Dually responsive multiblock copolymers via RAFT polymerization: Synthesis of temperature- and redox-responsive copolymers of PNIPAM and PDMAEMA

We report synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl)benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multiblock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)-terminated PNIPAM and PDMAEMA. The copolymers and their stimulus-responsive behavior were characterized by size exclusion chromatography, NMR, light scattering and atomic force microscopy. Due to the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided the copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as a core and cationic PDMAEMA as stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH, while molecular weight of the assemblies decreased.     

Synthesis Hexadecyl 3-{4-[2-Hydroxy-3（isopropylamino）propoxy]phenyl}propionate as Potential Ligand for Liposome Targeting to Ischemic Myocardium

Novel hexadecyl 3- { 4-[2-hydroxy-3（isopropylamino）propoxy]phenyl }propionate （HPP）was synthesized and its effect on delivery of liposomes into cultured cardiomyocytes was examined. The structure of HPP was characterized by IH NMR, 1R and MS. The amount of cardiomyocytes uptake of HPP-liposome was 3.9-fold higher than plain-liposome, and the increase was 6.2-fold when hypoxia happens. It indicated that HPP was a potential ligand for liposome targeting to ischemic myocardium.     

Syntheses,Characterization and Crystal Structures of Three Structurally Similar Dinuclear Schiff Base Cadmium(II) Complexes with Bridging Azide or Thiocyanate Ligands

Three novel Schiff base cadmium(II) complexes, derived from the end‐on (μ‐1,1‐N₃) azide or end‐to‐end (μ‐1,3‐NCS) thio cyanate bridges and similar tridentate Schiff base ligands, have been synthesized under similar synthetic procedures and their crystal structures determined by X‐ray diffraction methods. They are the dinuclear double end‐on azide‐bridged [Cd₂(L1)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 1 ), the dinuclear double end‐on azide‐bridged [Cd₂(L2)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 2 ), and the dinuclear double end‐to‐end thiocyanate‐bridged [Cd₂(L3)₂(NCS)₂(μ_1,3‐NCS)₂] ( 3 ), where L1, L2 and L3 are three similar tridentate Schiff bases obtained by condensation of 2‐pyridylaldehyde with N,N‐diethylethane‐1,2‐diamine, of 2‐pyridylaldehyde with N‐isopropylethane‐1,2‐diamine, and of 2‐pyridylaldehyde with N,N‐dimethylpropane‐1,3‐diamine, respectively. Each cadmium(II) centre in the complexes is in a distorted octahedral coordination. There is a crystallographic inversion centre in each of the complexes. The similar small ligands used as the secondary ligands in the preparation of the cadmium(II) complexes with similar Schiff bases can result in similar structures.     

New solid-gas metathetical synthesis of binary metal polysulfides and sulfides at intermediate temperatures: utilization of boron sulfides

A new simple synthetic method for binary metal polysulfides and sulfides was developed by utilizing an in situ formation of boron sulfides and their subsequent reactions with metal-source oxides in a closed container at intermediate temperatures above 350 degrees C at which the boron sulfides react in a gaseous form. The versatility of the new method is demonstrated with oxides of various transition metals (Ti, V, Mn, Fe, Ni, Nb, Mo, Ru, and W) and rare-earth metals (Y, Ce, Nd, Sm, Eu, Tb, and Er) as starting materials that exhibit different chemical characteristics. Regardless of the oxidation states of metals in the starting materials, the sulfidation reactions occurred quantitatively with stoichiometric mixtures of boron and sulfur, and within 24 h the reactions yielded pure products of TiS(2), TiS(3), VS(4), FeS(2), NiS(2), NbS(3), MoS(2), RuS(2), WS(2), Y(2)S(3), and RS(2) (R = Ce, Nd, Sm, Eu, Tb, and Er) which were the thermodynamically stable phases under the reaction conditions. The scope and implications of the new sulfidation method are also discussed.     

