Synthesis and mesomorphic properties of novel fishbone-like liquid crystalline polysilsesquioxanes VI. Fishbone-like,ester-based liquid crystalline polysilsesquioxanes

Two novel kinds of fishbone-like, ester-based, liquid crystalline, random copolysilsesquioxanes, LC₁-CH₃-P and LC₂-CH₃-P, have been synthesized for the first time by stepwise coupling polymerization (SCP) from trichlorosilane monomers (RSiCl₃) containing mesogenic ester groups, using three main steps including preaminolysis, hydrolysis and polycondensation. Two new monomers 4-(11-trichlorosilylundecloyloxy)phenyl 4-methoxybenzoate (M₁) and 4-(3-trichlorosilylpropoxy)phenyl 4-methoxybenzoate (M₂) have been synthesized by hydrosilylation reaction of trichlorosilane and the mesogens 4-n-undecenoyloxyphenyl 4-methoxybenzoate and 4-allyloxyphenyl 4-methoxy-benzoate, respectively, in the presence of dicyclopentadienylplatinum(II) chloride (Cp₂Ptcl₂) catalyst. The structures and mesomorphic properties of LC₁-CH₃-P and LC₂-CH₃-P were investigated by FTIR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, gel permeation chromatography, polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. It is proposed from the characterization data that these two polymers not only have an ordered ladder-like, double main chain, but also show thermotropic smectic behaviour with high clearing points and wide mesophase ranges (ΔT), which may hold promise for potential applications as highly stable gas chromatographic stationary phases.     

Spontaneous formation of liquid crystalline phases and phase transitions in highly concentrated plasmid DNA

The liquid crystalline (LC) properties of two supercoiled plasmid DNA samples, pBSK (2958 bp) and pGEM (3000 bp), have been studied using polarised light microscopy (PLM), circular dichroism (CD) and UV–Vis spectroscopy. The influence of methods of isolation on plasmid LC behaviour is described, and using PLM we have demonstrated the spontaneous formation of cholesteric fingerprint-like textures. Preliminary studies of LC phase transitions in pGEM show the irreversibility of LC phase formation, as a consequence of changes in the tertiary structure of supercoiled plasmids. Using UV–Vis spectroscopy a hyperchromic effect was observed with increasing temperature. The CD spectra clearly showed structural changes, and probably mismatching of DNA bases, during cooling. Finally, we have observed an irreversible phase transition in plasmid DNA which is very different from that previously reported in linear DNA.     

Study of the electrocaloric effect in ferroelectric liquid crystals

ABSTRACT

Electrocaloric effect (ECE) in two ferroelectric liquid crystalline (FLC) materials has been evaluated by mean of two indirect characterization methods: the photopyroelectric (PPE) technique and the polarization current reversal one. The obtained results show a good correspondence of the adiabatic temperature change associated with the ECE evaluated from both methods. This validates the possibility to use the PPE technique to investigate the ECE in FLCs. This study also demonstrates that FLCs can be used as electrocaloric material. More particularly, it shows that as for their solid homologous, liquid crystals displays more pronounced ECE in the vicinity of a first order transition than that measured near to second-order one.     

X-ray characterisation of local molecular orientation in the electroclinic effect of surface-stabilised SmA liquid crystals

The local molecular orientation in the electroclinic effect of the chiral smectic A phase in a surface-stabilised cell has been determined using a time-resolved synchrotron X-ray microbeam diffraction technique. Space- and time-resolved X-ray wide-angle halo scattering under an electric field reveals the static and dynamic intralayer molecular orientation. The molecular orientation varies spatially in accordance with the stripe texture and is dependent on the applied voltage. It has been found that the deviation of the molecular orientation from the rubbing direction depends strongly on the sample history. The relation between the apparent molecular orientation and the layer structure is discussed.     

