Weak noncovalent Si···F?C interactions stabilized fluoroalkylated rod-like polysilanes as ultrasensitive chemosensors

Noncovalent interactions, such as hydrogen bonding, metal coordination, and π-π stacking, are increasingly being utilized to develop well-ordered and self-organized supramolecular materials. Recently, new types of nonclassical weak interactions, such as C H···π, C H···F C, and C H···O, have been exploited in stabilizing the specific conformations of molecules and molecular assemblies in the solid state. These noncovalent interactions play an important role in materials comprised of polymer chains, because cooperative effects from a large number of weak interactions can lead to drastic changes in its conformation, several properties, and functionalities. The programmed design of synthetic helical polymer with well-defined molecular conformation has been the main subject in modern polymer science and engineering. Silicon-catenated polysilane is an ideal helical silicon quantum wire and polymers with unique photophysical properties. The present review highlights the spectroscopic evidences for through-space weak Si···F C interaction in poly(methyl-3,3,3-trifluoropropylsilane) ( 1 ) in noncoordinating and coordinating solvents by means of NMR (²⁹Si and ¹⁹F) and IR spectroscopies, and viscometric measurement. It was found that 1 is applicable for chemosensors with an extremely high sensitivity and selectivity toward fluoride ions in tetrahydrofuran (THF) and with high sensitivity for nitroaromatic compounds, detected by a decrease in the photoluminescence intensity in THF and in thin solid film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5060–5075, 2006     

Silaboration of [1.1.1]Propellane: A Storable Feedstock for Bicyclo[1.1.1]pentane Derivatives

The silaboration of [1.1.1]propellane enables direct introduction of B and Si functional groups onto the bicyclo[1.1.1]pentane (BCP) scaffold in high yield under mild, additive‐free conditions. The silaborated BCP can be obtained on a gram‐scale in a single step without the need for column‐chromatographic purification, and is storable and easy to handle, providing a versatile synthetic intermediate for BCP derivatives. We also describe various conversions of the C?B/C?Si bonds on the BCP scaffold, including development of a modified Suzuki–Miyaura cross‐coupling reaction at the highly sterically hindered bridgehead sp³ carbon center of the BCP skeleton using a combination of highly activated BCP boronic esters, copper(I) oxide, and a PdCl₂(dppf) catalyst system.     

Ring-Opened Hemiporphyrazines: Helical Molecules Exhibiting Circularly Polarized Luminescence

We designed and synthesized a new type of small helical molecule exhibiting intense circularly polarized luminescence (CPL) ( 1_2H ) by modifying a 20π-electron hemiporphyrazine with a large transition magnetic dipole moment. The hemiporphyrazine ring was opened and one additional pyridine unit was introduced, resulting in an overlap of two pyridine rings. X-ray structure analysis confirmed that 1_2H and its zinc complex ( 1_Zn ) adopt a helical geometry. A racemic mixture of 1_Zn was resolved into two enantiomers ((P)- and (M)- 1_Zn ), which exhibited CPL with a high luminescence dissymmetry factor (g_lum) value of ±2.1×10⁻². The origin of the large g_lum value was rationalized by means of DFT calculations. Helical structures could be formed in a diastereoselective manner by covalently attaching chiral units to the skeleton ( 1’_2H and 1’_Zn ). 1_Zn was found to possess chiral recognition ability for amines.     

Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.     

Rhodium-Catalyzed Highly Diastereo- and Enantioselective Synthesis of a Configurationally Stable S-Shaped Double Helicene-Like Molecule

An S-shaped double helicene-like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex-catalyzed highly diastereo- and enantioselective intramolecular double [2+2+2] cycloaddition of a 2-naphthol- and benzene-linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S-shaped double helicene-like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S-shaped double helicene-like molecule forms a trimer through the multiple C−H⋅⋅⋅π and C−H⋅⋅⋅O interactions in the solid-state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S-shaped double helicene-like molecule enhanced the chiroptical properties.     

Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na⁺), ammonium (NH₄⁺) and hydrazine (N₂H₅⁺) ions was developed by connecting an anion-exchange column in the I⁻-form after the separation column. For example, NH₄⁺ is converted to a UV-absorbing molecule, NH₄I, by the anion-exchange column in the I⁻-form after the ion-exclusion separation on anion-exchange column in the OH⁻-form with water eluent. As a result, the direct UV detection of Na⁺, NH₄⁺ and N₂H₅⁺ could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001-5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH₄⁺ in river and rain waters, or that of N₂H₅⁺ in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H⁺-form as the separation column and the anion-exchange conversion column.     

Regiocontrolled intramolecular cyclizations of carboxylic acids to carbon-carbon triple bonds promoted by acid or base catalyst

We systematically investigated, for the first time, the relationship between regioselectivity and acid/base effects in the cyclization reactions between carboxylic acids and carbon-carbon triple bonds. We found novel acid- and base-promoted cyclizations to selectively give isocoumarin or pyran-2(2H)-one and phthalide or furan-2(5H)-one skeletons, respectively, and established a catalytic version of regioselective heterocyclic ring synthesis. Density functional theory calculations and application to a short route to thunberginol A were also described. [reaction: see text].     

Silylmetalation of alkenes

Silylmetalation of alkenes is challenging due to the low reactivity of the substrates. In contrast, carbometalation of alkenes has been realized through several innovative methods, including activation of the reagent and the substrate. A similar approach could be applicable to silylmetalation of alkenes, and we have recently developed a bimetal activation method using zincate complexes for this purpose. Here, we describe how the silylzincation of alkenes was achieved. First, the strategies for carbometalation of alkenes will be summarized. Secondly, the history and development of silylzincation chemistry are briefly described. Then the details of our findings related to two types of silylzincation of alkenes, as well as recent progress in mechanistic studies, are discussed. The key point in the silylzincation of alkenes proved to be the bimetal activation of the substrate. One metal (copper or titanium) strongly coordinates and activates the alkene moiety, and the other metal (zinc) acts as the electron acceptor from the silyl group by way of the alkene moiety. This dual activation concept is expected to be applicable to other combinations of metals, as well as to new types of reactions.     

Anomalous magnetic field effects on photochemical reactions in ionic liquid under ultrahigh fields of up to 28 T

The magnetic field effects (MFEs) on photoinduced hydrogen abstraction reactions between benzophenone and thiophenol in an ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) imide (TMPA TFSI), were studied by a nanosecond laser flash photolysis technique under ultrahigh fields of up to 28 T. Extremely large and anomalous stepwise MFEs were observed for the first time. The escape yield of benzophenone ketyl radical decreased with increasing magnetic field strength (B) at 0 T相似文献   

Versatile self-assembled hybrid systems with exotic structures and unique functions

In this review article, we describe recent progress about exotic self-assembled systems with various dimensions including biomolecules, supramolecules, unique hydrophobic amphiphiles, polymers, nano-clusters, and colloidal particles. Construction of robust biomolecular assemblies with exotic structures, such as ring and hollow capsule, is achieved by rational designs of symmetric biomolecular conjugates. In addition, we comprehensively summarized leading-edge topics on optical/topological properties of self-assembled hybrid systems, such as circularly polarized luminescence or structural color. The preparation of colloidal amorphous array with photonic band gap-induced angle-independent structural color is also achieved in consideration of the following situations: i) two-body sphere–sphere potential, ii) disorder packing using different sizes of colloidal particles, and iii) softness of colloidal particles. Lastly, we demonstrated useful utilizations of exotic self-assembled objects. Flakelike microparticles were transcribed into various nano-flake metals and applied as temperature indicator for the local heating of an addictive. All findings described here show meaningful hybrid strategies in self-assembly techniques and their functionalization as well as materialization.