Effect of negative substrate bias on HWCVD deposited nanocrystalline silicon (nc-Si) films

The influence of the negative substrate bias on the interfacial and microstructural characteristics of nanocrystalline silicon (nc-Si) thin films was deposited by hot wire chemical vapor deposition (HWCVD). Structural characterization of nc-Si films was performed by small angle X-ray diffraction (SAXRD), Raman spectroscopy, X-ray reflectivity (XRR) and field emission scanning electron microscopy (FESEM). Crystalline fraction and crystallite size increases from 61.31 to 74.13% and 13.3 to 21.6 nm, respectively, with an increasing negative bias from 0 to ?200 V. Furthermore, the deposition rate of nc-Si films increases from 25 to 68 nm/min by increase of negative substrate bias from 0 to ?200 V.     

Microscopic analysis of ester hydrolysis reaction catalyzed by Candida rugosa lipase

The relationship between the kinetics of the lipase-catalyzed oil hydrolysis and the surface area distribution of oil droplets was investigated using ethyl decanoate and gum Arabic (GA) as a model oil and an emulsifier, respectively. Along an ethyl decanoate concentration gradient between 2 and 8 mM, the initial hydrolysis rate increased at 0.25% (w/v) GA but did not change at 1.0% (w/v) GA. At 0.25% GA, the surface area of droplets was narrowly distributed regardless of the ethyl decanoate concentration. However, at 1.0% GA and with ethyl decanoate concentrations higher than 2 mM, the fraction of relatively large droplets with a surface area larger than approximately 200 microm2, suddenly increased. The microscopy of ethyl decanoate emulsion during the hydrolysis reaction indicates that the large oil droplets were not hydrolyzed. At 20 mM ethyl decanoate where the hydrolysis rate remained the same between 0.25% and 1.0% GA, the surface area of droplets was narrowly distributed at 0.25% and 1.0% GA. Therefore, the constant hydrolysis rate observed in the emulsion of ethyl decanoate between 2 and 8 mM containing GA at 1.0%, is believed to be caused by the relatively large oil droplets with the interface quality differing from that of the small oil droplets.     

Association between excision repair cross-complementation group 1 polymorphism and clinical outcome of platinum-based chemotherapy in patients with epithelial ovarian cancer

ERCC1 is a DNA repair gene and has been associated with resistance to DNA damaging agents. In this study we hypothesized that a polymorphism of ERCC1 Asn118Asn (C -> T) might affect the platinum-resistance of epithelial ovarian cancer patients to platinum-taxane chemotherapy administered postoperatively. Using the SNapShot assay, we assessed this polymorphism in ERCC1 in 60 ovarian cancer patients. Platinum-resistance was defined as progression on platinum-based chemotherapy or recurrence within 6 months of completing therapy. Although not significant, platinum-resistance was less frequently observed in patients with the C/T+T/T genotype (P=0.064). Multivariate analysis showed that the C/T+T/T genotypes constituted an independent predictive factor of reduced risk of platinum-resistance in ovarian cancer (odds ratio 0.17, 95% confidence interval 0.04-0.74, P=0.018, Fisher's exact test). No significant correlation was observed between overall survival and the ERCC1 polymorphism. Our results suggest that genotyping of the ERCC1 polymorphism Asn118Asn may be useful for predicting the platinum-resistance of epithelial ovarian cancer patients. However, these findings require prospective confirmation.     

Optical modeling of liquid crystal biosensors

Optical simulations of a liquid crystal biosensor device are performed using an integrated optical/textural model based on the equations of nematodynamics and two optical methods: the Berreman optical matrix method [J. Opt. Soc. Am. 62, 502 (1972)] and the discretization of the Maxwell equations based on the finite difference time domain (FDTD) method. Testing the two optical methods with liquid crystal films of different degrees of orientational heterogeneities demonstrates that only the FDTD method is suitable to model this device. Basic substrate-induced texturing process due to protein adsorption gives rise to an orientation correlation function that is nearly linear with the transmitted light intensity, providing a basis to calibrate the device. The sensitivity of transmitted light to film thickness, protein surface coverage, and wavelength is established. A crossover incident light wavelength close to lambda(co) approximately 500 nm is found, such that when lambda>lambda(co) thinner films are more sensitive to the amount of protein surface coverage, while for lambda相似文献   

Spectroscopic characterizations of bridging cysteine ligand variants of an engineered Cu2(Scys)2 CuA azurin

Bridging cysteine ligands of the Cu(A) center in an engineered Cu(A) azurin were replaced with serine, and the variants (Cys116Ser and Cys112Ser Cu(A) azurin) were characterized by mass spectrometry, as well as UV-vis and electron paramagnetic resonance (EPR) spectroscopic techniques. The replacements resulted in dramatically perturbed spectroscopic properties, indicating that the cysteines play a critical role in maintaining the structural integrity of the Cu center. The replacements at different cysteine residues resulted in different perturbations, even though the two cysteines are geometrically symmetrical in the primary coordination sphere with respect to the two copper ions. The Cys112Ser variant contains two distinct type 2 copper centers, while the Cys116Ser variant has one type 1 copper center with slight tetragonal distortion. Both the UV-vis and EPR spectra of the Cys116Ser variant change with pH, and the pK(a) of the transition is 6.0. A type 1 copper EPR spectrum with A(||) = 26 G was obtained at pH 7.0, while a type 2 copper EPR spectrum with A(||) = 140 G was found at pH 5.0. Interestingly, lowering the temperature from 290 to 85 K resulted in conversion of the Cys116Ser variant from a type 1 copper center to a type 2 copper center, suggesting rearrangement of the ligand around the copper or binding of an exogenous ligand at low temperature. This difference in mutation effects at different cysteines may be due to different constraints exerted on the two cysteines by hydrogen-bonding patterns in the ligand loop.     

A three-coordinate and quadruply bonded Mo-Mo complex

Reaction of MoCl3(THF)3 with [Me2Si{NLi(Dipp)}2]2 (Dipp = 2,6-i-PrC6H3) afforded a triply bonded dimolybdenum complex 1,2-Mo2Cl2[Me2Si(NDipp)2]2 1, spanned by two Me2Si[N(Dipp)]2 ligands, thus resulting in a syn conformation. The air- and moisture-sensitive compound 1 was characterized by NMR spectroscopic, elemental, and single-crystal X-ray crystallographic analysis. Reduction of 1 by Na/Hg yielded the quadruply bonded dimeric complex Mo2[Me2Si(NDipp)2]2 2, which was also characterized by the aforementioned analytical methods. The Mo-Mo bond was determined to be 2.1784(12) A, which is considered a long quadruple bond. In addition, density functional theory (DFT) computations on compound 2 provided insight into the intriguing Mo-Mo quadruple bond.     

Molecular motion of tethered molecules in bulk and surface-functionalized materials: a comparative study of confinement

Achieving high degrees of molecular confinement in materials is a difficult synthetic challenge that is critical for understanding supramolecular chemistry on solid surfaces and control of host-guest complexation for selective adsorption and heterogeneous catalysis. In this Article, using 2H MAS NMR spectroscopy of tethered carbamates as a molecular probe, we systematically investigate the degree of steric confinement within three types of materials: two-dimensional silica surface, bulk amorphous microporous silica, and bulk amorphous mesoporous silica. The resulting NMR spectra are described with a simple two-site hopping model for motion and prove that the bulk silica network severely limits the molecular mobility of the immobilized carbamate at room temperature to the same degree as surface-functionalized materials at low-temperatures (approximately 210 K). Raising the temperature of the bulk materials to 413 K still demonstrates the effect of confinement, as manifested in significantly longer characteristic times for the immobilized carbamate relative to surface-functionalized materials at room temperature. The environment surrounding the carbonyl functionality of the immobilized carbamate is investigated using FT-IR spectroscopy, which shows the carbonyl stretching band to be equally shifted for all materials to lower wavenumbers relative to its noninteracting value in carbon tetrachloride solvent. These results suggest that electrostatic interactions between the carbonyl of the immobilized carbamate and silica surface may play an important role in confining the immobilized carbamate and nucleating the formation of a pore wall close to the immobilized carbamate during bulk materials synthesis.     

Heterostructured nanohybrid of zinc oxide-montmorillonite clay

We have synthesized heterostructured zinc oxide-aluminosilicate nanohybrids through a hydrothermal reaction between the colloidal suspension of exfoliated montmorillonite nanosheets and the sol solution of zinc acetate. According to X-ray diffraction, N2 adsorption-desorption isotherm, and field emission-scanning electron microscopic analyses, it was found that the intercalation of zinc oxide nanoparticles expands the basal spacing of the host montmorillonite clay, and the crystallites of the nanohybrids are assembled to form a house-of-cards structure. From UV-vis spectroscopic investigation, it becomes certain that calcined nanohybrid contains two kinds of the zinc oxide species in the interlayer space of host lattice and in mesopores formed by the house-of-cards type stacking of the crystallites. Zn K-edge X-ray absorption near-edge structure/extended X-ray absorption fine structure analyses clearly demonstrate that guest species in the nanohybrids exist as nanocrystalline zinc oxides with wurzite-type structure.