Helical twisting power of chiral titanium complexes in nematic compounds

We report the use of chiral bis-chelated imine-alkoxytitanium complexes as dopants for the conversion of a nematic into a cholesteric phase. High helical twisting power (HTP) is obtained in the liquid crystalline mixture ZLI-1695 (Merck, Darmstadt). Enlargement of the HTP is achieved by novel analogues of the titanium complexes, whose synthesis is described.     

Proton‐Transfer Polymerization (HTP): Converting Methacrylates to Polyesters by an N‐Heterocyclic Carbene

A new polymerization termed proton (H)‐transfer polymerization (HTP) has been developed to convert dimethacrylates to unsaturated polyesters. HTP is catalyzed by a selective N‐heterocyclic carbene capable of promoting intermolecular Umpolung condensation through proton transfer and proceeds through the step‐growth propagation cycles via enamine intermediates. The role of the added suitable phenol, which is critical for achieving an effective HTP, is twofold: shutting down the radically induced chain‐growth addition polymerization under HTP conditions (typically at 80–120 °C) and facilitating proton transfer after each monomer enchainment. The resulting unsaturated polyesters have a high thermal stability and can be readily cross‐linked to robust polyester materials.     

Trisulfide‐Bond Acenes for Organic Batteries

The molecular design of organic battery electrodes is a big challenge. Here, we synthesize two metal‐free organosulfur acenes and shed insight into battery properties using first‐principles calculations. A new zone‐melting chemical‐vapor‐transport (ZM‐CVT) apparatus was fabricated to provide a simple, solvent‐free, and continuous synthetic protocol, and produce single crystals of tetrathiotetracene (TTT) and hexathiapentacene (HTP) at a large scale. Single crystals of HTP showed better Li‐ion battery performance and higher cycling stability than those of TTT. A two‐step, three‐electron lithiation mechanism instead of the commonly depicted two‐electron mechanism is proposed for the HTP Li‐ion battery. The superior performance of HTP is linked to unique trisulfide bonding scenarios, which are also responsible for the formation of empty channels along the stacking direction. In‐depth theoretical analysis suggests that organosulfur acenes are potential prototypes for organic battery materials with tunable properties, and that the tuning of sulfur bonds is critical in designing these new materials.     

Catalytic Oxidation of Ascorbic Acid on 2D and 3D Monolayers of 4‐Hydroxythiophenol

Monolayers of 4‐hydroxythiophenol (4‐HTP) immobilized on gold electrode (2D SAMs) or gold nanoclusters (3D SAMs) lead to catalytic oxidation of ascorbic acid (AA). The catalytic role of the modified clusters was revealed by comparing the electrodes covered by 1,9‐nonanedithiol and the same nonanedithiol monolayer decorated by 4‐HTP protected clusters. The 4‐HTP protected gold nanoclusters supported on a metal surface using a monolayer of 1,9‐nonanedithiol as the bridge, transferred charge to ascorbic acid (AA) molecule in the solution more efficiently than when the same 4‐HTP monolayer was formed directly on the gold electrode.     

Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensors

A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5′‐Divinyl‐2,2′‐bipyridyl with tris(4‐bromophenyl)amine and with 4,4′‐dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, ¹H NMR, and ¹³C NMR. The polymer HTP had a number‐average molecular weight of 1895 and a weight‐average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV–vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer‐based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222–230, 2009     

Photochemically and Thermally Driven Full‐Color Reflection in a Self‐Organized Helical Superstructure Enabled by a Halogen‐Bonded Chiral Molecular Switch

Supramolecular approaches toward the fabrication of functional materials and systems have been an enabling endeavor. Recently, halogen bonding has been harnessed as a promising supramolecular tool. Herein we report the synthesis and characterization of a novel halogen‐bonded light‐driven axially chiral molecular switch. The photoactive halogen‐bonded chiral switch is able to induce a self‐organized, tunable helical superstructure, that is, cholesteric liquid crystal (CLC), when doped into an achiral liquid crystal (LC) host. The halogen‐bonded switch as a chiral dopant has a high helical twisting power (HTP) and shows a large change of its HTP upon photoisomerization. This light‐driven dynamic modulation enables reversible selective reflection color tuning across the entire visible spectrum. The chiral switch also displays a temperature‐dependent HTP change that enables thermally driven red, green, and blue (RGB) reflection colors in the self‐organized helical superstructure.     