铬系乙烯齐聚和聚合催化剂

综述了近年来国内外铬系催化剂的最新研究进展。介绍了该类催化剂齐聚和合的性能研究和应用，讨论了该催化剂长期引起争议的活性中心，活性价态，以及反应机理，并同时预测了铬系催化剂在工业和纳米技术方面的发展趋势。     

Enantioseparation of Amino Acid Derivatives with a Cellulose-Based Chiral Stationary Phase

Five structurally related amino acid derivatives were enantioseparated by HPLC with a commercially available chiral stationary phase, Chiralcel OD-H. The chromatographic experiments were performed in the normal phase mode. n-Hexane/polar alcohol was used as mobile phase. Excellent baseline enantioseparations could be obtained for all these solutes. The effects of the concentration of polar alcohol and the column temperature on the retentions and enantioseparations were studied in detail. From the van't Hoff plots the corresponding apparent thermodynamic parameters were derived. Mechanism aspects of chiral recognition were discussed based on the relationship between the thermodynamic parameters and the structures of the solutes. It was found that the substituent of the phenyl group on the residual group of the amino acid derivatives was close relevant to thermodynamic origin of enantioseparation. Much better enthalpy–entropy compensation effect was obtained by plotting the differential, rather than the original, thermodynamic parameters.     

Cadmium(II) and mercury(II) complexes of an NO2S2-donor macrocycle and its ditopic xylyl-bridged analogue

The NO2S2-donor macrocycle (L1) was synthesised from the ring closure reaction between Boc-N-protected 2,2'-iminobis(ethanethiol) (3) and 2,2'-(ethylenedioxy)bis(benzyl chloride) (4) followed by deprotection of the Boc-group. alpha,alpha'-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L1 to yield the corresponding N-linked product (L2). The X-ray structure of L2 (as its HBr salt) is described. A range of Cd(II) and Hg(II) complexes of L1 (6-9) and L2 (10-12) were prepared and characterised. Reaction of HgX2 (X = Br or I) with L1 afforded [Hg(L1)Br]2[Hg2Br6].2CH2Cl2 6 and [Hg(L1)I(2)] 7, respectively. For 6, the Hg(II) ion in the complex cation has a distorted tetrahedral coordination environment composed of S2N donor atoms from L1 and a bromo ligand. In 7 the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentate manner via one S and one N atom. The remaining two coordination sites are occupied by iodide ions. [Hg(L1)(ClO4)]ClO4 8 was isolated from the reaction of Hg(ClO4)2 and L1. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O2S2-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of Cd(NO3)(2).4H2O with L1 afforded [Cd(L1)(NO3)2](.)0.5CH2Cl2 9 in which L1 acts as a tridentate ligand, binding exo-fashion via its S2N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX2(X = Br or I) with L2 yielded the isostructural 2 : 1 (metal : ligand) complexes, [Hg2(L2)Br4] 10 and [Hg2(L2)I(4)] 11. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L2 and two coordinated halides. Contrasting with this, the reaction of L2 with Cd(NO3)(2).4H2O yielded a 1-D coordination network, {[Cd2(L2)(NO3)4].2CH2Cl2}n 12 in which each ring of L2 is exo-coordinated via two S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium via a nitroso (mu2-O) bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The [Cd(L2)0.5(NO3)2] units are linked by an inversion to yield the polymeric arrangement.     

Characterization and epitope mapping of two monoclonal antibodies against human CD99

CD99 plays a critical role in the diapedesis of monocytes, T cell differentiation, and the transport of MHC molecules. Engagement of CD99 by agonistic monoclonal antibodies has been reported to trigger multifactorial events including T cell activation as well as cell-cell adhesion during hematopoietic cell differentiation. In this study, to identify the functional domains participating in the cellular events, we mapped the epitopes of CD99, which are recognized by two agonistic CD99 monoclonal antibodies, DN16 and YG32. Using recombinant fusion proteins of GST with whole or parts of CD99, we found that both antibodies interact with CD99 molecules independently of sugar moieties. DN16 mAb detected a linear epitope located in the amino terminal region of CD99 while YG32 mAb bound another linear epitope in the center of the extracellular domain. To confirm that the identified epitopes of CD99 are actually recognized by the two mAbs, we showed the presence of physical interaction between the mAbs and the fusion proteins or synthetic peptides containing the corresponding epitopes using surface plasmon resonance analyses. The dissociation constants of DN16 and YG32 mAbs for the antigen were calculated as 1.27 x 10(-7) and 7.08 x 10(-9) M, respectively. These studies will help understand the functional domains and the subsequent signaling mechanism of CD99.     

Chiral polymer hosts for circularly polarized electroluminescence devices

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (g_abs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (g_PL) of the order of 10⁻³ were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of g_abs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (g_EL) of 1.09 × 10⁻⁴ and −1.02 × 10⁻⁴ at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications.