Self‐assembly and secondary structures of linear polypeptides tethered to polyhedral oligomeric silsesquioxane nanoparticles through click chemistry

In this study, we used click chemistry to synthesize a new macromolecular self‐assembling building blocks, linear polypeptide‐b‐polyhedral oligomeric silsesquioxane (POSS) copolymers, from a mono‐azido–functionalized POSS (N₃‐POSS) and several alkyne‐poly(γ‐benzyl‐L ‐glutamate) (alkyne‐PBLG) systems. The incorporation of the POSS unit at the chain end of the PBLG moiety allowed intramolecular hydrogen bonding to occur between the POSS and PBLG units, thereby enhancing the α‐helical conformation in the solid state, as determined through Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction analyses. POSS‐b‐PBLG underwent hierarchical self‐assembly, characterized using small‐angle X‐ray scattering, to form a bilayer‐like nanostructure featuring α‐helical or β‐sheet conformations and POSS aggregates. Thermogravimetric analysis indicated that the thermal degradation temperature increased significantly after incorporation of the POSS moiety, which presumably formed an inorganic protection layer on the nanocomposite's surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Using isothermal titration calorimetry to real-time monitor the heat of metabolism: a case study using PC12 cells and Aβ(1-40)

Isothermal titration calorimetry (ITC) is one of the most powerful means for direct determination of thermodynamic information associated with most physiochemical and biological processes. The deposition and aggregation of β-amyloid (Aβ) on cell membranes was considered as one of the primary factors in having Alzheimer's disease (AD). Recently, a growing body of evidence has suggested that plasma membrane could accelerate the accumulation of Aβ on the plasma membranes. However, the mechanism of AD is still a controversial issue. This study provided a biothermodynamic approach to real-time monitor the heat of metabolism involved in the co-incubation of PC12 cells and Aβ(1-40) by ITC. The effects of Aβ conformation and concentration of oligomeric Aβ on cytotoxicity were successfully distinguished by ITC. This approach with rapid and direct measurement may provide not only real-time information for the effects of Aβ species on living cells but also a platform for the screening of drug candidates for AD.     

Infrared spectroscopic study of thermal transitions in poly(methyl methacrylate)

The ester CD₃ stretching modes in a partially deuterated poly(methyl methacrylate) sample have been studied as a function of temperature and bands in the CD stretching region assigned to fundamentals in Fermi resonance with overtone/combination modes. Changes in band parameters (widths, shapes) are observed at specific temperatures. Time correlation functions and their variation with temperature were calculated for the most intense modes observed in this region of the spectrum. The correlation functions were modeled by assuming that there is a fast relaxation process characterized by a single relaxation time that is inhomogeneously broadened by a slower process, also characterized by a single relaxation time. The fast modulation is in the sub picosecond time range, while the slower process has a relaxation time of the order of 1-10 ps. Relaxation times and other parameters are sensitive to transitions observed both below and above the glass transition, as well as at the T_g itself. The high temperature transition corresponds to a liquid-liquid transition observed in other studies and predicted by theory. The lower temperature transition appears to correspond to the Vogel-Fulcher or Kauzmann temperature. Infrared spectroscopy and band shape analysis appear to be a useful probe of these transitions.     

Chiral Determination of Salbutamol,Salmeterol and Atenolol by Two-Dimensional LC–LC: Application to Urine Samples

A heart-cut two-dimensional high-performance liquid chromatography method for enantiomeric determination of salbutamol, salmeterol and atenolol in urine is presented. It involves the use of two separations in a liquid chromatography–liquid chromatography achiral–chiral coupling. Target compounds were previously separated in a primary column (Kinetex™ HILIC, 2.6 μm, 150 × 2.1 mm I.D.) with a mixture of MeOH:ACN:ammonium acetate buffer (5 mM, pH 6) 90:5:5 (v/v/v) as mobile phase at a flow rate of 0.40 mL min⁻¹. Enantiomeric separation was carried out by transferring peak of each compound through a switching valve to a vancomycin chiral column (Chirobiotic™ V, 2.6 μm, 150 × 2.1 mm I.D.) using MeOH:ammonium acetate buffer (2 mM, pH 4) 97:3 (v/v) as mobile phase at a flow rate of 0.50 mL min⁻¹. Ultraviolet detection was done at 227 nm. The method was applied to determine target analytes in urine samples after enzymatic hydrolysis with β-glucuronidase from Helix pomatia, followed by a solid-phase extraction procedure using Isolute^® HCX mixed-mode cartridges. Extraction recoveries ranged from 82 to 90 % in urine samples. Detection limits were 0.091–0.095 μg for each enantiomer of atenolol and between 0.058 and 0.076 and 0.18–0.14 μg for enantiomers of salbutamol and salmeterol, respectively (3 mL of urine). Linearity ranges were between 0.5 and 10 μg mL⁻¹. Intraday and interday reproducibilities of enantiomeric ratio and enantiomeric fraction, expressed as relative standard deviation, were between 1.9 and 9.0 %. The optimized method was successfully applied to the analysis of urine samples obtained from excretion studies in volunteers and in freeze-dried urine samples, containing urinary components with MW < 10,000 and components with MW > 10,000, spiked with different amounts of studied drugs.

     

Phase Transformation and Lithiation Effect on Electronic Structure of Li(x)FePO(4): An In-Depth Study by Soft X-ray and Simulations

Through soft X-ray absorption spectroscopy, hard X-ray Raman scattering, and theoretical simulations, we provide the most in-depth and systematic study of the phase transformation and (de)lithiation effect on electronic structure in Li(x)FePO(4) nanoparticles and single crystals. Soft X-ray reveals directly the valence states of Fe 3d electrons in the vicinity of Fermi level, which is sensitive to the local lattice distortion, but more importantly offers detailed information on the evolution of electronic states at different electrochemical stages. The soft X-ray spectra of Li(x)FePO(4) nanoparticles evolve vividly with the (de)lithiation level. The spectra fingerprint the (de)lithiation process with rich information on Li distribution, valency, spin states, and crystal field. The high-resolution spectra reveal a subtle but critical deviation from two-phase transformation in our electrochemically prepared samples. In addition, we performed both first-principles calculations and multiplet simulations of the spectra and quantitatively determined the 3d valence states that are completely redistributed through (de)lithiation. This electronic reconfiguration was further verified by the polarization-dependent spectra collected on LiFePO(4) single crystals, especially along the lithium diffusion direction. The evolution of the 3d states is overall consistent with the local lattice distortion and provides a fundamental picture of the (de)lithiation effects on electronic structure in the Li(x)FePO(4) system.     

Deoxygenative olefination reaction as the key step in the syntheses of deoxy and iminosugars

Just a spoonful of sugar! A new synthetic strategy involving the use of a deoxygenative olefination reaction as the key step was developed for the preparation of deoxy and iminosugars in their optically active form (see scheme). This strategy has been proven successful by the use of a pentose, hexose, heptose, and disaccharide as the starting materials. Furthermore, it was applied in a formal total synthesis of iminosugar (-)-1-deoxy-L-fuconojirimycin, which can inhibit α-L-fucosidase.     

纳米孔模板浸润法制备聚乙烯纳米线阵列的热导率的实验研究

采用纳米孔模板润湿技术制备了直径为200 nm的低密度聚乙烯(LDPE)纳米线阵列, 并利用纳秒激光闪光法测量了20—80℃时LDPE纳米线阵列的热导率. 测量得到室温时LDPE纳米线阵列的热导率为2.2 W/mK, 大约比其体材料的热导率高1个数量级, 并且纳米线阵列的热导率随温度的升高略有增加. 忽略纳米线之间的声子散射, 估算得到室温下单根LDPE纳米线的热导率高于5 W/mK. 本文制备LDPE纳米线热导率的提高源自其分子链定向度增加导致的低维导热效应的增强, 纳米线的分子链定向度受工艺过程中流体剪切、振动、分子链迁移运动、 纳米孔约束等几种因素的综合影响.     

A simple and accurate method to measure program/erase speed in a memory capacitor structure

With the merits of simple process and short fabrication period, the capacitor structure provides a convenient way to evaluate memory characteristics of charge trap memory devices. However, the slow minority carrier generation in a capacitor often makes an underestimation of the program/erase speed. In this paper, illumination around a memory capacitor is proposed to enhance the generation of minority carriers so that an accurate measurement of the program/erase speed can be achieved. From the dependence of the inversion capacitance on frequency, a time constant is extracted to quantitatively characterize the formation of the inversion layer. Experimental results show that under a high enough illumination, this time constant is greatly reduced and the measured minority carrier related program/erase speed is in agreement with the reported value in a transistor structure.     

Use of atomic force microscopy and fractal geometry to characterize the roughness of nano-, micro-, and ultrafiltration membranes

Membrane surface roughness alters the surface area accessible to foulants and may influence macroscopic properties, such as zeta potential. It is usually quantified by atomic force microscopy (AFM) at a single scan size. This would be appropriate if roughness is independent of scale. This study shows that the root-mean-square roughness, R_RMS, is scale (or scan size, L × L) dependent through the power law R_RMS = AL^3−D. The coefficient, A, is the roughness at a scan size of 1² μm². D is the fractal dimension that relates the increase in roughness to the increase in scan size. Values for A and D were determined for a range of micro- and ultrafiltration membranes using an AFM scan series covering at least three orders of magnitude in L. They were also determined for nanofiltration membranes by re-analysis of data in the literature. The results suggest that using the power law expression allows potentially greater discrimination among membrane types and provides a way to quantify membrane roughness over a range of scales. It was further observed that the coefficients A and D of PVDF membranes showed positive and negative correlations, respectively, with the molecular weight cut-off. Additionally, zeta potentials of PVDF membranes measured by the tangential streaming potential method became more negative with increasing A and more positive with increasing D, suggesting possible significant influence of roughness on hydrodynamic transport of ions.