Synthesis of low grafting density molecular brush from a poly(N‐alkyl urea peptoid) backbone

The synthesis of a molecular brush was accomplished by combining step‐growth polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization in a “grafting from” methodology. A symmetrical N‐alkyl urea peptoid sixmer containing alkyne functional groups was prepared using a divergent strategy, and the structure of the product was confirmed using NMR spectroscopy and mass spectrometry. A step‐growth process was used to prepare a linear poly(N‐alkyl urea peptoid) by reacting the diamine‐functionalized N‐alkyl urea peptoid sixmer with a diisocyanate. RAFT chain transfer agents were coupled to the poly(N‐alkyl urea peptoid) backbone through a copper‐catalyzed azide/alkyne cycloaddition reaction. The afforded macro‐RAFT agent was used to sequentially polymerize styrene and tert‐butyl acrylate block copolymer arms from the poly(N‐alkyl urea peptoid) backbone. The tert‐butyl groups were removed using dilute trifluoroacetic acid affording hydrophilic polyacrylic acid segments. The molecular brushes were observed to generate micelles in aqueous solution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Layer-by-layer assembled multilayer films of methoxypoly(ethylene glycol)-block-poly(α,l-glutamic acid) and chitosan with reduced cell adhesion

A methoxypoly(ethylene glycol)-block-poly(α,L-glutamic acid) (mPEGGA) diblock copolymer is synthesized. Using QCM measurements, it is shown that (CS/mPEGGA)(n) film construction takes place over two build-up stages (exponential-to-linear). UV-vis spectra reveal the regular increase of the multilayer film growth at different molecular weights of mPEGGA. Contact angle and surface morphology investigation prove that the hydrophilicity of CS/mPEGGA multilayer film-modified substrate becomes better and the surface becomes rough. Significantly reduced cell adhesion is observed on the CS/mPEGGA multilayer film coated surface.     

Quantification of human growth hormone by amino acid composition analysis using isotope dilution liquid-chromatography tandem mass spectrometry

We describe an accurate method for protein quantification based on conventional acid hydrolysis and an isotope dilution-HPLC-mass spectrometry (ID-HPLC-MS) method. Sample purity was confirmed using capillary zone electrophoresis, HPLC and MS. The analyte protein, human growth hormone (hGH), was effectively hydrolyzed by incubation with 8 M hydrochloric acid at 130 °C for 48 h, where at least 1 μM of hGH was treated to avoid possible degradation of released amino acids during hydrolysis. Using a reversed-phase column, the analytes (isoleucine, phenylalanine, proline and valine) were separated within 5 min using an isocratic eluent comprising 10% acetonitrile containing 0.1% trifluoroacetic acid. The detection limit (signal to noise ratio of 3) of amino acids was 5.5-6.2 fmol per injection. The quantification precision (RSD) of amino acids for intra- and inter-day assays was less than 0.98% and 0.39%, respectively. Comparison with other biochemical and instrumental methods revealed substantially higher accuracy and reproducibility of the ID-HPLC-MS/MS method as expected. The optimized hydrolysis and analytical conditions in our study were suitable for accurate quantification of hGH.     

多级复合半导体纳米材料的制备

金属氧化物、Ⅲ-Ⅴ、Ⅱ-Ⅵ等半导体纳米材料由于其独特的功能性质已广泛应用于光学、电子、太阳能转化、催化等领域,是当今先进材料领域的研究前沿与热点。随着科技的发展,人们对材料的高效、多功能要求已成为必然,对半导体材料发展要求亦如此。多组分复合、多层次结构协同是实现半导体纳米材料多功能化与高效化的有效途径。构筑多级结构组合纳米半导体,不但可以调控其能带结构而提高半导体材料的光电与催化性能,而且由于多级低维纳米结构聚集时形成的空间位阻效应可以有效克服纳米晶“易团聚”难题。本文提出多级结构组合纳米晶的概念、分类,结合近年来该领域的研究实践,较系统地综述了多级复合半导体纳米结构制备的最新研究进展。首先简要介绍了多级复合半导体纳米材料的概念与典型结构; 其次对典型多级复合半导体纳米材料的制备方法进行了重点评述,分别综述了液相法、气相法以及最新发展起来的静电纺丝等方法在多级结构半导体复合纳米材料制备中的应用实践。再其次,对以具有半导体特性的石墨烯及其功能化衍生物为基体的新型多级复合半导体纳米材料的制备做了综述。最后对半导体/半导体多级结构复合纳米材料的发展方向做了展望。     

Fluorine sites in glasses and transparent glass-ceramics of the system Na2O/K2O/Al2O3/SiO2/BaF2

The transparent glass-ceramics obtained in the silicate system Na₂O/K₂O/SiO₂/BaF₂ show homogeneously dispersed BaF₂ nano crystals with a narrow size distribution. The X-ray diffraction and the nuclear magnetic resonance spectroscopy were applied to glasses and the respective glass-ceramics in order to clarify the crystallization mechanism and the role of fluorine during crystallization. With an increasing annealing time, the concentration and also the number of crystals remain approximately constant. With an increasing annealing temperature, the crystalline fraction increases until a saturation limit is reached, while the number of crystals decreases and the size of the crystals increases. Fluoride in the glassy network occurs as Al-F-Ba, Al-F-Na and also as Ba-F structures. The latter are transformed into crystalline BaF₂ and fluoride is removed from the Al-F-Ba/Na bonds. However, some fluorine is still present in the glassy phase after the crystallization.     

Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum

We investigate the degradation path of MAPbI₃ (MA=methylammonium) films over flat TiO₂ substrates at room temperature by means of X‐ray diffraction, spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI₂. We describe how this degradation product is structurally coupled with the original MAPbI₃ lattice through the orientation of its constituent PbI₆ octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH₃NH₂ or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.     

Novel Method for the Fabrication of a Charge‐Transfer Complex Crystal by Photoirradiation

A novel method for the fabrication of a charge‐transfer complex crystal was developed. Photoirradiation of a solution of TPP[Co(tbp)(CN)₂] and TPP[Co(Pc)(CN)₂] (tbp=tetrabenzoporphyrin, Pc=phthalocyanine, TPP=tetraphenylphosphonium) gave a molecular conducting crystal of a charge‐transfer complex TPP[Co(tbp)(CN)₂]₂, which was produced by the process in which the photoexcited electron in tbp was transferred from the LUMO of tbp to that of Pc.     

Direct Anisotropic Growth of CdS Nanocrystals in Thermotropic Liquid Crystal Templates for Heterojunction Optoelectronics

The direct growth of CdS nanocrystals in functional solid‐state thermotropic liquid crystal (LC) small molecules and a conjugated LC polymer by in situ thermal decomposition of a single‐source cadmium xanthate precursor to fabricate LC/CdS hybrid nanocomposites is described. The influence of thermal annealing temperature of the LC/CdS precursors upon the nanomorphology, photophysics, and optoelectronic properties of the LC/CdS nanocomposites is systematically studied. Steady‐state PL and ultrafast emission dynamics studies show that the charge‐transfer rates are strongly dependent on the thermal annealing temperature. Notably, annealing at liquid‐crystal state temperature promotes a more organized nanomorphology of the LC/CdS nanocomposites with improved photophysics and optoelectronic properties. The results confirm that thermotropic LCs can be ideal candidates as organization templates for the control of organic/inorganic hybrid nanocomposites at the nanoscale level. The results also demonstrate that in situ growth of semiconducting nanocrystals in thermotropic LCs is a versatile route to hybrid organic/inorganic nanocomposites and optoelectronic devices.