Bis-chelated imine-alkoxytitanium complexes: novel chiral dopants with high helical twisting power in liquid crystals

Enantiomerically and diastereomerically pure bis-chelated imine-alkoxytitanium complexes 6 and 7 have been synthesized and used as chiral dopants for converting nematic into cholesteric phases. The dopants were tested in mainly commercially available nematic liquid crystalline compounds or mixtures: LC1 (BASF), ZLI-1695 and ZLI-1840 (Merck), as well as N-(4-methoxybenzylidene)-4'-butylaniline (MBBA). The values of the helical twisting power (HTP) were determined by the Grandjean-Cano method. Exceptionally high helical twisting powers were obtained. Thus, the titanium complex 6 h displayed a HTP value of 740 microm(-1) in MBBA, the highest HTP value reported. The helical twisting power has been found to depend strongly on the structure of the nematic phase and the substitution pattern of the chiral ligand in the titanium complexes 6 and 7. Crystal structure analysis of 6 f confirmed the A,R,R configuration of the metal complex. The chiral imine ligands 4 and 5 were derived from the regioisomeric amino alcohols 1 and 2.     

Identification of isomeric 5‐hydroxytryptophan‐ and oxindolylalanine‐containing peptides by mass spectrometry

Cells continuously produce reactive oxidative species that can modify all cellular components. In proteins, for example, cysteine, methionine, tryptophan (Trp), and tyrosine residues are particularly prone to oxidation. Here, we report two new approaches to distinguish two isomeric oxidation products of Trp residues, i.e. 5‐hydroxytryptophan (5‐HTP) and oxindolylalanine (Oia) residues, in peptides. First, 2‐nitrobenzenesulfenyl chloride, known to derivatize Trp residues in position 2 of the indole ring, was used to label 5‐HTP residues. The mass shift of 152.98 m/z units allowed identifying 5‐HTP‐ besides Trp‐containing peptides by mass spectrometry, whereas Oia residues were not labeled. Second, fragmentation of the Oia‐ and 5‐HTP‐derived immonium ions at m/z 175.08 produced ions characteristic for each residue that allowed their identification even in the presence of y₁ ions at m/z 175.12 derived from peptides with C‐terminal arginine residues. The pseudo MS³ spectra acquired on a quadrupole time‐of‐flight hybrid mass spectrometer displayed two signals at m/z 130.05 and m/z 132.05 characteristic for Oia‐containing peptides and a group of six signals (m/z 103.04, 120.04, 130.04, 133.03, 146.04, and 148.04) for 5‐HTP‐cointaining peptides. In both cases, the relative signal intensities appeared to be independent of the sequence providing a specific fingerprint of each oxidative modification. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of ethyl‐bridged diphenylphosphine oxide on flame retardancy and thermal properties of epoxy resin

Three commercialized flame retardants, 1,2‐bis(diphenylphosphinoyl)ethane (EDPO), 6,6‐(1,2‐phenethyl)bis‐6H‐dibenz[c,e][1,2]oxaphosphorin‐6,6‐dioxide (HTP‐6123), and hexa‐phenoxy‐cyclotriphosphazene (HPCTP), were used to prepare the flame retardant diglycidyl ether of bisphenol A (DGEBA) epoxy resin (EP) under the same experimental conditions. The effects of T_g, thermal stability, and water absorption properties of EP caused by the three flame retardants were investigated and compared, together with their flame retardant efficiency. Results showed that the introduction of the three flame retardants improved the flame retardant performance of EP but led to decreases in T_g and decomposition temperature. EDPO showed higher flame retardant efficiency than the other two flame retardants. EP/EDPO showed higher thermal stability, better flame retardant performance, higher T_g value, and lower water absorption than EP/HTP‐6123 and EP/HPCTP. The study discovered that EDPO and HTP‐6123 primarily act through the gas phase flame retardant mechanism, while HPCTP is primarily driven by the condensed phase mechanism.     

Pipelines, robots, crystals and biology: what use high throughput solving structures of challenging targets?

With recent advances in the technology and software underlying crystallographic structure solution, demands on both output and functional significance of X-ray structures are soaring. To achieve the required speed and quality also with ever larger and more difficult targets, combining HTP screening methods (robotics based or not) adopted from structural genomics initiatives with thorough expertise and dedicated characterization effort for each individual target is almost a must. I present concepts, practical considerations, and experiences on implementing an HTP technology platform for structural and functional studies on complexes, membrane proteins and other challenging targets. Emphasis lies on the environment of small academic groups engaged exclusively in hypothesis driven projects focused on specific biological systems. Suitability of given HTP protocols for particular target classes, benchmarking and quality control for procedures, and project management issues at the interface between extensive, broad parameter screening and intensive individual target work required by non-SG amenable targets are discussed.     

4‐hydroxythiophenol grafted PS‐b‐PAA block copolymers: Preparation and formation of porous and bowl‐shaped assemblies

4‐Hydroxythiophenol (HTP) grafted poly(styrene‐b‐acrylic acid) (PS‐b‐PAA) block copolymers (BCPs) (PS‐b‐PAA‐g‐HTP) was synthesized using the esterification reaction between the carboxyl groups and hydroxyl groups. Self‐assembly behavior of the graft copolymer in 1,4‐dioxane/water was investigated. Assemblies of different morphologies, porous, and bowl‐shaped structures, could be easily prepared. A possible mechanism for the formation of the porous and bowl‐shaped structures was discussed. The present study showed a facile method for the preparation of functionalized PS‐b‐PAA BCPs, which could easily self‐assembly into novel structures in aqueous solution. These assemblies may be used to generate new functional materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1551–1557     

含胆固醇和 4-(反式-正烷基环己基)苯甲酸结构单元的双液晶基元液晶化合物的合成及其性质

本文合成了一系列含有胆固醇和4-（反式-正烷基环己基）苯甲酸结构单元的新型双液晶基元液晶化合物。这些化合物中两个介晶基元是利用不同长度的氧烷酰基连接在一起。利用FT-IR、MS、1H NMR、POM、DSC 表证了所得化合物的结构和介晶性,并选择几种双液晶基元液晶测定了它们的机械黏度和在主体液晶中的螺旋扭曲力（HTP)。结果表明,绝大多数化合物显示较低相变温度的胆甾相（N*）,并且被选择的化合物的平均机械黏度和螺旋扭曲力类似于或优于胆甾醇任酸酯。     

Influence of a Change in Helical Twisting Power of Photoresponsive Chiral Dopants on Rotational Manipulation of Micro‐Objects on the Surface of Chiral Nematic Liquid Crystalline Films

Herein we report a group of five planar chiral molecules as photon‐mode chiral switches for the reversible control of the self‐assembled superstructures of doped chiral nematic liquid crystals. The chiral switches are composed of an asymmetrically substituted aromatic moiety and a photoisomerizing azobenzene unit connected in a cyclic manner through methylene spacers of varying lengths. All the molecules show conformational restriction in the rotation of the asymmetrically substituted aromatic moiety in both the E and Z states of the azobenzene units resulting in planar chirality with separable enantiomers. Our newly synthesized compounds in pure enantiomeric form show high helical twisting power (HTP) in addition to an improved change in HTP between the E and Z states. The molecule with a diphenylnaphthalene unit shows the highest ever known initial helical twisting power among chiral dopants with planar chirality. In addition to the reversible tuning of reflection colors, we employed the enantiomers of these five compounds in combination with four nematic liquid crystalline hosts to study their properties as molecular machines; the change in HTP of the chiral dopant upon photoisomerization induces rotation of the texture of the liquid crystal surfaces. Importantly, this study has revealed a linear dependence of the ratio of the difference between HTPs before and after irradiation against the absolute value of the initial HTP, not the absolute value of the change in helical twisting power between two states, on the angle of rotation of micro‐objects on chiral nematic liquid crystalline films. This study has also revealed that a change in irradiation intensity does not affect the maximum angle of rotation, but it does affect the speed of rotational reorganization of the cholesteric helix.     

A novel hyperbranched copolymer constituted of triphenylamine and divinyl bipyridyl units

A hyperbranched copolymer (HTP) containing triphenylamine and divinyl bipyridyl units has been synthesized via Heck coupling reaction from 5,5′-divinyl-2,2′-bipyridyl and tris(4-bromophenyl)amine. The polymer had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and was readily soluble in common organic solvents, such as THF, DMF and chloroform. The chemical structure of HTP was confirmed by FT-IR, ¹H NMR. Its thermal, electrochemical and optical properties have been investigated. The thermal analysis revealed that the polymer had a good thermal stability with the onset decomposition temperature at ca. 267 °C. The Uv-vis absorption and photoluminescence (PL) spectra exhibited that the Stokes shift between the absorption and emission of HTP was relatively large: 103 for HTP solution and 135 nm for HTP film. The electrochemical analysis showed that the electrochemical band gap of HTP was 0.92 eV. The fluorescence of the polymer in solution can be quenched by various transition metal ions and HTP showed different sensitivity in transition metal ions sensing.     

