Formation of luminescent nanocomposite assemblies via electrostatic interaction

A novel luminescent nanocomposite assembly was prepared in aqueous solutions, via the electrostatic interaction between poly(ethylene glycol)-b-poly(N,N-dimethylaminoethyl methacrylate) (PEG-b-PDMAEMA) double hydrophilic block copolymer (DHBC) and thioglycolic acid (TGA)-stabilized CdTe quantum dots (QDs). By tuning the molar ratios of QDs to DHBC, the nanocomposite assemblies could be well controlled and the dimension of these regular spherical QDs/PEG-b-PDMAEMA assemblies ranged from 40 to 75 nm in aqueous media. As the periphery of QDs/PEG-b-PDMAEMA nanocomposite assembly was composed of PEG segments when the PDMAEMA blocks and QDs were immobilized inside the assembly, the cytotoxicity of the assembly was significantly reduced, compared with that of pure PEG-b-PDMAEMA and QDs. The nanocomposite assembly also exhibited superior stability in salt solutions and remained strongly photoluminescent even when free radicals existed. Thus, the QDs/PEG-b-PDMAEMA nanocomposite assembly is potentially useful for a number of applications in biolabeling and imaging.     

Coordination driven axial chirality in a microporous solid assembled from an achiral linker via in situ C-N coupling

Metal mediated in situ C-N coupling between 4,4'-azobipyridine and disodium-trans-glutaconate at room temperature has formed a new multifunctional linker Z-dhpe which subsequently self-assembles with Zn(II) or Cd(II) resulting in a chiral or an achiral metal-organic framework, respectively, depending on its different coordination modes.     

Anion-induced structures and luminescent properties of chiral lanthanide-organic frameworks assembled by an achiral tripodal ligand

To confirm how different anions influence sup-ramolecular self-assembly of lanthanide-organic frameworks (LnOFs) as well as their luminescent properties, a new flexible achiral tripodal ligand, 1,1,1-tris-{[(2'-benzylaminoformyl)phenoxyl]methyl}ethane (L) and the LnOFs {[EuL(NO(3))(3)]·1.5CHCl(3)}(n) and [EuL(pic)(3)](n) have been designed and assembled. In the two LnOFs, {[EuL(NO(3))(3)]·1.5CHCl(3)}(n) demonstrates an unprecedented chiral noninterpenetrated two-dimensional (2D) honeycomblike (6,3) (hcb, Schla?fli symbol 6(3), vertex symbol 6·6·6) topological network, and [EuL(pic)(3)](n) confirms an unusual chiral LnOF with three-dimensional (3D) (10,3)-a (srs, SrSi(2), Schla?fli symbol 10(3), vertex symbol 10(2)·10(4)·10(4)) topological framework. Also the anion-induced structures and energy transfer processes in the luminescence behavior of the two LnOFs were discussed in detail.     

Self-disproportionation of enantiomers via achiral chromatography: a warning and an extra dimension in optical purifications

This tutorial review describes the self-disproportionation of enantiomers (SDE) of chiral, non-racemic compounds, subjected to chromatography on an achiral stationary phase using an achiral eluent, which leads to the substantial enantiomeric enrichment and the corresponding depletion in different fractions, as compared to the enantiomeric composition of the starting material. The physicochemical background of SDE is a dynamic formation of homo- or heterochiral dimeric or oligomeric aggregates of different chromatographic behavior. This phenomenon is of a very general nature as the SDE has been reported for different classes of organic compounds bearing various functional groups and possessing diverse elements of chirality (central, axial and helical chirality). The literature data discussed in this review clearly suggest that SDE via achiral chromatography might be expected for any given chiral enantiomerically enriched compound. This presents two very important issues for organic chemists. First, chromatographic purification of reaction products can lead to erroneous determination of the stereochemical outcome of catalytic asymmetric reactions and second, achiral chromatography can be used as a new, nonconventional method for optical purifications. The latter has tremendous practical potential as the currently available techniques are limited to crystallization or chiral chromatography. However, a further systematic study of SDE is needed to develop understanding of this phenomenon and to design practical chromatographic separation techniques for optical purification of non-racemic mixtures by achiral-phase chromatography.     

Chiral initiator-induces self-disproportionation of enantiomers via achiral chromatography: application to enantiomer separation of racemate

We report here the theoretical design and proof of principle of the first example of a conceptually new approach for the preparation of enantiomerically pure compounds from the racemates by chiral initiator-induced Self-Disproportionation of Enantiomers (SDE) via achiral chromatography.     

Induction of an aromatic six-membered nitrogen ring via cation-pi interaction

Nitrogen clusters have been intensively studied for their potential application as high-energy density materials, but a six-membered nitrogen ring (N6) was not found to be stable and aromatic. To explore the possibility of inducing an aromatic N6 ring via cation-pi interaction, quantum chemistry calculations were performed on the systems of Ca2N6, CaN6, CaN6(2-), N6, and N6(4-) at the B3LYP/6-311+G level. The optimized geometries reveal that the planar structure of the N6 ring is stable only in the Ca2N6 complex. The computed NBO and CHelpG charges demonstrate that the planar N6 moiety in the Ca2N6 complex is almost a 10pi-electron system. The predicted nucleus-independent chemical shift (NICS) values demonstrate that the N6 moiety is aromatic in comparison with the NICS values of benzene. The estimated enthalpy of formation for the Ca2N6 complex is 100.4 kcal/mol for the reaction of 2Ca and 3N2. The binding energy between the Ca2+ cation and the N6(4-) moiety is -1928.8 kcal/mol, with electrostatic interaction serving as the predominant component. When all the calculated results are taken into account, including the planar structure, 10pi-electron system, identical bond length, and negative NICS value of the N6(4-) moiety in the Ca2N6 complex, it is deduced that the alkaline earth metal Ca is capable of inducing an aromatic N6 ring through the cation-pi interaction formed by electron transfer from the Ca atom to the N6 ring.     

Regioselective insertion of 2-vinylpyridine in niobium and tantalum aryloxide complexes: an alternate route to pyridylalkyl metallacycles

A series of niobium and tantalum aryloxide complexes containing pyridylethyl ligation have been synthesized via 2-vinylpyridine insertion to metal hydride complexes.     

Coordination of sodium cation to an oxygen function and olefinic double bond to form molecular adduct ion in fast atom bombardment mass spectrometry

Steroidal allylic alcohols formed Na+ adduct ion peaks [M+Na]+ by the addition of NaCl in FAB mass spectrometry. A comparison of the intensities of the adduct ion peaks of allylic alcohols with those of the corresponding saturated alcohols and olefin suggested that the olefinic double bond and the proximal hydroxyl group had coordinated to Na+. The adduct ion was stable and did not undergo dehydroxylation. We suggest that the Na+ adduction will be useful for the molecular weight determination of allylic alcohols which are susceptible to dehydroxylation under FAB mass spectrometric conditions. Na+ adduct ions of alpha,beta-unsaturated carbonyl compounds were also investigated.     

Directed evolution of hybrid enzymes: Evolving enantioselectivity of an achiral Rh-complex anchored to a protein

The concept of utilizing the methods of directed evolution for tuning the enantioselectivity of synthetic achiral metal-ligand centers anchored to proteins has been implemented experimentally for the first time.     

A double heteroatom Mitsunobu coupling with amino hydroxybenzoic acids on solid phase: a novel application of the Mitsunobu reaction to form dendron building blocks

A new highly efficient double heteroatom Mitsunobu coupling with amino hydroxybenzoic acids on solid phase is described. The synthetic routes reported in this work are general and applicable for the preparation of diverse building blocks, controlling protection, arm length, chirality, and peripheral functional groups. These novel units can form unusual dendritic architectures, which could be incorporated into specific complex structures, expanding the scope of dendrimer science.     

Enantioseparation of 1-arylethanols via a supramolecular chiral host consisting of N-(2-naphthoyl)-L-aspartic acid and an achiral diamine

A supramolecular chiral host consisting of N-(2-naphthoyl)-L-aspartic acid (L-1) and meso-1,2-diphenylethylenediamine (2) is effective in enantioseparation of 1-arylethanols (up to 96% ee with 100% inclusion ratio). Here we report three different methods to prepare the inclusion crystals and discuss the chiral recognition mechanism on the basis of X-ray crystallography results.     

Supramolecular architecture consisting of an enantiopure amine and an achiral carboxylic acid: application to the enantioseparation of racemic alcohols

Three-dimensionally dissymmetric cavities are created from an enantiopure amine and an achiral carboxylic acid, which can incorporate the third components to realize the formation of closely packed crystals. The combination demonstrates enantioselective inclusion for 20 kinds of racemic alcohols. The inclusion phenomenon occurs not only during crystallization but also in the solid state.     

Palladium-catalyzed alkenylation of fluoro-substituted furans via C-H activation to form tetrasubstituted furans

A palladium-catalyzed oxidative Heck reaction of fluoro-substituted furans with alkenes was developed to afford tetrasubstituted furans in moderate to good yields.     