Fabrication of ozone gas sensor based on FeOOH/single walled carbon nanotube-modified field effect transistor

A novel ozone (O₃) sensor is fabricated using commercial metal oxide field effect transistor (MOSFET), modified with single-walled carbon nanotubes (SWCNTs). In this study, integrated circuit (IC: BS250) was selected as the selective probe for O₃ detection. For this purpose, a plastic cover on the surface of the drain was drilled to bare the drain surface, followed by its modification with nitrogen and sulfur-functionalized SWCNTs by chemical vapor deposition (CVD) process. The CVD-synthesized SWCNTs were then electrodeposited with FeOOH nanostructures. According to the figures of merit, the fabricated sensor gave a linear output from 20 to 450 parts per billion (ppb). Detection limit was also 4.1?ppb. Relative standard deviation (RSD) for seven replicate analyses was 3.61%. Based on 90% of maximum response (t₉₀), the response time was ～1.5?min. Calibration sensitivity was measured to 1.3?mV/ppb. No interference was observed, when introducing at least 500 folds of interferences of gaseous species such as H₂O, HCl, H₂S, O₂, H₂, CO, CO₂, NO₂, SO₂, Cl₂, C₂H₂, CH₄ and volatile organic compounds (VOCs) to 250?ppb of O₃ solution. Reliability of the sensor was also evaluated via determination of O₃ in different air samples.     

Gadolinium(III)‐Hydroxy Ladders Trapped in Succinate Frameworks with Optimized Magnetocaloric Effect

Two kinds of inorganic gadolinium(III)‐hydroxy “ladders”, [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd₂(OH)₂(suc)₂(H₂O)]_n ? 2n H₂O ( 1 ) and [Gd₆(OH)₈(suc)₅(H₂O)₂]_n ? 4n H₂O ( 2 ), respectively. Such coordination polymers could be regarded as alternating inorganic–organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg^?1 K^?1 for complex 1 and 48.0 J kg^?1 K^?1 for complex 2 . The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm^?3 K^?1 for complexes 1 and 2 , respectively.     

Probing Helical Hydrophobic Binding Sites in Branched Starch Polysaccharides Using NMR Spectroscopy

Branched starch polysaccharides are capable of binding multiple hydrophobic guests, but their exploitation as multivalent hosts and in functional materials is limited by their structural complexity and diversity. Linear α(1–4)‐linked glucose oligosaccharides are known to bind hydrophobic guests inside left‐handed single helices in solution and the solid state. Here, we describe the development of an amphiphilic probe that binds to linear α(1–4)‐linked glucose oligosaccharides and undergoes a conformational switch upon complexation, which gives rise to dramatic changes in the ¹H NMR spectrum of the probe. We use this probe to explore hydrophobic binding sites in the branched starch polysaccharides amylopectin and β‐limit dextrin. Diffusion‐ordered (DOSY), nuclear Overhauser effect (NOESY) and chemical shift perturbation (HSQC) NMR experiments are utilised to provide evidence that, in aqueous solution, branched polysaccharides bind hydrophobic guests in well‐defined helical binding sites, similar to those reported for complexation by linear oligosaccharides. By examining the binding affinity of the probe to systematically enzymatically degraded polysaccharides, we deduce that the binding sites for hydrophobic guests can be located on internal as well as external branches and that proximal α(1–6)‐linked branch points weaken but do not prevent complexation.     

Synthesis and Optical Properties of Water‐Soluble Polyglycerol‐Dendronized Rylene Bisimide Dyes

Four new water‐soluble polyglycerol‐dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core‐unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core‐unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron‐donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water.     

Near‐Infrared‐Controlled,Targeted Hydrophobic Drug‐Delivery System for Synergistic Cancer Therapy

Hydrophobicity has been an obstacle that hinders the use of many anticancer drugs. A critical challenge for cancer therapy concerns the limited availability of effective biocompatible delivery systems for most hydrophobic therapeutic anticancer drugs. In this study, we have developed a targeted near‐infrared (NIR)‐regulated hydrophobic drug‐delivery platform based on gold nanorods incorporated within a mesoporous silica framework (AuMPs). Upon application of NIR light, the photothermal effect of the gold nanorods leads to a rapid rise in the local temperature, thus resulting in the release of the entrapped drug molecules. By integrating chemotherapy and photothermotherapy into one system, we have studied the therapeutic effects of camptothecin‐loaded AuMP‐polyethylene glycol‐folic acid nanocarrier. Results revealed a synergistic effect in vitro and in vivo, which would make it possible to enhance the therapeutic effect of hydrophobic drugs and decrease drug side effects. Studies have shown the feasibility of using this nanocarrier as a targeted and noninvasive remote‐controlled hydrophobic drug‐delivery system with high spatial/temperal resolution. Owing to these advantages, we envision that this NIR‐controlled, targeted drug‐delivery method would promote the development of high‐performance hydrophobic anticancer drug‐delivery system in future clinical applications.