铝表面自组装端羟基聚酯胺膜的XPS和STM表征

制备了端羟基聚酯胺(HTP)在铝基片上的自组装膜并进行了XPS和STM表征,确认了HTP在铝基片上的吸附组装;由XPS的吸附时间扫描,自组装单分子膜(SAMs)随浸泡时间的延长而增厚,在2 h后达到平衡。由HTP在铝基片的STM三维图可以看到HTP自组装膜以团块形式组成,其间包含孔洞缺陷。提出了铝基片上HTP–SAMs的多羟基结构与膜上孔洞的共同作用是提高环氧类涂层附着力的主要原因。     

Helical twisting power of laterally aryl substituted chiral mesogens

The relationship between the helical twisting power (HTP) of cholesteric liquid crystals and the molecular structure of the chiral mesogens has been investigated. Rod-like mesogens are compared with analogues bearing a bulky lateral branch. Additionally, the HTP of induced cholesteric phases formed by chiral guest molecules in nematic host phases has been studied in terms of different molecular structures. The paper gives information on the influence of bulky lateral groups in mesogens on the HTP.     

TADDOLs with Unprecedented Helical Twisting Power in Liquid Crystals. Preliminary communication

A large number of TADDOL (α,α,α′, α′-tetraaryl-1,3-dioxolan-4,5-dimethanol) derivatives has been tested as chiral dopants for inducing conversion of nematic to cholesteric phases. With the Merck liquid-crystal materials ZLI-1695 and K15 , it was demonstrated that some TADDOLs have unprecedentedly high helical twisting powers (HTP). Thus, the TADDOL with four 9-phenanthryl α-substituents has a HTP in the achiral mesophase 4-(4-pentylphenyl)benzonitrile of 405 μm^?1 between 24 and 34°. The temperature-dependent HTP measurements have been performed by analyzing Grandjean textures microscopically (Cano method). The structure-dependent HTP of various types of TADDOL dopants is discussed. There are similarities between size and sign of HTP on the one hand, and between degree and relative topicity of enantioselectivity in reactions, on the other hand, as caused by TADDOLs and by 1,1′-binaphthols.     

Lehmann rotatory power: a new concept in cholesteric liquid crystals

By doping a nematic phase with a chiral molecule one obtains a cholesteric phase. Each chiral molecule is characterised by its helical twisting power (HTP) which is defined as HTP?=?q/(2πC) where q is the equilibrium pitch of the cholesteric phase and C the concentration (in wt%) of chiral molecules. In a similar way, we define the Lehmann rotatory power (LRP) as LRP?=?v/(2πC) where v is the thermomechanical Lehmann coefficient. By making compensated mixtures, we measured the HTP and the LRP of five chiral molecules (R811, S2011, CC, CB15 and CE4) dissolved in an eutectic mixture 8CB/8OCB. We found that, although these quantities were different, their ratio R?=?LRP/HTP changed little from one molecule to another. This result shows that the Lehmann effect is closely, but not completely, related to the twist of the phase.     

Long‐Lived Engineering of Glycans to Direct Stem Cell Fate

Glycans mediate many critical, long‐term biological processes, such as stem cell differentiation. However, few methods are available for the sustained remodeling of cells with specific glycan structures. A new strategy that enables the long‐lived presentation of defined glycosaminoglycans on cell surfaces using HaloTag proteins (HTPs) as anchors is reported. By controlling the sulfation patterns of heparan sulfate (HS) on pluripotent embryonic stem cell (ESC) membranes, it is demonstrated that specific glycans cause ESCs to undergo accelerated exit from self‐renewal and differentiation into neuronal cell types. Thus, the stable display of glycans on HTP scaffolds provides a powerful, versatile means to direct key signaling events and biological outcomes such as stem cell fate.     

On the parity in helical twisting power of Ru(III) 1,3-diketonates of C2 symmetry in nematic liquid crystals

It is demonstrated that the sign of helical twisting power (HTP) of an enantiomeric Ru(III) complex of type [Ru(acac)(2)L] can be switched by choosing L from either L(per) or L(para), which is elongated either perpendicular or parallel to the C(2) symmetry axis, and four states become available in combination with DeltaLambda-chirality of the metal center. Complexes 1-n, in which 4,4'-dialkoxylated dibenzoylmethanate ligands are used as L(per), and 2 having L(para) = 3-(4'-decyloxyphenyl)pentane-2,4-dionate ligand were prepared for this purpose. They were optically resolved into the enantiomers by means of a clay column chromatography, and their performance as chiral dopants was evaluated in nematic liquid crystals including a room-temperature system, N-methoxybenzylidene-4-n-butylaniline (MBBA), which allowed facile measurements of the helical pitch lengths and CD spectra in the induced chiral nematic states. The induced CD signals have provided a clear evidence for the helical inversion between the two structure types, 1 and 2, of the same chirality. The twisting power of these six-coordinate metal complexes and their structure versus twist sense correlations are interpreted by the shape model. Intrinsically high HTP of Delta-[Ru(acac)(2)L(per)] has also allowed for observation of the pitch band due to the selective reflection in the visible wavelength range at the doping level of 2 mol % in MBBA.