Highly enantioselective alkaloid synthesis via ene-type cyclizations catalyzed by cationic chiral palladium(II) complexes of PN-ligands with an achiral oxazoline unit

A highly efficient asymmetric alkaloid synthesis via ene-type cyclizations catalyzed by cationic chiral palladium(II) complexes of PN-ligands with an achiral gem-dimethyl oxazoline unit is shown to give 5-membered products with a quaternary carbon center, including a spiro-amide, almost quantitatively with extremely high enantiomeric excesses.     

The enthalpy of interaction between an aqueous solution of methionine and carboxyl cationites in the copper form

The influence of acidity of aqueous solutions of methionine on their interaction with carboxyl cationites in the copper form was studied by the calorimetric, sorption, and spectroscopic methods. The distribution of methionine between aqueous solutions and sorbents with the formation of Cu(II) cation complexes in both phases was observed over the pH range 5–12. The enthalpies of interaction between methionine and KB-2 and Kb-4 cationites in the copper form were determined at various pH.     

Evolution from lyotropic liquid crystal to helical fibrous organogel of an achiral fluorescent twin-tapered bi-1,3,4-oxadiazole derivative

We report an unprecedented hierarchical self‐assembly of an achiral twin‐tapered bi‐1,3,4‐oxadiazole derivative (2,2‐bis(3,4,5‐trioctanoxyphenyl)‐bi‐1,3,4‐oxadiazole, BOXD‐T8). This molecule can form a layer‐structured lyotropic liquid crystal and further forms a helical fibrous organogel in DMF at concentrations above 0.6 wt %. The self‐assembly process of BOXD‐T8 in DMF is accompanied by a change in its fluorescence. The pitches of the helical fibers are non‐uniform, and both left‐ and right‐handed helical fibers are observed in equal quantities. Intermolecular π–π interactions between aromatic segments have been demonstrated to be the driving force for aggregate formation. This helical structure of BOXD‐T8 is dependent on the solvent, concentration, and the layer‐structured intermediate liquid‐crystalline state.     

Violating the Aufbau principle: an efficient way to improve the stability of luminescent radicals

<正>The Aufbau principle,also known as"building-up"principle,is a method of explaining the arrangements of electrons within atoms of different chemical elements.The principle was initially introduced by Danish physicist Niels Bohr and the basic statements include"Electrons will fill orbitals in increasing order of energy,and each orbital can contain a maximum of two electrons,and these must have opposite     

Synthesis and structure of 2,5,8-triazido-s-heptazine: an energetic and luminescent precursor to nitrogen-rich carbon nitrides

Derivatized s-triazine (C3N3) precursors have seen significant recent use in the production of carbon nitride materials. Larger polycyclic molecular precursors, such as those containing an s-heptazine core (C6N7 or tri-s-triazine), may improve stability and order in carbon nitride products. In this Communication, we describe the synthesis and crystal structure of 2,5,8-triazido-s-heptazine (2). Synthesis of 2 was achieved from melon, an oligomeric s-heptazine synthesized by the pyrolysis of NH4SCN. Melon was converted to molecular 2,5,8-trichloro-s-heptazine, which was then transformed to the triazide upon reaction with (CH3)3SiN3. The crystal structure of 2 verifies that the s-heptazine is planar and the azides adopt a pinwheel-like C3h arrangement around the periphery. The s-heptazine core shows pi delocalization in the C-N bonds around the periphery (av. 1.33 A), while the internal planar C-N bonds are longer (1.40 A). The heptazine units pack into parallel, but offset, layered sheets in the crystal. The triazide 2 exhibits photoluminescence at 430 nm and rapidly and exothermically decomposes upon heating at 185 degrees C to produce a tan thermally stable carbon nitride powder with a formula near C3N4.     

Self-assembly of poly(9,9'-dihexylfluorene) to form highly ordered isoporous films via blending

Highly ordered hexagonal arrays of isoporous films prepared from poly(9,9'-dihexylfluorene) and polystyrene-grafted silica nanoparticles (Si-graft-PS) are presented. These close-packed arrays were formed in areas of many square millimeters. The pore size varied from 3.6 to 8.5 microm, depending on the concentration of Si-graft-PS and the processing conditions. Solid-state photoluminescence resulted in a significant red shift of up to 30 nm in these films compared to that in conventional processing techniques. These differences are attributed to enhanced aggregation of the polymers caused by polymer-solvent interactions. These highly ordered polymer films may find use in microelectronic and biological and/or chemical sensor applications.