive properties were studied over a wide range of particle concentrations and temperatures. PBnMA-g-NPs in the IL underwent the lower critical solution temperature (LCST) phase transition at lower temperatures with a broader transition temperature range as compared to the free PBnMA solution. Highly concentrated suspensions formed soft glassy colloidal arrays (SGCAs) exhibiting a soft-solid behavior and angle-independent structural color. For the first time, we report a discrete change in the angle-independent structural color of SGCAs with temperature because of a temperature-induced colloidal glass-to-gel transition. The interparticle interaction changed from repulsive to attractive at the LCST temperature, and it was characterized by a V-shaped rheological response and a direct electron microscope observation of the colloidal suspension in the IL. With unique rheological and optical properties as well as properties derived from the IL itself, the thermosensitive SGCAs may be of interest as a new material for a wide range of applications such as electrochemical devices and color displays.     

Efficient microwave-assisted tandem N- to S-acyl transfer and thioester exchange for the preparation of a glycosylated peptide thioester

A peptide carrying a mercaptomethylated proline derivative at the C-terminus was prepared by solid-phase peptide synthesis (SPPS) and converted to the thioester of 3-mercaptopropionic acid (MPA) by aqueous MPA under microwave irradiation conditions. This post-SPPS thioesterification reaction was successfully applied to the synthesis of a glycopeptide thioester composed of 25 amino acid (AA) residues, which was then used for the preparation of a 61-AA glycopeptide by the thioester condensation method.     

Efficient asymmetric synthesis of novel 4-substituted and configurationally stable analogues of thalidomide

The preparation of new thalidomide derivatives 4-methyl-(3S,4R)-3a and 4-phenyl-(3S,4S)-3b starting from pyroglutamic acids (2R,3R)-7a and (2R,3S)-7b, possessing an inappropriate stereochemistry, was successfully realized due to stereochemically complete epimerization at the alpha-stereogenic center upon formation of the corresponding N-phthaloyl anhydrides 9a,b. The demonstrated conformational stability of these new thalidomide derivatives provides solid experimental evidence for practical feasibility of the approach described here to overcome the inherent problem of configurational instability of thalidomide by introducing an alkyl or aryl group in the C4 position. [reaction: see text].     

Optimal tuning parameter estimation in maximum penalized likelihood method

In maximum penalized or regularized methods, it is important to select a tuning parameter appropriately. This paper proposes a direct plug-in method for tuning parameter selection. The tuning parameters selected using a generalized information criterion (Konishi and Kitagawa, Biometrika, 83, 875–890, 1996) and cross-validation (Stone, Journal of the Royal Statistical Society, Series B, 58, 267–288, 1974) are shown to be asymptotically equivalent to those selected using the proposed method, from the perspective of estimation of an optimal tuning parameter. Because of its directness, the proposed method is superior to the two selection methods mentioned above in terms of computational cost. Some numerical examples which contain the penalized spline generalized linear model regressions are provided.     

Mixed-valence states and crystal structure of biferrocene derivatives with long alkyl chains

Mixed-valence states have been investigated for a series of binuclear ferrocenium salts with long alkyl chains. In the triiodide salts with layered structures, an interesting even-odd character in the number of carbon atoms of the alkyl chain is observed in the relationship between the inter-layer distance and the mixed-valence state. 1, 1-didodecylbiferrocenium triiodide is found to be most interesting because this salt has a large potential for application to molecular-based devices.     

Highly regio- and stereocontrolled brominations of gem-difluorinated vinyloxiranes

gem-Difluorinated vinyloxiranes, which are useful synthetic intermediates for difluorinated compounds, were brominated regio- and stereoselectively. Introduction of bromide at the allylic epoxide carbon with inversion of stereochemistry was realized by MgBr₂·Et₂O to furnish an anti vic-bromohydrine, whereas the reaction with LiBr/AcOH afforded the other diastereomer selectively. Moreover, both reactions at high temperature allowed to obtain, the thermodynamically favored products, E-allylic alcohols dominantly.     

Cesium-ion selective electrodes based on calix[4]arene dibenzocrown ethers

Four calix[4]arene dibenzocrown ether compounds have been prepared and evaluated as Cs(+)-selective ligands in solvent polymeric membrane electrodes. The ionophores include 25,27-bis(1-propyloxy)calix[4]arene dibenzocrown-6 1, 25,27-bis(1-alkyloxy)calix[4]arene dibenzocrown-7s 2 and 3, and 25,27-bis(1-propyloxy)calix[4]arene dibenzocrown-8 4. For an ion-selective electrode (ISE) based on 1, the linear response concentration range is 1x10(-1) to 1x10(-6) M of Cs(+). Potentiometric selectivities of ISEs based on 1-4 for Cs(+) over other alkali metal cations, alkaline earth metal cations, and NH(4)(+) have been assessed. For 1-ISE, a remarkably high Cs(+)/Na(+) selectivity was observed, the selectivity coefficient (K(Cs,Na)(Pot)) being ca. 10(-5). As the size of crown ether ring is enlarged from crown-6 (1) to crown-7 (2 and 3) to crown-8 (4), the Cs(+) selectivity over other alkali metal cations, such as Na(+) and K(+), is reduced successively. Effects of membrane composition and pH in the aqueous solution upon the electrode properties are also discussed.